Parametric Studies on Film Cooling Effectiveness and Heat Transfer Coefficients over Gas Turbine Blade Leading Edge Surfaces

Abstract

The effect of various geometrical and flow parameters on the adiabatic film cooling effectiveness and heat transfer coefficients over the gas turbine stator blade leading edge models was carried out for the optimization of the geometrical and flow parameters. In this study, the 4:1 scaled up adiabatic blade leading edge test models were used with a geometry similar to that of a typical gas turbine nozzle guide vane. The film cooling hole geometrical parameters on the blade leading edge region like film cooling hole orientation angle (15°, 30° and 45°), inclination angle (20°, 25°, 30° and 35°), spanwise pitch to diameter ratio (3 and 4) and variation of hole exit shape (Circular, Fan, and Laidback Fan shapes) effects have been studied. Experiments were carried out using the Film Cooling Test Facility available at Heat Transfer Lab, Propulsion Division, CSIR - National Aerospace Laboratories, Bangalore. The experiments were conducted for adiabatic cooling effectiveness and heat transfer coefficients at a mainstream flow Reynolds number of 1 x 105 based on the leading edge diameter by varying the blowing ratios in the range of 1.0 to 2.5 at a density ratio of 1.3. The results were found for two pitch spanwise averaged values along the streamwise direction. A numerical study was also made for the same experimental cases to see the trends and deviations of the results and validation of the CFD. The numerical investigations were conducted with the help of ANSYS 14 Workbench, ICEM CFD meshing and FLUENT. From both the experimental and numerical results, adiabatic film cooling effectiveness and heat transfer coefficient values over the blade leading edge region were found to increase with an increase in hole orientation location from the stagnation line, with the decrease in hole inclination angle, with the lower hole pitch and with the increase in hole exit area. The numerical results also showed the same trends as that of the experimental values with minor deviations at some locations, and the peaks in the numerical results indicated the hole locations. Among the considered blowing ratios, the blowing ratio 2.0 has shown the higher cooling effectiveness, and the heat transfer coefficient values were found to be increasing with the increase in blowing ratios on all considered models.