Film Cooling on a Modern HP Turbine Blade: Part IV — Compound-Angle Shaped Holes

The performance and physics of film cooling with compound-angle shaped holes on a modern high-pressure turbine airfoil is studied in detail using state-of-the-art computational simulations. Computations model high-speed single-airfoil-passage cascade experiments, and computational results show good agreement with experimental data. Evaluation of physics includes examination of flow features and adiabatic effectiveness. The blowing ratios (M) simulated on the pressure surface (PS) of the blade are 1.5, 3.0, and 4.5, with a single density ratio of 1.52. On the pressure surface the dominant mechanism affecting coolant behavior is vorticity, which increasingly tucks hot crossflow under the coolant as the blowing ratio increases. Thus at high blowing ratios, a lower percentage of the coolant provides thermal protection for the blade until the vortices dissipate far downstream. Also, the vortex structures cause large lateral temperature gradients despite the lateral motion of the flow induced by the compound-angle injection. The dominance of vorticity can be attributed to poor diffusion of the coolant inside the diffuser of the film hole. On the suction surface (SS), the simulated blowing ratios are 1.0, 1.5, and 2.0, with a single density ratio of 1.52. Pressure gradients normal to the SS result in the flow pushing the coolant onto the blade. Also, vorticity is less dominant since diffusion of coolant inside the film hole is better due to low blowing ratios and due to a hole metering section that is almost 3 times longer than that of the PS hole. Hot crossflow ingestion into the film hole is observed at M = 2.0. Ingested crossflow causes heating of the surface inside the hole that extends down to the end of the hole metering section, where the surface temperatures are approximately equal to an average of the crossflow and coolant temperatures. These results demonstrate the inadequacy of 1-D, empirical design tools and demonstrate the need for a validated CFD-based film cooling methodology.