Experimental and numerical study of film cooling performance on turbine vanes with cylindrical and trapezoidal slot holes

Modern gas turbines operate beyond the thermal limits of metallic alloys, making film cooling indispensable for turbine blade protection. Although shaped-hole configurations can enhance film-cooling performance compared with conventional cylindrical holes, their geometric complexity often increases manufacturing difficulty. To simultaneously improve film-cooling performance and manufacturability, a trapezoidal slot-hole configuration featuring a simple geometry and continuous outlet is proposed and evaluated as an alternative film-cooling design for turbine applications. A systematic comparison between trapezoidal slot holes and conventional cylindrical holes was conducted on both the suction and pressure surfaces of a turbine guide vane through Pressure-Sensitive Paint measurements and Computational Fluid Dynamics simulations. Tests were conducted over a range of blowing ratios ( BRs ) using two rows of staggered holes. Results demonstrate that trapezoidal slot holes significantly outperform cylindrical holes: on the suction surface, they eliminate film detachment observed at BR ≥ 2.0 with cylindrical holes, improving area-averaged film cooling effectiveness by 26.8%–125.3% across BR = 0.5–3.0. On the pressure surface, they provide continuous spanwise coolant coverage, with area-averaged film cooling effectiveness increased by at least 32.4% and improved uniformity. Furthermore, trapezoidal slots exhibit a consistently higher discharge coefficient, indicating lower flow resistance and more efficient coolant delivery under lower supply pressure. The performance enhancement is attributed to suppressed jet lift-off and enhanced lateral coolant spreading. The optimal BR differs between surfaces, being lower on the pressure side. These findings offer practical guidance for designing high-efficiency profiled film cooling holes in gas turbines.