Numerical study on the drag characteristics of rigid submerged vegetation patches

Liu, Meng-Yang; Huai, Wenxin; Ji, Bin; Han, Peng

doi:10.1063/5.0060601

Cited by 30 publications

(5 citation statements)

References 78 publications

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“…This approach avoids the need to introduce additional empirical terms in the governing equation to account for the deceleration of the flow and generation of turbulence inside the porous region. This approach was used by Huai, Xue & Qian (2015), Chang et al (2017Chang et al ( , 2020 and Liu et al (2021) to simulate flow past emerged and submerged arrays of cylinders situated away from the channel banks and by Koken & Constantinescu (2020) to simulate flow past a rectangular array of emerged cylinders placed at one of the channel's sidewalls.…”

Section: Dmentioning

confidence: 99%

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Influence of submergence ratio on flow and drag forces generated by a long rectangular array of rigid cylinders at the sidewall of an open channel

Köken

2023

J. Fluid Mech.

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This paper discusses how the submergence ratio, defined as the ratio between the flow depth, D, and the height, h, of the solid rigid cylinders forming the array affects flow and turbulence structure inside and around a rectangular array of cylinders placed adjacent to one of the channel sidewalls. As the array becomes submerged, a vertical shear layer develops in between the top face of the array and the free surface, which strongly increases flow three-dimensionality and modifies how the momentum exchange between the array and the surrounding open water regions occurs with respect to the case of an emerged array where only a horizontal shear layer forms as part of the incoming flow approaching the array is deflected laterally. Eddy-resolving simulations are conducted for several values of the solid volume fraction, ϕ, and of the submergence ratio, 1.0 ≤ D/h ≤ 4.0. Similar to the limiting case of an emerged array (D/h = 1.0), the width- and depth-averaged streamwise velocity inside the array reaches a constant value after an initial adjustment region in the submerged-array cases. For D/h ≥ 1.33, the mean normal velocities through the top and side faces of the array do not become equal to zero downstream of the initial adjustment region. The flow inside the array reaches an equilibrium regime where the local flux of fluid leaving the array through its side face is balanced by the local flux of fluid entering the array through its top face. This regime is observed until close to the end of the array. For D/h ≥ 2.0, the horizontal shear layer vortices do not generate successive regions of high and low streamwise velocity and bed friction velocity inside the array, as is observed in the emerged cases. With respect to the emerged case, the size of the shear layer vortices and the shear layer width increase for low submergence ratios before decreasing rapidly for D/h ≥ 1.33. Significant three-dimensional effects are present inside the array and the horizontal shear layer for cases with both emerged and submerged arrays. In the ϕ = 0.08 cases, strong upwelling and downwelling motions are observed inside the array for D/h ≥ 1.33, while the circulation of the streamwise-oriented cell of secondary flow forming close to the lateral face of the array peaks when the submergence ratio is close to 1.33. For constant ϕ, the total streamwise drag force normalized with the height and width of the array increases with increasing submergence ratio. As the array submergence increases, the cylinders near the front of the array contribute less to the total force acting on the cylinders forming the array. For constant D/h, the total streamwise drag force acting on the array increases with ϕ for the submerged and emerged cases.

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Section: Dmentioning

confidence: 99%

“…(2017, 2020) and Liu et al. (2021) to simulate flow past emerged and submerged arrays of cylinders situated away from the channel banks and by Koken & Constantinescu (2020) to simulate flow past a rectangular array of emerged cylinders placed at one of the channel's sidewalls.…”

Section: Introductionmentioning

confidence: 99%

Influence of submergence ratio on flow and drag forces generated by a long rectangular array of rigid cylinders at the sidewall of an open channel

Köken

2023

J. Fluid Mech.

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“…The Semi-Implicit Method for Pressure Linked Equations (SIMPLE) scheme that especially fits the complex flow and boundary conditions was adopted as the time marching method to ensure convergence and stability [21,22]. For the spatial discretization, the gradient term used the Least Square Cell-Based method, the pressure term employed the algorithm PRESTO!, and the volume fraction term adopted the Central Difference Scheme, which can obtain more accurate results in the LES turbulence model [12,16].…”

