The swimming of manta rays

Abstract

Manta rays propel themselves by combining oscillating and undulating motions of flexible surfaces. We describe two experiments to study the effects of excitation and flexibility on the wake flowfield: experiments on undulating and flapping three-dimensional fins of elliptical planform, and experiments on pitching two-dimensional panels of rectangular planform with varying flexibility. To interpret the results on thrust and efficiency, we propose scalings for aspect ratio and flexibility, and develop a stability analysis called wake resonance theory. Here we focus on the insights provided by wake resonance theory.