Influence of Hole Inlet Geometry on the Film Cooling Effectiveness from Shaped Film Cooling Holes

The effect of film cooling hole inlet geometry is experimentally investigated in this study. Detailed film cooling effectiveness distributions are obtained on a flat plate using Pressure Sensitive Paint (PSP). The inlet of a traditional 12 degrees - 12 degrees - 12 degrees, laidback, fanshaped hole varies from a traditional "round" opening to an oblong, racetrack shaped opening. In this study, a single racetrack inlet with an aspect ratio of 2:1 is compared to the round inlet. For both designs, the holes are inclined at theta = 30 degrees relative to the mainstream. Blowing ratios of 0.5, 1.0, and 1.5 are considered as the coolant to mainstream density ratio varies between 1.0 and 4.0. For all cases, the freestream turbulence intensity is maintained at 7.5%. With the introduction of the racetrack shaped inlet, the coolant spreads laterally across the diffuse, laidback fanshaped outlet. The centerline film cooling effectiveness is reduced with the enhanced lateral spread of the coolant. However, the benefit of the shaped inlet is also observed with an increase in the area averaged film cooling effectiveness, compared to the traditional round inlet. Not only does the shaped inlet promote spreading of the coolant, it is also believed the racetrack shape suppresses turbulence within the hole allowing for enhanced film cooling protection near the film cooling holes.