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Abstract
A three-hole-branch geometry for film cooling is proposed. Each branch is made up of a streamwise 30°-angled circular hole with a circular hole of the same diameter on each side of it. These three holes share the same inlet area on the coolant supply side. Three side hole inclination angles of 30°, 37.5°, and 45° and three branch angles (the angle between the main and side holes) generated nine configurations that were tested for four blowing ratios of 0.5, 1, 1.5, and 2. To their benefits, these straight-through circular holes could easily be laser drilled on the airfoils or other gas turbine hot section surfaces. For comparative evaluation of these film hole geometries, the commonly used 7°-7°-7° diffusion hole geometry with the same inlet hole diameter was tested as a baseline under otherwise identical conditions. The pressure-sensitive paint (PSP) technique was utilized to test these geometries for their film cooling effectiveness. Depending on the branch geometry, for the same amount of coolant, some configurations were found to be superior to the baseline case for stream- or spanwise film cooling distributions while for the steeper side hole angles, these branched holes did not perform as well as the baseline case. The main conclusion is that the three holes with the same inclination angle of 30° exhibited the best film cooling effectiveness performance including the baseline geometry.
Highlights
Gas turbines are widely used in the industry to provide power for electric generators, aircrafts, trains, and ships
The blowing ratio increases from left to right corresponding to the values from 0.5 to 2, respectively
A visual comparison of these geometries shows that when the side and main holes have the same inclination angle of 30o (α1 = α2 = 30°, Figures 8–10), better coverage is achieved
Summary
Gas turbines are widely used in the industry to provide power for electric generators, aircrafts, trains, and ships. To maximize the power output and improve the efficiency, the turbine inlet temperature has been consistently increased. The increasing high inlet temperature may cause elevated thermal loads on the components that will damage the turbine airfoils and other hot sections, which reduces the durability of the whole system. Several features are in use to protect the turbine hot sections. Airfoil designs in modern gas turbines may include rib-roughened cooling cavities, pin banks, impingement holes and inserts, film holes and slots, thermal barrier coatings, and other features for thermal protection against the combustor gases. The main objective in designing the airfoil circuits, including the film cooling scheme, is gaining maximum coolant coverage with minimum spent air and minimum aerodynamic losses. Experimental as well as numerical, encompassing many aspects of film cooling, including branched hole geometries, have been reported in the open literature over the past several decades
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