Effect of Crossflows on the Discharge Coefficient of Film Cooling Holes

Abstract

The strongest flow parameter governing the film cooling effectiveness provided by a row of holes is the blowing rate. Precise setting of the blowing rate at the design stage requires accurate data for the discharge coefficient of the holes. The effects of crossflow on the discharge coefficient have received scant attention in published work to date. In the present work, the discharge coefficient of single rows of holes has been measured in a specially constructed isothermal rig over a wide range of geometric and flow conditions. Mainstream and coolant Mach numbers have been varied independently over the range 0 to 0.4 for pressure ratios in the range 0 to 2. Cooling hole length to diameter ratios were varied between 2 and 6, and inclinations of 30, 60, and 90 deg were used. The results show that the influence of crossflow is strong and complex, particularly with regard to that on the coolant side. A large range of data is presented sufficient to permit the discharge coefficient to be inferred for many cases of practical importance. Suggestions are also made for a promising theoretical approach to this problem.