Turbulent Heat Transfer and Large Coherent Structures in Trailing-edge Cutback Film Cooling
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Film cooling is a key technology for improving the thermal efficiency and power output of gas turbines. The trailing-edge section of high-pressure turbine blades can be efficiently cooled by ejecting a film over a cutback on the pressure side of the blade. In this paper, results of Large–Eddy Simulations (LES) are presented that match an existing experimental setup. Altogether, eight simulations with the blowing ratio M varying as the only parameter were performed over a range from M = 0.35 to 1.4. Reasonably good agreement between LES and experiments were obtained for flow field statistics and adiabatic film-cooling effectiveness ηaw. Within a limited range of blowing ratios, an increase in the blowing ratio results in a counter-intuitive decrease of the cooling effectiveness. The present work suggests a mechanism that can explain this behavior. The visualization and analysis of large coherent structures showed that there exists dominant clockwise-rotating structures that can give rise to a combined upstream- and wall-directed turbulent heat flux. This turbulent heat flux represents the main contribution of the total heat flux and causes a significantly intensified thermal mixing process, which in turn results in the counter-intuitive decrease of the cooling effectiveness.
KeywordsLarge–Eddy simulation Large coherent structures Turbulent mixing Heat transfer Film cooling
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