Analytical model of the mean velocity distribution in an open channel with double-layered rigid vegetation

Huai, Wenxin; Wang, Wei-Jie; Hu, Yang; Chen, Qiuwen; Yang, Zhonghua

doi:10.1016/j.advwatres.2014.04.001

Cited by 93 publications

(50 citation statements)

References 30 publications

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“…For example, individual plant species with differing spatial distributions of leaf area and stems have been shown to not significantly alter f [ Nikora et al ., ]. Indeed, there is an extensive literature in “ecohydraulics” that addresses the effect of vegetation on the bulk flow, mean velocity, and the vertical distribution of turbulent stresses in uniform open channel flow subjected to various driving gradients [ Järvelä , ; Poggi et al ., ; Carollo et al ., ; Huthoff et al ., ; Nepf and Ghisalberti , ; Poggi et al ., ; Huai et al ., ; Luhar et al ., ; Katul et al ., ; Nepf , ; Konings et al ., ; Siniscalchi et al ., ; Huai et al ., ; Okamoto and Nezu , ; Huai et al ., ; Wang et al ., ; Banerjee et al ., ]. The specific case here, however, with emergent vegetation interacting with a nonuniform and complex flow in the absence of a strong driving land surface gradient, has yet to be explored.…”

Section: Introductionmentioning

confidence: 99%

Steady nonuniform shallow flow within emergent vegetation

Wang

Huai

Thompson

et al. 2015

Water Resources Research

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Surface flow redistribution on flat ground from crusted bare soil to vegetated patches following intense rainfall events elevates plant available water above that provided by rainfall. The significance of this surface water redistribution to sustaining vegetation in arid and semiarid regions is undisputed. What is disputed is the quantity and spatial distribution of the redistributed water. In ecohydrological models, such nonuniform flows are described using the Saint-Venant equation (SVE) subject to a Manning roughness coefficient closure. To explore these assumptions in the most idealized setting, flume experiments were conducted using rigid cylinders representing rigid vegetation with varying density. Flow was induced along the streamwise x direction by adjusting the free water surface height H(x) between the upstream and downstream boundaries mimicking the nonuniformity encountered in nature. In natural settings, such H(x) variations arise due to contrasts in infiltration capacity and ponded depths during storms. The measured H(x) values in the flume were interpreted using the SVE augmented with progressively elaborate approximations to the roughness representation. The simplest approximation employs a friction factor derived from a drag coefficient (C d ) for isolated cylinders in a locally (but not globally) uniform flow and upscaled using the rod density that was varied across experiments. Comparison between measured and modeled H(x) suggested that such a ''naive'' approach overpredicts H(x). Blockage was then incorporated into the SVE model calculations but resulted in underestimation of H(x). Biases in modeled H(x) suggest that C d must be varying in x beyond what a local or bulk Reynolds number predicts. Inferred C d (x) from the flume experiments exhibited a near-parabolic shape most peaked in the densest canopy cases. The outcome of such C d (x) variations is then summarized in a bulk resistance formulation that may be beneficial to modeling runon-runoff processes on shallow slopes using SVE.

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Section: Introductionmentioning

confidence: 99%

Steady nonuniform shallow flow within emergent vegetation

Wang

Huai

Thompson

et al. 2015

Water Resources Research

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“…The effects of discontinuous immersed vegetation patches on flow turbulence in an open channel were investigated by Zhao et al [5] using a large eddy simulation (LES) model. An analytical model was proposed by Huai et al [6] for analyzing the dissemination of streamwise velocity in an open waterway with double-layered vegetation. Previous researchers have proposed numerical models for vegetation in open channel flows.…”

Section: Introductionmentioning

confidence: 99%

To Investigate the Flow Structure of Discontinuous Vegetation Patches of Two Vertically Different Layers in an Open Channel

