Influence of Channel Aspect Ratio and Curvature on Flow, Secondary Circulation, and Bed Shear Stress in a Rectangular Channel Bend
Publication: Journal of Hydraulic Engineering
Volume 138, Issue 12
Abstract
Flow within an alluvial channel bend is significantly affected by channel geometry, including curvature ratio (bend radius/channel width, ) and aspect ratio (channel width/flow depth, ). High curvature bends () can experience substantially more erosion than milder curvature bends. This study employs a three-dimensional Reynolds-Averaged Navier-Stokes (RANS) model to investigate the effects of curvature ratio and aspect ratio on bend flow with respect to a high curvature () base case in a 135° bend. Experimental data are used to validate the RANS model predictions for the high curvature base case with a flat bed (FB) and an equilibrium deformed bed (DB). Five curvature ratios (1.5, 3, 5, 8, and 10) and four aspect ratios (5.00, 6.67, 9.09, and 12.50) are investigated. Results show that a decrease in or for the FB cases results in a strong increase in total circulation of the regions associated with the primary cell of cross-stream circulation (), an increase in maximum bed shear stress, and an increase in the contribution of the cross-stream component to the total magnitude of bed shear stress. The values of and also affect the structure of the cross-stream flow. The primary cell of cross-stream circulation splits into two clockwise-rotating cells at low values and the cell situated closer to the inner wall induces strong ejections of vorticity. At high values, a secondary counter-clockwise rotating cell forms at the outer bank. At lower values, the primary cell splits into two clockwise-rotating cells. This study shows that the position and size of regions of high bed shear stress, and thus the capacity of the flow to entrain sediment, depend strongly on bend curvature.
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Acknowledgments
The authors would like to thank Benoît Doutreleau for his help in collecting experimental data for R2C1.5H20FB, and to Dr. Koen Blanckaert for his help and comments related to the discussion of the capabilities of analytical models used to characterize the strength of secondary flow and peak bank stress in curved channels. The authors would also like to thank Dr. Talia Ekin Tokyay for her advice on setting up the Fluent runs.
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© 2012 American Society of Civil Engineers.
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Received: Mar 16, 2011
Accepted: Jun 11, 2012
Published online: Nov 15, 2012
Published in print: Dec 1, 2012
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