Computational investigation on a self-propelled pufferfish driven by multiple fins

Based on experimental measurements of a live fish, a numerical model is established for a pufferfish driven by the locomotion of its multiple flexible fins. The self-propelled motion of the fish is investigated under unsteady swimming conditions, including the accelerating and subsequent quasi-steady stages, to analyse the motion mechanisms of a real fish model with multiple flexible fins. Present numerical approach combines Computational Fluid Dynamics (CFD) and Multi-Body Dynamics (MBD), which allows for the analysis of the interaction between fluid and a fish with multiple fins. Benefitting from the available experimental data of the live fish, the deformation of each fin surface can be prescribed, and we name this condition as flexible in this paper. To elucidate the impact of flexible fins on the propulsion performance of fish swimming, simulations are also performed for rigid fins with the same kinematic motion profiles imposed on the leading edge of fin surfaces. With the developed tool, unsteady hydrodynamic forces, vortex interaction between body and fins associated with MPF swimming mode are numerically predicted. The obtained results highlight the effect of flexibility of fins on thrust generation and efficiency improvement for fish undergoing free swimming.