Hydrodynamics and turbulence in emergent and sparsely vegetated open channel flow

Maji, Soumen; Pal, Debasish; Hanmaiahgari, Prashanth Reddy; Gupta, Umesh P.

doi:10.1007/s10652-017-9531-2

Cited by 21 publications

(4 citation statements)

References 31 publications

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“…Inside the patch, the magnitude of vertical normal stress is small as compared to the streamwise and lateral normal stresses and Reynolds shear stress decreases along the centreline of the patch in the downstream. Furthermore, flow velocity decreases within the vegetation, which can lead to deposition of sediment which accelerates with the time and acts like a catalyst to the larger morphological changes in the river [37,39].…”

Section: Drag and Frictional Characteristicsmentioning

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: Drag and Frictional Characteristicsmentioning

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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“…Balachandar et al [8] and Tachie and Balachandar [17] deduced that even in a near-wake region of the flow, the self-preserving characteristics can be established in terms of the time-averaged velocity distributions by using appropriate velocity and length scales. Maji et al [18] analyzed the self-preserving behaviour in the interior and the wake region of the vegetation patch regarding the mean flow velocities in the streamwise and wall-normal directions and turbulence intensities, RSS, and turbulent kinetic energy (TKE). They observed that the time-averaged streamwise velocity distributions depict self-preserving characteristics for both emergent and sparse vegetation patches in their outer, interior, and wake regions when scaled by their depth-averaged value.…”

Section: Introductionmentioning

confidence: 99%

Self-Preservation of Turbulence Statistics in the Wall-Wake Flow of a Bed-Mounted Horizontal Pipe

Devi

Hanmaiahgari

Balachandar

et al. 2021

Fluids

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This research article analyzed the self-preserving behaviour of wall-wake region of a circular pipe mounted horizontally over a flat rigid sand bed in a shallow flow in terms of mean velocity, RSS, and turbulence intensities. The study aims to investigate self-preservation using appropriate length and velocity scales.in addition to that wall-normal distributions of the third-order correlations along the streamwise direction in the wake region are analyzed. An ADV probe was used to record the three-dimensional instantaneous velocities for four different hydraulic and physical conditions corresponding to four cylinder Reynolds numbers. The results revealed that the streamwise velocity deficits, RSS deficits, and turbulence intensities deficits distributions displayed good collapse on a narrow band when they were non-dimensionalized by their respective maximum deficits. The wall-normal distance was non-dimensionalized by the half velocity profile width for velocity distributions, while the half RSS profile width was used in the case of the RSS deficits and turbulence intensities deficits distributions. The results indicate the self-preserving nature of streamwise velocity, RSS, and turbulence intensities in the wall-wake region of the pipe. The third-order correlations distributions indicate that sweep is the dominant bursting event in the near-bed zone. At the same time, ejection is the dominant bursting event in the region above the cylinder height.

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Section: Withinmentioning

confidence: 76%

“…In their work, the Reynolds stress after the vegetated patch decreased with distance which aligns with the findings of the present study. In contrast, Maji et al (2017) found a decrease in the Reynolds stress after a patch of emergent vegetation. In their case, however, the vegetated patch did not cover the whole width of the flume, thus producing an increase in the velocity and the Reynolds stress in the lateral area free of plants and a decrease behind the plants where the velocity of the flow was also reduced.…”

Section: Discussionmentioning

confidence: 86%

Mean residence time of lagoons in shallow vegetated floodplains

Serra

Font

Soler

et al. 2021

Hydrological Processes

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Lagoons interspersed within wetlands are expected to increase the residence time of the flow in the system which, in turn, will lead to enhanced pollutant removal thus ensuring a good ecological status of the ecosystem. In this study, lagoons interspersed in vegetated wetlands have been mimicked in the laboratory to develop a theoretical model to establish the impact three major driving parameters (the vegetation density surrounding a lagoon, the depth aspect ratio [length vs. depth] of the lagoon and the circulating flowthrough the Reynolds number) have on determining the residence time of the flow in the lagoon. The results indicate that, according to the maximum free available area of the flow, the presence of vegetation (Juncus maritimus) decreases the residence time. In addition, an increase in the Reynolds number of the circulating flow in the wetlands also resulted in a decrease in the lagoon residence time. Nevertheless, lagoon residence times were found to depend on the depth of the lagoon, with deeper lagoons having higher residence times. The length of the lagoon, however, was found not to affect the residence time. High lagoon residence times in either natural or constructed wetlands are desirable because they enhance pollutant removal from the water. Although, if the residence times are too long, this may lead to anoxic water conditions that could in fact threaten the wetland's ecosystem.

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Hydrodynamics and turbulence in emergent and sparsely vegetated open channel flow

Cited by 21 publications

References 31 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

Self-Preservation of Turbulence Statistics in the Wall-Wake Flow of a Bed-Mounted Horizontal Pipe

Mean residence time of lagoons in shallow vegetated floodplains

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