Chemical Kinetics of Electronically Excited Air Species Near Surface of Ablating Hypersonic Vehicle

Many diagnostic techniques for use in high-enthalpy flows rely on the seeding or tracking of electronically excited species in air, thus, understanding the chemical kinetics of these species is vital. However, the carbon-containing species that are injected into the flow via thermal ablation change the composition of the gas, including the electronically excited species. We use a two-temperature, reacting flow CFD solver and introduce finite-rate chemistry for the A³Σ_u⁺, B³Π_g, and C³Π_u states of molecular nitrogen and the A²Σ⁺3sσ, B²Π_r, C²Π_r3pπ, and D²Σ⁺3pσ states of nitric oxide. With this method, we evaluate how the concentrations of these excited species change due to the thermal and transport effects of carbon ablation in a high-speed flow. Due to the ablative consumption of atomic oxygen and nitrogen near the surface of the vehicle, we see a decrease of more than 75 % in the A-states of both N₂ and NO, which affects the near-surface heat balance. These differences highlight critical inaccuracies of chemistry modelling when disregarding ablation-driven chemistry, and their inclusion will increase future modelling accuracy of high-speed diagnostic techniques that rely on electronically excited air species.