Experimental optimization of butterfly-shaped film cooling hole configuration with a 30 degree injection angle

Abstract

Film cooling is one of the external cooling techniques that is widely applied to the hot-gas path components of a gas turbine, forming a thin film of a coolant on the surface to prevent the direct convective heat transfer between combustion gas and components. The film cooling effectiveness (FCE) is significantly influenced by the geometry of the injection hole. Therefore, it is important to adjust the shape parameters in order to derive the optimal hole configuration under given flow conditions. In a previous study, a butterfly-shaped film cooling hole configuration (BSHC), which combines the advantages of fan-shaped holes and anti-vortex holes, was proposed. In this study, an investigation into the optimal shape design of the BSHC was performed using the design of experiments. The forward expansion angle, lateral expansion angle, and twisted angle were defined as design variables. Before the optimization, the effect of each design variable on local and averaged FCE was analysed. Generally, a high FCE could be obtained when the forward expansion angle was small within a range of 7⁰ - 15⁰. However, at high blowing ratios, high effectiveness was also observed even with a large forward expansion angle. Both the lateral expansion angle and the twisted angle had high FCE near the centre point, 11⁰ and 20⁰, respectively. The response surface of the overall averaged FCE was predicted using the Kriging model. The optimized BSHC under a density ratio of 2.0 and blowing ratio of 2.0 was determined and named OPT BSHC. The OPT BSHC showed 8.6 % and 10.5 % higher FCE respectively, compared to two types of the optimized fan-shaped holes that were optimized under the same conditions.