On the Varying Tail-Beat Frequency in High-Density Fish School

Fish schooling has been studied thoroughly in order to understand their physical strengths and benefits. It has been proven that schooling creates a hydrodynamic benefit for individual fish in a school as well as providing protection from predators.  In this study, numerical simulations utilizing an immersed-boundary-method-based incompressible Navier-Stokes flow solver are used to investigate the impact of undulation frequency on two-dimensional fish-like bodies swimming with carangiform locomotion in a high-density diamond-shaped school. Frequencies were selected to range from 0.46 to 1.11 Hz. This research analyzes the impact on individual fish performance as well as overall school average values by examining thrust coefficient, power coefficient, and propulsive efficiency. As the undulation frequency of the school is increased, the results come to a peak efficiency that the school can operate at. As the frequency continues to increase, the thrust and power consumption significantly increases while the average propulsive efficiency decreases due to the affected downstream momentum and wake structure of the school. The insights revealed from this study will contribute to a better understanding of physical mechanisms used by fish schools as well as providing new information to be used for bio-inspired underwater swarm robots.