Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session AB: Bio-Fluid Dynamics: Swimming |
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Chair: Jeff Eldredge, University of California, Los Angeles Room: Hilton Chicago Waldorf |
Sunday, November 20, 2005 8:00AM - 8:13AM |
AB.00001: Fish Pectoral Fin Hydrodynamics; Part I: Kinematics and DPIV Measurements of Propulsion and Maneuvering Peter G. Madden, George V. Lauder, Haibo Dong, Meliha Bozkurttas, Rajat Mittal The flexibility and shape change of fish pectoral fins gives fish a great degree of control over fluid forces. Two camera high speed (500 fps) high resolution digital video was taken and digitized to measure 3D fin conformation during steady swimming and maneuvering. During steady swimming, pectoral fins cup forward into the flow in the chordwise direction with leading edges at both the upper and lower fin boundaries. Fin surface area changes by over 25{\%} through the course of a beat. While maneuvering, the upper and lower leading edges can move independently to adjust the direction of generated forces. Measurement of flow in a plane behind the pectoral fin using high frame rate (500 fps) stereo particle imaging velocimetry (PIV) shows strong vortices forming at both edges during both outstroke and instroke. The relative magnitude of the upper and lower vortices and the resultant fluid jet direction are found to vary with different maneuvering directions. [Preview Abstract] |
Sunday, November 20, 2005 8:13AM - 8:26AM |
AB.00002: Fish Pectoral Fin Hydrodynamics; Part II: Numerical Simulations and Analysis H. Dong, M. Bozkurttas, R. Mittal, P.G. Madden, G.V. Lauder High-fidelity numerical simulations are being used to examine the key hydrodynamic features and thrust performance of the pectoral fin of a bluegill sunfish which is moving at a constant forward velocity. The numerical modeling approach employs a parallelized immersed boundary solver which can perform direct (DNS) or large-eddy simulation (LES) of flow past highly deformable bodies such as fish pectoral fins. The three-dimensional, time-dependent fin kinematics is obtained via a stereo-videographic technique and experiments also provide PIV data which is used to validate the numerical simulations. The primary objectives of the CFD effort are to quantify the thrust performance of the bluegill sunfish pectoral fin as well as to establish the mechanisms responsible for thrust production. Simulations show that the pectoral fin produces a relatively large amount of thrust at all phases in the fin motion while limiting the magnitude of the transverse forces. The motion of the fin produces a distinct system of connected vortices which are examined in detail in order to gain insight into the thrust producing mechanisms. [Preview Abstract] |
Sunday, November 20, 2005 8:26AM - 8:39AM |
AB.00003: Fish Pectoral Fin Hydrodynamics; Part III: Low Dimensional Models via POD Analysis M. Bozkurttas, H. Dong, R. Mittal, P. Madden, G.V. Lauder The highly complex kinematics of the pectoral fin and the resulting hydrodynamics does not lend itself easily to analysis based on simple notions of pitching/heaving/paddling kinematics or lift/drag based propulsive mechanisms. A more inventive approach is needed to dissect the fin gait and gain insight into the hydrodynamic performance of the pectoral fin. The focus of the current work is on the hydrodynamics of the pectoral fin of a bluegill sunfish in steady forward motion. The 3D, time-dependent fin kinematics is obtained via a stereo-videographic technique. We employ proper orthogonal decomposition to extract the essential features of the fin gait and then use CFD to examine the hydrodynamics of simplified gaits synthesized from the POD modes. The POD spectrum shows that the first two, three and five POD modes capture 55{\%}, 67{\%}, and 80{\%} of the motion respectively. The first three modes are in particular highly distinct: Mode-1 is a ``cupping'' motion where the fin cups forward as it is abducted; Mode-2 is an ``expansion'' motion where the fin expands to present a larger area during adduction and finally Mode-3 involves a ``spanwise flick'' of the dorsal edge of the fin. Numerical simulation of flow past fin gaits synthesized from these modes lead to insights into the mechanisms of thrust production; these are discussed in detail. [Preview Abstract] |
Sunday, November 20, 2005 8:39AM - 8:52AM |
