Flow structure and pressure pulsation characteristics of jet flow at the rear of underwater vehicle

This paper investigates the supersonic gas jet flow characteristics of an underwater vehicle at different vertical moving speeds using experimental and numerical methods. A high-speed camera was employed to capture the multiphase flow structures, and pressure sensors were used to measure the tail pressure of the underwater vehicle. Numerical simulations were performed based on the overset grid method, and vortex flow fields were used to visualize the multiphase flow structures. These results indicate that the jet flow characteristics of the underwater vehicle during vertical movement differ from those in a still-water environment. The smaller the expansion ratio of the nozzle and the higher the vertical velocity, the larger the amplitude of cavity oscillation. During the ventilation process, the bottom pressure of the vehicle shows a transient pressure peak, wide pulsation at the initial stage, high-frequency oscillation at the working stage, and stopped pulsation after the water outlet. The shear flow induced by the vehicle's high-speed motion can suppress high-frequency tail jet oscillation. Additionally, it is found that the tail bubble flow structures are influenced by jet state: under-expanded jets yield high-stiffness tail bubbles with near-field wave systems less affected by the bubble surface, whereas over-expanded jets bend after flow velocity decays to subsonic due to asymmetric cavity walls and vortex structures.