Investigation on the effect of hole diameter and wall thickness on the overall cooling effectiveness of turbine vane leading edge

Abstract

This study focused on three single-layer wall models for the leading edge and compared the overall cooling effectiveness (ϕ) under different film hole diameters and wall thicknesses. The three vanes ensured the same film hole exit area. The surface temperature was measured by an infrared thermal imager. The distribution of flow and heat transfer was obtained by computational fluid dynamics. The mainstream Reynolds number based on vane chord was 165,000. The experimental temperature ratio of the main flow and the coolant was 1.98, which was close to the real engine operating condition. Four typical mass flow ratios (MFRs) were performed, including 0.35%, 0.52%, 0.69% and 1.02%. The results indicate that the small-diameter model exhibits efficient coolant distribution and enhanced film coverage. This consequently results in a rise in ϕ by 0.06 to 0.09. In addition, vanes with the same hole diameter but different wall thicknesses have similar coolant distributions and film coverage. However, they differ in terms of heat transfer distribution. The thick-walled vane transfers approximately 70% of the heat flux from the sidewall of the hole, while the thin-walled vane transfers approximately 50%. Furthermore, ϕ of the thick-walled vane shows a greater increase as the MFR increases. Nevertheless, the difference in ϕ values between the two vanes at the same MFR condition is not significant. Finally, the wall thickness to hole diameter ratio (t/D) is proposed as a design consideration. When t/D is equal to 3.45, the ϕ is higher than the other two. This suggests that the optimal value of t/D for the structure might lie between 2.4 and 8.64, potentially approximately 3.45.