Hydrodynamic Characteristic Analysis of the Biomimetic Undulatory Fins

Underwater motion control constitutes a critical technology for marine exploration and operational systems. While conventional propeller propulsion has achieved technological maturity, its inherent limitations—including significant mechanical noise, reduced efficiency in low Reynolds number regimes, and near-field flow disturbances—constrain adaptability in complex mission scenarios. Bionic undulating fin propulsion, inspired by biological locomotion mechanisms, has emerged as a pivotal research direction for next-generation underwater thrusters due to its high efficiency, low noise signature, and minimal flow disturbance characteristics. This study establishes a three-dimensional hydrodynamic model of undulating fins and systematically investigates their propulsion power characteristics under varying kinematic parameters through immersed boundary method-based numerical simulations. The research reveals that motion constraints imposed by the actuation mechanism induce periodic shedding of lateral vortex structures in the fin’s transverse flow field, resulting in propulsive energy dissipation. Concurrently, three-dimensional asymmetric evolution of trailing-edge vortices causes longitudinal kinetic energy losses. By quantitatively analyzing the fluid-structure interaction mechanisms between vortices and fin kinematics, this work elucidates the hydrodynamic origins of propulsion power loss under actuation constraints. The findings provide theoretical foundations for optimizing bio-inspired fin design and implementing closed-loop control strategies, offering substantial engineering significance for enhancing the environmental adaptability and mission reliability of underwater robotic systems.