RBCC发动机的引射模态是使RBCC飞行器实现低速甚至零速起飞的关键，其采用火箭射流为来流进行引射增压以增强冲压流动的做功能力，同时也利用火箭本身产生额外推力。但这就造成了RBCC发动机在引射模态下比冲性能较低，完成飞行器加速所需的燃料较多，极大地影响飞行器的整体运载效率。因此，对于RBCC发动机在引射模态下的性能研究就显得至关重要。不同于冲压发动机，RBCC发动机由于在流道内安装了引射火箭，故发动机内不仅存在进气道流动和燃烧流动之间的匹配，还存在火箭射流与进气道、燃烧室内流动间的匹配，使得流态愈发复杂。而发动机内的流动形态又直接决定了发动机性能，故深化发动机内的流动匹配研究对于发动机的性能优化具有重要指导意义。

本文利用数值仿真方法和理论手段，对于RBCC发动机在引射模态下的纯引射流态和引射补燃流态进行了研究。基于数值方法深入探究了火箭主流状态对于引射流态转变的影响规律以及火箭与进气道、燃烧室匹配下的流态特性，并结合气动理论揭示了不同引射流态的相互转换机制和迟滞变化原理，掌握了火箭主流与进气道流动、燃烧室压力匹配的物理机制。最终通过以上认识建立了一套用于评估RBCC发动机在引射模态下流态和性能的快速分析方法。

首先，采用定常二维数值模拟方法研究了火箭主流总温、总压和组分变化对于引射流态和性能的影响规律，并关注了引射流动在反压变化过程中的演化过程。发现引射流动存在两种典型的流动形态，这两种流态在引射能力和抗反压能力上互有优势，会随着火箭主流状态或者发动机反压的变化而发生相互转换，且转换过程存在迟滞现象。经过非定常数值计算和气动理论分析，发现是高温火箭主流与空气来流掺混形成的高压造成了引射流态的转换，而转换中的迟滞现象则是维持不同流态所需的极限反压不一致导致的。

然后通过数值仿真方法对于火箭主流与进气道、燃烧室之间的流动匹配进行了系统研究。研究发现进气道喉道通过和火箭主流的耦合作用不仅会造成引射流态发生转变的总温点相比于无进气道喉道约束工况有所升高，还会限制火箭主流在高速飞行工况下的引射能力。尾喷管喉道尺寸必须与火箭主流的抗反压能力相匹配才能在提高燃烧压力的同时维持引射流量的稳定，以实现发动机的高比冲性能。基于气动、燃烧理论分析得到了RBCC发动机在引射模态下的所有全流道流动图谱，通过分析认为在进气道、混合段和燃烧室内均产生壅塞的流动形态能表现出相对最优的发动机推力和比冲性能。

最后，着眼于快速分析RBCC发动机在引射模态下的流态及性能的需求，基于热完全气体模型建立了一套简化建模分析方法：在进气道和混合段采用基于上下游流动匹配的零维方法，而对于流动较复杂的燃烧室采用基于求解Euler方程组的准一维方法。利用该快速分析方法对于进气道喉道、混合段和燃烧室均处于壅塞状态的流态进行了计算研究。发现增大火箭主流总压能提高发动机的整机推力，但对比冲性能不产生积极作用。在固定发动机出口面积下，增大火箭主流出口面积对于发动机冲压推力的增益并不显著，且由于减小了发动机引射比，导致发动机的整体比冲性能下降明显。火箭主流总温的提高会通过降低燃烧室入口总压和燃料燃烧效率的方式降低发动机冲压推力，但总温升高对火箭推力/比冲性能的提高有积极意义（总温不超过火箭材料的承受极限），故在实际发动机设计中要对以上两方面进行综合考量。通过调节火箭主流出口马赫数，可使固定总压、总温和出口面积的火箭主流与不同飞行马赫数下的发动机内冲压流动进行匹配，使发动机内流动在喉道、混合段和燃烧室处于壅塞状态。该简化建模方法可为发动机的前期理论设计提供方向上的指导。

The ejection mode of the RBCC engine is the key to enable the RBCC aircraft to achieve low or even zero speed takeoff. It uses the rocket jet to help pump more air into the engine and pressurize the flow to improve its work potential, and also uses the rocket itself to generate additional thrust for the engine. However, this results in the lower specific impulse performance of the RBCC engine in the ejection mode, and more fuel is required to complete the acceleration of the aircraft, which greatly affects the overall carrying efficiency of the aircraft. Therefore, it is of great importance to study the performance of RBCC engine in ejection mode. Unlike ramjet engines, RBCC engines are equipped with the ejector rocket, so there is not only a match between the inlet flow and combustion flow in the engine, but also the match between the rocket jet and the flow in the inlet and combustion chamber, it makes the flow pattern much more complicated. The flow pattern in the engine directly determines the performance of the engine, so deepening the research on the flow matching in the engine has important guiding significance for the optimization of engine performance.

