NUMERICAL SIMULATION OF INTERACTION BETWEEN HIGH ENTHALPY REFLECTED SHOCK WAVE AND BOUNDARY LAYER

In a high-enthalpy shock tube, the interaction between the reflected shock and the boundary layer can induce shock bifurcation, which is accompanied by complex local non-equilibrium and non-uniformity. The non-equilibrium and non-uniformity can greatly affect the wall pressure and heat flux measurement in a shock tube experiment. In this work, two-dimensional simulations considering thermochemical non-equilibrium are conducted to investigate the shock bifurcation in high-enthalpy conditions. The objectives are to interpret the formation mechanism of local non-equilibrium and non-uniformity and the effects on the characteristic parameters of shock bifurcation structures. It is found that the thermochemical non-equilibrium has a great influence on the local temperature and heat release rate, while the influence on the holistic shock structures can be neglected. The local thermochemical non-equilibrium in shock bifurcation is dominated by two mechanisms. One is controlled by dissociation reaction and compression. The other one is controlled by recombination reaction and expansion. The wall heat transfer reduces the total energy of the gas in the stagnation bubble, resulting in a decrease in the size of the bifurcated shock and the area of the non-equilibrium region, but the difference between the translational and vibrational temperature of the gas near the oblique shock wave will increase. It is observed that the local high-pressure region near the wall induced by the wall jet will cause a huge wall heat flux. A modified model considering chemical reaction is developed, which can effectively predict the oblique shock angle of bifurcated foot in high-enthalpy conditions. The height of the triple point of the bifurcated foot under adiabatic wall conditions is greater than that under isothermal wall conditions. The stagnant bubble, the complex vortex structure, and the wall heat transfer cause the height of the triple point to increase approximately linearly. Three factors are introduced to interpret the change rule of reflected shock velocity, which decrease first and then increase gradually.