Abstract: CFD method was used to examine effects of primary rocket pressure on the ejection and combustion in the whole flow field in a center-strut Rocket Based Combined Cycle (RBCC) engine at subsonic flight conditions. The simulations show that both the bypass ratio and engine performance increase with the primary rocket pressure as high as 26MPa and meanwhile no Fabri-choking appears in the mixing duct. The bypass ratio increased to be 22.4% and 40.0% at Ma=0 and Ma=0.8，respectively. The thrust not only produced by the primary rocket but also by the combustor and the aft vehicle body increase with increasing the primary rocket pressure and as a result the engine thrust impulse increased up to 11.5% and 25.3% at Ma=0 and Ma=0.8，respectively. Based on the detailed flow studies in the paper，it is concluded that primary rocket pressure plays an important role to improve engine performance at subsonic flights for a RBCC configured in multiple modes.

Key words: Rocket based combined cycle；Ejector mode；Primary rocket；Bypass ratio

摘要： 为了研究火箭冲压组合动力循环(RBCC)发动机主火箭室压对引射模态发动机性能的影响，针对宽范围飞行的二元中心支板式构型，分析了引射模态亚声速飞行阶段发动机工作特点，采用发动机与飞行器前后体集成的全流道数值模拟计算方法，研究了主火箭室压对RBCC亚声速飞行阶段燃烧室流动燃烧及发动机性能的影响。结果表明:主火箭室压增至26MPa时，由于主火箭喷管面积扩张比相应增大，使得主火箭喷管出口射流欠膨胀程度没有增大，避免了Fabri壅塞现象的产生，同时增大的主火箭射流马赫数使主火箭射流对第一级凹腔下游二次流道的挤压作用明显减弱，综合作用使得Ma=0和Ma=0.8条件下引射比分别提高了22.4%和40.0%；全流道计算结果表明在亚声速飞行阶段，提高主火箭室压一方面提升了主火箭推力，另一方面提升了燃烧室及后体推力，综合作用使得发动机比冲分别提高了11.5%和25.3%。提高主火箭室压有利于提升宽范围飞行RBCC发动机亚声速飞行阶段发动机性能。

关键词: 火箭冲压组合动力循环；引射模态；主火箭；引射比