Hydrodynamic performance of oscillating elastic propulsors with tapered thickness

Abstract

Using fluid–structure interaction computational modelling, the hydrodynamic performance of bio-inspired elastic propulsors with tapered thickness that oscillate in an incompressible Newtonian fluid at Reynolds number $Re = 2000$ is investigated. The thickness tapering leads to an acoustic black hole effect at the trailing edge of the propulsor that slows down and attenuates flexural waves, thereby minimizing the flexural wave reflection and enhancing travelling wave propulsion. The simulations reveal that, by tuning the propulsor thickness profile modulating the acoustic black hole effect, the tapered propulsors can be designed to vastly outperform the uniformly thick propulsors in terms of the hydrodynamic efficiency and thrust, especially for the post-resonance frequencies. The enhanced hydrodynamic performance is directly linked to the ability of the tapered propulsors to generate travelling waves with a large amplitude displacement at the trailing edge. The results have implications for the development of highly efficient bio-mimetic robotic swimmers and, more generally, the better understanding of the undulatory aquatic locomotion.