Study On The Transient Separation Process Of Coanda Wall-attached Jet Under Passive Controlled Excitation

Fluid thrust vector technology is a research hotspot and development direction in the field of thrust vector technology,which can significantly enhance the mobility and agility of aircraft.Fluid thrust vectoring technology based on Coanda effect has advantages of large vector angle,high control efficiency and small thrust loss,but the problems of uncontrolled wall-separation and wall-attachment of jet seriously hinder its further development and application.The research designs a fluid thrust vectoring nozzle based on passive secondary flow,and uncontrolled wall-separation and wallattachment of jet in the control process are studied.Firstly,the characteristics of steady-state jet flow are studied.The spatial flow structure of steadystate separated jet,steady-state wall-attached jet and Coanda wall flow structure of nozzle are clarified.The pressure distribution of steady-state wall-attached jet is obtained,and pressure characteristics of various near wall flow structures such as separation bubble and reattachment line are obtained.Secondly,the characteristics of jet deflection flow field are studied.Variations of flow fields and structures such as separation bubble and reattachment line in the process of wall-attachment and wallseparation are proposed.According to these variations,the process of wall-attachment and wallseparation are divided into different stages.The results show that vector deflections of the process of wall-attachment and wall-separation are both discontinuous.The process of wall-attachment can be divided into three phases: Slow Deflection,Quick Deflection and Separation Bubble Shrinking.Similarly,the process of wall-separation can be divided into three phases: Slow Separation,Separation Bubble Rupture and Quick Separation.Finally,the mechanical characteristics of jet deflection are studied.The variations of nozzle vectoring thrust and the pressure distribution of Coanda wall in the process of wall-attachment and wallseparation are obtained.Combined with the characteristics of jet deflection flow field and the mechanical characteristics of jet deflection,the process of wall-attachment and wall-separation are comprehensively expounded.The study in this paper lays a theoretical foundation for the design of fluid thrust vector device and the optimization of thrust vector deflection control efficiency.