The effect of manufacturing tolerances on the performance of gas turbine air system metering holes with chamfered inlets

The current study represents an experimental and steadystate computational analysis of the mass flow through a single metering orifice with uniform and non-uniform chamfers. Chamfered holes have been used extensively in air-systems for the ease of production and their (relatively high) discharge coefficient is insensitive to typical chamfer depth tolerances. This work extends the understanding of chamfer tolerances by investigating non-uniform chamfers due to angular misalignment of the chamfer tool relative to the hole. The range of the deviation angles between the axis of the tool and the axis of the metering orifice was 0-12 degrees. The tests were performed in the pressure ratio range of 1.1…1.48, representing the range between idle and take-off operation points. A 3D CFD analysis of the tests using the Shear-Stress Transport (SST) k–ω model to simulate the mean flow field inside the metering orifice has also been completed. The results showed that at large pressure ratios, representative of the take-off operation point, the metering orifice with non-uniform chamfers showed reduction in mass flow delivery as high as 4%. A threshold in metering holes performance was detected for the tool inclination of 9.50 . At low pressure ratios, for conditions typically representative of idle operation point, a small deviation angle causes mass flow increase across the orifice.