Abstract
A moving elastic airfoil leads to fluid-structure interaction, complicating the flow field. Although the flow field around a moving elastic airfoil is complicated, elastic airfoils have some advantages. Recently, very thin membrane airfoils have also attracted attention. However, the flow field and the interaction between it and the deformation of the thin membrane are not fully understood. In this study, we investigate the flow field around a membrane airfoil based on the flapping motion of a butterfly wing. The deformation of a butterfly wing and the behavior of vortices that roll up from the leading edge, trailing edge, and wing tip as it flaps are quantitatively examined. The relationship between wing deformation and vortex behavior is also investigated. The fine arch wing shape contributes to the development of vorticity and the dynamic behavior of the vortex ring on the downstroke. However, on the upstroke, the complicated wing shape cannot generate developed vortices and the vortex ring remains mostly unchanged.
