Transition detection by temperature sensitive paint at cryogenic temperatures in the European Transonic Wind tunnel (ETW)

The identification of laminar-turbulent boundary layer transition on wind tunnel models provides essential data for modern wing design. However, simulating true flight Reynolds numbers with scaled models requires the use of cryogenic wind tunnels. Transition detection in ´warm´ wind tunnels can be realized using commercially available IR cameras. In parallel, the temperature sensitive paint (TSP) technique is well established as an additional tool. In cryogenic testing, IR imaging becomes more difficult because of the reduction in radiated energy and the shift to longer wavelengths. Therefore, the TSP technique has become a promising alternative here. However, applying temperature sensitive paint in a large-scale cryogenic wind tunnel like the European Transonic Wind tunnel (ETW) needs specific modification of existing TSP formulations. Cooperative tests in the ETW therefore were performed by DLR and NAL (Japan). In these measurements, NAL´s paint and DLR´s mobile PSP/TSP system for data acquisition and evaluation were used. Some efforts were made to adapt the system to specific conditions given at the ETW wind tunnel. So for the first time it was successfully realized to perform a TSP luminescent paint test at cryogenic temperatures in a commercial wind tunnel.