On Application of Surface Measurement Techniques for Cryogenic High Reynolds Number Investigations on Wind Tunnel Models

High Reynolds number experiments make high demands on the wind tunnel model and on measurement techniques. A very smooth surface and a high spatial as well as temporal resolution are required. Especially for the detection of characteristic frequencies of flow instabilities, a high temporal resolution is needed. Since both the surface hot-wire and the newly developed Pressure Sensitive Copolymer technique provide these properties, these methods were applied to wind tunnel models for transition experiments carried out in the European Transonic Windtunnel and its pilot facility. The general measurement principles are described in detail to clarify their specific application to the various models. The performed experiments deal with the influence of leading edge roughness on the laminar turbulent transition. Additionally, investigations on the influence of the Reynolds number by changing total pressure and temperature has been carried out. The results are analysed using several methods.