| Author | Title | Year | Journal/Proceedings | Reftype | DOI/URL |
|---|---|---|---|---|---|
| Beckers, D. and Eldredge, J.D. | Deep reinforcement learning of airfoil pitch control in a highly disturbed environment using partial observations | 2024 | Phys. Rev. Fluids Vol. 9, pp. 093902arXiv: 2404.01506 |
article | DOI |
| Abstract: This study explores the application of deep reinforcement learning (RL) to design an airfoil pitch controller capable of minimizing lift variations in randomly disturbed flows. The controller, treated as an agent in a partially observable Markov decision process, receives non-Markovian observations from the environment, simulating practical constraints where flow information is limited to force and pressure sensors. Deep RL, particularly the TD3 algorithm, is used to approximate an optimal control policy under such conditions. Testing is conducted for a flat plate airfoil in two environments: a classical unsteady environment with vertical acceleration disturbances (i.e., a Wagner setup) and a viscous flow model with pulsed point force disturbances. In both cases, augmenting observations of the lift, pitch angle, and angular velocity with extra wake information (e.g., from pressure sensors) and retaining memory of past observations enhances RL control performance. Results demonstrate the capability of RL control to match or exceed standard linear controllers in minimizing lift variations. Special attention is given to the choice of training data and the generalization to unseen disturbances. | |||||
BibTeX:
@article{Beckers2024,
author = {Diederik Beckers and Jeff D. Eldredge},
title = {Deep reinforcement learning of airfoil pitch control in a highly disturbed environment using partial observations},
journal = {Phys. Rev. Fluids},
year = {2024},
volume = {9},
pages = {093902},
doi = {https://doi.org/10.1103/PhysRevFluids.9.093902}
}
|
|||||
| Eldredge, J.D. and Le Provost, M. | Bayesian inference of vorticity in unbounded flow from limited pressure measurements | 2024 | J. Fluid Mech. Vol. 986, pp. A18 |
article | DOI |
| Abstract: We study the instantaneous inference of an unbounded planar flow from sparse noisy pressure measurements. The true flow field comprises one or more regularized point vortices of various strength and size. We interpret the true flow’s measurements with a vortex estimator, also consisting of regularized vortices, and attempt to infer the positions and strengths of this estimator assuming little prior knowledge. The problem often has several possible solutions, many due to a variety of symmetries. To deal with this ill-posedness and to quantify the uncertainty, we develop the vortex estimator in a Bayesian setting. We use Markov-chain Monte Carlo and a Gaussian mixture model to sample and categorize the probable vortex states in the posterior distribution, tailoring the prior to avoid spurious solutions. Through experiments with one or more true vortices, we reveal many aspects of the vortex inference problem. With fewer sensors than states, the estimator infers a manifold of equally-possible states. Using one more sensor than states ensures that no cases of rank deficiency arise. Uncertainty grows rapidly with distance when a vortex lies outside of the vicinity of the sensors. Vortex size cannot be reliably inferred, but the position and strength of a larger vortex can be estimated with a much smaller one. In estimates of multiple vortices their individual signs are discernible because of the non-linear coupling in the pressure. When the true vortex state is inferred from an estimator of fewer vortices, the estimate approximately aggregates the true vortices where possible. | |||||
BibTeX:
@article{Eldredge2024a,
author = {Eldredge, Jeff D. and Le Provost, Mathieu},
title = {Bayesian inference of vorticity in unbounded flow from limited pressure measurements},
journal = {J. Fluid Mech.},
year = {2024},
volume = {986},
pages = {A18},
doi = {https://doi.org/10.1017/jfm.2024.343}
}
|
|||||
| Li, Y., Eldredge, J.D., Lavine, A.S., Fisher, T.S. and Drolen, B.L. | A conjugate heat transfer model of oscillating heat pipe dynamics, performance, and dryout | 2024 | Int. J. Heat Mass Tran. Vol. 227, pp. 125530 |
article | DOI |
| Abstract: Oscillating heat pipes (OHPs) consist of a serpentine capillary channel partially filled with liquid that is embedded in a thermally-conducting solid. They have significant advantages for cooling electronics and aerospace systems. The model reported here aims to capture the essential physics of an OHP with minimal complexity and treats some parameters typically derived from correlations or experiments (such as the film thickness and film triple point velocity) as functions with tunable constants to be estimated by data assimilation. This model contains two modules. The first uses a novel and flexible formulation of the conducting solid, solving the two-dimensional heat equation in a thin plate, with evaporators and condensers as immersed forcing terms and the OHP channel as an immersed line source. The second module solves one-dimensional fluid motion and heat transfer equations within the fluid-filled channels based on mass, momentum, and energy conservation, nucleate boiling, and bubble dryout. It extends the commonly-used film evaporation-condensation model, allowing both variable liquid film thickness and length and thereby enabling the model to capture dryout. These modules are weakly coupled, in that wall temperature in the channels are obtained from the first module and heat flux from the channels determines the line source strength. After minimal training, the thermal conductance calculated by this model shows good agreement with a wide range of experiments performed by Drolen et al. [1]. In particular, the model successfully predicts the experimentally-observed transition from stable OHP operation to dryout, for the first time to the authors’ knowledge. | |||||
BibTeX:
@article{LiOHP2024,
author = {Yuxuan Li and Jeff D. Eldredge and Adrienne S. Lavine and Timothy S. Fisher and Bruce L. Drolen},
title = {A conjugate heat transfer model of oscillating heat pipe dynamics, performance, and dryout},
journal = {Int. J. Heat Mass Tran.},
year = {2024},
volume = {227},
pages = {125530},
doi = {https://doi.org/10.1016/j.ijheatmasstransfer.2024.125530}
}
|
|||||
| Liu, Z., Beckers, D. and Eldredge, J.D. | Model-Based Reinforcement Learning for Control of Strongly-Disturbed Unsteady Aerodynamic Flows | 2024 | arXiv:2408.14685 | misc | DOI URL |
| Abstract: The intrinsic high dimension of fluid dynamics is an inherent challenge to control of aerodynamic flows, and this is further complicated by a flow's nonlinear response to strong disturbances. Deep reinforcement learning, which takes advantage of the exploratory aspects of reinforcement learning (RL) and the rich nonlinearity of a deep neural network, provides a promising approach to discover feasible control strategies. However, the typical model-free approach to reinforcement learning requires a significant amount of interaction between the flow environment and the RL agent during training, and this high training cost impedes its development and application. In this work, we propose a model-based reinforcement learning (MBRL) approach by incorporating a novel reduced-order model as a surrogate for the full environment. The model consists of a physics-augmented autoencoder, which compresses high-dimensional CFD flow field snaphsots into a three-dimensional latent space, and a latent dynamics model that is trained to accurately predict the long-time dynamics of trajectories in the latent space in response to action sequences. The robustness and generalizability of the model is demonstrated in two distinct flow environments, a pitching airfoil in a highly disturbed environment and a vertical-axis wind turbine in a disturbance-free environment. Based on the trained model in the first problem, we realize an MBRL strategy to mitigate lift variation during gust-airfoil encounters. We demonstrate that the policy learned in the reduced-order environment translates to an effective control strategy in the full CFD environment. | |||||
BibTeX:
@misc{Liu2024,
author = {Zhecheng Liu and Diederik Beckers and Jeff D. Eldredge},
title = {Model-Based Reinforcement Learning for Control of Strongly-Disturbed Unsteady Aerodynamic Flows},
year = {2024},
url = {https://arxiv.org/abs/2408.14685},
doi = {https://doi.org/10.48550/arXiv.2408.14685}
}
|
|||||
| Mousavi, H. and Eldredge, J.D. | Bayesian Inference for Estimating Heat Sources through Temperature Assimilation | 2024 | arXiv:2405.02319 | misc | DOI |
| Abstract: This paper introduces a Bayesian inference framework for two-dimensional steady-state heat conduction, focusing on the estimation of unknown distributed heat sources in a thermally-conducting medium with uniform conductivity. The goal is to infer heater locations, strengths, and shapes using temperature assimilation in the Euclidean space, employing a Fourier series to represent each heater's shape. The Markov Chain Monte Carlo (MCMC) method, incorporating the random-walk Metropolis-Hasting algorithm and parallel tempering, is utilized for posterior distribution exploration in both unbounded and wall-bounded domains. Strong correlations between heat strength and heater area prompt caution against simultaneously estimating these two quantities. It is found that multiple solutions arise in cases where the number of temperature sensors is less than the number of unknown states. Moreover, smaller heaters introduce greater uncertainty in estimated strength. The diffusive nature of heat conduction smooths out any deformations in the temperature contours, especially in the presence of multiple heaters positioned near each other, impacting convergence. In wall-bounded domains with Neumann boundary conditions, the inference of heater parameters tends to be more accurate than in unbounded domains. | |||||
BibTeX:
@misc{Mousavi2024,
author = {Hanieh Mousavi and Jeff D. Eldredge},
title = {Bayesian Inference for Estimating Heat Sources through Temperature Assimilation},
year = {2024},
doi = {https://doi.org/10.48550/arXiv.2405.02319}
}
|
|||||
| Pantoja, J.L., Shehadeh, T.S., Lee, M.M., Eldredge, J.D. and Kiang, S.C. | Geometrical Factors Affect Wall Shear Stress in Saccular Aneurysms of the Infrarenal Abdominal Aorta | 2024 | Ann. Vasc. Surg. Vol. 108, pp. 76-83 |
article | DOI URL |
| Abstract: Low wall shear stress (WSS) is predictive of aortic aneurysm growth and rupture. Yet, estimating WSS in a clinical setting is impractical whereas measuring aneurysm geometry is feasible. This study investigates the association between saccular aneurysm geometry of the infrarenal aorta and WSS. | |||||
BibTeX:
@article{Pantoja2024,
author = {Pantoja, Joe Luis and Shehadeh, Thaer S. and Lee, Mary M. and Eldredge, Jeffrey D. and Kiang, Sharon C.},
title = {Geometrical Factors Affect Wall Shear Stress in Saccular Aneurysms of the Infrarenal Abdominal Aorta},
journal = {Ann. Vasc. Surg.},
publisher = {Elsevier},
year = {2024},
volume = {108},
pages = {76--83},
url = {https://doi.org/10.1016/j.avsg.2024.04.015},
doi = {https://doi.org/10.1016/j.avsg.2024.04.015}
}
|
|||||
| Beckers, D. and Eldredge, J.D. | Wind tunnel effects on gust-interaction simulations | 2023 | Theor. Comp. Fluid Dyn. Vol. 37, pp. 533-548 |
article | DOI URL |
| Abstract: Large-amplitude flow disturbances, or gusts, can drastically alter the aerodynamic forces on an airfoil and are regularly investigated through wind tunnel (or water tunnel) experiments. The gusts generated in those experiments are often further analyzed using numerical simulations, but usually without fully accounting for the wind tunnel walls or gust generator. The current work investigates the wind tunnel effects on the predicted lift response and flow field using a computational framework that models the viscous flow around the airfoil but treats the tunnel walls and gust generation as inviscid boundary conditions. We apply this model to three examples and compare the predicted gust response with the responses predicted by a free-space viscous model and a classical unsteady aerodynamics model to highlight the wind tunnel effects. We find that the wind tunnel modeling introduces non-negligible effects depending on the airfoil and gust configurations. These effects include the confinement effect of the wind tunnel walls and the triggering of flow separation when it does not occur in the corresponding free-space model. In the last example, we also note that this virtual counterpart of an actual wind tunnel can be paired with experiments through data assimilation to increase the accuracy of the gust response or perform parameter estimation. | |||||
BibTeX:
@article{Beckers2023,
author = {Beckers, Diederik and Eldredge, Jeff D.},
title = {Wind tunnel effects on gust-interaction simulations},
journal = {Theor. Comp. Fluid Dyn.},
year = {2023},
volume = {37},
pages = {533--548},
url = {https://doi.org/10.1007/s00162-023-00668-9},
doi = {https://doi.org/10.1007/s00162-023-00668-9}
}
|
|||||
| Dumoulin, D., Eldredge, J.D. and Chatelain, P. | A lightweight vortex model for unsteady motion of airfoils | 2023 | J. Fluid Mech. Vol. 977, pp. A22 |
article | DOI |
| Abstract: A low-order vortex model has been developed for analysing the unsteady aerodynamics of airfoils. The model employs an infinitely thin vortex sheet in place of the attached boundary layer and a sheet of point vortices for the shed shear layer. The strength and direction of the vortex sheet shed at the airfoil trailing edge are determined by an unsteady Kutta condition. The roll-up of the ambient shear layer is represented by a unique point vortex, which is consistently fed circulation by the last point vortex of the free vortex sheet. The model's dimensionality is reduced by using three tuning parameters to balance representational accuracy and computational efficiency. The performance of the model is evaluated through experiments involving impulsively started and heaving and pitching airfoils. The model accurately captures the dynamics of the development and evolution of the shed vortical structure while requiring minimal computational resources. The validity of the model is confirmed through comparison with experimental force measurements and a baseline unsteady panel method that does not transfer circulation in the free vortex sheet. | |||||
BibTeX:
@article{Dumoulin2023,
author = {Dumoulin, Denis and Eldredge, Jeff D. and Chatelain, Philippe},
title = {A lightweight vortex model for unsteady motion of airfoils},
journal = {J. Fluid Mech.},
publisher = {Cambridge University Press},
year = {2023},
volume = {977},
pages = {A22},
doi = {https://doi.org/10.1017/jfm.2023.997}
}
|
|||||
| Le Provost, M., Baptista, R., Eldredge, J.D. and Marzouk, Y. | An adaptive ensemble filter for heavy-tailed distributions: tuning-free inflation and localization | 2023 | arXiv: 2310.08741 | misc | DOI URL |
| Abstract: Heavy tails is a common feature of filtering distributions that results from the nonlinear dynamical and observation processes as well as the uncertainty from physical sensors. In these settings, the Kalman filter and its ensemble version - the ensemble Kalman filter (EnKF) - that have been designed under Gaussian assumptions result in degraded performance. t-distributions are a parametric family of distributions whose tail-heaviness is modulated by a degree of freedom ν. Interestingly, Cauchy and Gaussian distributions correspond to the extreme cases of a t-distribution for ν=1 and ν=∞, respectively. Leveraging tools from measure transport (Spantini et al., SIAM Review, 2022), we present a generalization of the EnKF whose prior-to-posterior update leads to exact inference for t-distributions. We demonstrate that this filter is less sensitive to outlying synthetic observations generated by the observation model for small ν. Moreover, it recovers the Kalman filter for ν=∞. For nonlinear state-space models with heavy-tailed noise, we propose an algorithm to estimate the prior-to-posterior update from samples of joint forecast distribution of the states and observations. We rely on a regularized expectation-maximization (EM) algorithm to estimate the mean, scale matrix, and degree of freedom of heavy-tailed t-distributions from limited samples (Finegold and Drton, arXiv preprint, 2014). Leveraging the conditional independence of the joint forecast distribution, we regularize the scale matrix with an l1 sparsity-promoting penalization of the log-likelihood at each iteration of the EM algorithm. By sequentially estimating the degree of freedom at each analysis step, our filter can adapt its prior-to-posterior update to the tail-heaviness of the data. We demonstrate the benefits of this new ensemble filter on challenging filtering problems. | |||||
BibTeX:
@misc{Provost2023,
author = {Le Provost, Mathieu and Baptista, Ricardo and Eldredge, Jeff D. and Marzouk, Youssef},
title = {An adaptive ensemble filter for heavy-tailed distributions: tuning-free inflation and localization},
year = {2023},
url = {https://arxiv.org/abs/2310.08741},
doi = {https://doi.org/10.48550/arXiv.2310.08741}
}
|
|||||
| Beckers, D. and Eldredge, J.D. | Planar potential flow on Cartesian grids | 2022 | J. Fluid Mech. Vol. 941, pp. A19 |
article | DOI URL |
| Abstract: Potential flow has many applications, including the modelling of unsteady flows in aerodynamics. For these models to work efficiently, it is best to avoid Biot–Savart interactions. This work presents a grid-based treatment of potential flows in two dimensions and its use in a vortex model for simulating unsteady aerodynamic flows. For flows consisting of vortex elements, the treatment follows the vortex-in-cell approach and solves the streamfunction–vorticity Poisson equation on a Cartesian grid after transferring the circulation from the vortices onto the grid. For sources and sinks, an analogous approach can be followed using the scalar potential. The combined velocity field due to vortices, sinks and sources can then be obtained using the Helmholtz decomposition. In this work, we use several key tools that ensure the approach works on arbitrary geometries, with and without sharp edges. First, the immersed boundary projection method is used to account for bodies in the flow and the resulting body-forcing Lagrange multiplier is identified as the bound vortex sheet strength. Second, sharp edges are treated by decomposing the vortex sheet strength into a singular and non-singular part. To enforce the Kutta condition, the non-singular part can then be constrained to remove the singularity introduced by the sharp edge. These constraints and the Poisson equation are formulated as a saddle-point system and solved using the Schur complement method. The lattice Green's function is used to efficiently solve the discrete Poisson equation with unbounded boundary conditions. The method and its accuracy are demonstrated for several problems. | |||||
BibTeX:
@article{beckers2021planar,
author = {Diederik Beckers and Jeff D. Eldredge},
title = {Planar potential flow on Cartesian grids},
journal = {J. Fluid Mech.},
year = {2022},
volume = {941},
pages = {A19},
url = {https://arxiv.org/abs/2102.11910},
doi = {https://doi.org/10.1017/jfm.2022.238}
}
|
|||||
| Deparday, J., He, X., Eldredge, J.D., Mulleners, K. and Williams, D.R. | Experimental quantification of unsteady leading-edge flow separation | 2022 | J. Fluid Mech. Vol. 941, pp. A60 |
article | DOI URL |
| Abstract: We propose here a method to experimentally quantify unsteady leading-edge flow separation on aerofoils with finite thickness. The methodology relies on the computation of a leading-edge suction parameter based on measured values of the partial circulation around the leading-edge and the stagnation point location. We validate the computation of the leading-edge suction parameter for both numerical and experimental data under steady and unsteady flow conditions. The leading-order approximation of the definition of the leading-edge suction parameter is proven to be sufficiently accurate for the application to thin aerofoils such as the NACA0009 without a-priori knowledge of the stagnation point location. The higher-order terms including the stagnation point location are required to reliably compute the leading-edge suction parameter on thicker aerofoils such as the NACA0015. The computation of the leading-edge suction parameter from inviscid flow theory does not assume the Kutta condition to be valid at the trailing edge which allows us to compute its value for separated flows. The relation between the leading-edge suction parameter and the evolution of the shear layer height is studied in two different unsteady flow conditions, a fixed aerofoil in a fluctuating free-stream velocity and a pitching aerofoil in a steady free-stream. We demonstrate here that the instantaneous value of the leading-edge suction parameter based on the partial circulation around the leading edge is unambiguously defined for a given flow field and can serve as a directly quantitative measure of the degree of unsteady flow separation at the leading edge. | |||||
BibTeX:
@article{deparaday2021,
author = {Julien Deparday, Xiaowei He, Jeff D. Eldredge, Karen Mulleners, David R. Williams},
title = {Experimental quantification of unsteady leading-edge flow separation},
journal = {J. Fluid Mech.},
year = {2022},
volume = {941},
pages = {A60},
url = {https://arxiv.org/abs/2110.08384},
doi = {https://doi.org/10.1017/jfm.2022.319}
}
|
|||||
| Eldredge, J.D. | A method of immersed layers on Cartesian grids, with application to incompressible flows | 2022 | J. Comput. Phys. Vol. 448, pp. 110716 |
article | DOI URL |
| Abstract: The immersed boundary method (IBM) of Peskin (J. Comput. Phys., 1977), and derived forms such as the projection method of Taira and Colonius (J. Comput. Phys., 2007), have been useful for simulating flow physics in problems with moving interfaces on stationary grids. However, in their interface treatment, these methods do not distinguish one side from the other, but rather, apply the motion constraint to both sides, and the associated interface force is an inseparable mix of contributions from each side. In this work, we define a discrete Heaviside function, a natural companion to the familiar discrete Dirac delta function (DDF), to define a masked version of each field on the grid which, to within the error of the DDF, takes the intended value of the field on the respective sides of the interface. From this foundation we develop discrete operators and identities that are uniformly applicable to any surface geometry. We use these to develop extended forms of prototypical partial differential equations, including Poisson, convection-diffusion, and incompressible Navier-Stokes, that govern the discrete masked fields. These equations contain the familiar forcing term of the IBM, but also additional terms that regularize the jumps in field quantities onto the grid and enable us to individually specify the constraints on field behavior on each side of the interface. Drawing the connection between these terms and the layer potentials in elliptic problems, we refer to them generically as immersed layers. We demonstrate the application of the method to several representative problems, including two-dimensional incompressible flows inside a rotating cylinder and external to a rotating square. | |||||
BibTeX:
@article{eldredge2021method,
author = {Jeff D. Eldredge},
title = {A method of immersed layers on Cartesian grids, with application to incompressible flows},
journal = {J. Comput. Phys.},
year = {2022},
volume = {448},
pages = {110716},
url = {https://arxiv.org/abs/2103.04521},
doi = {https://doi.org/10.1016/j.jcp.2021.110716}
}
|
|||||
| Le Provost, M., Baptista, R., Marzouk, Y. and Eldredge, J.D. | A low-rank ensemble Kalman filter for elliptic observations | 2022 | Proceedings of the Royal Society A Vol. 478(2266), pp. 20220182 |
article | DOI URL |
| Abstract: We propose a regularization method for ensemble Kalman filtering (EnKF) with elliptic observation operators. Commonly used EnKF regularization methods suppress state correlations at long distances. For observations described by elliptic partial differential equations, such as the pressure Poisson equation (PPE) in incompressible fluid flows, distance localization cannot be applied, as we cannot disentangle slowly decaying physical interactions from spurious long-range correlations. This is particularly true for the PPE, in which distant vortex elements couple nonlinearly to induce pressure. Instead, these inverse problems have a low effective dimension: low-dimensional projections of the observations strongly inform a low-dimensional subspace of the state space. We derive a low-rank factorization of the Kalman gain based on the spectrum of the Jacobian of the observation operator. The identified eigenvectors generalize the source and target modes of the multipole expansion, independently of the underlying spatial distribution of the problem. Given rapid spectral decay, inference can be performed in the low-dimensional subspace spanned by the dominant eigenvectors. This low-rank EnKF is assessed on dynamical systems with Poisson observation operators, where we seek to estimate the positions and strengths of point singularities over time from potential or pressure observations. We also comment on the broader applicability of this approach to elliptic inverse problems outside the context of filtering. | |||||
