Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session D32: Focus Session: Vortex Dynamics in Fluid-Structure Interactions II |
Hide Abstracts |
Chair: Darren Crowdy, Imperial College London Room: 33C |
Sunday, November 18, 2012 2:15PM - 2:28PM |
D32.00001: Analytical solutions for hollow vortex pairs in a channel Christopher Green, Darren Crowdy Motivated by the problem of vortex rings travelling along tubes, we study the two-dimensional analogue comprising a counter-rotating vortex pair travelling along a straight-walled channel. By modelling the vortices as a pair of so-called hollow vortices we are able to find a class of solution in closed mathematical form. Solutions for both a single vortex pair and a periodic array of vortex pairs will be presented. Connections with classical solutions due to both Michel (1890) and Pocklington (1895) will be made. [Preview Abstract] |
Sunday, November 18, 2012 2:28PM - 2:41PM |
D32.00002: Hollow Vortices in Flow Past a Flat Plate Alan Elcrat, Luca Zannetti Closed and open hollow wakes are considered as analytic models for the 2D inviscid steady flow past a plate normal to the stream. It is shown that only open configurations which satisfy the Kutta condition exist. The main argument is based on considering a plate located on the edge of a step with varying height. It is shown that solutions for open wakes exist for backward, null and forward-facing steps, while closed wakes only exist for backward-facing steps. The occurrence of secondary separation has been modeled by adding a hollow region attached to the downstream corner. Peculiar accuracy issues of the problem are pointed out which may explain other contradictory results from the literature. It is shown how the Kirchhoff wake is a limiting solution for certain values of the governing parameters. [Preview Abstract] |
Sunday, November 18, 2012 2:41PM - 2:54PM |
D32.00003: Vortex Dynamics at Early Time Stages of Viscous Flow past a Finite Plate Ling Xu, Monika Nitsche We use numerical simulations to revisit a fundamental problem of viscous flow past a finite flat plate. We resolved the boundary layer separation and roll-up from very early time to relatively large times. Details of vorticity structure in the boundary layer at early times are shown, these features have not been studied before. In particular, we will present details of the negative vorticity region, the entrainment between the positive and negative vorticity and the scales of circulation shedding rate from the plate tip, maximum velocity and core vorticity. [Preview Abstract] |
Sunday, November 18, 2012 2:54PM - 3:07PM |
D32.00004: Frequency spectrum and scale dependence of a propulsive self-excited vortex generator Robert Whittlesey, John Dabiri We describe the development and characterization of a passive device that creates a train of vortex rings from a steady incoming flow. The device consists of a collapsible tube enclosed in an air-tight chamber which undergoes self-excited oscillations under specific conditions of flow rate and transmural pressure. An experimental parameter study was conducted in order to determine the oscillation frequency spectrum of the device, and its dependence on the nozzle diameter. For certain combinations of flow rate and transmural pressure, the frequency of self-excited oscillations, and hence vortex formation, is independent of device size over an order of magnitude range of device volume. These results have a particular interest for the development of vehicles utilizing vortex-enhanced propulsion (Ruiz et al, JFM, 2011). Continued work in this area has focused on the implementation of this device to a self-propelled submarine. [Preview Abstract] |
Sunday, November 18, 2012 3:07PM - 3:20PM |
D32.00005: Three-Dimensional Vortex Design by Hydrofoil Acceleration Martin Scheeler, Dustin Kleckner, William Irvine We demonstrate the use of accelerated hydrofoils (airfoils in water) for the generation of vortex loops of arbitrary shape in three dimensions. The technique allows not only the patterning of shape, but non-trivial topology. We study both the process of vortex production and the subsequent vortex evolution using ultra-fast 3D laser scanning tomography. [Preview Abstract] |
Sunday, November 18, 2012 3:20PM - 3:33PM |
