Experimental optimization of a fan-shaped film cooling hole with 30 degrees-injection angle and 6-hole length-to-diameter ratio

Abstract

In this study, the effect of the shape parameters of fan-shaped holes on film cooling effectiveness was experimentally investigated and the optimum values of each shape parameter to maximize the overall averaged film cooling effectiveness were presented. Among the shape parameters of a fan-shape hole, the injection angle and the hole length to diameter ratio (L/D) were fixed as 30 degrees and 6, respectively, and the three shape parameters, the forward expansion angle, the lateral expansion angle, and the metering length ratio, were selected as variables. The design points of each parameter were selected using the Box-Behnken design method, and the optimized values of each parameter were obtained using RSM (Response Surface Methodology). The film cooling effectiveness was measured using the PSP (pressure sensitive paint) technique. The experiment was conducted under the condition of two density ratios (1.0 and 2.0) and four blowing ratios (1.0, 1.5, 2.0, and 2.5). Results showed that the film cooling effectiveness was generally higher for the higher density ratio condition, but the effect of the blowing ratio was not consistent. The main effect analysis showed that film cooling effectiveness increased as the forward and the lateral expansion angles increased, and the metering length became shorter. However, optimization results showed that the optimized hole had a smaller forward expansion angle due to the interaction effect between each shape parameter. The film cooling effectiveness of the optimized hole was higher than that of the reference hole by 52.4% near the gas turbine operating condition.