Evaluation of Global Thermography Methods for Hypersonic Aeroheating Measurements

An experiment was conducted in the 20-Inch Mach 6 Air Tunnel at NASA’s Langley Research Center to compare the performance of two global thermography techniques. Surface heating measurements on a 19.2%-scale model of the ROTEX-T flight vehicle were obtained via phosphor thermography and infrared thermography. The cone-flare-cylinder geometry provides a complex flowfield with separation and reattachment shocks, necessitating thermography methods with both sensitivity and high dynamic range. Laminar VULCAN-CFD solutions are used to evaluate performance on the canonical geometry. Tests were conducted over freestream Reynolds numbers between 3.3×106 m−1 and 27.0×106 m−1 at a nominal 0° angle of attack, overlapping both flight conditions and prior ground test conditions. Phosphor thermography underpredicted heating rates at low Reynolds numbers due to poor sensitivity at surface temperatures lower than 330 K, but showed good agreement at higher freestream conditions. The infrared measurements were within 10% of the computations on the cone in all cases and demonstrated superior resolution to phosphor thermography. In the case of a laminar reattaching boundary layer, the infrared measurements showed 20% lower heating on the flare as compared to the laminar CFD solutions. Streamwise temperature gradients were investigated as a potential cause of this disagreement and are shown to have a strong effect on flare heating rates predicted by computations.