Effect of twist, camber and spanwise bending on the aerodynamic performance of flapping wings

Abstract

Insect wings change its shape dynamically through the interactions of the structure, and the aerodynamic and inertial forces when flapping, which can greatly affect its aerodynamic performances. While the detailed change of the wing shape has been extensively measured with high-speed photogrammetry, its implications on the flapping wing aerodynamics are poorly understood. In order to clarify the linking between the wing deformation and the flapping wing aerodynamics, the aerodynamic effect of the wing deformation in terms of the twist, the camber and the spanwise bending have been systematically investigated by means of the computational fluid dynamic analyses of a hovering hawkmoth with artificially deformed flapping wings. With the appropriate magnitude and phase, the twist and the camber are found to enhance the aerodynamic efficiency of flapping wing by redirecting the aerodynamic force vector on the wing so as to reduce the drag or increase the lift. The spanwise bending can increase the aerodynamic force without the redundant increase in aerodynamic power by appropriately adjusting the speed of the wing. We specified the magnitude and the phase of deformation that give the highest efficiency in the range of the study, and pointed out that, while the twist and the camber can enhance the efficiency, the deformation beyond the optima can reduce the aerodynamic efficiency drastically. The results in this study revealed the aerodynamic contributions of each kind of wing deformation, and will be of great implications for the design of bio-inspired micro air vehicles.