Can Tip Vortices Enhance Lift of a Flapping Wing?

An experiment was conducted to show that tip vortices can increase lift both by creating a low-pressure region near the wing tip and by anchoring the leading-edge vortex (LEV) to delay or even prevent it from shedding. The focus was on a hovering flapping flat plate at Re = 100 based upon maximum translational speed and wing chord, experiencing no freestream. The simplified kinematic motions were governed by some equations. The translational position h(t) is a function of time t and depends further on the plunging amplitude h a and the flapping frequency f. The phase lag between the pitching and the plunging motions was denoted as φ. The spanwise variation in the 3D case shows remarkable changes in the aerodynamic loadings. Thus, it is confirmed that tip vortices can either promote or make little impact on the aerodynamics of low aspect ratio flapping wings.