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 AV: Flight I |
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Chair: Jane Wang, Cornell University Room: 205A-D |
Sunday, November 22, 2009 8:00AM - 8:13AM |
AV.00001: Optimization Study for Hovering Flapping Flight Humberto Bocanegra Evans, James J. Allen, B.J. Balakumar A scaled robotic hummingbird model was used to perform a flow
analysis of hovering flight at a range of Reynolds numbers
(1,750$ |
Sunday, November 22, 2009 8:13AM - 8:26AM |
AV.00002: Flapping counter torque (FCT) in animal flight: Experimental results and mathematical models Bo Cheng, Xinyan Deng From our previous studies on a range of insects from fruit flies to cockatoos during fast yaw turning maneuvers (body saccades), we found that body rotation causes a substantial aerodynamic counter torque, termed as flapping counter-torque (FCT), which acts in the opposite direction of turning. In this study, we show that FCT exists in all roll, pitch and yaw axes and are linearly dependent on the flapping frequency and rotational velocity, respectively. We measured the FCTs systematically (by varying wing beat frequency and body turning velocity) on a pair of dynamically scaled robotic model wings. Furthermore, we developed mathematical FCT models based on quasi-steady analysis for roll, pitch and yaw axes. The results show that the experimental data matches the prediction of the analytical models. FCT induced passive damping accounts for a large part of the deceleration in saccade of animal flight, and implies passive rotational stability of the angular velocity dynamics in flapping flight. [Preview Abstract] |
Sunday, November 22, 2009 8:26AM - 8:39AM |
AV.00003: Controlling Pitching Instability in 3D Flapping Flight Song Chang, Jane Wang Flying insects actively control their wings to maintain the stability in steady flight as well as to execute maneuvers. The control strategies depend on the coupling of sensory feedback loops of insects and the underlying dynamics of the 3D flapping flight. In this talk, we first present a general method for efficiently simulating the 3D flapping flight of the coupled wing-body system in the quasi-steady limit. We then quantify the stability of the periodic solutions that correspond to equilibrium flight. The analysis shows that the flapping system exhibits an inherent instability in pitching, and this instability can be further understood in a reduced-order model. We propose a simple control strategy for stabilizing the pitching by modulating wing motions. [Preview Abstract] |
Sunday, November 22, 2009 8:39AM - 8:52AM |
AV.00004: Fruit flies use flight auto-stabilization to recover from aerial ``stumbles'' Leif Ristroph, Attila Bergou, Gunnar Ristroph, Katherine Coumes, Gordon Berman, John Guckenheimer, Z. Jane Wang, Itai Cohen Just as manned flight was made possible by control mechanisms, the flapping-wing flight of animals also relies on strategies that ensure recovery from disturbances. Previous studies performed on tethered and dissected insects indicate that the sensory, neurological, and musculoskeletal systems play important roles in flight control. Such studies, however, have yet to produce an integrative model of flight stability since they do not incorporate the interaction of these systems with free-flight aerodynamics. Here, we directly investigate control and stability through the application of brief torques to free-flying fruit flies and measurement of their behavioral response. High-speed video and a new motion tracking method capture the aerial ``stumble'', and we discover that flies respond to gentle disturbances by accurately returning to their original orientation. This accurate and fast recovery motivates a feedback control model that includes the insect's ability to sense body rotations, process this information, and actuate the wing motions that generate corrective aerodynamic torque. Thus, as with modern fighter jets, the common fruit fly employs an auto-stabilization scheme that maintains its flight course and allows for navigation through complex aerial environments. [Preview Abstract] |
Sunday, November 22, 2009 8:52AM - 9:05AM |
AV.00005: Fruit flies modulate passive wing pitching to induce in-flight turns Attila Bergou, Leif Ristroph, John Guckenheimer, Itai Cohen, Jane Wang To control their ?ight, insects must have mechanisms to modulate their wing kinematics. Exactly how insects control their wing motions to execute observed flight maneuvers is poorly understood. Here, we measure the wing and body kinematics of freely flying fruit flies performing turns and, in conjunction with numerical simulations and mathematical models, probe how they control their wing motion to ultimately alter their flight path. We find that these flies induce sharp turns by applying an overall bias to the passive pitching motion of their wings. We present a simple mechanical model for the wing actuation that quantitatively predicts the turning dynamics of the insect. [Preview Abstract] |
Sunday, November 22, 2009 9:05AM - 9:18AM |
