水下固体火箭发动机垂直气体射流结构和推力影响研究

To investigate the flow structure of vertical gaseous jets of solid rocket motor in deep water under the effect of buoyancy, and to reveal the characteristics of thrust, the axisymmetric geometric model was established for numerical studies. VOF (Volume of fluid) multi-phase model was adopted in gas-water two-phase coupling simulation in conditions with or without buoyancy. The feature of two-phase flow field beyond the nozzle exit was analysed and oscillation of integration of pressure on the back walls and thrust of the motor were monitored. It is concluded that simulation results with buoyancy are more consistent with tests. The profile of Mach number in gas of momentum part leads to the bulging and necking of the gas and water interfaces, and this furtherly results in the oscillation of back pressure. The range of back pressure under design conditions changes from 0.327 to 2.43 times of the ambient pressure. The unstable back pressure leads to the oscillation of integration of pressure on the back walls and thrust of the motor with frequency of 736.89Hz. In the whole jetting process, the evolution of gas-water interfaces is gradually transformed from Kelvin-Helmholtz (K-H) instability dominated by velocity gradient to Rayleigh-Taylor (R-T) instability dominated by gravity and buoyancy.