BibTeX:
@article{leprovost2022lrenkf,
author = {Le Provost, Mathieu and Baptista, Ricardo and Marzouk, Youssef and Eldredge, Jeff D.},
title = {A low-rank ensemble Kalman filter for elliptic observations},
journal = {Proceedings of the Royal Society A},
year = {2022},
volume = {478},
number = {2266},
pages = {20220182},
url = {https://doi.org/10.1098/rspa.2022.0182},
doi = {https://doi.org/10.1098/rspa.2022.0182}
}
|
|||||
| An, X., Williams, D.R., Eldredge, J.D. and Colonius, T. | Lift coefficient estimation for a rapidly pitching airfoil | 2021 | Exp. Fluids Vol. 62(1), pp. 1-12 |
article | DOI URL |
| Abstract: We develop a method for estimating the instantaneous lift coefficient on a rapidly pitching airfoil that uses a small number of pressure sensors and a measurement of the angle of attack. The approach assimilates four surface pressure measurements with a modified nonlinear state space model (Goman–Khrabrov model) through a Kalman filter. The error of lift coefficient estimates based only on a weighted-sum of the measured pressures are found to be noisy and biased, which leads to inaccurate estimates. The estimate is improved by including the predictive model in an conventional Kalman filter. The Goman–Khrabrov model is shown to be a linear parameter-varying system and can therefore be used in the Kalman filter without the need for linearization. Additional improvement is realized by modifying the algorithm to provide more accurate estimate of the lift coefficient. The improved Kalman filtering approach results in a bias-free lift coefficient estimate that is more precise than either the pressure-based estimate or the Goman–Khrabrov model on their own. The new method will enable performance enhancements in aerodynamic systems whose performance relies on lift. | |||||
BibTeX:
@article{an2021lift,
author = {An, Xuanhong and Williams, David R and Eldredge, Jeff D and Colonius, Tim},
title = {Lift coefficient estimation for a rapidly pitching airfoil},
journal = {Exp. Fluids},
year = {2021},
volume = {62},
number = {1},
pages = {1--12},
url = {https://link.springer.com/article/10.1007/s00348-020-03105-3},
doi = {https://doi.org/10.1007/s00348-020-03105-3}
}
|
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| Chang, Y.-J., Benharash, P., Dutson, E.P. and Eldredge, J.D. | Smoothed particle hydrodynamics simulation of biphasic soft tissue and its medical applications | 2021 | Med. Biol. Eng. Comput. Vol. 59(1), pp. 227-242 |
article | DOI |
| Abstract: Modeling the coupled fluid and elastic mechanics of blood perfused soft tissues is important for medical applications. In particular, the current study aims to capture the effect of tissue swelling and the transport of blood through damaged tissue under bleeding or hemorrhaging conditions. The soft tissue is considered as a dynamic porohyperelastic material with blood-filled voids. A biphasic formulation—effectively, a generalization of Darcy's law—is utilized, treating the phases as occupying fractions of the same volume. A Stokes-like friction force and a pressure that penalizes deviations from volume fractions summing to unity serve as the interaction force between solid and liquid phases. The resulting equations for both phases are discretized with the method of Smoothed Particle Hydrodynamics (SPH). The solver is validated separately on each phase and demonstrates good agreement with exact solutions in test problems. Simulations of oozing, hysteresis, swelling, drying and shrinkage, and tissue fracturing and hemorrhage are shown in the paper. | |||||
BibTeX:
@article{chaeld21,
author = {Chang, Yi-Jui and Benharash, Peyman and Dutson, Erik P. and Eldredge, Jeff D.},
title = {Smoothed particle hydrodynamics simulation of biphasic soft tissue and its medical applications},
journal = {Med. Biol. Eng. Comput.},
year = {2021},
volume = {59},
number = {1},
pages = {227--242},
doi = {https://doi.org/10.1007/s11517-020-02283-w}
}
|
|||||
| Eldredge, J., le Provost, M., Baptista, R. and Marzouk, Y. | Applications of ensemble Kalman filtered vortex modeling to gust--wing interactions | 2021 | AIAA SciTech Forum 2021. AIAA Paper 2021-1936 | misc | DOI URL |
| Abstract: Lightweight aerial vehicles can be strongly affected by environmental disturbances (gusts). It is important to have tools for estimating their aerodynamic response to such gusts and toother disturbances, such as agile maneuvers and flow actuators. In recent work, a framework has been developed for predicting the state of disturbed aerodynamic flows, without prior knowledge of the disturbance, by assimilating surface pressure measurements into an ensembleof aggregated vortex models. In this framework, a randomized ensemble of inexpensive models are advanced in each step to forecast the flow state, and then corrected in a linear analysisstep by assimilating new measurements. Further advances to this Ensemble Kalman filterframework have been made in a recent paper (Le Provost and Eldredge 2020). In the present work, we demonstrate the use of the improved framework on encounters of a two-dimensionalflat plate with gusts of various amplitudes. In particular, we explore the dependence of the aerodynamic response on the gust strength and configuration, and show that the estimation framework works well even for very large amplitude disturbances. | |||||
BibTeX:
@misc{eldredge2021applications,
author = {Eldredge, Jeff and le Provost, Mathieu and Baptista, Ricardo and Marzouk, Youssef},
title = {Applications of ensemble Kalman filtered vortex modeling to gust--wing interactions},
year = {2021},
url = {https://drive.google.com/open?id=1VpqOpE3p1qeqmhwXh9oskf-bkQGWuoWc},
doi = {https://doi.org/10.2514/6.2021-1936}
}
|
|||||
| Eldredge, J.D. | ViscousFlow: A framework for simulating viscous incompressible flows about arbitrary body shapes [BibTeX] |
2021 | Zenodo. DOI: 10.5281/zenodo.4473257 | misc | DOI |
BibTeX:
@misc{viscousflow,
author = {Eldredge, Jeff D.},
title = {ViscousFlow: A framework for simulating viscous incompressible flows about arbitrary body shapes},
year = {2021},
doi = {https://doi.org/10.5281/zenodo.4473257}
}
|
|||||
| Le Provost, M., Baptista, R., Marzouk, Y. and Eldredge, J. | A low-rank nonlinear ensemble filter for vortex models of aerodynamic flows | 2021 | AIAA SciTech 2021 Forum. AIAA Paper 2021-1937 | misc | DOI URL |
| Abstract: Robustly estimating the separated flow about an airfoil is critical in the design of any closed loop controller. Darakananda et al. (Phys. Rev. Fluids, 2018) successfully used an ensemble Kalman filter (EnKF) to sequentially estimate the flow using an inviscid vortex model anddistributed surface pressure readings. To tackle challenging inference problems with limited observations, classical localization schemes suppress correlations at long distances. However, these techniques would be harmful in our case due to the existence of physical long-range interactions between vortices and pressure readings. Instead, these interactions are best described as interactions between clusters of variables. This work proposes a systematic procedure toidentify these clusters of variables from a nonlinear observation model. By projecting the states and observations onto these new sets of variables, the inference is performed in a low dimensional subspace of the state and the observations. To perform consistent inference with the nonlinear model, we use the stochastic map filter (SMF): a natural generalization of the EnKF that relies on interpretable nonlinear prior-to-posterior transformations (Spantini etal., arXiv, 2019). We combine the identification of these clusters of variables with the SMF toderive a low-rank nonlinear ensemble filter. This filter is assessed on the response of a translating plate at 20 that undergoes strong and overlapping pulses applied near the leading-edge. Our framework outperforms the EnKF at estimating the surface pressure distribution along the entire plate, with only two pressure sensors (placed at the edges of the plate) for collecting measurements. | |||||
BibTeX:
@misc{le2021low,
author = {Le Provost, Mathieu and Baptista, Ricardo and Marzouk, Youssef and Eldredge, Jeff},
title = {A low-rank nonlinear ensemble filter for vortex models of aerodynamic flows},
year = {2021},
url = {https://drive.google.com/open?id=1Vp-AYaks9Yof2nZLQA4Itb3p9c_CTxdG},
doi = {https://doi.org/10.2514/6.2021-1937}
}
|
|||||
| Le Provost, M. and Eldredge, J.D. | Ensemble Kalman filter for vortex models of disturbed aerodynamic flows | 2021 | Phys. Rev. Fluids Vol. 6(5), pp. 050506 |
article | DOI URL |
| Abstract: The task of dynamic flow estimation is to construct an approximation of an evolving flow---and particularly, its response to disturbances---using measurements from available sensors. Building from previous work by Darakananda et al. (Phys Rev Fluids 2018), we further develop an ensemble Kalman filter (EnKF) framework for aerodynamic flows based on an ensemble of randomly-perturbed inviscid vortex models of flow about an infinitely-thin plate. In the forecast step, vortex elements in each ensemble member are advected by the flow and new elements are released from each edge of the plate; the elements are aggregated to maintain an efficient representation. The vortex elements and leading edge constraint are corrected in the analysis step by assimilating the surface pressure differences across the plate measured from the truth system. We show that the overall framework can be physically interpreted as a series of adjustments to the position and shape of an elliptical region of uncertainty associated with each vortex element. In this work, we compare the previously-used stochastic EnKF with the ensemble transform Kalman filter (ETKF), which uses a deterministic analysis step. We examine the response of the flat plate at 20∘ in two perturbed flows, with truth data obtained from high-fidelity simulation at Reynolds number 500. In the first case, we apply a sequence of large-amplitude pulses near the leading edge of the plate to mimic flow actuation. In the second, we place the plate in a vortex street wake behind a cylinder. In both cases, we show that the vortex-based framework accurately estimates the pressure distribution and normal force, with no a priori knowledge of the perturbations. We show that the ETKF is consistently more robust than the stochastic EnKF. Finally, we examine the mapping from measurements to state update in the analysis step through SVD of the Kalman gain. | |||||
BibTeX:
@article{provost2021ensemble,
author = {Le Provost, M. and Eldredge, J. D.},
title = {Ensemble Kalman filter for vortex models of disturbed aerodynamic flows},
journal = {Phys. Rev. Fluids},
year = {2021},
volume = {6},
number = {5},
pages = {050506},
url = {https://arxiv.org/abs/2008.11309},
doi = {https://doi.org/10.1103/PhysRevFluids.6.050506}
}
|
|||||
| Leung, D.B., Eldredge, J.D. and Gordon, M.S. | A simplified computational model of possible hydrodynamic interactions between respiratory and swimming-related water flows in labriform-swimming fishes | 2021 | Bioinspiration and Biomimetics Vol. 16(3), pp. 036002 |
article | DOI |
| Abstract: Hydrodynamic interactions in bony fishes between respiratory fluid flows leaving the opercular openings and simultaneous flows generated by movements of downstream pectoral fins are both poorly understood and likely to be complex. Labriform-swimming fishes that swim primarily by moving only their pectoral fins are good subjects for such studies. We performed a computational fluid dynamics (CFD) investigation of a simplified two-dimensional model of these interactions based on previously published experimental observations of both respiratory andpectoral fin movements under both resting and slow steady swimming conditions in two similar labriform swimmers: the bluegill sunfish (Lepomis macrochirus) and the largemouth bass (Micropterus salmoides). We carried out a parametric study investigating the effects that swimming speed, strength of opercular flow, and phase difference between the pectoral fin motion and the opercular opening and closing have on the thrust and side slip forces generated by the pectoral fins during both the abduction and adduction portions of the fin movement cycle.We analyzed pressure distributions on the fin surface to determine physical differences in flowswith and without opercular jets. The modeling indicates that complex flow structures emerge from the coupling between the opercular jets and vortex shedding from pectoral fins. The jets from the opercular openings appear to exert significant influence on the forces generated by the fins; they are potentially significant in the maneuverability of at least some labriform swimmers.The numerical simulations and the analysis establish a framework for study of these interactions in various labriform swimmers in a variety of flow regimes. Similar situations in groups of fishes using other swimming modes should also be investigated. | |||||
BibTeX:
@article{leung2021,
author = {Leung, David B. and Eldredge, Jeff D. and Gordon, Malcolm S.},
title = {A simplified computational model of possible hydrodynamic interactions between respiratory and swimming-related water flows in labriform-swimming fishes},
journal = {Bioinspiration and Biomimetics},
year = {2021},
volume = {16},
number = {3},
pages = {036002},
doi = {https://doi.org/10.1088/1748-3190/abdab7}
}
|
|||||
| Canuto, D., Pantoja, J.L., Han, J., Dutson, E.P. and Eldredge, J.D. | An ensemble Kalman filter approach to parameter estimation for patient-specific cardiovascular flow modeling | 2020 | Theor. Comput. Fluid Dyn. Vol. 34, pp. 521-544 |
article | DOI URL |
| Abstract: Many previous studies have shown that the fidelity of three-dimensional cardiovascular flow simulations depends strongly on inflow and outflow boundary conditions that accurately describe the characteristics of the larger vascular network. These boundary conditions are generally based on lower-dimensional models that represent the upstream or downstream flow behavior in some aggregated fashion. However, the parameters of these models are patient-specific, and no clear technique exists for determining them. In this work, an ensemble Kalman filter (EnKF) is implemented for the purpose of estimating parameters in cardiovascular models through the assimilation of specific patients' clinical measurements. Two types of models are studied: a fully zero-dimensional model of the right heart and pulmonary circulation, and a coupled 0D-1D model of the lower leg. Model parameters are estimated using measurements from both healthy and hypertensive patients, and demonstrate that the EnKF is able to generate distinct parameter sets whose model predictions produce features unique to each measurement set. Attention is also given towards the quality of model predictions made in the absence of direct clinical counterparts, as well as techniques to improve filter robustness against shrinking ensemble covariance. | |||||
BibTeX:
@article{canutojde20,
author = {Canuto, Daniel and Pantoja, Joe L. and Han, Joyce and Dutson, Erik P. and Eldredge, Jeff D.},
title = {An ensemble Kalman filter approach to parameter estimation for patient-specific cardiovascular flow modeling},
journal = {Theor. Comput. Fluid Dyn.},
year = {2020},
volume = {34},
pages = {521--544},
url = {https://drive.google.com/open?id=1vr8J2oFddoA8A0QN0VxrjPUYNt0u4exR},
doi = {https://doi.org/10.1007/s00162-020-00530-2}
}
|
|||||
| Ebrahimi, N.D., Eldredge, J.D. and Ju, Y.S. | Three-dimensional characteristics of the jet flows induced by a pitching plate in a quiescent fluid | 2020 | J. Fluid Mech. Vol. 887, pp. A25 |
article | DOI |
| Abstract: Jet flows induced by pitching cantilever plates provide a power-efficient solution for fluid acceleration and cooling enhancement. In such applications, the time-averaged (mean) properties of the induced jet flows are of great importance. We report a combined experimental and numerical study on the three-dimensional (3-D) characteristics of the mean jet downstream of a harmonically pitching cantilever plate in a quiescent fluid. These characteristics are then correlated with the transient 3-D vortex structures emanated from the trailing and side edges. Our particle image velocimetry and 3-D numerical simulations reveal that the mean induced jet has two distinct regions – a shrinking region immediately downstream of the trailing edge followed by an abrupt expansion region – separated by a necking point. We investigate the transient 3-D wake vortex evolution downstream of the plate to help elucidate the physics underlying the geometry of the mean jet. Our observations suggest that the breakdown of the shed vortex structure and reorientation of the consequent substructures are the primary factors governing the shape of the jet. These factors in turn are controlled primarily by the plate width and the amplitude of the oscillations. The results presented in this study improve our understanding of the complicated 3-D geometry of the induced mean jet in oscillating plates and facilitate optimal design of devices that operate based on this principle, such as piezoelectric fans. | |||||
BibTeX:
@article{ebrahimijde20,
author = {Ebrahimi, Navid Dehdari and Eldredge, Jeff D. and Ju, Y. Sungtaek},
title = {Three-dimensional characteristics of the jet flows induced by a pitching plate in a quiescent fluid},
journal = {J. Fluid Mech.},
year = {2020},
volume = {887},
pages = {A25},
doi = {https://doi.org/10.1017/jfm.2020.2}
}
|
|||||
| Le Provost, M. and Eldredge, J.D. | Mean transport of inertial particles in viscous streaming flows | 2020 | Phys. Rev. Fluids Vol. 5(5), pp. 054302 |
article | URL |
| Abstract: Viscous streaming has emerged as an effective method to transport, trap, and cluster inertial particles in a fluid. Previous work has shown that this transport is well described by the Maxey--Riley equation augmented with a term representing Saffman lift. However, in its straightforward application to viscous streaming flows, the equation suffers from severe numerical stiffness due to the wide disparity between the time scales of viscous response, oscillation period, and slow mean transport, posing a severe challenge for drawing physical insight on mean particle trajectories. In this work, we develop equations that directly govern the mean transport of particles in oscillatory viscous flows. The derivation of these equations relies on a combination of three key techniques. In the first, we develop an inertial particle velocity field via a small Stokes number expansion of the particle's deviation from that of the fluid. This expansion clearly reveals the primary importance of Faxén correction and Saffman lift in effecting the trapping of particles in streaming cells. Then, we apply Generalized Lagrangian Mean theory to unambiguously decompose the transport into fast and slow scales, and ultimately, develop the Lagrangian mean velocity field to govern mean transport. Finally, we carry out an expansion in small oscillation amplitude to simplify the governing equations and to clarify the hierarchy of first- and second-order influences, and particularly, the crucial role of Stokes drift in the mean transport. We demonstrate the final set of equations on the transport of both fluid and inertial particles in configurations involving one cylinder in weak oscillation and two cylinders undergoing such oscillations in sequential intervals. Notably, the new equations allow numerical time steps that are O(10^3) larger than the existing approach with little sacrifice in accuracy, allowing more efficient predictions of transport. | |||||
BibTeX:
@article{leprovostjde20,
author = {Le Provost, Mathieu and Eldredge, Jeff D.},
title = {Mean transport of inertial particles in viscous streaming flows},
journal = {Phys. Rev. Fluids},
year = {2020},
volume = {5},
number = {5},
pages = {054302},
url = {https://drive.google.com/open?id=1vteHhZC8B_TqldeK4Ji_uP4JRciIprZq}
}
|
|||||
| Le Provost, M., Hou, W. and Eldredge, J.D. | Deep learning and data assimilation approaches to sensor reduction in estimation of disturbed separated flows | 2020 | AIAA SciTech 2020, Orlando, Florida. AIAA Paper 2020-0799. | misc | DOI URL |
| Abstract: Unsteady loads created by environmental perturbations - namely gusts - can strongly affect small and light-weighted aerial vehicles. To control vehicle’s behavior in this perturbed environment, a robust, cheap and accurate estimator of the surrounding flow field and aerodynamic load is essential. Low-order inviscid vortex models constitute an attractive solution to this problem. For aerodynamic applications, the role of viscosity is primarily to inject vorticity into the flow. Intrinsically, this mechanism can’t be captured by an inviscid model and need to be modeled. In modern inviscid models, the vorticity shedding criterion is set by the critical leading edge suction parameter (LESP) (Ramesh et al., Theor. Comput. Fluid Dyn., 2013). Without satisfying closure model, the critical LESP has been estimated from data assimilation (Darakananda et al., Phys. Rev. Fluids, 2018) and deep learning (Hou et al., AIAA J., 2019). Refining these works, we explore the influence of the spatial distribution of sensors throughthese two questions: what is the optimal placement of the pressure sensors? How many sensors are required to accurately estimate the LESP? For the deep learning model, a weight vector is determined which measures the influence of each pressure sensor on the final estimate. This weight vector is regularized by the L1 norm to promote sparsity. The number of sensors used is shrunk from 126 to 3 without significant loss of accuracy. Our deep learning framework is interpreted as the learning of a Koopman invariant subspace for the LESP and angle of attack.In the ensemble Kalman filter framework, an iterative algorithm based on the representers identifies the most impactful sensors. We reduce the number of sensors from 50 to 30. | |||||
BibTeX:
@misc{provosthou20,
author = {Le Provost, Mathieu and Hou, Wei and Eldredge, Jeff D.},
title = {Deep learning and data assimilation approaches to sensor reduction in estimation of disturbed separated flows},
year = {2020},
url = {https://drive.google.com/open?id=1r_PATLrqaliWrYVYMzPXlgm9dja1H7US},
doi = {https://doi.org/10.2514/6.2020-0799}
}
|
|||||
| Brenner, M.P., Eldredge, J.D. and Freund, J.B. | Perspective on machine learning for advancing fluid mechanics | 2019 | Phys. Rev. Fluids Vol. 4(10), pp. 100501 |
article | DOI URL |
| Abstract: A perspective is presented on how machine learning (ML), with its burgeoning popularity and the increasing availability of portable implementations, might advance fluid mechanics. As with any numerical or experimental method, ML methods have strengths and limitations, which are acknowledged. Their potential impact is high so long as outcomes are held to the long-standing critical standards that should guide studies of flow physics. | |||||
BibTeX:
@article{brenner2019,
author = {Brenner, M. P. and Eldredge, J. D. and Freund, J. B.},
title = {Perspective on machine learning for advancing fluid mechanics},
journal = {Phys. Rev. Fluids},
year = {2019},
volume = {4},
number = {10},
pages = {100501},
url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.4.100501},
doi = {https://doi.org/10.1103/PhysRevFluids.4.100501}
}
|
|||||
| Caprace, D.-G., Winckelmans, G., Chatelain, P. and Eldredge, J.D. | Wake Vortex Detection and Tracking for Aircraft Formation Flight | 2019 | AIAA AVIATION 2019, Dallas, TX, AIAA Paper 2019-3329 | misc | DOI URL |
| Abstract: Formation flying is known to improve the aerodynamic efficiency of a follower aircraft flying close to the wake vortices of a leader. In this study, two wake sensing strategies designed to locate these vortices are exposed. The first one is based on dedicated measurements of the follower wing circulation distribution and on the control surfaces deflections. The second one relies on measurements from its flight dynamics (position, velocity) and control surfaces. Both techniques implement an Ensemble Kalman Filter for the propagation in time of the non-linear surrogate model, which involves Prandtl lifting lines for the aerodynamics, and a simplified equation of motion. The resulting estimators are tested under steady and unsteady flight conditions, using reference data obtained from the numerical simulation of the associated wake flows using CFD. As a result, an accurate estimation of the wake parameters is produced by both methods, even in configurations where a symmetry was known to hamper the filter efficiency. Noisy configurations are also considered through the addition of ambient turbulence in the simulations. In that case, the second method proves more sensitive to external perturbations. |
