Temperature-Sensitive Paint measurements in combination with Carbon-Fiber-Reinforced Plastic models in cryogenic conditions

For aerodynamic profile tests on aircraft models, transition detection is generally of great interest. Under ambient flow conditions the infrared technique (IR) is a well-established image-based method to carry this out. In high Reynolds number tests which are conducted at cryogenic temperatures and at high pressures the IR technique does not work very well, whereas the Temperature-Sensitive Paint (TSP) technique is in principle well-suited to operate under these conditions. Boundary layer transition detection by means of TSP generally requires an artificial temperature step to enhance the temperature difference between the laminar and turbulent boundary layers. This paper presents the combination of TSP and Carbon-Fiber-Reinforced Plastic (CFRP) to generate a well-defined temperature difference by means of an internal electrical model surface heater to detect laminar-turbulent transition. The model integration for the TSP technique is advanced even further by integrating the TSP coating into the CFRP model manufacturing process. After pre-testing CFRP and TSP in the laboratory, wind tunnel experiments were conducted in the Cryogenic Ludwieg Tube Göttingen (KRG) and in the Pilot European Transonic Windtunnel (PETW) for laminar-turbulent transition detection on a two-dimensional laminar profile model for Reynolds numbers up to 20 million.