| Resumo : |
Advances in gas turbine technology are focused on increasing efficiency with the minimum of maintenance possible and extended service life. However, the improvement in efficiency results in increase of the thermal loads, and, therefore, the development of efficient technologies for the cooling of aeroengines is required. In this way, the present work refers to the numerical investigation on internal and external cooling strategies applied in turbines. The methodology developed to analyze such strategies is based on the flat-plate approach and computational fluid dynamics (CFD) techniques, being the flow, in the study domain, considered viscous, turbulent and incompressible. The ANSYS CFX version 15.0 program is used to solve the general equations of fluid mechanics by the Reynolds Average Navier-Stokes (RANS) steady state method and the Shear Stress Transport (SST) model turbulence. External cooling is studied in different film cooling geometries (square, cylindrical, fan-shaped and laidback fan-shaped) and evaluated through the film cooling effectiveness. As a result, the fan shaped bore was shown to be the most effective, showing improvement in the effectiveness of the film cooling around to 36% in relation to the square hole, 27% in relation to the cylindrical hole and 9% in relation to the laidback hole fan shaped. However, the combined effects of internal and external cooling is studied through a highly sophisticated scheme, called louver, which combines the effects of impingement and film cooling. Due to the opportunity identified in the literature, different geometries of turbulators (pins, ribs, cavities and dimples) were implemented in the channel between the impingement and the film cooling, with the purpose of evaluating the impact of these geometries on the film cooling effectiveness over the flat plate surface in comparison to the louver scheme without turbulators. This study concluded that the pin fins P2 proved to be the most promising because they increased in 7% the film cooling effectiveness, while the pin fins P1 did not show significant gains in film cooling effectiveness. Ribs R4 also have a good potential to increase the effectiveness, because na increase of 4% in film cooling effectiveness was observed. However, cavity and dimples turbulators did not show relevant improvements in film cooling effectiveness. |