R. J. Hardy
The Influence of Three-Dimensional Topography on Turbulent Flow Structures Over Dunes in Unidirectional Flows
Hardy, R. J.; Best, J. L.; Marjoribanks, T. I.; Parsons, D. R.; Ashworth, P. J.
Authors
J. L. Best
T. I. Marjoribanks
D. R. Parsons
P. J. Ashworth
Abstract
Dunes are the most prevalent bedform present in sand-bedded rivers and their morphology typically comprises multiple scales of three-dimensional topography. However, our understanding of flow over dunes is predicated largely on two-dimensional models, a condition which is rare in nature. Here, we present results of Large Eddy Simulations over a static, three-dimensional dune field, using a two- and three- dimensional topographic realisation, to investigate the interaction between bed topography and turbulent flow structures. We show that flow over two-dimensional bedforms increases the velocity over the stoss slope and reduces the size of the leeside separation zone as compared to 3D topography. Flow over three-dimensional bedforms generates twice as many vortices as over two-dimensional bedforms, and these vortices are longer, wider and taller than flow over their two-dimensional counterparts. Turbulence is dominated by hairpin-shaped vortices and Kelvin-Helmholtz instabilities that interact with the bed in the brink point region of the dune crest and down the lee slope, and generate high shear stresses for long durations. These results are used to propose a new conceptual model showing the differences between flow over two- and three-dimensional bedforms. The findings highlight how the size, morphology and stacking of coherent flow structures into larger flow superstructures may be critical in sediment entrainment, and may dictate the relationship between event duration and magnitude that drives sediment impulses at the bed. This will ultimately lead to an increased in the three-dimensionality of bedform morphology.
Citation
Hardy, R. J., Best, J. L., Marjoribanks, T. I., Parsons, D. R., & Ashworth, P. J. (2021). The Influence of Three-Dimensional Topography on Turbulent Flow Structures Over Dunes in Unidirectional Flows. Journal of Geophysical Research: Earth Surface, 126(12), Article e2021JF006121. https://doi.org/10.1029/2021JF006121
Journal Article Type | Article |
---|---|
Acceptance Date | Nov 1, 2021 |
Online Publication Date | Nov 9, 2021 |
Publication Date | 2021-12 |
Deposit Date | Apr 2, 2022 |
Publicly Available Date | Oct 27, 2022 |
Journal | Journal of Geophysical Research: Earth Surface |
Print ISSN | 2169-9011 |
Electronic ISSN | 2169-9011 |
Publisher | American Geophysical Union |
Peer Reviewed | Peer Reviewed |
Volume | 126 |
Issue | 12 |
Article Number | e2021JF006121 |
DOI | https://doi.org/10.1029/2021JF006121 |
Keywords | Dunes; Large Eddy Simulation; Topography |
Public URL | https://hull-repository.worktribe.com/output/3905782 |
Files
Published article
(4.5 Mb)
PDF
Publisher Licence URL
http://creativecommons.org/licenses/by/4.0
Copyright Statement
© 2021. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
You might also like
Managing estuaries under a changing climate: A case study of the Humber Estuary, UK
(2022)
Journal Article
On the turbulence dynamics induced by a surrogate seagrass canopy
(2022)
Journal Article
Sand mining far outpaces natural supply in a large alluvial river
(2021)
Journal Article
2020-Vision: understanding climate (in)action through the emotional lens of loss
(2021)
Journal Article