Overall Effectiveness for a Film Cooled Turbine Blade Leading Edge With Varying Hole Pitch

Overall effectiveness, phi, for a simulated turbine blade leading edge was experimentally measured using a model constructed with a relatively high conductivity material selected so that the Biot number of the model matched engine conditions. The model incorporated three rows of cylindrical holes with the center row positioned on the stagnation line. Internally the model used an impingement cooling configuration. Overall effectiveness was measured for pitch variation from 7.6d to 11.6d for blowing ratios ranging from 0.5 to 3.0, and angle of attack from -7.7 deg to +7.7 deg. Performance was evaluated for operation with a constant overall mass flow rate of coolant. Consequently when increasing the pitch, the blowing ratio was increased proportionally. The increased blowing ratio resulted in increased impingement cooling internally and increased convective cooling through the holes. The increased internal and convective cooling compensated, to a degree, for the decreased coolant coverage with increased pitch. Performance was evaluated in terms of laterally averaged phi, but also in terms of the minimum phi. The minimum phi evaluation revealed localized hot spots which are arguably more critical to turbine blade durability than the laterally averaged results. For small increases in pitch (from p/d = 7.6 to 9.6) there was only a small decrease in performance, but at p/d = 11.6 a significant reduction was observed.