Mutual Information and Sensitivity Analysis of a T6 Expansion Tunnel Experiment

The development and refinement of hypersonic flow models relies heavily on validation with experimental data from ground test facilities. Experiments at the T6 Stalker Tunnel at Oxford University have leveraged optical emission spectroscopy (OES) to probe the flow around a blunt test article immersed in 5-6 km/s hypersonic flow, with the aim of characterizing reactions relevant to plasma formation. To guide interpretation of the experimentally measured spectra, which have not yet been fully processed, a combined analysis using both sensitivity and mutual information metrics is performed to identify the model parameters that most affect the predicted spectral features. Predictions of the observed spectra are generated using the computational fluid dynamics (CFD) code LeMANS and the radiation code NEQAIR. Parameter sensitivity is quantified primarily using mutual information (MI), which directly captures how much an experimental measurement, with its associated uncertainty, reduces the uncertainty in each model parameter. Analysis of the chosen test condition indicates that reactions involving nitric oxide, including Zel'dovich reactions and dissociation with atomic partners, drive predictions of most of the spectral features in the wavelength range of the spectrometers, from 200 to 850 nm. Future work will incorporate uncertainty in the rate parameters within the non-Boltzmann radiation solver to better separate where the CFD rate parameters can be isolated from those used to model the emission.