부산대학교 도서관

Improving the cooling effectiveness of turbine blades is one of the key drivers in gas turbine engine performance. Transpiration cooling describes an ideal arrangement that maximises this cool-ing effectiveness through the use of porous structures. High internal surface area and uniform cool-ant distribution are some of its main benefits. However, physical limitations in manufacturing and materials mean that this arrangement is impractical to implement. This research identifies some of the key properties that makes transpiration cooling success-ful and recreate them with geometric features already within the bounds of existing manufacturing capabilities. The use of simple, small round film cooling holes, in tight staggered arrays at varying locations around the blade profile was found to generate exceptional levels of film effectiveness. A series of experimental campaigns were carried out to quantify the effects of different parameters in driving this high film effectiveness. Features placed on the early suction surface of the blade running at low blowing ratios were seen to be perform particularly well, with film effectiveness levels above 90% being maintained to the trailing edge. Analytical modelling of the results demonstrated that the overall array of film holes generates films that behave similarly to tangential injection slots. A saturated film core was identified, which remained effectively separate from the turbulent boundary layer. Further analysis suggested that the performance of the suction surface films could be explained by these operating in a laminar-like regime, contradicting many commonly held assumptions used for suction surface film modelling. Investigations into the nature of the interactions between the individual film cooling jets were also carried out using numerical simulations. These illustrated some of the beneficial outcomes of positioning film holes in close proximity to each other. The effects of counter rotating vortex pairs and boundary layer velocity profiles were identified as key mechanisms driving these interactions. Crucially, the magnitude of these interactions was found to outweigh any effect of individual film hole geometry. The present work culminated in a series of metal effectiveness tests on turbine blade geometries. These were used to obtain a complete measure of the performance of high porosity cooling arrays within a double walled cooling scheme. The aim of these experiments was to showcase the potential breakthrough in film cooling that had been unlocked by the high porosity array approach. Results in this experiment demonstrated that metal effectiveness values for the proposed systems already exceeded those of mature state of the art cooling arrangements.