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Sixth International Symposium on Turbulence and Shear Flow Phenomena
June, 22-24, 2009 , Seoul National University, Seoul, Korea

DOI: 10.1615/TSFP6

LARGE-SCALE COHERENT STRUCTURES IN ROUGH-BED TURBULENT OPEN-CHANNEL FLOW

pages 1137-1141
DOI: 10.1615/TSFP6.1810
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ABSTRACT

This paper reports the results obtained from a Direct Numerical Simulation (DNS) regarding the large-scale coherent structures in turbulent open-channel flow with a rough bed. The gravel bed is represented by a hexagonal arrangement of spheres with a diameter of a quarter of flow depth. The length of the structures are shown to be longer than the computational box, roughly 10 times the effective flow depth, and the width tends to be one order of magnitude smaller than the length. The parallel meandering structures mainly locate in the inter-mediate region of the channel and are composed of a group of quasi-streamwise vortices and asymmetric hairpin vortices, with signatures of elongated local maximum of streamwise velocity in the middle. It is also found that these structures contribute substantially to both of the Reynolds Stress (RS) and Turbulent Kinetic Energy (TKE).

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