Numerical Investigations on the Drag-Thrust Transition of an Asymmetric Sinusoidal Pitching Foil

We numerically investigated the hydrodynamics of a foil undergoing the asymmetric sinusoidal pitching motion when the thickness-based Strouhal number StD and amplitude ratio AD vary from 0.1 to 0.3 and 0.5 to 2.0, respectively. The asymmetric oscillation is achieved by making the downstroke slower than the upstroke, and vice versa. The result uncovers that the drag-thrust boundary can be advanced via enhancing the asymmetry in oscillation. The P+S wake emerged at the asymmetric pitching is found that produces both negative and positive propulsive force, hence appearing around the drag-thrust boundary.