Numerical simulation of sweeping motion effects on the hovering dragonflies

In this paper, the typical hovering mode of dragonflies with different sweeping motions is numerically simulated by solving three-dimensional unsteady Navier-Stokes equations to explore the effects of stroke deviation on aerodynamic performance. A bionic wing model of dragonflies is applied, conducting a rotating motion around the parallel wing root axis-flapping, a rotating motion around the vertical axis-sweeping, and a rotating motion around 1/4 chord-pitching. Different parameters relevant to the aerodynamics of three-dimensional flapping tandem-wing have been studied, notably the sweeping amplitude. The results of this research show that for the hovering dragonflies, the sweeping motion increases the vertical force slightly, but the power consumption increases severely compared with the vertical force. The sweeping motion delays the shedding of trailing edge vortices during the stroke reversal. The leading edge vortices gradually increase in radius and fall off from the heel to the tip. Our research can provide reference for the design of dragonfly-like aircraft with multi degree of freedom motion.