AV.00006: Flapping counter force - a unique flight stabilizing mechanism enabled by flapping wings Hu Dai, Haoxiang Luo, Xinyan Deng The flyers in nature are more sensitive to disturbances than the much-larger airplanes, and meanwhile, many of them (e.g., insects) lack the geometrical features that airplanes typically have, e.g., the vertical/horizontal tails. Therefore, a passive flight stabilizing mechanism would be of particular importance to the biological flyers, who otherwise would have to spend a great deal of effort to actively control their flight. It was recently found that insects and other flying animals possess a unique passive stabilization mechanism that stems from the coupling between their body movement and the flapping-wing motion (Hedrick, Cheng and Deng, Science, 2009). More specifically, the unsteady movement of the flyer's body in a disturbed flight modifies the effective kinematics of the wing, creating a resistant force that counteracts the body motion. In this work, we use direct numerical simulations to compute the flapping counter force associated with a two-dimensional wing, and the transient process of the disturbed body motion is also computed via flow-structure interaction. The flyer's body is represented by a lumped mass, and the flow around the wing is resolved by the simulations to accurately account for the force production mechanism. The computed force and the body transition will be compared with a quasi-steady analysis. [Preview Abstract] |
Sunday, November 22, 2009 9:18AM - 9:31AM |
AV.00007: Aerodynamics of Dragonfly in Hover: Force measurements and PIV results Xinyan Deng, Zheng Hu We useda pair of dynamically scaled robotic dragonfly model wings to investigate the aerodynamic effects of wing-wing interaction in dragonflies. We follow the wing kinematics of real dragonflies in hover, while systematically varied the phase difference between the forewing and hindwing. Instantaneous aerodynamic forces and torques were measured on both wings, while flow visualization and PIV results were obtained. The results show that, in hovering flight, wing-wing interaction causes force reduction for both wings at most of the phase angle differences except around 0 degree (when the wings are beating in-phase). [Preview Abstract] |
Sunday, November 22, 2009 9:31AM - 9:44AM |
AV.00008: Aerodynamics of Dragonfly in Forward Flight: Force measurements and PIV results Zheng Hu, Xinyan Deng We used a pair of dynamically scaled robotic dragonfly model wings to investigate the aerodynamic effects of wing-wing interaction in dragonflies. We follow the wing kinematics of real dragonflies in forward flight, while systematically varied the phase difference between the forewing and hindwing. Instantaneous aerodynamic forces and torques were measured on both wings, while flow visualization and PIV results were obtained. The results show that, in forward flight, wing-wing interaction always enhances the aerodynamic forces on the forewing through an upwash brought by the hindwing, while reduces the forces on the hindwing through a downwash brought by the forewing. [Preview Abstract] |
Sunday, November 22, 2009 9:44AM - 9:57AM |
AV.00009: Lift production of a hovering pyramid in an oscillatory airflow Annie Weathers, Brendan Folie, Bin Liu, Stephen Childress, Jun Zhang We investigate the dynamics of rigid, hollow ``pyramids'' placed within a background airflow, oscillating with zero mean. The asymmetry of the body introduces a net upward force. We find that when the amplitude of the airflow is above a threshold, the net lift exceeds the weight and the object hovers. Our results show that the objects hover at far smaller air amplitudes than would be required by a quasi-steady theory. We find that paired vortices are generated during each period of the oscillatory flow, which provide the lift. We also observe that lighter objects do not necessarily hover more easily, because they tend to be entrained by the flow, reducing the relative motion and the resultant lift. In fact a finite flow amplitude is observed to be required for hovering in the limit of zero body mass. [Preview Abstract] |
Sunday, November 22, 2009 9:57AM - 10:10AM |
AV.00010: Aerodynamic force variation in an inclined hovering motion by kinematic and geometric controls Hyungmin Park, Haecheon Choi Due to the excellent flight capability with a high maneuverability, dragonfly flight has been a great interest in various fields. In the present study, we construct a one-paired dynamically scaled dragonfly wing model, perform an inclined hovering motion by wing flapping in a white-oil tank, and measure the normal and tangential forces on the wing. First, we investigate the effect of kinematic parameters of wing motion such as the attack angle ($\alpha$), pitching duration, pitching timing, etc. The Reynolds number is 1,900 or 2,430 depending on the wing shape. We find that the aerodynamic forces vary greatly with these kinematic parameters. On the other hand, the corrugation on the wing surface has been found to increase the lift force in gliding flight. In this study, we investigate the effect of surface corrugation on the force of the flapping wing. With the corrugation, the drag force slightly increases during a downstroke (high $\alpha$) and the lift force increases during an upstroke (small $\alpha$), respectively, resulting in the increase of the mean vertical force by $10 \sim 30\%$ depending on the wing trajectory. We further investigate the force variation by kinematic and geometric controls using flow visualization and the result will be shown in the presentation. [Preview Abstract] |
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