Experimental and Numerical Investigation of Heat Transfer and Film Cooling Effectiveness of a Highly Loaded Turbine Blade Under Steady and Unsteady Wake Flow Condition
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The current study investigates the heat transfer and film-cooling effectiveness on a highly loaded turbine blade under steady and periodic unsteady wake induced flow conditions from both experimental and numerical simulation points of view. For the experimental measurements, the cascade facility in Turbomachinery Performance and Flow Research Lab (TPFL) at Texas A&M University was used to simulate the periodic unsteady flow condition inside gas turbine engines. The current paper includes steady and unsteady inlet flow conditions. Moving wakes, originated from upstream stator blades, are simulated inside the cascade facility by moving rods in front of the blades. The flow coefficient is maintained at 0.8 and the incoming wakes have a reduced frequency of 3.18. For film-cooling effectiveness study a special blade was designed and inserted into the cascade facility that has a total of 617 holes distributed along 13 different rows on the blade surfaces. 6 rows cover the suction side, 6 other rows cover the pressure side and one last row feeds the leading edge. There are six coolant cavities inside the blade. Each cavity is connected to one row on either sides of the blade, except for the closest cavity to leading edge since it is connected to the leading edge row as well. The rows that are connected to the same cavity have identical injection hole numbers, arrangement (except for leading edge) and compound angles. Coolant is injected from either sides of the blade through the 6 cavities to form a uniform distribution along the lateral extent of the blade. In order to increase the effectiveness, the coolant injection holes are shaped holes. In the regions close to the end-walls of the cascade the holes have compound angles to overcome the effects of horseshoe and passage vortices. To study the film cooling effectiveness, the blade surfaces were covered with Pressure Sensitive Paint (PSP) excited with green light. Experiments were performed for Reynolds number of 150,000 and the average blowing ratio of coolant was maintained at one for all rows throughout the experiments. For heat transfer coefficient measurements, the liquid crystal method was used. For that reason the surfaces of the blade were covered by liquid crystal sheets and it was tested at the same Reynolds number. As computational platform, a RANS based solver was selected for this study. Sliding mesh technique was incorporated into the simulations to produce moving wakes. Experimental and numerical investigations were performed to determine the effect of flow separation, and pressure gradient on film-cooling effectiveness in the absence of wakes. Moreover, the effect of impinging wakes on the overall film coverage of blade surfaces and heat transfer coefficient was studied. Comparison of numerical and experimental results reveals deficiencies of numerical simulation.
