Uncertainty Analysis of Slug Calorimeters in the NASA HyMETS Arc-Jet Facility

Abstract

The objective of this work is to perform an uncertainty analysis of the deduced stagnation heat flux environment on a slug calorimeter in the Hypersonic Materials Environmental Test System arc-jet facility located at NASA Langley Research Center. Analytical solutions are developed for boundary-value problems on the slug sensor accounting for nonideal effects, including spatial variation in the slug heat flux, multidimensional thermal conduction, and backface losses, which depart from the state-of-the-art method derived from the American Society of Testing and Materials. The analytical solutions are compared and optimized to experimental backface slug thermocouple data for a high- and low-enthalpy test condition. The results indicate that the epistemic uncertainty of the deduced stagnation heat flux on the slug calorimeter is at most ±2.5% for both conditions. Using a numerical approach to evaluate the aleatory uncertainty component in the slug stagnation heat flux, there is a compromise between the sample size and filter frequency of slug backface thermal data points when evaluating the deduced stagnation heat flux standard deviation. The total (mixed) uncertainty in the deduced stagnation heat flux is determined to be up to ±4%, which is at least a 60% reduction from the standard uncertainty used in the state-of-the-art method.