Optimization of fan-shaped film cooling holes for enhancing cooling effectiveness under variable coolant inlet pressure ratios

In traditional film cooling design, holes had the same geometry in the same row of the blade and the same zone of the endwall. However, film cooling holes operate at different conditions when the positions are different, even in the same row. Additionally, geometry variables of the film cooling holes with the best cooling performance vary with the aerodynamic conditions. Optimization of film cooling hole geometry and arrangement has been paid much attention in recent years to improve the cooling performance. In this paper, a fan-shaped film cooling hole has been optimized on a plate model under variable coolant inlet pressure ratios to obtain the geometry parameters with better and more robust cooling performance. Two design variables, i.e., injection angle and expand angle were studied in the optimization. The coolant inlet pressure was different for each case during the optimization. The optimization objective was to increase the mean value and decrease the variance value of the area average cooling effectiveness downstream of the hole exit. The optimization system consisted of a self-programming parametric design and mesh generation tool, a CFD solver and a genetic algorithm (GA) coupled with surrogate model. At first, numerical simulation results were validated against the measured data, and agreed well with the experiment results. Range of the design variables were determined according to the sensitive analysis of the design variables. It was indicated that the film cooling hole obtained by the optimization showed remarkably higher cooling effectiveness than that of the original scheme. With the pressure ratio changing, the optimized cooling hole obtained could keep relatively high effectiveness. Additionally, the optimized film cooling hole was applied on a typical gas turbine vane endwall to examine the cooling performance in cascade passage. It could be observed that the optimal film holes performed better than that of the original design.