Effect of Unsteady Wake on Full Coverage Film-Cooling Effectiveness for a Gas Turbine Blade

*† The effect of film cooling holes placed along the span of a fully-cooled high pressure turbine blade in a 5 bladed linear cascade on film cooling effectiveness is studied using the Pressure Sensitive Paint (PSP) technique. Effect of showerhead injection at the leading edge and the presence of compound angled, cylindrical holes on the pressure and suction side are also examined. Four rows of compound angled film cooling holes are provided on the pressure side while two such rows are provided on the suction side of the blade. Another three rows of holes are drilled at 30 o to the surface on the leading edge to capture the effect of showerhead film coolant injection. The coolant is injected at four different average blowing ratios of 0.3, 0.6, 0.9 and 1.2. Presence of wake due to an upstream vane is studied by placing a periodic set of rods upstream of the test blade. The wake is controlled by using two different rod diameters of 3.2mm and 4.8mm. The wake rods can be clocked by changing their stationary positions in front of the test blade to simulate a progressing wake. Effect of wake is recorded at four phase locations with equal intervals. The free stream Reynolds number, based on the axial chord length and the exit velocity, is 750,000 and the inlet and the exit Mach numbers are 0.27 and 0.44, respectively resulting in a blade pressure ratio of 1.14. Turbulence intensity level at the cascade inlet is 6% with an integral length scale of around 5cm. Results show that the presence of a stationary upstream wake can result in lower film cooling effectiveness on the blade especially on the suction side of the blade. Varying blowing ratios can have a significant impact on film-cooling effectiveness distribution with a blowing ratio of 0.9 showing highest effectiveness.

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