Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session GJ: Bio-Fluids: Undulatory Flapping I |
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Chair: Eric Lauga, University of California, San Diego Room: 102A |
Monday, November 24, 2008 8:00AM - 8:13AM |
GJ.00001: Lift and drag of cetacean flippers Mark Murray, Paul Weber, Laurens Howle, Frank Fish Field observation and collection of biological samples has resulted in cetacean (whales, dolphins and porpoises) flipper geometry being known for most species. However, the hydrodynamic properties of cetacean flippers have not been rigorously tested and thus their performance characteristics are unknown. Here, conducting water tunnel testing using scale models of cetacean flippers derived via computed tomography (CT) scans, as well as computational fluid dynamic (CFD) simulations, we present a baseline work to determine the hydrodynamic characteristics of cetacean flippers. We found that flippers of similar planform shape had similar hydrodynamic performance characteristics. Furthermore, one group of flippers of planform shape similar to a modern swept wing was found to have lift coefficient versus angle of attack curves that were biphasic rather than linear in nature, which was caused by the onset of vortex-dominated lift. Drag coefficient versus angle of attack curves were found to be less dependant on planform shape. [Preview Abstract] |
Monday, November 24, 2008 8:13AM - 8:26AM |
GJ.00002: DPIV measurements of dolphins performing tailstands Yae Eun Moon, Erica Sherman, Frank Fish, Terrie Williams, Timothy Wei In the past few years, we have adapted DPIV to permit measurements of flow around swimming mammals (human and dolphin). In this study, we apply this technique to measure flow associated with a dolphin performing a tail stand; the behavior in which the dolphin lifts and holds itself vertically out of the water by rapid and strong oscillations of its tail. The objective of this work was i) to validate the ability to compute thrust production from vortices generated by the tail motions and ii) to develop a quantitative measure of the thrust production capability of a dolphin. Data from numerous tail stands taken from two different Atlantic bottlenose dolphins will be presented. Independent thrust comparisons are developed by monitoring how much of the dolphins' bodies were held above the water during the tailstand behavior. The presentation includes both movies showing flow velocity overlayed on the original dolphin videos as wall as plots of thrust as a function of percent body weight lifted from the water. The data clearly demonstrate that dolphins produce thrust on the order of their body weight, far more than necessary to overcome turbulent boundary layer drag. [Preview Abstract] |
Monday, November 24, 2008 8:26AM - 8:39AM |
GJ.00003: On the hydrodynamics of fishlike swimming: Anguilliform vs. Carangiform locomotion Iman Borazjani, Fotis Sotiropoulos Comparing anguilliform and carangiform swimming experimentally is a great challenge due to issues such as obtaining 3D flow and pressure fields around the live fish, control over the live fish, etc. Numerical simulations can be a powerful tool to complement experiments in this respect. We carry out a systematic numerical study to compare virtual anguilliform and carangiform swimmers. Using simulations for tethered virtual swimmers we study the effects of Reynolds number (Re) on swimming performance. We found that the carangiform swimmers' efficiency increases as the Re increases while the anguilliform efficiency peaks in the transitional regime due to the difference in either kinematics or shape of the virtual swimmers. To study the effects of shape and kinematics separately, we perform a series of self-propelled simulations by prescribing the anguilliform kinematics on the carangiform body and vice versa. The computed results provide novel insights into the performance of each mode of swimming in various flow regimes and help reconcile and clarify experimental observations with live fish. [Preview Abstract] |
Monday, November 24, 2008 8:39AM - 8:52AM |
GJ.00004: Thrust Production in a Mechanical Swimming Lamprey Megan Leftwich, Alexander Smits To develop a comprehensive model of lamprey locomotion, we use a robotic lamprey as a means of investigating the surface pressure and wake structure during swimming. A programmable microcomputer actuates 11 servomotors that produce a traveling wave along the length of the lamprey body. The waveform is based on the motion of the American eel (Anguilla rostrata), as described by Tytell and Lauder (2004) and kinematic studies of living lamprey. The amplitude of the phase-averaged surface pressure distribution along the centerline of the robot increases toward the tail, which is consistent with previous momentum balance experiments indicating that thrust is produced mainly at the tail. The phase relationship between the pressure signal and the vortex shedding from the tail is also examined. The project is supported by NIH CNRS Grant 1R01NS054271. [Preview Abstract] |
Monday, November 24, 2008 8:52AM - 9:05AM |
GJ.00005: An integrative CFD model of lamprey swimming Chia-yu Hsu, Tyler McMillen, Lisa Fauci Swimming due to sinusoidal body undulations is observed across the full spectrum of swimming organisms, from microscopic flagella to fish. These undulations are achieved due to internal force-generating mechanisms, which, in the case of lamprey are due to a wave of neural activation from head to tail which gives rise to a wave of muscle activation. These active forces are also mediated by passive structural forces. Here we present recent results on a computational model of a swimming lamprey that couples activation of discrete muscle segments, passive elastic forces, and a surrounding viscous, incompressible fluid. The fluid dynamics is modeled by the Navier-Stokes equations at appropriate Reynolds numbers, where the resulting flow field and vortex shedding may be measured. [Preview Abstract] |
