Double-Row Discrete-Hole Cooling: an Experimental and Numerical Study

Abstract

Double-row discrete-hole cooling arrangements offer several advantages over single-row systems yet the detailed cooling mechanism is less completely understood than for the single-row. This is partly because there have been fewer studies of this geometry and partly because the flow structure is more complex. The present paper presents detailed flow-field and concentration measurements around the injection holes for double-row injection on a flat plate at 30 deg to the mainstream. The experiments span values of the blowing injection mass velocities from 0.25 to 1.0 times the free stream mass velocity and for two boundary layer thicknesses just upstream of the injection. In contrast to single-row injection the cooling effectiveness rise monotonically with M over the range studied. Computer simulation of these flows and similar experiments of [7] has been made using a three-dimensional finite-difference code that embodies a semi-elliptic treatment of the flow field in the neighborhood of the injection holes in conjunction with a two-equation turbulence model with non-isotropic effective transport coefficients. It emerged from the calculations, that, for injection velocities up to 50 percent of the free stream value, levels of film-cooling effectiveness are extremely well predicted beyond about 10 diameters behind the leading row of holes. Around the holes themselves, however, there are certain discrepancies which become more serious as the injection level is raised.