A Numerical Study Of The Evolution Of Perturbations In Hypersonic Flat Plate Boundary Layer At High Altitude

Velocity and temperature discontinuity on wall surface occure when sustained hypersonic flights fly at high altitude where air is rarefied, it is very different from supersonic flights. How the effect of low density on flow characteristic and drag is an important issue worth study.In this paper, Navier-Stokes equations and slip boundary conditions are used to study the evolution of 2-D disturbance in a hypersonic fate plate boundary layer with the oncoming flow of Mach number 8. The friction coefficient and heat transfer on surface of flat plate are also studied to compare with those of non-slip boundary conditions. The conclusions are:1.The effect of non-liner can't be ignored when the amplitude of T-S wave reach to 0.007 in 2-D hypersonic flat plate boundary layer. It can be seen by the change of instability region and the fluctuation of upper branch of neutral curve. Growth rate of perturbation become positive and negative alternatively when go through the branch and the amplitude growth curve fluctuates. But the same result hasn't occur when study evolution of disturbance at low altitude with Mach=8 and high altitude with Mach=4.5.2. The friction coefficient and heat transfer become smaller along the streamwise. As temperature of the wall decreases, friction coefficient diminishes whereas heat transfer increases.3. In the 2-D wedge flow. As the angle of the wedge increase, the value of Kn becomes larger.4. Compared with the result with non-slip boundary conditions, the friction coefficient and heat transfer on the wall decreases under slip boundary conditions.