Transition Detection at Cryogenic Temperatures using Temperature Sensitive Paint in the European Transonic Windtunnel (ETW)

Abstract

The identification of laminar-turbulent boundary layer transition on models in cryogenic wind tunnels gives essential data for modern wing design. Among other techniques, transition detection can be done using IR cameras which show good results in ‘warm’ wind tunnels. In cryogenic testing the IR technique becomes more difficult to realize because of the reduction in radiated energy and the shift to longer wavelengths. Therefore, an IR camera operating for example at 120K shows low resolution and sensitivity and needs very sophisticated system due to the low temperature in the cryogenic wind tunnel. The temperature sensitive paint (TSP) technique has become a promising alternative here. This technique has been developed at NAL of Japan since 1997. Some modifications of existing TSP formulations had to be undertaken to apply the technique to a large-sized cryogenic wind tunnel such as the European Transonic Windtunnel (ETW). For image and data acquisition, DLR’s mobile measurement system (which was developed for Pressure Sensitive Paint (PSP) measurements in “warm” wind tunnels) could be used but had to be adapted to the special conditions given in the ETW wind tunnel.