Impact of flapping trajectory and foil gap on induced thrust of a flapping foil

Abstract

Wings and fins with tandem configuration are commonly observed in a flock of birds or schools of fish for enhanced performance while flying and summing. Emerging study on these subject underpinned by flapping foil is challenging. However, our study focuses on the tandem hydrofoil by varying the conventional (vertical heave and pitch motion) flapping motion to two new flapping trajectories: (i) elliptical and (ii) fishtail flapping trajectories. The hydrodynamic efficiency, such as propulsive efficiency and wake structure of the tandem hydrofoil, are examined using computational methods. The effect of Strouhal number (St) and inter-foil spacing are also discussed along with the flapping trajectories. The results show that by implementing the two new flapping trajectories, the induced thrust of the hind foil can be enhanced up to 45% compared to the simple flapping. This study shed new light on improving the biomimetic propulsion device, as it aims to enhance the elicited thrust of the hydrofoil.