Effects of vibrational nonequilibrium on hypersonic shock-wave/laminar boundary-layer interactions

Recent numerical simulations of hypersonic double-cone and hollow-cylinder flare experiments have incorrectly predicted the sizes of separation regions, even at total enthalpies as low as 5.44 and 5.07 MJ/kg. This study investigates the effects of vibrational nonequilibrium to explain these discrepancies. According to an assessment of various flow models under post-shock conditions in comparison with state-specific simulations, the predictions obtained by treating the vibrational modes of molecular nitrogen and oxygen as a single mode, a strategy adopted routinely by the aerospace computational fluid dynamics community, are in close agreement with the state-specific results in terms of post-shock temperature and density profiles, whereas separation of the vibrational modes and assumption of calorically perfect gases would lead to evident errors. The double-cone flow is found to be sensitive to different flow models. In contrast, their effects on hollow-cylinder flare flow are insignificant. Given that the most representative flow model still underestimates the sizes of the separation regions for double cone flow and overestimates those for hollow-cylinder flare flow, it is concluded that inaccurate modeling of vibrational nonequilibrium may not be responsible for the discrepancies observed at the lowest total enthalpies. Suggestions for further study are also presented.