Model Wall and Recovery Temperature Effects on Experimental Heat-Transfer Data Analysis

Theme T phase-change coating technique for obtaining quantitative measurements of the heat transfer to bodies in hypersonic wind tunnels offers economies of both time and money when compared to thin-skin thermocouple techniques, and also yields highly detailed heating distributions not possible With previous methods. The procedures required in utilizing this technique result in data being obtained over long test time intervals and, therefore, at model wall temperature levels and gradients not normally encountered in thin-skin testing. During a phasechange coating test, data at various model locations are obtained at different times, with time intervals sufficiently large to allow significant temperature gradients to exist on the model when the data are obtained. Increased model wall temperature results in an increased sensitivity of phase-change-derived heat-transfer coefficients to the adiabatic wall temperature. Basic analytic procedures are used to illustrate the impact of model and reference adiabatic wall temperatures on the accuracy of experimental heat-transfer data. Inaccurate knowledge of adiabatic wall conditions results in measured heat-transfer coefficient inaccuracies which increase as wall temperatures approach the local adiabatic value. High model wall temperatures and wall temperature gradients affect both the level and distribution of measured heat-transfer coefficient.