Fin-fin Interactions in Schooling Fish: How Median Fins Impact Inter-fish Wake Interactions and Group Performance

There exists an increased interest in understanding how hydrodynamic interactions between grouped fish can improve the performance of the school. However, fish models in these studies typically ignore the median fin (dorsal and anal fin) structures. Even though median fins are known to enhance the performance and wake structures of a single fish, the omission of these fin structures in schooling studies means the contributions of median fins to inter-fish performance enhancement is unknown. To address this gap, we construct a series of schooling configurations in which the median fins are systematically added to the fish models. The most simplistic model is a leader and follower, both only featuring the trunk and caudal fin. To isolate the effect of leader fin-fin interaction on the schooling interaction, the leader and follower median fins are introduced in subsequent configurations. Wake and force information is solved by using an in-house developed immersed boundary method-based incompressible Navier-Stokes flow solver. The findings presented in this talk highlight how the fin-fin interaction of the leader fish produces an enhanced wake-body interaction with the follower, reducing the follower's hydrodynamic drag. Furthermore, the addition of the follower's median fins results in enhancement of its wake capture with the leader's vortices. In the context of designing bio-robotic schooling swimmers, the results of this study highlight the importance of including median fins on the robots as their contributions to schooling interactions, not just solitary swimming, are significant.