Sweep- and dihedral-angle effects on gliding aerodynamics of a migratory dragonfly using a faithful hindwing model

This study conducts a numerical investigation of the aerodynamic characteristics of the hindwing of Pantala flavescens, a migratory dragonfly, with particular emphasis on quantifying the effects of sweep and dihedral angles during gliding flight. Unlike most insect species that rely predominantly on flapping flight, dragonflies alternate between flapping and gliding, using the latter to conserve energy during less dynamic phases. Their wings feature a corrugated structure formed by thin membranes stretched over a complex vein network. Previous studies have demonstrated that the interaction between the leading-edge separation vortex and the lambda-vortex enables such wings to sustain high aerodynamic performance at low Reynolds numbers. However, their three-dimensional aerodynamic characteristics remain insufficiently understood from a quantitative standpoint. Building upon prior work in which a faithful geometric model of the hindwing was constructed from high-resolution three-dimensional scan data, the present study systematically explores the influence of hindwing geometry on aerodynamic performance. In particular, parametric variations in sweep and dihedral angles are evaluated using steady-state Reynolds-averaged Navier-Stokes simulations to elucidate the underlying flow mechanisms responsible for the observed aerodynamic trends. %he sweep angle was found to exert a dominant influence on aerodynamic efficiency, with its impact on the lift-to-drag ratio reaching one order of magnitude greater than that of the dihedral angle. The aerodynamic performance is found to be robust across variations in angle of attack and hindwing orientation. Flow visualizations further identify the leading-edge vortices and their stabilization as key contributors to aerodynamic robustness.