AB.00004: Computational Modeling of the Dolphin Kick in Competitive Swimming A. Loebbeck, R. Mittal, H. Dong, R. Mark, G. Bhanot, R. Walkup Numerical simulations are being used to study the fluid dynamics of the dolphin kick in competitive swimming. This stroke is performed underwater after starts and turns and involves an undulatory motion of the body. Highly detailed laser body scans of elite swimmers are used and the kinematics of the dolphin kick is recreated from videos of Olympic level swimmers. We employ a parallelized immersed boundary method to simulate the flow associated with this stroke in all its complexity. The simulations provide a first of its kind glimpse of the fluid and vortex dynamics associated with this stroke and hydrodynamic force computations allow us to gain a better understanding of the thrust producing mechanisms. [Preview Abstract] |
Sunday, November 20, 2005 8:52AM - 9:05AM |
AB.00005: Wake Structure and Thrust Production of a Low Aspect Ratio Pitching Panel James Buchholz, Alexander Smits The wake structure and thrust performance of a low aspect ratio panel pitching in a uniform flow is investigated experimentally. The wake undergoes transitions in its structure with variation in nondimensional flapping frequency. At low frequency, the wake represents a three-dimensional von K\'{a}rm\'{a}n vortex street. With increasing frequency, the wake divides into two distinct trains of vortical structures spreading in the transverse direction followed by a spanwise thickening of the wake. The fundamental constituent of each of these wake structures is a sequence of horseshoe vortices shed from the trailing edge and adjacent spanwise-oriented edges of the panel. Time evolution and transitions in the wake can be understood in terms of interactions between these horseshoe vortices. A three-dimensional vortex model of the wake will be presented, and the relationship between thrust performance and wake transitions will be discussed. [Preview Abstract] |
Sunday, November 20, 2005 9:05AM - 9:18AM |
AB.00006: Thrust Production and Wake Structure of a Batoid-Inspired Oscillating Fin Richard Clark, Alexander Smits Experiments are reported on the hydrodynamic performance of a flexible fin. The fin replicates some features of the pectoral fin of a batoid fish (such as a ray or skate) in that it is actuated in a traveling wave motion, with the amplitude of the motion increasing linearly along the span from root to tip. Thrust is found to increase with non-dimensional frequency, and an optimal oscillatory gait is identified. Power consumption measurements lead to the computation of Froude efficiency, and an optimal efficiency condition is evaluated. Wake visualizations are presented, and a vortex model of the wake near zero net thrust is suggested. Strouhal number effects on the wake topology are also illustrated. [Preview Abstract] |
Sunday, November 20, 2005 9:18AM - 9:31AM |
AB.00007: Performance of hydrofoils with humpback whale-like leading edge protuberances. Alexandra Levshin, Charles Henoch, Hamid Johari The humpback whale (\textit{Megaptera novaeangliae}) is extremely maneuverable, compared to other whale species, despite its large size and rigid body. Turning maneuvers are especially evident during pursuit of prey. The agility of humpback whale has been attributed to their use of pectoral flippers. The thick flippers have large aspect ratios, and large scale protuberances are present on the leading edge. The flippers do not flap during turning maneuvers. The cross-section of the flipper has a profile similar to a NACA 63$_{4}$-021 airfoil. The amplitude of leading edge protuberances ranges from 2.5 to 12{\%} of the chord, with a spanwise extent of 10 to 50{\%} the chord depending on the location along the span. It has been hypothesized that the `bumpy' leading edge is used for flow control. To examine the effects of protuberances on the leading edge of hydrofoils, a series of rectangular foils with bumpy leading edges were manufactured. The leading edge is sinusoidal in the spanwise direction with amplitudes and wavelengths comparable to that of humpback whale's flippers. The forces and moments on these bumpy foils were measured in a water tunnel and compared with a smooth leading edge foil. [Preview Abstract] |
Sunday, November 20, 2005 9:31AM - 9:44AM |
