Study on Effects of Spanwise-Expansion Parameters on Film Cooling Effectiveness of Diffusion Shaped Hole Configurations

Diffusion shaped holes are widely used on aero-engine turbine blades for film cooling. The effect of the spanwise-expansion angle and spanwise width of the hole exit on the film cooling effectiveness of diffusion shaped holes was investigated in this study. The film cooling effectiveness was obtained through the pressure-sensitive paint (PSP) technique on a plate model at five momentum ratios (0.11, 0.43, 0.97, 1.73, and 2.71). A numerical simulation was performed to analyze the flow mechanism. The laid-back fan-shaped (LBFS) holes and the fan-shaped holes with three spanwise-expansion angles (FS-A: 7 deg, 11 deg, and 15 deg) and with three spanwise widths of the hole exits (FS-B: 1.7d, 2.3d, and 3.4d) were used for the study. The results revealed that the film cooling effectiveness of fan-shaped holes (FS-A) increases monotonically as the spanwise-expansion angle increases, while the film cooling effectiveness of the LBFS holes increases first and then decreases as the spanwise-expansion angle increases. However, the film cooling effectiveness of the two kinds of holes (LBFS and FS-B) both increase first and then decrease with the increase of the spanwise width of hole exit. The mainstream intrusion occurred at the same spanwise width of the hole exit of 3.4d for both kinds of holes. The laid-back fan-shaped hole possessed high resistance to cooling performance decline. The importance of the spanwise width of the hole exit as a key parameter was emphasized in this study.