Impingement is the most commonly used method of cooling in the hot stages of gas turbines. This is often combined with film cooling to further increase the cooling performance. The mainstream flow where in the coolant films discharge often has large stream wise pressure variations. All existing studies on coupled film and impingement cooling concentrated on the effect of the film depletion on the impingement heat transfer. This study investigates the impact of impingement on film cooling, where the jets impinging on a flat plate are depleted through arrays of film cooling holes in the presence of pressure gradient in the main gas path. The main characteristic of the test setup is that there is an impingement wall on the backside of the film effusion wall. The fluid used for both impingement flow and main flow is air. The impingement flow is heated as opposed to the usual practice of heating mainflow, and the array of film holes are configured under the impingement jet hole arrays such that there is no direct impingement on the film holes. The static pressure variations and Mach number (0.01 to 0.3) in the mainstream underneath the flat plate are controlled by inserts with varying flow area. The detailed temperature distribution on the film-covered surface is measured using the Temperature Sensitive Paint (TSP) technique, and film cooling effectiveness is calculated from the measurements. Results are presented for averaged impingement jet Reynolds numbers of 5000 and 8000. The effect of impingement on film effectiveness is studied by comparing the results from the two cases: one where film flow is directly supplied from a plenum and the other where the post- impingement flow is depleted through film effusion holes. The results are presented for cylindrical film cooling holes which are inclined at angles of 20 deg and 30 deg with respect to the target plate surface. The variation of the effectiveness of the film hole arrays along the mainstream are studied in detail. It is observed that the impingement through jet effects the pressure distribution on the target plate with film holes, which in turn affects the blowing rates of each row. The change in the blowing ratios because of a different pressure distribution on the impingement side of the target plate causes the effectiveness to change. From the results it is observed that the farther rows of impingement are affected by the pressure distribution underneath the film holes and have more flow through the film cooling rows, this increases the inlet flow of the films which increase the blowing ratios and in turn decreases the effectiveness of the film cooling holes. The pressure distribution and the change of effectiveness are studied in detail.
| Identifer | oai:union.ndltd.org:ucf.edu/oai:stars.library.ucf.edu:etd-2009 |
| Date | 01 January 2006 |
| Creators | Peravali, Anil |
| Publisher | STARS |
| Source Sets | University of Central Florida |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Electronic Theses and Dissertations |
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