Proper and efficient cooling of the turbine airfoil leading edge is imperative in increasing the airfoil life and overall efficiency of the gas turbine. To enhance the heat transfer coefficient in the leading-edge cavities, they are often roughened on three walls with ribs of different geometries. The cooling flow for these geometries usually enters the cavity from the airfoil root and flows radially to the airfoil tip or, in the most recent designs, enters the leading edge cavity from the adjacent cavity through a series of crossover holes on the partition wall between the two cavities. In the latter case, the cross-over jets impinge on a smooth leading-edge wall and exit through the showerhead film holes, “gill” film holes on the pressure and suction sides, and, in some cases, forms a cross-flow in the leading-edge cavity and is ejected through the airfoil tip hole. In this investigation, the impingement heat transfer coefficient was measured on both smooth and roughened leading-edge walls. Most reported studies cover the impingement on a flat smooth surface with round jets. This investigation dealt with two new features in airfoil leading-edge cooling concept: a curved and roughened target surface as well as impingement with racetrack shaped holes. Results of circular crossover jets impinging on the same surface geometries were reported by these authors previously. Experimental heat transfer results are presented for the impingement of racetrack shaped cross-over jets, with major hole (jet) axes at and 45° angles to the cooling cavity’s radial axis, on 1) a smooth curved leading-edge wall, 2) a wall roughened with conical bumps, and 3) a wall roughened with tapered radial ribs. The tests were run for a range of inlet and exit flow arrangements and jet Reynolds numbers and the results were compared with those of round cross-over jets. The major conclusions of this study are: a) racetrack crossover holes are much more efficient than circular holes in cooling of the leading-edge surface, b) the overall heat transfer performance of racetrack cross-over holes is superior to that of 45° racetrack cross-over holes, c) there is a heat transfer enhancement of up to 70% for roughening the target surface, and d) the driving factor in heat transfer enhancement is the increase in surface area.

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