Stagnation-point heating of Fire II with a non-Boltzmann radiation model

Abstract

The present work analyzes the stagnation-point radiative heating in the Fire II flight experiment by devising a collisional-radiative model with non-local absorption. In the stagnation-line flow-field calculations, a viscous shock layer method with a thermochemical nonequilibrium model is utilized. In the radiation calculations, a line-by-line method with the non-Boltzmann electronic populations is employed by adopting the quasi-steady state approach of the electronic master equation calculations. In constructing the electronic master equation, the best set of the electron and heavy-particle impact excitation rates is proposed to achieve better agreement with the measured radiative heating flight data. In the flow-radiation coupling procedure, the effect of the non-local absorption is modeled by devising an iterative process between the quasi-steady state electronic master equation and the radiative transfer equation calculations. Escape factors of the strongest atomic lines and the diatomic nitrogen vacuum ultraviolet systems with the non-local absorption effect are also proposed to more efficiently consider the non-local nature of the radiative transition. When compared with the experimental data from the Fire II trajectories, it is found that the present collisional-radiative model with the non-local absorption improves the ability to predict non-Boltzmann radiative heating.