The Optimization Design of the Nozzle Section for the Water Jet Propulsion System Applied in Jet Skis

The performance of a water jet propulsion system is related to the inlet duct, rotor, stator, and nozzle. Generally, the flow inlet design must fit the bottom line of the hull, and the design of the inlet duct is often limited by stern space. The entire section, from the rotor to the nozzle through the stator, must be designed based on system integration in that the individual performance of these three components will influence each other. Particularly, the section from the rotor to the nozzle significantly impacts the performance of a water jet propulsion system. This study focused on nozzle design and established referable analysis results to facilitate subsequent integrated studies on the design parameters regarding nozzle contour. Most existing studies concentrate on discussions on rotor design and the tip leakage flow of rotors or have replaced the existing complex computational domain with a simple flow field. However, research has yet to implement an integrated, optimal design of the section from the rotor to the nozzle. Given the above, our program conducted preliminary research on this system integration design issue, discussed the optimal nozzle for this section in-depth, and proposed design suggestions based on the findings. This program used an existing model as the design case. This study referred to the actual trial data as the design conditions for the proposed model. Unlike prior references' simple flow field form, this study added a jet ski geometry and free surface to the computational domain. After the linear hull shape was considered, the inflow in the inlet duct would be closer to the actual condition. Based on the numerical calculation result, this study recommends that the optimal nozzle outlet area should be 37% of the inlet area and that the nozzle contour should be linear. Furthermore, for the pump head, static pressure had a more significant impact than dynamic pressure.