Enhanced hydrodynamic performance of biomimetic tapered propulsor

Through millions of years of evolution, fish have achieved unmatched swimming velocities and efficiencies. Different species of fish use different parts and sections of their flexible bodies to pass down waves from their head to their fins that propel the fish forward. On one hand of the spectrum anguilliform fish (eel-like) use travelling waves generated through their entire body while thunniform fish generate standing waves using their caudal fins for propulsion. Different swimming types can be characterized by examining the nature of the wave propagation in terms of the standing wave ratio (SWR). Standing wave type of propulsion generally yields higher swimming velocities at the cost of efficiency. Although travelling wave based propulsion is generally more efficient, it is not trivial to generate travelling waves within a relatively short elastic structures. Using three-dimensional fully coupled fluid-structure interaction simulations, we showed that fin tapering is an effective approach to generate travelling waves in underwater propulsors. Through different tapering shapes, we demonstrate that SWR is a robust metric characterizing to the hydrodynamic efficiency of tapered plates.