Using thickness tapering to enhance hydrodynamic performance of elastic propulsors*

Using computational modelling, we probe the hydrodynamic performance of bio-inspired elastic propulsors with tapered thickness. The simulations reveal that thickness tapering drastically increases the hydrodynamic efficiency and thrust generated by oscillating elastic propulsors. Furthermore, tapered propulsors can maintain high performance for a wide range of actuation frequencies. We relate the hydrodynamic benefit of thickness tapering to the emerging 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 compare propulsors with different thickness profiles and demonstrate that propulsors that exhibit traveling waves yield the best hydrodynamic performance. The results have implications for the development of highly efficient bio-mimetic robotic swimmers and, more generally, enhance our understanding of undulatory locomotion.