Optimization of temperature-sensitive paint formulation for large-scale cryogenic wind tunnels

In this paper, a new Temperature-Sensitive Paint (TSP) technique for boundary-layer transition detection in a production-type large cryogenic wind tunnel is present. The formulation of Ru(trpy) based TSP system has been optimized in terms of luminescence intensity and robustness. The optimum dye-binder-solvent combination has been determined through systematic sample tests. A new binder has been introduced and the resulting coating was found free from cracking at cryogenic temperatures. This is contrary to the silicone-based pervious cryogenic TSP that are subject to micro cracks at reduced temperatures. The new TSP can meet the root-mean-square roughness requirement less than 0.15 μm. Experiments in the NAL 0.1-m Transonic Cryogenic Wind Tunnel have shown that transition occurs earlier on the unpolished surface than the polished surface, although the roughness value itself increasing by polishing. This suggests that the waviness of the coating could affect on the growth of instability in boundary layers.