Phosphor Thermography Technique in Hypersonic Wind Tunnels: First Results

Probative research is being conducted at ONERA on a new technique for measuring heat transfer in wind tunnels. This method is based on the heat sensitivity of a luminescent coating applied to the model. This coating emits visible light when it is excited by UV light, and the emission properties depend mainly on its temperature. Discrete measurements with a special photothermometer were made during preliminary blowdown wind tunnel tests. The results agreed well with other discrete measurements, such as thin-film measurements. The main advantage of this new technique is to provide thermographic measurements. This requires a video system, a digital image processing system, and a data reduction technique that is more sophisticated than the discrete data reduction technique. The thermographic system that was defined and calibrated is described in this paper. The first results obtained on a sphere are in satisfactory agreement with a prediction based on the Fay-Riddell theory. Consequently, this method is currently considered to be a valid heat flux meaurement technique.