Delayed action leads to faster turning of fish by interaction with neighbor

Abstract

Schooling fish exhibit captivating biological behaviors that have garnered interest from both biologists and engineers. While the undulatory motion of fish in schools has been extensively studied, rapid turning within these schools remains underexplored. This paper presents a three-dimensional computational fluid dynamics (CFD) model of a fast-start scenario involving two fish to investigate the influence of spatial and phase differences on swimming performance. Our findings indicate that, by leveraging the wake of the upstream fish, a downstream fish can enhance its travel distance by up to 34.4% and its rotational angle by up to 41.6%. The optimal travel distance is achieved when the starting jet of the front fish aligns with the center of mass (COM) of the downstream fish. Conversely, the largest rotational angle is observed when this jet precedes the center of mass. The research further identifies a vortex phase matching phenomenon in fish schools during rapid turns. The phase difference, or the downstream fish's delayed response, allows it to harness the wake for improved transitional and rotational movement. However, this approach might decrease the average angular velocity, which represents the rotational angle divided by the total duration of turning and waiting. Our study concludes that, with a specific phase difference, this delayed action facilitates faster fish turns by utilizing the wake created by the neighboring fish.