Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session ET: Biolocomotion IV: Morphology of Flying and Swimming |
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Chair: Jifeng Peng, University of Alaska Fairbanks Room: Long Beach Convention Center Grand Ballroom B |
Sunday, November 21, 2010 4:10PM - 4:23PM |
ET.00001: Small, sleek, and in control: The body plan, sensory-neural control, and flight stability of insects Leif Ristroph, Attila Bergou, John Guckenheimer, Z. Jane Wang, Itai Cohen Flying insects have evolved sophisticated sensory-neural systems, and here we argue that the fast reaction times of these systems reflect the need to overcome an intrinsic flight instability. We formulate a theory that shows how the body plan and flapping-wing aerodynamics determine the instability growth rate, which in turn dictates the response time needed to suppress it. We experimentally validate this theory by manipulating the flight, sensors, and body plan of fruit flies. The theory is general enough to describe a broad class of flying insects and also furnishes stability criteria for flapping-wing robots. Plausible body plans for the first flyers are determined by conjecturing that these insects were intrinsically stable and only later evolved fast-acting controls for the added benefit of flight agility. [Preview Abstract] |
Sunday, November 21, 2010 4:23PM - 4:36PM |
ET.00002: Drag Measurements over Embedded Cavities Modeled after Butterfly Scales in Low Reynolds Number Couette Flow Robert Jones, Amy Lang Recent research has shown that symmetric, embedded square cavities can reduce the net drag acting on a surface through the formation of embedded vortices. It is hypothesized that the scales on butterfly wings (approximately 100 microns in length), though asymmetric, may act in a similar way resulting in greater flying efficiency. In this experimental study, cavities were modeled based on the geometry observed for bristled butterfly scales. Plates were designed to have parallelogram-shaped embedded cavities with an approximate 2:1 length to depth aspect ratio. The plates were suspended in high viscosity mineral oil above a rotating belt to generate a Couette flow condition such that the cavity Re was maintained in a similar regime as that occurring for the flow over butterfly scales. The net drag forces were measured with a force gauge and compared to flat plate measurements in the same facility. The variation in drag over a range of Reynolds numbers was analyzed. [Preview Abstract] |
Sunday, November 21, 2010 4:36PM - 4:49PM |
ET.00003: The Effect of Wing Scales on Monarch Butterfly Flight Characteristics Angela Shaw, Robert Jones, Amy Lang Recent research has shown that the highly flexible wings of butterflies in flapping flight develop vortices along their leading and trailing edges. Butterfly scales (approximately 100 microns in length) have a shingled pattern and extend into the boundary layer. These scales, which make up approximately 3{\%} of the body weight or less, could play a part in controlling separation and vortex formation in this unsteady, three-dimensional complex flow field. A better understanding of this mechanism may lead to bio-inspired applications for flapping wing micro-air vehicles. In this study, the flight performance of Monarch (\textit{Danaus plexippus}) butterflies with and without scales was analyzed. Scales were removed from the upper and lower wing surfaces and specimens were videotaped at 600 frames per second. Variation in flapping patterns and flight fitness were observed. [Preview Abstract] |
Sunday, November 21, 2010 4:49PM - 5:02PM |
ET.00004: Explanation of the effects of leading-edge tubercles on the aerodynamics of airfoils and finite wings Mehdi Saadat, Hossein Haj-Hariri, Frank Fish A computational study was conducted to explain the aerodynamic effect of leading edge tubercles on maximum lift coefficient, stall angle of attack (AoA), drag, and post stall characteristics for airfoils as well as finite wings. Past experiments demonstrated airfoils with leading edge tubercles do not improve Cl$_{max}$, drag, or stall AoA but smoothen post stall characteristics to a great degree. In contrast to airfoils, finite wings with L.E. tubercles improved all aerodynamic characteristics. We explain the stall mechanism of the tubercled wing by considering each L.E. tubercle as a combination of a swept forward and a swept backward wing.There are 3 mechanisms (streamline curvature, accelerated stall, and upwash) that cause Cl$_{max}$ of airfoils with L.E. tubercles always be lower than that of smooth airfoils. We also identify two additional mechanisms which are responsible for improved post-stall characteristics of airfoils with L.E. tubercles. Finally, we discuss why finite wings with L.E. tubercles have higher Cl$_{max}$ and lower drag than their smooth L.E. counterparts by studying effects of wing tip, sweep, and taper ratio. [Preview Abstract] |
Sunday, November 21, 2010 5:02PM - 5:15PM |
ET.00005: Hydrodynamics of penguin wing models Flavio Noca, Nhut Cuong Duong, Jerome Herpich The three-dimensional kinematics of penguin wings were obtained from movie footage in aquariums. A 1:1 scale model of the penguin wing (with an identical planform but with a flat section profile and a rigid configuration) was actuated with a robotic arm in a water channel. The experiments were performed at a chord Reynolds number of about $10^4$ (an order of magnitude lower than for the observed penguin). The dynamics of the wing were analyzed with force and flowfield measurements. The two main results are: 1. a net thrust on both the upstroke and downstroke movement; 2. the occurence of a leading edge vortex (LEV) along the wing span. The effects of section profile, wing flexibility, and a higher Reynolds number will be investigated in the future. [Preview Abstract] |
Sunday, November 21, 2010 5:15PM - 5:28PM |
ET.00006: The Performance of Finite-span Hydrofoils with Humpback Whale-like Leading Edge Protuberances Derrick Custodio, Charles Henoch, Hamid Johari The effects of leading edge protuberances on the lift and drag performance of finite-span hydrofoils were examined in a series of water tunnel experiments. The leading edge protuberances are analogous to the tubercles on humpback whale pectoral flippers. The hydrofoils have a rectangular planform and an aspect ratio of 4. The hydrofoil section profile is based on NACA 63(4)-021, and the leading edge has a sinusoidal geometry with constant amplitude and wavelength. The hydrofoil angle of attack was varied up to 30\r{ }, and the freestream velocity ranged from 1.8 to 5.4 m/s. Results indicate that the hydrofoils with leading edge protuberances do not stall in the traditional manner. Below 12\r{ } lift increased linearly with angle of attack. Beyond this angle, the lift either attained a nearly constant value or increased slowly up to 30\r{ } depending on the Reynolds number. Drag increased continuously with the angle of attack, and was not dependent on the Reynolds number. These observations are consistent with our previous infinite span hydrofoil data, and may be explained in terms of the flow modifications created by the leading edge protuberances. [Preview Abstract] |
