Hydrodynamic Stability And Transition Prediction With The Chemical Equilibrium Gas Model

The high-temperature real gas effects on hydrodynamic stability and transition prediction in supersonic boundary layers on a flat plate are investigated. Thermodynamic parameters, such as viscosity and thermal conductivity and specific heat, are greatly altered by real gas effects which are mainly caused by the extremely high temperature inside boundary layers. It affects both of the base flow and stability properties. Calculation is performed using the 7-species chemical equilibrium model, where viscosity and thermal conductivity are calculated using a mixing rule. The energy transport which is due to the diffusion of species is also taken into account. The flat plat base flow is computed under the conditions of Mach number 10-20, wall temperature 500-3500 K, flight altitude 20-30.5km. The flow stability is analyzed. Moreover, the N number of relatively growth rate of disturbance is given. The base flow is given by Blasius solution which adopts the chemical equilibrium model. The canonical e-N method is used to predict the transition.We obtain some conclusions. In the scenario of high-Mach number flow, the most obvious feature of flat plat stability is the merge between second and third mode, effecting transition together. In addition, as the parameters, such as Mach number, wall temperature, flight altitude, vary, the variation trends of real gas instability model are almost the same as that of perfect gas. In the case of flat plate, after considering the real gas effects, first mode's growth rate reduces, so as the growth region. By contrast, second mode's largest growth rate increases, the whole trend moves to the low frequency region. In addition, the unstable frequency band turns out to be narrower. The delay of second and third modes merge occurs. In the upstream, the envelope line of N is larger, while in the downstream, the envelope line of N is relatively lower. In a nutshell, the perfect model overestimates the growth rate, we conclude that this transition prediction method is relatively conservative.