非对称喷管起动过程数值模拟研究

Numerical Simulation of Asymmetric Nozzle Starting Process

关键词:  超燃冲压发动机  起动过程  喷管  激波  数值模拟

Key words:  Scramjet  Starting process  Nozzle  Shock  Numerical stmulation

摘要:

为研究起动过程中激波运动对非对称喷管性能的影响，采用非定常数值模拟方法对基于最大推力理论设计的超燃冲压发动机喷管地面起动过程开展了研究。结果表明，喷管起动过程中由于进口气体与管内气体压比较大，主激波形成并向下游运动；为匹配主激波扫掠后的高压区和进口气流膨胀形成的低压区，形成一道左行的二次激波。起动过程可分成两个阶段：第一阶段是主激波与二次激波共同扫掠阶段，主激波在喷管进口产生并向下游运动，此阶段推力大幅上升；当主激波扫过上壁面末端时喷管升力大幅升高。第二阶段是二次激波扫掠阶段，左行的二次激波随主流向下游运动，推力小幅下降并趋于稳定，升力显著降低并趋于稳定。进一步研究了运动激波速度的变化，发现主激波速度持续减小，二次激波相对于主流的左行速度在喷管内和离开喷管后分别增大和减小。进一步地，对比了一维运动激波理论推导出的激波速度和数值模拟的激波速度，发现可以用一维运动激波理论预测起动时间，但需考虑喷管下壁面末端膨胀波的影响。

Abstract:

To study the influence of shock motion on the asymmetric nozzle performance during the ground starting process of scramjet nozzle， the unsteady numerical simulation method is used to simulate the starting process of the scramjet nozzle designed by the maximum thrust theory. During the nozzle starting process， the primary shock is formed and moves downstream due to the high-pressure radio of the airflow in the inlet to the airflow in the nozzle. In order to match the high-pressure region swept by the primary shock and the low-pressure region formed by the expansion of the inlet flow， a left-running secondary shock is formed. The nozzle starting process can be divided into two stages. In the first stage， the primary shock wave and the secondary shock sweep together. The primary shock is generated at the nozzle inlet and moves downstream， and the thrust increases significantly. When the primary shock sweeps the end of the upper wall， the lift increases substantially. The second stage is the sweep stage of the secondary shock. The secondary left-running shock moves downstream with the core flow. The thrust decreases slightly and tends to be stable， and the lift decrease significantly and tends to be stable. Then， the evolution mechanism of moving shock in the starting process is further studied， the change of shock velocity is analyzed. The results show that the velocity of the primary shock continues to decrease， and the left-hand velocity of the secondary shock wave relative to the core flow increases in the nozzle and decreases after leaving the nozzle. Furthermore， the shock velocity derived from one-dimensional moving shock wave theory and the numerical simulation shock velocity are compared， it is found that the starting time can be predicted by one-dimensional moving shock theory， but the influence of the expansion wave at the bottom of the nozzle should be considered.