|||||
BibTeX:
@misc{caprace19,
author = {Caprace, D.-G. and Winckelmans, G. and Chatelain, P. and Eldredge, J. D.},
title = {Wake Vortex Detection and Tracking for Aircraft Formation Flight},
year = {2019},
url = {https://drive.google.com/open?id=1_f96dSjPAw2OXwDPPtkOoo74TfWN2ahK},
doi = {https://doi.org/10.2514/6.2019-3329}
}
|
|||||
| Darakananda, D. and Eldredge, J.D. | A versatile taxonomy of low-dimensional vortex models for unsteady aerodynamics | 2019 | J. Fluid Mech. Vol. 858, pp. 917-948 |
article | DOI URL |
| Abstract: Inviscid vortex models have been demonstrated to capture the essential physics ofmassively separated flows past aerodynamic surfaces, but they become computationally expensive as coherent vortex structures are formed and the wake is developed. In this work, we present a two-dimensional vortex model in which vortex sheets represent shear layers that separate from sharp edges of the body and point vortices represent the rolled-up cores of these shear layers and the other coherent vortices in the wake. We develop a circulation transfer procedure that enables each vortex sheet to feed its circulation into a point vortex instead of rolling up. This procedure reduces the number of computational elements required to capture the dynamics of vortex formation while eliminating the spurious force that manifests when transferring circulation between vortex elements. By tuning the rate at which the vortex sheets are siphoned into the point vortices, we can adjust the balance between the model's dimensionality and dynamical richness, enabling it to span the entire taxonomy of inviscid vortex models. This hybrid model can capture the development and subsequent shedding of the starting vortices with insignificant wallclock time and remain sufficiently low-dimensional to simulate long time horizon events such as periodic bluff-body shedding. We demonstrate the viability of the method by modeling the impulsive translation of a wing at various fixed angles of attack, pitch-up maneuvers that linearly increase the angle of attack from 0 to 90 degrees, and oscillatory pitching and heaving. We show that the proposed model correctly predicts the dynamics of large-scale vortical structures in the flow by comparing the distributions of vorticity and force responses from results of the proposed model with a model using only vortex sheets and, in some cases, high-fidelity viscous simulation. | |||||
BibTeX:
@article{darakjde2018,
author = {Darakananda, D. and Eldredge, J. D.},
title = {A versatile taxonomy of low-dimensional vortex models for unsteady aerodynamics},
journal = {J. Fluid Mech.},
year = {2019},
volume = {858},
pages = {917--948},
url = {https://drive.google.com/open?id=15z7f2cRW4Dk7gMHwT80Kjh2FxnU7tieq},
doi = {https://doi.org/10.1017/jfm.2018.792}
}
|
|||||
| Ebrahimi, N.D., Eldredge, J.D. and Ju, Y.S. | Wake vortex regimes of a pitching cantilever plate in quiescent air and their correlation with mean flow generation | 2019 | J. Fluids Struct. Vol. 84, pp. 408-420 |
article | DOI URL |
| Abstract: Jet flows induced by oscillating cantilever plates enable power-efficient cooling enhancement and fluid acceleration. We report a combined experimental and numerical study of the vortex regimes present in the wake of a harmonically oscillating thin cantilever plate in a quiescent fluid and analyze their effect on the flow generation downstream. We use Particle Image Velocimetry (PIV) in conjunction with two-dimensional numerical simulations to investigate the vortex evolution around the trailing edge of the plates with different geometries and vibrational properties. Our observations suggest the existence of three distinct regimes in the wake: non-propagating, intermediate and propagating. Comparing the temporal decay of the vortex circulation in different regimes shows that different mechanisms are involved in the formation of these vortical patterns. A regime map is proposed next, denoting the incident of each vortex regime as a function of relevant dimensionless parameters. Our analysis of the mean jet on the normal mid-plane, as quantified by the momentum-averaged Reynolds number Re_jet, shows that the induced jet downstream the trailing edge is tightly correlated with the identified vortex regimes.The present study improves our understanding of vortex generation and propagation in oscillating cantilevers and facilitates optimized design and operation of piezoelectric fans and similar devices. | |||||
BibTeX:
@article{ebrahimijde18,
author = {Ebrahimi, N. D. and Eldredge, J. D. and Ju, Y. S.},
title = {Wake vortex regimes of a pitching cantilever plate in quiescent air and their correlation with mean flow generation},
journal = {J. Fluids Struct.},
year = {2019},
volume = {84},
pages = {408--420},
url = {https://drive.google.com/open?id=1628m8wmRYGBM8GsHUJNt5mQrEEm1TNxy},
doi = {https://doi.org/10.1016/j.jfluidstructs.2018.11.010}
}
|
|||||
| Eldredge, J.D. | Mathematical Modeling of Unsteady Inviscid Flows [BibTeX] |
2019 | Vol. 50 |
book | DOI |
BibTeX:
@book{inviscidbook,
author = {J. D. Eldredge},
title = {Mathematical Modeling of Unsteady Inviscid Flows},
publisher = {Springer},
year = {2019},
volume = {50},
doi = {https://doi.org/10.1007/978-3-030-18319-6}
}
|
|||||
| Eldredge, J.D. and Jones, A.R. | Leading-Edge Vortices: Mechanics and Modeling | 2019 | Annu. Rev. Fluid Mech. Vol. 51, pp. 75-104 |
article | DOI |
| Abstract: The leading-edge vortex (LEV) is known to produce transient high lift in a wide variety of circumstances. The underlying physics of LEV formation, growth, and shedding are explored for a set of canonical wing motions including wing translation, rotation, and pitching. A review of the literature reveals that, while there are many similarities in the LEV physics of these motions, the resulting force histories can be dramatically different. In two-dimensional motions (translation and pitch), the LEV sheds soon after its formation; lift drops as the LEV moves away from the wing. Wing rotation, in contrast, incites a spanwise flow that, through Coriolis tilting, balances the streamwise vorticity fluxes to produce an LEV that remains attached to much of the wing and thus sustains high lift. The state of the art of vortex-based modeling to capture both the flow field and corresponding forces of these motions is reviewed, including closure conditions at the leading edge and approaches for data-driven strategies. | |||||
BibTeX:
@article{jdearfm19,
author = {Eldredge, J. D. and Jones, A. R.},
title = {Leading-Edge Vortices: Mechanics and Modeling},
journal = {Annu. Rev. Fluid Mech.},
year = {2019},
volume = {51},
pages = {75--104},
doi = {https://doi.org/10.1146/annurev-fluid-010518-040334}
}
|
|||||
| Hou, W., Darakananda, D. and Eldredge, J.D. | Machine learning-based detection of aerodynamic disturbances using surface pressure measurements | 2019 | AIAA J. Vol. 57(12), pp. 5079-5093 |
article | DOI URL |
| Abstract: Aerodynamic disturbances, due to gusts or maneuvers or a combination, leave a signature in the pressures exerted on the wing surface. In this work, we explore the question: To what extent can the characteristics of these disturbances be parsed from the measured pressures alone? We apply a supervised learning algorithm based on several layers of neural networks. The overall machine learning architecture is trained and tested on aerodynamic disturbance data generated by an inviscid vortex method applied to a two-dimensional flat plate undergoing a smooth pitch-up maneuver. As a surrogate for an incident gust, we perturb the critical leading-edge suction parameter (LESP), which in turn dynamically changes the flux of vorticity from the leading edge. The results are used to train the algorithm to estimate the LESP and angle of attack histories from the surface pressure. We use two different approaches. In the first, a purely machine learning strategy, we use a combination of convolutional and recurrent neural networks that accept surface pressure measurements as input. The overall architecture is shown to achieve an accurate estimation of the LESP and angle of attack. In the second approach, we integrate machine learning with a dynamical systems framework to learn a dynamical model for the angle of attack and LESP. We show that this machine-learned system identification (MLSID) approach achieves somewhat higher accuracy compared to the purely machine learning approach with fewer parameters. In both approaches, we show that overfitting is mitigated by injecting random noise into the input pressures. | |||||
BibTeX:
@article{houjdeaiaaj19,
author = {Hou, W. and Darakananda, D. and Eldredge, J. D.},
title = {Machine learning-based detection of aerodynamic disturbances using surface pressure measurements},
journal = {AIAA J.},
year = {2019},
volume = {57},
number = {12},
pages = {5079--5093},
url = {https://arc.aiaa.org/doi/pdf/10.2514/1.J058486},
doi = {https://doi.org/10.2514/1.J058486}
}
|
|||||
| Hou, W., Darakananda, D. and Eldredge, J.D. | Machine learning based detection of flow disturbances using surface pressure measurements | 2019 | AIAA SciTech 2019, San Diego, California. AIAA Paper 2019-1148 | misc | URL |
| Abstract: Discrete vortex methods have been demonstrated in recent years to efficiently capturethe physics of separated airfoil flows, often with the help of a criterion that specifiesthe instantaneous release of vorticity from the leading edge of the airfoil. The releaseis determined by the degree to which the suction exceeds a threshold, called the criticalleading-edge suction parameter (LESP). The value of this critical LESP is not known apriori, and, particularly in the presence of external disturbances such as incident gusts andairfoil maneuvers, may vary in time. However, the fidelity of the vortex model, and itsutility for estimating flows, depend crucially on this critical LESP as well on knowledgeof the airfoil's angle of attack, which may also be varying in time. This study focuses onthe question: To what extent can these two time-varying model parameters be detectedfrom surface pressure measurements? To address this question, we apply a combinationof state-of-the-art algorithms in machine learning. In the first approach, we demonstratea purely machine learning approach, using a combination of convolutional and recurrentneural networks that accept surface pressure measurements as input. The overall architectureis shown to achieve a reasonably accurate prediction of the LESP; the structure isgeneralized to the task of detecting angle of attack with minor modifications. In the secondapproach, we integrate machine learning with a dynamical systems framework to learn alinear dynamical model for the time-varying angle of attack in the presence of gusts. Weshow that this machine-learned system identification approach achieves higher accuracycompared to the purely machine learning approach with fewer parameters. However, itsuse for predicting the LESP requires further work. | |||||
BibTeX:
@misc{houjde19,
author = {Hou, W. and Darakananda, D. and Eldredge, J. D.},
title = {Machine learning based detection of flow disturbances using surface pressure measurements},
year = {2019},
url = {https://drive.google.com/open?id=166yCcckX4HDP3iZ-A_-tu-ylEor5-vaF}
}
|
|||||
| Li, L., Maccabi, A., Abiri, A., Juo, Y.-Y., Zhang, W., Chang, Y.-J., Saddik, G.N., Jin, L., Grundfest, W.S., Dutson, E.P., Eldredge, J.D., Benharash, P. and Candler, R.N. | Characterization of Perfused and Sectioned Liver Tissue In A Full Indentation Cycle Using A Visco-hyperelastic Model | 2019 | J. Mech. Behav. Biomed. Mater. Vol. 90, pp. 591-603 |
article | DOI URL |
| Abstract: Realistic modeling of biologic material is required for optimizing fidelity in computer-aided surgical training and assistance systems. The modeling of liver tissue has remained challenging due to its nonlinear viscoelastic properties and high hysteresis of the stress-strain relation. While prior studies have described the behavior of liver tissue during the loading status (in elongation, compression, or indentation tests) or unloading status (in stress relaxation or creep tests), a hysteresis curve with both loading and unloading processes was incompletely defined. We seek to use a single material model to characterize the mechanical properties of liver tissue in a full indentation cycle ex vivo perfused and then sectioned. Based on measurements taken from ex-vivo perfused porcine livers, we converted force-displacement curves to stress-strain curves and developed a visco-hyperelastic constitutive model to characterize the liver's mechanical behavior at different locations under various rates of indentation (1, 2, 5, 10, and 20 mm/s). The proposed model is a mixed visco-hyperelastic model with up to 6 coefficients. The normalized root mean square standard deviations of fitted curves are less than 5% and 10% in low (< 0.05) and high strain (>0.3) conditions respectively. | |||||
BibTeX:
@article{li2018characterization,
author = {Li, L. and Maccabi, A. and Abiri, A. and Juo, Y.-Y. and Zhang, W. and Chang, Y.-J. and Saddik, G. N. and Jin, L. and Grundfest, W. S. and Dutson, E. P. and Eldredge, J. D. and Benharash, P. and Candler, R. N.},
title = {Characterization of Perfused and Sectioned Liver Tissue In A Full Indentation Cycle Using A Visco-hyperelastic Model},
journal = {J. Mech. Behav. Biomed. Mater.},
publisher = {Elsevier},
year = {2019},
volume = {90},
pages = {591--603},
url = {https://drive.google.com/open?id=1648LxJrIPWRmEHXhAyaIi4irdRnXiDfs},
doi = {https://doi.org/10.1016/j.jmbbm.2018.11.006}
}
|
|||||
| Canuto, D., Chong, K., Bowles, C., Dutson, E.P., Eldredge, J.D. and Benharash, P. | A regulated multiscale closed-loop cardiovascular model, with applications to hemorrhage and hypertension | 2018 | International Journal for Numerical Methods in Biomedical Engineering Vol. 34(6), pp. e2975 |
article | DOI URL |
| Abstract: A computational tool is developed for simulating the dynamic response of the human cardiovascular system to various stressors and injuries. The tool couples 0‐dimensional models of the heart, pulmonary vasculature, and peripheral vasculature to 1‐dimensional models of the major systemic arteries. To simulate autonomic response, this multiscale circulatory model is integrated with a feedback model of the baroreflex, allowing control of heart rate, cardiac contractility, and peripheral impedance. The performance of the tool is demonstrated in 2 scenarios: neurogenic hypertension by sustained stimulation of the sympathetic nervous system and an acute 10% hemorrhage from the left femoral artery. | |||||
BibTeX:
@article{Canuto2018,
author = {Canuto, D. and Chong, K. and Bowles, C. and Dutson, E. P. and Eldredge, J. D. and Benharash, P.},
title = {A regulated multiscale closed-loop cardiovascular model, with applications to hemorrhage and hypertension},
journal = {International Journal for Numerical Methods in Biomedical Engineering},
publisher = {Wiley Online Library},
year = {2018},
volume = {34},
number = {6},
pages = {e2975},
url = {https://drive.google.com/open?id=12RUYQG18FA-_QGY9PpYewso08uRmLQjJ},
doi = {https://doi.org/10.1002/cnm.2975}
}
|
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| Darakananda, D., Eldredge, J.D., da Silva, A.F.C., Colonius, T. and Williams, D.R. | EnKF-based Dynamic Estimation of Separated Flows with a Low-Order Vortex Model | 2018 | AIAA SciTech 2018, Kissimmee, Florida. AIAA Paper 2018-0811 | misc | URL |
| Abstract: A data-driven vortex model of the unsteady aerodynamics of a two-dimensional separated flow is constructed. The vortex model relies on a standard collection of regularized vortex elements that interact mutually and with an infinitely-thin flat plate. In order to maintain a low-dimensional representation, with fewer than O(100) degrees of freedom, a novel aggregation procedure is developed and utilized in which vortex elements are coalesced at each time step. A flow state vector, composed of vortex elements properties as well as the critical leading-edge suction parameter of Ramesh and Gopalarathnam (J. Fluid Mech., 2014), is advanced within an ensemble Kalman filter (EnKF) framework. In this framework, surface pressure measurements, sampled from a truth case, are used to correct the states of an ensemble of randomly-initiated vortex element models. The estimation algorithm is applied to several scenarios of a flat plate impulsively started at 20 degrees angle of attack at Reynolds number 500, in which the truth case comprises a high-fidelity Navier--Stokes simulation. The algorithm provides a good estimate of the flow as well as the aerodynamic force in both the baseline undisturbed case (a separated flow) as well as in the presence of one or more incident gusts, despite lack of a priori knowledge of the incident gust character. | |||||
BibTeX:
@misc{darwinaiaa18,
author = {Darakananda, D. and Eldredge, J. D. and da Silva, A. F. C. and Colonius, T. and Williams, D. R.},
title = {EnKF-based Dynamic Estimation of Separated Flows with a Low-Order Vortex Model},
year = {2018},
url = {https://drive.google.com/open?id=113dckQiDUqn922dEmg8Y8_Dy_cMuuHDD}
}
|
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| Darakananda, D., da Silva, A.F.d.C., Colonius, T. and Eldredge, J.D. | Data-assimilated low-order vortex modeling of separated flows | 2018 | Phys. Rev. Fluids Vol. 3(12), pp. 124701 |
article | DOI |
| Abstract: Vortex models have been used for decades as computationally-efficient tools to investigate unsteady aerodynamics. However, their utility for separated flows---particularly, when such flows are subjected to incident disturbances---has been hindered by the trade-off between the model's physical fidelity and its expectation for fast prediction (e.g. relative to computational fluid dynamics). In this work, it is shown that physical fidelity and speed can be simultaneously achieved by assimilating measurement data into the model to compensate for unrepresented physics. The underlying inviscid vortex model captures the transport of vortex structures with a standard collection of regularized vortex elements that interact mutually and with an infinitely-thin flat plate. In order to maintain a low-dimensional representation, with fewer than O(100) degrees of freedom, a novel aggregation procedure is developed and utilized in which vortex elements are coalesced at each time step. A flow state vector, composed of vortex element properties as well as the critical leading-edge suction parameter, is advanced within an ensemble Kalman filter (EnKF) framework. In this framework, surface pressure is used to correct the states of an ensemble of randomly-initiated vortex models. The overall algorithm is applied to several scenarios of an impulsively started flat plate, in which data from a high-fidelity Navier--Stokes simulation at Reynolds number 500 are used as a surrogate for the measurements. The assimilated vortex model efficiently and accurately predicts the evolving flow as well as the normal force in both the undisturbed case (a separated flow) as well as in the presence of one or more incident gusts, despite lack of a priori knowledge of the gust's characteristics. | |||||
BibTeX:
@article{darakjdeprf18,
author = {Darakananda, D. and da Silva, A. F. de C. and Colonius, T. and Eldredge, J. D.},
title = {Data-assimilated low-order vortex modeling of separated flows},
journal = {Phys. Rev. Fluids},
year = {2018},
volume = {3},
number = {12},
pages = {124701},
doi = {https://doi.org/10.1103/PhysRevFluids.3.124701}
}
|
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| An, X., Williams, D.R., da Silva, A.F.C., Colonius, T. and Eldredge, J.D. | Response of the Separated Flow over an Airfoil to a Short-Time Actuator Burst | 2017 | 47th AIAA Fluid Dynamics Conference, Denver, CO, June 2017. AIAA Paper 2017-3315 | misc | URL |
| Abstract: Experimental measurements of the flow structure evolving in the separated flow over an NACA 0009 wing at 12o angle of attack were obtained with particle image velocimetry, surface pressures, and force transducer measurements of the lift coefficient and pitching moment coefficient. Phase-averaged two-dimensional velocity field measurements provide details of the separated shear layer evolution following a four-pulse burst sequence from a synthetic jet actuator. The flow field development is quite similar to the observations made by Brzozowski, et al. (2010), who used a pulsed-combustion actuator that is orders of magnitude stronger than the synthetic jet. Proper orthogonal decomposition of the PIV data sets showed that the combination of the time-varying coefficients modes 1 and 2 correlate with the negative of the lift coefficient response. The surface pressure signals were correlated with the roll up and convection of the large-scale vortex structure that follows the actuator burst input. A spatially localized region of high pressure occurs below and slightly behind a ``kink'' that forms in the shear layer. A localized region of high surface pressure that follows the kinked region correlates with the lift reversal that occurs within 2.0t+ after the burst signal was triggered. | |||||
BibTeX:
@misc{an2017,
author = {An, X. and Williams, D. R. and da Silva, A. F. C. and Colonius, T. and Eldredge, J. D.},
title = {Response of the Separated Flow over an Airfoil to a Short-Time Actuator Burst},
year = {2017},
url = {https://drive.google.com/open?id=12G7DAjSkNgHwhcweozXbiOf97VDa-ISO}
}
|
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| Bowles, C., Canuto, D., Teran, J., Dutson, E., Plurad, D., Eldredge, J. and Benharash, P. | Current Methods and Advances in Simulation of Hemorrhage after Trauma [BibTeX] |
2017 | The American Surgeon Vol. 83(10), pp. 1137-1141 |
article | URL |
BibTeX:
@article{b,
author = {Bowles, C. and Canuto, D. and Teran, J. and Dutson, E. and Plurad, D. and Eldredge, J. and Benharash, P.},
title = {Current Methods and Advances in Simulation of Hemorrhage after Trauma},
journal = {The American Surgeon},
year = {2017},
volume = {83},
number = {10},
pages = {1137--1141},
url = {http://www.ingentaconnect.com/content/sesc/tas/2017/00000083/00000010/art00025}
}
|
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| Chong, K., Jiang, C., Ram, D., Santhanam, A., Terzopoulos, D., Benharash, P., Dutson, E., Teran, J. and Eldredge, J.D. | Visualization of vascular injuries in extremity trauma | 2017 | Med. Biol. Eng. Comput. Vol. 55(9), pp. 1709-1718 |
article | DOI URL |
| Abstract: A tandem of particle-based computational methods is adapted to simulate injury and hemorrhage in the human body. In order to ensure anatomical fidelity, a three-dimensional model of a targeted portion of the human body is reconstructed from a dense sequence of CT scans of an anonymized patient. Skin, bone and muscular tissue are distinguished in the imaging data and assigned with their respective material properties. An injury geometry is then generated by simulating the mechanics of a ballistic projectile passing through the anatomical model with the material point method. From the injured vascular segments identified in the resulting geometry, smoothed particle hydrodynamics (SPH) is employed to simulate bleeding, based on inflow boundary conditions obtained from a network model of the systemic arterial tree. Computational blood particles interact with the stationary particles representing impermeable bone and skin and permeable muscular tissue through the Brinkman equations for porous media. The SPH results are rendered in post-processing for improved visual fidelity. The overall simulation strategy is demonstrated on an injury scenario in the lower leg. | |||||
BibTeX:
@article{Chong2017,
author = {Chong, K. and Jiang, C. and Ram, D. and Santhanam, A.nd and Terzopoulos, D. and Benharash, P. and Dutson, E. and Teran, J. and Eldredge, J. D.},
title = {Visualization of vascular injuries in extremity trauma},
journal = {Med. Biol. Eng. Comput.},
publisher = {Springer},
year = {2017},
volume = {55},
number = {9},
pages = {1709--1718},
url = {https://drive.google.com/open?id=11hxqKNd8bT49Y9_SZBcMU2pa80OXbMtD},
doi = {https://doi.org/10.1007/s11517-017-1619-9}
}
|
|||||
| Darakananda, D. | Vortex Models for Data Assimilation [BibTeX] |
2017 | School: University of California, Los Angeles | phdthesis | URL |
BibTeX:
@phdthesis{darwinthesis17,
author = {Darakananda, Darwin},
title = {Vortex Models for Data Assimilation},
