Application of Temperature Sensitive Paint to investigate laminar-to-turbulent transition on nacelles

The Temperature Sensitive Paint (TSP) method has the potential to measure boundary-layer transition on complex 3-D wind tunnel models like nacelles. TSP can visualize the surface boundary-layer conditions as temperature distribution based on different heat transfer coefficients in the laminar and turbulent flow. By heating up the model surface, temperature difference between laminar and turbulent boundary-layer regimes are enhanced and appear as bright/ dark differences in the captured TSP images. Three different model-heating methods have been investigated in this study: change of flow temperature, electrical heating, and infrared heating using Laser light. In this paper, the applicability of the different heating methods has been investigated to a generic nacelle model and was tested in laboratory and in the cryogenic transonic pilot European Wind Tunnel (PETW). The measurements were performed at test conditions in the temperature range from 115 to 290 K, at Mach numbers M = 0.2 and M = 0.5.