Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session BV: Flight II |
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Chair: Scott Kelly, University of North Carolina at Charlotte Room: 205A-D |
Sunday, November 22, 2009 10:30AM - 10:43AM |
BV.00001: Flow Field of Flexible Flapping Wings Erik S\"{a}llstr\"{o}m, Lawrence Ukeiley The flow field around several flexible flapping Zimmerman planform wings of aspect ratio 7.65 and a semispan of 75 mm is investigated using particle image velocimetry (PIV) in a quiescent environment. The wings are made from carbon fiber skeletons and covered with a thin layer of Capran. The skeletons consist of reinforced leading edges and chordwise battens in an attempt to decouple chordwise and spanwise flexibility as much as possible. The flow field from several phases throughout the flapping cycle will be presented. These flow fields consist of the phase averaged velocities in multiple PIV planes. These planes will include both those orientated in the streamwise and spanwise directions to build up a three dimensional representation of the flow in the vicinity of the wing and calculate the resultant vorticity field. The vortical features of these flow fields will be identified and discussed through the use of vortex identification methods. The discussion of the flow measurements will be coupled with force measurements and wing deflection data for a detailed view of mechanisms related to flapping flight and study how the formation of vorticity relates to the generation of aerodynamic forces. [Preview Abstract] |
Sunday, November 22, 2009 10:43AM - 10:56AM |
BV.00002: Tumbling dynamics of flexible wings Daniel Tam, John Bush, Michael Robitaille, Arshad Kudrolli We are broadly interested in elucidating the role of flexibility in passive flight. In particular, we examine the role of bending on the flight of autorotating winged seedpods through an experimental investigation of tumbling rectangular paper strips freely falling in air. Our results suggest the existence of a critical length above which the wing bends. We develop a theoretical model that demonstrates that this buckling is prompted by inertial forces associated with the tumbling motion, and yields a buckling criterion consistent with that observed. We further develop a reduced model for the flight dynamics of flexible tumbling wings, that illustrates the effect of aeroelastic coupling on flight characteristics and explains experimentally observed variations in the wing's falling speed and range. Other modes of flexible passive flight are discussed as well as biological implications for the dispersal of seed pods. [Preview Abstract] |
Sunday, November 22, 2009 10:56AM - 11:09AM |
BV.00003: An implemental formulation of Newton dynamics of free insect flight Sheng Xu A free-flying insect flies and maneuvers by coupling aerodynamics and Newton dynamics. In this talk, I will present a formulation of Newton dynamics for this coupling. This formulation is clear, concise, and simple for implementation. It passes a few basic tests. [Preview Abstract] |
Sunday, November 22, 2009 11:09AM - 11:22AM |
BV.00004: Aerodynamics of a single-degree-of-freedom toy ornithopter Ramiro Chavez Alarcon, B.J. Balakumar, James J. Allen The flow field around a flight-worthy toy ornithopter is investigated using PIV diagnostics in combination with load cells to understand the aerodynamics during nominally steady flight and turning. Phase-locked measurements of the wake and inflow are performed using an automated PIV system around the flapping wings of the ornithopter with the ornithopter fixed to a load-cell inside a 1.3m x 1.2m wind tunnel test section. The mildly oscillating free flight of the ornithopter is compared to the wake measurements to understand the causes of the unsteadiness. Further, the modulation of the wake that causes the turning motion of the ornithopter is explained using the wake structure measurements. [Preview Abstract] |
Sunday, November 22, 2009 11:22AM - 11:35AM |
BV.00005: Flapping-wing mechanical butterfly on a wheel Ramiro Godoy-Diana, Benjamin Thiria, Daniel Pradal We examine the propulsive performance of a flapping-wing device turning on a ``merry-go-round'' type base. The two-wing flapper is attached to a mast that is ball-bearing mounted to a central shaft in such a way that the thrust force produced by the wings makes the flapper turn around this shaft. The oscillating lift force produced by the flapping wings is aligned with the mast to avoid vibration of the system. A turning contact allows to power the motor that drives the wings. We measure power consumption and cruising speed as a function of flapping frequency and amplitude as well as wing flexibility. The design of the wings permits to change independently their flexibility in the span-wise and chord-wise directions and PIV measurements in various planes let us examine the vorticity field around the device. A complete study of the effect of wing flexibility on the propulsive performance of the system will be presented at the conference. [Preview Abstract] |
Sunday, November 22, 2009 11:35AM - 11:48AM |
BV.00006: Similarities and differences in the wake structure generated by different species of bats Tatjana Hubel, Nickolay Hristov, Sharon Swartz, Kenneth Breuer Flight kinematics and morphology differ greatly between the approx. 1200 bat species and the goal of our project is to understand how these differences affect the flight mechanisms, the generation of aerodynamic forces, and the resultant wake structures. Multiple individuals of three diverse species of bat were flown in the wind tunnel. The three species have different morphology, wing aspect ratio and wing loading, and exhibit different flight behaviors appropriate to their different ecologies. Particle Image Velocimetry in the cross-stream (Trefftz) plane acquired at 200 Hz was used to map the time-resolved wake velocities behind the bat, while three synchronized high-speed cameras monitored the wing motion. The measurements were taken at several flight speeds. Early predictions based on kinematic measurements suggest the development of discrete vortex rings as well as the generation of negative circulation in the wing tip area during the end of the downstroke. These hypotheses are tested and discussed, and the results show distinct differences between the species and as functions of flight speed. [Preview Abstract] |
