Effects of Inclination Angle, Orientation Angle, and Hole Length on Film Cooling Effectiveness of Rectangular Diffusion Holes

Film-cooling effectiveness of rectangular diffusion holes under an inclination angle α = 45 deg, an orientation angle β = 45 deg, and a length-to-diameter ratio of L/D = 8.5 were, respectively, examined in a flat-plate experimental facility using the pressure sensitive paint (PSP) technique. Experiments were performed at a density ratio of DR = 1.38 and a mainstream turbulence intensity of Tu = 3.5%. The semicircle sidewall rectangular diffusion hole varied at three cross-sectional aspect ratios, i.e., AS = 3.4, 4.9, and 6.6. The tested results were compared with the baseline design with an inclination angle α = 30 deg, an orientation angle β = 0 deg, and a length-to-diameter ratio L/D = 6. A three-dimensional (3D) numerical simulation method was employed to analyze the flow field. The experimental results showed that the increased inclination angle converted the bi- or tri-peak effectiveness pattern of the baseline design to a single-peak pattern, weakened the lateral diffusion of coolant, and consequently decreased cooling effectiveness obviously. The decreased magnitude amplified with the increase of cross-sectional aspect ratio and blowing ratio. The adding of orientation angle seriously weakened the cooling effectiveness of the baseline design, and the blowing ratio and cross-sectional aspect ratio had almost no effect on overall cooling effectiveness. The elongated hole length provided a uniform distribution of lateral cooling effectiveness, which produced differential effects on the bi- or tri-peak pattern. The elongated hole length decreased the cooling effectiveness on the near hole region, but had less effects on overall cooling effectiveness, except the high blowing ratio.