Abstract
A multi-block-and overset grid-based computational fluid dynamic (CFD) study was implemented for the unsteady flows surrounding a hovering hawkmoth with the realistic body-wing geometrical and kinematic models. The computed results show that downwash produced by a flapping hawkmoth has time dependency fairly. In particular, weak downwash is detected during downstroke, in contrast; strong downwash is predicted during upstroke. The reason the strong downwash is produced is that the combination of leading-edge vortex, shedding trailing-edge vortex and wing tip vortex forms a ring-shaped vortex characterized by strong downward-flows in the center of it during downstroke. The remarkable downward-flows travel to bottom area of a flapping insect during upstroke when the ring-shaped vortex is shed by wing rotation and flapping wings push it downward. Moreover downwash distribution does not exhibit a circle shape that has been explained by the Rankin-Fluid momentum theory.
