耦合尾喷管堵盖运动的水下固体火箭发动机点火启动过程特性

Characteristics of Ignition Start-up Process of Underwater Solid Rocket Motor with the Effect of Nozzle Closure

为研究水下固体火箭发动机点火启动过程的流场特征与工作特性,对尾喷管堵盖分离约束下的点火燃气泡演化过程进行数值模拟。采用流体体积多相流模型与动网格技术,建立耦合喷管堵盖运动的水下燃气射流仿真模型。对点火初期燃气泡形貌瞬态演化和流场参数的振荡特性进行分析,揭示变深度下发动机点火的初始推力脉动特征及形成机制。研究结果表明:点火开盖初期压差驱动堵盖强烈地冲击液相,尾壁空间产生高压区形成初始推力峰;点火深度越深,燃气泡沿轴向的增长速度越慢、长度越短,颈部出现收缩时刻越提前,流场参数和发动机推力的脉动特性越强;深水下燃气泡颈部收缩后,发动机喷口激波系出现往复振荡,导致尾壁空间产生压力振荡形成多个脉动推力峰,激波系的不稳定运动是推力出现脉动的主导因素。

To investigate the flow field and working characteristics of the underwater solid rocket motor at the initial stage of ignition,the gas bubble evolution process under the constraint of nozzle closure separation is numerically simulated.Based on the VOF multiphase model and dynamic mesh technique,a numerical model of underwater gas jet with the effect of nozzle closure is established.The transient evolution of gas bubble morphology and the oscillation characteristics of flow field parameters are analyzed.The characteristics and formation mechanism of initial thrust pulsation after ignition at variable depths are revealed.The results show that:at the initial stage of nozzle opening,the pressure difference drives the closure to strongly impact the liquid phase,causing a high pressure zone in the tail wall space and the formation of an initial thrust peak;as the ignition depth increases,the axial growth rate is slower and the length becomes shorter,the gas bubble has neck contraction in advance,and the pulsation characteristics of the flow field parameters and thrust of the motor become stronger;at the initial stage of ignition in deep water,the shock wave near nozzle exit has reciprocating oscillations,and the pressure oscillation in the tail wall space forms multiple fluctuating thrust peaks.It is demonstrated that the unstable motion of shock waves is the leading factor of thrust pulsation.