Heat management is an essential part of combustor design, as operating temperatures within the combustor generally exceed safe working temperatures of the materials employed in its construction. Two principal methods used to manage this heat are impingement and film cooling. Impingement heat transfer refers to jets of impinging fluid delivered by orifices integrated into internal structures in order to remove undesired heat. This mode of heat transfer has a relatively high effectiveness, making it an attractive method of heat management. As such, a considerable number of studies have been done on the subject providing a substantial body of useful knowledge. However, there are innovative cooling configurations being used in gas turbines which generate compressibility and temperature ratio effects on heat transfer which are currently unexplored. Presented here are data showing that these effects have a significant impact on heat transfer and new correlations are presented to account for temperature ratio and Mach number effects for a range of conditions. These findings are significant and can be applied to impinging flows in other areas of a gas turbine engine such as turbine blades and vanes. Film cooling refers to the injection of coolant onto a surface through an array of sharply angled holes. This is done in a manner that allows the coolant to remain close to the surface where it provides an insulating layer between the hot gas freestream and the cooler surface. In order to improve turbine efficiency, research efforts in film cooling are directed at reducing film cooling flow without decreasing turbine inlet temperatures. Both impingement cooling and film cooling are heavily utilized in combustor liners. Frequently, cooling air first impinges against the back side of the liner, then the spent impingement fluid passes through film cooling holes. This arrangement combines the convective heat transfer of the impinging jets convection as the coolant passes through the film cooling holes and the benefits that come from having a thin film of cool air between the combustor wall and the combustion products. In order to improve the understanding of internal cooling in gas turbine engines, the influence of previously unexplored physical parameters such as compressible flow effects and temperature ratio in impingement flows and variable blowing ratio in a film cooling array must be examined. Prior to this work, there existed in the available literature only an extremely limited exploration of compressibility effects in impingement heat transfer and the results of separately examining the effects of Mach number and Reynolds number. The film cooling literature provides no information for a full array of film cooling holes along a contraction at high blowing ratios. Exploring these effects and conditions adds to the body of available data and allows the validation of numerical predictions.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:509943 |
| Date | January 2009 |
| Creators | Goodro, Robert Matthew |
| Contributors | Gillespie, David ; Ligrani, Phillip M. |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:51596540-f4cf-480c-aa40-7fc5b9a97abb |
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