10. Full-Coverage Effusion Cooling in External Forced Convection: Sparse and Dense Hole Arrays

To illustrate forced convection, external flow effects and phenomena, considered are full coverage effusion cooling arrangements. Parameters and phenomena considered include: (1) blowing ratio BR, (2) magnitude of main flow streamwise static pressure gradient (quantified by mainstream passage contraction ratio Cr values of 1, 3, 4, and 5), (3) streamwise development (quantified by variations with x/D), (4) effusion cooling hole inclination angle α, and (5) effusion hole spacing, ranging from dense to sparse (characterized by X/D values of 6 and 18, and Y/D values of 3, 5, and 7). As such, the film cooling holes in adjacent streamwise rows are staggered with respect to each other, with sharp edges, and streamwise inclination angles of either 20 degrees or 30 degrees, with respect to the liner surface. Data are provided for turbulent film cooling, blowing ratios (at the test section entrance) of 2.0, 5.0, and 10.0, coolant Reynolds numbers of 12,000 for BR = 5.0, freestream temperatures from 75 °C to 115 °C, a film hole diameter of 7 mm, and density ratios from 1.15 to 1.25. Data include local, line-averaged, and spatially-averaged adiabatic film effectiveness data and local, line-averaged, and spatially-averaged heat transfer coefficient data. Varying blowing ratio values are utilized along the length of the contraction passage, which contains the cooling hole arrangement, when contraction ratio is different from 1. Dependence on blowing ratio indicates important influences of coolant concentration and distribution. For example, line-averaged and spatially-averaged adiabatic effectiveness data show vastly different changes with blowing ratio BR for the configurations with contraction ratios of 1 and 4. These changes from acceleration are thus mostly due to different blowing ratio distributions along the test section.