Numerical Investigation of Hydrodynamics in a U-Shaped Open Channel Confluence Flow with Partially Emergent Rigid Vegetation

Abstract

The effects of partially emergent rigid vegetation on the hydrodynamics of a curved open-channel confluence flow were simulated using OpenFOAM. The numerical model using the Volume of Fluid method and the RNG k-ε turbulence model in the Reynolds-averaged Navier–Stokes equations was first validated by existing experimental data with good agreement. Then the characteristics of hydrodynamics were analyzed in aspects of separation zone, water level, streamwise velocities, secondary flows, bed shear stress and flow resistance. Some main conclusions can be drawn from the results. Compared to the non-vegetated cases, the separation zones in vegetated cases are smaller in both length and width. With higher vegetation Solid Volume Fraction (SVF), the separation zone is divided into two parts, a smaller one right after the confluence point and a larger one on the second half of the curved reach after the confluence. The main circulation cell shrinks and the circulation near the concave bank moves towards the channel midline. The differences in velocities and bed shear stress between the convex and concave banks become larger with a higher SVF. Under the same SVF, a larger vegetation density has more disturbance on the tributary than a larger stem diameter.

Keywords

• U-shape open channel
• confluence flows
• emergent rigid vegetation
• separation zone
• bed shear stress
• OpenFOAM