Aerodynamic characteristics of hoverflies during hovering flight

© 2018 Elsevier Ltd Aerodynamic characteristics of hoverflies during hovering flight are studied with a three-dimensional sharp-interface immersed boundary method. The wing of hoverfly is modelled with a rectangular generic wing. Simulations are conducted in two groups: One group of simulations are conducted to determine the equilibrium kinematics of the wings with and without alula; the other group of simulations are conducted to study the effects of pitching phase differences between the wing and the alula on the performance of the wings. The forces, aerodynamic power, efficiency and vortical structures are discussed in detail. It is found that the wing without alula experiences larger angle of attack at equilibrium flight. This difference causes 5% more aerodynamic power compared to the wing with alula. By performing simulations of the wing without alula, and wings with alula flapping 45° ahead, in phase with and 45° behind the wing, we find that the wing with alula flapping in phase produces largest lift, but its efficiency is lowest. Vortical structure analysis shows that the vortical structures of the wing with alula flapping 45° ahead are similar to those of the wing without alula. The alula provides stabilizing effect on the leading edge vortex for the wings with alula flapping 45° ahead and in phase.