Heat transfer measurements in a supersonic wind tunnel through inverse temperature data reduction: application to a backward facing step

An inverse heat transfer data reduction method is presented, which allows performing quantitative heat transfer measurements using pre-heated models in a blow-down supersonic wind tunnel. The flow under investigation is a backward-facing step (BFS) at Mach 3. Temperature measurements are performed by means of infrared thermography. The inverse heat transfer procedure is used to calculate the surface heat flux from the measured surface temperature in time by taking into account multi-dimensional and unsteady conduction effects. The robustness and sensitivity of the data reduction algorithm is assessed using synthetic experiments where aspects such as measurement noise, calibration errors, conductivity errors, etc. are addressed. The BFS flow is investigated for laminar, transitional and turbulent-separating boundary layers. It is found that for the laminar and transitional cases, the Stanton number and normalized separation length are influenced by the step height. For turbulent separation, this is only marginally the case; however the Stanton number downstream of reattachment increases with step height. For the transitional separation, large heat transfer peaks are measured at reattachment, of magnitude up to twice the reference values for a developed turbulent boundary layer.