Aerodynamic Effects of Structural Flexibility in Two-Dimensional Insect Flapping Flight

Abstract

Interaction between a flexible flapping wing and the ambient fluid is of considerable importance in realistic flapping flight. In this paper, two-dimensional fluid structure interaction simulations are conducted to examine realistic flow features of insects' flapping motion and to investigate aerodynamic change due to structural flexibility of insect wings under a forward-flight condition. Three types of airfoils are considered to reflect structural deformation. Compared with earlier studies regarding two-dimensional rigid-airfoil simulations, the same key physical phenomena and flow patterns could be observed in the flexible case. For example, lift is mainly generated during downstroke by effective angle of attack and leading-edge vortex, while a large amount of thrust is impulsively generated at the end of upstroke by vortex pairing and vortex staying. On the other hand, the quantitative aspect of flowfields is somewhat different. Structural deformation does affect aerodynamic force generation pattern, and thus structural flexibility has a significant impact on aerodynamic performance. Aerodynamic force coefficient and propulsive efficiency are enhanced compared with the case of a rigid airfoil. In addition, numerical simulations are performed to inspect effects of aerodynamic parameters such as the Reynolds number and reduced frequency. From extensive numerical comparisons, it is observed that key physical phenomena such as vortex pairing and vortex staying are still observed in other flow conditions.