Flow Interactions and Performance Benefits in Fish Schools

In nature fish are known to aggregate into large schools or collectives. It has long been argued that these collectives are formed for social reasons, as a protection strategy against predators, and even to save energy. However, our knowledge of the fluid dynamic interactions that occur among individuals and their collective energetics is based mostly on two-dimensional analyses. Here, we examine the role of three-dimensionality in altering the flow interactions, the force generation, and the energetics of two interacting swimmers. We model our two swimmers as simple finite-span pitching propulsors. Additionally, the positions of the two propulsors are configured in mixtures of canonical side-by-side and in-line arrangements. The forces and moments are then measured as the two wings undergo sinusoidal pitching motions over a large range of synchrony and spacing. Our aim is to identify the flow mechanisms that improve or degrade propulsive performance of individuals within a collective as well as to identify flow mechanisms that give rise to fluid-mediated forces among individuals.