Trends in film cooling effectiveness caused by increasing angle of diffusion through a row of conical holes

Previous studies have concluded that increasing the diffusion angle in conical film cooling holes leads to an improvement in film cooling effectiveness. Discharge coefficient and film cooling effectiveness measurements are conducted to characterize these effects. Three test-plates, each with one row of eight pure conical-shaped cooling holes of diffusion angles of 2, 4, and 6 degrees, with respect to the hole-centerline, are used in this study. In addition, the effects of an added entry-length (cylindrical starting section) are also investigated in the form of a 2-degree conical hole with a 4-diameter cylindrical entry-length. Area ratios for these holes range from 1.7 to 2.83. Coolant is injected at 35 degrees to the horizontal, into the main flow. The interactions between the coolant jets downstream of the injection point are also investigated. Temperature sensitive paint, TSP, is the technique used to acquire the temperature distribution downstream of the cooling holes, and thus, ascertain the laterally-averaged film cooling effectiveness. Data are obtained for blowing ratios ranging from 0.5 to 1.5. Results and trends are compared with those published on a study on conical holes by the authors, as well as published data for shaped holes, which indicate that the higher conical angles do increase laterally-averaged effectiveness. Moreover, the added entry-length, while providing a metering diameter, does improve the effectiveness in the near-hole region particularly at the higher blowing ratios.