Dynamic Behavior of a Vortex Ring over a Butterfly Wing and Its Dynamic Lift

Abstract

Recently, the mechanism of butterfly flight has attracted significant attentions in biohydrodynamics. Especially, a number of recent studies have examined the flow field around an insect wing. However, the detailed flow structure around insect wing and its growth process have not been understood. The purpose of the present study is to clarify the dynamic behavior of the vortices around the flapping butterfly wing. Moreover, we estimated the dynamic lift produced by the butterfly wing using the circulation of the vortex ring. A vortex ring is formed over the butterfly wings when the wings flap downward to the bottom dead position, and then passes through the butterfly completely and grows until reaching the wake at the bottom dead position. The dynamic lift produced by the butterfly wing in flapping downward estimated using the circulation of the vortex ring. The dynamic lift becomes large rapidly as the vortex ring develops over the wing sufficiently. Maximum lift is about four times of the gravity of the butterfly at -30 deg.