Coefficient of discharge of 30° inclined film cooling holes with rounded entries or exits

Abstract

The coefficients of discharge of 30° inclined holes having a length to diameter ratio of 6, and rounded entries or exits have been measured for a range of crossflow conditions. The rounding radius varied from 0 to 1 hole diameters, and the crossflow Mach numbers from 0 to 0.5. Rounding the hole inlet was found to be beneficial, with increases of up to 15% being obtained at high coolant inlet side crossflow Mach numbers. Rounding the exit produced no significant benefit. The crossflow effects have been correlated using inlet and outlet additive loss coefficients. These reflect the changes in pressure drop across the hole necessary to maintain the hole mass flow rate when crossflows are applied. The correlated data have been incorporated in a computer program which gives good predictions of discharge coefficient in the presence of either a coolant crossflow or a mainstream crossflow or both.