A master equation model resolving individual vibrational states via a database of ab initio rate coefficients is coupled to the Lees–Dorodnitsyn boundary-layer equations for stagnation-line flow. Using this framework, nitrogen and oxygen boundary layers are analyzed at pressures ranging from Formula: see text to 10 atm with nose radii from 1 mm to 10 m, using a noncatalytic wall boundary condition. Significant differences between the translational–rotational and vibrational temperatures occur at the wall for small nose radii and low pressures, indicating incomplete vibrational thermalization. Overpopulation of high-lying vibrational levels due to recombination is observed in all calculations, even when the translational–rotational and vibrational temperatures are equilibrated. This non-Boltzmann overpopulation suppresses recombination rates by a factor of 1.4–6 relative to Boltzmann predictions, with stronger effects observed in oxygen than in nitrogen. These differences substantially alter wall heating: in oxygen, Boltzmann versus non-Boltzmann rates yield differences exceeding 50% when the nose radius is 1 m or larger and up to 20% for a 10 cm nose; in nitrogen, differences are typically 10% or less, except for the largest nose radius of 10 m. Sensitivity analysis further reveals that atomic mass fractions and convective heating are controlled by recombination pathways to intermediate vibrational levels.
Aiken et al. (Sat,) studied this question.