Large eddy simulation of compound angle effects on cooling effectiveness and flow structure of fan-shaped holes

Large eddy simulation (LES) was utilized to investigate the influence of applying various compound angle (CA), on film-cooling effectiveness and turbulent flow structures. The baseline cooling hole was a 7-7-7 laidback fan-shaped hole, where this hole is located at a flat plate surface with a pitchwise spacing of 6D, and the hole was inclined at 30-degrees with respect to the mainstream hot-gas flow. Five different cooling hole orientations (CA0, CA15, CA30, CA45 and CA60) were numerically simulated using a constant density ratio of 1.5 and two blowing ratios (M = 1.0 and 3.0). The time-averaged computational results for the thermal and flow fields were validated by comparison with experimental data from previous literature. The simulation results revealed that under a low blowing ratio (M = 1.0), cooling performance was not affected significantly by the compound angle, but at the higher blowing ratio there was a considerable improvement of 40% for the CA60 hole over the CA0 hole, this improvement was especially pronounced in the lateral direction. The vorticity-field investigation showed that as the compound angle increased, the magnitude of the streamwise vorticity also increased while it becoming more asymmetric. In addition, time-space evaluation and spectral analysis of the velocity fluctuations indicates higher unsteadiness and greater turbulent statistics when using holes with larger compound angles.