Characteristics Of Shock Train Structure And Unsteady Motion In A Mixing Duct

There exist complex and unsteady flow disturbance in the shock train flow field of the mixing duct,including shock-shock interaction,shock-mixing layer interaction,shockboundary layer interaction,flow separation and so on.In order to understand the structure and the unsteady motion characteristics of the shock train,experiment and numerical calculation were conducted to study the complex flow field.Firstly,the background flow field in the mixing duct is studied.By analyzing the local flow field of area at the rear edge of the clapboard,it is concluded that the mixing layer and the initial shocks together account for the complex background flow structures.The match relationships of static pressure and Ma between the primary and secondary flow significantly affect the direction of mixing layer development and the structure of background flow field.Three types of background flow field are proposed,namely shockscatter flow field,shock-overlap flow field and fully matched flow field.Secondly,the shock train flow field in the mixing duct is studied.The match relationships of static pressure and Ma between the primary and secondary flow have an impact on the shape of the separation shock and shock refraction type and 4 typical shock train structures are obtained by comparison and analysis.In addition,multiple flow disturbances in the fine flow field are investigated,which indicate that the fully matched flow field has the characteristics of sub-super-sub-sonic flow.Thirdly,the unsteady motion characteristics of the shock train in the mixing duct are studied.Based on the analysis of the forward motion process,the influence of the wall pressure gradient on the velocity variation of shock train is studied and the wall pressure match hypothesis is proposed to explain the jump and slow motion patterns.In addition,the structure variation of the shock train during the movement is also analyzed.To clarify the influence of the inflow parameters on the shock train structure,the shock polar and wavefront Ma contour lines are used to conduct the detailed analysis.Finally,the hysteresis phenomenon of the shock train motion is studied.Steady state of the slow movement pattern,unsteady state of the jump movement pattern and the mutual transformation between the states are analyzed.It is discovered that the wall pressure gradient is a dormant factor in the hysteresis phenomenon.