Numerical investigation of the flow characteristics through discontinuous and layered vegetation patches of finite width in an open channel

Abstract

In this study, a computational method is used to investigate the flow properties and turbulence characteristics through discontinuous and vertically double layered vegetation patches of finite width in an open channel. A three dimensional Reynolds stress turbulence model was implemented utilizing FLUENT (ANSYS). After the validation of the numerical model, flow characteristics were investigated against varying vegetation density (St/d and Ss/d, where St = spacing between taller vegetation elements, d = diameter of vegetation, Ss = spacing between smaller vegetation elements) and vegetation patch width. Various profiles and contour plot distributions of mean stream-wise and depth averaged velocities, turbulent kinetic energy and turbulent intensities at specified critical locations and sections simulated by the model are presented in this paper. In almost all the cases, mean stream-wise velocities directly behind the smaller and larger vegetation elements showed fluctuations, with sharp inflection points at the top of the smaller vegetation elements. Velocities were amplified above the vegetation zones, whereas deceleration in the velocity magnitudes was observed within the vegetation zones i.e., below the top of vegetation. Inside the vegetation patch zones, the turbulent intensity was higher as compared to that in the gap zones. The turbulent intensity was increased for dense vegetation case (St/d = 6.66 and Ss/d = 3.34) as compared to that of sparse arrangement of vegetation (St/d = 10 and Ss/d = 5). Hence, a clear difference in flow characteristics between the vegetated and non-vegetated zones was observed.