Discharge Coefficients of Cooling Holes With Radiused and Chamfered Inlets

The flow of cooling air within the internal passages of gas turbines is controlled and metered using orifices formed of holes in disks and casings. The effects of inlet radiusing and chamfering of these holes on the discharge coefficients forms the subject of this paper. Experimental results for a range of radiusing and chamfering ratios for holes of different length-to-diameter ratios are presented covering the range of pressure ratios of practical Interest. The results indicate that radiusing and chamfering are both beneficial in increasing the discharge coefficient. Increases of 10–30 percent are possible. Chamfered holes give the more desirable performance characteristics in addition to being easier to produce than radiused holes.