Sunday, November 22, 2009 11:48AM - 12:01PM |
BV.00007: Propulsive performance of oscillating batoid-inspired fins Daniel Quinn, Daphne Rein-Weston, Peter Dewey, Melissa Green, Alexander Smits Thrust producing ray-like pectoral fins were actuated to drive a low friction carriage through a stationary tow tank. A DC servo motor powered a gear train that produced a traveling wave motion along the chord of the fin. The amplitude of the traveling wave increased linearly along the span from root to tip. A digital optical encoder attached to the carriage tracked the position and velocity as it was propelled through the water by the oscillating fin. Velocity profiles were acquired from trials using different planforms inspired by members of the eagle ray family, as well as an idealized elliptical fin. Traveling wave frequency and wavelength were varied to investigate the propulsive performance of different gaits. Preliminary flow visualization was also performed to describe the structure of the wakes generated by the various planform geometries and locomotory gaits. [Preview Abstract] |
Sunday, November 22, 2009 12:01PM - 12:14PM |
BV.00008: The fluid dynamics of mayfly naiads K. Abdelaziz, E. Balaras, K. Kiger The present work is focused on the study of mayfly naiads (nymphs) as a possible biological model for the efficient generation of external circulation currents in low to intermediate Reynolds number flows. Our primary objective is to validate a series of high-fidelity simulations we conducted by comparisons to experimental results obtained at an earlier stage of the project. For this purpose a realistic 3D model of the mayfly is constructed. It includes the abdomen, thorax, head, and six pairs of gills. Each gill is represented by two, zero-thickness rigid plates, which are hinged to at the location of the primary flexion line. The kinematics for all gills are prescribed and derived from the experiments. In particular, the trajectory of a set of points recorded in the experiments is translated into a sequence of Euler angles, which are then fed to a three-level kinematic chain enabling the derivation of all rigid body kinematics in the inertial frame. A Navier-Stokes solver in Cartesian coordinates is used and boundary conditions on the complex moving bodies are imposed with an embedded-boundary, direct forcing approach. The phase averaged numerical results are in good agreement with the corresponding particle image velocimetry (PIV) data from the experiment. The effects of gill kinematics and Reynolds number will also be discussed. [Preview Abstract] |
Sunday, November 22, 2009 12:14PM - 12:27PM |
BV.00009: The Rufous Hummingbird in hovering flight -- full-body 3D immersed boundary simulation Paulo Ferreira de Sousa, Haoxiang Luo, Humberto Bocanegra Evans Hummingbirds are an interesting case study for the development of micro-air vehicles since they combine the high flight stability of insects with the low metabolic power per unit of body mass of bats, during hovering flight. In this study, simulations of a full-body hummingbird in hovering flight were performed at a Reynolds number around 3600. The simulations employ a versatile sharp-interface immersed boundary method recently enhanced at our lab that can treat thin membranes and solid bodies alike. Implemented on a Cartesian mesh, the numerical method allows us to capture the vortex dynamics of the wake accurately and efficiently. The whole-body simulation will allow us to clearly identify the three general patterns of flow velocity around the body of the hummingbird referred in Altshuler et al. (Exp Fluids 46 (5), 2009). One focus of the current study is to understand the interaction between the wakes of the two wings at the end of the upstroke, and how the tail actively defects the flow to contribute to pitch stability. Another focus of the study will be to identify the pair of unconnected loops underneath each wing. [Preview Abstract] |
Sunday, November 22, 2009 12:27PM - 12:40PM |
BV.00010: PIV-based study of the gliding osprey aerodynamics in a wind tunnel Roi Gurka, Alex Liberzon, Gregory Kopp, Adam Kirchhefer, Daniel Weihs The hunting flight of an osprey consists of periods where the bird glides while foraging for prey. High quality measurements of aerodynamics in this flight mode are needed in order to estimate the daily energy expenditure of the bird accurately. An experimental study of an osprey model in a wind tunnel (BLWTL, UWO) was performed in order to characterize the aerodynamic forces using particle image velocimetry (PIV). The model was a stuffed osprey with mechanical joints allowing control of the the wing (angle of attack, tilt) and tail orientation. Two-dimensional velocity realizations in the streamwise-normal plane were obtained simultaneously in the two fields of view: above the wing and in the wake of the wing. Mean and turbulent flow characteristics are presented as function of angle of attack based on measurements taken at 4 different angles of attack at three different locations over the wingspan. The main outcome is the accurate estimate of the drag from the measurements of momentum thickness in the turbulent boundary layer of the osprey wing. Moreover, the gradient of the momentum thickness method was applied to identify the separation point in the boundary layer. This estimate has been compared to the total drag calculated from measurements in the wake of the wing and with a theoretical prediction. [Preview Abstract] |
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