Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session AN: Vortex Dynamics and Vortex Flows I |
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Chair: Yoshi Kimura, Nagoya University Room: Long Beach Convention Center 202C |
Sunday, November 21, 2010 8:00AM - 8:13AM |
AN.00001: A comparison of vortex and pseudo-spectral methods at high Reynolds numbers Anthony Leonard, Wim van Rees, Petros Koumoutsakos We validate the hybrid particle-mesh vortex method against a pseudo-spectral method in simulations of the Taylor-Green vortex and colliding vortex tubes at Re = 1600 - 10,000. The spectral method uses the smooth filter introduced in [1]. In the case of the Taylor-Green vortex, we observe very good agreement in the evolution of the vortical structures albeit small discrepancies in the energy spectrum only for the smallest length scales. In the collision of two anti-parallel vortex tubes at Re = 10 000, there is very good agreement between the two methods in terms of the simulated vortical structures throughout the first reconnection of the tubes. The maximum error in the effective viscosity is below 2.5\% and 1\% for the vortex method and the pseudo-spectral method respectively. At later times the agreement between the two methods in the vortical structures deteriorates even though there is good agreement in the energy spectrum. Both methods resolve an unexpected vortex breakdown during the second reconnection of the vortex tubes.\\[4pt] [1] Hou, T. and Li, R., 2007. Computing nearly singular solutions using pseudo-spectral methods. J. of Comput. Phys., 226:379-397. [Preview Abstract] |
Sunday, November 21, 2010 8:13AM - 8:26AM |
AN.00002: Vortex methods with immersed lifting lines applied to LES of wind turbine wakes Philippe Chatelain, Laurent Bricteux, Gregoire Winckelmans, Petros Koumoutsakos We present the coupling of a vortex particle-mesh method with immersed lifting lines. The method relies on the Lagrangian discretization of the Navier-Stokes equations in vorticity-velocity formulation. Advection is handled by the particles while the mesh allows the evaluation of the differential operators and the use of fast Poisson solvers. We use a Fourier-based fast Poisson solver which simultaneously allows unbounded directions and inlet/outlet boundaries. A lifting line approach models the vorticity sources in the flow. Its immersed treatment efficiently captures the development of vorticity from thin sheets into a three-dimensional field. We apply this approach to the simulation of a wind turbine wake at very high Reynolds number. The combined use of particles and multiscale subgrid models allows the capture of wake dynamics with minimal spurious diffusion and dispersion. [Preview Abstract] |
Sunday, November 21, 2010 8:26AM - 8:39AM |
AN.00003: Vortex methods for fluid-structure interaction problems with deforming geometries and their application to swimming Mattia Gazzola, Philippe Chatelain, Petros Koumoutsakos We present a vortex particle-mesh method for fluid-structure interaction problems. The proposed methodology combines implicit interface capturing, Brinkmann penalization techniques, and the self-consistent computation of momentum transfer between the fluid and the structure. In addition, our scheme is able to handle immersed bodies characterized by non-solenoidal deformations, allowing the study of arbitrary deforming geometries. This attractively simple algorithm is shown to accurately reproduce reference simulations for rigid and deforming structures. Its suitability for biological locomotion problems is then demonstrated with the simulation of self-propelled anguilliform swimmers. [Preview Abstract] |
Sunday, November 21, 2010 8:39AM - 8:52AM |
AN.00004: A Lagrangian Vortex Method for the Barotropic Vorticity Equation on a Rotating Sphere Robert Krasny, Lei Wang We present a Lagrangian vortex method for the barotropic vorticity equation on a rotating sphere. The method solves for the flow map using Lagrangian particles and panels. The velocity is computed by evaluating the Biot-Savart integral on the sphere. An adaptive refinement strategy is implemented to maintain accuracy over long times. Results are presented for propagating Rossby-Haurwitz waves and localized vortex interactions. [Preview Abstract] |
Sunday, November 21, 2010 8:52AM - 9:05AM |
AN.00005: A Multi-moment vortex method for 2D viscous fluids David Uminsky, C. Eugene Wayne, Alethea Barbaro, Vitalii Ostrovskyi In this talk we introduce a new vortex method which incorporates Hermite moment corrections to radially symmetric Gaussian basis functions. Convergence of the Hermite expansion is proven and the added Hermite moments allow for each particle to deform under convection. We analyze the case of a single particle with many Hermite moments in the context of a shear diffusion example and discuss the improved spatial accuracy of the method. Time permitting, we will provide some examples of a large number of particles with fewer Hermite moments and discuss the trade off between computational efficiency and spatial accuracy. [Preview Abstract] |
Sunday, November 21, 2010 9:05AM - 9:18AM |
