Hypersonic International Flight Research Experimentation Flight 2 Unstart Reliability Analysis

The objective of this work was to assess the unstart reliability of the Hypersonic International Flight Research Experimentation Flight 2 system. To do this, a quantification of margins and uncertainties framework was used for comparing the predicted combustion-induced shock location to the predicted last stable shock location within the isolator. Uncertainty sources included parametric uncertainty in the flight conditions, the heat release model, and turbulence modeling, as well as model verification errors. Additionally, an estimate of the model-form uncertainty was established by comparing the model to measured ground-test data. A computationally efficient nonintrusive polynomial chaos approach was used to propagate parametric uncertainty through the computational fluids dynamics models of both the ground-test configuration and the flight vehicle. Compared to direct-connect ground-test data, computational fluid dynamics predictions yielded about two duct heights of model-form uncertainty. This was applied to a prediction of the flight vehicle unstart margin at the Mach 6.5 flight condition. Building up all of the computational model uncertainty (including parametric uncertainty, verification errors, and the determined model-form uncertainty), the 95%-probability-level-based confidence ratio, which is a ratio of a statistical margin measure to the total uncertainty, was found to be 0.31 for the flight system.