Pressure Gradient Effects on Film Cooling

Abstract

Film cooling effectiveness was studied experimentally using a flat plate test facility with a single row of inclined round holes which injected high density, cryogenically cooled air. A pressure distribution representative of the suction side of a gas turbine blade was imposed on the test plate using a top wall contour. Values of the acceleration parameter ranged from K = 1.5 × 10−6 at the injection location to K = −0.5 × 10−6 at 50 D downstream. Effectiveness results were compared with previously reported zero pressure gradient results obtained in the same facility. Experiments were performed at a density ratio of DR = 1.6 with a range of blowing ratios from M = 0.4 to 1.5 and momentum flux ratios from I = 0.10 to 1.4. Lateral distributions of adiabatic effectiveness results were determined at streamwise distances from 3 D to 15 D downstream of the injection holes. When the cooling jets did not completely detach, the application of the pressure gradient improved the lateral spread of the jets immediately downstream of the film cooling holes and increased the decay rate of the laterally averaged effectiveness. However, overall changes in effectiveness were small. When the cooling jets were completely detached (at I = 1.4, M = 1.5), the pressure gradient distribution had essentially no effect on the jet effectiveness.