Comparison of Film Effectiveness and Cooling Uniformity of Conical and Cylindrical-Shaped Film Hole With Coolant-Exit Temperature Correction

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Abstract
Data from conical-shaped film cooling holes are extremely sparse in open literature, especially the cooling uniformity characteristic, an important criterion for evaluating any film cooling design. The authors will compare the performance of conical-shaped holes to cylindrical-shaped holes. Cylindrical-shaped holes are often considered a baseline in terms of film cooling effectiveness and cooling uniformity coefficient. The authors will study two coupons with conical-shaped holes, which have 3° and 6° diffusion angles, named CON3 and CON6, respectively. A conjugate heat transfer computational fluid dynamics model and an experimental wind tunnel will be used to study these coupons. The three configurations: cylindrical baseline, CON3, and CON6, have a single row of holes with an inlet metering diameter of 3 mm, length-to-nominal diameter of 4.3, and an injection angle of 30°. In this study, the authors will also take into account the heat transfer into the coolant flow from the coolant channel. In other words, the coolant temperature at the exit of the coolant hole will be different than that measured at the inlet, and the conjugate heat transfer model will be used to correct for this difference. For the numerical model, the realizable k-ɛ turbulent model will be applied with a second order of discretization and an enhanced wall treatment to provide the highest accuracy available. Grid independent studies for both cylindrical-shaped film cooling holes and conical-shaped holes will be performed, and the results will be compared to data in open literature as well as in-house experimental data. Results show that conical-shaped holes considerably outperform cylindrical-shaped holes in film cooling effectiveness at all blowing ratios. In terms of cooling uniformity, conical-shaped holes perform better than cylindrical-shaped holes for low- and midrange blowing ratios, but not at higher levels.