• Water Engineering Research
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• v.6 no.3
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• pp.101-112
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• 2005

This paper presents the state of the art of the CFD applications to vegetated open-channel flows. First, important aspects of the physics of vegetated flows found through the laboratory experiments are briefly reviewed. Then, previous CFD applications to one-dimensional vertical structure, partly-vegetated flows, compound open-channel flows with floodplain vegetation, and fully three-dimensional numerical simulations are reviewed. Finally, topics for further researches such as relationship between the resistance and flexural rigidity, additional drag due to foliages, and melting the experience of CFD with the depth-averaged modeling, are suggested.

• Journal of Korea Water Resources Association
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• v.38 no.10 s.159
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• pp.871-883
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• 2005

This paper investigates the impacts of turbulent anisotropy on the mean flow and turbulence structures in vegetated open-channel flows. The Reynolds stress model, which is an anisotropic turbulence model, is used for the turbulence closure. Plain open-channel flows and vegetated flows with emergent and submerged plants are simulated. Computed profiles of the mean velocity and turbulence structures are compared with measured data available in the literature. Comparisons are also made with the predictions by the k-$\epsilon$ model and by the algebraic stress model. For plain open-channel flows and open-channel flows with emergent vegetation, the mean velocity and Reynolds stress profiles by isotropic and anisotropic turbulence models were hardly distinguished and they agreed well with measured data. This means that the mean flow and Reynolds stress is hardly affected by anisotropy of turbulence. However, anisotropy of turbulence due to the damping effect near the bottom and free surface is successfully simulated only by the Reynolds stress model. In open-channel flows with submerged vegetation, anisotropy of turbulence is strengthenednear the vegetation height. The Reynolds stress model predicts the mean velocity and turbulence intensity better than the algebraic stress model or the k-$\epsilon$ model. However, above the vegetation height, the k-$\epsilon$ model overestimates the mean velocity and underestimates turbulence intensity Sediment transport capacity of vegetated open-channel flows is also investigated by using the computed profiles. It is shown that the isotropic turbulence model underestimates seriously suspended load.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.3B
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• pp.247-257
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• 2009

In the present paper, turbulent open-channel flows with alternate vegetated zones are numerically simulated using threedimensional model. The Reynolds-averaged Navier-Stokes Equations are solved with the ${\kappa}-{\varepsilon}$ model. The CFD code developed by Olsen(2004) is used for the present study. For model validation, the partly vegetated channel flows are simulated, and the computed depth-averaged mean velocity and Reynolds stress are compared with measured data in the literature. Comparisons reveal that the present model successfully predicts the mean flow and turbulent structures in vegetated open-channel. However, it is found that the ${\kappa}-{\varepsilon}$ model cannot accurately predict the momentum transfer at the interface between the vegetated zone and the non-vegetated zone. It is because the ${\kappa}-{\varepsilon}$ model is the isotropic turbulence model. Next, the open channel flows with alternate vegetated zones are simulated. The computed mean velocities are compared well with the previously reported measured data. Good agreement between the simulated results and the experimental data was found. Also, the turbulent flows are computed for different densities of vegetation. It is found that the vegetation curves the flow and the meandering flow pattern becomes more obvious with increasing vegetation density. When the vegetation density is 9.97%, the recirculation flows occur at the locations opposite to the vegetation zones. The impacts of vegetation on the flow velocity and the water surface elevation are also investigated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2B
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• pp.179-189
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• 2010

This paper presents a numerical investigation of vorticity generation in fully vegetated open-channel flows. The Reynolds stress model is used for the turbulence closure. Open-channel flows with rough bed-smooth sidewalls and smooth bed-rough sidewalls are simulated. The computed vectors show that in channel flows with rough bed and rough sidewalls, the free-surface secondary currents become relatively smaller and larger, respectively, compared with that of plain channel flows. Also, open-channel flows over vegetation are simulated. The computed bottom vortex occupies the entire water depth, while the free-surface vortex is reduced. The contours of turbulent anisotropy and Reynolds stress are presented with different density of vegetation. The budget analysis of vorticity equation is carried out to investigate the generation mechanism of secondary currents. The results of the budget analysis show that in plain open-channel flow, the production by anisotropy is important in the vicinity of the wall and free-surface boundaries, and the production by Reynolds stress is important in the region away from the boundaries. However, this rule is not effective in vegetated channel flows. Also, in plain channel flows, the vorticity is generated mainly in the vicinity of the free-surface and the bottom, while in vegetated channel flows, the regions of the bottom and vegetation height are important to generate the vorticity.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.813-820
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• 2014

This study presents a numerical modeling of mean flow and turbulence structures of partly-vegetated open-channel flows. For this, Reynolds-averaged Navier-Stokes equations with vegetation drag terms are solved numerically using the non-linear k-${\varepsilon}$ model. The numerical model is applied to laboratory experiments of Nezu and Onitsuka (2001), and simulated results are compared with data from measurement and computations by Kang and Choi's (2006) Reynolds stress model. The simulation results indicate that the proposed numerical model simulates the mean flow well. Twin vortices are found to be generated at the interface between vegetated and non-vegetated zones, where turbulence intensity and Reynolds stress show their maximums. The model simulates the pattern of the Reynolds stress well but under-predicts the intensity of Reynolds stress slightly.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5B
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• pp.529-537
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• 2006

This paper investigates the impacts of the drag-related weighting coefficients on mean velocity and turbulence structures. The transport equations for the Reynolds stress of vegetated open-channel flows are derived by using the temporal- and horizontal-averaging scheme. It is found that the total Reynolds stress of vegetated open channel flows consists of the Reynolds stress due to temporally fluctuating velocities and the Reynolds stress due to spatially fluctuating velocities. The drag-related weighting coefficient $C_{fk}$ for the total Reynolds stress component is found to be unit, while the coefficient for the Reynolds stress due to temporally fluctuating velocities can be negligible. This is the reason why very small weighting coefficients in previous studies yield very good agreements with measured data. In other words, the Reynolds stress due to spatially fluctuating velocities remains still unknown, especially due to the large number of measuring locations. Through a developed Reynolds stress model, vegetated open-channel flows are simulated and compared with measured data from the literature. Comparisons reveal that the computed mean flow and Reynolds stress structures are hardly affected by the drag-related weighting coefficients. However, the computed turbulence intensity profiles are significant different with the drag-related weighting coefficients. A budget analysis of the transport equations for the Reynolds stress component is carried to investigate why turbulence intensity is affected by the drag-related weighting coefficients.

• Proceedings of the Korea Water Resources Association Conference
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• 1999.05a
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• pp.535-540
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• 1999

• Proceedings of the Korea Water Resources Association Conference
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• 2002.05b
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• pp.946-951
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• 2002

• Proceedings of the Korea Water Resources Association Conference
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• 2000.05a
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• pp.553-558
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• 2000

• Journal of Korea Water Resources Association
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• v.33 no.S1
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• pp.553-558
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• 2000