Study on the flow structure around discontinued vertically layered vegetation in an open channel

Anjum, Naveed; Tanaka, Norio

doi:10.1007/s42241-019-0040-2

Cited by 19 publications

(16 citation statements)

References 20 publications

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“…Anjum and Tanaka [32] used discontinuous and vertically doubled layered patches and simulated it numerically for varying vegetable density and patches. Large-scale turbulence followed by saw-tooth distribution within the patches and low turbulence in the non-vegetation regions was observed.…”

Section: Flume Wallmentioning

confidence: 99%

A Review on Hydrodynamics of Free Surface Flows in Emergent Vegetated Channels

Maji

Hanmaiahgari

Balachandar

et al. 2020

Water

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This review paper addresses the structure of the mean flow and key turbulence quantities in free-surface flows with emergent vegetation. Emergent vegetation in open channel flow affects turbulence, flow patterns, flow resistance, sediment transport, and morphological changes. The last 15 years have witnessed significant advances in field, laboratory, and numerical investigations of turbulent flows within reaches of different types of emergent vegetation, such as rigid stems, flexible stems, with foliage or without foliage, and combinations of these. The influence of stem diameter, volume fraction, frontal area of stems, staggered and non-staggered arrangements of stems, and arrangement of stems in patches on mean flow and turbulence has been quantified in different research contexts using different instrumentation and numerical strategies. In this paper, a summary of key findings on emergent vegetation flows is offered, with particular emphasis on: (1) vertical structure of flow field, (2) velocity distribution, 2nd order moments, and distribution of turbulent kinetic energy (TKE) in horizontal plane, (3) horizontal structures which includes wake and shear flows and, (4) drag effect of emergent vegetation on the flow. It can be concluded that the drag coefficient of an emergent vegetation patch is proportional to the solid volume fraction and average drag of an individual vegetation stem is a linear function of the stem Reynolds number. The distribution of TKE in a horizontal plane demonstrates that the production of TKE is mostly associated with vortex shedding from individual stems. Production and dissipation of TKE are not in equilibrium, resulting in strong fluxes of TKE directed outward the near wake of each stem. In addition to Kelvin–Helmholtz and von Kármán vortices, the ejections and sweeps have profound influence on sediment dynamics in the emergent vegetated flows.

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Section: Flume Wallmentioning

confidence: 99%

A Review on Hydrodynamics of Free Surface Flows in Emergent Vegetated Channels

Maji

Hanmaiahgari

Balachandar

et al. 2020

Water

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“…Maltese et al () concentrated on flow patterns that developed behind the submerged patches of vegetation. A computational fluid dynamics (CFD)–based method was adopted by Anjum and Tanaka () and Weber, Zhang, Nardin, Sukhodolov, and Wolter () to study the influence of aquatic vegetation on flow structures in an open channel. The resistance due to emergent vegetation in a subcritical flow was experimentally investigated by Pasha and Tanaka ().…”

Section: Introductionmentioning

confidence: 99%

Investigating the turbulent flow characteristics in an open channel with staggered vegetation patches

Ghani

Anjum

Pasha

et al. 2019

River Research & Apps

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In the present study, flow around circular and staggered vegetation patches was investigated numerically. For turbulence modelling, the Reynolds-averaged Navier-Stokes technique and Reynolds stress model were adopted. The numerical model was validated with the experimental data using varying vegetation density and flow velocities. The simulated results of mean stream-wise velocities were in close agreement with the experimental results. The results show that the mean stream-wise velocity in the downstream regions of vegetation patches were reduced, whereas the velocity in the free stream regions were increased. The influence of neighbouring and staggered vegetation patches on the flow was observed. The vegetation patches with larger nondimensional flow blockage (aD = 2.3, where a is the frontal area per volume of patches, and D is the diameter of vegetation patches) offered more turbulence when compared to the patches with a smaller flow blockage (aD = 1.2). Larger turbulence in the form of kinetic energy and turbulent intensity was recorded within the vegetation as well as the regions directly behind the patches. Negative Reynolds stresses were observed at the top of submerged vegetation. The turbulence characteristics peaked at the top of vegetation, that is, z/h = 1.0 (where z is the flow depth, and h is the vegetation height), which may be migrated vertically as the frontal area of the vegetation patch is increased. This high frontal area also increased stream-wise velocity above the vegetation, leading to an increased variation in turbulence around the vegetation canopy.

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“…Horstman et al (2018) tried to replicate a real mangrove vegetation distribution in the laboratory and found that there was a reduction of strength in heterogeneous canopy layer as compared with homogeneous type. Different numerical and analytical models of heterogeneous vegetation also indicate the difference in treatments concerning homogeneous vegetation (Anjum & Tanaka, 2020a, 2020b; Huai et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

“…This research also attempts to address the flow nature differences between single‐layered and multi‐layered vegetation in a compound vegetated channel, which have never been investigated before. The study considers multi‐layered (three‐layered) vegetation, which differs from previous studies where mostly double‐layered vegetation was considered (Anjum & Tanaka, 2020a, 2020b; Li et al, 2014; Huai et al, 2014; Tang et al, 2021). Although vegetation height and distribution are more random in the real field, the author used three layers of vegetation to reduce complexity during analysis.…”

Section: Introductionmentioning

confidence: 99%

“…The study considers multi-layered (three-layered) vegetation, which differs from previous studies where mostly double-layered vegetation was considered (Anjum & Tanaka, 2020a, 2020bLi et al, 2014;Huai et al, 2014;Tang et al, 2021). Although vegetation height and distribution are more random in the real field, the author used three layers of vegetation to reduce complexity during analysis.…”

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confidence: 99%

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Flow behaviour in a multi‐layered vegetated floodplain region of a compound channel

Barman

Kumar

2022

Ecohydrology

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Riparian vegetation plays a crucial role in determining the flow behaviour in the channel. The effect of flow on the slope and main channel varies based on the size, type, and density of floodplain vegetation in a compound channel. Though real field vegetation distribution is non‐uniform, most studies mainly concentrate on uniformly distributed vegetation with fixed vegetation height. This paper attempts to address this issue through laboratory studies as it was not explored properly. Flow properties like velocity, Reynolds shear stress, turbulence intensities, and turbulent kinetic energy behave differently in heterogeneous vegetated channel compared with the homogeneous vegetated channel. These flow properties in the slopes and main channel section are more pronounced for uniformly distributed vegetation than non‐uniform distribution. The multi‐layered/varying vegetation height showed higher velocity, turbulent intensity, and turbulent kinetic energy than single‐layered/constant vegetation height on slopes and main channel sections. Integral scales (Taylor and Euler) analysis showed greater magnitude for uniform multi‐layered vegetation than non‐uniform multi‐layered vegetation. Further, the study of octant analysis reveals that internal outward and internal inward interaction events dominate the slope floodplain interaction section, which is not seen in no‐vegetation cases. These studies give a better perspective to understand flow in heterogenous vegetation and move closer to real field scenarios.

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Study on the flow structure around discontinued vertically layered vegetation in an open channel

Cited by 19 publications

References 20 publications

A Review on Hydrodynamics of Free Surface Flows in Emergent Vegetated Channels

A Review on Hydrodynamics of Free Surface Flows in Emergent Vegetated Channels

Investigating the turbulent flow characteristics in an open channel with staggered vegetation patches

Flow behaviour in a multi‐layered vegetated floodplain region of a compound channel

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