Effect of Reynolds number on hydrodynamics of undulating elastic propulsors with tapered thickness*

Thickness tapering leads to enhanced hydrodynamic performance of oscillating elastic propulsors by drastically increasing the hydrodynamic thrust and efficiency compared to elastic propulsors with uniform thickness. Thickness tapering leads to the acoustic black hole effect at the propulsor trailing edge that minimizes the wave reflection and promotes the development of the traveling waves propagating along the propulsor length. We use fluid-structure interaction computational modeling to explore the hydrodynamic mechanism leading to the enhanced hydrodynamics of tapered propulsors. In particular, we probe the effects Reynolds number and viscosity on the emerging flow patterns, hydrodynamic forces, and especially how the performance gains of propulsor thickness tapering can either be assisted or hindered. Our simulations provide useful guidelines for designing efficient bio-mimetic robotic swimmers.