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Effects of Surface Geometry and Blowing Ratio on Film Cooling Performance at Airfoil Trailing Edge Investigated by Using Large Eddy Simulation

DOI: 10.1615/IHTC15.gtb.008914
pages 3399-3413

Akira Murata
Department of Mechanical Systems Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan

Ena Mori
Tokyo University of Agriculture and Technology

Kaoru Iwamoto
Department of Mechanical Engineering, Tokyo University of Science, Noda-shi, Chiba 278-8510; Department of Mechanical System Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan


KEY WORDS: Gas turbine, Turbulent transport, Heat transfer enhancement, Film cooling, Dimple, Finite volume method

Abstract

Cooling at trailing edge of turbine airfoil is one of the most difficult problems because of its thin shape: high thermal load from both surfaces, hard-to-cool geometry of narrow passages, and at the same time demand for structural strength. In this study, both heat transfer coefficient and film cooling effectiveness on pressure-side cutback surface were numerically simulated by using large eddy simulation with a dynamic Smagorinsky model. Three different cutback geometries were examined: smooth surface and two roughened surfaces with spherical and teardrop-shaped dimples. The Reynolds number of the main flow defined by the mean velocity and two times of the channel height was 20,000 and the blowing ratio was varied in 0.5, 1.0, and 1.5. The present numerical results quantitatively agreed with previous experimental results for the blowing ratio of 1.0 and 1.5. As the installation of dimples on the cutback surface modified only the cooling flow region, overall film cooling performance of the dimpled cases were higher than the smooth case; the teardrop-shaped dimple case was higher than the spherical dimple case. The leading-edge slope of the teardrop-shaped dimple suppressed the flow separation within the dimple and gave higher or equal thermal shield and higher convective cooling as compared to the other geometries.

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