A new method to enhance the propulsion performance of cycloidal underwater vehicles: From no flaps to double flaps

The propulsion performance and maneuverability of underwater vehicles are often difficult to achieve simultaneously. For example, while cycloidal underwater vehicles possess excellent maneuverability, their propulsion performances are relatively limited. To address this limitation, this study designs an underwater vehicle equipped with two cycloidal propellers and explores the use of leading-edge and trailing-edge double-flap blades to enhance propulsion performance. First, the feasibility of improving the virtual camber effect of the cycloidal propeller by adding double flaps is analyzed from a theoretical perspective. Second, a prototype underwater vehicle equipped with two cycloidal propellers is developed, and experiments are conducted to verify its ability to perform predetermined maneuvers such as forward motion, lateral motion, and in situ turning. Finally, the double-flap blades are integrated into the cycloidal–propelled prototype, and computational fluid dynamics simulations are performed to analyze the hydrodynamic performance of no-flap and double-flap configurations under different operating modes, thereby verifying the propulsion enhancements introduced by the flaps and elucidating the underlying mechanisms. The results show that the cycloidal underwater vehicle equipped with leading-edge and trailing-edge double-flap blades achieves up to a 72.3% increase in forward motion propulsion speed compared with the no-flap configuration, while effectively reducing speed fluctuations. In lateral motion mode, the increased hydrodynamic drag results in only a 9.9% improvement in maximum speed. In in situ turning mode, the turning speed of the vehicle increases by 26.6%. Moreover, in forward motion, lateral motion, and in situ turning modes, the thrust coefficient and torque coefficient of the double flaps underwater vehicle increase significantly compared with the no-flap configuration, thereby achieving the goal of enhancing propulsion performance without compromising maneuverability. This study proposes and validates a method for improving the propulsion performance of cycloidal underwater vehicles, providing scientific support for the development of next-generation prototype autonomous underwater vehicles.