STUDY ON THE INFLUENCE OF CARANGIFORM FISH MEDIAN FINS INTERACTION ON AUTONOMOUS SWIMMING PERFORMANCE

Fish can achieve higher propulsion performance through the interaction among their median fins (dorsal fin, anal fin and caudal fin) than swimming with only the caudal fin. However, most current studies are still based on the body caudal fin model, using the swinging propulsion of the trunk and caudal fin to study the swimming performance and swimming mechanism of fish. To understand the influence of median fins interaction on the autonomous swimming performance of carangiform fish, in this study, a real geometric model of the fish body was established using a high-precision three-dimensional laser scanner, and three-dimensional numerical simulation was conducted on the autonomous swimming behavior of carangiform fish with complete median fins. By solving the swimming process of the fish body accelerating from a stationary state to a cruising state, the swimming performance of the carangiform fish under different phase differences was compared, and the vortex dynamics at the tail of the fish body was analyzed in detail. The results indicate that the posterior body vortices (PBV) caused by the swinging and shedding of the dorsal and anal fins are captured by the leading edge of the tail fin and interact with the leading edge vortices (LEV) during backward propagation, enhancing the strength of the LEV and greatly improving the swimming performance of carangiform fish. Compared with the swimming model that only relies on the caudal fin and body, the thrust has increased by up to 26.11%, the efficiency has increased by up to 18.15%, and the swimming speed has increased by up to 60.14%. This paper reveals the mechanism of the carangiform fish interaction between the median fins, clarifies the hydrodynamic mechanism by which the interaction between the median fins enhances the autonomous swimming performance of carangiform fish, and provides new insights for the study of carangiform fish swimming performance and swimming mechanism.