Analysis of the effect of rigid vegetation patches on the hydraulics of an open channel flow with Realizable k-ε and Reynolds stress turbulence models

Abstract

In this study, the effect of vegetation patches naturally located in the river and stream bed on flow characteristics was observed under laboratory conditions by using representative rigid vegetation. Then, the behavior of rigid vegetation was compared with two different (Realizable k-ε and Reynolds Stress) turbulence models using a CFD software (ANSYS-Fluent). Firstly, our use of models was validated. Then, they were used for numerical simulation. The velocity distributions energy dissipation, and turbulent intensities, at the determined points for the patches located in the downstream part, were analyzed with graphics and simulations. The vertical distribution of the average velocities was calculated at typical locations downstream. The magnitude of flow velocities was observed to decrease within the vegetation patch zone. The minimum values of the velocity magnitude were observed just behind the vegetation structures. Higher velocities were simulated in the vegetation patch regions compared with the gap regions. This identifies that the gap areas are appropriate for the deposition of sediments and advantageous for aquatic living beings in terms of physical atmosphere and nutriment. A maximum of 7 % energy dissipation difference occurred between the highest and lowest SVF values. For equal SVF values, a 1 % energy dissipation difference was obtained. This situation can be associated with the number of rods, and rod spacing being equal to the rod diameter. The 3-D turbulence intensity was only numerically measured and compared. Between the Realizable k-ε model and the RES model, the maximum 0.05 %turbulence density difference was observed (for SC1 and SC3 scenarios). We can associate this situation with the vortex and complex turbulent flow, which is formed from the channel bottom to the water surface, depending on the diameter of the rigid vegetation and the rod sequence. It was observed that there are effective methods to predict the flow model within both models.