school = {University of California, Los Angeles},
year = {2017},
note = {eldredge},
url = {https://drive.google.com/open?id=10ql0ty6YFAmqDhNKnGe0Bm1adu6-64HV}
}
|
|||||
| Huang, C.-J. | Numerical Tool Development of Fluid-Structure Interactions in Upper Airway for Investigation of Obstructive Sleep Apnea [BibTeX] |
2017 | School: University of California, Los Angeles | phdthesis | URL |
BibTeX:
@phdthesis{chuangthesis17,
author = {Huang, C.-J.},
title = {Numerical Tool Development of Fluid-Structure Interactions in Upper Airway for Investigation of Obstructive Sleep Apnea},
school = {University of California, Los Angeles},
year = {2017},
note = {eldredge},
url = {https://drive.google.com/open?id=15DNxIfsbwKH4fMo3t7Si2stdo3EJGB5C}
}
|
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| An, X., Williams, D.R., Eldredge, J.D. and Colonius, T. | Modeling dynamic lift response to actuation | 2016 | 54th AIAA Aerospace Sciences Meeting, San Diego, CA. AIAA Paper 2016-0058 | misc | URL |
| Abstract: The dynamic lift response of an airfoil to sinusoidal amplitude variations from a synthetic jet actuator was studied. The wing was at a fixed angle of attack, and the actuator operated in a 'burst-mode' with a fixed duty cycle. The actuator burst amplitude was used as a control signal, which was varied between an 'off' condition and the actuator saturation voltage. Three dimensionless frequencies were examined, corresponding to k = fc/U= 0.064, 0.128, and 0.25. Hysteresis loops in the lift increment were observed, whose shapes were dependent on the control frequency. Three different approaches to modeling the lift increment response were explored: a linear convolution approach, a nonlinear time delay and decay model, and a combination of those two. The linear convolution captures the high frequency content of the lift response, but becomes inaccurate when the actuator burst period is less than 3.5 convective times. The time delay and decay model reproduces the low frequency component of the lift response, but not the high frequency. When the control frequency becomes large, (k = 0.25), then the largest time-varying lift increment is produced near the minimum of the actuator voltage. | |||||
BibTeX:
@misc{anwilliams16,
author = {X. An and D. R. Williams and J. D. Eldredge and T. Colonius},
title = {Modeling dynamic lift response to actuation},
year = {2016},
url = {https://drive.google.com/open?id=1-g3k-QVekAavFLbWFvDmYHqrPwnj2HE3}
}
|
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| Chong, K., Kelly, S.D., Smith, S.T. and Eldredge, J.D. | Transport of inertial particles by viscous streaming in arrays of oscillating probes | 2016 | Phys. Rev. E Vol. 93(1), pp. 013109 |
article | DOI URL |
| Abstract: A mechanism for the transport of microscale particles in viscous fluids is demonstrated. The mechanism exploits the trapping of such particles by rotational streaming cells established in the vicinity of an oscillating cylinder, recently analyzed in previous work. The present work explores a strategy of transporting particles between the trapping points established by multiple cylinders undergoing oscillations in sequential intervals. It is demonstrated that, by controlling the sequence of oscillation intervals, an inertial particle is effectively and predictably transported between the stable trapping points. Arrays of cylinders in various arrangements are investigated, revealing a technique for constructing arbitrary particle trajectories. It is found that the domain from which particles can be transported and trapped by an oscillator is extended, even to regions in which particles are shielded, by the presence of other stationary cylinders. The timescales for transport are examined, as are the mechanisms by which particles are drawn away from an obstacle toward the trapping point of an oscillator. | |||||
BibTeX:
@article{chong16,
author = {Chong, K. and Kelly, S. D. and Smith, S. T. and Eldredge, J. D.},
title = {Transport of inertial particles by viscous streaming in arrays of oscillating probes},
journal = {Phys. Rev. E},
year = {2016},
volume = {93},
number = {1},
pages = {013109},
url = {https://drive.google.com/open?id=1-pxXMNsnfAmb2XT514k5PjBSWcboik7M},
doi = {https://doi.org/10.1103/PhysRevE.93.013109}
}
|
|||||
| Darakananda, D., Eldredge, J.D., Colonius, T. and Williams, D.R. | A vortex sheet/point vortex dynamical model for unsteady separated flows | 2016 | 54th AIAA Aerospace Sciences Meeting, San Diego, CA. AIAA Paper 2016-2072 | misc | URL |
| Abstract: This paper presents a hybrid vortex sheet/point vortex method for modeling unsteady/separated flows. We use vortex sheets to capture the dynamics of the shear layers immediately behind a wing in motion. The sheets provide a natural way of capturing vortex shedding, a feature missing from many point vortex models. We overcome the high computational cost traditionally associated with vortex sheet methods by approximating the spiraling cores of the sheets using point vortices with time-varying circulation. Circulation is continuously truncated from the tips of the vortex sheets and fed into their associated point vortices. To compensate for the discontinuous force response that results from this redistribution of vorticity, we adjust the velocity of the variable strength point vortices. We demonstrate the viability of the method by modeling the impulsive translation of a wing at a fixed angle of attack. We show that the proposed model correctly predicts the dynamics of large-scale vortical structures in the flow by comparing the distribution of vorticity from results of high-fidelity simulation, a model using only vortex sheets, and the proposed model. For the test cases attempted, the hybrid model predicts similar force responses to those of the sheet-only model, while being orders of magnitude faster. | |||||
BibTeX:
@misc{darakeldredge16,
author = {D. Darakananda and J. D. Eldredge and T. Colonius and D. R. Williams},
title = {A vortex sheet/point vortex dynamical model for unsteady separated flows},
year = {2016},
url = {https://drive.google.com/open?id=10CAUg_Ds-lU-rUdpbRPpVONldYK307ni}
}
|
|||||
| Eldredge, J.D. and Mittal, R. | Recent developments in multiphysics computational models of physiological flows | 2016 | Theor. Comput. Fluid Dyn. Vol. 30(1-2), pp. 1-2 |
article | DOI URL |
| Abstract: A mini-symposium on computational modeling of fluid--structure interactions and other multiphysics in physiological flows was held at the 11th World Congress on Computational Mechanics in July 2014 in Barcelona, Spain. This special issue of Theoretical and Computational Fluid Dynamics contains papers from among the participants of the mini-symposium. The present paper provides an overview of the mini-symposium and the special issue. | |||||
BibTeX:
@article{Eldredge2016,
author = {Eldredge, J. D. and Mittal, R.},
title = {Recent developments in multiphysics computational models of physiological flows},
journal = {Theor. Comput. Fluid Dyn.},
publisher = {Springer},
year = {2016},
volume = {30},
number = {1--2},
pages = {1--2},
url = {https://drive.google.com/open?id=138W7cU9fxFIiyslkeaxB83GKdreZbRPO},
doi = {https://doi.org/10.1007/s00162-016-0381-1}
}
|
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| Greene, P.T., Eldredge, J.D., Zhong, X. and Kim, J. | A high-order multi-zone cut-stencil method for numerical simulations of high-speed flows over complex geometries | 2016 | J. Comput. Phys. Vol. 316, pp. 652-681 |
article | DOI URL |
| Abstract: In this paper, we present a method for performing uniformly high-order direct numerical simulations of high-speed flows over arbitrary geometries. The method was developed with the goal of simulating and studying the effects of complex isolated roughness elements on the stability of hypersonic boundary layers. The simulations are carried out on Cartesian grids with the geometries imposed by a third-order cut-stencil method. A fifth-order hybrid weighted essentially non-oscillatory scheme was implemented to capture any steep gradients in the flow created by the geometries and a third-order Runge--Kutta method is used for time advancement. A multi-zone refinement method was also utilized to provide extra resolution at locations with expected complex physics. The combination results in a globally fourth-order scheme in space and third order in time. Results confirming the method's high order of convergence are shown. Two-dimensional and three-dimensional test cases are presented and show good agreement with previous results. A simulation of Mach 3 flow over the logo of the Ubuntu Linux distribution is shown to demonstrate the method's capabilities for handling complex geometries. Results for Mach 6 wall-bounded flow over a three-dimensional cylindrical roughness element are also presented. The results demonstrate that the method is a promising tool for the study of hypersonic roughness-induced transition. | |||||
BibTeX:
@article{Greene2016,
author = {Greene, P. T. and Eldredge, J. D. and Zhong, X. and Kim, J.},
title = {A high-order multi-zone cut-stencil method for numerical simulations of high-speed flows over complex geometries},
journal = {J. Comput. Phys.},
publisher = {Elsevier},
year = {2016},
volume = {316},
pages = {652--681},
url = {https://drive.google.com/open?id=14TpoC82Z6Q4jJ_4H8Z5OB8MnLxqawHAU},
doi = {https://doi.org/10.1016/j.jcp.2016.04.032}
}
|
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| Huang, C.-J., Huang, S.-C., White, S.M., Mallya, S.M. and Eldredge, J.D. | Toward numerical simulations of fluid--structure interactions for investigation of obstructive sleep apnea | 2016 | Theor. Comput. Fluid Dyn. Vol. 30(1-2), pp. 87-104 |
article | DOI URL |
| Abstract: Obstructive sleep apnea (OSA) is a medical condition characterized by repetitive partial or complete occlusion of the airway during sleep. The soft tissues in the airway of OSA patients are prone to collapse under the low-pressure loads incurred during breathing. This paper describes efforts toward the development of a numerical tool for simulation of air--tissue interactions in the upper airway of patients with sleep apnea. A procedure by which patient-specific airway geometries are segmented and processed from dental cone-beam CT scans into signed distance fields is presented. A sharp-interface embedded boundary method based on the signed distance field is used on Cartesian grids for resolving the airflow in the airway geometries. For simulation of structure mechanics with large expected displacements, a cut-cell finite element method with nonlinear Green strains is used. The fluid and structure solvers are strongly coupled with a partitioned iterative algorithm. Preliminary results are shown for flow simulation inside the three-dimensional rigid upper airway of patients with obstructive sleep apnea. Two validation cases for the fluid--structure coupling problem are also presented. | |||||
BibTeX:
@article{Huang2016,
author = {Huang, C.-J. and Huang, S.-C. and White, S. M. and Mallya, S. M. and Eldredge, J. D.},
title = {Toward numerical simulations of fluid--structure interactions for investigation of obstructive sleep apnea},
journal = {Theor. Comput. Fluid Dyn.},
publisher = {Springer},
year = {2016},
volume = {30},
number = {1-2},
pages = {87--104},
url = {https://drive.google.com/open?id=14E6eC3FuZZLgYGe8nX2cVFiOZxmM0px6},
doi = {https://doi.org/10.1007/s00162-015-0368-3}
}
|
|||||
| Huang, C.-J., Huang, S.-C., White, S.M., Mallya, S.M. and Eldredge, J.D. | Erratum to: Toward numerical simulations of fluid--structure interactions for investigation of obstructive sleep apnea [BibTeX] |
2016 | Theor. Comput. Fluid Dyn. Vol. 30(1-2) |
article | DOI URL |
BibTeX:
@article{Huang2016a,
author = {Huang, C.-J. and Huang, S.-C. and White, S. M. and Mallya, S. M. and Eldredge, J. D.},
title = {Erratum to: Toward numerical simulations of fluid--structure interactions for investigation of obstructive sleep apnea},
journal = {Theor. Comput. Fluid Dyn.},
year = {2016},
volume = {30},
number = {1-2},
url = {https://drive.google.com/open?id=120uRT58_GCRtTliFrHp79dl4-1Ks6LRH},
doi = {https://doi.org/10.1007/s00162-015-0372-7}
}
|
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| Kafashi, S., Strayhorn, R., Eldredge, J.D., Kelly, S.D., Woody, S.C. and Smith, S.T. | Theoretical and experimental study of the dynamic response of absorber-based, micro-scale, oscillatory probes for contact sensing applications | 2016 | Rev. Sci. Instrum. Vol. 87(6), pp. 065005 |
article | DOI URL |
| Abstract: This paper presents two models for predicting the frequency response of micro-scale oscillatory probes. These probes are manufactured by attaching a thin fiber to the free end of one tine of a quartz tuning fork oscillator. In these studies, the attached fibers were either 75 μm diameter tungsten or 7 μm diameter carbon with lengths ranging from around 1 to 15 mm. The oscillators used in these studies were commercial 32.7 kHz quartz tuning forks. The first theoretical model considers lateral vibration of two beams serially connected and provides a characteristic equation from which the roots (eigenvalues) are extracted to determine the natural frequencies of the probe. A second, lumped model approximation is used to derive an approximate frequency response function for prediction of tine displacements as a function of a modal force excitation corresponding to the first mode of the tine in the absence of a fiber. These models are used to evaluate the effect of changes in both length and diameter of the attached fibers. Theoretical values of the natural frequencies of different modes show an asymptotic relationship with the length and a linear relationship with the diameter of the attached fiber. Similar results are observed from experiment, one with a tungsten probe having an initial fiber length of 14.11 mm incrementally etched down to 0.83 mm, and another tungsten probe of length 8.16 mm incrementally etched in diameter, in both cases using chronocoulometry to determine incremental volumetric material removal. The lumped model is used to provide a frequency response again reveals poles and zeros that are consistent with experimental measurements. Finite element analysis shows mode shapes similar to experimental microscope observations of the resonating carbon probes. This model provides a means of interpreting measured responses in terms of the relative motion of the tine and attached fibers. Of particular relevance is that, when a ``zero'' is observed in the response of the tine, one mode of the fiber is matched to the tine frequency and is acting as an absorber. This represents an optimal condition for contact sensing and for transferring energy to the fiber for fluid mixing, touch sensing, and surface modification applications. | |||||
BibTeX:
@article{kafashi16,
author = {Kafashi, S. and Strayhorn, R. and Eldredge, J. D. and Kelly, S. D. and Woody, S. C. and Smith, S. T.},
title = {Theoretical and experimental study of the dynamic response of absorber-based, micro-scale, oscillatory probes for contact sensing applications},
journal = {Rev. Sci. Instrum.},
year = {2016},
volume = {87},
number = {6},
pages = {065005},
url = {https://drive.google.com/open?id=13Eh4eZKBAYs1UCMCalQTqJtlqOf_lMM4},
doi = {https://doi.org/10.1063/1.4954164}
}
|
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| Eldredge, J.D. and Darakananda, D. | Reduced-order two- and three-dimensional vortex modeling of unsteady separated flows | 2015 | 53rd AIAA Aerospace Sciences Meeting, Kissimmee, FL. AIAA Paper 2015-1749 | misc | URL |
| Abstract: This paper presents extensions to ongoing efforts to develop model reduction techniques for unsteady aerodynamics. The overarching objective of these efforts is to construct a data-driven modeling framework that preserves the important non-linear interactions in the aerodynamic flows associated with rapid maneuvers, particularly those involving dynamic stall. The current study consists of two primary developments from previous work. First, a 'bootstrapping' technique is presented that enables our previously-developed model optimization procedure to incorporate new data as it becomes available. The technique is demonstrated on a two-dimensional point vortex model of the rapid pitch-up of a flat plate in a steady free stream, optimized from high-fidelity simulation data. The bootstrapping ensures that the model optimization converges much faster, and operates in a form that pushes the technique from post-processing toward a predictive capacity. Second, a three-dimensional low-order vortex model is constructed, based on the dynamics of a small number of vortex loops with time-varying strength. In the model, the loops evolve according to a dynamical equation that is derived from the impulse matching principle, extended here from the previous two-dimensional point vortex context. The three-dimensional model is demonstrated, using a basic phenomenological sub-model for determining loop strengths, on simple maneuvers of low aspect ratio flat plates. | |||||
BibTeX:
@misc{jdedarak15,
author = {J. D. Eldredge and D. Darakananda},
title = {Reduced-order two- and three-dimensional vortex modeling of unsteady separated flows},
year = {2015},
url = {https://drive.google.com/open?id=11PZZsU2LMkPA3j47LHEW6OdikhZ7U9Jr}
}
|
|||||
| Medina, A., Eldredge, J.D., Kweon, J. and Choi, H. | Illustration of wing deformation effects in three-dimensional flapping flight | 2015 | AIAA J. Vol. 53(9), pp. 2607-2620 |
article | DOI URL |
| Abstract: This study numerically investigates the aerodynamic effects of deformation on three-dimensional low aspect ratio wings engaged in hover kinematics. The immersed-boundary finite-volume method is used to solve the Navier--Stokes equations. Deformations are actively prescribed and are represented as deflections about axes that transect the rectangular planform. Two distinct deformation modes associated with tip and root deflection are explored, in addition to a rigid wing counterpart. Variation of the phase between deflection and flapping enables mimicry of a range of wing behavior observed in nature. It is found the introduction of root or tip deflection can increase efficiency by as much as 19.5% or 19.0% respectively. The development of vortical structures about the wing is investigated. It is shown that while the rotational axis of the leading-edge vortex is insensitive to deformation, the shape and orientation of cores of the vortex is modified. | |||||
BibTeX:
@article{medina2015illustration,
author = {Medina, A. and Eldredge, J. D. and Kweon, J. and Choi, H.},
title = {Illustration of wing deformation effects in three-dimensional flapping flight},
journal = {AIAA J.},
publisher = {American Institute of Aeronautics and Astronautics},
year = {2015},
volume = {53},
number = {9},
pages = {2607--2620},
url = {https://drive.google.com/open?id=14b04Fhkxieo8viNW5nDny6t4iyWBlM2E},
doi = {https://doi.org/10.2514/1.J053706}
}
|
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| Wang, C. and Eldredge, J.D. | Strongly coupled dynamics of fluids and rigid-body systems with the immersed boundary projection method | 2015 | J. Comput. Phys. Vol. 295, pp. 87-113 |
article | DOI URL |
| Abstract: A strong coupling algorithm is presented for simulating the dynamic interactions between incompressible viscous flows and rigid-body systems in both two- and three-dimensional problems. In this work, the Navier--Stokes equations for incompressible flow are solved on a uniform Cartesian grid by the vorticity-based immersed boundary projection method of Colonius and Taira. Dynamical equations for arbitrary rigid-body systems are also developed. The proposed coupling method attempts to unify the treatment of constraints in the fluid and structure---the incompressibility of the fluid, the linkages in the rigid-body system, and the conditions at the interface---through the use of Lagrange multipliers. The resulting partitioned system of equations is solved with a simple relaxation scheme, based on an identification of virtual inertia from the fluid. The scheme achieves convergence in only 2 to 5 iterations per time step for a wide variety of mass ratios. The formulation requires that only a subset of the discrete fluid equations be solved in each iteration. Several two- and three-dimensional numerical tests are conducted to validate and demonstrate the method, including a falling cylinder, flapping of flexible wings, self-excited oscillations of a system of many linked plates in a free stream, and passive pivoting of a finite aspect ratio plate under the influence of gravity in a free stream. The results from the current method are compared with previous experimental and numerical results and good agreement is achieved. | |||||
BibTeX:
@article{wang2015strongly,
author = {Wang, C. and Eldredge, J. D.},
title = {Strongly coupled dynamics of fluids and rigid-body systems with the immersed boundary projection method},
journal = {J. Comput. Phys.},
publisher = {Elsevier},
year = {2015},
volume = {295},
pages = {87--113},
url = {https://drive.google.com/open?id=102zbiZvdxECSB7G74pbrxDw-dQxH4Ap4},
doi = {https://doi.org/10.1016/j.jcp.2015.04.005}
}
|
|||||
| Young, E.K. | Numerical Simulations of the Mechanics of Vitrectomy [BibTeX] |
2015 | School: University of California, Los Angeles | phdthesis | URL |
BibTeX:
@phdthesis{eyoungthesis15,
author = {Young, E. K.},
title = {Numerical Simulations of the Mechanics of Vitrectomy},
school = {University of California, Los Angeles},
year = {2015},
note = {eldredge},
url = {https://drive.google.com/open?id=15PUulEEZH142Cgai_3PRI9z98LoGSz-U}
}
|
|||||
| Eldredge, J.D., Senocak, I., Dawson, P., Canino, J., Liou, W.W., LeBeau, R., Hitt, D.L., Rumpfkeil, M.P. and Cummings, R.M. | A best practices guide to CFD education in the undergraduate curriculum | 2014 | Int. J. Aerodyn. Vol. 4(3-4), pp. 200-236 |
article | DOI URL |
| Abstract: The AIAA Fluid Dynamics Technical Committee formed a working group in 2010 to explore how to include computational fluid dynamics (CFD) in undergraduate education. The following article is the best practices guide resulting from that working group, and is intended to guide the development of CFD instructional content in undergraduate aerospace and mechanical engineering curricula. The article addresses a growing need for new engineers to become `intelligent users' of CFD: that is, to be able to obtain a solution of a flow, and to critically assess the quality of the result. The article distils the concepts of CFD into curricular elements, and establishes reasonable expected outcomes for undergraduate-level instruction of these concepts. It then provides numerous case studies of existing CFD courses, presented in a hierarchy of various `profiles' -- from CFD light to CFD heavy -- for inclusion in courses with lecture, laboratory or design formats. Specific needs of mechanical engineering programmes are also discussed. Hardware, software, and textbook resources are also briefly reviewed. | |||||
BibTeX:
@article{Eldredge2014,
author = {Eldredge, J. D. and Senocak, I. and Dawson, P. and Canino, J. and Liou, W. W. and LeBeau, R. and Hitt, D. L. and Rumpfkeil, M. P. and Cummings, R. M.},
title = {A best practices guide to CFD education in the undergraduate curriculum},
journal = {Int. J. Aerodyn.},
publisher = {Inderscience Publishers},
year = {2014},
volume = {4},
number = {3-4},
pages = {200--236},
url = {https://drive.google.com/open?id=13zoTjLgI9EAQl5cIHfndx4yVCFvL1Ne5},
doi = {https://doi.org/10.1504/IJAD.2014.067580}
}
|
|||||
| Greene, P.T., Eldredge, J.D., Zhong, X. and Kim, J. | Numerical Simulation of High-Speed Flows Over Complex Geometries with a High-Order Multi-Zone Cut-Cell Method | 2014 | 52nd Aerospace Sciences Meeting, National Harbor, Maryland. AIAA Paper 2014-0426 | misc | URL |
| Abstract: Results are presented for a new code designed to perform high-order direct numerical simulations of high-speed flows over arbitrary geometries. The simulations were performed on a Cartesian grid with the geometries imposed by a third-order cut-cell method. A multi-zone refinement method is also implemented to provide extra resolution at locations with expected complex physics. The simulations also utilize a fifth-order hybrid WENO scheme to capture any steep gradients in the flow created by the geometries. The combination results in a globally fourth-order scheme. Two-dimensional and three-dimensional test cases show good agreement with previous results and will be presented. Results confirming the high order of convergence will also be shown. The code was designed for studying the effects of isolated roughness elements on the stability of hypersonic boundary layers. Preliminary results for Mach 6 flow over a three-dimensional cylindrical roughness element will also be presented. | |||||
BibTeX:
@misc{greene14,
author = {Greene, P. T. and Eldredge, J. D. and Zhong, X. and Kim, J.},
