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 G17: Biofluids: Locomotion IV - Liquids; Experiments and Numerical Simulations |
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Chair: Keith Moored, Lehigh University Room: 305 |
Monday, November 25, 2013 8:00AM - 8:13AM |
G17.00001: Quantitative analysis of fish wake dynamics using volumetric PIV data Leah Mendelson, Alexandra Techet In the study of swimming hydrodynamics, the fluid impulse in the wake is used to quantify the momentum transferred by the fish as it swims. This impulse is typically computed from planar PIV measurements of the wake circulation and geometry by assuming an axisymmetric vortex ring model. However, in many propulsive and maneuvering scenarios, three-dimensional effects are of substantial importance, and wake features are not often an isolated, symmetric vortex ring. Volumetric PIV data provides a complete measure of the vortex geometry and orientation, and circulation can be determined over multiple planar slices through the volume. Using sample datasets obtained from synthetic aperture PIV (SAPIV), we demonstrate how the availability of volumetric PIV data enables more detailed analysis of hydrodynamic impulse and characterize the uncertainty created by planar measurements. Special attention is paid to unsteady maneuvering behaviors that generate asymmetric and linked wake features. [Preview Abstract] |
Monday, November 25, 2013 8:13AM - 8:26AM |
G17.00002: On the effect of flexibility on the performance of a bio-inspired fin Stefano Chiazza, Florian H.J. Bremer, Alexander J. Smits Experiments are performed to examine the flowfield characteristics of bio-inspired fins of different flexibility. The measurements are performed in a water channel at a fixed frequency of oscillation and different flow velocities covering the free-swimming condition. Thrust and efficiency measurements are complemented by PIV and flow visualizations studies. The wake topology is analyzed at different Strouhal numbers for each flexibility, and the differences between accelerating, decelerating, and free-swimming fins are identified. [Preview Abstract] |
Monday, November 25, 2013 8:26AM - 8:39AM |
G17.00003: ABSTRACT WITHDRAWN |
Monday, November 25, 2013 8:39AM - 8:52AM |
G17.00004: Scaling the hydrodynamic performance of heaving flexible panels Daniel Quinn, George Lauder, Alexander Smits We present an experimental investigation of flexible panels actuated with heave oscillations at their leading edge. Our methods consist of kinematic video analysis, particle image velocimetry (PIV), and direct force measurements. Both the trailing edge amplitude and the mode shapes of the panel are found to scale with dimensionless ratios originating from the Euler-Bernoulli beam equation. Time-averaged thrust increases with heaving frequency, but also shows localized boosts around resonant frequencies where the trailing edge amplitude is maximized. For a constant heave amplitude, the time-averaged thrust coefficient is shown to be a function of Strouhal number over a wide range of conditions. Instantaneous thrust shows two peaks per oscillation cycle, occurring during the mid up- and down-stroke of the leading edge. [Preview Abstract] |
Monday, November 25, 2013 8:52AM - 9:05AM |
G17.00005: Lift enhancement by spanwise oscillation in forward translation of a rectangular wing at low Reynolds number Shizhao Wang, Xing Zhang, Guowei He The effects of bat-inspired spanwise oscillation on the aerodynamic performance of a translating rectangular wing at Reynolds number 300 are investigated numerically. The spanwise oscillation of the wing is in the sinusoidal form, with two control parameters being the amplitude and the frequency. Compared with the wings in pure translation, it is observed that in range of the parametric space onsidered in this work, spanwise oscillation is effective in enhancing lift, augmenting lift-drag ratio. To elucidate the mechanism of lift enhancement, the wake structure behind a wing in the combined motion of translation and spanwise oscillation is compared with that behind a purely translating wing. The phenomenon of lift enhancement in oscillating wings is also analysed by using an approximation formula that associates the lift force with Lamb's vector. It is found that spanwise oscillation produces compact and strong side-edge vortices (SEVs) which apply large downward induced velocity on the LEVs and press them onto the upper surface of the wing.The re-positioning of LEVs (due to the presence of SEVs) benefits lift generation. The novel wing kinematics (combination of translation and spanwise oscillation) of this work has the potential for application in micro air vehicles (MAVs). [Preview Abstract] |
Monday, November 25, 2013 9:05AM - 9:18AM |
