Film effectiveness performance for a shaped hole on the suction side of a scaled-up turbine blade

Surface curvature has been shown to have significant effects on the film cooling performance of round holes, but the present literature includes very few studies dedicated to curvature’s effects on shaped hole geometries despite their prevalence in turbine blade and vane designs. Experiments were performed on two rows of holes placed on the suction side of a scaled-up gas turbine blade model in a low-Mach-number linear cascade wind tunnel. The test facility was set up to match a high-Mach-number pressure distribution without modifying the blade’s geometry or including contoured end walls to accelerate the flow. By adjusting the positions of the movable walls in the tunnel test section, the suction side pressure distribution could be matched to the design distribution. One row was placed in a region of high convex surface curvature; the other, in a region of low convex curvature. Other geometric and flow parameters near the rows were matched in the design of the experiment, including hole geometry and spacing. The hole geometry was a standard 7-7-7 shaped hole. In addition, local freestream conditions for the rows were measured and set to match as closely as possible. Comparison of the adiabatic effectiveness results from the two rows revealed trends similar to those seen in previous literature for round holes. The high curvature row outperformed the low curvature row at lower coolant injection rates, having wider jets and higher centerline effectiveness. But as the injection rate was increased, the low curvature row surpassed the high curvature row in effectiveness. The driver behind this behavior was the surface-normal pressure gradient that arose from the convex surface curvature. As flow traveled around the surface, centripetal acceleration produced a pressure gradient directed towards the surface, effectively pushing jets toward the blade wall. However, at higher blowing ratios, the jets’ high momenta overcame the effects of this pressure gradient. At these injection rates, the high curvature row’s jets’ trajectories did not follow the surface as it curved away. The high surface curvature exacerbated the adverse effects of jet separation on film cooling performance.