Hydrodynamic Interactions in Schooling Fish: A Comparative Study of BCF and MPF Swimmers

Fish locomotion involves two primary propulsion strategies: Body-Caudal Fin (BCF) and Median-Paired Fin (MPF) modes, each with distinct body compositions. BCF swimmers have propulsors downstream of their body trunks, while MPF swimmers possess propulsors parallel to them. Despite these differences, both types have been observed swimming in groups. To investigate the hydrodynamic effects of different propulsion strategies in schooling, this study employs a tuna and a manta ray model, representing BCF and MPF swimmers, respectively. Three-dimensional (3D) numerical simulations were utilized to compare the flow features and hydrodynamic interactions of a tuna-like and ray-like swimmer pair. Detailed flow analysis revealed beneficial fin-fin and body-fin interactions in staggered configurations. The vortex-capturing mechanism played a crucial role in the hydrodynamic benefits of the staggered follower. These findings shed light on the performance differences between BCF and MPF swimmers in schooling and provide valuable insights into vortex interactions for bio-inspired robotics and underwater vehicle design.