3D numerical modelling of open-channel flow with submerged vegetation

Abstract

Velocity distributions in channels partially covered with vegetation have been computed using a three dimensional model. The Navier-Stokes equations were solved, using the SIMPLE method and the k-∊ turbulence model. The vegetation was modeled as vertical cylinders. A formula for the drag force on the vegetation was included as a sink term in the Navier-Stokes equations. The advantage with this method compared with using large roughness is that effects of the vegetation over the whole water depth can be taken into account, instead of only affecting the velocity near the bed. The numerical model was tested against three laboratory experiments from straight flumes with uniform flow, where vegetation partially covered the cross-section. The velocity and vegetation density varied in both vertical and horizontal directions in the different cases. The experiments also included varying crosssectional shapes. All tests gave fairly good correspondence between computed and measured velocity profiles.