G17.00006: Hydrodynamics of foils swimming in a side-by-side configuration Peter Dewey, Keith Moored, Daniel Quinn, Alexander Smits Experimental and computational results are presented on a pair of hydrofoils undergoing pitch oscillations in a side-by-side configuration. The time-averaged forces and propulsive efficiency are independently measured for each foil for a range of separation distances and oscillation phase differentials between the two foils. The results are compared to an isolated foil to determine if the presence of a second foil can yield an improvement to the propulsive characteristics of the system. While the exact performance of the side-by-side foils is strongly dependent on the separation distance and phase differential between the foils, it is found that under certain configurations an enhancement in net thrust is achieved by the presence of a second foil. The wake patterns shed by the foils as they oscillate are also examined and compared to the propulsive characteristics. A series of four stable wake configurations are observed that depend on the phase differential between the foils. [Preview Abstract] |
Monday, November 25, 2013 9:18AM - 9:31AM |
G17.00007: Mimicking fish-like kinematics using fluid-structure interactions Benjamin Thiria, Sophie Ramananarivo, Ramiro Godoy-Diana We present here a new experiment on a clamped-free elastic slender plate under local harmonic forcing. In air, the solution consists in a sum of standing waves, whose frequencies, wavelengths and mode shapes are given by the Young modulus and the geometry. In more dense fluid, as water, and for specific parameters of the experiment, the solution switch from this standing waves solution to a pure propagating behavior leading to a fish-like kinematics. The existence of this regime allows to simply generate a propagating wave in a finite elastic medium avoiding a complex implementation of synchronized local perturbations all along the body. We show that the triggering of the propagating solution is due to the nonlinear nature of the fluid damping. [Preview Abstract] |
Monday, November 25, 2013 9:31AM - 9:44AM |
G17.00008: Dynamically Coupled Fluid-Body Interactions with a Versatile Multi-Domain Immersed Boundary Library Chengjie Wang, Jeff D. Eldredge A computational algorithm is developed to simulate dynamically coupled interaction between fluid and rigid bodies. The basic computational framework is built upon a multi-domain immersed boundary method library, whirl, developed in previous work. The multi-domain approach inspired by Colonius and Taira (2008) is intended to cover a large simulation domain with multiple bodies by using a hierarchy of nested domains with different sizes and grid resolutions. This approach enables a versatile and economical use of computational resources. The library hides the details of the fully parallel treatment from the code developer, leading to simple construction of 2D or 3D solvers. In the present case, the incompressible Navier-Stokes equations are solved in vorticity-streamfunction form. The rigid body equations of motion are assembled with the flow equations with immersed boundary forces. The resulting saddle point system is solved in strongly coupled form by the Schur complement reduction method. The resulting scheme is tested by several numerical examples, such as vortex induced oscillation of a cylinder in 2D. Preliminary results are shown for the flapping of a low-aspect-ratio hinged wing at low Reynolds number. The results are compared with previous simulations and experiments. [Preview Abstract] |
Monday, November 25, 2013 9:44AM - 9:57AM |
G17.00009: Clear Delineation of Added-Mass and Vortex- Induced Forces Generated by Flapping Wing Chao Zhang, Tyson Hedrick, Rajat Mittal The force and moment experienced by a body immersed in a fluid depends strongly on its motion (trajectory, acceleration, rotation etc) as well as nearby flow structures such as vortices and boundary layers. A number of past studies have attempted to delineate the relative contribution of various components such as added-mass, attached and shed vortices, and viscous stresses on the total force produced by biological and bioinspired flapping wings. In the current study, we extend a previous analysis (M. S. Howe, 1995) to more precisely delineate the contributions of each of these components to the total force. The analysis is applied via high-fidelity computational fluid dynamics models and we use this analysis to shed light on the various flow mechanisms and features that are responsible for lift generation in insects over a range of scales. [Preview Abstract] |
Monday, November 25, 2013 9:57AM - 10:10AM |
G17.00010: ABSTRACT WITHDRAWN |
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