Computational study of hole shape effect on film cooling performance

Film cooling effectiveness has been studied by using a computational approach based on solving the Reynolds-averaged Navier-Stokes equations. A wind tunnel test configuration is considered with a total of four cooling hole geometries as a cylindrical hole, a cylindrical hole with an upstream wedge (called 'ramp' thereafter), a shaped diffuser, and a double console slot. In all cases, the hole centreline has an inclination angle of 35° against the mainstream airflow and the blowing ratio is unity. Choosing the cylindrical model as a baseline, simulations have been carried out for grid convergence and turbulence model influence studies. Results are compared with available experimental data and other numerical predictions and good agreement has been achieved. Further computations continue with three remaining geometries, using the baseline flow conditions and configuration. Comparing to the results from the baseline model, it was found that the centreline adiabatic cooling effectiveness has shown incremental increases for the 'ramp' model, while results from the console slot model and the shape diffuser model have exhibited significant improvements by a factor of 1.5 and 2, respectively. The reason for such a step change in cooling effectiveness is mainly due to the weakening of the vortex structures in the vicinity of the hole exit, thus significantly reducing the entrainment of surrounding 'hot' fluids