Performance evaluation and optimization for two-dimensional fish-like propulsion

Hydrodynamic characteristics of fish-like propulsion have been of interest to researchers in the fields of fluid mechanics and biology. The paper aims to present a systematic hydrodynamic study to further understand propulsion performance of fish-like swimming. The study is a numerical investigation based on a unified kinematic model and different self-propulsion undulation conditions. Propulsion performance and hydrodynamic characteristics are analyzed according to the simulation results. The theory demonstration shows that the propulsion efficiency is independent of the frequency when the frequency is large enough. With increasing wavelength, the undulation mode gradually becomes the oscillation mode, and performance metrics tend to limit values. The relations between propulsion performance and fluid field non-dimensional numbers are also discussed. The results show that a high efficiency propulsion for fish requires a high St and low Re conditions. An optimization index that emphasizes time cost for the entire swimming process is proposed to optimize the swimming for migrating a given distance. Under the optimal condition, Froude efficiency for the fish-like undulation is about 0.52 with a 2.4BL/s of swimming speed. The findings will offer some new insights into understanding the swimming mechanism of fish-like propulsion.