Research On Motion Of Shock Train In The Isolator With The Bump

The isolation is a buffer between the inlet and the combustion chamber of the scramjet engine.The aircraft needs more power and heat release during the acceleration process.The shock train in the isolation section moves to the inlet under the pressure of the combustion chamber.In order to prevent the shock train from being pushed out of the inlet,the position of the shock train is monitored to facilitate the margin control of the engine.When the airflow passes through the air inlet,a shock wave is inevitably formed.The shock wave reflects and intersects in the isolation section,which is called backwave.Due to the interaction between the shock wave and the boundary layer,there is pressure gradient in the wall pressure of the isolation.The shock train exhibits a jump and an oscillating motion characteristic during the upstream movement,which is unfavorable for shock train position monitoring.Therefore,the bump is used to change the flow field in the isolation,thereby changing the motion characteristics of the shock train.Firstly,th e design of the bump is carried out and the influence of the bump parameters on the background wave system is analyzed.Secondly,the motion characteristics of the shock train under the bump control are studied experimentally.Finally,the influence of the bump on the performance parameters of the isolated section is analyzed.The work carried out by this topic is as follows:Firstly,the design method of bump is studied to change the background wave system in the isolation.The bump weakens the shock wave boundary layer interaction by deflecting the airflow in the boundary layer before SWBLI.The shape of bump is approximated by the fold line,and the fold line coordinates can be obtained by the relationship between the pressure ratio and the airflow deflection which is caused by shockwave.The numerical simulation method is used to analyze the influence of the geometric parameters of the bump and the installation position on the backwave of the isolation.In the rectangular isolation,the backwave has a unilateral multi-action mode and an multilateral multi-action mode.When the shocktrain moves to the region of unilateral multi-action mode,the shock wave will jump and oscillate.The effect of the bump on the unilateral multi-mode in the isolated segment can be divided into direct action and reflection.Each action mode is divided into two aspects,which is included acting on the upstream shock and acting on the downstream shock.Secondly,in the ground experimental system,the motion characteristics of the shock train under the bump control are studied.The difference of the height and the installation position of the bump will make the backwave different,and the motion characteristics of the shock train will be different.When the bump directly acts on the upstream shock wave,the bump which height is different are studied.Due to the reduction of the reverse pressure gradient at the upstream shock wave and the acceleration of the airflow caused by the bump,the jump of the shock train is suppressed.The speed decreases and as the height of the bulge increases,the position after the jump is closer to the downstream,but the reverse pressure gradient at the downstream shock increases,and the oscillation characteristics of the shock train become stronger.When the installation position of the bump is different,the action modes for the single-sided multi-mode is also different.When the bump is installed on the bottom wall and directly acts on the downstream shock wave,the jump characteristic of the shock train becomes weak,and the shock train movement is more tortuous.When the bump is installed on the upper wall,it is a reflection effect on the single-sided multi-mode.If the upstream shock is reflected,the reverse pressure gradient at the downstream shock will be greatly increased,the oscillation characteristic of the shock train will be intensified,and the movement will be more tortuous;During the downstream shock reflection,the reverse pressure gradient at the downstream shock is greatly reduced,the shock train oscillation characteristics are weakened,and the amplitude and velocity of the jump are also reduced.Finally,the influence of the bump on the performance parameters of the isolation is analyzed.Because of the direct action on the upstream shock,the bulge hinders the jump of the shock train,and the isolation's resistance to backpressure is slightly improved.In the other three modes,the isolation's resistance to backpressure is slightly reduced.The bump is disturbance to the supersonic flow,which will form a separate shock wave and reattach shock wave.Therefore,when the bump is installed in the isolation,the recovery cofficient of the total pressure in the isolation is slightly reduced.The bump forms a raised structure in the isolation section,which is subject to additional pressure.Therefore,when the bulge directly acts on the upstream shock wave,the resistance of the isolation section is increased.When the bulge is installed on the upper wall,the upper wall will also bear additional pressure,but the friction is reduced,so the resistance is also reduced.When the bulge directly acts on the downstream shock,the pressure direction is opposite to that of other bumps so the resistance of the isolation section is also reduced.