Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session E17: Biofluids: Locomotion III - Flying |
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Chair: Iman Borazjani, University at Buffalo Room: 305 |
Sunday, November 24, 2013 4:45PM - 4:58PM |
E17.00001: Lift enhancement in flying snakes Anush Krishnan, John Socha, Pavlos Vlachos, Lorena Barba Flying snakes use a unique method of aerial locomotion: they jump from tree branches, flatten their bodies and undulate through the air to produce a glide. The shape of their body cross-section during the glide plays an important role in generating lift. We present a computational investigation of the aerodynamics of the cross-sectional shape. We performed two-dimensional simulations of incompressible flow past the anatomically correct cross-section of the species Chrysopelea paradisi, which show that a significant enhancement in lift appears at an angle of attack of 35 degrees, for Reynolds numbers 2000 and above. Previous experiments on physical models also demonstrated an increased lift and at the same angle of attack. The simulations point to the lift enhancement arising from the early separation of the boundary layer on the dorsal surface of the snake profile, without stall. The separated shear layer rolls up and interacts with secondary vorticity in the near-wake, inducing the primary vortex to remain closer to the body and thus cause enhanced suction, resulting in higher lift. In physical experiments, the flow is inherently 3-D due to fluid instabilities, and it is intriguing that the enhanced lift also appears in the two-dimensional simulations. [Preview Abstract] |
Sunday, November 24, 2013 4:58PM - 5:11PM |
E17.00002: On the hydrodynamics of ray-like swimming Richard G. Bottom II, Iman Borazjani, Erin Blevins, George V. Lauder There are substantial differences in body shape and motion of stingrays relative to other fish, which drastically affect the hydrodynamics of locomotion. Discovering the flow physics of ray-like locomotion is invaluable not only from a biological standpoint but also for practical application in the development of novel, bio-inspired, man-made vehicles. Here we first develop an analytical model for the stingray's body and fin motion based on experimental laser scan of body shape in the freshwater stingray Potamotrygon orbignyi, and on experimental 3D kinematic data of the wing and body surface obtained from freely-swimming stingrays. The accurate model for the stingray motion is constructed by Fourier analysis of the experimental data resulting in a traveling wave equation with an amplitude coefficient, which is spatially dependent across the fin. Based on this model, we carry out large eddy simulations of the stingray using the immersed boundary method, i.e., the motion of the stingray body is prescribed based on the model, and the motion of the center of mass is calculated. We validate our simulations against experimental data. The simulations reveal the 3D structure of the wake and quantify the swimming performance under different conditions. [Preview Abstract] |
Sunday, November 24, 2013 5:11PM - 5:24PM |
E17.00003: Experimental study of the fluid structure interaction for falling cards Ruijun Tian, Coulton Sadler, Fangjun Shu In this experimental study, high-speed visualization and PIV measurements were conducted to investigate the dynamic evolution of the flow field generated by gravity driven falling cards. Experiments were done in both water and air using glass slides, which are transparent to avoid laser blockage. Fluttering motion (card sliding from side to side while descending) was observed in water while tumbling motion (card rotates w.r.t. it long axis) happened in air. High-speed images of the falling cards were acquired and processed to analyze its kinematics including velocities and accelerations, both translational and rotational. From the card kinematics, the instantaneous fluid dynamic forces/torque were derived, they were related to the surrounding flow field measured using PIV. It is found that the leading edge vortex plays an important role in falling mode. Its evolution and shedding is closely related to the change of translational and angular acceleration of the falling plates, thus influence the falling mode. In the same fluid, a narrow card intends to tumble while a wide card intends to flutter, mainly due to increased moment of inertia. An empirical or theoretical theory is to be developed to predict the motion and trajectory of a gravity driven falling card. [Preview Abstract] |
Sunday, November 24, 2013 5:24PM - 5:37PM |
E17.00004: An elastic body impacting the water surface; inspired by diving birds Sunghwan Jung, Alex Ochs, Sean Gart We investigate how a soft elastic body responds to water-entry impact analogous to a bird diving into water to catch prey. Dumbbell shaped objects made of two acrylic spheres connected by an elastic rod are dropped into water. A buckling threshold was found by varying impact force and elastic rod stiffness. This threshold may have implication as to how birds are able to safely dive into water at high speeds and avoid any neck-injury. [Preview Abstract] |
Sunday, November 24, 2013 5:37PM - 5:50PM |
E17.00005: Could flapping foil propulsion become a commercial shipping reality? Brenden Epps Since the 1990s, fluid dynamicists have made great strides towards understanding the physics of flapping foil propulsion. However, to date, few commercial shipping vessels employ this technology. Why? How does the efficiency of a flapping hydrofoil compare to that of a conventional screw propeller? What technical challenges exist, and how might we overcome them in order to make flapping foil propulsion a reality for commercial shipping vessels? [Preview Abstract] |
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