Vegetation in open channels will improve the water quality there and providing favorable space for various lives, but it will reduce the flow carrying capacity of the channel by introducing additional resistance to th...
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Vegetation in open channels will improve the water quality there and providing favorable space for various lives, but it will reduce the flow carrying capacity of the channel by introducing additional resistance to the flow. In this paper a Large Eddy Simulation (LES) model has been developed to study the mean flow and turbulence in open channel with vegetation. In the model the vegetation domain is represented by a drag force layer. One equation model is used for subgrid scale turbulence closure. The length scale of turbulence l is proportional to the grid size and the turbulence energy k is obtained from the solution of the turbulence energy transport equatioa The model has been applied to simulate cases of open channel flow with emergent or submerged vegetation. For emergent vegetation occupied in a part of an open channel, transverse shear is produced by vegetation drag. Organized large eddies are developed at the interface between the vegetated and non-vegetated regions and the organized flow structure clearly has a life cycle. At the interface the transverse velocity profile exhibits a steep gradient, which induces significant mass and momentum exchange, acts as a source of vorticity, and generates high Reynolds stresses. For submerged vegetation in open channel, the flow near the top of vegetation is unstable and rolls up into discrete vortices. The turbulent intensity and the Reynolds stresses are the strongest there. Interaction of vortices results in a shear layer above the top of vegetation. The agreement between the numerical results and the available experimental data is satisfactory. The present model is a useful tool for further study of turbulent flow with vegetation, as well as for certain engineering applications.
This paper presents a numerical study on free-surface flow in curved open-channel. A new improved SIMPLEC algorthm with velocity-pressure-free-surface coupled correction is developed and validated. Such algorithm diff...
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This paper presents a numerical study on free-surface flow in curved open-channel. A new improved SIMPLEC algorthm with velocity-pressure-free-surface coupled correction is developed and validated. Such algorithm differt from the traditional SIMPLEC algorithm and includes three correction equations which are named as the velocity correction equation, the free-surface correction equation derived from the continuity equation with the kinematic boundary conditions on the free-surface and the bottom bed, and the pressure correction equation taking the same formation as the traditional SIMPLEC algorithm does. The new improved method, in this study is used to solve the incompressible, three-dimensional, Reynolds-averaged Navier-Stoges equation set combined with the standard κ-ε model and/or the low Reynolds number κ-ε model for free-surface viscous flow in curved open-channels. The power law scheme (POW) is used to discretize the convection terms in these equations with a finite-volume method. The practical cases studied are free-surface flow through the 180° curved open-channel with different hydraulic discharge rates. The comparisons between computations and experiments reveal that the model is capable of predicting the detailed velocity field, including changes in secondary motion, the distribution of bed shear, and the variations of flow depth in both the transverse and the longitudinal directions. Based on the modeling results, the new improved SIMPLEC algorithm is feasible and effective for numerical study on free-surface viscous flow in curved open-channels.
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