Unsworth, CA, Parsons, DR, Hardy, RJ et al. (4 more authors) (2018) The Impact of Nonequilibrium Flow on the Structure of Turbulence Over River Dunes. Water Resources Research, 54 (9). pp. 6566-6584. ISSN 0043-1397
Abstract
Most past experimental investigations of flow over river dunes have focused on conditions that match semiempirical flow‐depth scaling laws, yet such equilibrium conditions are of limited value because they rarely occur in natural channels. This paper quantifies the structure of mean and turbulent flow over fixed 2‐D laboratory dunes across a range of nonequilibrium conditions within the dune flow regime. The flow field was quantified using 2‐D particle imaging velocimetry for 12 conditions, including flows that are too deep, too shallow, too fast, or too slow for the size of the fixed dunes. The results demonstrate major departures in the patterns of the mean flow and structure of turbulence when compared to dunes formed under equilibrium flow conditions. The length of flow reattachment scales linearly with the ratio of mean depth‐averaged streamwise velocity to shear velocity at the dune crest ( urn:x-wiley:00431397:media:wrcr23540:wrcr23540-math-0001), which provides a new predictive measure for flow reattachment length. Depth‐averaged vertical velocities at the dune crest ( urn:x-wiley:00431397:media:wrcr23540:wrcr23540-math-0002) show a parabolic relationship with urn:x-wiley:00431397:media:wrcr23540:wrcr23540-math-0003, peaking at urn:x-wiley:00431397:media:wrcr23540:wrcr23540-math-0004 ~0.60 m/s, which matches the relationship of dune aspect ratio with transport stage present in mobile bed conditions. The spatial location of the turbulent wake was found to vary with flow depth and velocity, with lower urn:x-wiley:00431397:media:wrcr23540:wrcr23540-math-0005 and greater flow depths causing the wake to rise toward the free surface. Deeper flows are likely to show less flow convergence over the crests of dunes due to reduced interaction of turbulence with the free surface, resulting in a reduction of transport stage.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2018 American Geophysical Union. All Rights Reserved. Reproduced in accordance with the publisher's self-archiving policy. |
Keywords: | dune; river; turbulence; Quadrant structure; Coherent flow structures; Non‐equilibrium |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 30 Oct 2018 14:25 |
Last Modified: | 24 Feb 2019 01:38 |
Status: | Published |
Publisher: | American Geophysical Union |
Identification Number: | 10.1029/2017WR021377 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:137904 |