| As a new propulsion system based on the detonation,ram rotating detonation engine has higher theoretical thermal cycle efficiency,smaller entropy increasing and more compact structure,which has a broad prospect in the future development.However,the unique ring structure of the isolator and the severe back pressure environment in the combustion chamber will put forward higher requirements for the isolator of engine.In this paper,the numerical simulation method is used to study the inflow and the fuel injection mixture in the isolator under the condition of detonation wave back pressure.Firstly,in this paper,the flow field of the three-dimensional annular isolator under the simulated rotating detonation wave,and the flow field structure of the annular isolator is preliminarily understood,and the influencing factors are analyzed.In the annular isolator,the first shock wave and the rotating oblique shock wave at the downstream are used to realize the deceleration and pressurization of the air flow.The first shock wave is a circular shock wave perpendicular to the axis,which represents the range of the flow field that the downstream simulated rotating detonation wave can affect,which can well explain the anti-backpressure performance of the isolator.The influence of the expansion ratio on the flow field in the annular isolator is studied.The flow field of the straight annular isolator is stable with strong regularity,but its anti-backpressure ability is weak;with the increase of expansion ratio,the separation area begins to appear,and with the increase of expansion ratio,the instability of flow field structure increases gradually,the main flow direction begins to deflect,but the influence range of the outlet rotating backpressure decreases continuously.So that the anti-backpressure ability of the isolator increases continuously.The influence of the parameters of the outlet rotating backpressure on the flow field of the isolator is summarized.It is found that the increase of the backpressure frequency will lead to the decrease of the disturbance area and increase the anti-backpressure performance,but at the same time,it will lead to the increase of the total pressure loss.The influence area of the outlet rotating backpressure will increase with the increase of the amplitude of the pulsation,and the high amplitude of the pulsation will also lead to the increase of the strength of the rotating oblique shock wave,which will lead to the increase of the total pressure loss.Subsequently,the mixing characteristics of the fuel injection under the rotating back-pressure was analyzed.The influence of the backpressure parameters on the injection mixing efficiency in the isolator is studied from the injection depth,mixing efficiency and total pressure loss.Fuel injection will block the propagation of the oblique shock wave,reduce the influence area of the outlet backpressure,and improve the anti-backpressure ability of the isolator.Moreover,the injection can restrain the separation zone and increase the stability of the flow field.The front of the injection position can increase the mixing efficiency and penetration depth of the fuel,and the total pressure loss can also be reduced.The influence of pulsation amplitude on the mixing efficiency is not great,and the increase of pulsation amplitude can slightly increase the mixing efficiency.Finally,the numerical simulation of the whole rotating detonation engine is carried out to analyze the influence of the real rotating detonation wave on the flow field structure in the isolator.A detonation ignite mode for viscous case is proposed.By comparing the propagation of rotating detonation wave with different Mach numbers,it is found that the combustion state of detonation wave with Mach 1.75 is the best.Mach1.5 is the second,and that with Mach 2.0 is the worst.With the increase of Mach number,the separation region of the isolator also increases,and the stability of the isolator becomes worse. |
