On turning maneuverability in self-propelled burst-and-coast swimming

Abstract

Fish have evolved remarkable underwater turning maneuverability, primarily under active control. This allows them to execute turns within confined spaces, such as during C-start rapid turning. In our study, conducted through computational fluid dynamics simulations of a self-propelled swimmer, we revealed that burst-and-coast swimming patterns can generate various turning behaviors purely through passive fluid–body interactions. The burst-and-coast swimming is characterized by the alternating tail movements between continuous undulating burst phases (bp) and non-undulating or gliding coast phases (cp). Through extensive systematic three-dimensional (3D) simulations, we found that both the burst-and-coast duty cycle—the ratio of burst duration to the total cycle duration—and the swimmer's undulation frequency inhibit turning maneuverability, which is quantified by the curvature of swimming trajectories. We also found there is an optimal Reynolds number that maximizes turning maneuverability. Further analysis suggests that the turning maneuverability is probably due to the persistent presence of the Wagner effect during burst phases and the Magnus effect during coast phases, which differs from the mechanism of actively generating lateral forces by asymmetric continuous flapping. These insights not only advance our understanding of fish locomotion control mechanisms but also provide guidelines for designing underwater robots with improved navigational capabilities.