Anjum

Ghani

Pasha

et al. 2018

Water

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Abstract:In the present study, the flow structure of discontinuous double-layered vegetation patches was investigated using a 3D Reynolds stress turbulence model (RSM). The channel domain was built using GAMBIT (Geometry and Mesh Building Intelligent Toolkit). For the simulation and postprocessing, FLUENT (ANSYS) was used to analyze the distribution of the mean velocity, Reynolds stresses, and other flow properties against two different flow conditions. The results captured by the turbulence model at specific locations and the cross section are presented in the form of various velocity profiles and contour plots. In the gap portion, the velocity was visibly lower than that in the vegetation areas, while the influence of patch distribution was not visible in the overlying flow layer. The velocity profiles at critical locations were categorized by numerous modulation points and velocity projections close to the bed, principally for positions straight after the vegetation structures. A distinction in the velocity at the topmost of the smaller vegetation structure was prominent. Reynolds stresses, turbulent kinetic energy, and turbulence intensity exhibited large fluctuations inside the vegetation regions and just behind the vegetation structures compared with in the gap regions.

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“…For the channel flow with vegetation, the bed and wall boundary shear stress are both assumed to be negligible compared with the drag force on the vegetation (Nepf and Vivoni, ; Stone and Shen, ). Therefore, the governing equation for fully developed one‐dimensional vegetated flow may be described as the momentum equation of steady uniform flow (Klopstra et al ., ; Ghisalberti and Nepf, ; Defina and Bixio, ; Baptist et al ., ; Kubrak et al ., ; Huai et al ., ):

\frac{1}{ρ} \frac{\partial τ (z)}{\partial z} = F_{v} - g S_{o}

…”

Section: Model Developmentmentioning

confidence: 99%

“…As a pre‐requisite for the analysis of flow resistance, pollutant mixing process, biomass, and so on, the study on the velocity profile in an open‐channel with vegetation has drawn the attention of many researchers (e.g. Tsujimoto and Kitamur, , Shimizu and Tsujimoto, ; Klopstra et al ., ; Meijer and Van Velzen, ; Nepf and Koch, ; Nepf and Vivoni, ; Lopez and Garcia, ; Ghisalberti and Nepf, ; Defina and Bixio, ; Baptist et al ., ; Kubrak et al ., ; Huai, et al ., ; ; Yang and Choi, ; Dimitris and Panayotis, ; Nepf, ; Nguyen, ; Tang and Ali, ; Hao et al ., ; Tang, ). Among them, owing to differences in flow conditions and vegetation types, several analytical methods for predicting the velocity profile have been proposed based on one‐dimensional streamwise momentum equations of vegetated flow.…”

Section: Introductionmentioning

confidence: 99%

A mixing‐length‐scale‐based analytical model for predicting velocity profiles of open‐channel flows with submerged rigid vegetation

Tang

2018

Water & Environment J

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In open-channel flows with submerged vegetation, the vertical velocity profile can often be described by two layers: the vegetation layer in the lower region and the surface layer in the upper non-vegetated region. In this paper, a new mixing-length scale of eddy is proposed for predicting the vertical velocity profile of flow in an open-channel with submerged rigid vegetation. The analytical model of velocity profile is based on the momentum equation of flow where the turbulent eddy viscosity is assumed to have a linear relationship with the local velocity. The proposed model was tested against different datasets from the literature. The 22 datasets used cover a range of submergence [flow depth (H)/vegetation height (h) = 1.25 ~ 3.38], different vegetation densities of ah = 0.11 ~ 1.85 (a defined as the frontal area of the vegetation per unit volume) and bed slopes (S o = 1.8 × 10 −6 ~4.0 × 10 −3 ). This study showed that the proposed model can predict the velocity profiles well against all datasets, and that the mixing length scale of eddies (λ) is well related with both vegetation height (h) and flow depth of surface layer (i.e. the height of non-vegetation layer, H-h). Close examination of λ in the proposed model showed that when λ = 0.03 √ h(H − h), the model predicts vertical velocity profiles well for all datasets used except for very shallow submergence (i.e. H/h < 1.5).

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Analytical model of the mean velocity distribution in an open channel with double-layered rigid vegetation

Cited by 93 publications

References 30 publications

Steady nonuniform shallow flow within emergent vegetation

Steady nonuniform shallow flow within emergent vegetation

To Investigate the Flow Structure of Discontinuous Vegetation Patches of Two Vertically Different Layers in an Open Channel

A mixing‐length‐scale‐based analytical model for predicting velocity profiles of open‐channel flows with submerged rigid vegetation

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