The Effect of Crossflow Velocity on the Film Cooling Effectiveness of Fan Shaped Holes

Abstract Film cooling is a critical method used in modern gas turbine engines to maintain turbine metal temperatures within material limits, ensuring engine longevity. Coolant is injected through holes onto vane/blade surfaces, where it interacts with the main flow, creating complex flow patterns that influence both cooling efficiency and aerodynamic performance. Cylindrical holes, though simple, suffer a significant drop in performance at high flow rates due to the formation of high-momentum jets at the hole exit. Fan-shaped holes, however, offer an effective alternative, particularly in engines exposed to high turbine inlet temperatures. These holes diffuse coolant flow near the exit, creating lower momentum flows that adhere better to the airfoil surface, improving cooling efficiency. This study focuses on a 7 degree lateral and laidback fan-shaped hole. First, numerical methods and mesh grids are validated against experimental data from Karen A. Thole et al. regarding laterally averaged film effectiveness. The effects of secondary flows on cooling performance are examined for both cylindrical and fan-shaped holes. Afterthat, specific models are created to focus main objectives of this paper. The numerical models of 7-7-7 fan shaped hole with the same mainstream conditions are performed with same pressure ratio (1.05) across the cooling hole and different internal crossflow velocity (0 Ma, 0.1 Ma, 0.2 Ma, 0.25 Ma). The study shows that fan-shaped holes have a higher discharge coefficient than cylindrical ones, due to the diffusion effect lowering throat static pressure, allowing for better coolant flow. Also, higher crossflow velocity causes higher blowing ratio for fan shaped hole considering same pressure ratio across hole.