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 A17: Biofluids: Locomotion I - Swimming and Flapping |
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Chair: Michael Plesniak, George Washington University Room: 305 |
Sunday, November 24, 2013 8:00AM - 8:13AM |
A17.00001: On the hydrodynamics of fish schooling Iman Borazjani, Mohsen Daghooghi A Considerable number of fish species swim in a coordinated manner within approximately constant and equal distance from each other, forming a pattern which is referred to as a fish school. It is believed that fish schooling results in more efficient swimming. However, no experimental evidence has conclusively shown the hydrodynamic effects of neighboring fish on swimming, probably due to the challenges involved in measuring the performance under controlled conditions in a school. We investigate possible hydrodynamical effects of fish schooling by constructing an infinite school of virtual swimmers based on a mackerel fish body and carangiform kinematics. We carry out our self-propelled simulation based on prescribed undulations of the fish body (assuming that all of the fish in the school move in exact same manner) and calculating motion of the center of mass. One of the most important geometrical factors of the fish schooling pattern seems to be the distance between two adjacent fish in the school. Therefore, we examined fish schools with different distances of two adjacent fish. [Preview Abstract] |
Sunday, November 24, 2013 8:13AM - 8:26AM |
A17.00002: The lateral line system of fish as a ``hydrodynamic antenna'' Jun Zhang, Leif Ristroph, James Liao The lateral line of fish is a specialized flow detection system comprised of pressure- and shear-responsive sensors distributed over the body surface. Here, we explore how the arrangement of these sensors is related to the hydrodynamic information contained in flows. Using a cast model of a rainbow trout placed in a water tunnel, we devise ways to mimic the flows encountered by swimming fish while measuring the near-body flow field. Comparing our results to anatomical studies indicates that the lateral line sensors are well positioned to detect temporal and spatial changes in flow signals. These findings support a view of the lateral line as a ``hydrodynamic antenna'' that allows sophisticated behaviors such as rheotaxis and prey detection and tracking. [Preview Abstract] |
Sunday, November 24, 2013 8:26AM - 8:39AM |
A17.00003: Reduced-order model of fish-like swimming due to shedding of unsteady point vortices Phanindra Tallapragada Reduced order models of biomimetic swimming in an ideal fluid, relying on the shedding of point vortices at short intervals of time, are useful to illuminate the essential underlying dynamics of locomotion in fluids. However these reduced order models still possess a state space that is very high dimensional, thus presenting challenges to develop control algorithms. A two-dimensional model that fully couples the motion of the solid boundary and the fluid containing singular distributions of vorticity is presented. The model relies on the shedding of unsteady point vortices, from the tip of a fish-like hydrofoil, in place of many steady point vortices. The subsequent reduction in the dimension of the state space makes the model more amenable to control algorithms. A simple case of the heading-angle control of a fish-like body will be illustrated. The model also has the advantage of being computationally significantly less demanding. More interestingly from a theoretical point of view, the reduced order model illustrates the connection between vortex shedding and velocity constraints encountered in rigid body mechanics. [Preview Abstract] |
Sunday, November 24, 2013 8:39AM - 8:52AM |
A17.00004: Flow Structures and Efficiency of Swimming Fish school: Numerical Study Yuzuru Yatagai, Yuji Hattori The flow structure and energy-saving mechanism in fish school is numerically investigated by using the volume penalization method. We calculate the various patterns of configuration of fishes and investigate the relation between spatial arrangement and the performance of fish. It is found that the down-stream fish gains a hydrodynamic advantage from the upstream wake shed by the upstream fish. The most efficient configuration is that the downstream fish is placed in the wake. It reduces the drag force of the downstream fish in comparison with that in solo swimming. [Preview Abstract] |
Sunday, November 24, 2013 8:52AM - 9:05AM |
A17.00005: Computational design of flapping kinematics of a flexible finite-span foil Seungpyo Hong, Jinmo Lee, Donghyun You While many of the effects of chordwise flexibility of a two-dimensional plate or a foil under pitching motions are revealed in recent computational and experimental research, the effects of flexibility of a three-dimensional foil on the manipulation of wing-tip vortices as well as leading-/trailing-edge vortices are rarely understood. The present study aims at identifying flow physics associated with flapping motions of flexible finite-span foils and the effects of the flapping kinematics and flexibility of the foil on the propulsive performance. The propulsive performance and fluid dynamics of wing-tip vortices leading-edge and trailing-edge vortices associated with the thrust generation are investigated in detail by conducting numerical simulations of flow over a flapping foil with different span-to-chord aspect ratios and bending stiffness using a recently developed coupled immersed boundary method and computational structural dynamics. [Preview Abstract] |
Sunday, November 24, 2013 9:05AM - 9:18AM |
