The influence of crossflow velocities on hydrodynamic characteristics of the underwater vehicle with swing nozzle

Swing nozzle, as one of the underwater thrust vector control technologies, is a significant method to enhance the maneuverability and anti-interference ability of the underwater vehicles. In this paper, the Dynamic Fluid Body Interaction method coupled with Shear Stress Transport k–ω model, Volume of Fluid method, and Proportional-Derivative control method are used to simulate the underwater motion stage of the vehicle controlled by the swing nozzle under different crossflow velocities. Compared with typical experimental results, it is found that the numerical method can effectively capture the evolution of the tail cavity bubble and the thrust. As the crossflow velocity increases, the deviation of the tail cavity bubble from the symmetry axis of the underwater vehicle becomes more pronounced. Additionally, the reentrant flow exhibits a more significant deviation from the nozzle axis. This phenomenon contributes to the reduction of pressure fluctuations on the bottom of the underwater vehicle and mitigates transient impacts during the initial stage of ignition. Following ignition, the shock wave in the tail cavity bubble causes alternating positive and negative pressure differentials at the upstream and downstream surfaces of the underwater vehicle's tail section. It is an important factor causing the underwater vehicle's moment oscillation. It is also found that greater crossflow velocities can induce substantial pitch moment on the underwater vehicle, and the optimization of control parameters is required to enhance control system robustness.