Parameterization of the modeling variables in velocity analytical solutions of open-channel flows with double-layered vegetation

Singh, Prateek Kumar; Rahimi, Hamidreza; Tang, Xiaonan

doi:10.1007/s10652-018-09656-8

Cited by 26 publications

(12 citation statements)

References 19 publications

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“…Thus, multiple layers, that is, low velocity zone within the height of short vegetation, inflection zone around the top boundary of SV, and high velocity zone above the short vegetation height, exist in the velocity profile through DLV and SV. This indicates a similarity with the velocity profiles found by previous researcher (Huai et al, 2014; Singh, Rahimi, & Tang, 2019). The velocity structure scheme through DLV (Case A) shows that the mixing layer region due to inflection nearby the top of short vegetation layer is limited because of the external drag by the tall vegetation layer, which results in reduced sharpness of velocity gradient over this region of flow.…”

Section: Resultssupporting

confidence: 90%

Investigating the turbulent flow behaviour through partially distributed discontinuous rigid vegetation in an open channel

Anjum

Tanaka

2020

River Research & Apps

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Riparian vegetation does not only affect the channel flow carrying capacity, but also plays significant roles in water management, stream restoration, and river rehabilitation. This study numerically investigates the flow characteristics through longitudinally discontinuous rigid vegetation occupying half width of the channel, with the help of three-dimensional software FLUENT in which a Reynolds stress turbulence model was adopted. Three varying conditions of vegetation were considered comprising of vertically double-layered vegetation (DLV), submerged vegetation (SV), and emergent vegetation (EV) while keeping the same vegetation density, as well as a varying discharge condition against DLV was also tested. The results indicated that the flow distribution becomes more complex through DLV and SV followed by multiple layers with an inflectional instability in the vertical velocity profile around submerged canopy top, as compared to the flow through EV where the uniform distribution of flow over the canopy column was observed. The velocity in the canopy zone decreased considerably because of the resistance due to vegetation, which influenced the channel carrying capacity, in comparison to that in the non-vegetated zone. The flow velocities through the obstructed part of the channel, that is, canopy zone, in DLV arrangement reduced by a percentage difference of approximately 42 and 37% compared to that of SV and EV arrangements, respectively; whereas it was reduced by approximately 55% when the discharge was twice while keeping the same configuration of DLV. The inflectional instabilities and estimated mixing layer over the interfacial zone suggested a stronger lateral exchange of momentum for DLV configuration in comparison to that of SV and EV. Within the gaps between the patch zones, the flow velocity, turbulent kinetic energy, and turbulent intensity reduced significantly due to blockage effect and sheltering offered by the vegetation patches, signifying a positive flow response towards aquatic life and sediment deposition.

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Section: Resultssupporting

confidence: 90%

Investigating the turbulent flow behaviour through partially distributed discontinuous rigid vegetation in an open channel

Anjum

Tanaka

2020

River Research & Apps

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“…However, due to different types of vegetation and flow conditions, various methods are proposed for predicting velocity profiles. For the flows with submerged vegetation, the most common method is a two-layer approach, in which different analytical models are applied in the lower vegetation layer and the upper surface layer, using a mixing-layer analogy (Klopstra et al, 1997;Meijer & Van Velzen, 1999;Defina & Bixio, 2005;Baptist, et al, 2007;Huai, et al 2009;Yang & Choi, 2010;Nepf, 2012;Singh et al 2019;Tang, 2018). Klopstra et al (1997) proposed a two-layer model of velocity: one in the vegetation layer and one above it called the surface layer.…”

Section: Introductionmentioning

confidence: 99%

Evaluating Two-Layer Models for Velocity Profiles in Open-Channels with Submerged Vegetation

