| Description |
The present study focuses on the effects of bulk flow pulsations on film cooling effectiveness and heat transfer. Film cooling is used in the turbines of gas turbine engines to minimize the detrimental effects which result from exposure of metal surfaces to hot combustion chamber gases. A single row of holes inclined at an angle of 35° from the test surface is used to inject coolant into the boundary layer along the bottom surface of a wind tunnel. Each hole diameter is 2.22 cm, spanwise spacing between adjacent holes is 3 hole diameters, and the hole length to diameter ratio is 4.0. This film cooling configuration is important because similar arrangements are frequently employed in gas turbine engines. Experimental results are presented which describe the effects of different pulsation frequencies and different blowing ratios on film cooling effectiveness distributions, iso-energetic Stanton number ratio distributions, and overall performance parameter distributions. For freestream velocities of 1.0, 3.2, and 10.0 m/s, results are presented for a blowing ratio of 0.5 and for pulsation frequencies ranging from 0.4 to 8.0; Hz. At a freestream velocity of 3.2 m/s, additional results are presented at pulsation frequencies of 1.0 and 8.0 Hz for blowing ratios of 0.5, 1.0, 1.5, and 2.0. Results show that spanwise-averaged adiabatic effectiveness, spanwise-averaged iso-energetic Stanton number ratios, and spanwise-average film effectiveness parameters change by important amounts as the pulsation frequency increases. The results provide clear evidence of the dramatic impact of bulk flow pulsations on film cooling effectiveness and heat transfer. |
