Enhanced film cooling effectiveness by wall-roughness in cooling hole of turbine blade

The film cooling is investigated numerically for gas turbine blade cooling. Film cooling performance is vital for blade safe operation. By calculating the film cooling effectiveness, the wall roughness inside the cooling hole effect is evaluated. Wall roughness by a turbulence promoter of aspect ratio K = L/h from 6 to 14, varying the pitch L and keeping constant the height h. Blowing ratio range from M = 0.5 to 2 and fixed mainstream Reynolds number, Re = 2.0 x 105 are tested. The cooling hole and flat plate surface with angle of 35o is used to compare the results and validate the CFD approach assessing the turbulence models k-ε RNG and RSM. A swirl flow develops inside the cooling hole due to installing the turbulence promoter. The coolant discharge turbulence parameters modify the normal case. The momentum and heat transfer rates have an impact on the film cooling performance. The results indicate film cooling effectiveness and surface protection enhancement of 9.84%, and 19.4%, respectively, for the best aspect ratio and blowing ratio. The coolant roughness may be used to improve the design of coolant hole and to reduce the number of orifices needed for safe gas turbine blades.