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 HT: Biolocomotion VI: Flapping and Flying II |
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Chair: Henry Fu, University of Nevada Reno Room: Long Beach Convention Center Grand Ballroom B |
Monday, November 22, 2010 10:30AM - 10:43AM |
HT.00001: Optimization of Kinematics of a Flapping Wing Mechanism Ryan George, Scott Thomson, Christopher Mattson, Mark Colton, Mike Tree Flapping flight offers several potential advantages over conventional fixed wing flight, such as agility and maneuverability in confined spaces, potentially decreased noise and detectability, and hovering capability. In this presentation, a water tunnel-based flapping wing apparatus is introduced that allows for arbitrary wing trajectories in three rotational degrees of freedom and simultaneous measurements of lift and thrust production. An optimal flapping trajectory for takeoff is found using hardware-in-the-loop optimization methodology. Wing motion derived from high-speed imaging of a ladybug during takeoff is used as a first iteration of the hardware-in-the-loop optimization. Using real-time force measurements and a gradient-based optimization approach, the algorithm searches for the optimal trajectory for a variety of parameters such as lift or efficiency. Hardware performance is assessed. Results from the optimization routine, including the final flapping trajectory are reported for both rigid and compliant wings. [Preview Abstract] |
Monday, November 22, 2010 10:43AM - 10:56AM |
HT.00002: Aerodynamic tricks for pitching oscillation and visual stabilization in a hovering bird Jian-Yuan Su, Shang-Chieh Ting, Jing-Tang Yang We experimentally investigate how small birds attain a stabilized vision and body posture during hovering. Wing-beats of finches and passerines executing asymmetrical hovering provide lift merely during the downstroke. The downstroke lift is significantly greater than the bird weight, thereby causing a pitch-up swing of the bird body. A hovering bird skillfully and unceasingly tunes the position and orientation of lift force to stabilize its vision, so that the eye displacement is approximately one-tenth less than the tail, causing an illusion that the bird body is rotating about the eye. The hovering birds also spread and fold periodically their tail with an evident phase relationship with respect to the beating wings. We found that hovering birds use their tail to intercept the strong downward air-flow induced by the downstroking wings, and sophisticatedly spread their tail upon the arrival of the downward air-flow, rendering a pitch-up moment that effectively counteracts the pitch-down body rotation. Hence during hovering the bird essentially undergoes a dynamically-stable pitching oscillation, and concurrently attains a stabilized vision. [Preview Abstract] |
Monday, November 22, 2010 10:56AM - 11:09AM |
HT.00003: Optimal frequency for flow energy harvesting using flapping foils and its relation with wake instability Qiang Zhu Inspired by the correlation between the propulsion efficiency of a flapping foil propeller and stability of the wake behind it (which leads to the optimal Strouhal number for propulsion), we numerically simulated a foil in energy harvesting mode, and investigated the relation between wake stability and the energy harvesting efficiency (defined as the portion of incoming flow energy extracted by the system). The base flow is computed using a Navier-Stokes algorithm and the flow stability analysis is performed numerically via the Orr-Sommerfield equation. The wake is found to be convectively unstable and the frequency of the most (spatially) unstable mode fw is determined. The optimal efficiency occurs when fw is close to f (the oscillation frequency of the foil), which is achieved when f is close to 0.15 (hereby f is normalized by the chord length and the speed of incoming flow). In addition, for this ``foil-wake resonance'' to happen there must be significant leading edge separation associated with large effective angles of attack. [Preview Abstract] |
Monday, November 22, 2010 11:09AM - 11:22AM |
HT.00004: The advantage of wing-wing interaction in unsteady motion Tuyen Quang Le, Doyoung Byun, Soo Hyung Park, Jin Hwan Ko, Hoon Choel Park The role of elytra in aerodynamic performance of flapping flight has been numerically investigated for beetle flight. In a case of hovering flight, the relatively small vertical or horizontal forces were generated by the elytra and no significant contribution to aerodynamic force from elytra and hindwing interaction of Coleopteran insect. On the other hand, the flapping elytra may increase the total force around 20{\%} on both wings by the wing-wing interaction such as flow blocking and flow acceleration between the wings in forward flight. The flow blocking and acceleration strongly depends on phase angle, gap between wings. Additionally, the optimal condition for thrust force generation and aerodynamic efficiency was found from parameter study of in- and out-phase angles combined with gap between two airfoils. [Preview Abstract] |
Monday, November 22, 2010 11:22AM - 11:35AM |
HT.00005: Lift generation by a two-dimensional symmetric flapping wing Takaji Inamuro, Keigo Ota, Kosuke Suzuki Two-dimensional symmetric flapping flight is investigated by an immersed boundary-lattice Boltzmann method. In the method we can treat the moving boundary problem efficiently on the Cartesian grid. First, we investigate the effect of the Reynolds number on flows around symmetric flapping wings under no-gravity field and find that at high Reynolds numbers asymmetric vortices are appeared and the time-averaged lift force is induced on the wings, while at low Reynolds numbers only symmetric vortices are appeared around the wings and no lift force is induced. Also, the effect of the initial position of the wings on the lift force is investigated. Secondly, we carry out free flight simulations under gravity field for various Reynolds and Froude numbers and find the region where upward flights are possible. [Preview Abstract] |
