Combination of Temperature-Sensitive Paint and Carbon Nanotubes for Transition Detection

For transition detection measurement in wind tunnels by means of Temperature-Sensitive Paint (TSP) or InfraRed Thermography (IRT), a sufficient temperature difference between laminar and turbulent boundary layer areas has to be established. If the Temperature difference, naturally occurring under adiabatic wall temperature conditions, is too small to be recognized by IRT or TSP, the magnitude of the temperature change in the laminar-to-turbulent transition area has to be enhanced artificially. Mainly known are two different methods based on heat transfer from the wind-tunnel flow to the model substrate to generate temperature differences: a) Temperature steps in the flow (cooling or heating of the flow) and b) Electrical heating of the model surface (established technique is using heating elements inside the model). A new technique arises from the use of carbon nanotubes (CNT). Materials based on that have a very high electrical heating capability (>1,000 lager than Copper) and can be mixed in a surface coating. Compared to classical heating foils the CNT coating technique has the advantage that a higher spatial homogeneity with respect to heating can be achieved and the applicable thickness of a CNT coating is in the order of micrometers. The presented paper describes the further development of the application of CNT in combination with TSP for transition detection in wind tunnels at high Reynolds numbers.