Setting Robust Manufacturing Tolerances for Turbine Trailing Edge Film Cooling

Abstract The trailing edge of a high-pressure turbine blade presents a challenge to turbine cooling engineers. Its thin nature requires that film cooling holes are manufactured through electrode discharge machining (EDM), a process which requires high precision in order to prevent extreme variations in hole geometry and location. Previous studies on manufacturing tolerances have looked at fan-shaped holes and only onflat plates. This study aims to understand the extremes of possible manufacturing variations in the trailing edge cutback region of a high pressure turbine blade to help set appropriate manufacturing limits. A row of cylindrical film holes with a radial inclination of 30° was tested and used as the benchmark. Several film hole configurations were then tested over a range of blowing ratios. These included film hole shifts between cutback section and ejection plane as well as cutback step shifts, resulting in a change in the thickness of the cutback thickness. The experiments were carried out in the high velocity 2D linear cascade experimental facility using pressure sensitive paint (PSP) to measure film effectiveness. At low blowing ratios, most manufacturing variations were found to have very little effect on film cooling effectiveness. At higher blowing ratios, higher offsets between the cutback section and the film hole ejection plane were found to have greater detrimental effects on film cooling effectiveness. A numerical study was completed to complement the experimental findings and support the understanding of manufacturing limits in trailing edge film holes.