A general procedure for infrared thermography heat transfer measurements in hypersonic wind tunnels

Abstract Heat transfer measurements in hypersonic wind tunnels are particularly challenging when dealing with fully three-dimensional geometries and/or flows with high spatial temperature gradients. In the present work, a full and consistent description of a general procedure to perform infrared thermography heat transfer measurements is proposed. Radiometric and optical camera calibration, spectral directional emissivity characterization, model oscillations correction and 3D surface temperature reconstruction problems are theoretically and practically analyzed along with new solutions. A novel hybrid heat transfer problem is proposed. This technique is based on the solution of the direct problem during the wind tunnel unsteady start-up to accurately estimate the initial condition for the inverse problem solution during the quasi-steady test phase. The data reduction procedure was validated through an experimental campaign conducted in the Boeing/AFOSR Mach-6 Quiet Tunnel on a sharp cone at 0 deg angle of attack. The experimental Stanton number obtained by solving a one-dimensional heat transfer problem is in agreement with the theoretical laminar solution for a range of free-stream conditions with an average error between − 1.1 ÷ 0.64 % and a standard deviation of 1.55%. Finally, a two-dimensional heat transfer problem has been solved when the cone is tested at 6 deg angle of attack demonstrating the IR procedure capability to analyze multi-dimensional flows and to take into account tangential conduction effects caused by surface temperature gradients due to the presence of crossflow vortices.