title = {Numerical Simulation of High-Speed Flows Over Complex Geometries with a High-Order Multi-Zone Cut-Cell Method},
year = {2014},
url = {https://drive.google.com/open?id=1-b-N_peMpVUFuzjMjmL7RwtkSS9IQnDJ}
}
|
|||||
| Hemati, M.S., Eldredge, J.D. and Speyer, J.L. | Wake Sensing for Aircraft Formation Flight | 2014 | Journal of Guidance, Control, and Dynamics Vol. 37(2), pp. 513-524 |
article | DOI URL |
| Abstract: It is well established that flying aircraft in formation can lead to improved aerodynamic efficiency. However, successfully doing so is predicated on having knowledge of the lead aircraft`s wake position. Here, a wake sensing strategy for estimating the wake position and strength in a two-aircraft formation is explored in a simplified proof-of-concept setting. The wake estimator synthesizes wing-distributed pressure measurements, taken on the trailing aircraft, by making use of an augmented lifting line model in conjunction with both Kalman-type and particle filters. Simple aerodynamic models are introduced in constructing the filter to enable fundamental wake sensing challenges to be identified and reconciled. The various estimation algorithms are tested in a vortex-lattice simulation environment, thus allowing the effects of modeling error to be analyzed. It is found that biases in the position estimates no longer arise if a particle filter is used in place of the Kalman-type filters. Filter divergence is observed when the relative aircraft separations are held fixed. This divergent behavior can be alleviated with the introduction of relative aircraft motions, for example in the form of a cross-track dither signal. | |||||
BibTeX:
@article{hematiwake14,
author = {Hemati, M. S. and Eldredge, J. D. and Speyer, J. L.},
title = {Wake Sensing for Aircraft Formation Flight},
journal = {Journal of Guidance, Control, and Dynamics},
year = {2014},
volume = {37},
number = {2},
pages = {513--524},
url = {https://drive.google.com/open?id=1-vsaEfy8eXix8fNHkrQlcY2AXlNXwnDi},
doi = {https://doi.org/10.2514/1.61114}
}
|
|||||
| Hemati, M.S., Eldredge, J.D. and Speyer, J.L. | Improving Vortex Models via Optimal Control Theory | 2014 | J. Fluids Struct. Vol. 49, pp. 91-111 |
article | DOI URL |
| Abstract: Low-order inviscid point vortex models have demonstrated success in predicting the qualitative behavior of aerodynamic forces resulting from unsteady lifting surface maneuvers. However, the quantitative agreement is often lacking as a result of applying a Kutta condition at both edges in a fundamentally unsteady flow. The present work considers the low-order Eldredge-Wang impulse matching vortex model of a pitching plate. A constrained minimization problem is constructed within an optimal control framework and solved by means of variational principles. That is, we relax the Kutta condition imposed at the plate's edges and seek the time rate of change of the vortex strength that minimizes the discrepancy between the model-predicted and high-fidelity simulation force histories, while adhering to the dynamics of the low-order model. The framework developed provides a systematic means of determining the shortcomings of low-order point vortex models, thus providing a path to improvement and refinement. We find that the Kutta condition still holds quite well at the trailing edge, but that the leading edge model requires adjustment. These results will aid our understanding of appropriate leading and trailing edge boundary conditions, and lead to improvements of low-order vortex models of maneuvering aerodynamic flight. |
|||||
BibTeX:
@article{hemati14,
author = {Hemati, M. S. and Eldredge, J. D. and Speyer, J. L.},
title = {Improving Vortex Models via Optimal Control Theory},
journal = {J. Fluids Struct.},
year = {2014},
volume = {49},
pages = {91--111},
url = {https://drive.google.com/open?id=11OwuthLuWL_dEzd3DtFjYhJv_BoZ9EKw},
doi = {https://doi.org/10.1016/j.jfluidstructs.2014.04.004}
}
|
|||||
| Wang, C. | High-Fidelity Simulation and Low-OrderModeling of Bio-inspired Fluid Dynamics [BibTeX] |
2014 | School: University of California, Los Angeles | phdthesis | URL |
BibTeX:
@phdthesis{cwangthesis14,
author = {Wang, C.},
title = {High-Fidelity Simulation and Low-OrderModeling of Bio-inspired Fluid Dynamics},
school = {University of California, Los Angeles},
year = {2014},
note = {eldredge},
url = {https://drive.google.com/open?id=159JdKEZhUZaPKmvPvA8Vsa2aKsNRz1vk}
}
|
|||||
| Chong, K. | Particle Manipulation in Viscous Streaming [BibTeX] |
2013 | School: University of California, Los Angeles | phdthesis | URL |
BibTeX:
@phdthesis{kchongthesis13,
author = {Chong, K.},
title = {Particle Manipulation in Viscous Streaming},
school = {University of California, Los Angeles},
year = {2013},
note = {eldredge},
url = {https://drive.google.com/open?id=14tqTS_kF7DEUrVYiBx527pZUZ5f5hnX7}
}
|
|||||
| Chong, K., Kelly, S.D., Smith, S. and Eldredge, J.D. | Inertial particle trapping in viscous streaming | 2013 | Phys. Fluids Vol. 25, pp. 033602 |
article | DOI URL |
| Abstract: The motion of an inertial particle in a viscous streaming flow of Reynolds number order 10 is investigated theoretically and numerically. The streaming flow created by a circular cylinder undergoing rectilinear oscillation with small amplitude is obtained by asymptotic expansion from previous work, and the resulting velocity field is used to integrate the Maxey--Riley equation with the Saffman lift for the motion of an inertial spherical particle immersed in this flow. It is found that inertial particles spiral inward and become trapped inside one of the four streaming cells established by the cylinder oscillation, regardless of the particle size, density and flow Reynolds number. It is shown that the Faxen correction terms divert the particles from the fluid particle trajectories, and once diverted, the Saffman lift force is most responsible for effecting the inward motion and trapping. The speed of this trapping increases with increasing particle size, decreasing particle density, and increasing oscillation Reynolds number. The effects of Reynolds number on the streaming cell topology and the boundaries of particle attraction are also explored. It is found that particles initially outside the streaming cell are repelled by the flow rather than trapped. | |||||
BibTeX:
@article{chong13,
author = {Chong, K. and Kelly, S. D. and Smith, S. and Eldredge, J. D.},
title = {Inertial particle trapping in viscous streaming},
journal = {Phys. Fluids},
year = {2013},
volume = {25},
pages = {033602},
url = {https://drive.google.com/open?id=13QgFS4eC1tj0JmUB-wEEukja14eZrQYD},
doi = {https://doi.org/10.1063/1.4795857}
}
|
|||||
| Hemati, M. | Vortex-Based Aero- and Hydrodynamic Estimation [BibTeX] |
2013 | School: University of California, Los Angeles | phdthesis | URL |
BibTeX:
@phdthesis{mhematithesis13,
author = {Hemati, M.},
title = {Vortex-Based Aero- and Hydrodynamic Estimation},
school = {University of California, Los Angeles},
year = {2013},
note = {eldredge},
url = {https://drive.google.com/open?id=15-8ZCt6x2FjcbKFrMh3MkklAM1bYWcV6}
}
|
|||||
| Hemati, M.S., Eldredge, J.D. and Speyer, J.L. | Improving Vortex Models via Optimal Control Theory | 2013 | 51st AIAA Aerospace Sciences Meeting, January 2013, Grapevine, TX. AIAA 2013-0351 | misc | URL |
| Abstract: Low-order inviscid point vortex models have demonstrated success in predicting the qualitative behavior of aerodynamic forces resulting from unsteady lifting surface maneuvers. However, the quantitative agreement is often lacking as a result of applying a Kutta condition at both edges in a fundamentally unsteady flow. The present work considers the low-order Eldredge-Wang impulse matching vortex model of a pitching plate. A constrained minimization problem is constructed within an optimal control framework and solved by means of variational principles. That is, we relax the Kutta condition imposed at the plate's edges and seek the time rate of change of the vortex strength that minimizes the discrepancy between the model-predicted and high-fidelity simulation force histories, while adhering to the dynamics of the low-order model. The framework developed provides a systematic means of determining the shortcomings of low-order point vortex models, thus providing a path to improvement and refinement. We find that the Kutta condition still holds quite well at the trailing edge, but that the leading edge model requires adjustment. These results will aid our understanding of appropriate leading and trailing edge boundary conditions, and lead to improvements of low-order vortex models of maneuvering aerodynamic flight. | |||||
BibTeX:
@misc{hemati13,
author = {Hemati, M. S. and Eldredge, J. D. and Speyer, J. L.},
title = {Improving Vortex Models via Optimal Control Theory},
year = {2013},
url = {https://drive.google.com/open?id=116d3RTGYDxnikpHliHEp4pvnD9r4F4NI}
}
|
|||||
| Medina, A. | The Aerodynamics of Deforming Wings at Low Reynolds Number [BibTeX] |
2013 | School: University of California, Los Angeles | phdthesis | URL |
BibTeX:
@phdthesis{amedinathesis13,
author = {Medina, A.},
title = {The Aerodynamics of Deforming Wings at Low Reynolds Number},
school = {University of California, Los Angeles},
year = {2013},
note = {eldredge},
url = {https://drive.google.com/open?id=14sIsGCLIc8L_az0eA8mIRhaHmoYJpI4f}
}
|
|||||
| Wang, C. and Eldredge, J.D. | Low-order phenomenological modeling of leading-edge vortex formation | 2013 | Theor. Comput. Fluid Dyn. Vol. 27(5), pp. 577-598 |
article | DOI URL |
| Abstract: A low-order point vortex model for the two-dimensional unsteady aerodynamics of a flat plate wing section is developed. A vortex is released from both the trailing and leading edges of the flat plate, and the strength of each is determined by enforcing the Kutta condition at the edges. The strength of a vortex is frozen when it reaches an extremum, and a new vortex is released from the corresponding edge. The motion of variable-strength vortices is computed in one of two ways. In the first approach, the Brown--Michael equation is used in order to ensure that no spurious force is generated by the branch cut associated with each vortex. In the second approach, we propose a new evolution equation for a vortex by equating the rate of change of its impulse with that of an equivalent surrogate vortex with identical properties but constant strength. This impulse matching approach leads to a model that admits more general criteria for shedding, since the variable-strength vortex can be exchanged for its constant-strength surrogate at any instant. We show that the results of the new model, when applied to a pitching or perching plate, agree better with experiments and high-fidelity simulations than the Brown--Michael model, using fewer than ten degrees of freedom. We also assess the model performance on the impulsive start of a flat plate at various angles of attack. Current limitations of the model and extensions to more general unsteady aerodynamic problems are discussed. | |||||
BibTeX:
@article{wangjde13:1j,
author = {Wang, C. and Eldredge, J. D.},
title = {Low-order phenomenological modeling of leading-edge vortex formation},
journal = {Theor. Comput. Fluid Dyn.},
year = {2013},
volume = {27},
number = {5},
pages = {577--598},
url = {https://drive.google.com/open?id=13HPFy0zvN3vho-8_B_kdzN0NdOALKG2w},
doi = {https://doi.org/10.1007/s00162-012-0279-5}
}
|
|||||
| Calkins, M.A., Aurnou, J.M., Eldredge, J.D. and Julien, K. | The influence of fluid properties on the morphology of core turbulence and the geomagnetic field | 2012 | Earth Planet. Sci. Lett. Vol. 359, pp. 55-60 |
article | DOI URL |
| Abstract: Here we investigate the effects of fluid properties on the morphology and dynamics of convection in the Earth's outer core. The results of two quasi-geostrophic convection simulations are carried out at comparable convective velocities for fluids in which the ratio between the kinematic viscosity and thermal diffusivity (the Prandtl number, Pr) is 0.1 and 10. The Pr=0.1 case is representative of thermal convection in a liquid metal, whereas the Pr=10 case is representative of chemical convection. We find the influence of the Prandtl number to be significant; low Prandtl number fluids have a propensity for large-scale coherent vortex formation and slowly varying dynamics. Conversely, the high Prandtl case is dominated by significantly smaller length scales and more rapidly varying dynamics. However, both cases have zonal flows with similar strength, demonstrating that Reynolds stresses in high Prandtl number convection can be large when the buoyancy forcing is strong. By using a simple kinematic magnetic induction model we show that the structure of the magnetic field is not a direct indication of the underlying convective morphology when the magnetic diffusivity is large, as in Earth's core. Thus, our simulation results imply that the convective turbulence differs between thermally and chemically dominated convection, but that it may be difficult to determine the dominant forcing from geomagnetic field structure alone. | |||||
BibTeX:
@article{Calkins2012,
author = {Calkins, M. A. and Aurnou, J. M. and Eldredge, J. D. and Julien, K.},
title = {The influence of fluid properties on the morphology of core turbulence and the geomagnetic field},
journal = {Earth Planet. Sci. Lett.},
publisher = {Elsevier},
year = {2012},
volume = {359},
pages = {55--60},
url = {https://drive.google.com/open?id=14B6lHySAtKtu2Dun1QnHrT-KDT2rsbwP},
doi = {https://doi.org/10.1016/j.epsl.2012.10.009}
}
|
|||||
| Calkins, M.A., Noir, J., Eldredge, J.D. and Aurnou, J.M. | The effects of boundary topography on convection in Earth's core | 2012 | Geophys. J. Int. Vol. 189(2), pp. 799-814 |
article | DOI URL |
| Abstract: We present the first investigation that explores the effects of an isolated topographic ridge on thermal convection in a planetary core‐like geometry and using core‐like fluid properties (i.e. using a liquid metal‐like low Prandtl number fluid). The model's mean azimuthal flow resonates with the ridge and results in the excitation of a stationary topographic Rossby wave. This wave generates recirculating regions that remain fixed to the mantle reference frame. Associated with these regions is a strong longitudinally dependent heat flow along the inner core boundary; this effect may control the location of melting and solidification on the inner core boundary. Theoretical considerations and the results of our simulations suggest that the wavenumber of the resonant wave, LR, scales as Ro^−1/2, where Ro is the Rossby number. This scaling indicates that small‐scale flow structures [wavenumber m O(10^2-10^3)] in the core can be excited by a topographic feature on the core--mantle boundary. The effects of strong magnetic diffusion in the core must then be invoked to generate a stationary magnetic signature that is comparable to the scale of observed geomagnetic structures [m < O(10)]. | |||||
BibTeX:
@article{Calkins2012a,
author = {Calkins, M. A. and Noir, J. and Eldredge, J. D. and Aurnou, J. M.},
title = {The effects of boundary topography on convection in Earth's core},
journal = {Geophys. J. Int.},
publisher = {Blackwell Publishing Ltd Oxford, UK},
year = {2012},
volume = {189},
number = {2},
pages = {799--814},
url = {https://drive.google.com/open?id=14VqE-zt3vpWHwNaoJQYUcElRw2elSY2T},
doi = {https://doi.org/10.1111/j.1365-246X.2012.05415.x}
}
|
|||||
| Hemati, M., Eldredge, J. and Speyer, J. | Wake Sensing for Aircraft Formation Flight | 2012 | AIAA Guidance, Navigation and Control Conference, Minneapolis, August 2012. AIAA Paper 2012-4768 | misc | URL |
| Abstract: It is well established that flying aircraft in formation can lead to improved aerodynamic efficiency. However, successfully doing so is predicated on having knowledge of the lead aircraft wake position. Here, we develop a wake sensing strategy to estimate the wake position and strength in a two-aircraft formation. The wake estimator synthesizes wing-distributed pressure measurements, taken on the trailing aircraft, by making use of an augmented lifting line model in conjunction with both Kalman-type and particle filters. The various estimation algorithms are tested in a vortex-lattice simulation environment, thus enabling the effects of modeling error to be analyzed. It is found that biases in the position estimates no longer arise if a particle filter is used in place of the Kalman-type filters. Filter divergence is observed when the relative aircraft separations are held fixed. This divergent behavior can be alleviated with the introduction of relative aircraft motions, for example in the form of a cross-track dither signal. |
|||||
BibTeX:
@misc{hemati12,
author = {Hemati, M. and Eldredge, J. and Speyer, J.},
title = {Wake Sensing for Aircraft Formation Flight},
year = {2012},
url = {https://drive.google.com/open?id=10MGecSgwAxwGbwCh9YSFgorJhIJEKeBG}
}
|
|||||
| Chun, Y., Hur, S.C., Kealey, C.P., Levi, D.S., Mohanchandra, K.P., Di Carlo, D., Eldredge, J.D., Vinuela, F. and Carman, G.P. | Intra-aneurysmal flow reductions in a thin film nitinol flow diverter | 2011 | Smart Mater. Struct. Vol. 20(5), pp. 055021 |
article | DOI URL |
| Abstract: A novel hyper-elastic thin film nitinol (HE-TFN) covered stent has been developed to promote aneurysm occlusion by diminishing flow in the aneurysm. Laboratory aneurysm models were used to assess the flow changes produced by stents covered with different patterns of HE-TFN placed across the aneurysm neck in the parent vessel. The flow diverters were constructed by covering Wingspan stents (Boston Scientific) with different HE-TFNs (i.e., of 82% and 77% porosity) and deployed in both in vitro wide-neck and fusiform glass aneurysm models. In wide-neck aneurysms, the 82% porous HE-TFN stent reduced mean flow velocity in the middle of the sac by 86 ± 1%, while the 77% porous stent reduced the velocity by 93 ± 5% (n = 3). Local wall shear rates were also significantly reduced by about 98% in this model after device placement. Tests conducted on the fusiform aneurysm revealed smaller intra-aneurysmal flow velocity reduction by 48 ± 3% for the 82% porous stent and by 59 ± 7% for the 77% porous stent. The wall shear was reduced by approximately 50% by HE-TFN stents in fusiform models. These results suggest that HE-TFN covered stents have the potential to promote thrombosis in both wide-neck and fusiform aneurysm sacs. | |||||
BibTeX:
@article{Chun2011,
author = {Chun, Y. and Hur, S. C. and Kealey, C. P. and Levi, D. S. and Mohanchandra, K. P. and Di Carlo, D. and Eldredge, J. D. and Vinuela, F. and Carman, G. P.},
title = {Intra-aneurysmal flow reductions in a thin film nitinol flow diverter},
journal = {Smart Mater. Struct.},
publisher = {IOP Publishing},
year = {2011},
volume = {20},
number = {5},
pages = {055021},
url = {https://drive.google.com/open?id=14Gz0OeVLBUKbVSG-0jsK2qXG8h0ci9d7},
doi = {https://doi.org/10.1088/0964-1726/20/5/055021}
}
|
|||||
| Eldredge, J.D. and Wang, C. | Improved low-order modeling of a pitching and perching plate | 2011 | AIAA Paper 2011-3579. Presented at 41st AIAA Fluid Dynamics Conference, Honolulu, HI | misc | URL |
| Abstract: A low-order point vortex model for the unsteady aerodynamics of agile flight of micro air vehicles is developed further in this work. A vortex is released from both the trailing and leading edges of the flat plate section, and the strength of each is determined by enforcing the Kutta condition at the edges. We derive a new evolution equation for the vortex position by equating the rate of change of its impulse with that of an equivalent surrogate vortex with identical properties but constant strength. This approach leads to a model that admits more general criteria for shedding (i.e. freezing the strength of the vortex) than the previous model developed by the authors, based on the Brown-Michael equation (AIAA Paper 2010-4281). We show that the results of the new model, when applied to a pitching or perching wing, agree much better with experiments and high-fidelity simulations than the previous model. Current limitations of the model and extensions to more general unsteady aerodynamic problems are discussed. | |||||
BibTeX:
@misc{jdewang11:1j,
author = {Eldredge, J. D. and Wang, C.},
title = {Improved low-order modeling of a pitching and perching plate},
year = {2011},
url = {https://drive.google.com/open?id=11_wQuFSHLsClKC9HaLv9o4H4bkCmHRJ6}
}
|
|||||
| Ferrari, M. | Modeling of Passive Acoustic Liners from High Fidelity Numerical Simulations [BibTeX] |
2011 | School: University of California, Los Angeles | phdthesis | URL |
BibTeX:
@phdthesis{ferrarithesis11,
author = {Ferrari, M.},
title = {Modeling of Passive Acoustic Liners from High Fidelity Numerical Simulations},
school = {University of California, Los Angeles},
year = {2011},
note = {eldredge},
url = {https://drive.google.com/open?id=15Wh-rtEEpgsVQ5qN3Tmh5NTaeqnBNbgs}
}
|
|||||
| Greene, P.T., Eldredge, J.D., Zhong, X. and Kim, J. | Numerical Study of Hypersonic Flow Over an Isolated Roughness with a High-Order Cut-Cell Method | 2011 | 41st AIAA Fluid Dynamics Conference, Honolulu, Hawaii. AIAA Paper 2011-3249 | misc | URL |
| Abstract: Results are presented for direct numerical simulations of hypersonic flow over an isolated roughness element located on a flat plate. The simulations were performed on a Cartesian grid with the roughness geometry imposed by a third-order cut-cell method. The simulations also utilize a fifth-order WENO scheme to capture any steep gradients in the flow created by the roughness. The combination results in a globally fourth-order scheme. Two-dimensional and three-dimensional test cases show very good agreement with results obtained from a body-fitted grid simulation. Preliminary results for Mach 6 flow over a k/δ = 0.75 cylindrical roughness are reported. In addition, results from a series of simulations of Mach 6 flow over a three-dimensional Gaussian roughness performed with a body-fitted grid are presented. | |||||
BibTeX:
@misc{greene11,
author = {Greene, P. T. and Eldredge, J. D. and Zhong, X. and Kim, J.},
title = {Numerical Study of Hypersonic Flow Over an Isolated Roughness with a High-Order Cut-Cell Method},
year = {2011},
url = {https://drive.google.com/open?id=1498tHiEbWq4K47t46zWv2WX5w8suT-eW}
}
|
|||||
| Juan, T. | A Computational Study of the Flow Through a Vitreous Cutter [BibTeX] |
2011 | School: University of California, Los Angeles | phdthesis | URL |
BibTeX:
@phdthesis{tjuanthesis11,
author = {Juan, T.},
title = {A Computational Study of the Flow Through a Vitreous Cutter},
school = {University of California, Los Angeles},
year = {2011},
note = {eldredge},
url = {https://drive.google.com/open?id=15UvLdz-l2Hti8IRAtUFLRrqy1Hmxhf2g}
}
|
|||||
| Lagha, M., Kim, J., Eldredge, J.D. and Zhong, X. | Near-wall dynamics of compressible boundary layers | 2011 | Phys. Fluids Vol. 23(6), pp. 065109 |
article | DOI URL |
| Abstract: The coherent structures populating the inner-region of a compressible boundary layer with free-stream Mach number equal to 2.5 are analyzed by means of direct numerical simulations of the Navier--Stokes equations. This study shows similarity with the incompressible case in the sense that turbulence in the near-wall region can be sustained without fluctuations in the outer region, proving the existence of a local cycle within the near-wall region. The dynamics are further simplified by making use of the coherence of the inner region. The wall-normal velocity component in this region is split into two: one coherent part representing vortices spanning all the inner-region, and one incoherent part representing the background turbulence. By damping the latter part, the statistical features of the flow are only slightly influenced, showing that the coherent part is essential in determining the flow characteristics. Flow dynamics and turbulence structures within this coherent part are examined. It is shown that the near-wall region is populated by crescent-shaped vortical structures, which are associated with regions with strong positive Reynolds shear stress production. The structure of the flow associated with these regions shares several features with the so-called internal shear layers. | |||||
BibTeX:
@article{lagha2011near,
author = {Lagha, M. and Kim, J. and Eldredge, J. D. and Zhong, X.},
title = {Near-wall dynamics of compressible boundary layers},
journal = {Phys. Fluids},
publisher = {AIP},
year = {2011},
volume = {23},
number = {6},
pages = {065109},
url = {https://drive.google.com/open?id=12LLjrKTzIDp80tIHl6A38xIVTEXxn_Xn},
doi = {https://doi.org/10.1063/1.3600659}
}
|
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| Lagha, M., Kim, J., Eldredge, J.D. and Zhong, X. | A numerical study of compressible turbulent boundary layers | 2011 | Phys. Fluids Vol. 23(1), pp. 015106 |
article | DOI URL |
