The Discharge Coefficient of Flared Film Cooling Holes

Abstract

The coefficient of discharge (Cd) of flared film cooling holes is reported for a range of pressure ratios, geometries and flow conditions. The geometry of the holes used was typical of present day designs produced by the method of electrical discharge machining or spark erosion. Cd data are given for normal (90°) holes and for 30° inclined holes. The effects of the following geometrical and flow parameters have been investigated and are reported. Effect of the length of the cylindrical portion of the hole prior to the flare. Effect of the deletion of the layback of the hole flare Effect of the presence of cross flow on the inlet to and on the outlet from the hole. Effect of the orientation of the cross flow relative to the axial direction of the hole. The flare increases Cd over that for a cylindrical hole. Eliminating the layback has little effect on Cd, but reducing the length of the cylindrical portion has a marked adverse effect when an inlet cross flow is present. As for cylindrical holes, an inlet cross flow reduces Cd for normal holes, but flared holes can maintain higher Cd’s than cylindrical holes, provided that the cylindrical inlet to the flare is sufficiently long.