AN.00006: Computational Fluid Dynamic Analysis of Hydrodynamic forces on inundated bridge decks Bushra Afzal, Junke Guo, Kornel Kerenyi The hydraulic forces experienced by an inundated bridge deck have great importance in the design of bridges. Flood flows or hurricane add significant hydrodynamic loading on bridges, possibly resulting in failure of the bridge superstructures. The objective of the study is to establish validated computational practice to address research needs of the transportation community via computational fluid dynamic simulations. The reduced scale experiments conducted at Turner-Fairbank Highway Research Center establish the foundations of validated computational practices to address the research needs of the transportation community. Three bridge deck prototypes were used: a typical six-girder highway bridge deck, a three-girder deck, and a streamlined deck designed to better withstand the hydraulic forces. Results of the study showed that the streamlined deck significantly reduces drag, lift, and moment coefficient in comparison to the other bridge deck types. The CFD results matched the experimental data in terms of the relationship between inundation ratio and force measured at the bridge. The results of the present research will provide a tool for designing new bridges and retrofitting old ones. [Preview Abstract] |
Sunday, November 21, 2010 9:18AM - 9:31AM |
AN.00007: Interaction of Vortex Rings and Steady Jets with Multiple Permeable Screens Mustafa N. Musta, Paul S. Krueger DPIV measurements of the interaction of a vortex ring impinging on a rudimentary porous medium formed from several parallel, transparent permeable screens was made previously for screens with 49.5{\%}, 58.95, and 84{\%} open area ratio ($\phi )$ and jet Reynolds number (\textit{Re}) in the range 1000-2000. The results indicated the vortex ring split into smaller vortical structures after its interaction with the first screen. For the $\phi $ =84{\%} screens the flow formed jets which reorganized into a transmitted like vortex ring which was not observed for lower $\phi $. The present work seeks to provide a more detailed investigation of the flow through the matrix of screens using DPIV. Measurements were made for vortex rings and steady jets interacting with screens with variable spacing and open area ratios of 49.5{\%}-84{\%}. The vortex rings were generated with a piston-cylinder vortex ring generator using piston stroke-to-diameter ratios and \textit{Re} in the ranges 2-4 and 2000-4000, respectively. The vortex ring results show similar flow structures observed qualitatively in the lower \textit{Re} tests. The steady jets rapidly expand to fill the matrix of screens after interacting with an approximately fixed number of screens for low $\phi $ and the decay of kinetic energy is strongly influenced by $\phi$. [Preview Abstract] |
Sunday, November 21, 2010 9:31AM - 9:44AM |
AN.00008: Instantaneous Global Separation on a Vanishing Wing David Rival, Martin Wibawa, Michael Triantafyllou Inspired by Taylor's analytical treatment of an impulsively-accelerated, vanishing circular disk,\footnote{G. I. Taylor, ``Formation of a Vortex Ring by Giving an Impulse to a Circular Disk and then Dissolving it Away,'' J. Applied Physics \textbf{24}, 104 (1953)} the authors have examined the transfer of circulation from a vanishing wing's hypothetical bound vortex into the wake. The study was performed experimentally in a water towing tank by rapidly removing a moving wing at incidence. By applying lead-precipitate and PIV techniques, the transfer of circulation from the two boundary layers into a vortex pair in the wake could be observed. By tracking the strength of these two shed vortices, it was found that the net circulation transferred into the wake was equal in strength to that of the bound vortex. However, contrary to standard vorticity transfer from a stalled foil, the time scales associated with this transfer process are found to be much more rapid in nature. This opens up new possibilities for biomimetic propulsion mechanisms based on this concept of rapid area change. [Preview Abstract] |
Sunday, November 21, 2010 9:44AM - 9:57AM |
AN.00009: A simplified analog for a rotorcraft-in-ground-effect flow using a forced impinging jet Jayson Geiser, Ken Kiger The phenomenon of rotorcraft brown-out is defined as the intense suspension and re-ingestion of sand during the take-off and landing of a rotor-lifted aircraft. To mitigate the problem of rotorcraft brown-out, the non-equilibrium sediment suspension process that occurs within a typical rotorcraft wake must be understood. We attempt to understand the most basic aspects of this complex flow through the use of an axisymmetric forced impinging jet. While this flow neglects the swirl component associated with a rotorcraft, it does reproduce the typical coherent vortex structures, and permits their repeatable generation within an axisymmetric mean stagnation flow. The goal of the current work is to determine the forcing conditions that produce isolated, but intense and repeatable structures that can be followed through their interaction with the wall boundary. Stereo PIV imaging is applied to detail the breakdown of a vortex ring in the wall jet zone. The secondary vortex generation and decay are observed experimentally with 3-D vector fields, and their results are interpreted with respect to their significance in the context of sediment mobilization. [Preview Abstract] |
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