Differential Pressure Signal Sensed by Pairs of Freely-Swimming Flapping Foils Correlates with the Swimmer's Spatial Organization

The lateral line of fish includes a subsystem that detects hydrodynamic pressure gradients and is thought to be important in swimming behaviors such as schooling. Here, we explore how the differential pressure detected by this sensory system varies when swimming in pairs compared to solitary swimming. Using high-fidelity CFD models of a pair flapping foils that are swimming freely in tandem, side-by-side, and staggered spatial patterns, we mimic the flows encountered during free swimming while measuring pressure gradients with fine spatial and temporal resolution along each swimmer. The pressure gradients "seen" by a swimmer carry information about its spatial position and flapping phase relative to the neighboring swimmer and are markedly distinct from the pressure gradients observed when swimming alone. These findings support a view that flow sensing via the lateral line is sufficient for close proximity schooling and could inspire the development of flow sensing and control mechanisms for near-field swimming in underwater robotic vehicles.