The Control Mechanism Investigation Of Micro Jet Technology For Supersonic Flow Field

Supersonic aircraft is usually associated with complex flow field structure,for example,boundary transition,turbulent layer,shock wave,shock wave/boundary interaction,and they will adversely affect the aircraft performance,so need to use flow control method to improve it.As a kind of effective flow control technology,micro jet has obvious improvements for the shock wave,flow separation,and the unsteady pressure oscillation flow phenomenon of the supersonic flow field,and there is a broad application prospects in the field of supersonic flow control.An numerical investigation was conducted to study the influence of different micro jet on the supersonic flow field for a 24 degree compression corner.The ejecting direction is vertical to incoming flow.There produces bow shock wave,barrel shock wave,mach disk,and counter-rotating vortex pair under the interaction of micro jet and the supersonic flow.The downstream velocity of micro jet reduced by the bow shock wave can weaken the intensity of separation shock wave on the compression corner.As the main controller,high energy fluid is brought into the bottom of the boundary layer to make it to be fuller to strengthen the ability resisting the separation with the downwash effect of vortex pair.The control mechanism is explored from the injection total pressure,streamwise position of micro jet,and nozzle type in this paper.In the control investigation of different total pressure micro jet for the supersonic flow field,when the injection total pressure ratio(injection total pressure/free stream total pressure)is above 0.6,the vorticity decays weakly and the space between the vortex core and the wall is bigger so that higher energy fluid is brought into the bottom of the boundary layer near the wall and make it difficult to separate.Weighing the control result and injection power,the scheme,when the total pressure ratio is 0.6,is the best.The boundary layer separation area is restrained by nearly 70%,the distance of the intersection point of ? shock and the wall is reduced by almost 37%,and the separation shock intensity is weaken by nearly 12% under this scheme.In the control investigation of different position micro jet for the supersonic flow field,when the injection total pressure ratio is 0.6,the activation trend of the low energy near the wall of the boundary layer increases in the 15 times exit diameter,and then decreases downstream of the micro jet.Making full use of the control advantage within this distance is benefit to weaken the separation,so the micro jet placed around the separation position is best.Under this option,The boundary layer separation area is restrained by nearly 90%,the distance of the intersection point of ? shock and the wall is reduced by almost 40%,and the separation shock intensity is weaken by nearly 14%.In the control investigation of different style micro jet for the supersonic flow field,when the injection total pressure ratio is 0.6,the distance between the wall and the vortex core of the vortex generated by coupling of laval nozzle micro jet and mainstream is larger because of the higher exit velocity.Although the vortex strength is slightly weaker,the activation ability of the low energy near the wall of the boundary layer is stronger.Under its action,although the separation zone area isn't further decreased,the distance of separation position and reattachment position is cut more,by almost 70%.In addition,the distance of the intersection point of ? shock and the wall is reduced by almost 50%,and the separation shock intensity is weaken by nearly 15%.