Jun Zhang, Department of Physics and Courant Institute, New York University

"On Unidirectional Flapping Flight of a Symmetric Wing"

Friday February 9th, 4pm, Phillips 332
(refreshments served in Phillips 330 starting at 3:30)

Abstract: The locomotion of most fish and birds is realized by flapping wings or fins transverse to the direction of travel. Here, we study experimentally the dynamics of a symmetric wing that is "flapped" up and down but is free to move in the horizontal direction. In this table-top prototypical experiment, we show that flapping flight occurs abruptly at a critical flapping frequency as a symmetry-breaking bifurcation. We then investigate the separate effects of the flapping frequency, the flapping amplitude, the wing geometry and the influence from the solid boundaries nearby. Through dimensional analysis, we found that there are two dimensionless parameters well describe this intriguing problem that deals with fluid-solid interaction. The first one is the dynamical aspect ratio that combines four length scales, which includes the wing geometry and the flapping amplitude. The second parameter, the Strouhal number, relates the flapping efforts to it resultant forward flight speed. Overall, we emphasize the robustness of the thrust-generating mechanisms determining the forward flight speed of a flapping wing, as observed in our experiments.