Local Heat Transfer Measurement in an Internal Cooling Passage of a Gas Turbine Blade and its Direct Numerical Simulation

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In order to clarify the structure of turbulent flow governing the heat transfer in a rotating system, the experiments of smooth and rib-roughened ducts and the numerical analysis were performed. In the experiments, two different experimental setups were used. One is for straight-duct experiment and the other is for serpentine-duct experiment. The square-straight-duct results measured by using 204 thermocouples showed the variation of heat transfer coefficient in both streamwise and peripheral directions. The case of 90 degrees rib arrangement showed the locally maximum heat transfer between the two consecutive ribs. When the ribs were inclined to 60 degrees, the secondary flow induced by this inclination caused the augmentation in heat transfer. In the rectangular serpentine duct case, the rib inclination effect was examined changing the inclination angle from 45 to 90 degrees by using 458 thermocouples. The maximum heat transfer was obtained around the angle of 45-60 degrees.In the numerical analysis, the rotating square smooth duct case was simulated by using the finite difference method. The Reynolds number defined by using the half side length and the friction velocity was 350 and the rotation number was varied from 0 to 1.0. Because of the computational resource limitation, the Smagorinsky model was introduced. The numerical results showed the effect of the Coriolis force on the peripheral variation of heat transfer and the laminarization near the suction side. When the extension to the more complicated duct configuration is considered, the introduction of the parallel computing technique and the universal sub-grid scale model will be essential as a next step.