Experimental Study of Wing-Wake Interactions of Insect Flapping Wing

An experimental study is conducted to investigate wing-wake interactions of a flapping wing of an insect in hovering and forward flight. Unsteady aerodynamic forces acting on a flapping wing are measured using a dynamically scaled mechanical model in a water tunnel, which simulates hovering and forward flapping flight of insects. In addition, flow visualization is made around the scaled flapping wing model using digital particle image velocimetry (DPIV). A flapping wing experiences wing-wake interaction that the wing interacts with the wake induced in the previous stroke, called wake capture. We investigate effects of parameters of a flapping wing on the wake capture. The results indicate that the wake capture is principally dependent on the two parameters: reduced frequency and timing of feathering rotation. And the flow visualization shows that the vortex pair with counter-rotating, which induces a strong jet flow between the two vortices themselves, enhances wake capture effect. The wake capture effect in forward flight appears in a different manner from in hovering flight. While the wake capture is more effective in the stroke reversal from the down- to up-stroke, it is slight effective in the stroke reversal from the up- to down-stroke.