On bio-inspired induced drag reduction techniques

Abstract

The current study was aimed at identifying wing planform geometries which favours low induced drag. The geometries were defined by mathematical functions and following a subsequent parametric study, with a focus on sweep angle and taper ratio, inspired by birds wings and aquatic animals flukes or caudal fins planforms. The parametric studies were carried out using a vortex lattice method (VLM) which was validated with experimental data from literature. The main finding is a confirmation of the fact that the maximum Oswald efficiency factor, e is not exclusive to an elliptical wing planform. Despite its apparent simplicity, in fact a swept-back-tapered wing with a linear chord distribution can reach e = 1, the limit or minimum induced drag established from elliptical lift distribution. Moreover, the crescent wing geometry, such as the one displayed by the swift, can even surpass this limit.