Hydrodynamics of larval fish quick turning: A computational study

Abstract

A three-dimensional fluid–body interaction model was established to study the hydrodynamics of larval fish at a quick start with a turning angle of approximately 80°. The bending curves of the larval fish were attained by extracting the middle line of fish snapshots from a previously published paper. The fluid–body interaction was implemented to empower the self-propelling function of the larval fish. In this study, the swimmer’s kinematics of the body as well as hydrodynamics at preparatory and propulsive stages of the larval fish were extensively analysed. It shows that during the preparatory stage, the larval fish produces a significant force against the escaping direction. Nevertheless, this force leads to a large turning torque, helping to accomplish a quick turning. During the propulsive stage, the force increases quickly in the escape direction, resulting in a large velocity for the escape. The characteristics of body motion and the flow field are consistent with the previous observation on adult fish: the bimodal mode on velocity and tangential acceleration and three jets of fluids. In addition, the research also reveals that the forces generated at anterior and posterior parts of the larval fish generally point to the opposite directions at both preparatory and propulsive strokes of C-start.