Characteritics Of Shock Train In The Flowfield With Supersonic Mixing Layer

Rocket-scramjet combined engine is an efficienty way to extend the working range of scramjet.The outflow of rocket and scramjet enter the mixing chamber at the same time and form a complex background flowfield with supersonic mixing layer,which make a significant impact on the shock train within the engine.To help understand the highly complex flowfield in the mixer and clarify the key factors influencing the mixer performance to sustain backpressure,in this paper,the numerical simulation and theory analysis were conducted to study the complex flowield.Firstly,the numerical research on the supersonic flow patterns in the mixer of Rocket-scramjet combined engine was conducted under the flight condition of Mach 3 and the height of 12 km.Two types of “shock-train/mixing-layer/shock-train” flow patterns occur in the mixer due to the interaction of shock train and supersonic mixing layer.By clarifying the fine flow characteristics,a preliminary exploration on the fluid mechanism is made.And,the paper summarizes and identify three main influencing factors of the matching performance of Mach numbers,static pressures and static temperatures.Secondly,a simplified two dimensional mixer model with constant area is employed to study the shock train in the flowfield within supersonic mixing layer.Then,the numerical simulations were carried out at the various Mach number of inlet1 and inlet 2 respectively to study the influence of inflow Mach number on the shock train.It is shown that five types of shock train occurs in the mixer.And,in this paper,a new type of shock train in ducts is defined as ” Inverse normal shock-train”,in which the leading shock is similar to a double inverse Mach reflection system but distinct from it.Then,Combining the free-interaction theory with shock wave-Mach number gradient interaction model,the shock polar is used to conduct a detailed analysis to clarify the influence of rocket exhaust Mach on the pattern of leading shock.Finally,the shock train in the mismatch background flowfield with supersonic mixing layer is studied.And,comparing the flowfields with various the pressure ratio between the rocket exhaust and ramjet airflow,the motions of shock train are emphatically analyzed.The background shock waves interacts with the shock train and seperated zones,which has a great influence on the patterns of shock train.And,the adverse pressure gradient due to the interaction of background shock waves and wall boundary layer mainly leads to the fast shock movement.Then,the effect of rocket-ramjet static temperature ratio on the shock train is analyzed.The higher static temperature ratio leads to the less ability to sustain adverse pressure.