Flow characteristics of underwater supersonic gas jets formed by the scarfed nozzle

Underwater supersonic gas jets formed by the scarfed nozzle are commonly found in underwater propulsion systems. The investigation is conducted using both experimental and numerical methods. High-speed imaging and image processing techniques are employed in the experiments, and the Volume of Fluid (VOF) model is used in the numerical simulations. The effects of different nozzle expansion states on the jet flow characteristics are studied. The study focuses on the flow dynamics and instabilities of the underwater gas jets, considering two stages of jet formation: the initial gas bubble and the stable conical structure. It is found that asymmetric characteristics appear in the jet morphology, pressure and gas-liquid interface oscillations, and thrust of the scarfed nozzle. Significant pressure oscillations occur in the initial stage. However, the gas-liquid interface continues to exhibit oscillations with asymmetric behavior, which weakens as the inlet pressure increases. The deflection characteristics of the thrust direction are heavily influenced by the non-axisymmetric geometry and lateral forces exerted on the asymmetric wall of the nozzle. These findings contribute to a more profound comprehension of the intricate mechanism of underwater gas jets of the scarfed nozzle, thereby facilitating the development of more efficient and stable underwater propulsion systems.