Monday, November 24, 2008 9:05AM - 9:18AM |
GJ.00006: Hydrodynamic interactions between laterally-spaced undulating ``fish'' Jeany L. Zhang, Jeff D. Eldredge It is generally accepted that fish achieve hydrodynamic benefits by swimming in schools, though the mechanisms used to achieve these benefits are not completely understood. In particular, the influence of lateral separation between fish has not been well characterized. In this work, it is shown that substantial increases in thrust can be obtained by fish swimming in parallel with no streamwise separation. The target of study is a two-dimensional fish-shaped profile generated about an undulating backbone. The fluid dynamics of single and multiple fish, tethered in a free-stream flow, are simulated with the viscous vortex particle method. The Reynolds number is maintained relatively low at 100. The Strouhal number of a single fish is varied to determine the value at which mean net force on the fish is zero. Then, with Strouhal number fixed, the relative distance and phase of two fish are systematically varied. It is found that the largest increase in overall thrust occurs when the fish undulate with mirror symmetry. With mirror symmetry maintained, the overall thrust decreases monotonically, but in a complex manner, as distance is increased. Systems with three fish are also studied. Finally, some preliminary results of free-swimming fish are examined. [Preview Abstract] |
Monday, November 24, 2008 9:18AM - 9:31AM |
GJ.00007: Wake shed by an accelerating carangiform fish Shang-Chieh Ting, Jing-Tang Yang We reveal an important fact that momentum change observed in the wake of an accelerating carangiform fish does not necessarily elucidate orientations of propulsive forces produced. An accelerating Crucian Carp (\textit{Carassius auratu}s) was found to shed a wake with net forward fluid momentum, which seemed drag-producing. Based on Newton's law, however, an accelerating fish is expected to shed a thrust wake with net rearward fluid momentum, rather than a drag wake. The unusual wake pattern observed is considered to be resulted primarily from the effect of pressure gradient created by accelerating movements of the fish. Ambient fluids tend to be sucked into low pressure zones behind an accelerating fish, resulting in forward orientations of jets recognizable in the wake. Accordingly, as to an accelerating fish, identifying force orientations from the wake requires considering also the effect of pressure gradient. [Preview Abstract] |
Monday, November 24, 2008 9:31AM - 9:44AM |
GJ.00008: Fish Manoeuvres and Morphology Kiran Singh, Timothy Pedley The extraordinary manoeuvrability observed in many fish is attributed to their inherent flexibility, which might be enhanced by the use of appendages like fins. The aim of this work is to understand the role of morphological adaptations, such as body shape and deployment of median fins, on manoeuvrability and internal body dynamics. The 3d vortex lattice numerical method was employed to analyse the hydrodynamics for arbitrary body planforms of infinitesimal thickness. The internal structure of the body due to the combined skeletal system and soft tissue, is represented as an active Euler-Bernoulli beam, in which the time-dependent bending moment distribution is calculated from body inertia and the hydrodynamic pressure difference across the body. C-turns are the manoeuvre of choice for this work and the response for three different species of fish are examined. Angelfish({\it Pterophyllum eimekei}), pike ({\it Esox sp}) and tuna ({\it Thunnus albacares}) were chosen for their differences in body profile, median fin use and manoeuvrability. Net direction change and bending moment response to prescribed backbone flexure are calculated and used to interpret the influence of body profile on manoeuvrability and muscle work done. Internal stresses may be computed from anatomical data on muscle fibre distribution and recruitment. To the future, it is intended to extend this work to other typical manoeuvres, such as fast starts for which muscle activation patterns have been measured quite widely. [Preview Abstract] |
Monday, November 24, 2008 9:44AM - 9:57AM |
GJ.00009: Full Eulerian finite difference computation for fluid-structure coupling problem Kazuyasu Sugiyama, Shintaro Takeuchi, Satoshi Ii, Shu Takagi, Yoichiro Matsumoto A new simulation method for solving fluid-structure coupling problems has been developed. An efficient and robust numerical algorithm is achieved by extending standard incompressible fluid flow solvers based on a full Eulerian formulation. All the basic equations are numerically solved on a fixed Cartesian grid in a finite difference scheme. A volume-of-fluid approach, which has been developed for computing multiphase flows, is applied to describing the multi-component geometry. The temporal change in the solid deformation is described on the Eulerian frame by updating a left Cauchy-Green deformation tensor, which represents constitutive equations for the Cauchy stress of hyperelastic materials such as Mooney-Rivin and St. Venant- Kirchhoff ones. The present simulation method is validated by showing good agreement with available numerical data (Zhao {\em et al.} (2008) J. Comput. Phys. {\bf 227}, 3114), and by demonstrating reversibility in shape of the hyperelastic material. [Preview Abstract] |
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