Analysis of biomimetic caudal fin shapes for optimal propulsive efficiency

Biomimetic caudal fin propulsion systems are a topic of growing interest recently. However, the choice of a particular caudal fin shape for a given robotized underwater vehicle is not straightforward. In order to address this problem, numerical simulations are performed assuming laminar flow, considering the operational regimes of small underwater vehicles. The numerical models are validated against results from literature and then used to compare the propulsive performance of caudal fin shapes ranging from a rectangular fin to a highly forked tail with various combinations of geometric parameters. The optimal shape of the tail based on propulsive efficiency is shown to exist between these two extremes. The presence of leading edge vortices in caudal fins is also shown to have an important role in achieving propulsive performance. The underlying mechanisms and the cause for high thrust and power consumption are discussed in detail with more focus on relating such parameters directly with the geometrical features such as the amount of forking and fin leading edge angle. Researchers can use these insights to arrive at optimal designs for small robotic vehicles with flapping fin-like propulsion, as the relations between geometric features and swimming performance are clearly brought out.