Quantitative Visualization of Full-Coverage Discrete-Hole Film Cooling

Abstract

Water tunnel experiments were carried out to study full-coverage discrete-hole film cooling for geometries applicable to gas turbine combustor liners. The cooling holes were spaced at a pitch to diameter ratio of 6.5 and had an injection angle of 20° to the cooled surface. The mainstream flow direction was in line with the cooling holes. Blowing ratios from 0.5 to 5.7 were studied, which is a range typical of combustor liners. A unique multiple plane PLIF (planar laser-induced fluorescence) technique was used to measure time-averaged film cooling concentration at various heights above the surface to be cooled. Three-dimensional data sets were generated to quantitatively visualize cooling-jet film coverage, structure, and interaction. Film coverage as close as 0.25 mm (0.010 in.) from the surface was measured, thereby yielding data that approach adiabatic film effectiveness. Two sets of film cooling experiments were conducted. One set used a model with a relatively small array of 2.54 mm (0.100 in.) holes, meant to be a large-scale model of hole sizes encountered in combustor liners. The second set used a large array of 0.51 mm (0.020 in.) nominal diameter laser-drilled holes, manufactured in the same manner as combustor liner cooling holes. The results show that near-wall film coverage is minimum for blowing ratios from 1.7 to 3.3. At blowing ratios less than 1.7 and greater than 3.3, the film coverage was improved. Jet structure and interaction was also observed. In particular, jet separation behavior and coalescence were visualized, and both were generally a function of blowing ratio.

Effects of Effusion Cooling Pattern Near the Dilution Hole for a Double-Walled Combustor Liner—Part II: Flowfield Measurements

“…In addition, they found that once the flow was fully developed, the momentum flux ratio of the effusion jets did not affect the penetration height. In another flow visualization study of an effusion liner without dilution holes, Fric et al [11] found that the film coverage from the effusion jets was made worse as the blowing ratio increased between M eff,in ¼ 1.7-3.3, while the coverage of the effusion film improved beyond this range, resulting from an increased level of coolant.…”

Effects of Effusion Cooling Pattern Near the Dilution Hole for a Double-Walled Combustor Liner: Part 2 — Flowfield Measurements

“…In addition, they found that once the flow was fully developed, the momentum flux ratio of the effusion jets did not affect the penetration height. In another flow visualization study of an effusion liner without dilution holes, Fric et al [11] found that the film coverage from the effusion jets was made worse as the blowing ratio increased between Meff,in = 1.7 to 3.3, while the coverage of the effusion film improved beyond this range, resulting from an increased level of coolant.…”

A 3-dimensional, coupled, DNS, heat transfer model and solution for multi-hole cooling

“…of the cooling system. The direct effect of the coolant jet, which is often evaluated by using an adiabatic wall, has been investigated widely as in Lin et al [1] and Fric et al [2], and it is a dominant effect at high blowing ratio (M P 1). The other two effects, however, can be more important for a high efficiency, low blowing ratio cooling system, such as a multihole cooling system for multi-hole CMC materials that can have a relatively large number of holes and percentage open area with minimal cost penalty.…”