Aerodynamics on a faithful hindwing model of a migratory dragonfly based on 3D scan data

Abstract

In this study, we examined the aerodynamics around the hindwing of a faithfully reproduced Pantala Flavescens (globe wanderer) under gliding conditions. The dragonfly wing is corrugated, with numerous veins running through the entire wing. This convexoconcave geometry improves the lift-to-drag ratio under low Reynolds number conditions. However, until now, aerodynamic analyses have only been performed on 2D chordwise cross-sections of the wing and pseudo-3D shapes extending the profiles spanwise. The aerodynamic performance of a 3D geometry that faithfully replicates all wing veins has yet to be investigated. Therefore, we prepared a faithful analytical model by 3D scanning the hindwing of a Pantala Flavescens specimen; as a migratory dragonfly, it is capable of long-duration and long-distance flight. In our simulation results, the V-shaped groove formed by the large wing veins was covered by separation vortices, resulting in a pseudo-smooth wing surface. The role of the differently-sized wing veins is supposedly to inhibit separation. The faithful reproduction of the wings provides a better understanding of the 3D flow structure and directly leads to a precise estimation of the underlying aerodynamic characteristics. Accurate performance must be evaluated by simulating a faithful geometry in low angle of attacks, where aerodynamic efficiency is required for long-distance flight.