Wall temperature effects in high-enthalpy supersonic turbulent channel flows considering air dissociation

Direct numerical simulations of temporally evolving high-enthalpy supersonic turbulent channel flows are performed at a Mach number of 3.0 and Reynolds number of 4880. The high-enthalpy air is assumed to behave as a chemical and thermal equilibrium of five-species mixture. The wall temperatures in the range of 1733.2 K to 4100.0 K to study the influence of wall temperature on the chemical activity, turbulent statistics and aerodynamic characteristics. The results show that the chemical activity is remarkable because the air is relatively sufficient dissociated. When the wall temperature higher than 2300 K, an extreme value can be observed in the distributions of mean and fluctuating mass fraction of atomic nitrogen close to the wall. Many of the influence of wall temperature on the turbulent statistics which hold for low-enthalpy conditions also hold for high-enthalpy conditions, including mean and fluctuating velocity, recovery enthalpy, and strong Reynolds analogy. As the wall temperature increases, the turbulent momentum flux and turbulent heat flux decrease, the turbulent mass flux mainly depends on species mass fractions fluctuations. The integral formulas of decomposing the aerodynamic characteristics are proposed, and the predicted heat flux and skin friction are all in good agreement with those direct estimation. The wall temperature does not change the primarily contributions of aerodynamic characteristics. Although the turbulent heat flux term is approximately 6%, its part of turbulent transport of enthalpy significantly increases with increasing wall temperature. The turbulent Schmidt number is insensitive to wall temperature.