Sunday, November 21, 2010 5:28PM - 5:41PM |
ET.00007: Why fishes have a fish shape Christophe Eloy, Lionel Schouveiler The relation between form and function for elongated swimmers is revisited by solving a multi-objective optimization problem. We consider elongated fishes of varying elliptic cross-section whose motion is prescribed by a time-periodic curvature. The two semi-axes of the cross-section, the curvature amplitude and phase are assumed to vary continuously along the fish length. Hydrodynamic forces acting on such fishes are modeled in the elongated-body limit by considering both reactive and resistive forces. Applying Newton's second law, the heave and pitch amplitude and phase, as well as the swimming velocity can be found. The total power needed can also be calculated yielding the swimming efficiency. The multi-objective optimization consists in finding the fish shape and associated motion which corresponds to maximum efficiency, maximum velocity or any trade-off between the two. This optimization problem is solved using a genetic algorithm whose principle is to start with an initial random population and to evolve it by mutation and selection. We find that the most efficient shape resembles existing fishes and arguments are given to explain the relation between this particular fish form and performance. [Preview Abstract] |
Sunday, November 21, 2010 5:41PM - 5:54PM |
ET.00008: Viscous to inertial pumping transitions in a robotic gill plate array Mary Larson, Ken Kiger Biological oscillating appendage systems are known to exhibit distinct patterns of movement based on their Reynolds number. Flapping kinematics (net flow perpendicular to appendage stroke plane) are associated with Re $>$ 100, while rowing kinematics (flow in the direction of appendage motion) are typically associated with Re $<$ 1. Previous studies of pumping by mayfly nymph gill plate arrays have shown a transition between rowing and flapping at a Re $\approx$ 5. Although the flow generated by the animal could be documented, the limited range of behavior of the animal prevented a detailed study of why and how such a pumping mechanism might be optimized. Towards this end, a two-degree-of-freedom robotic oscillating plate array has been constructed, which allows for the variation of the Reynolds number, plate spacing, plate shape, and stroke/pitch amplitude beyond what is exhibited by the animal system. Using PIV, these combinations allow the individual influence of each feature on the pumping efficiency to be observed, and elucidate how it may be optimized for engineered devices. The current results will compare this simplified system to the flow generated by the typical mayfly, to determine how effectively the model performs in comparison to the more complex animal system. [Preview Abstract] |
Sunday, November 21, 2010 5:54PM - 6:07PM |
ET.00009: A Hydrodynamic Model of Lateral Line of Fish for Vortex Sensing Zheng Ren, Kamran Mohseni In this study, potential flow theory is adopted to model flow field around a fish-like body in the presence of a Karman vortex street moving along one side of the body. The external flow field is modeled in two dimensions while a fish-like body is obtained by Joukowski Transformation. Pressure distribution on the body surface is computed according to the model. The lateral line trunk canal (LLTC) of a fish is modeled as a slight tube along its body with pores uniformly distributed along the surface of the tube. With the external flow known, the flow inside LLTC driven by the pressure gradient between a pair of consecutive pores has been solved analytically. Furthermore, parametric studies are performed in order to determine the effect of various flow parameters on the pressure distribution on body surface and flow distribution inside the LLTC. The results indicate that the signature of the vortex street can be found by measuring the flow velocity distribution inside the LLTC, which serves as a possible elucidation on how a fish sense the vortex street from the flow filed inside its LLTC. Hence, it is reasonable to suggest that the LLTC of a fish is able to detect the signature of the wake vortices shed by a nearby object or fish. [Preview Abstract] |
Sunday, November 21, 2010 6:07PM - 6:20PM |
ET.00010: Flow Transport in Microtubes Inspired by Insect Respiratory Systems Yasser Aboelkaasem, Anne Staples The mechanics of insect respiration and tracheal ventilation generally follow either highly discontinuous, or cyclic gas exchange patterns. In the former, gases are exchanged by diffusion, while in the latter, recent imaging of internal respiratory flow dynamics in insects performed at the x-ray synchrotron imaging facility at Argonne indicates that convective gas exchange is accomplished by changes in internal pressure due to rhythmic compressions of the tracheal tubes that comprise the respiratory network. These localized tracheal compressions are induced by global body movements and are used to enhance the oxygen transport to the tissue. Inspired by the dynamics of insect respiratory networks in the cyclic gas exchange regime, we study fluid transport in a mixed rigid/elastic microtube that undergoes localized single and multiple periodic collapses. The latter induces a streaming of flows and therefore enhances convection and flow transport in the tube downstream of the collapse site. The shape of the microtube, the material properties, and the compression and reinflation spatial and temporal profiles are selected to mimic those observed in insect tracheal tubes. A low Reynolds number assumption and lubrication theory are used to develop a mathematical model for the system. The effects of tube shape, collapse amplitude, collapse-to-collapse distance, and collapse phase lags on the net flow rate, pressure gradient, wall shear stress, velocity are investigated. [Preview Abstract] |
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