Investigations On Characteristics Of Supersonic Blunt Trailing Edge Mixing Layer And Its Active Control

Mixing layer as a key issue of combined engines has a significant impact on the performance of a combined engine.All along,researchers have studied the mixing layer extensively,hoping to master the flow mechanism of the mixing layer,and then provide guidance for the control of the mixing layer.In this paper,we study the supersonic blunt-trailing-edge mixing layer,which is more common in practical physics,and study the characteristics of the mixing layer with backflow zone.Two kinds of flow control methods(active and self-sustaining)are proposed to control the development of mxing layer actively.In this paper,the current research on the flow field structure of supersonic blunt-trailing-edge mixing layer is reviewed from the experimental point of view,the main influencing factors of the flow field,the research progress of turbulent mixing mechanism and blending control method is summarized.On this basis,an active blending control method based on synthetic jet is proposed.Based on the working pattern of aspirating wind tunnel,the dual Mach number nozzle method was used to design the supersonic blunt trailing mixing layer wind tunnel model.The design Mach numbers were 1.5 and 2.5 respectively.The actual flow Mach number was 1.37 and 2.39.In order to ensure the quality of the flow field on the upper and lower surfaces of the plate,the overall layout of the nozzle is that plate is set in the middle of the nozzle contours.Flow control components and plate integrated design,the way through the groove connection,to ensure tightness.At the same time,according to the preliminary simulation and literature research,designing two kinds of flow control components,active and self-sustaining.Establish the flow simulation model and verify the numerical method.Aiming at the complex flow pattern of supersonic blunt-trailing-edge mixing layer,a Dynamic Mode Decompositon(DMD)method is proposed.By analyzing the one-dimensional,two-dimensional and typical circular flow problem of cylinder,it is found that the DMD method not only has the ability of recognizing modes,but also obtains the spectral characteristics and growth characteristics of the corresponding modes,which is of great significance for the instability analysis.In the case of two-dimensional unsteady problems,the analysis produces two symmetrical modes that are only opposite in frequency,suggesting the assumption of the frequency domain,which is well explained.The experimental study on supersonic blunt-trailing-edge mixing layer was carried out.The fine structure of instantaneous flow field was obtained by NPLS system.Comparing with the typical supersonic mixing layer,it was found that turbulent flow was formed in the early development of mixing layer.The relationship between reattachment instability and blending instability,the influence of pressure mismatch and boundary layer transition on the supersonic blunt-trailing-mixing layer flow were studied.The experimental results show that the instability of reattach point is not related to the mixing instability of the re-developed mixing layer.The transition of the boundary layer has no significant effect on the mixing instability of the re-developed mixing layer.However,the pressure mismatch mainly results in re-developed mixing layer is biased to the low pressure side.Based on experimental methods,the effect of two kinds of flow control methods on flow field control are studied.Due to the quality of incoming flow and other reasons,no relevant results have been obtained.The large-eddy simulation is used to study the flow characteristics and control effects of the supersonic blunt-trailing-edge mixing layer and its two flow control methods(active and self-sustaining)in terms of flow field structure,wake characteristics and unsteady spectral characteristics.Under uncontrolled conditions,the flow field structure similar to the experiment results,but the simulation results showed the characteristics of regular changes.The strong instability appeared in the experiment did not appear.The mixing properties of the re-development mixing layer increased rapidly in the initial stage,then gentle gradually.Getting the evolution law of the instability of the flow field,and the feature frequency of re-developed mixing layer is 43 KHz.Under the control conditions,the active method has little change to the flow field,while the self-sustaining method has a good control effect,and the blending thickness increases nearly two times.Because the driving frequency of the films is much smaller than the characteristic frequency of the flow field,the effect of film vibration on flow field is not obvious.The DMD method is used to initially analyse the modes of the simulation structure and analyse the influence of different frequency modes on the characteristics of the flow field.The DMD method can obtain the characteristic frequency of the flow field which is consistent with the result of spectrum analysis.By means of corresponding mode superposition,the corresponding modes expression of the characteristic frequency in the flow field is obtained,which is of great significance for understanding the flow mechanism.