Numerical simulation of the self-propelled swimming performances and mechanisms of a biomimetic robotic fish with undulating fins under different fin waveforms.

This article focuses on the numerical investigation of self-propelled swimming performance and propulsion mechanisms of a biomimetic robotic fish with undulating fins (BRFUF) operating in the median/paired fin (MPF) swimming mode. Using a computational fluid dynamics (CFD) coupled fluid–body interaction model, the study systematically analyzes how fin waveform characteristics, wavelength (λ), and maximum fin ray oscillation angle amplitude (γ0) affect swimming speed, hydrodynamic forces, surface pressure distributions, and vortex dynamics. Results indicate that larger fin oscillation amplitudes and longer wavelengths enhance cruising velocity and thrust by generating stronger high-pressure regions and larger backward jet flows associated with vortex structures on the fin surface, which produce reactive added-mass forces propelling the fish forward. The findings elucidate the thrust generation mechanism in MPF undulatory swimming and provide theoretical guidance for designing high-performance biomimetic robotic fish.