DISCHARGE COEFFICIENTS OF HOLES ANGLED TO THE FLOW DIRECTION

In the cooling passages of gas turbine blades, branches are often angled to the direction of the internal flow. This is particularly the case with film cooling holes. Accurate knowledge of the discharge coefficient of such holes at the design stage is vital so that the holes are correctly sized, thus avoiding wastage of coolant and the formation of hot spots on the blade. This paper describes an experimental investigation to determine the discharge coefficient of 30 deg inclined holes with various degrees of inlet radiusing and with the axis of the hole at various orientation angles to the direction of the flow. Results are given for nominal main flow Mach numbers of 0, 0.15, and 0.3. The effects of radiusing, orientation, and crossflow Mach number are quantified in the paper, the general trends are described and the criteria for optimum performance are identified.