Experimental Research On Ramp Flow Separation Control Based On Pulsed Jet Excitation

As a ubiquitous natural phenomenon,flow separation exists widely in the engineering field and daily life.Flow separation may cause a series of adverse effects,such as causing aircraft stalls and increasing energy consumption of automobiles and ships.At present,analyzing the flow separation phenomenon and suppressing the flow separation is one of the popular research contents of scholars at home and abroad.In recent years,researches on flow separation control have focused on adding flow control methods such as spoilers,pulse jet inhalation,and zero-mass jet.Among various control methods,the pulse jet active blowing control method has simple structure and energy consumption The advantages such as lower are widely used in active control technology.In this paper,a 25°back ramp is taken as the research object,and an experimental study of flow separation control based on pulse jet excitation is carried out.According to the influence of the flow control method on the control effect,various control methods are analyzed and compared,and the active control method of pulse blowing vertically upward through the slit is determined.In this paper,the25°back ramp experimental model is taken as the research object.A 1 mm wide slit is set at the front end of the position where the flow separation occurs on the back ramp.Make an impact,and then suppress flow separation.Before the flow control,the exit speed characteristics of the exciter have been measured,the exit speed of the exciter meets the experimental requirements,and the influence of the three parameters of the blower frequency,blowing duty-cycle and flow rate of the exciter on the separation control effect under unsteady state is measured to get the best control parameter value.The experiment found that under the optimal control parameters(pulse blowing frequency f_e=100 Hz,blowing duty-cycle?=0.5,blowing volume flow Q=120 L/min),the distance between the separation point and the re-adhesion point(recirculation bubble length)X_R/h is reduced by up to 40%,and flow separation is significantly inhibited.At this time,even if the outlet speed continues to increase,it will not change.Based on the experimental study of the control mechanism of the air blow by the slit actuator,the surface pressure above the ramp and the vortex frequency after the ramp separation were measured by the pressure scanning valve and the constant temperature hot wire anemometer.The analysis and measurement results show that the pulse blowing through the slit adds disturbance to the upper flow field.The disturbance increases the separated vortex release structure,and also enhances the energy transfer in the shear layer and the vortex release periodicity after the separation of the upper flow field at the separation point,the shedding vortex structure falls faster to the downstream plate,so the length of the recirculation bubble will be significantly reduced.At the same time,the recirculated bubbles after the control will be closer to the ramp,and the surface pressure coefficient of the ramp along the flow direction after the control has decreased significantly compared without the control situation.