Abstract
The trailing edge of the high pressure turbine blade and vane presents significant challenges to the turbine cooling engineer. The current research has focused specifically on the effect of cutback surface protuberance, or “land”, shapes on film cooling effectiveness. A set of six different land geometries has been investigated in a large scale model of the trailing edge pressure side ejection slot exit. Slot height and width and lip height was maintained. Pressure sensitive paint was used to measure adiabatic film cooling effectiveness at five blowing ratios ranging from 0.6 to 1.4 in increments of 0.2. High-resolution full surface distributions of film cooling effectiveness both on the cutback surface and the top of the lands were recorded. It was found that tapering the lands did not significantly increase effectiveness on the lands and slightly reduced effectiveness near the lands. Using a diffuser shape improved average effectiveness greatly and gave the best overall performance up to the end of the lands except at the lowest blowing ratio of 0.6, where having no lands was slightly better.
Highlights
Current designs feature high pressure turbine entry temperatures that far exceed the blade and vane material melting point, and require the use of air film cooling to shield the exterior surface from the hot mainstream gas and maintain an acceptable metal temperature and component life
Blue regions show poor coverage from the nitrogen coolant and correspond to low film cooling effectiveness and red regions correspond to high effectiveness
While the simplified nature of the experimental model limits the direct applicability of the measurements to a real blade or vane, the current research has successfully compared six land shape designs and shown the relative performance of each in terms of effectiveness
Summary
Current designs feature high pressure turbine entry temperatures that far exceed the blade and vane material melting point, and require the use of air film cooling to shield the exterior surface from the hot mainstream gas and maintain an acceptable metal temperature and component life. This use of air is detrimental to engine efficiency since a reduced amount of work is extracted from it by the engine and its introduction back into the mainstream incurs aerodynamic losses. This means that if the amount of cooling air required becomes too large, the reduction of efficiency due to cooling can outweigh the increase in efficiency due to a high turbine entry temperature [1].
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