Temperature and heat flux measurement on hot models in short-duration facilities

Temperature and heat flux measurement on hot models in short-duration facilities

An electrical preheating technique applied to a carbon-based model in an impulse facility has previously demonstrated surface temperatures around 2500 K, but the measurement of heat flux at such elevated surface temperatures was not previously achieved. A technique for fast-response surface temperature measurement of an electrically preheated carbon-phenolic model using an indium gallium arsenide detector with in situ calibration via a visible/near-infrared spectrometer is assessed through application in a short-duration cold-flow hypersonic wind tunnel. The method is reliable: the scatter in temperatures determined from successive acquisitions of the spectrometer data had a standard deviation of 3 K at a mean temperature of about 1500 K; the standard deviation of the Indium gallium arsenide detector results from the visible/near-infrared spectrometer data was 11 K at a temperature of about 1100 K after the termination of the hypersonic flow. The surface temperature history from the Indium gallium arsenide detector was analyzed using a one-dimensional transient heat conduction model to deduce the surface heat flux. Good agreement with an engineering correlation for stagnation point heat flux is demonstrated; however, uncertainties are large (±33%), as the thermal properties of the particular carbon-phenolic material were not available. The method is suitable for application in impulse facilities, but the effusivity (√pck) for the heat shield material will need to be accurately defined for reliable deduction of surface heat flux.

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