Influence Of Key Parameters On Hypersonic Boundary Layer Transition

Boundary layer transition is one of the key points to the aerodynamic and thermal design of hypersonic aircrafts.In recent years,the research on the mechanism of hypersonic boundary layer transition has become a prevalent issue in aerospace field.Freestream total temperature,wall temperature and nose bluntness are the three key factors that affects the transition of the boundary layer.It is very important to study the principle and internal discipline of these three key factors on the transition of the hypersonic boundary layer.The exploration of the mathematical relationship between the transition position of the boundary layer and the key factors is vital for an in-depth understanding of boundary layer transition mechanism.During the development of the hypersonic boundary layer,when the disturbance from freestream reaches a certain amplitude,the laminar flows break down and become turbulence.According to the characteristics of the linear growth of the perturbation in the boundary layer development,the linear stability analysis method is utilized to explore the change of growth rate and frequency of the instability of each mode in the transition process when the three important factors are changed.The effect of total temperature,wall temperature,and nose bluntness on hypersonic boundary layer instabilities are discussed.Utilizing the e-N method,N value of instability of different frequencies are solved.The statistical relationship between each key parameter and the transition position of the boundary layer are explored to build an applicable mathematical model.Through the Mach 6 wind tunnel test,the frequency and amplitude of instability of blunt cones with various bluntness radii are measured to verify the development of instability in the hypersonic blunt cone boundary layer and the influence of different bluntness on the stability of the boundary layer.As results indicate,for the Mach number greater than 4,the second-mode instability in the boundary layer begins to grow and gradually dominates the transition.The research is conducted based on the freestream of Mach 6 and unit Reynold number of 1×10⁷m^-1.When freestream total temperature or wall temperature increases,the hypersonic boundary layer flow become more stable.And the increased nose bluntness(0.05?5mm)has the same effect.However,due to the influences of the three factors on the background flow and instability differ,the evolution mechanism involved is also distinct.According to the influence research of various factors,exploring the transition mechanism of the boundary layer and the prediction of transition position,as well as mathematical modeling between the transition position and key factors of the boundary layer,provide numerical support for the prediction of the hypersonic boundary layer transition in engineering.