Multiscale coupling simulation of surface catalytic effect on hypersonic aerothermodynamic environment

Abstract

The complicated heat and mass transfer at the high-temperature gas-solid interface of a thermal protection material under highly non-equilibrium conditions is of high importance to hypersonic flows. Surface catalysis, an exothermic reaction that refers to the recombination of dissociated atoms at the surface, and its effect on the aerothermodynamic environment has been investigated by researchers, especially focusing on oxygen recombination process. To further identify the nitrogen recombination mechanism, a hybrid CFD-RMD multiscale simulation method is employed in this work to qualitatively investigate its effect on aerothermodynamic environment prediction under hyperthermal non-equilibrium condition. Taking carbon-based phenolic resin (PR) composite as a typical material with 300 K, the nitrogen recombination coefficient obtained from atomistic-scale RMD simulation is coupled with the continuum two-temperature Navier-Stokes model to capture the catalytic effects and the heat / mass transfer at high temperature: A catalytic benchmark simulation is conducted under a Mach number of 9.7, and the heat flux distribution along the surface coupled with the RMD-derived nitrogen recombination coefficient of 0.0704 is obtained, which result is comparable with the published wind tunnel experimental data and the finite-rate catalytic result is 10 %∼30 % lower than the fully catalytic assumption result. The nitrogen recombination coefficient of PR is theoretically found to increase with thermal dissociation fraction of the free stream and decrease with the wall temperature due to the catalysis-ablation competitive mechanism. The influence of the recombination coefficient on the heat transfer at the surface is also quantitatively analyzed for evaluating the surface catalysis effect on aerothermodynamic heating.