Investigation on the propulsive efficiency of undulating fin propulsor

Gymnarchus niloticus exhibits notable maneuverability, enabling it to navigate at low speeds within complex spaces while minimizing disturbances to the surrounding environment. It's primarily propelled by an undulating dorsal fin. In this work, the effects of different amplitude and frequency parameters on the propulsive efficiency of the undulating fin are extensively investigated using a three-dimensional numerical model. The micro-element method divided the undulating fin surface into several sample units. The propulsive efficiency, thrust, and input power were analyzed by numerical simulation to investigate how motion parameters influence its performance. By analyzing the flow field, this work reveals the mechanisms behind thrust generation and clarifies the significant factors influencing its magnitude. An undulating fin hydrodynamic experiment platform was designed and constructed, with experimental results demonstrating good concordance with numerical simulation outcomes. The results show that increasing amplitude decreases propulsive efficiency while it initially increases and then decreases with an increase in frequency; moreover, higher frequencies contribute to improved propulsion stability. The thrust at both ends of the fin surface is significantly lower than in other positions. These insights into thrust distribution patterns on undulating fins provide valuable methods and theoretical support for shape optimization designs.