| Description |
The present study focuses on the investigation of heat transfer and film effectiveness beneath film cooled turbulent boundary layers. Film cooling is used in the components 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 of an airstream in a wind tunnel. Each hole diameter is 2.22 ern, and spanwise spacing between adjacent holes is 3 hole diameters. A heat transfer test surface containing 126 copper-constantan thermocouples is used to measure surface temperature distributions downstream of the injection holes. The project required development of a number of experimental procedures, software, and apparatus. Experimental results show the effects of different blowing ratios and different data processing schemes on film cooling effectiveness distributions. Three sets of experimental results are obtained at each flow condition. Data are obtained with two trips placed in the test section upstream from the injection holes for three different blowing ratios of 0.2, 0.5, and 0.75. Data obtained with one trip placed in the test section upstream of the injection holes with a blowing ratio of 0.5 are also presented. The trips are used to initiate turbulent behavior in the boundary layer developing over the trip. At a blowing ratio of 0.2, film effectiveness values near the exit of the holes are high but decrease rapidly with downstream distance. With blowing ratios of 0.5 and 0.75, film effectiveness values decrease less rapidly with downstream distance. At a blowing ratio of 0.75, the film lifts off of the test surface just downstream of the holes which reduces local film effectiveness at these locations. After the film reattaches to the test surface, spanwise-averaged film effectiveness is nearly constant with streamwise distance along the length of the test section. |
