Investigating the turbulent flow characteristics in an open channel with staggered vegetation patches

In the present study, flow around circular and staggered vegetation patches was investigated numerically. For turbulence modelling, the Reynolds-averaged Navier-Stokes technique and Reynolds stress model were adopted. The numerical model was validated with the experimental data using varying vegetation density and flow velocities. The simulated results of mean stream-wise velocities were in close agreement with the experimental results. The results show that the mean stream-wise velocity in the downstream regions of vegetation patches were reduced, whereas the velocity in the free stream regions were increased. The influence of neighbouring and staggered vegetation patches on the flow was observed. The vegetation patches with larger nondimensional flow blockage (aD = 2.3, where a is the frontal area per volume of patches, and D is the diameter of vegetation patches) offered more turbulence when compared to the patches with a smaller flow blockage (aD = 1.2). Larger turbulence in the form of kinetic energy and turbulent intensity was recorded within the vegetation as well as the regions directly behind the patches. Negative Reynolds stresses were observed at the top of submerged vegetation. The turbulence characteristics peaked at the top of vegetation, that is, z/h = 1.0 (where z is the flow depth, and h is the vegetation height), which may be migrated vertically as the frontal area of the vegetation patch is increased. This high frontal area also increased stream-wise velocity above the vegetation, leading to an increased variation in turbulence around the vegetation canopy.