Brendan J. Murphy
Flow separation at the inner (convex) and outer (concave) banks of constant-width and widening open-channel bends
Murphy, Brendan J.; Blanckaert, Koen; Kleinhans, Maarten G.; Mclelland, Stuart J.; Uijttewaal, Wim S.J.; Murphy, Brendan; van de Kruijs, Anja; Parsons, Daniel R.; Uijttewaal, Wim S. J.; Chen, Qiuwen
Authors
Koen Blanckaert
Maarten G. Kleinhans
Professor Stuart McLelland S.J.McLelland@hull.ac.uk
Deputy Director of the Energy and Environment Institute
Wim S.J. Uijttewaal
Brendan Murphy
Anja van de Kruijs
Daniel R. Parsons
Wim S. J. Uijttewaal
Qiuwen Chen
Abstract
There is a paucity of data and insight in the mechanisms of, and controls on flow separation and recirculation at natural sharply-curved river bends. Herein we report on successful laboratory experiments that elucidate flow structure in one constant-width bend and a second bend with an outer-bank widening. The experiments were performed with both a flat immobile gravel bed and mobile sand bed with dominant bedload sediment transport. In the constant-width bend with immobile bed, a zone of mainly horizontal flow separation (vertical rotational axis) formed at the inner bank that did not contain detectable flow recirculation, and an outer-bank cell of secondary flow with streamwise oriented rotational axis. Surprisingly, the bend with widening at the outer bank and immobile bed did not lead to a transverse expansion of the flow. Rather, flow in the outer-bank widening weakly recirculated around a vertical axis and hardly interacted with the inner part of the bend, which behaved as a constant-width bend. In the mobile bed experiment, downstream of the bend apex a pronounced depositional bar developed at the inside of the bend and pronounced scour occurred at the outside. Moreover the deformed bed promoted flow separation over the bar, including return currents. In the constant-width bend, the topographic steering impeded the generation of an outer-bank cell of secondary flow. In the bend with outer-bank widening, the topographic steering induced an outward expansion of the flow, whereby the major part of the discharge was conveyed in the central part of the widening section. Flow in the outer-bank widening was highly three dimensional and included return currents near the bottom. In conclusion, the experiments elucidated three distinct processes of flow separation common in sharp bends: flow separation at the inner bank, an outer-bank cell of secondary flow, and flow separation and recirculation in an outer-bank widening. © 2012 John Wiley & Sons, Ltd.
Citation
Blanckaert, K., Kleinhans, M. G., Mclelland, S. J., Uijttewaal, W. S., Murphy, B., van de Kruijs, A., Parsons, D. R., & Chen, Q. (2013). Flow separation at the inner (convex) and outer (concave) banks of constant-width and widening open-channel bends. Earth surface processes and landforms : the journal of the British Geomorphological Research Group, 38(7), 696-716. https://doi.org/10.1002/esp.3324
Journal Article Type | Article |
---|---|
Acceptance Date | Aug 30, 2012 |
Online Publication Date | Oct 16, 2012 |
Publication Date | Jun 6, 2013 |
Deposit Date | Nov 13, 2014 |
Journal | Earth Surface Processes And Landforms |
Print ISSN | 0197-9337 |
Publisher | Wiley |
Peer Reviewed | Peer Reviewed |
Volume | 38 |
Issue | 7 |
Pages | 696-716 |
DOI | https://doi.org/10.1002/esp.3324 |
Keywords | Flow separation; Open‐channel bend experiments; Morphology laboratory |
Public URL | https://hull-repository.worktribe.com/output/369165 |
Publisher URL | http://onlinelibrary.wiley.com/doi/10.1002/esp.3324/abstract;jsessionid=2D4A94C33DE038123B47EA55477B4143.f02t03 |
Contract Date | Nov 13, 2014 |
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