Gas-Phase Recombination Effect on Surface Heating in Nonequilibrium Hypersonic Flows

摘要

The direct simulation Monte Carlo method is used to examine the relative impact of atom recombination in the gas phase and at the catalytic wall on the heat flux in hypersonic airflows over a cylinder. Good agreement is observed between the numerical results and the available experimental data for a Knudsen number of 0.001 and a flow velocity of 6 km/s when both the gas and surface reactions are included. Variation of the freestream flow density and velocity has shown that the gas recombination (mostly from nitrogen atoms) dominates at Knudsen numbers of 0.001 and lower and velocities of 6 km/s and higher; the surface recombination is more important otherwise. The increase in the heat flux due to the gas recombination is extremely sensitive to the wall is important for temperatures of about or lower than 1000 K. For the baseline case of a Knudsen number of 0.001 and a velocity of 6 km/s, the heat flux on a 2000 K noncatalytic wall is three times lower than on a 300 K catalytic wall.