| Abstract: Compressible turbulent boundary layers with free-stream Mach number ranging from 2.5 up to 20 are analyzed by means of direct numerical simulation of the Navier--Stokes equations. The fluid is assumed to be an ideal gas with constant specific heats. The simulation generates its inflow condition using the rescaling-recycling method. The main objective is to study the effect of Mach number on turbulence statistics and near-wall turbulence structures. The present study shows that supersonic/hypersonic boundary layers at zero pressure gradient exhibit close similarities to incompressible boundary layers and that the main turbulence statistics can be correctly described as variable-density extensions of incompressible results. The study also shows that the spanwise streak's spacing of 100 wall units in the inner region (y+≈15) still holds for the considered high Mach numbers. The probability density function of the velocity dilatation shows significant variations as the Mach number is increased, but it can also be normalized by accounting for the variable-density effect. The compressible boundary layer also shows an additional similarity to the incompressible boundary layer in the sense that without the linear coupling term, near-wall turbulence cannot be sustained. | |||||
BibTeX:
@article{lagha2011numerical,
author = {Lagha, M. and Kim, J. and Eldredge, J. D. and Zhong, X.},
title = {A numerical study of compressible turbulent boundary layers},
journal = {Phys. Fluids},
publisher = {AIP},
year = {2011},
volume = {23},
number = {1},
pages = {015106},
url = {https://drive.google.com/open?id=12WG2kJxOmO1_i03PHzGq2YYSvzZHnIxj},
doi = {https://doi.org/10.1063/1.3541841}
}
|
|||||
| Wilson, M.M. and Eldredge, J.D. | Performance improvement through passive mechanics in jellyfish-inspired swimming | 2011 | Int. J. Non-Linear Mech. Vol. 46(4), pp. 557-567 |
article | DOI URL |
| Abstract: This computational investigation explores the effect that passively responsive components of a body can have on swimming performance. The swimmer is an articulated two-dimensional system of linked rigid bodies that is prescribed with a reciprocating shape change loosely inspired by jellyfish mechanics. The six constituent hinges can be either actively controlled by fully prescribing the kinematics, or passively responsive by substituting a torsion spring in place of an actuator. The computational solver is a high-fidelity viscous vortex particle method with coupled fluid-body interactions. The prescribed kinematic Reynolds numbers involved in this investigation fall within the range 70 to 700. Several configurations are explored, including cases with passively responsive hinges and cases in which pairs of the hinges were held in a rigid locked position. Certain choices of passive structure lead to optimal swimming speed and efficiency. This is elucidated by a simple model, which shows that optimal performance is obtained through a balance of maximized deflection of peripheral bodies and phasing that draws benefits from both reactive and resistive force mechanisms. A study is also made of an inviscid swimmer but, due to the reciprocating kinematics of the system, the swimmer is unable to achieve meaningful locomotion, showing that vortex shedding is essential to break the symmetry of the kinematics. | |||||
BibTeX:
@article{wiljde11,
author = {Wilson, M. M. and Eldredge, J. D.},
title = {Performance improvement through passive mechanics in jellyfish-inspired swimming},
journal = {Int. J. Non-Linear Mech.},
year = {2011},
volume = {46},
number = {4},
pages = {557--567},
url = {https://drive.google.com/open?id=148p88Qyp75gmPPACEt1_hLDQ5Me1Fae9},
doi = {https://doi.org/10.1016/j.ijnonlinmec.2010.12.005}
}
|
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| Calkins, M.A., Noir, J., Eldredge, J.D. and Aurnou, J.M. | Axisymmetric simulations of libration-driven fluid dynamics in a spherical shell geometry | 2010 | Phys. Fluids Vol. 22(8), pp. 086602 |
article | DOI URL |
| Abstract: We report on axisymmetric numerical simulations of rapidly rotating spherical shells in which the axial rotation rate of the outer shell is modulated in time. This allows us to model planetary bodies undergoing forced longitudinal libration. In this study we systematically vary the Ekman number, 10−7≤E≲10−4, which characterizes the ratio of viscous to Coriolis forces in the fluid, and the libration amplitude, Δϕ. For libration amplitudes above a certain threshold, Taylor--Görtler vortices form near the outer librating boundary, in agreement with the previous laboratory experiments of Noir et al. [Phys. Earth Planet. Inter. 173, 141 (2009)]. At the lowest Ekman numbers investigated, we find that the instabilities remain spatially localized at onset in the equatorial region. In addition, nonzero time-averaged azimuthal (zonal) velocities are observed for all parameters studied. The zonal flow is characterized by predominantly retrograde flow in the interior, with a stronger prograde jet in the outer equatorial region. The magnitude of the zonal flow scales as the square of the librational forcing, e^2, where e=Δϕf and f is the dimensionless libration frequency defined as the ratio between the libration frequency and the mean angular rotation rate. In addition, the zonal flow is primarily independent of the Ekman number, implying that the zonal flow does not depend on the viscosity of the fluid. The simulations show that the zonal flow is driven by nonlinearities in the Ekman boundary layer; it is not driven by Taylor--Görtler vortices or by inertial waves in the fluid interior. Application of our results suggests that many librating bodies in the solar system are above the onset for centrifugal instabilities, with values up to ∼30 times supercritical. However, the spatial localization of the instabilities at onset in our simulations suggests that their effects are limited on the global dynamics of librating bodies. We find that the zonal flows driven by libration in axisymmetric spherical shells are unlikely to produce significant planetary magnetic fields, but will likely generate nonzero mean torques on the bounding surfaces. | |||||
BibTeX:
@article{Calkins2010,
author = {Calkins, M. A. and Noir, J. and Eldredge, J. D. and Aurnou, J. M.},
title = {Axisymmetric simulations of libration-driven fluid dynamics in a spherical shell geometry},
journal = {Phys. Fluids},
publisher = {AIP},
year = {2010},
volume = {22},
number = {8},
pages = {086602},
url = {https://drive.google.com/open?id=13PoNUBI8-R3C1HOH9vpgomlc8UxkNHok},
doi = {https://doi.org/10.1063/1.3475817}
}
|
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| Eldredge, J. and Wang, C. | High-Fidelity Simulations and Low-Order Modeling of a Rapidly Pitching Plate | 2010 | AIAA Paper 2010-4281, 40th AIAA Fluid Dynamics Conference, Chicago | misc | URL |
| Abstract: A thin flat plate undergoing a rapid pitch-up maneuver in a steady free stream is studied with both high-fidelity numerical simulations at Reynolds number 1000 and a low-order inviscid point vortex model. The pitching rate and axis position are systematically varied, and their effect on the generated aerodynamic forces is inspected. It is found that the maximum lift and drag developed during the pitch-up both increase nearly linearly with increasing pitch rate, though the rates of increase diminish as the pitching axis is moved aft. Furthermore, the maximum lift-to-drag ratio tends to saturate with increasing pitch rate, with the asymptotic value decreasing as the axis is moved aft. The forces predicted by the low-order inviscid Brown-Michael model are compared with the high-fidelity results. Good qualitative agreement is achieved, though the point vortex model tends to over-predict both components of force. The lift force obtained from the model is decomposed into inertial reaction and circulatory components, and their relative contributions are inspected. | |||||
BibTeX:
@misc{jdewang10:1j,
author = {Eldredge, J. and Wang, C.},
title = {High-Fidelity Simulations and Low-Order Modeling of a Rapidly Pitching Plate},
year = {2010},
url = {https://drive.google.com/open?id=14C5xZsjT27nt9aa11TzAfL4xlQnC3lsH}
}
|
|||||
| Eldredge, J.D. and Chong, K. | Fluid transport and coherent structures of translating and flapping wings | 2010 | Chaos Vol. 20, pp. 017509 |
article | DOI URL |
| Abstract: The Lagrangian coherent structures (LCS) of simple wing cross-sections in various low Reynolds number motions are extracted from high-fidelity numerical simulation data and examined in detail. The entrainment process in the wake of a translating ellipse is revealed by studying the relationship between attracting structures in the wake and upstream repelling structures, with the help of blocks of tracer particles. It is shown that a series of slender lobes in the repelling LCS project upstream from the front of the ellipse and 'pull' fluid into the wake. Each lobe is paired with a corresponding wake vortex, into which the constituent fluid particles are folded. Flexible and rigid foils in flapping motion are studied, and the resulting differences in coherent structures are used to elucidate their differences in force generation. The clarity with which these flow structures are revealed, compared to the vorticity or velocity fields, provides new insight in the vortex shedding mechanisms that play an important role in unsteady aerodynamics. | |||||
BibTeX:
@article{jdechong10:1j,
author = {Eldredge, J. D. and Chong, K.},
title = {Fluid transport and coherent structures of translating and flapping wings},
journal = {Chaos},
year = {2010},
volume = {20},
pages = {017509},
url = {https://drive.google.com/open?id=12eV5Fx7Nt0uaangDE5-xZC3RdS0zYsA0},
doi = {https://doi.org/10.1063/1.3273036}
}
|
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| Eldredge, J.D., Toomey, J. and Medina, A. | On the roles of chord-wise flexibility in a flapping wing with hovering kinematics | 2010 | J. Fluid Mech. Vol. 659, pp. 94-115 |
article | DOI URL |
| Abstract: The aerodynamic performance of a flapping two-dimensional wing section with simplified chord-wise flexibility is studied computationally. Bending stiffness is modeled by a torsion spring connecting two or three rigid components. The leading portion of the wing is prescribed with kinematics that are characteristic of biological hovering, and the aft portion responds passively. Coupled simulations of the Navier--Stokes equations and the wing dynamics are conducted for a wide variety of spring stiffnesses and kinematic parameters. Performance is assessed by comparison of the mean lift, power consumption, and lift per unit power, with those from an equivalent rigid wing, and two cases are explored in greater detail through force histories and vorticity snapshots. From the parametric survey, four notable mechanisms are identified through which flexible wings behave differently from rigid counterparts. Rigid wings consistently require more power than their flexible counterparts to generate the same kinematics, as passive deflection leads to smaller drag and torque penalties. Aerodynamic performance is degraded in very flexible wings undergoing large heaving excursions, caused by a premature detachment of the leading-edge vortex. However, a mildly flexible wing has consistently good performance over a wide range of phase differences between pitching and heaving -- in contrast with the relative sensitivity of a rigid wing to this parameter -- due to better accommodation of the shed leading-edge vortex into the wake during the return stroke, and less tendency to interact with previously-shed trailing-edge vortices. Furthermore, a flexible wing permits lift generation even when the leading portion remains nearly vertical, as the wing passively deflects to create an effectively smaller angle of attack, similar to the passive pitching mechanism recently identified for rigid wings. It is found that an effective pitch angle can be defined that accounts for wing deflection to align the results with those of the equivalent rigid wing. | |||||
BibTeX:
@article{jdetoom:3j,
author = {Eldredge, J. D. and Toomey, J. and Medina, A.},
title = {On the roles of chord-wise flexibility in a flapping wing with hovering kinematics},
journal = {J. Fluid Mech.},
year = {2010},
volume = {659},
pages = {94--115},
url = {https://drive.google.com/open?id=13AbZiUSQfKHR0vSj5N2RniYmjLYmD2tv},
doi = {https://doi.org/10.1017/S0022112010002363}
}
|
|||||
| Juan, T., Hubschman, J.-P. and Eldredge, J.D. | A Computational Study of the Flow Through a Vitreous Cutter | 2010 | J. Biomech. Eng. Vol. 132, pp. 121005 |
article | DOI URL |
| Abstract: Vitrectomy is an ophthalmic microsurgical procedure that removes part or all of the vitreous humor from the eye. The procedure uses a vitreous cutter consisting of a narrow shaft with a small orifice at the end through which the humor is aspirated by an applied suction. An internal guillotine oscillates back and forth across the orifice to alter the local shear response of the humor. In this work, a computational study of the flow in a vitreous cutter is conducted in order to gain better understanding of the vitreous behavior and provide guidelines for a new vitreous cutter design. The flow of a Newtonian surrogate of vitreous in a two-dimensional analog geometry is investigated using a finite difference-based immersed boundary method with an algebraically formulated fractional-step method. A series of numerical experiments is performed to evaluate the impact of cutting rate, aspiration pressure, and opening/closing transition on the vitreous cutter flow rate and transorifice pressure variation during vitrectomy. The mean flow rate is observed to increase approximately linearly with aspiration pressure and also increase nearly linearly with duty cycle. A study of time-varying flow rate, velocity field, and vorticity illuminates the flow behavior during each phase of the cutting cycle and shows that the opening/closing transition plays a key role in improving the vitreous cutter's efficacy and minimizing the potential damage to surrounding tissue. The numerical results show similar trend in flow rate as previous in vitro experiments using water and balanced saline solution and also demonstrate that high duty cycle and slow opening/closing phases lead to high flow rate and minor disturbance to the eye during vitrectomy, which are the design requirements of an ideal vitreous cutter. | |||||
BibTeX:
@article{juan2010,
author = {Juan, T. and Hubschman, J.-P. and Eldredge, J. D.},
title = {A Computational Study of the Flow Through a Vitreous Cutter},
journal = {J. Biomech. Eng.},
year = {2010},
volume = {132},
pages = {121005},
url = {https://drive.google.com/open?id=110u023UTLglJtWVLZvJIr4czYQKwUVrc},
doi = {https://doi.org/10.1115/1.4002796}
}
|
|||||
| Ol, M.V., Altman, A., Eldredge, J.D., Garmann, D.J. and Lian, Y. | Résumé of the AIAA FDTC Low Reynolds Number Discussion Group's Canonical Cases | 2010 | 48th AIAA Aerospace Sciences Meeting. AIAA Paper 2010-1085 | misc | URL |
| Abstract: The AIAA Fluid Dynamics Technical Committee's Low Reynolds Number Discussion Group has introduced several canonical pitch motions, with objectives of (1) experimental-numerical comparison, (2) assessment of closed-form models for aerodynamic force coefficient time history, and (3) exploration of the vast and rather amorphous parameter space of the possible kinematics. The baseline geometry is a flat plate of nominally 2.5% thickness and round edges, wall-to-wall in ground test facilities and spanwise-periodic or 2D in computations. Motions are various smoothings of a linear pitch ramp, hold and return, of 40 degree and 45 degree amplitude. In an attempt to discern acceleration effects, sinusoidal and linear-ramp motions are compared, where the latter have short runs of high acceleration and thus high noncirculatory lift and pitch. Parameter variations include comparison of the flat plate with an airfoil and ellipse, variation of reduced frequency, pitch pivot point location and comparison of pitch to quasi-steady equivalent plunge. All motions involve strong leading edge vortices, whose growth history depends on pitch pivot point location and reduced frequency, and which can persist over the model suction-side for well after motion completion. Noncirculatory loads were indeed found to be localized to phases of motion where acceleration was large. To the extent discernible so far, closed-form models of lift coefficient on the pitch upstroke are relatively straightforward, but not so on the downstroke, where motion history effects complicate the return from stall. Broad Reynolds number independency, in flowfield evolution and lift coefficient, was found in the 10^3 to 10^4 range. | |||||
BibTeX:
@misc{OLEldAIAA10:1j,
author = {Ol, M. V. and Altman, A. and Eldredge, J. D. and Garmann, D. J. and Lian, Y.},
title = {Résumé of the AIAA FDTC Low Reynolds Number Discussion Group's Canonical Cases},
year = {2010},
url = {https://drive.google.com/open?id=10AzlRpdpiaItmL5ICWyilVSrIdY3cEqw}
}
|
|||||
| Parsons, N., Zhong, X., Kim, J. and Eldredge, J. | Numerical Study of Hypersonic Receptivity with Thermochemical Non-Equilibrium on a Blunt Cone | 2010 | 40th AIAA Fluid Dynamics Conference, Chicago, Illinois. AIAA Paper 2010-4446 | misc | URL |
| Abstract: There is renewed interest in physical phenomena leading to laminar-turbulent transition in hypersonic boundary layers. In high-temperature flows characteristic of hypersonic vehicles, the degree of chemical and thermal non-equilibrium becomes significant. However, not many studies have been conducted on the non-equilibrium effect on the receptivity process to free-stream acoustic disturbances. The goal of this paper is, first, to present a code capable of accurately modeling free-stream acoustic disturbances with non-equilibrium effects, and, second, to present preliminary findings on the non-equilibrium effects on receptivity. This is done by examining Mach 15.3 flow over a blunt cone with nose radius 6.35 × 10^−3 m and half angle 7◦ and imposing free-stream fast acoustic wave disturbances using a high-order shock-fitting finite-difference solver. Results were computed for flows using both thermochemical non-equilibrium and perfect gas models and were then compared to determine the non-equilibrium effects. Complex wave structures were found in the boundary layer for each gas model when a free-stream acoustic disturbance wave was introduced. The non-equilibrium gas case was found to have higher perturbation amplitudes and had its maximum perturbation amplitude nearer to the blunt nose. |
|||||
BibTeX:
@misc{parsons10,
author = {Parsons, N. and Zhong, X. and Kim, J. and Eldredge, J.},
title = {Numerical Study of Hypersonic Receptivity with Thermochemical Non-Equilibrium on a Blunt Cone},
year = {2010},
url = {https://drive.google.com/open?id=13qcO5Eg7RpybyG6UYlXVsFbIm0LOgO5X}
}
|
|||||
| Rehman, S.F. | High order methods for numerical studies of receptivity in high-speed flows [BibTeX] |
2010 | School: University of California, Los Angeles | phdthesis | URL |
BibTeX:
@phdthesis{rehmanthesis10,
author = {Rehman, S. F.},
title = {High order methods for numerical studies of receptivity in high-speed flows},
school = {University of California, Los Angeles},
year = {2010},
note = {eldredge},
url = {https://drive.google.com/open?id=15XMZaXl1nO-SSeE1z5XMXif_WP9f7hPl}
}
|
|||||
| Rehman, S.F., Eldredge, J.D., Zhong, X.L. and Kim, J. | A simple and robust approach for higher order hybrid shock capturing methods | 2010 | 40th AIAA Fluid Dynamics Conference and Exhibit, AIAA Paper 2010-4453 | misc | URL |
| Abstract: In this work, we present a simple hybrid finite difference scheme which simultaneously achieves low numerical dissipation in smooth flow regions and robust shock capturing near flow discontinuities. Shock capturing is carried out with a standard first-order upwind scheme, while a high-order upwind-biased scheme is used away from discontinuities. A smoothness indicator adapted from the previous work of Ren et al. is used to detect discontinuities, and the two schemes are smoothly blended with no adjustable parameters. This new methodology is simpler than most previous hybrid approaches, which generally rely on a weighted essentially non-oscillatory (WENO) scheme for shock capturing. By avoiding the expensive weighting of stencils of varying order of accuracy, the present method achievesconsiderable time savings, while retaining the robustness of the WENO method. The new method is demonstrated on several model problems, from inviscid one-dimensional to viscous two-dimensional examples. | |||||
BibTeX:
@misc{rehmanaiaa10:1j,
author = {Rehman, S. F. and Eldredge, J. D. and Zhong, X. L. and Kim, J.},
title = {A simple and robust approach for higher order hybrid shock capturing methods},
year = {2010},
url = {https://drive.google.com/open?id=13fr3SNBFnCy1Va6w9e52o6i98N5Il1FZ}
}
|
|||||
| Eldredge, J. | A reconciliation of viscous and inviscid approaches to computing locomotion of deforming bodies | 2009 | Exper. Mech. Vol. 50(9), pp. 1349-1353 |
article | DOI URL |
| Abstract: We present a formulation for coupled solutions of fluid and body dynamics in problems of biolocomotion. This formulation unifies the treatment at moderate to high Reynolds number with the corresponding inviscid problem. By a viscous splitting of the Navier-Stokes equations, inertial forces from the fluid are distinguished from the viscous forces, and the former are further decomposed into contributions from body motion in irrotational fluid and ambient fluid vorticity about an equivalent stationary body. In particular, the added mass of the fluid is combined with the intrinsic inertia of the body to loosen restrictions on time-step size. The resulting dynamical equations can potentially illuminate the role of vorticity in locomotion, and the fundamental differences of locomotion in real and perfect fluids. | |||||
BibTeX:
@article{eldexpmech09,
author = {J. D. Eldredge},
title = {A reconciliation of viscous and inviscid approaches to computing locomotion of deforming bodies},
journal = {Exper. Mech.},
year = {2009},
volume = {50},
number = {9},
pages = {1349--1353},
url = {https://drive.google.com/open?id=1-ctv-IrVa-BMEk8tic3Ju97nzrRzeilC},
doi = {https://doi.org/10.1007/s11340-009-9275-0}
}
|
|||||
| Eldredge, J.D., Wang, C. and M. V., OL | A Computational Study of a Canonical Pitch-Up, Pitch-Down Wing Maneuver | 2009 | 39th AIAA Fluid Dynamics Conference. AIAA Paper 2009-3687 | misc | URL |
| Abstract: The simple canonical problem of a two-dimensional wing profile undergoing a single linear pitch-up/pitch-down maneuver in a uniform flow is studied computationally with direct numerical simulation of the Navier--Stokes equations. The effects of pitch rate and Reynolds number are both studied, for both elliptical and thin flat-plate profiles. In particular, flows at Reynolds numbers of 10^2--10^4 are computed, and the resulting lift, drag and vortex shedding are examined. It is found that, during the pitch-up, all forces increase monotonically with increasing pitch rate, and that large pitch rates produce a net thrust and negative lift during most of the pitch-down interval. The pitch-up lift is notably larger as Reynolds number increases. A flat plate generally produces greater lift than an elliptical wing, at the cost of greater drag. At low pitch rates, a large leading-edge vortex is formed during the pitch-up and is shed during the pitch-down, and wake vortices are weak and relatively diffuse. In contrast, high pitch rates lead to stronger, more compact leading-edge and wake vortices. The wake vortices exhibit distinct pairing, and the leading-edge vortex shows less tendency to separate. Surface pressure distributions, which are used to connect the force generation with these shedding observations, confirm the important role of the leading-edge vortex in lift generation. During pitch-down, at low pitch rates the lift from the leading-edge vortex overcomes the downforce to produce positive lift, whereas downforce dominates at high pitch rates. Vorticity fields at Reynolds number 10^4 compare very well with corresponding results of OL (AIAA Paper 2009-3686) in the companion experimental study. | |||||
BibTeX:
@misc{EldWanOl09:1j,
author = {Eldredge, J. D. and Wang, C. and OL, M. V.},
title = {A Computational Study of a Canonical Pitch-Up, Pitch-Down Wing Maneuver},
year = {2009},
url = {https://drive.google.com/open?id=13Ehps90lHvLtqNJYkIxuu1FX1ko2T9Ie}
}
|
|||||
| Greene, P.T., Eldredge, J.D., Zhong, X. and Kim, J. | A Numerical Study of Purdue's Mach 6 Tunnel with a Roughness Element | 2009 | 47th AIAA Aerospace Sciences Meeting, Orlando, Florida. AIAA Paper 2009-0174 | misc | URL |
