Determination of heat transfer into a wedge model in a hypersonic flow using temperature-sensitive paint

Heat loads on spacecraft traveling at hypersonic speed are of major interest for their designers. Several tests using temperature-sensitive paints (TSP) have been carried out in long duration shock tunnels to determine these heat loads; generally paint layers were thin, so that certain assumptions could be invoked to enable a good estimate of the thermal parameter rho.c.k (a material property) to be obtained - the value of this parameter is needed to determine heat loads from the TSP. Very few measurements have been carried out in impulse facilities (viz. shock tunnels such as the High Enthalpy Shock Tunnel Göttingen (HEG)), where test times are much shorter. Presented here are TSP temperature measurements and subsequently derived heat loads on a ramp model placed in a hypersonic flow in HEG (specific enthalpy h0 = 3.3 MJ/kg, Mach number M = 7.4, temperature T_inf = 277 K, density rho_inf = 11 g/m^3). A number of fluorescence intensity images were acquired, from which, with the help of calibration data, temperature field data on the model surface were determined. From these the heat load into the surface was calculated, using an assumption of a 1D, semi-infinite heat transfer model. rho.c.k for the paint was determined using an insitu calibration with a Medtherm coaxial thermocouple mounted on the model; Medtherm rho.c.k is known. Finally presented are sources of various measurement uncertainties, arising from: (1) estimation of rho.c.k; (2) intensity measurement in the chosen interrogation area; (3) paint time response