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MULTI-SCALE COHERENT STRUCTURES OF SPATIALLY ADVANCING TURBULENT FLOWS IN CURVED CHANNEL

Koji Matsubara
Faculty of Engineering, Niigata University: Professor, Doctor of Engineering, Ikarashi 2-no cho 8050, Nishi-ku, Niigata 950-2181, Japan; Pacific Rim Solar Fuel System Research Center, Niigata University, Ikarashi 2-no cho 8050, Nishi-ku, Niigata 950-2181, Japan

Akihiko Matsui
Department of Mechanical and Production Engineering, Niigata University Ikarashi 2-nocho 8050, Nishi-ku, Niigata-shi 950-2181, Japan

Takahiro Miura
Department of Mechanical and Production Engineering, Niigata University Ikarashi 2-no-cho 8050, Nishi-ku, Niigata-shi 950-2181, Japan

Koji Kawai
Department of Mechanical and Production Engineering, Niigata University Ikarashi 2-nocho 8050, Nishi-ku, Niigata-shi 950-2181, Japan

Mutsuo Kobayashi
Faculty of Engineering, Niigata University Ikarashi 2-nocho 8050, Niigata 950-21, Japan

Hitoshi Suto
Fluid Dynamics Sector, Civil Engineering Research Laboratory, Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-city, Chiba, 270-1194, Japan

Abstract

Direct numerical simulation was performed for the spatially advancing turbulent flow in a two-dimensional curved channel. The inlet flow of the curved channel was the fully developed turbulence which was additively simulated by the straight channel driver. The radius ratio of the curved part, a, was set 0.92, and the frictional Reynolds number, Rer0, was assigned 150. Computational volume was changed in three kinds of its spanwise extent. However, discussion was mainly given to the prediction by the largest extent (7.2 times the channel half width) where 512 × 61 × 128 grid points were allocated. Computationally solved mean velocity and other statistics showed trends generally consistent with the experiment by Kobayashi et al. (1991), and the numerical validity was thus confirmed. Time-mean velocity vectors illustrated that the ejection from the outer wall grows into the organized flow of the large-scale streamwise vortices. The power spectrum analysis implied that the fine-scale structures such as the low-speed streaks and the microscopic ejection near the outer wall of the straight channel created the initial seeds of the organized wave which grew the large scale vortices extending almost over the channel width.