| Abstract: The effects of surface roughness on the stability of hypersonic flow are of great importance to hypersonic vehicles. The overall goal of our research is to provide a better understanding of the effects of surface roughness on transitional and turbulent hypersonic boundary layers. Direct numerical simulations have been performed of flow in the Boeing/AFOSR Mach 6 quiet wind tunnel at Purdue University. Three-dimensional simulations were performed of the nozzle without any roughness and 2D simulations were performed with an isolated roughness element located on the wall of the nozzle. Two different roughness heights were simulated, both of which were less then the local undisturbed boundary layer thickness. The roughness elements produced a combination of Mach wave and expansion fan in the nozzle. The influence of the roughness elements on the flow is investigated in this paper. It is found that the presence of the elements has a substantial effect on the boundary layer and stability profiles downstream of the element. | |||||
BibTeX:
@misc{greene10,
author = {Greene, P. T. and Eldredge, J. D. and Zhong, X. and Kim, J.},
title = {A Numerical Study of Purdue's Mach 6 Tunnel with a Roughness Element},
year = {2009},
url = {https://drive.google.com/open?id=13UEVNuiVtFoadjb70bRBE2Ei4RJU_Zk9}
}
|
|||||
| Lagha, M., Zhong, X., Eldredge, J. and Kim, J. | A Hybrid WENO Scheme for Simulation of Shock Wave-Boundary Layer Interaction | 2009 | 4th AIAA Aerospace Sciences Meeting, Orlando, Florida. AIAA Paper 2009-1136 | misc | URL |
| Abstract: The ultimate goal of this study is to develop a robust and accurate numerical method for simulation of hypersonic turbulent boundary layers. A hybrid numerical method, coupling a fifth-order weighted essentially non-oscillatory (WENO) scheme for shock capturing and a centered fourth-order finite difference scheme for computing turbulence away from the shock, is considered. It is applied, in this paper, to a benchmark problem in which shock-shock and shock-vortex interactions are present. It is shown that this method captures the shocks robustly and computes the flow away from the shocks accurately. Then, a spatially evolving turbulent boundary layer at Mach number 2.5 is considered. The issue of turbulent inflow generation, using rescaling/recycling method, is addressed. | |||||
BibTeX:
@misc{laghaaiaa09:1j,
author = {Lagha, M. and Zhong, X. and Eldredge, J. and Kim, J.},
title = {A Hybrid WENO Scheme for Simulation of Shock Wave-Boundary Layer Interaction},
year = {2009},
url = {https://drive.google.com/open?id=14X0F1n_RxK6ytr-gRyYiDTKgRNLLNFBI}
}
|
|||||
| Mendez, S. and Eldredge, J.D. | Acoustic modeling of perforated plates with bias flow for large-eddy simulations | 2009 | J. Comput. Phys. Vol. 228(13), pp. 4757-4772 |
article | DOI URL |
| Abstract: The study of the acoustic effect of perforated plates by Large-Eddy Simulations is reported. The ability of compressible Large-Eddy Simulations to provide data on the flow around a perforated plate and the associated acoustic damping is demonstrated. In particular, assumptions of existing models of the acoustic effect of perforated plate are assessed thanks to the Large-Eddy Simulations results. The question of modeling the effect of perforated plates is then addressed in the context of thermo-acoustic instabilities of gas turbine combustion chambers. Details are provided about the implementation, validation and application of a homogeneous boundary condition modeling the acoustic effect of perforated plates for compressible Large-Eddy Simulations of the flow in combustions chambers cooled by full-coverage film cooling. | |||||
BibTeX:
@article{mendez2009acoustic,
author = {Mendez, S. and Eldredge, J. D.},
title = {Acoustic modeling of perforated plates with bias flow for large-eddy simulations},
journal = {J. Comput. Phys.},
publisher = {Elsevier},
year = {2009},
volume = {228},
number = {13},
pages = {4757--4772},
url = {https://drive.google.com/open?id=10h__DuBFe1HGA5kfPjNe93r4wv82vuyh},
doi = {https://doi.org/10.1016/j.jcp.2009.03.026}
}
|
|||||
| Ol, M.V., Eldredge, J.D. and Wang, C. | High-Amplitude Pitch of a Flat Plate: an Abstraction of Perching and Flapping | 2009 | International Journal of Micro Air Vehicles Vol. 1(3), pp. 203-216 |
article | DOI URL |
| Abstract: We compare water tunnel experiment and 2D vortex-particle computation for a generalization of the classical problem of flat-plate constant-rate pitch and related motions, at frequencies and Reynolds numbers relevant to Micro Air Vehicle applications. The motivation is problems of maneuvering, perching and gust response. All of the examined flows evince a strong leading edge vortex. Increasing pitch rate tends to tighten the leading edge vortex and to produce a trailing-edge vortex system dominated by a counter-rotating pair. Pitch pivot point location is crucial to the leading edge vortex size and formation history, and to its subsequent behavior in convecting over the airfoil suction-side. Despite the respective limitations of the experiment and computations, agreement in vorticity fields between the two at an overlapping case at Re = 10,000 is good, whence it is possible to use the computation to obtain integrated force data unavailable in the experiment. These were studied for Re= 100 and 1000. Lift prediction from the computation shows a direct proportionality of lift to the pitch rate on the pitch upstroke. Finally, we compare pitch vs. plunge, and find that quasi-steady prediction is reasonably successful in predicting a combined pitch-plunge that effectively cancels the leading edge vortex, but not in canceling the trailing vortex system. | |||||
BibTeX:
@article{OLEldMAV09:1j,
author = {Ol, M. V. and Eldredge, J. D. and Wang, C.},
title = {High-Amplitude Pitch of a Flat Plate: an Abstraction of Perching and Flapping},
journal = {International Journal of Micro Air Vehicles},
year = {2009},
volume = {1},
number = {3},
pages = {203--216},
url = {https://drive.google.com/open?id=12h8Pi6j6bQI-nHw9uZ1tRUBB91H5rzTj},
doi = {https://doi.org/10.1260/175682909789996186}
}
|
|||||
| Rehman, S.F., Eldredge, J.D., Zhong, X. and Kim, J. | An evaluation of shock-capturing methods on a hypersonic boundary layer receptivity problem | 2009 | 47th AIAA Aerospace Sciences Meeting, Orlando, Florida. AIAA Paper 2009-0941 | misc | URL |
| Abstract: Understanding of transition of hypersonic boundary layers is critical for future development of re-entry vehicles. The receptivity of such a boundary layer to external flow disturbances is not well understood, particularly when the surface has finite-sized roughness. In this work, we explore the use of shock capturing for study of hypersonic boundary layer receptivity. In such problems, the interaction of the low-amplitude disturbances with shock structures may not be properly accounted for due to the localized dissipation inherent in the method. Previously-developed previously-developed WENO-based third- and fifth order shock capturing methods are applied to a receptivity problem, the Mach 4.5 flow past a flat plate with a sharp leading edge. This problem has been studied previously with a high-order shock fitting scheme. The shock-fitted solution is used to evaluate shock capturing schemes in terms of accuracy, efficiency and stability. Also, the significance of the leading edge singularity will be studied, which was not possible with a shock fitting method. | |||||
BibTeX:
@misc{rehmanaiaa09:1j,
author = {Rehman, S. F. and Eldredge, J. D. and Zhong, X. and Kim, J.},
title = {An evaluation of shock-capturing methods on a hypersonic boundary layer receptivity problem},
year = {2009},
url = {https://drive.google.com/open?id=13TiKzgLlQwL3CfXbQiHFUjw5302n6nIF}
}
|
|||||
| Toomey, J. | Numerical and experimental studies of flexibility in flapping wing aerodynamics [BibTeX] |
2009 | School: University of California, Los Angeles | phdthesis | URL |
BibTeX:
@phdthesis{toomeythesis09,
author = {Toomey, J.},
title = {Numerical and experimental studies of flexibility in flapping wing aerodynamics},
school = {University of California, Los Angeles},
year = {2009},
note = {eldredge},
url = {https://drive.google.com/open?id=15RCHUfmkdHVnpqmwq0YqL8RnxmShXFqg}
}
|
|||||
| Wilson, M.M., Peng, J., Dabiri, J.O. and Eldredge, J.D. | Lagrangian coherent structures in low Reynolds number swimming | 2009 | J. Phys.: Condens. Matter Vol. 21(20), pp. 204105 |
article | DOI URL |
| Abstract: This work explores the utility of the finite-time Lyapunov exponent (FTLE) field for revealing flow structures in low Reynolds number biological locomotion. Previous studies of high Reynolds number unsteady flows have demonstrated that ridges of the FTLE field coincide with transport barriers within the flow, which are not shown by a more classical quantity such as vorticity. In low Reynolds number locomotion (O(1)-O(100)), in which viscous diffusion rapidly smears the vorticity in the wake, tthe FTLE field has the potential to add new insight to locomotion mechanics. The target of study is an articulated two-dimensional model for jellyfish-like locomotion, with swimming Reynolds number of order 1. The self-propulsion of the model is numerically simulated with a viscous vortex particle method, using kinematics adapted from previous experimental measurements of a live medusan swimmer. The roles of the ridges of the computed forward- and backward-time FTLE fields are clarified by tracking clusters of particles both backward and forward in time. It is shown that a series of ridges in front of the fish in the forward-time FTLE field transport slender fingers of fluid toward the lip of the bell orifice, which are pulled once per contraction cycle into the wake of the fish, where the fluid remains partitioned. A strong ridge in the backward-time FTLE field reveals a persistent barrier between fluid inside and outside the subumbrellar cavity. The system is also analyzed in a body-fixed frame subject to a steady free stream, and the FTLE field is used to highlight differences in these frames of reference. | |||||
BibTeX:
@article{wilsonjde09:1j,
author = {Wilson, M. M. and Peng, J. and Dabiri, J. O. and Eldredge, J. D.},
title = {Lagrangian coherent structures in low Reynolds number swimming},
journal = {J. Phys.: Condens. Matter},
year = {2009},
volume = {21},
number = {20},
pages = {204105},
url = {https://drive.google.com/open?id=131NxUDp6eIwm9hlpIsAdL6BK8I4fsQhV},
doi = {https://doi.org/10.1088/0953-8984/21/20/204105}
}
|
|||||
| Zhang, J.L. and Eldredge, J.D. | A viscous vortex particle method for deforming bodies with application to biolocomotion | 2009 | Int. J. Numer. Meth. Fluids Vol. 59, pp. 1299-1320 |
article | DOI URL |
| Abstract: Bio-inspired mechanics of locomotion generally consist of the interaction of flexible structures with the surrounding fluid to generate propulsive forces. In this work, we extend, for the first time, the viscous vortex particle method (VVPM) to continuously deforming two-dimensional bodies. The VVPM is a high-fidelity Navier-Stokes computational method that captures the fluid motion through evolution of vorticity-bearing computational particles. The kinematics of the deforming body surface are accounted for via a surface integral in the Biot-Savart velocity. The spurious slip velocity in each time step is removed by computing an equivalent vortex sheet and allowing it to flux to adjacent particles; hence, no-slip boundary conditions are enforced. Particles of both uniform and variable size are utilized, and their relative merits are considered. The placement of this method in the larger class of immersed boundary methods is explored. Validation of the method is carried out on the problem of a periodically deforming circular cylinder immersed in a stagnant fluid, for which an analytical solution exists when the deformations are small. We show that the computed vorticity and velocity of this motion are both in excellent agreement with the analytical solution. Finally, we explore the fluid dynamics of a simple fish-like shape undergoing undulatory motion when immersed in a uniform free stream, to demonstrate the application of the method to investigations of biomorphic locomotion. |
|||||
BibTeX:
@article{zhangjde09:1j,
author = {Zhang, J. L. and Eldredge, J. D.},
title = {A viscous vortex particle method for deforming bodies with application to biolocomotion},
journal = {Int. J. Numer. Meth. Fluids},
year = {2009},
volume = {59},
pages = {1299--1320},
url = {https://drive.google.com/open?id=12p1-_47M7S0-uTY6egiEUnCUjsQuQ0Li},
doi = {https://doi.org/10.1002/fld.1867}
}
|
|||||
| Eldredge, J. | Dynamically coupled fluid-body interactions in vorticity-based numerical simulations | 2008 | J. Comput. Phys. Vol. 227, pp. 9170-9194doi:10.1016/j.jcp.2008.03.033 |
article | DOI URL |
| Abstract: A novel method is presented for robustly simulating coupled dynamics in fluid--body interactions with vorticity-based flow solvers. In this work, the fluid dynamics are simulated with a viscous vortex particle method. In the first substep of each time increment, the fluid convective and diffusive processes are treated, while a predictor is used to independently advance the body configuration. An iterative corrector is then used to simultaneously remove the spurious slip -- via vorticity flux -- and compute the end-of-step body configuration. Fluid inertial forces are isolated and combined with body inertial terms to ensure robust treatment of dynamics for bodies of arbitrary mass. The method is demonstrated for dynamics of articulated rigid bodies, including a falling cylinder, flow-induced vibration of a circular cylinder and free swimming of a three-link `fish'. The error and momentum conservation properties of the method are explored. In the case of the vibrating cylinder, comparison with previous work demonstrates good agreement. | |||||
BibTeX:
@article{jdevvpm:2j,
author = {J. D. Eldredge},
title = {Dynamically coupled fluid-body interactions in vorticity-based numerical simulations},
journal = {J. Comput. Phys.},
year = {2008},
volume = {227},
pages = {9170--9194},
url = {https://drive.google.com/open?id=104qav3PwGslvfTGLaS0oX35zqWnVBl14},
doi = {https://doi.org/10.1016/j.jcp.2008.03.033}
}
|
|||||
| Eldredge, J.D. and Pisani, D. | Passive locomotion of a simple articulated fish-like system in the wake of an obstacle | 2008 | J. Fluid Mech. Vol. 607, pp. 279-288 |
article | DOI URL |
| Abstract: The behaviour of a passive system of two-dimensional linked rigid bodies in the wake of a circular cylinder at Re=100 is studied computationally. The three rigid bodies are connected by two frictionless hinges, and the system (`fish') is initially aligned with a streamwise axis three diameters behind the cylinder. Once flow symmetry is broken, the wake rolls up into a Kármán vortex street in which the fish is stably trapped, and the passing large-scale vortices induce an undulatory shape change in the articulated system. It is found that, for certain fish lengths relative to cylinder diameter, the fish is propelled upstream toward the cylinder. Furthermore, the fish is propelled equally effectively when the hinges are locked, confirming that induced body undulation is not necessary for achieving a net thrust. An analysis of the forces on constituent bodies shows that leading-edge suction and negative skin friction on the forward portion of the fish are in competition with positive skin friction on the aft portion; propulsion is achieved when the forebody contributions dominate those on the aftbody. It is shown that the so-called `suction zone' behind the cylinder that enables this passive propulsion is double the length of that without a fish present. | |||||
BibTeX:
@article{pisanijde:1j,
author = {Eldredge, J. D. and Pisani, D.},
title = {Passive locomotion of a simple articulated fish-like system in the wake of an obstacle},
journal = {J. Fluid Mech.},
year = {2008},
volume = {607},
pages = {279--288},
url = {https://drive.google.com/open?id=10EqlbFGIwqfnQaK25H_A5165dR3XrjX-},
doi = {https://doi.org/10.1017/S0022112008002218}
}
|
|||||
| Eldredge, J.D., Wilson, M. and Hector, D. | An Exploration of Passive and Active Flexibility in Biolocomotion through Analysis of Canonical Problems | 2008 | Advances in Science and Technology Vol. 58, pp. 212-219 |
article | DOI URL |
| Abstract: Most aquatic creatures achieve motility through the dynamic interaction of their flexible body with the surrounding medium. This flexibility is used to provide a spectrum of active and passive control, allowing the creature to sometimes prescribe its shape changes and at other times extract energy from the fluid. This mix is particularly important in the moderate Reynolds number regime, in which wake vortices play an important energetic role. A well-devised control strategy for a bio-inspired vehicle should perhaps must exploit such flexion and energy exchange; as yet, we lack sufficient understanding to develop such a strategy. In this work, we present two canonical problems that distill fundamental modes of fluid/flexible body mechanics in biological systems, which are analyzed using high-fidelity numerical simulation. The first system consists of an articulated three-link swimmer considered in free-swimming. The second system involves an articulated jellyfish, in which the active/passive flexibility mix is explored by designation of the individual hinges. | |||||
BibTeX:
@article{EldWilHec08:1j,
author = {Eldredge, J. D. and Wilson, M. and Hector, D.},
title = {An Exploration of Passive and Active Flexibility in Biolocomotion through Analysis of Canonical Problems},
journal = {Advances in Science and Technology},
year = {2008},
volume = {58},
pages = {212-219},
url = {https://drive.google.com/open?id=12Ufqzaapqh-L1BOe_iDQF8oX28zRv0jn},
doi = {https://doi.org/10.4028/www.scientific.net/AST.58.212}
}
|
|||||
| Toomey, J. and Eldredge, J.D. | Numerical and experimental study of the fluid dynamics of a flapping wing with low order flexibility | 2008 | Phys. Fluids Vol. 20, pp. 073603 |
article | DOI URL |
| Abstract: A simple canonical problem for understanding the role of flexibility in flapping wing flight is investigated numerically and experimentally. The problem consists of a two-dimensional two-component wing structure connected by a single hinge with a damped torsion spring. One component of the wing is driven with hovering flapping wing kinematics, while the other component responds passively to the fluid dynamic and inertial/elastic forces. Numerical simulations are carried out with the viscous vortex particle method with strongly coupled body dynamics. The experiments are conducted in a water tank with suspended particles for flow visualization. The system is analyzed in several different kinematic test cases that are designed to span a broad parametric range of flapping. Hinge deflection is used as the primary metric for comparison; the agreement between computation and experiment is very good in all cases. The trajectories of shed vortices are also compared, again with favorable agreement. Fluid forces and moments are computed in the numerical simulation at two different Reynolds numbers. It is found that the rate and timing of wing rotation primarily controls the generation of lift; in contrast, the translational acceleration has little effect. Likewise, kinematics with rotation transition well separated from translation transition are captured utilizing rotation-only kinematics. Reynolds number has little effect on the wing deflection but does influence the mean lift generated by the wing. |
|||||
BibTeX:
@article{toomjde:2j,
author = {Toomey, J. and Eldredge, J. D.},
title = {Numerical and experimental study of the fluid dynamics of a flapping wing with low order flexibility},
journal = {Phys. Fluids},
year = {2008},
volume = {20},
pages = {073603},
url = {https://drive.google.com/open?id=10zgkhJvC5LQ28L0lsvdT4Iuc471ujzmA},
doi = {https://doi.org/10.1063/1.2956372}
}
|
|||||
| Zhang, J.L. | Numerical Studies of Hydrodynamics of Fish Locomotion and Schooling by a Vortex Particle Method [BibTeX] |
2008 | School: University of California, Los Angeles | phdthesis | URL |
BibTeX:
@phdthesis{zhangthesis08,
author = {Zhang, J. L.},
title = {Numerical Studies of Hydrodynamics of Fish Locomotion and Schooling by a Vortex Particle Method},
school = {University of California, Los Angeles},
year = {2008},
note = {eldredge},
url = {https://drive.google.com/open?id=15YI2P8dwvkjflrqLunYnJCsURBkEJanu}
}
|
|||||
| Eldredge, J.D. | The dynamics and acoustics of viscous two-dimensional leapfrogging vortices | 2007 | J. Sound Vib. Vol. 301(1-2), pp. 74-92 |
article | DOI URL |
| Abstract: The dynamics and acoustics of two identical pairs of counter-rotating vortices in viscous compressible flow are investigated. Each finite-sized vortex has an initially Gaussian distribution of vorticity. The dilating vortex particle method---developed in previous work---is used for the high-fidelity solution of the full compressible Navier--Stokes equations in the nearfield and a portion of the acoustic field; the radiated sound is extrapolated from a Kirchhoff surface adjusted for mean flow. The trailing vortex pair periodically slips through the leading pair, producing a sharp acoustic pulse. During the ensuing relaxation period as the cores return to horizontal alignment, filaments of vorticity are stripped from the outer part of each vortex while its inner core remains intact, and a small oscillatory acoustic signal is emitted. In contrast to previous studies of inviscid patches of uniform vorticity, this signal is much weaker than the slip-through pulses. Passive particles in the vortex cores are used to explore the filament evolution and core dynamics. The elastic deformation of the inner core, which is a crucial source of sound in previous patch studies, is found to be insignificant to sound production in these smooth cores. Instead, the weak oscillatory component of sound is generated by the anchors of filamentary structures as they rotate about the core. After several slip-through cycles, the pairs coalesce to form a single counter-rotating pair, and the sound emissions become weak and sinusoidal. | |||||
BibTeX:
@article{Eldredge2007a,
author = {Eldredge, J. D.},
title = {The dynamics and acoustics of viscous two-dimensional leapfrogging vortices},
journal = {J. Sound Vib.},
publisher = {Elsevier},
year = {2007},
volume = {301},
number = {1-2},
pages = {74--92},
url = {https://drive.google.com/open?id=122YWzk0nk1G4o2OMZDqH6CXw4GWQtDSP},
doi = {https://doi.org/10.1016/j.jsv.2006.09.015}
}
|
|||||
| Eldredge, J.D. | Numerical simulation of the fluid dynamics of 2D rigid body motion with the vortex particle method | 2007 | J. Comput. Phys. Vol. 221, pp. 626-648 |
article | DOI URL |
| Abstract: A viscous vortex particle method is presented for computing the fluid dynamics of two-dimensional rigid bodies in motion. The Navier--Stokes equations are solved using a fractional step procedure. Smooth particles carry vorticity and exchange strength to account for convection and viscous diffusion. The spurious slip resulting from this half-step is identified with a surface vortex sheet, and the slip is eliminated by diffusing the sheet to adjacent particles. Particles are remeshed every few time steps to a Cartesian grid with a `body-ignorant' interpolation using simple symmetric stencils. Kelvin's circulation theorem remains enforced by accounting for the circulation leaked into the body during this procedure, and redistributing it to the particles in the subsequent sheet diffusion. The stability and convergence with respect to numerical parameters are explored in detail, with particular focus on the residual slip velocity. The method is applied to two problems that demonstrate its utility for investigating biological locomotion: a flapping elliptical wing with hovering insect kinematics, with good agreement of forces with previous simulations and experiments; and a three-linkage `fish' undergoing undulatory mechanics. | |||||
BibTeX:
@article{jdevvpm:1j,
author = {Eldredge, J. D.},
title = {Numerical simulation of the fluid dynamics of 2D rigid body motion with the vortex particle method},
journal = {J. Comput. Phys.},
year = {2007},
volume = {221},
pages = {626--648},
url = {https://drive.google.com/open?id=13ENTCpLMTwlA-R_uQUGsn3uHWa_6Z6kd},
doi = {https://doi.org/10.1016/j.jcp.2006.06.038}
}
|
|||||
| Eldredge, J.D., Bodony, D.J. and Shoeybi, M. | Numerical Investigation of the Acoustic Behavior of a Multi-perforated Liner | 2007 | 13th AIAA/CEAS Aeroacoustics Conference. AIAA Paper 2007-3683. | misc | URL |
