Investigation of High-Enthalpy Cylinder Flow Using Ab Initio Air Chemistry Data

This study evaluates the performance of recent ab initio air chemistry kinetic data to simulate a high-enthalpy hypersonic flow around a cylinder under the conditions obtained in the High Enthalpy Shock Tunnel Göttingen (HEG) facility. Prior empirical models, such as Park and Dunn–Kang, were shown to underpredict surface heat flux data at a freestream enthalpy of approximately [Formula: see text] (HEG I), whereas very good predictions were obtained at a lower freestream enthalpy condition of [Formula: see text] (HEG III). Such a discrepancy has generally been attributed to enhanced surface catalycity under the HEG I conditions. Here, using the HEG I test case, simulations are conducted using NASA’s FUN3D computational fluid dynamics solver with a custom 38-reaction, five-species air model incorporating ab initio dissociation and exchange rates alongside Dunn–Kang recombination rates. A two-stage global sensitivity analysis framework is employed: an initial binary screening identifies six dominant reactions influencing stagnation-point heat flux, followed by a detailed Sobol analysis of their Arrhenius parameters (pre-exponential factor, temperature exponent, and activation energy) within uncertainty bounds. Surrogate models, including random forests, XGBoost, kriging, and Gaussian processes, facilitate efficient variance decomposition and uncertainty quantification, revealing key sensitivities in dissociation, exchange, and recombination processes. Calibration of parameters aligns predictions with experimental heat flux data, potentially enhancing fidelity over legacy empirical rates. The findings here may highlight the importance of gas-phase recombination versus surface catalycity as a potential explanation for the observed heating measurements under high-enthalpy, high-density conditions.