Numerical Simulation of Flow over a Rough Bed
Publication: Journal of Hydraulic Engineering
Volume 133, Issue 4
Abstract
This paper presents results of a direct numerical simulation (DNS) of turbulent flow over the rough bed of an open channel. We consider a hexagonal arrangement of spheres on the channel bed. The depth of flow has been taken as four times the diameter of the spheres and the Reynolds number has been chosen so that the roughness Reynolds number is greater than 70, thus ensuring a fully rough flow. A parallel code based on finite difference, domain decomposition, and multigrid methods has been used for the DNS. Computed results are compared with available experimental data. We report the first- and second-order statistics, variation of lift/drag and exchange coefficients. Good agreement with experimental results is seen for the mean velocity, turbulence intensities, and Reynolds stress. Further, the DNS results provide accurate quantitative statistics for rough bed flow. Detailed analysis of the DNS data confirms the streaky nature of the flow near the effective bed and the existence of a hierarchy of vortices aligned with the streamwise direction, and supports the wall similarity hypothesis. The computed exchange coefficients indicate a large degree of mixing between the fluid trapped below the midplane of the roughness elements and that above it.
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Acknowledgments
This work was carried out under Grant No. GR/M85241 from the U.K. Engineering and Physical Science Research Council (EPSRC). Additional computing resources and support were provided by the U.K. Turbulence Consortium from HPC Grant No. GR/R64957/01. The writers gratefully acknowledge the support of these organizations. Invaluable comments from the reviewers and the Associate Editor for the improvement of the paper are also gratefully acknowledged.
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Published In
Journal of Hydraulic Engineering
Volume 133 • Issue 4 • April 2007
Pages: 386 - 398
Copyright
© 2007 ASCE.
History
Received: Sep 20, 2004
Accepted: Sep 14, 2006
Published online: Apr 1, 2007
Published in print: Apr 2007
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