Section: Numerical Setupmentioning

confidence: 99%

Propagation and Separation of Downslope Gravity Currents over Rigid and Emergent Vegetation Patches in Linearly Stratified Environments

Lin

Dongrui

et al. 2022

JMSE

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Large eddy simulation (combined with the mixture model) and laboratory experiment were used to investigate the impact of emergent and rigid vegetation on the dynamics of downslope gravity currents in stratified environments. The reliability of the numerical model was assessed with the corresponding laboratory measurements. The results show that the vegetation cylinders lead to severe lateral non-uniformity of the current front, causing more evident lobe and cleft structures. In stratified environments, the smaller driving force leads to less propagating velocity until the current separates from the slope. The transition point (from acceleration to deceleration phases) of current velocity appears earlier as the vegetation becomes denser. The peak value of the bulk entrainment coefficient Ebuik is inversely proportional to the vegetation density, while the final converged value of Ebuik is proportional to the vegetation density. Vegetation patches make the degree of fluctuation of the instantaneous entrainment coefficient Einst more intense, and even negative values appear locally, indicating that the gravity current is detrained into the ambient fluid. The velocity profiles of gravity current develop multi-peak patterns in stratified environments due to fingering intrusive patterns. Our analysis reveals that as the vegetation density increases, the generated wakes behind vegetation cylinders increase local entrainment and mixing, causing the density of current flow from vegetation to decrease and reach the neutral buoyancy layer of ambient fluids earlier, finally leading to a smaller separation depth.

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“…On this basis, the turbulent diffusion coefficient, t D , is usually related to velocity magnitude m u and eddies scale e l , i.e., t e m D l u [11] . In channels with submerged canopies, the drag forces of vegetation are discontinuous in the vertical direction due to the presence of a strong shear region at the top of canopies and thus dominate the hydrodynamic features of flow fields [12][13][14] . In accordance with the velocity and turbulence features, the flow field is usually divided into several layers, which can be found in the review of Nepf [10] in detail.…”

Section: Introduction mentioning

confidence: 99%

Longitudinal dispersive coefficient in channels with aquatic vegetation: A review

Yang¹,

Fang²,

Yang³

et al. 2023

J Hydrodyn

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The determination of longitudinal dispersion coefficient in rivers is necessary for pollution control, environmental risk assessment, and management. In rivers with aquatic vegetation, the flow field is remarkably modified by canopies, which affects velocity profiles and dispersion characteristics dominated by the heterogeneity of the velocity field. The dispersion is deduced from lateral and vertical longitudinal velocity gradients for compound channels with vegetated floodplains and rectangular channels with river-wide vegetation, respectively. Although many efforts have been exerted to clarify the dispersion process in different conditions and predict the diffusion of contaminants in vegetated rivers, no studies have introduced it systematically. This study reviews the dispersion coefficient characteristics, including magnitude, main impacted factors, and relationships with flow and vegetation features, in channels with aquatic canopies considering the variation of impact factors changing with the different vegetation and river morphology scenarios. Several typical methodologies for determining longitudinal dispersion coefficients are also summarized to understand the dispersion processes and concepts. Apart from the pioneer outcomes of previous studies, the review also emphasizes the deficiency of existing studies and suggests possible future directions for improving the theory of dispersion in vegetated channels.

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Numerical study on the drag characteristics of rigid submerged vegetation patches

Cited by 30 publications

References 78 publications

Influence of submergence ratio on flow and drag forces generated by a long rectangular array of rigid cylinders at the sidewall of an open channel

Influence of submergence ratio on flow and drag forces generated by a long rectangular array of rigid cylinders at the sidewall of an open channel

Propagation and Separation of Downslope Gravity Currents over Rigid and Emergent Vegetation Patches in Linearly Stratified Environments

Longitudinal dispersive coefficient in channels with aquatic vegetation: A review

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