Modeling complex flow structures and drag around a submerged plant of varied posture

Boothroyd, R. J. , Hardy, R. J., Warburton, J. and Marjoribanks, T. I. (2017) Modeling complex flow structures and drag around a submerged plant of varied posture. Water Resources Research, 53(4), pp. 2877-2901. (doi: 10.1002/2016WR020186)

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Abstract

Although vegetation is present in many rivers, the bulk of past work concerned with modeling the influence of vegetation on flow has considered vegetation to be morphologically simple and has generally neglected the complexity of natural plants. Here we report on a combined flume and numerical model experiment which incorporates time‐averaged plant posture, collected through terrestrial laser scanning, into a computational fluid dynamics model to predict flow around a submerged riparian plant. For three depth‐limited flow conditions (Reynolds number = 65,000–110,000), plant dynamics were recorded through high‐definition video imagery, and the numerical model was validated against flow velocities collected with an acoustic Doppler velocimeter. The plant morphology shows an 18% reduction in plant height and a 14% increase in plant length, compressing and reducing the volumetric canopy morphology as the Reynolds number increases. Plant shear layer turbulence is dominated by Kelvin‐Helmholtz type vortices generated through shear instability, the frequency of which is estimated to be between 0.20 and 0.30 Hz, increasing with Reynolds number. These results demonstrate the significant effect that the complex morphology of natural plants has on in‐stream drag, and allow a physically determined, species‐dependent drag coefficient to be calculated. Given the importance of vegetation in river corridor management, the approach developed here demonstrates the necessity to account for plant motion when calculating vegetative resistance.

Item Type:Articles
Additional Information:Richard J. Boothroyd was funded under Natural Environmental Research Council (NERC) PhD Studentship 1313876. The flume experiments were funded through NERC grant NE/F010060/1.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Boothroyd, Dr Richard
Authors: Boothroyd, R. J., Hardy, R. J., Warburton, J., and Marjoribanks, T. I.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Journal Name:Water Resources Research
Publisher:American Geophysical Union
ISSN:0043-1397
ISSN (Online):1944-7973
Published Online:17 March 2017
Copyright Holders:Copyright © 2017 The Authors
First Published:First published in Water Resources Research 53(4): 2877-2901
Publisher Policy:Reproduced under a Creative Commons License

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