Influence of guide vanes and nozzle channel geometry on the performance of waterjet propellers for outboard motors

Abstract

This study aims to enhance the performance and safety of small waterjet propulsion systems for outboard motors. A numerical simulation approach was employed to analyze the effects of guide vane quantity, nozzle attack angle, and inner flow channel geometry on propulsion performance and cavitation resistance. The results indicate that the number of guide vanes exhibits minimal influence on hydrodynamic performance. As the number of guide vanes increases, the declines in head, thrust, and propulsion efficiency remain marginal. Consequently, moderately increasing the number of guide vanes can improve the operational safety and stability of the waterjet propulsion system with only minor performance trade-offs. Within the investigated attack angle range (0°–15°), the straight-tube channel demonstrates superior hydrodynamic performance compared to the divergent channel, with the most pronounced advantages observed at a 10° attack angle. Specifically, the hydraulic head, thrust, and propulsion efficiency increase by 6.62%, 6.53%, and 4.45%, respectively, under this configuration. In contrast, the divergent-channel design shows slightly enhanced cavitation resistance but requires compromising propulsion performance. For both channel types, the propulsion efficiency initially increases and then decreases with rising attack angles, while the average cavitation value gradually decreases. At a 10° attack angle, the average cavitation value is smaller, and propulsion efficiency improves by more than 15% compared to 0°. Therefore, by setting an appropriate nozzle attack angle, it is possible to significantly enhance both propulsion efficiency and cavitation resistance. Taking both hydrodynamic performance and cavitation resistance into account, the optimal configuration involves a straight-tube flow channel with 3–5 guide vanes, a vane thickness of 7 mm, and a 10° nozzle attack angle.