AB.00008: Nonlinear resonance control of unsteady hydrodynamic actuators Promode R. Bandyopadhyay, Alberico Menozzi, Anuradha Annaswamy The nonlinear resonance properties of inferior olive neurons, that are responsible for restoring balance in animals, are considered for control of periodic flapping foils. The approach is motivated by a need to make the unsteady foils of a recently demonstrated Biorobotic Autonomous Underwater Vehicle at NUWC fault tolerant because many foils work in phase to allow the vehicle undertake precision maneuvering motions. Limit cycle properties are used to restore variables such as roll, pitch bias and frequency subsequent to pulse or impulse disturbances. Stabilization is demonstrated in a full scale foil in a water tank. [Preview Abstract] |
Sunday, November 20, 2005 9:44AM - 9:57AM |
AB.00009: Flow induced by a jellyfish Seiji Ichikawa, Osamu Mochizuki The purpose of this study is to understand experimentally a propulsion mechanism of a jellyfish for applying its mechanism to a soft-matter micro robot. The traveling of a jellyfish is governed by viscous force because of following reasons: the main component of jellyfish is water whose percentage is 98{\%}, and the Reynolds number is low. We observed the motion of a jellyfish by a motion-capture camera, and measured the vector field of flow around a jellyfish by using a PIV system. A jellyfish is principally propelled by a vortex ring ejected at the contracting phase of a jellyfish motion. It is interesting that it never stop traveling even at the expanding phase. A vortex ring observed at the inside of a jellyfish at the expanding phase is found to play an important rule for traveling at the expanding phase. We discuss that the inside vortex ring with the opposite vorticity contribute decrease in shear stress of the inside boundary layer and increase in circulation of the shed vortex ring. [Preview Abstract] |
Sunday, November 20, 2005 9:57AM - 10:10AM |
AB.00010: Numerical simulations of flying and swimming of biological systems with the viscous vortex particle method Jeff Eldredge Many biological mechanisms of locomotion involve the interaction of a fluid with a deformable surface undergoing large unsteady motion. Analysis of such problems poses a significant challenge to conventional grid-based computational approaches. Particularly in the moderate Reynolds number regime where many insects and fish function, viscous and inertial processes are both important, and vorticity serves a crucial role. In this work, the viscous vortex particle method is shown to provide an efficient, intuitive simulation approach for investigation of these biological systems. In contrast with a grid-based approach, the method solves the Navier--Stokes equations by tracking computational particles that carry smooth blobs of vorticity and exchange strength with one another to account for viscous diffusion. Thus, computational resources are focused on the physically relevant features of the flow, and there is no need for artificial boundary conditions. Building from previously-developed techniques for the creation of vorticity to enforce no-throughflow and no-slip conditions, the present method is extended to problems of coupled fluid--body dynamics by enforcement of global conservation of momenta. The application to several two-dimensional model problems is demonstrated, including single and multiple flapping wings and free swimming of a three-linkage fish. [Preview Abstract] |
Sunday, November 20, 2005 10:10AM - 10:23AM |
AB.00011: On the estimation of swimming and flying forces from wake measurements John O. Dabiri This paper addresses the question of the minimum number of wake properties whose combination is sufficient to determine locomotive forces from wake measurements. In particular, it is shown that the vorticity field is by itself insufficient to determine locomotive forces, and must be combined with a parameter analogous to the fluid pressure. The measurement of this parameter in the wake is shown to be identical to a calculation of the added-mass contribution from fluid surrounding vortices in the wake, and proceeds identically to a measurement of the added-mass traditionally associated with fluid surrounding solid bodies. A model is developed to approximate the contribution of wake vortex added-mass to locomotive forces, given a combination of velocity and vorticity field measurements in the wake. Previous wake analyses are re-examined in light of these results to infer the existence and importance of wake vortex added-mass in those cases. It is shown that the commonly used time-averaged wake-based force estimates are not sufficient to prove that an animal is generating the locomotive forces necessary to sustain flight or maintain neutral buoyancy. [Preview Abstract] |
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