Numerical Study On Unsteady Characteristics Of Internal And External Flow And Starting Performance Of Inlet During Inlet Cover Separation Process Of Hypersonic Vehicle

Inlet cover protects the precise components in scramjet engine and decreases the control difficulty of fluctuation before the aircraft reaches to the relay condition,which is widely used in various high-speed aircrafts.In order to explore the unsteady characteristics of internal and external flow field during the inlet cover separation process,numerical calculations based on the dynamic grid technique are conducted.Firstly,the dynamic grid techniques are summarized based on the 2D inlet cover separation process.The smoothing and remeshing method,the overset method,the sliding and layering method were compared.All of them can capture the typical characteristics of the steady and unsteady flow.The advantages and disadvantages of each dynamic grid technique is summarized.Because the grid update of smoothing and remeshing method is easy to fail for complex models,and it is troublesome to divide the grid domain by the sliding and laying method,subsequent work is based on the overset method.Secondly,flow characteristics of 2D inlet on the inlet cover blocked and separation process are studied.A flow model based on forward facing step is proposed to improve the iteration speed of inlet cover blocked flow field,which can be inspired for rapid estimation of aerodynamic forces with large separation zone.The flow evolution of the inlet cover separation process is analyzed,and the variation characteristics of the separation zone in front of inlet cover are figured out.Thirdly,flow characteristics of 3D inlet on the inlet cover blocked and separation process under the working conditions are studied.The V-swept shock wave and the backward facing step both affect the internal flow.The time history of mass flow rate on the inlet throat is analyzed,and two formulas for predicting the movement of inlet cover are summarized.Fourthly,the flow variation during the inlet cover separation process under different freestream Mach number is studied.Three typical starting/unstarting flow evolution processes are analyzed.The mass flow surge on throat and the self-sustaining of shoulder separation zone which is induced by the V-shock wave are two important factor that causes inlet unstarts.Finally,three methods to improve the inlet starting performance based on inlet cover are proposed.The flow evolution on the inlet cover separation process under different opening time are analyzed.It is verified that the inlet starting performance can be improved by reducing the inlet cover’s mass,shifting the rotating axis backward and inlet cover modification.