Improvements of the adiabatic film cooling by using two-Row holes of different geometries and arrangements

Existing researches on two-row film cooling mainly focused on double-jet film cooling. However, researches on the effects by combining different kinds of hole shapes on film cooling performance are quite limited. In order to improve the film cooling effectiveness, the three-dimensional numerical method is utilized to investigate the effects of a novel structure composed of two-row holes with different shapes and arrangements on the adiabatic film cooling effectiveness with the blowing ratio of M = 1.5. To achieve this purpose, 30 different cases with two-row holes are designed and their film cooling effectiveness are compared with those of other seven cases with a single hole. Cases with two-row holes are designed by setting cylindrical, elliptical, or super-elliptical holes as the first-row, and arranging cylindrical holes with 30 deg, 45 deg, 60 deg, and 90 deg compound angles as the second row. The realizable k–ε turbulence model with enhanced wall function is utilized for all cases under identical boundary conditions. Similar film cooling performances are observed for cases with elliptical and super-elliptical holes being the first row, since the maximum deviation of film cooling effectiveness is less than 10%. It is found that the case integrates both a cylindrical hole and a cylindrical hole with 90 deg compound angle can greatly improve the film cooling performance with a higher discharge coefficient. However, the staggered case with an elliptical hole as both first- and second row gives the best film cooling effectiveness and the worst discharge coefficient due to the biggest resistance for the coolant flowing into the film hole.