Numerical study of the cruising–maneuvering motion of a fish-like swimmer using the co-propulsion of the caudal fin and pectoral fin under self-propulsion

The mechanism of fast and high maneuvering swimming of fish under the cooperative propulsion of multiple fins has not been fully studied. To fill the research gap in the process of numerical simulation on the motion performance, hydrodynamic characteristics, and flow field of fish-like swimmers cruising and maneuverability under the coupled propulsion of body and/or caudal fin (BCF) swimming mode and median and/or paired fin (MPF) swimming mode, a numerical solution method of multibody dynamics coupling under the combined propulsion of body-caudal-pectoral fin is established. The coupling mechanism of fast and efficient swimming in BCF mode and high maneuverability in MPF mode is systematically studied. Our results revealed that the fish-like swimmer can make full use of the advantages of both swimming modes under the combined propulsion of the caudal fin and pectoral fin to achieve maneuvering steering and fast cruising. When the pectoral fins adjust the direction of swimming, the forward velocity of the fish-like swimmer decreases significantly in the unfolding stage of the pectoral fins. When the pectoral fins are maneuvering, the fish-like swimmer is able to steer stably, and at the end of the maneuvering, the fish-like swimmer is able to cruise steadily. The vortex dynamics analysis revealed that the well-developed tip vortex and trailing-edge vortex are the key factors for the generation of shedding vortex rings in the pectoral and caudal fins. The generation of two vortex rings in one cycle is a necessary condition for the caudal fin or pectoral fin to generate continuous thrust.