Dynamic Behaviors of a Vortex Ring on a Butterfly and a Small Flapping Robot

Abstract

Butterflies fly combining wing flapping and gliding efficiently and have beautiful flight patterns. Micro-Air-Vehicles (MAVs) and micro-flight robots that mimic the flight mechanisms of insects have been attracting significant attention in recent years. A number of MAVs and micro-flight robots that use various devices have been reported. However, these robots were not practical. A number of studies on the mechanism of butterfly flight have been carried out. Moreover, a number of recent studies have examined the flow field around an insect wing, such as a leading edge vortex (LEV) structure using the first digital particle image velocimetry (DPIV). We have carried out the PIV measurement around a butterfly wing and have visualized a vortex ring formed on the wing clearly. On the other hand, we developed a small flapping robot without tail wings, which is similar to the butterfly. The purpose of the present study is to clarify the dynamic behaviors of the vortex rings formed on the wings of the butterfly and the small flapping robot. A vortex ring is formed over the wings of the butterfly and small flapping robot with stable flight when the wings flap downward. An another vortex ring is formed below the butterfly wings when the wings flap upward and it was smaller than that in downward flapping motion because of the elastic deformation of the wings. Both vortex rings pass through the butterfly completely at the top and bottom dead position in the flapping motion.