Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session H18: Biofluids: Flapping and Flying II |
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Chair: Fangjun Shu, New Mexico State University Room: 28D |
Monday, November 19, 2012 10:30AM - 10:43AM |
H18.00001: Three-dimensional flow about penguin wings Flavio Noca, Bassem Sudki, Michel Lauria Penguins, contrary to airborne birds, do not need to compensate for gravity. Yet, the kinematics of their wings is highly three-dimensional and seems exceedingly complex for plain swimming. Is such kinematics the result of an evolutionary optimization or is it just a forced adaptation of an airborne flying apparatus to underwater swimming? Some answers will be provided based on flow dynamics around robotic penguin wings. Updates will also be presented on the development of a novel robotic arm intended to simulate penguin swimming and enable novel propulsion devices. [Preview Abstract] |
Monday, November 19, 2012 10:43AM - 10:56AM |
H18.00002: Numerical simulation of self-propulsion of flapping flexible plates Xi-Yun Lu, Ru-Nan Hua Self-propulsion of flapping flexible plates has been studied numerically by means of an immersed boundary-lattice Boltzmann method for the fluid dynamics around the plate and a finite element method for the deformable flapping motion of the plate. Both the two- and three-dimensional flexible plates are investigated to reveal the propulsion properties and their differences. As a result of the fluid-plate interaction, three typical movement regimes have been identified and can be briefly described as forward, backward, and irregular movements which mainly depend on the flapping amplitude and bending rigidity. It is found that there exists an optimal range of the bending rigidity for large propulsive speed or high efficiency in the forward movement regime, consistent with the observation and measurement of swimming and flying animals. The results obtained in this study provide physical insights into understanding of the propulsive mechanisms of the flapping fin or wing of animals. [Preview Abstract] |
Monday, November 19, 2012 10:56AM - 11:09AM |
H18.00003: Measuring and Analyzing the Birds Flight Alexander Friedl, Christian J. K\"ahler To tackle the long-standing problem of precisely measuring shape and profiling of free-flying birds we developed a technique to determine the shape of naturally textured surfaces. The measurement principle is based on a calibrated stereoscopic camera setup that delivers the height information through the identification of characteristic texture elements in each concurrent camera image using highly developed optical flow algorithms. This allows estimating the motion and height information of each pixel based on the analysis over time. The reconstructed upper surface of the wing is calculated in temporal coherence with the whole image sequence and hence shows low sensitivity to disturbances and high spatial accuracy and resolution. The measurement technique is used to evaluate experimental data obtained within measurement campaigns with two freely flying birds. The slowly, but silently flying barn owl was chosen in contrast to the fast and agile flying lanner falcon. The experiments were carried out within two facilities to respect the different flying performances of the animals and allow for as little disturbances as possible and feasible. Details of the experimental campaigns as well as the measurement methodology will be illustrated during the presentation. [Preview Abstract] |
Monday, November 19, 2012 11:09AM - 11:22AM |
H18.00004: Improving Vortex Models via Optimal Control Theory Maziar Hemati, Jeff Eldredge, Jason Speyer Flapping wing kinematics, common in biological flight, can allow for agile flight maneuvers. On the other hand, we currently lack sufficiently accurate low-order models that enable such agility in man-made micro air vehicles. Low-order point vortex models have had reasonable success in predicting the qualitative behavior of the aerodynamic forces resulting from such maneuvers. However, these models tend to over-predict the force response when compared to experiments and high-fidelity simulations, in part because they neglect small excursions of separation from the wing's edges. In the present study, we formulate a constrained minimization problem which allows us to relax the usual edge regularity conditions in favor of empirical determination of vortex strengths. The optimal vortex strengths are determined by minimizing the error with respect to empirical force data, while the vortex positions are constrained to evolve according to the impulse matching model developed in previous work. We consider a flat plate undergoing various canonical maneuvers. The optimized model leads to force predictions remarkably close to the empirical data. Additionally, we compare the optimized and original models in an effort to distill appropriate edge conditions for unsteady maneuvers. [Preview Abstract] |
Monday, November 19, 2012 11:22AM - 11:35AM |
H18.00005: Unsteady lift of a flapping rectangular wing with spanwise stretching-and-retracting Shizhao Wang, Guowei He, Tianshu Liu, Xing Zhang The unsteady lift acting on a bat-inspired flapping wing model at Reynolds number 300 is numerically investigated. The flapping wing model consists of a rectangular flat-plat with a sinusoidally varying wingspan. The wingspan reaches maximum at the middle of the downstroke, and minimum at the middle of upstroke. It is found that the spanwise stretching-and-retracting during the flapping can enhance lift acting on the wing. The enhancement of lift is not only caused by the difference of lift surface area between the downstroke and upstroke, but also benefits from the increase in the lift coefficient. The enhancement of the vortex force is investigated by examining the flow structures. The spanwise stretching-and-retracting during flapping affects the shedding of the tip vortices and evolution of the leading-edge vortex. The interaction between the detached tip vortices and leading-edge vortex causes a weak negative wake capture mechanisms during the upstroke, which results in a decrease in the magnitude of the minus lift and a increase in the average lift coefficient. [Preview Abstract] |
Monday, November 19, 2012 11:35AM - 11:48AM |
H18.00006: Effect of gust on force generation around a robotic hummingbird wing Eloy Marquez, Ruijun Tian, Fangjun Shu Among the computational, theoretical and experimental studies on the high efficiency flapping flight, many are focused on the mystery of hovering. Most of these studies were conducted under steady in flow conditions. However, real-life ornithopters in the field have to routinely tackle gust and directional changes of the wind. These sudden perturbations could produce significant effect on humming bird hovering due to the small Reynolds numbers. Our experimental work was performed in a water channel using a two degree-of-freedom humming bird model. The dynamic response of the hovering motion to gust from different directions was investigated. PIV was used to measure the effect of the gust on the surrounding flow field including vortex evolution. In addition, a six-component force/torque sensor was used to measure the real-time lift and drag forces generated by the wing with and without gust. Results show that gust changes the magnitude of lift force in one stroke. However, the time-averaged lift force keeps approximately constant. [Preview Abstract] |
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