Effect of temperature-sensitive-paint thickness on global heat transfer measurement in hypersonic flow

Heat flux measurement in a hypersonic wind tunnel is one of the necessary requirements for designing the nextgeneration reentry vehicle. Heat flux is usually calculated from a temporal change in temperature on a model surface. Temperature-sensitive paint provides a global temperature measurement technique based on photochemical reaction. This technique was applied to a hypersonic shock tunnel test, but there were uncertainties caused by the thickness of the temperature-sensitive-paint layer. In this study, the relationship between the temperature-sensitive-paint layer thickness and the measurement accuracy of heat flux was investigated. The models were tested at Mach 10 in the Japan Aerospace Exploration Agency's 0.44-m hypersonic shock tunnel and the heat flux, caused by aerodynamic heating on the model surface, was measured. A comparison between temperature-sensitive-paint data and conventional thermocouple data showed that the measurement error changed with the paint layer thickness. Then a three-dimensional wing-body model was tested to demonstrate the validity of temperature-sensitive paint of an optimized thickness, and a complicated heat flux pattern caused by the shock wave/shock-wave interaction was observed.