High Reynolds Number Transition Detection by Means of Temperature Sensitive Paint

Abstract

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 cryogenic testing, IR imaging becomes more difficult because of the reduction in radiated energy and the shift to longer wavelengths. Therefore, the temperature sensitive paint method has become a promising alternative here. Transition detection measurements were carried out using different models in several cryogenic wind tunnels, namely the European Transonic Windtunnel, the pilot facility of the European Transonic Windtunnel, the cryogenic wind tunnel in cologne and the cryogenic Ludwieg Tube facility of in Gottingen. With the temperature sensitive paint method, similar information can be obtained as for IR imaging in warm wind tunnels, but with higher spatial resolution. This means, that one can determine the instability leading to transition, namely Tollmien-Schlichting or crossflow instabiltiy, observe laminar separation bubbles (and turbulent reattachment), detect flow separation and locate shocks as well as vortex signatures.