Detailed film cooling measurements on a cylindrical model with simulated TBC spallation
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Detailed heat transfer coefficient and film effectiveness distributions are presented on a cylindrical leading-edge model with simulated thermal barrier coating (TBC) spallation using a transient liquid crystal technique. Tests were performed in a low speed wind tunnel on a cylindrical model in a crossflow with two rows of injection holes. Mainstream Reynolds number based on the cylinder diameter was 100900. The two rows of injection holes were 15 from stagnation. The film holes were spaced 4 hole diameters and were angled 30 and 90 to the surface in the spanwise and streamwise directions respectively. The simulated spallation cavities were rectangular in shape and had rounded edges. The simulated spallation was placed at two locations 20-40 (S3) and 35-55 (S4) respectively. The cylinder surface was coated with thermochromic liquid crystals and a transient test was run to obtain the heat transfer coefficients and film effectiveness values. The effect of coolant blowing ratio was studied for blowing ratios of 0.4, and 0.8. Results show that the Nusselt numbers increase with an increasing blowing ratio. However, the reverse is true for the film effectiveness at lower turbulence level. An increase in free-stream turbulence has very little effect on Nusselt numbers but an increase in free-stream turbulence reduces the film effectiveness significantly at low blowing ratios. In general, presence of spallation enhances Nusselt numbers and produces a strong variation in film effectiveness distributions.