Tuning the multi-phase flow characteristics of underwater supersonic gas jet with inertial solid particles

The multi-phase flow characteristics of underwater supersonic jet are significant to the overall performance of underwater solid rocket motor. In this study, a gas-solid-liquid multi-phase flow model considering the effect of solid particles is established accounting for the supersonic over-expanded gas jet underwater. Parametric analysis of the underwater depth and the diameter of the solid particles (Al₂O₃) are conducted to investigate the tuning effect of solid particles on the multi-phase flow characteristics of the underwater supersonic gas jet. The results show that the multi-phase flow structure is greatly affected by interaction between the supersonic gas jet and water. With the increase of underwater depth, the size of gas bubbles decreases due to deformation and breakup processes. Under the influence of shear force between the gas jet and water, the necking phenomenon downstream of the nozzle is enhanced, leading to the fluctuations of pressure and velocity of the jet. For the gas jet without solid particles, with increase of time, the structure of the gas jet is heavily deformed, which experiences high interface instability due to the shear effect between gas jet and water. The existence of solid particles significantly inhibits the fluctuations of the gas jet. However, the addition of either too large or too small particles leads to locally reversed pressure gradient. Compared with the gas jet with particles of 100 μm, significant discontinuity occurs in the gas jet with d = 80 and 120 μm particles. The addition of solid particles with medium size ( d = 100 μm) leads to a decrease by 45% in the local pressure fluctuation magnitude. The tuning effects of the medium-size solid particles are related to the suppression of high-frequency Kelvin-Helmholtz instability in the near field and the suppression of low-frequency Rayleigh-Taylor instability in the far field.