Hydrodynamics of metachronal propulsors in aquatic swimmers

Aquatic swimmers, including crustaceans, ctenophores and polychaetes, often rely on the coordination of an array of small propulsors to generate their swimming thrust. While the morphology of these structures vary greatly, they share common kinematic patterns in how they bend and how they coordinate their movements as an antiplectic metachronal wave. In order to examine the hydrodynamics associated with these kinematic patterns we used microPIV techniques to quantify the flow around the propulsors of different species of aquatic swimmers (including ctenophores, crustaceans and polychaetes). We found that the bending of the propulsors during the effective stroke interacted with the surrounding fluid by generating vorticity fields that aligned with the inflexion of the bending propulsor. Quantification of the pressure fields around individual propulsors revealed that the propulors predominately transported fluid and generated thrust by pulling fluid (along negative pressure regions) from behind the propulsor during the effective stroke. The reliance on negative pressures, rather than positive pressures, provides insight into the shared bending and metachronal kinematics.