Numerical Investigation of Elliptical Motion on Propulsion Performance of a Flapping Hydrofoil

The elliptical motion is proposed on a flapping hydrofoil for propulsion instead of the traditional two degrees of freedom motion, plunging/pitching motion. A synchronously periodic horizontal motion (surge) together with vertical motion (heave) and rotating motion (pitch) constitute the elliptical motion. A NACA0012 hydrofoil is placed in two-dimensional turbulent flow with the Reynolds number fixed at 40000. Two parameters are presented to describe different elliptical motions, the ratio of heaving amplitude and surging amplitude, the difference between surge and heave. The elliptical motion can significantly improve the thrust and propulsive efficiency compared with traditional motion. Besides, there exists an optimal parameter to get a maximum time-averaged thrust coefficient and efficiency. This study can provide a guidance for the engineering design of the motion trajectory on biomimetic underwater vehicles.