Monday, November 22, 2010 11:35AM - 11:48AM |
HT.00006: Low-order Modeling of Bio-inspired Pitching and Perching at Low Reynolds Number Chengjie Wang, Jeff D. Eldredge A low-order inviscid point vortex model is used to simulate the pitching and perching motion of a thin flat plate at low Reynolds number. These motions induce coherent vortex shedding at the leading edge, which has a profound influence on the generated force. The low-order method is based on the inviscid Brown-Michael point vortex model, which accounts for the unsteady aerodynamics by tracking a small number of vortices with time-varying strengths. For the pitching motion, the results from the low-order model are compared with high fidelity simulations under different pitching rate and axis position, and this comparison shows a good qualitative agreement. The perching motion is characterized by larger rotations and an unsteady translation. The low-order model results are compared with previous experiments conducted in a water tunnel, and good qualitative agreement is achieved. To investigate the mechanism of force generation, the force obtained from the model is decomposed into inertial reaction and circulatory components, and their relative contributions are inspected. [Preview Abstract] |
Monday, November 22, 2010 11:48AM - 12:01PM |
HT.00007: Experimental study of the wing-rotation mechanism using a mechanical flapper operating at high Reynolds numbers (10$^{5}\sim $10$^{6})$ Yu-Hung Chang, Shang-Chieh Ting, Jing-Tang Yang This work aims to investigate whether the `wing-rotation' mechanism remains effective for flapping wings operating at Reynolds numbers ranging between 10$^{5}$ and 10$^{6}$. We also address the feasibility of evaluating transient lift forces based on a modified vortex-ring model. The experiments were conducted with a biomimetic mechanical flapper that partially emulates the dominant motions of flapping wings of hovering \textit{Zosterops japonicus} and \textit{Erythrura gouldiae}. Lift forces produced by the flapping wing of the mechanical flapper were directly measured via a load cell, and indirectly evaluated using a modified vortex-ring model, according to the wing wake flow-fields quantified by DPIV. Lift forces evaluated through the vortex-ring model were found to be of values approximately 15{\%} less than those measured by the load cell. It was also found that an increase in the pitching frequency of the flapping wing is capable of enhancing the lift production. This finding suggests that for a flapping wing, the `wing-rotation' mechanism remains effective for high Reynolds numbers in a range 10$^{5}\sim $10$^{6}$. [Preview Abstract] |
Monday, November 22, 2010 12:01PM - 12:14PM |
HT.00008: Elasticity Estimation of Thin Flap Using Optical PIV Velocity Fields John Westerdale, Marek Belohlavek, Eileen McMahon, Panupong Jiamsripong, Jeffery Heys, Michele Milano We estimate the elasticity of a thin, cellulose acetate flap using forcing data derived from optical particle imaging velocimetry (optical-PIV) velocity fields. The flap is fixed on one end to a stand submerged within a PIV tank and deformed using a water jet pulse. PIV is then performed at the interface between the thin sheet and water jet throughout the deformation cycle; the resulting velocity field allows the determination of instantaneous pressure measurements via Poisson's equation. An optimal estimation technique utilizing ensemble Kalman filtering is coupled with a finite element analysis program to determine the sheet's elasticity. Results show good agreement with actual elasticity measurements for both homogeneous and non-homogeneous elasticity sheets. In addition, we performed a quantitative study to determine the optimal vector density for a given element size to achieve an accurate elasticity estimation value. Considering the success of this technique using optical-PIV, it should also be possible for in-vitro elasticity estimates based on ultrasound-PIV measurements. [Preview Abstract] |
Monday, November 22, 2010 12:14PM - 12:27PM |
HT.00009: Analysis of the Flapping Dynamics of a Slender Within a Soap-Film Flow Tunnel Rocco Portaro, Mohamed Fayed, Hamid Ait Abderrahmane, Hoi Dick Ng A thin slender placed within a two-dimensional parallel laminar flow yields to a complex coupling dynamics between the flapping of the thin fibre and the surrounding fluid flow. In this study, this complex interaction is revisited experimentally using a soap-film flow tunnel as proposed by Zhang et al. (2000) [Nature 408, pp. 835]. The dynamics of the slender and the flow wake are imaged using a high-speed camera and a low pressure sodium lamp for the light source. Image processing technique is used to analyze the flapping of the slender and the ensued flow wake structure. These results are further examined using nonlinear time series and multifractal method. The results are compared with previous experiments and numerical modelling. [Preview Abstract] |
Monday, November 22, 2010 12:27PM - 12:40PM |
HT.00010: Wing compliance in self-propelled flapping flyers Sophie Ramananarivo, Benjamin Thiria, Ramiro Godoy-Diana Wing flexibility governs the flying performance of flapping wing flyers. Here we use the self-propelled flapping-wing model mounted on a ``merry-go-round'' described by Thiria and Godoy-Diana (Phys. Rev. E 82, 015303, 2010) to investigate the effect of chord-wise wing compliance on the propulsive performance of the system. The bending of the wings, which is driven mainly by wing inertia in the present experiments, redistributes the aerodynamic forces engendered by the flapping motion and improves the efficiency of the system for a wide range of wing flexibilities and flapping frequencies. A detailed analysis of the phase dynamics between the leading and trailing edges of the wings allows us to pinpoint the mechanisms that limit the beneficial effect of wing compliance. [Preview Abstract] |
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