D32.00006: An Experimental Investigation on the Interference of the Multiple Wind Turbines with Different Layout Patterns in Atmospheric Boundary Layer Winds Hui Hu, Wei Tian, Ahmet Ozbay We report an experimental study to investigate the wake interferences of multiple wind turbines in atmospheric boundary layer (ABL) winds. The experimental study is conducted by taking advantages of the large-scale Aerodynamic/Atmospheric Boundary Layer (AABL) Wind Tunnel available at Iowa State University to quantify the performances of an array of wind turbine models with aligned and staggered arrangement patterns. In addition to measuring dynamic wind loads (both forces and moments) and the power outputs of the wind turbine models, advanced flow diagnostic techniques such as digital Particle Image Velocimetry (PIV) is used to conduct detailed flow field measurements to quantify the flow characteristics of the surface winds and wake interferences among the multiple wind turbines with different layout patterns. The detailed flow field measurements are correlated with the dynamic wind loads and power output measurements to elucidate underlying physics for the optimal design of the wind turbine array layout with the ultimate goal of higher total power yield and better durability of the wind turbines operating in more realistic environments. [Preview Abstract] |
Sunday, November 18, 2012 3:33PM - 3:46PM |
D32.00007: Von K\'arm\'an vortex streets: analytical solutions with distributed vorticity Darren Crowdy, Christopher Green We present analytical solutions for both staggered and unstaggered von K\'arm\'an vortex streets. Instead of point vortices, we employ a distributed vorticity model consisting of arrays of hollow vortices whose shapes are determined as part of the solution scheme (it is a free boundary problem). The new solutions are compared with purely numerical solutions based on the vortex patch model computed by Saffman \& Schatzman in 1981. [Preview Abstract] |
Sunday, November 18, 2012 3:46PM - 3:59PM |
D32.00008: Structure and stability of the finite-area von Karman street P. Luzzatto-Fegiz, C.H.K. Williamson By using a recently developed numerical method, we explore in detail the equilibria for a Karman street of uniform, large-area vortices. We construct a reliable implementation of an energy argument to find superharmonic instabilities. This leads us to organize flows into families with fixed impulse $I$, and to construct diagrams of the flow energy $E$ and horizontal spacing $L$. Families of large-$I$ streets exhibit a turning point in $L$, and terminate with ``cat's eyes'' vortices (as also suggested by previous investigators). However, for low-$I$ streets, the solution families display a multitude of turning points (leading to multiple possible streets, for given $L)$, and terminate with teardrop-shaped vortices. This is radically different from previous suggestions in the literature. These two qualitatively different limiting states are connected by a special street, whereby vortices from opposite rows touch, such that each vortex exhibits three corners. Furthermore, by following the family of $I$ = 0 streets to small $L$, we access a large, hitherto unexplored regime, involving streets with $L$ much smaller than previously believed possible. For each solution family, our stability approach also reveals a single superharmonic bifurcation, leading to new vortex streets, which exhibit lower symmetry. [Preview Abstract] |
Sunday, November 18, 2012 3:59PM - 4:12PM |
D32.00009: Nonholonomic Mechanics and Fluid-Body Interactions Scott Kelly, Phanindra Tallapragada Certain velocity constraints arising in idealized models for fluid-body interactions, including the Kutta condition classically applied at the trailing cusp of a Joukowski hydrofoil experiencing lift, are formally equivalent to nonintegrable constraints arising in the mechanics of finite-dimensional mechanical systems. This equivalence allows hydrodynamic problems involving vortex shedding and related phenomena to be framed in the context of geometric mechanics on manifolds, and for essential mechanisms of biomorphic aquatic propulsion to be interpreted in terms of symmetry-breaking and generalized momentum equations. We illustrate this perspective using simple examples that highlight parallels between the finite- and infinite-dimensional cases. [Preview Abstract] |
Sunday, November 18, 2012 4:12PM - 4:25PM |
D32.00010: Fluid structure interaction with low and high order flexibility using volume penalization Jianxiong Sheng, Thomas Engels, Dmitry Kolomenskiy, Kai Schneider We present a new numerical scheme for the simulation of deformable objects immersed in a viscous incompressible fluid. The two-dimensional Navier--Stokes equations are discretized with an efficient Fourier pseudo-spectral scheme. Using the volume penalization method arbitrary inflow conditions can be enforced, together with the no-slip conditions at the boundary of the immersed solid object. The code is validated using classical fluid-structure interaction benchmarks, a channel flow with an immersed cylinder and attached flexible foil. We make a comparison between numerical simulations of deformable foils of two different types. The first consists of two rigid plates linked with a torsion spring (low-order flexibility). The second is a flexible plate modeled using a non-linear beam equation (high-order flexibility). We also compare these results with numerical simulations and experiments carried out by Toomey and Eldredge (Phys. Fluids 20, 073603, 2008). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700