The Functional Role of Wing Corrugations in Living Systems

Abstract

Questions concerning the functional role of spanwise wing corrugation in living systems are experimentally investigated. Attention was initially directed to this problem by observation of the irregular shape of many insect wings as well as other studies indicating higher lift on these wings. First, a flow visualization scheme was used to observe and photograph streamlines around two different wing sections. One of these, a sheet metal model with geometry matching that of a butterfly wing, was studied at a chord Reynolds number of 1500 and at a Reynolds number of 80 based on corrugation depth. A steady-state recirculation region near the model leading edge was found, and the separated flow region above this recirculation zone formed a laminar reattachment to the model. A second thicker wing was corrugated on the upper surface. Closed streamlines inside these upper surface corrugations were photographed at Reynolds numbers of 8000 and 3800 based on chord length, and 200 and 90 based on corrugation depth. Reductions in pressures on the corrugated upper wing surface relative to a smooth upper wing surface were then measured.