Numerical studies on hydrodynamics of flapping foils

The flapping foil based on bionics is a sort of simplified model, which can imitate the motion of the wings or fins of animals. Based on the backgrounds of underwater vehicle with high capabilities of propulsion, the paper focuses on the hydrodynamics of flapping foils with different motion models. According to different biological prototypes, numerical simulations of different motion models of flapping foils are conducted. In the paper, a universal motion model is adopted and the motion parallel to the flow direction is considered. The force coefficients, torque coefficient, and field characteristics are extracted and analyzed. And then the thrust efficiency is calculated. The results indicate that the motion parallel to the flow direction leads to different trajectories and the force situation changes correspondingly, vortex rings exists in the wake and jet stream can be induced resulting in a positive thrust force. The study results of this paper would provide the theoretical reference for the design of underwater vehicle based on flapping propulsion.