Experimental and computational evalutation of flow characteristics for advanced film cooling hole geometries

Film cooling is crucial in the field of gas turbines to protect the blade surfaces from the hot combustion gases. Several hole geometries have been studied in the past in an effort to optimize the cooling effectiveness of the holes while maintaining the structural integrity of the blade and low manufacturing costs. To understand the cooling effectiveness of the various hole geometries, the flow structures that develop as the coolant jet interacts with the hot mainstream must be understood. The present paper compares the results obtained from 2D Particle Image Velocimetry (PIV) measurements with CFD predictions using standard Reynolds-Averaged Navier Stokes (RANS) models with a commercially available code. The study is conducted for flat plate film cooling via conventional cylindrical holes, shaped holes (10° flare/laidback), and a tripod anti-vortex hole (AV) design. A constant blowing ratio (BR) of 0.5 was used for all the experiments, except for an additional measurement for the AV design at a BR of 1.0. Computational fluid dynamic (CFD) calculations were made with a standard k-epsilon model and compared to PIV results. The results show the counter-rotating vortices developing for cylindrical and shaped holes up to 5D and 3D respectively from the hole exit. AV holes showed no vortex formation, further supporting its higher cooling performance. Moreover, the present results indicate no separation of the coolant jet for AV or shaped holes as expected, while cylindrical holes displayed a small separation with a vertical extent of ∼0.1D. The CFD model was able to capture the main structures of the flow, but further efforts will concentrate in improving the representation of the flow normal to the flat plate surface.