The effects of an embedded vortex on a film cooled turbulent boundary layer.

Abstract

This study was designed to model some of the secondary flow effects on endwalls, blades, and combustion chambers of gas turbine engines. Measurements were made in a turbulent boundary layer developing over a flat plate, using a single row of injection holes spaced three diameters apart inclined at 30 degrees with respect to horizontal. The hole diameter to boundary layer thickness ratio, non-dimensional injection temperatures, and blowing rates were the same as exist in turbine first stages. The injection system was designed to provide uniform injection temperatures for various blowing rates with discharge coefficients ranging from 0.58 to 0.73. The heat transfer surface was designed to provide constant heat flux with adjustable temperature range. Experimental heat transfer results were obtained with a turbulent boundary layer only, with boundary layer and injection of film cooling, with boundary layer and embedded vortex, and finally with boundary layer, film cooling, and embedded vortex. Results with a turbulent boundary layer only show excellent agreement with correlations accounting for unheated starting length. Results with film cooling only show expected trends, and results with embedded vortex only show excellent agreement with data from the literature. The effects of the vortex on heat transfer in the film cooled boundary layer are significant and important: (]) On the downwash side of the vortex, heat transfer is augmented, effects of the film cooling are negated and local "hot-spots" will exist in engines. (2) Near the upwash side of the vortex coolant is pushed to the side of the vortex, appearing to augment the protection provided by film cooling.