The Transition Prediction Of Boundary Layers On A Hypersonic Plat With Consideration Of The Variable Specific Heat

Research on the transition problem of hypersonic boundary layers needs to consider the real gas effects due to the high air temperature. That is in order to successfully predict the transition locations of hypersonic boundary layers, we must consider the effects of temperature on the thermophysical parameters. When the temperature is less than 2500K, there exists a kind of fixed relationship between the temperature and the specific heat ratio. Considering the differences between the specific heat ratio varying with temperature and the constant specific heat ratio as 1.4 etc., this paper analyzes the stability of flows of Mach 6 and 8 boundary layers on a hypersonic plat with isothermal walls, and using the improved e-N method predict their transition locations. The following conclusions can be drawn:1 After Stability Analysis of boundary layers on a hypersonic plat with isothermal walls, we find it is difficult to obtain an equivalent specific heat ratio for simplified calculation, it is needed to take the impact of temperature on specific heat ratio ? into account, in Numerical Calculation the values of ? must be in accordance with the temperature of flow field in the boundary layer. To predict the transition location, it is no longer appropriate to take specific heat ratio as 1.4.2 The wall temperature has influence on the stability and transition locations of the boundary layer as follows: with the decrease of wall temperature, the first mode neutral curve retreats back and becomes narrow, when the wall temperature drops to some extent the first mode neutral curve disappears; The second mode neutral curve shows a falling and forward tendency with the decrease of wall temperature, which means expansion of the region instability and decrease of the frequency instability. The transition location of the first mode drops behind with the decrease of wall temperature, but the second mode is just opposite.3 For the boundary layers of the adiabatic wall, the transition location of Mach 8 is close to the one of Mach 6, for the boundary layers of isothermal wall whose wall temperatures are the same multiples of the temperatures of their adiabatic walls conditions, the transition locations of Mach 6 is behind the ones of Mach 8. For the boundary layers of the adiabatic wall and isothermal wall of which the temperature is not too much lower than adiabatic wall (the wall temperatures are higher than 0.8 time of Tad), the transition of Mach 6 is decided by the first mode, for the other boundary layers of isothermal wall (the wall temperatures are lower than 0.66 time of Tad)the transition of Mach 6 is decided by the second mode; For the boundary layers of the adiabatic wall and isothermal wall, the transition locations of Mach 8 are all decided by the second mode.