Large eddy simulations of a circular cylinder at Reynolds numbers surrounding the drag crisis

Lloyd, T.; James, Marion

doi:10.1016/j.apor.2015.11.009

Cited by 23 publications

(9 citation statements)

References 28 publications

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“…

k

represents the SGS kinetic energy for the Smagorinsky model and is given by

k = 2 (|, c_{k} / c_{e}) Δ^{2} {({\bar{S}}_{i j} - {(|, 1 / 3) \bar{S}}_{k k})}^{2}

, where

Δ

is the filter width and values of

c_{e} = 1.048

and

c_{k} = 0.05

are taken here (

c_{e}

and

c_{k}

are related to the classical Smagorinksy constant according to

C_{s} = {(c_{k}^{3} / c_{e})}^{1 / 4}

which yields

C_{s} = 0.104

[ Lysenko et al ., ]). All simulations were carried out in OpenFOAM version 2.3.0, which has been widely used for modeling flow around bluff bodies [ Lloyd and James , ; Lysenko et al ., ; Sidebottom et al ., ]. The incompressible solver pimpleFoam was used, which has the merged PISO‐SIMPLE algorithm implementation.…”

Section: Numerical Modelingmentioning

confidence: 99%

A new model for predicting the drag exerted by vegetation canopies

Farooji

Lowe

Ghisalberti

2017

Water Resources Research

106

130

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The influence of vegetation canopies on the flow structure in streams, rivers, and floodplains is heavily dependent on the cumulative drag forces exerted by the vegetation. The drag coefficients of vegetation elements within a canopy have been shown to be significantly different from the well‐established value for a single element in isolation. This study investigates the mechanisms that determine canopy flow resistance and proposes a new model for predicting canopy drag coefficients. Large Eddy Simulations were used to investigate the fine‐scale hydrodynamics within emergent canopies with solid area fractions ( λ) ranging from 0.016 to 0.25. The influences of three mechanisms in modifying canopy drag, namely, blockage, sheltering, and delayed separation, were investigated. While the effects of sheltering and delayed separation were found to slightly reduce the drag of very sparse canopies, the blockage effect significantly increased the drag of denser canopies ( λ≳0.04). An analogy between canopy flow and wall‐confined flow around bluff bodies is used to identify an alternative reference velocity in the definition of the canopy drag coefficient; namely, the constricted cross‐section velocity (Uc). Through comparison with both prior experimental data and the present numerical simulations, typical formulations for the drag coefficient of a single cylinder are shown to accurately predict the drag coefficient of staggered emergent canopies when Uc is used as the reference velocity. Finally, it is shown that this new model can be extended to predict the bulk drag coefficient of randomly arranged vegetation canopies.

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“…

k

represents the SGS kinetic energy for the Smagorinsky model and is given by

k = 2 (|, c_{k} / c_{e}) Δ^{2} {({\bar{S}}_{i j} - {(|, 1 / 3) \bar{S}}_{k k})}^{2}

, where

Δ

is the filter width and values of

c_{e} = 1.048

and

c_{k} = 0.05

are taken here (

c_{e}

and

c_{k}

are related to the classical Smagorinksy constant according to

C_{s} = {(c_{k}^{3} / c_{e})}^{1 / 4}

which yields

C_{s} = 0.104

Section: Numerical Modelingmentioning

confidence: 99%

A new model for predicting the drag exerted by vegetation canopies

Farooji

Lowe

Ghisalberti

2017

Water Resources Research

106

130

View full text Add to dashboard Cite

show abstract

“…The hat

\overset{}{true}

denotes spatially filtered variables. All simulations were conducted using OpenFOAM version 2.3.0, which has been widely used for modeling flow around bluff bodies (Lloyd & James, ; Lysenko et al, , ; Sidebottom et al, ).…”

Section: Numerical Modelingmentioning

confidence: 99%

Predicting Bed Shear Stresses in Vegetated Channels

Farooji

Ghisalberti

Lowe

2018

Water Resources Research

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Shear stresses on vegetated beds play an important role in driving a wide range of processes at the sediment‐water interface, including sediment transport. Existing methods for the estimation of bed shear stress are not applicable to vegetated beds due to the significant alteration of the near‐bed velocity profile and turbulence intensities by the vegetation. In addition, bed shear stress distributions are highly spatially variable in the presence of vegetation. In this study, computational fluid dynamics simulations were used to investigate the spatial variability of bed shear stresses in the presence of emergent vegetation (modeled as arrays of circular cylinders) and the variation of bed stress with characteristics of both the bulk flow and the array. A recently proposed model that assumes a linear variation of stress in the viscous layer immediately above the bed is shown to be a reliable tool for estimating the spatially averaged bed shear stress over a wide range of flow conditions and vegetation densities. However, application of this model is found to be restrictive due to the lack of a reliable predictive tool for the thickness of the viscous layer. Based on a balance between turbulent kinetic energy production in the vegetation stem wakes and the viscous dissipation of turbulent kinetic energy at the bed, an enhanced formulation is proposed to predict the thickness of the viscous layer, which significantly improves the accuracy of model predictions. This improved model enhances the predictive capability for important benthic processes (such as sediment transport) in vegetated aquatic systems.

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“…Several modeling aspects may be considered. On one hand, when coarse grids are used in LES, the effect of the numerical modeling on the flow resolution is increased [20]. On the other hand, effects of the subgrid modeling become more pronounced as well.…”

Section: Overviewmentioning

confidence: 99%