Numerical study of nonsinusoidal motion effect on plunging airfoil propulsion

The effect of nonsinusoidal motion on plunging airfoil aerodynamics for thrust generation was numerically studied with a 2-D NACA0012 airfoil at Re=10⁴. A nonsinusoidal parameter K was employed to realize various nonsinusoidal motions. The results reveal that nonsinusoidal motion has a noticeable effect on the aerodynamic performance, as it affects the instantaneous force coefficients, maximum thrust coefficients, and flow structures. An increase in K results in better thrust generation performance at a fixed St, especially for K>0. It is also found that the nonsinusoidal motions have notable effect on the wake pattern, and a larger K induces stronger reverse von Karman vortex in the wake, which in turn leads to the thrust generation enhancement. However, the propulsive efficiency decreases with the increasing K because of the larger scale of leading edge separation caused by the larger K.