A17.00006: Critical Point Analysis of Unsteady Flow Separation from a Pitching Plate Faegheh Hooman, Paul S. Krueger Unsteady flow separation is of interest for force and moment generation by flapping airfoils, but it is often difficult to determine how small differences in the motion lead to differences in the flow field and resulting forces. To better understand the flow evolution during unsteady separation in pitching maneuvers, analysis was performed of two numerical data sets for the pitch-up of a two-dimensional flat plate in a free stream flow with Re$=$1000 provided by Prof. J.D. Eldredge at UCLA. In each data set, flow was characterized by identifying the first order critical points of the velocity field and their eigenvalues to locate the vortical structures and separation and attachment points as well as the relative locations of these features. The evolution of the flow structure was evaluated quantitatively using a tracking algorithm to pair related critical points in sequential frames. The critical points were further analyzed to understand relationships between the flow configuration and the hydrodynamics including the drag coefficient and lift coefficient. Results from the two data sets will be compared to quantitatively assess the differences in the flow structures. [Preview Abstract] |
Sunday, November 24, 2013 9:18AM - 9:31AM |
A17.00007: Volumetric PIV Behind a Flapping Wing in an Incoming Vortex Flow Oscar Curet, Cyndee Finkel, Karl von Ellenrieder, Daniel Bissell The propulsive surfaces of flying and swimming animals interact with vortices shed by their own bodies or other animals, if they are traveling in groups. The interaction of the propulsive surface with these structured vortices might be fundamental for stability and/or decreasing the cost of transport. In this work, we investigate the wake generated by a flapping wing in an incoming vortex flow. We used a NACA0012 wing model with aspect ratio of 2, and a d-profile cylinder to generated the incoming vortices. The model was tested in a water channel at a Reynolds number of approximately 10,000, which is relevant to many biological swimmers and flyers. The flow structure generated by the flapping wing was measured using three-dimensional Particle Image Velocimetry (3-D PIV). A series of experiments were performed for different Strouhal numbers, \textit{St }$=$\textit{ fL/U}, where $f$ is the flapping frequency, $L$ is the amplitude of oscillation, and $U$ is the incoming flow speed. We present the 3-D flow field of the flapping wing in an incoming vortex flow and compare it with the structure of a flapping wing with an undisturbed incoming flow. [Preview Abstract] |
Sunday, November 24, 2013 9:31AM - 9:44AM |
A17.00008: Modeling and Navigation of Artificial Helical Swimmers in Channels Fatma Zeynep Temel, Alperen Acemoglu, Serhat Yesilyurt Recent developments in micro/nanotechnology and manufacturing techniques make use of micro robots for biomedical applications realizable. Controlled in-channel navigation of swimming micro robots is necessary for medical applications performed in conduits and vessels in living bodies. Successful design and control of micro swimmers can be achieved with full understanding of hydrodynamic behavior inside channels and their interaction with channel walls and resultant flows. We performed experimental and modeling studies on untethered mm-sized magnetic helical swimmers inside glycerol-filled rectangular channels. In experiments it is observed that rotation of swimmers in the direction of helical axis leads to forward motion due to fluidic propulsion and lateral motion due to traction forces near the wall. Effects of surface roughness, swimming direction and rotation frequency on the swimmers' speed are analyzed. The flow induced by the tail motion is visualized using micro-particle image velocimetry and analyzed at different radial positions using Computational Fluid Dynamics models. Results indicate that at low frequencies traction forces are effective, however as frequency increases fluid forces become dominant and fluid flow is affecting the swimming motion of helical swimmers. [Preview Abstract] |
Sunday, November 24, 2013 9:44AM - 9:57AM |
A17.00009: Forward and backward motion of artificial helical swimmers in cylindrical channels Alperen Acemoglu, Fatma Zeynep Temel, Serhat Yesilyurt Motion of micro swimmers in confined geometries such as channels is important due to its relevance in in vivo medical applications such as minimally invasive surgery and drug delivery. Here, swimmers with diameters 0.8 mm and lengths 2 to 3 mm are produced with a 3D printer and cylindrical Nd$_{2}$Fe$_{14}$B magnets are placed inside the bodies. Rotating external magnetic field is used for the actuation of artificial swimmers. Different body and tail geometries are produced and experiments are conducted with a glycerol filled circular channel. Result demonstrate that decreasing channel diameter directly affects the forward motion of the swimmer due to the increasing drag. It is observed that step-out frequency, which defines maximum frequency at which the swimmer can establish a synchronous rotation with the external magnetic field, depends on the geometry of the swimmer and the channel diameter. There are significant differences between low and high frequency motion and forward and backward swimming. Longer tails enable higher forward velocities in high frequencies than backward ones, whereas forward and backward velocities are approximately the same at low frequencies. Furthermore backward motion is more stable than the forward one; at high frequencies, swimmers travel almost at the center of the channel for backward motion, and follow a helical trajectory near the wall during the forward motion. According to simulation results there is a flow which is induced by the rotation of the swimmer rotation that affects the swimmer's trajectory. [Preview Abstract] |
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