Aerodynamics of dragonfly flight

Abstract

The material property, kinematics and computational fluid dynamics of the dragonfly Sympetrum flaveolum are investigated. The elastic modulus of the leading edge spar of a hindwing, obtained through vibration tests, was found to be similar to rubber with small strain. The flapping motions of the hindwing are recorded using high-speed videography. Two distinct flapping patterns are revealed as a simple figure-eight (S8) and a double figure-eight (D8). The in-flight kinematic models of the two flapping patterns are integrated into the computational fluid dynamic model of a live-sized dragonfly hindwing. The computed aerodynamic force and flow information reveals better aerodynamic performances in D8 than in S8. Most importantly, we propose two new lift enhancing mechanisms through the simulations: (1) increasing the amount of the reduction of the translational acceleration during wing rotations; (2) forming of the vortex tube to stabilise the vortices around the wing to prevent shedding.