3D numerical investigation of flow behavior in an open channel with uniform and layered vegetation patches under varying submergence conditions

Abstract

Staggered vegetation patches (central and outer) in an open channel have a significant effect on flow structure and river geomorphology. Although investigation on vegetation patches has been done in the past, however none of the past studies was carried out for varying submergence conditions from outer to central patches or for layered staggered patches with varying submergence. This knowledge gap has been attempted to bridge in this study. In this research work, a numerical technique has been used to analyze the flow behavior in a riverine flow by modeling central and outer vegetation patches as rigid elements in a rectangular channel. The influence of various vegetation patch configurations and submergence conditions were studied on flow characteristics. Computational fluid dynamics (CFD) package FLUENT was used for simulation purposes. Results showed that the flow in the central region of the channel was highly non-uniform, having a longitudinal distribution of velocities with alternating peaks and troughs throughout the central portion of the channel. However, in the outer regions, the velocity pattern acquired sawtooth distribution inside the patch regions (PR) but stabilized in the free regions (FR). Outer FR has 9% less velocities as compared to central FR. Moreover, the inflection point in velocity profiles and the bulge in contour plots was observed which triggered the shear layer at the top of submerged vegetation and at the interface of outer FR and central PR or vice versa. A complex pattern of secondary flow was also observed due to the turbulence anisotropy in the channel and its magnitude ranged from 0.1 to 3.7% of average velocity U. The results also showed that the state of submergence has a notable effect on the flow blockage and percentage of discharge passing through various regions.