Measurement uncertainty and sensitivity analyses on freestream parameters in a hypersonic impulse facility: A perturbation-based framework

Quantifying measurement uncertainty in short-duration impulse facilities is critical for data credibility but remains particularly challenging due to rapidly evolving, high-enthalpy flow conditions with limited diagnostic time scales. This study systematically develops and demonstrates a robust, generalized perturbation-based framework to estimate uncertainties in key measured quantities and assess their sensitivity to derived freestream parameters in a shock tunnel. The sensitivity analysis reveals that freestream parameters, such as static pressure, temperature, density, and velocity are highly sensitive to tunnel shock speed (Us) and stagnation pressure (P5), while showing moderate dependence on the driven-tube fill pressure (P1), and temperature (T1). The effect of stagnation enthalpy on these sensitivities is also examined and found to have minimal influence across the studied range (2.4–7.5 MJ/kg). By conducting systematic experiments in such a facility, the repeatability errors in surface heat flux and pressure-derived coefficient (CP) are found to be well within the predicted uncertainty bounds of ±10% and ±9.5%, respectively, underscoring the robustness of the framework. The proposed methodology establishes a seamless approach for uncertainty evaluation in impulse facilities and supports more reliable interpretation of aerodynamic data under transient, high-enthalpy conditions, with potential applicability to future hypersonic test strategies.