Collisional Radiative Modeling of Electronically Excited States in a Hypersonic Flow

The hypersonic, nonequilibrium thermochemistry flow over a cylinder was modeled to study nitric oxide (NO) ultraviolet (UV) emissions. The main focus of this work is to model the populations of the electronically excited states of N₂ and NO because the transitions from those states to ground states are responsible for UV emissions. Collisional radiative models were constructed for the purpose of predicting the electronically excited state populations using two approaches, the quasi-steady-state (QSS) method and a MassTR method. These methods were applied to flows generated by the direct simulation Monte Carlo method of ground state species for two types of collisional radiative models. The results showed that when the coupling between the formation of electronically excited states and flow transport was modeled, this resulted in higher populations of the electronically excited states of N₂ (A³Σ_u) and NO in the expansion and wake regions of the flow compared to the QSS result where flow transport is not included. In addition, it was shown that the N₂ (A³Σ_u ) state is responsible for the most of the NO(A) state population downstream of the stagnation region.