Can hair help you swim faster? Yes, if you ask shrimp!

Bio-inspired underwater robots have the potential to start a new era of marine exploration by achieving high maneuverability and efficiency through simplified biological characteristics, including kinematics and morphology. Hair-bearing appendages are present in many metachronal, drag-based swimmers propelling at intermediate Reynolds number (Re) and act as either paddles or rakes, depending on the induced flow regime and morphology. However, studies on leakiness have focused on low Re flows and simplified geometries, and their results are thus not applicable to understanding the hydrodynamics of most metachronal swimmers. Here, we use a scaled-up swimming appendage with varied morphologies to characterize leakiness within a relevant range of Re numbers. Key kinematic and morphological characteristics of Palaemon paludosus, a representative marine metachronal organism, are integrated. We perform two-dimensional velocimetry experiments and acquire force transducer measurements to investigate the role of setae in thrust generation, tip vortex shedding, and performance. Our results illustrate the role of setae at the intermediate Re regime for the first time. This study will inform the engineering of underwater solutions, from bio-inspired robotics to particle filtering.