Collective Hydrodynamics of Robotic Fish

Many animals in nature travel in groups either for protection, survival, or endurance. Among these, fish do so under the burden of hydrodynamic loads, which incites questions about the significance of the multi-body fluid-mediated interactions that facilitate collective swimming. We study such interactions in the idealized setting of a rotational array of robotic fish whose tails undergo a prescribed flapping motion, but whose swimming speed is determined as a natural result of the hydrodynamic effects. Specifically, we examine how the measured collective speed of the swimmers varies with the imposed frequency and amplitude of their tail flapping, the phase difference between the tail motions of neighboring robots in the array, and the spacing between the fish. We use time-resolved volumetric particle tracking velocimetry to capture the three-dimensional flow field surrounding the interacting fish. By exploring a wide parameter space, we identify the conditions under which multi-body hydrodynamics interactions enhance or impede the swimming performance of a robotic fish array relative to the performance of an identical solo swimmer.