Waterjet–hull interaction is the hot point and research focus in the research of waterjet-propelled crafts. This paper presents numerical studies on the interaction between a waterjet system and a catamaran. Numerical simulations of both bare hull and self-propulsion hull were carried out based on the URANS method. The SST k-ω model is selected for the closure of the URANS equations. The level set method together with the dynamic overset grid approach is used for the simulations. The body force model with the PI speed controller is used to simulate the rotational motion of the rotor in the simulations for the self-propulsion hull. Moreover, uncertainty analyses of the numerical method are conducted to verify the accuracy of the numerical solver. The numerical results of the bare hull and self-propulsion hull are compared in detail, such as the wave pattern, pressure distribution, hull attitude, and so on. The waterjet reduces the pressure on the hull surface near the stern and makes the height of the wave near the stern lower. This leads to a more violent change in hull attitude and the thrust deduction is positive, ranging from 0.1 to 0.2. The energy conversion is analyzed based on the ITTC recommended procedures, which shows the overall efficiency of the waterjet behind the hull is about 0.75~0.8 times the free stream efficiency.

The submerged waterjet exhibits advantages such as uniform inflow, minimal flow distortion, and excellent acoustic performance, making it particularly suitable for high-speed vessels. This study investigates the open-water characteristics of the submerged waterjet and develops a body force model for the submerged waterjet propulsion system. First, under uniform inflow conditions, numerical simulations were performed using the body force method by replacing the rotor with a virtual blade and simultaneously replacing both the rotor and stator. The results of the body force model were then compared in detail with those obtained using the sliding mesh method. Second, the influence of the inflow velocity plane position on the results of the body force model was analyzed. The results indicate that the body force method, which replaces both the rotor and stator with a virtual blade, fails to accurately simulate the forces acting on various components of the propeller and the true distribution of the propeller’s flow field. In contrast, the method that replaces only the rotor with a virtual blade produces results for component forces and flow fields that are largely consistent with the results of the sliding mesh method, demonstrating the stability and reliability of the body force model. Additionally, the position of the inflow velocity plane has no significant effect on the model’s computational results.