| Abstract: The acoustic response of a turbulent flow through an aperture in a multi-perforated liner is computed with incompressible large-eddy simulation (LES). The effect of a large array of apertures is accounted for by simulating a single jet with periodic conditions in both directions tangential to the liner. Turbulent grazing flows are included in the regions above and below the aperture, which is tilted in the tangential flow direction as in practical film cooling liners. The mass flow through the aperture is modulated with a small sinusoidal perturbation superposed on a mean component. The acoustic response is determined by measuring the fluctuating pressure difference across the aperture that results from forcing at a range of different frequencies. The Rayleigh conductivity of the aperture, which is related to the acoustic impedance of the liner, is calculated at each frequency. Good agreement is found when compared with existing theory, when the latter is modified in ad hoc fashion for the thickness and tilting of the aperture. The behavior of the flow inside the aperture and its relationship to the acoustic response are discussed. | |||||
BibTeX:
@misc{eldredgebodony07,
author = {Eldredge, J. D. and Bodony, D. J. and Shoeybi, M.},
title = {Numerical Investigation of the Acoustic Behavior of a Multi-perforated Liner},
year = {2007},
url = {https://drive.google.com/open?id=10IchwVRB69lSC0OLcihW8StkB4g68eJA}
}
|
|||||
| Rehman, S.F. and Eldredge, J.D. | Numerical Investigation of a Bias-Flow Perforated Liner for Damping of Thermoacoustic Instabilities | 2007 | Proceedings of GT2007, ASME Turbo Expo 2007, Montreal, Canada. Paper GT2007-27319 | misc | URL |
| Abstract: Lean premixed prevaporized (LPP) gas turbine generators are naturally prone to thermoacoustic instabilities. Strategic placement of passive damping devices can provide simple, effective fixes for such unstable behavior. In this work, the thermoacoustic damping characteristics of a perforated liner with mean bias flow are examined. A recently-developed theoretical model, along with accompanying experimental investigation, has demonstrated that a bias-flow liner can very effectively absorb incident acoustic waves. Here, a modular simulation tool is utilized to examine the capability of the liner for stabilizing an unstable ducted flame. The simulation tool represents the acoustic interactions between duct elements in the form of transfer matrices, which can be modularly arranged for exploring a variety of configurations. An unstable thermoacoustic system is produced with a gain-delay flame model in a duct. The frequencies and growth rates of the linear model are examined. It is shown that, by tailoring the liner porosity and the bias flow, unstable modes of the thermoacoustic system can be stabilized. Furthermore, it is found that, for a double liner system, there is an optimal liner porosity for a given choice of bias flow, at which the modal decay rate is maximized. |
|||||
BibTeX:
@misc{rehman07,
author = {Rehman, S. F. and Eldredge, J. D.},
title = {Numerical Investigation of a Bias-Flow Perforated Liner for Damping of Thermoacoustic Instabilities},
year = {2007},
url = {https://drive.google.com/open?id=11XVfPjz7FQHNwostmVZ6a_rSuizPmjQe}
}
|
|||||
| Shukla, R.K. and Eldredge, J.D. | An inviscid model for vortex shedding from a deforming body | 2007 | Theor. Comput. Fluid Dyn. Vol. 21, pp. 343-368 |
article | DOI URL |
| Abstract: An inviscid vortex sheet model is developed in order to study the unsteady separated flow past a two-dimensional deforming body which moves with a prescribed motion in an otherwise quiescent fluid. Following Jones (J Fluid Mech 496, 405--441, 2003) the flow is assumed to comprise of a bound vortex sheet attached to the body and two separate vortex sheets originating at the edges. The complex conjugate velocity potential is expressed explicitly in terms of the bound vortex sheet strength and the edge circulations through a boundary integral representation. It is shown that Kelvin's circulation theorem, along with the conditions of continuity of the normal velocity across the body and the boundedness of the velocity field, yields a coupled system of equations for the unknown bound vortex sheet strength and the edge circulations. A general numerical treatment is developed for the singular principal value integrals arising in the solution procedure. The model is validated against the results of Jones (J Fluid Mech 496, 405--441, 2003) for computations involving a rigid flat plate and is subsequently applied to the flapping foil experiments of Heathcote et al. (AIAA J, 42, 2196--2204, 2004) in order to predict the thrust coefficient. The utility of the model in simulating aquatic locomotion is also demonstrated, with vortex shedding suppressed at the leading edge of the swimming body. | |||||
BibTeX:
@article{shuklajde:1j,
author = {Shukla, R. K. and Eldredge, J. D.},
title = {An inviscid model for vortex shedding from a deforming body},
journal = {Theor. Comput. Fluid Dyn.},
year = {2007},
volume = {21},
pages = {343--368},
url = {https://drive.google.com/open?id=11G9UDp2jpTxUlNOtyxfD1iX2rQSpVcAO},
doi = {https://doi.org/10.1007/s00162-007-0053-2}
}
|
|||||
| Eldredge, J., Shoeybi, M. and Bodony, D. | Numerical investigation of the acoustic behavior of a multi-perforated liner | 2006 | Center for Turbulence Research, Proceedings of the Summer Program 2006 | inproceedings | URL |
| Abstract: The acoustic response of a turbulent flow through a multi-perforated liner is computed with incompressible Large-Eddy Simulation (LES). The effect of an array of apertures is accounted for by simulating a single jet with periodic conditions in both directions tangential to the plate. Flows that are parallel to the plate are included in the regions above and below the aperture, which is tilted in the tangential flow direction as in practical film-cooling liners. The mass flow rate through the aperture is forced with a small sinusoidal perturbation superposed on a mean component. The acoustic behavior is determined by measuring the fluctuating pressure difference across the aperture that results from the forcing. In this work, two different forcing frequencies are considered. The transfer function between forcing and response, which represents the acoustic impedance of the liner, is calculated for these frequencies. Good agreement is found when compared with existing theory, when the latter is modified for the thickness and tilting of the aperture. | |||||
BibTeX:
@inproceedings{jdectr06a,
author = {Eldredge, J. and Shoeybi, M. and Bodony, D.},
title = {Numerical investigation of the acoustic behavior of a multi-perforated liner},
booktitle = {Center for Turbulence Research, Proceedings of the Summer Program 2006},
year = {2006},
url = {https://drive.google.com/open?id=11wBkOpKYV4F6ac2bc0RYVICc1HyuhlsT}
}
|
|||||
| Eldredge, J.D. | Numerical simulations of undulatory swimming at moderate Reynolds number number | 2006 | Bioinspir. Biomim. Vol. 1, pp. S19-S24 |
article | DOI URL |
| Abstract: We perform numerical simulations of the swimming of a three-linkage articulated system in a moderately viscous regime. The computational methodology focuses on the creation, diffusion and transport of vorticity from the surface of the bodies into the fluid. The simulations are dynamically coupled, in that the motion of the three-linkage swimmer is computed simultaneously with the dynamics of the fluid. The novel coupling scheme presented in this work is the first to exploit the relationship between vorticity creation and body dynamics. The locomotion of the system, when subject to undulatory inputs of the hinges, is computed at Reynolds numbers of 200 and 1000. It is found that the forward swimming speed increases with the Reynolds number, and that in both cases the swimming is slower than in an inviscid medium. The vortex shedding is examined, and found to exhibit behavior consistent with experimental flow visualizations of fish. | |||||
BibTeX:
@article{jdebio06:1j,
author = {Eldredge, J. D.},
title = {Numerical simulations of undulatory swimming at moderate Reynolds number number},
journal = {Bioinspir. Biomim.},
year = {2006},
volume = {1},
pages = {S19-S24},
url = {https://drive.google.com/open?id=10aUhsUQa3poPU5LC3YACBHRSAm8nrROM},
doi = {https://doi.org/10.1088/1748-3182/1/4/S03}
}
|
|||||
| Mendez, S., Eldredge, J., Nicoud, F., Poinsot, T., Shoeybi, M. and Iaccarino, G. | Numerical investigation and preliminary modeling of a turbulent flow over a multi-perforated plate | 2006 | Center for Turbulence Research, Proceedings of the Summer Program 2006, pp. 57-72 | inproceedings | URL |
| Abstract: Wall-resolved Large-Eddy Simuations (LES) of a turbulent flow around a multi-perforated plate are presented. Periodic conditions are used in both directions tangential to the plate so that only one or a few micro-jets are computed. Comparisons between one and four holes computations show that single-hole domain calculations allow the capture of the essential characteristics and statistics of the flow. The results from two different numerical codes and strategies also compare favorably with the existing experimental data in the case of a large-scale cold flow with effusion. The overall quality of the simulations being established, further analysis of the flow structure is performed. Two results relevant to further modeling studies are obtained: the jet angle somewhat departs from the hole angle, and the velocity profile in the jet is highly inhomogeneous with a strong recirculation zone in the downstream side. Preliminary testing of a simple dynamic model for the normal velocity is also presented. A robust algorithm for implementing this model in coupled computational domains is developed. Deficiencies in the model are identified and discussed. | |||||
BibTeX:
@inproceedings{mendez06,
author = {Mendez, S. and Eldredge, J. and Nicoud, F. and Poinsot, T. and Shoeybi, M. and Iaccarino, G.},
title = {Numerical investigation and preliminary modeling of a turbulent flow over a multi-perforated plate},
booktitle = {Center for Turbulence Research, Proceedings of the Summer Program 2006},
year = {2006},
pages = {57--72},
url = {https://drive.google.com/open?id=1-qMYx5J2WhMRdLy1kB71S0_1XqB8Bx-g}
}
|
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| Toomey, J. and Eldredge, J.D. | Numerical and experimental investigation of the role of flexibility in flapping wing flight | 2006 | 36th AIAA Fluid Dynamics Conference, San Francisco, California. AIAA Paper 2006-3211 | misc | URL |
| Abstract: The role of flexibility in flapping wing flight is explored using dynamically-scaled experiments and numerical simulations. To limit the dimension of the parameter space, the target of study is a two-dimensional two-component wing connected by a hinge with a torsional spring. The motion of the lead body is prescribed with flapping kinematics, while the trailing body motion is passive. Experiments are conducted in a water tank, enabling flow visualization with suspended particles. Numerical simulations rely on the viscous vortex particle method (VVPM) for coupled fluid-body dynamics. In both the experiments and the computations, the behavior of the wing is characterized by monitoring the evolution of the hinge angle, with favorable agreement between them. Flow structures are identified and compared for representative cases. Analysis of lift force and energy consumption from numerical simulations indicates that wing flexibility can improve wing performance when measured in terms of energy spent per unit lift. | |||||
BibTeX:
@misc{toomjde:1j,
author = {Toomey, J. and Eldredge, J. D.},
title = {Numerical and experimental investigation of the role of flexibility in flapping wing flight},
year = {2006},
url = {https://drive.google.com/open?id=12l7pDU2fdtmVFq2MmITExmWW3oEH4r3Y}
}
|
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| Eldredge, J.D. | The acoustics of two-dimensional leapfrogging vortices | 2005 | 11th AIAA/CEAS Aeroacoustics Conference, Monterey, California. AIAA Paper 2005-2954. | misc | URL |
| Abstract: The acoustics of two identical pairs of counter-rotating vortices in viscous compressible flow are investigated. Each vortex is finite sized, and has an initially Gaussian distribution of vorticity. The dilating vortex particle method---developed in previous work---is used for the fully-resolved solution of the compressible Navier--Stokes equations in the nearfield and a portion of the acoustic field, and a Kirchhoff method is used to extrapolate the radiated sound. The trailing vortex pair slips through the leading pair, producing a sharp acoustic pulse. During the ensuing relaxation period as the cores return to horizontal alignment, a small high-frequency sound is emitted. In contrast to previous studies of inviscid patches of uniform vorticity, this high-frequency sound is much smaller in magnitude than the slip-through pulses. By analyzing the dynamics of passive tracer particles in the vortex cores, it is found that inner core deformation is not responsible for this high-frequency component. Instead, it is generated by the anchors of filamentary structures as they rotate about the core. After several slip-through cycles, the pairs coalesce to form a single counter-rotating pair, and the sound emissions become weak and sinusoidal. | |||||
BibTeX:
@misc{jdeaiaaleapfrog05,
author = {Eldredge, J. D.},
title = {The acoustics of two-dimensional leapfrogging vortices},
year = {2005},
url = {https://drive.google.com/open?id=12pfC09gyGAJ4DpW0vy-_o0G2C3MSZPPS}
}
|
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| Eldredge, J.D. | Efficient tools for the simulation of flapping wing flows | 2005 | 43rd AIAA Aerospace Sciences Meeting, Reno, Nevada. AIAA Paper 2005-0085 | misc | URL |
| Abstract: The development of novel strategies for lift and propulsion using flapping wings requires the use of computational tools that are at once efficient and capable of handling complex deforming boundary motion. In this work we present the use of a viscous vortex particle method for the simulation of the flow produced by a two-dimensional rigid wing in pitching and plunging motion of moderate Reynolds number. By its Lagrangian nature, this method is able to automatically adapt to important flow structures. Efficiency is ensured by using vorticity-bearing computational elements that are distributed only to the extent that vorticity itself is spread through its convection and diffusion; no effort is needed for irrotational regions of flow. Moreover, the correct behavior of the velocity at infinity is automatically satisfied, obviating the need for an artificial boundary treatment. Results of the dynamically shed vorticity and the forces exerted are presented for a single stroke of a flapping elliptical wing. | |||||
BibTeX:
@misc{eldredge:8j,
author = {Eldredge, J. D.},
title = {Efficient tools for the simulation of flapping wing flows},
year = {2005},
url = {https://drive.google.com/open?id=10HGguy0wwperOEYgY6JOdU-x-vJ_B_6U}
}
|
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| Eldredge, J.D. | On the interaction of higher duct modes with a perforated liner system with bias flow | 2004 | J. Fluid Mech. Vol. 510, pp. 303-331 |
article | DOI URL |
| Abstract: We explore the three-dimensional interaction of higher acoustic modes with bias-flow perforated liners in cylindrical and annular ducts. Pressure fluctuations in the vicinity of the liners excite the production and shedding of vorticity from the rims of apertures in the liners. An effective liner compliance is used which accounts for this transfer of acoustical into vortical energy. The investigation is facilitated by a Green's function solution of the Helmholtz equation in a lined section of duct, allowing calculation of the amplitudes of exiting wave modes due to incoming acoustic disturbances. A system containing an arbitrary number of concentric liners and the hollow cavities formed between them can be modelled. The results for an incident plane wave are compared with those from our previously developed one-dimensional model, with excellent agreement. We demonstrate that results for all modes that travel parallel to the liner, including higher circumferential modes in narrow annular gaps, exhibit self-similar behaviour, and that liner design rules developed for planar duct modes can be adapted accordingly. The acoustic absorption can be strongly enhanced by downstream duct reflection for wavelengths larger than twice the liner length, but is less affected at higher frequencies that allow persistent pressure minima along the liner. Across larger frequency ranges, the liner systems are shown to permit two types of resonance associated with the duct and the cavities, respectively, and a third of Helmholtz type, associated with the system as a whole. The effect of these resonances on incident modes is demonstrated, and, in particular, we explore their enhancement of acoustic absorption. | |||||
BibTeX:
@article{eldredge:7j,
author = {Eldredge, J. D.},
title = {On the interaction of higher duct modes with a perforated liner system with bias flow},
journal = {J. Fluid Mech.},
year = {2004},
volume = {510},
pages = {303--331},
url = {https://drive.google.com/open?id=1-XBfk40hNxubxzd0pdDZkHN_U2R20Dyf},
doi = {https://doi.org/10.1017/S0022112004009504}
}
|
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| Eldredge, J.D. and Dowling, A.P. | The absorption of axial acoustic waves by a perforated liner with bias flow | 2003 | J. Fluid Mech. Vol. 485, pp. 307-335 |
article | DOI URL |
| Abstract: The effectiveness of a cylindrical perforated liner with mean bias flow in its absorption of planar acoustic waves in a duct is investigated. The liner converts acoustic energy into flow energy through the excitation of vorticity fluctuations at the rims of the liner apertures. A one-dimensional model that embodies this absorption mechanism is developed. It utilizes a homogeneous liner compliance adapted from the Rayleigh conductivity of a single aperture with mean flow. The model is evaluated by comparing with experimental results, with excellent agreement. We show that such a system can absorb a large fraction of incoming energy, and can prevent all of the energy produced by an upstream source in certain frequency ranges from reflecting back. Moreover, the bandwidth of this strong absorption can be increased by appropriate placement of the liner system in the duct. An analysis of the acoustic energy flux is performed, revealing that local differences in fluctuating stagnation enthalpy, distributed over a finite length of duct, are responsible for absorption, and that both liners in a double-liner system are absorbant. A reduction of the model equations in the limit of long wavelength compared to liner length reveals an important parameter grouping, enabling the optimal design of liner systems. | |||||
BibTeX:
@article{eldredge:4j,
author = {Eldredge, J. D. and Dowling, A. P.},
title = {The absorption of axial acoustic waves by a perforated liner with bias flow},
journal = {J. Fluid Mech.},
year = {2003},
volume = {485},
pages = {307--335},
url = {https://drive.google.com/open?id=11TmLTMigfexItJn1L6LlZXlVWzVZl84U},
doi = {https://doi.org/10.1017/S0022112003004518}
}
|
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| Eldredge, J.D., Colonius, T. and Leonard, A. | A vortex particle method for two-dimensional compressible flow | 2002 | J. Comput. Phys. Vol. 179, pp. 371-399 |
article | DOI URL |
| Abstract: A vortex particle method is developed for simulating two-dimensional, unsteady compressible flow. The method uses the Helmholtz decomposition of the velocity field to separately treat the irrotational and solenoidal portions of the flow, and the particles are allowed to change volume to conserve mass. In addition to having vorticity and dilatation properties, the particles also carry density, enthalpy, and entropy. The resulting evolution equations contain terms that are computed with techniques used in some incompressible methods. Truncation of unbounded domains via a nonreflecting boundary condition is also considered. The fast multipole method is adapted to compressible particles in order to make the method computationally efficient. The new method is applied to several problems, including sound generation by corotating vortices and generation of vorticity by baroclinic torque. | |||||
BibTeX:
@article{eldredge:2j,
author = {Eldredge, J. D. and Colonius, T. and Leonard, A.},
title = {A vortex particle method for two-dimensional compressible flow},
journal = {J. Comput. Phys.},
year = {2002},
volume = {179},
pages = {371--399},
url = {https://drive.google.com/open?id=10tw7H2rK7xCjM21SoGcnbuiEF6eOz3eA},
doi = {https://doi.org/10.1006/jcph.2002.7060}
}
|
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| Eldredge, J.D., Colonius, T. and Leonard, A. | A dilating vortex particle method for compressible flow | 2002 | J. Turbul. Vol. 3(36), pp. N36 |
article | DOI URL |
| Abstract: Vortex methods have become useful tools for the computation of incompressible fluid flow. In this work, a vortex particle method for the simulation of unsteady two-dimensional compressible flow is developed. By decomposing the velocity into irrotational and solenoidal parts, and using particles that are able to change volume and that carry vorticity, dilatation, enthalpy, entropy and density, the equations of motion are satisfied. Spatial derivatives are treated using the method of particle strength exchange with high-order-accurate, non-dissipative kernels. The new vortex method is applied to co-rotating and leapfrogging vortices in compressible flow, with the far acoustic field computed using a two-dimensional Kirchhoff surface. | |||||
BibTeX:
@article{eldredge:5j,
author = {Eldredge, J. D. and Colonius, T. and Leonard, A.},
title = {A dilating vortex particle method for compressible flow},
journal = {J. Turbul.},
year = {2002},
volume = {3},
number = {36},
pages = {N36},
url = {https://drive.google.com/open?id=11yEjixXe8AjvRIDqA1AYLWxK0UubJCvG},
doi = {https://doi.org/10.1088/1468-5248/3/1/036}
}
|
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| Eldredge, J.D., Leonard, A. and Colonius, T. | A general deterministic treatment of derivatives in particle methods | 2002 | J. Comput. Phys. Vol. 180, pp. 686-709 |
article | DOI URL |
| Abstract: A unified approach to approximating spatial derivatives in particle methods using integral operators is presented. The approach is an extension of particle strength exchange, originally developed for treating the Laplacian in advection--diffusion problems. Kernels of high order of accuracy are constructed that can be used to approximate derivatives of any degree. A new treatment for computing derivatives near the edge of particle coverage is introduced, using ``one-sided'' integrals that only look for information where it is available. The use of these integral approximations in wave propagation applications is considered and their error is analyzed in this context using Fourier methods. Finally, simple tests are performed to demonstrate the characteristics of the treatment, including an assessment of the effects of particle dispersion, and their results are discussed. | |||||
BibTeX:
@article{eldredge:1j,
author = {Eldredge, J. D. and Leonard, A. and Colonius, T.},
title = {A general deterministic treatment of derivatives in particle methods},
journal = {J. Comput. Phys.},
year = {2002},
volume = {180},
pages = {686--709},
url = {https://drive.google.com/open?id=111JwBV5DoTs97pIdmlm0WLwJz-9IYmvk},
doi = {https://doi.org/10.1006/jcph.2002.7112}
}
|
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| Eldredge, J., Colonius, T. and Leonard, A. | A vortex particle method for compressible flows | 2001 | 15th AIAA Computational Fluid Dynamics Conference, Anaheim, California. AIAA Paper 2001-2641 | misc | URL |
| Abstract: A vortex particle method for the simulation of two-dimensional compressible flows is developed. The computational elements are Lagrangian particles that carry vorticity, dilatation, enthalpy, entropy and density. The velocity field is decomposed into irrotational and solenoidal parts,which allows its calculation in terms of the particles' vorticity and dilatation. The particle coverage is truncated and incident acoustic waves are absorbed using a suitable boundary treatment. A Kirchhoff surface formulation is developed for computing the far-field sound. The method is applied to a co-rotating vortex pair and the results are discussed. | |||||
BibTeX:
@misc{eldredge:3j,
author = {Eldredge, J. and Colonius, T. and Leonard, A.},
title = {A vortex particle method for compressible flows},
year = {2001},
url = {https://drive.google.com/open?id=13E_19DL8pqaRQvF6qTCT-Vg0lraLs0eM}
}
|
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| Eldredge, J.D. | A Dilating Vortex Particle Method for Compressible Flow, with Application to Aeroacoustics [BibTeX] |
2001 | School: Caltech | phdthesis | URL |
BibTeX:
@phdthesis{eldredge:6j,
author = {Eldredge, J. D.},
title = {A Dilating Vortex Particle Method for Compressible Flow, with Application to Aeroacoustics},
school = {Caltech},
year = {2001},
url = {https://drive.google.com/open?id=12x_eLejtUg4XGTI4M1pqxOX4Wj_WnMXL}
}
|
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