Experimental Study on the Film Cooling Characteristics of Three Complex Tip Structures

The turbine blades of aircrafts must be properly cooled to prevent engine failure. Thus, to investigate the influence of the tip structure on the film cooling effect, pressure-sensitive paint test technology was used to determine the adiabatic film cooling effectiveness in this study. The experiment was completed in a cascade comprising three straight blades. The effects of the blowing ratio, density ratio, tip clearance, and tip structure on film cooling efficiency were analyzed. The experimental results demonstrated that, as the blowing ratio increased, the film coverage area and film cooling efficiency increased under most experimental conditions. However, the film cooling efficiency was found to initially increase, and subsequently decrease, as the blowing ratio increased. The respective influences of the density ratio and tip clearance on the film cooling efficiency were found to be significant. The density ratio experiments revealed that a high-density ratio can result in better film coverage than the low-density-ratio air. The tip clearance experimental results indicated that a small tip clearance promotes an increase in film cooling efficiency; this is because the small tip clearance negatively affects the main stream leakage flow, which can reduce the film coverage area. Under the conditions of the Base case 2 configuration, a blowing ratio of 2.1, and a tip clearance of 0.6%h, the average film cooling efficiency of the blade tip was 0.22. Among the three blade tip structures applied in this study, Base case 2 demonstrated higher film cooling efficiency than the other two blade tip structures under the conditions of the same blowing ratio, tip clearance, and density ratio.