In this paper, numerical simulation methods and theoretical methods are used to study the pure jet flow regime and the jet supplementary combustion flow regime of the RBCC engine in the ejection mode. Based on numerical methods, the influence of the the rocket jet on the transformation of jet flow regimes and the flow regime characteristics under the matching of the rocket, inlet and combustion chamber are deeply explored. Combined with aerodynamic theory, the mutual conversion mechanism and hysteresis changes of different jet flow regimes are revealed. Also master the physical mechanism of rocket flow and inlet flow and combustion chamber pressure matching. Finally, based on the above knowledge, a set of rapid analysis methods for evaluating the flow pattern and performance of the RBCC engine in the ejection mode is established.

First, the steady two-dimensional numerical simulation method is used to study the influence of the total temperature, total pressure and composition of the rocket jet on the jet flow regime and performance at low speeds, and the evolution process of the jet flow in the back pressure change process is paid attention to. It is found that there are two typical flow regimes of ejection flow. These two flow regimes have advantages in ejection ability or anti-backpressure ability over each other. They will be converted to each other as the state of the rocket flow or the engine backpressure changes, and the process has hysteresis. After unsteady numerical simulation and aerodynamic theory analysis, it is found that the high pressure formed by the mixing of the high-temperature rocket jet and the incoming air flow caused the transition of the jet flow regime, and the hysteresis in the transition is the caused by the inconsistency of limit back pressures required to maintain different flow regimes.

Through numerical simulation method, the flow matching between the rocket flow and the inlet and combustion chamber is systematically studied. It is found that under the condition that the inlet throat restricts the ejection flow, the ejection flow will also undergo a flow state hysteresis change with the change of the total temperature of the primary flow, but the decrease of the ejection flow rate causes the flow regimes to change at higher total temperatures compared to the ejection flow under the condition without inlet throat restricting the ejection flow. The rocket jet has the effect of ejecting air only under low subsonic flight conditions, and only exerts a pressurizing effect at higher flight speeds. The use of Laval nozzles can greatly increase the pressure in the combustion chamber, but the high pressure of the combustion chamber must be matched by the anti-backpressure capability of the rocket jet to maintain the stability of the ejection flow, so that the engine has better thrust and specific impulse performance. Based on the numerical results and theoretical analysis, all the flow patterns of the RBCC engine in the ejection mode are summarized and evaluated. It is believed that the flow patterns that produce choking in the intake duct, mixing section and combustion chamber can show a relatively optimal engine thrust and specific impulse performance.

Focusing on requirements of the rapid analysis of the flow pattern and performance of the RBCC engine in the ejection mode, a simplified modeling and analysis method is established based on the thermally perfect gas model. In the inlet and mixing section, a zero-dimensional method based on upstream and downstream flow matching is used, and a quasi-one-dimensional method based on solving Euler equations is used for the combustion chamber with more complicated flow. Using this rapid analysis method, the flow pattern in which the inlet throat, mixing section and combustion chamber are all in a choked state is studied. It is found that increasing the total pressure of the rocket jet can increase the thrust of the engine, but does not have a positive effect on the impulse performance. Under the fixed engine exit area, increasing the rocket’s exit area does not significantly increase the ram thrust of the engine, and due to the reduction of the engine ejection ratio, the overall specific impulse performance of the engine decreases significantly. The increase in the total temperature of the rocket jet will reduce the ram thrust of the engine by reducing the total pressure at the inlet of the combustion chamber and the fuel combustion efficiency, but the increase in the total temperature has a positive effect on the improvement of the rocket’s thrust/specific impulse performance (the total temperature does not exceed the rocket material’s withstand limit), so the above two aspects should be comprehensively considered in the actual engine design. By adjusting the rocket flow outlet Mach number, the rocket flow with fixed total pressure, total temperature and outlet area can be matched with the ram flow in the engine under different flying Mach numbers, so that the flow can be choked in the inlet throat, mixing section and combustion chamber.

This paper has carried out a systematic study on the flow pattern of the RBCC engine in the ejection mode, revealed the change law of different ejection flow regimes and the hysteresis mechanism, obtained all the flow patterns of the ejection flow regime, and based on the established rapid analysis method for evaluating engine flow pattern and performance, the matching method of rocket jet and ram flow under different working conditions and the performance of the whole engine are studied, which provides a guiding direction for the design of RBCC engine.