Film Cooling for Cylindrical and Fan-Shaped Holes Using Pressure-Sensitive Paint Measurement Technique

A systematic study was performed to investigate the combined effects of film-hole geometry, blowing ratio, density ratio, and freestream turbulence intensity on a flat-plate film cooling. Detailed film-cooling effectiveness was obtained using a pressure-sensitive-paint technique. Four common geometries were used in this study: simple-angled cylindrical and fan-shaped holes, and compound-angled (beta = 45 deg) cylindrical and fan-shaped holes. Each plate contained one row with seven holes, and the hole diameter D and hole-length-to-diameter ratio (L/D) are 4 mm and 7.5, respectively. The effects of the blowing ratio M, coolant-to-mainstream-density ratio DR, and freestream turbulence intensity Tu were tested within the ranges of 0.3 similar to 2.0, 1.0 similar to 2.0, and 0.5 similar to 6%, correspondingly. Detailed variations of the laterally averaged effectiveness from low to high blowing ratios were obtained for three density ratios. The results indicated that effectiveness increased as increasing density ratio in general for all geometries. Fan-shaped holes outweighed cylindrical ones in effectiveness at higher blowing ratios. An additional compound-angle enhanced effectiveness for cylindrical holes. For increasing turbulence intensity, effectiveness decreased for shaped holes but slightly increased for cylindrical ones. The experimental data of simple-angled fan-shaped holes were validated with empirical correlation limited to DR = 1.7 similar to 2.0, and an improved correlation was proposed to predict effectiveness at DR = 1.0 similar to 2.0.