Experimental and Computational Film Cooling with Backward Injection for Cylindrical and Fan-Shaped Holes
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A systematic study was performed to investigate the combined effects of hole geometry, blowing ratio, and density ratio on flat plate film cooling with backward injection. Detailed film cooling effectiveness distributions were measured by pressure sensitive paint (PSP) mass transfer technique. Four common geometries were used for backward injection: simple angled cylindrical holes and fan-shaped holes, and compound angled cylindrical holes and fan-shaped holes. There are seven holes in a row on each plate and each hole is 4 mm in diameter. The hole length to diameter ratio (L/D) is 7.5. Blowing ratio (M) ranges from 0.3 to 2.0 and coolant to mainstream density ratios (DR) are 1, 1.5, and 2. The results show backward injection is not sensitive to variations of blowing and density ratios compared to forward injection. Film cooling of both simple and compound angled cylindrical holes is better than that of shaped holes by backward injection. Compound angled cylindrical holes show non-uniform lateral coolant accumulation which can potentially cool turbine blade corner regions where coolant is hard to approach by traditional forward injection. Computational results derived from ANSYS FLUENT are presented for thermal flow visualization and pressure field of typical simple angle cylindrical hole by forward and backward injections. Backward injection for the cylindrical holes outweighs forward one in terms of improved coolant uniformity and wider coolant coverage. However, backward injection provides much less film cooling protection as compared with forward injection for the fan-shaped holes.
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Proceedings of the 15th International Heat Transfer Conference
