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One popular method for the protection of gas turbines' hot sections from high-temperature combustor gases is film cooling. Substantial amounts of research have been conducted to accomplish this task with the minimum cooling flow, maximum surface coverage, and minimal aerodynamic inefficiencies or structural penalties. In this study, a combined experimental and numerical investigation was conducted on three selected film-cooling hole geometries. These geometries were designed with the same initial metering (feed) section, a cylindrical hole of 30 °inclination angle, followed by three different forward expansion section geometries. The expansion sections had a 7 °laid-back angle and a 17 °expansion angle in each lateral direction. However, different interior corner radii were used to blend the metering hole to the exit area, creating three different expansion geometries with almost the same exit areas. In practice, this variation in expansion geometry could represent manufacturing faults or tolerances in laser drilling of the film holes. This study shows that the variations in film-cooling effectiveness are not significant even though the expansion geometries are significantly different. The Pressure Sensitive Paint (PSP) technique was used to obtain the detailed distribution of film-cooling effectiveness on the surface area downstream of these film holes. Adiabatic film cooling effectiveness was measured at blowing ratios of 0.5, 1.0, and 2.0. CFD models of these film holes were also run, and the results were compared with the test data. The major conclusions of this study were that these proposed new geometries produced higher film effectiveness than the conventional 7 °-7 °-7 °diffusion film holes, for the same exit area, the expansion section geometry of the film holes did not have a significant effect on the film coverage, and the numerical results were in good agreement with the test data.

Film cooling technology is a commonly used method for thermal protection of gas turbines’ hot sections. A new, shaped, film cooling hole is proposed in this study. The geometry is made of a straight-through cylindrical feed hole at an inclination angle of 30° followed by an expansion section. The expansion section is created by the rotation of the same circular hole on the inclination plane about an axis normal to that plane which passes through the center of the feed hole exit area. This shape was designed to decrease the deteriorating effects of kidney vortices by proper distribution of the coolant flow emerging from the hole exit area. Cases with four rotation angles (7°, 14°, 17.5°, and 21°) were studied both experimentally and numerically and for the blowing ratios of 0.5, 1, and 2.0. For comparisons, the commonly used 7°-7°-7° diffusion hole geometry was also tested under otherwise identical conditions. For data collection, the pressure-sensitive paint (PSP) technique was used to measure the film cooling effectiveness. Streamwise- and spanwise-averaged film effectiveness results were obtained to compare the performance of different geometries. The main conclusions were that the case of 21° rotation angle produced the highest film effectiveness and outperformed the 7°-7°-7° diffusion hole geometry.