Large-Amplitude Intermittent Swimming in Viscous and Inviscid Flows

Abstract

Recently, it was demonstrated in an inviscid flow that burst-and-coast or intermittent swimming can save energy when compared with continuous swimming and that the energy savings are maximized for large-amplitude pitching motions where flow separation is likely to occur. This paper examines the effects of flow separation on altering inviscid flow predictions. As such, viscous and inviscid flow simulations are presented of a hydrofoil pitching intermittently with large-amplitude motions. It is observed that leading-edge vortex formation and shedding in a viscous flow significantly alter the wake dynamics from the inviscid flow solutions where only trailing-edge shedding is modeled. Moreover, the inviscid flow solutions predict higher peak force production, lower cost of transport, and lower optimal duty cycles than the viscous flow solutions. Despite these differences, the trends in the force production and energetics seen in a viscous flow are well captured by the inviscid flow simulations. Importantly, both predict energy savings on the order of 10–30% for intermittent swimming, and the energy savings increase when the amplitude of motion is increased even when significant leading-edge separation occurs.