水下固体火箭发动机垂直气体射流结构和推力影响研究

为了探究高背压水介质条件下，固体火箭发动机垂直气体射流在浮力影响下的流场结构和发动机推力特点，建立了轴对称几何模型，在考虑有/无浮力的条件下，采用VOF(Volume of Fluid)多相流模型进行气体-水两相耦合仿真计算，获取尾流气体射流流场结构，以及发动机尾部壁面受力和推力振荡曲线进行分析。研究结果表明，考虑浮力的仿真结果更加符合试验结果；射流动量段气体的马赫数分布会导致喷管出口附近的气-水界面产生周期性胀鼓-颈缩，从而引起尾部空间背压振荡，在设计工况下，尾部压力变化范围为环境水深压强的0.327到2.43倍；背压振荡将引起尾壁面受力振荡和推力振荡，振荡频率为736.89Hz；气体射流喷出过程中，气-水界面由速度梯度主导的开尔文-亥姆赫兹（K-H）不稳定性逐渐转变为由重力和浮力主导的瑞利-泰勒（R-T）不稳定性。

Flow Structures of Vertical Gaseous Jets and Effects of Thrust of Underwater Solid Rocket Motor

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 will lead to the bulging and necking of the gas and water interfaces, and this will furtherly result 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.