Experimental and numerical investigations on mixing flow of film cooling by using twisted holes

Abstract

Increment in turbine inlet temperature (TIT) is essential for further improvement in thermal efficiency and higher power output of next generation gas turbine engines. Over past decades, significant effort has been made to increase the TIT through development of effective cooling strategies to maintain the blade temperature below the melting point of blade material. Film cooling techniques have been extensively researched to achieve higher TIT. This work was carried out experimentally and numerically to determine the enhancement of film cooling through the use of twisted film cooling hole. The existing combustor test rig was modified to suit experimental investigations of twisted hole film cooling on a flat plate. The Reynolds number was set at Red = 6200 to investigate the turbulent flow regime. The computational fluid dynamics (CFD) software was employed for the numerical simulation of the experimental configurations and other geometries of the twisted cooling hole. High mesh density was applied in the flow domain to capture the significant details of the flow induced by the twisted cooling hole. Three different cooling hole shapes of circular, rectangular and twisted rectangular were investigated under a constant temperature boundary condition and variable thermo-physical properties. The CFD processes were verified through various methods. Simulated results were compared to the experimental measurements giving good agreement and therefore the validation was satisfactory. The results showed that the twisted cooling holes provide a better cooling effectiveness compared to the smooth one. It was found that the cooling effectiveness was enhanced at lower blowing ratios by about 1.1-1.5 times than that of a smooth film cooling hole. This effectiveness enhancement was accompanied by an appreciable increase in heat transfer coefficient in the range of 1.2- 1.6. The improvement in the thermal performance was also found to be in the range of 1.2-1.5. Eventually, the heat transfer coefficient correlation relevant to the parameter studied in the present work was proposed.