Tang¹

2019

GEP

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For submerged vegetated flow, the velocity profile has two distinctive distributions in the vegetation layer in the lower region and the surface layer in the upper non-vegetated region. Based on a mixing-layer analogy, different analytical models have been proposed for the velocity profile in the two layers. This paper evaluates the four analytical models of Klopstra et al., Defina & Bixio, Yang et al. and Nepf against a wide range of independent experimental data available in the literature. To test the applicability and robust of the models, the author used the 19 datasets with various relative depths of submergence, different vegetation densities and bed slopes (1.8 × 10 −6-4.0 × 10 −3). This study shows that none of the models can predict the velocity profiles well for all datasets. The three models except Yang's model performed reasonably well in certain cases, but Yang's model failed in most the cases studied. It was also found that the Defina model is almost the same as the Klopstra model, if the same mixing length scale of eddies (λ) is used. Finally, close examination of the mixing length scale of eddies (λ) in the Defina model showed that when λ/h = 1/40(H/h) 1/2 , this model can predict velocity profiles well for all the datasets used.

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“…The complexity of vegetated channel flow can be interpreted in multiple mechanisms over the depth of flow (Katul et al, 2011;Nikora et al, 2013;Huai et al, 2014). The multiple mechanisms over different layers of flow can be modelled independently (Carollo et al, 2002;Huai et al, 2014;Tang, 2018aTang, , 2018bSingh et al, 2019). As a pre-requisite for the analysis in resistance and pollutant mixing process of flow and so on, the vertical velocity distribution in vegetated channel flow has drawn great attention of researchers (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Tsujimoto & Kitamur, 1990, Shimizu & Tsujimoto, 1994Nepf & Koch, 1999;Ghisalberti & Nepf, 2004;Kubrak, et al, 2008;Tang & Knight, 2009;Tang et al, 2010Tang et al, , 2011Nguyen, 2012;Hao et al, 2014). Many investigators have attempted to predict vertical velocity distribution based on semi-empiricism and/or analytical solution of the momentum equation with closure schemes, in which the modelling of eddy viscosity is to describe the turbulent stresses (Klopstra et al, 1997;Meijer & Van Velzen, 1999;Defina & Bixio, 2005;Baptist et al, 2007;Huai, et al, 2009Huai, et al, , 2014Yang & Choi, 2010;Dimitris & Panayotis, 2011;Nepf, 2012;Nikora et al, 2013;Tang, 2018aTang, , 2019aSingh et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

“…The flow structure in this region is governed through the mixing length of eddy and vertical turbulent transport of momentum from the surface flow, with the negligible contribution from the pressure gradient. The effect of the shear length scale can be related to the vegetation height and flow depth (Klopstra et al, 1997;Defina & Bixio, 2005;Tang, 2018aTang, , 2018bTang, , 2019aSingh et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

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An Improved Analytical Model for Vertical Velocity Distribution of Vegetated Channel Flows

Tang¹

2019

GEP

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The existence of vegetation plays an important role to protect the ecosystem and water environment in natural rivers and wetlands, but it alters the velocity field of flow, consequently influencing the transport of pollutant and biomass. As a prerequisite for the analysis of environmental capacity in a channel, the vertical velocity distribution of flows has attracted much research attention; however, there is yet lack of a good prediction model available. For the channel with submerged vegetation, the vertical velocity distribution in the lower vegetation layer will be different from that in the upper flow layer of non-vegetation. In this paper, after review on the most recent two-layer model proposed by Baptist et al., the author has proposed an improved two-layer analytical model by introducing a different mixing length scale (λ). The proposed model is based on the momentum equation of flow with the turbulent eddy viscosity assumed as a linear relationship with the local velocity. The proposed model is compared with the Baptist model for different datasets published in the literature, which shows that the proposed analytical model can improve the vertical velocity distribution prediction well compared with the Baptist model for a range of data. This study reveals that the λ is well related with the submergence of vegetation (H/h), as suggested by

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Parameterization of the modeling variables in velocity analytical solutions of open-channel flows with double-layered vegetation

Cited by 26 publications

References 19 publications

Investigating the turbulent flow behaviour through partially distributed discontinuous rigid vegetation in an open channel

Investigating the turbulent flow behaviour through partially distributed discontinuous rigid vegetation in an open channel

Evaluating Two-Layer Models for Velocity Profiles in Open-Channels with Submerged Vegetation

An Improved Analytical Model for Vertical Velocity Distribution of Vegetated Channel Flows

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