Wall temperature effects on wall heat flux in high-enthalpy turbulent boundary layers

Abstract

The wall temperature significantly varies the turbulent statistics and coherent structures in high-speed wall-bounded turbulence under the low-enthalpy condition. The present study set out to investigate whether this is also the case for high-enthalpy turbulent boundary layers that incorporate the chemical reactions of multi-species gas mixture. For that purpose, we perform direct numerical simulations for high-enthalpy turbulent boundary layers at the Mach number of 4.5 and the momentum Reynolds number of 2400 with three groups of wall temperature. Statistical results show that the effects of wall temperature on the mean flow properties are similar to those of low-enthalpy flows, and the chemical reactions only affect the mean temperature without leaving strong impacts on the statistics of velocity. The wall heat flux and the physical processes thereof are further analyzed. The mass diffusion effects are increased by the rising wall temperature due to the more sufficient dissociation of the molecules. The wall heat flux fluctuations are also slightly enhanced, with the lower skewness and the higher kurtosis, and show more prominent structures of traveling wave packets and weaker streaks, as well as the less coherent vortices in the vicinity of the extreme positive wall heat flux events. The organizations of the mass species are also altered substantially by the rising wall temperature due to the stronger impacts of chemical reactions on the flow dynamics.