反压诱导方式对超燃冲压发动机隔离段流动特性影响

为了探究传统机械限流方式同燃烧释热对隔离段流动特性影响的异同，采用实验结合数值计算的方法研究了限流方式与实际燃烧诱导压升的差异.使用氢燃料进行不同当量比的燃烧实验，并使用燃烧室出口安装楔块的方式进行限流实验，对比了来流条件相同，且隔离段出口压比相同时两种实验下的压力分布.使用经过验证的数值方法模拟了不同隔离段出口压力下燃烧状态及对应的限流状态，对比了两种状态下隔离段流场细节.实验结果表明:激波链即将进入隔离段时，两者的压力分布大致相同；激波链进入隔离段后，隔离段出口压比2.3，两者的壁面压力分布有明显差别.此状态下的计算结果表明:燃烧状态下隔离段内分离区首先出现于下壁面，激波链向上偏折；而限流状态分离区出现于上壁面，两者的流场会有一定差异.反压继续增大的计算结果表明:隔离段出口压比达3.0时，两者的隔离段内流场差别逐渐减小并最终趋于一致.燃烧反压场与限流实验的模拟反压场一致时，才能直接采用限流实验的结果评估反压对进气道的扰动风险. 

Effects of back pressure induction methods on scramjet isolator flow characteristics

Experimental and numerical methods were utilized to investigate the back pressure effect on isolator flow characteristics by combustion or by flow choking. Combustion experiment with different hydrogen fuel equivalent ratios and wedge-blocked were conducted under the same airflow condition and the same isolator exit pressure ratio. Combustion and corresponding flow choking situations with different isolator exit pressures were investigated numerially to compare the flowfield details in the isolator under two situations. Experimental results indicate that when the shock train is about to enter the isolator, the same pressure distribution is achieved with these two choking methods; but when the isolator exit pressure ratio reaches 2.3, which means the shock train has entered the isolator, there is a significant difference between these two situations.Numerial result for these two situations suggest that separation zone for the combustion situation originally appears in the lower wall, but in the flow choking situation it appears in the upper wall, indicating that the shock train under combustion situation deflects upward and differs from that under the flow choking situation. When isolator exit pressure ratio reaches 3.0, the difference between two situations decreases, indicating that the difference may disappear eventually with the increasing back pressure. These results show that, only when the back pressure field by combustion and by flow choking experiment simulation is confirmed similar, flow choking experiment result can be used to assess the inlet unstart risk by back pressure.