On the role of vortical structures in aerodynamic performance of a hovering mosquito

Abstract

Mosquitoes have slimmer wings, higher flapping frequencies, and much lower amplitudes than most other insects. These unique features signify special aerodynamic mechanisms. Besides the leading-edge vortex, which is one of the most common mechanisms of flapping-wing flight, mosquitoes have two distinctive mechanisms: trailing-edge vortex and rotational drag. In this study, the three-dimensional flow field around a hovering mosquito is simulated by using the immersed boundary method. The numerical results agree well with previous experimental data. Mechanisms unique to mosquitoes are identified from the instantaneous pressure and vorticity fields. The flow domains, containing several vortical structures produced by the flapping wings, are divided into different regions for quantitatively analyzing the contribution of vortical structures to the lift. Advection of the trailing-edge vortex and production of the leading-edge vortex each contribute peaks in lift. Passive deformation of the wings is also important, as it stabilizes delayed stall and decreases by 26% the maximum aerodynamic power required for hovering flight. In addition, the lift coefficient and power economy are improved as the Reynolds number increases, which explains the better ability of larger mosquitoes to seek and feed on hosts from the aerodynamic point of view.