Prediction performances of turbulence models in examining the flow characteristics of vegetated channels: CFD computations and experimentally validation

Abstract

The performance of turbulence models was investigated to predict the flow and turbulence features of the vegetated channel using Computational Fluid Dynamics (CFD). The Ansys Fluent, CFD software was implemented for the numerical studies. The flow was three-dimensional, incompressible, steady, and turbulent. Ten turbulence models, provided by Ansys Fluent were implemented for the comparative study. The numerical model was validated against an experimental study conducted in the literature. The numerical studies show that the renormalization group k-ε model (RNG) is the most successful model for predicting the flow characteristics of the vegetated channel with RMSE value of 0.2752. At the same time, the Reynolds Stress Model (RSM) gives the least successful predictive performance, indicated by an RMSE value of 0.4302. Moreover, the Spalart-Allmaras (S-A) model offers the shortest computation time with a value of 6652.393 sec, whereas the SST k-ω model proves to be the most time-consuming with a value of 11952.219 sec. The velocity of water flow in a channel is not uniform as it is slower at the surface of leaves and faster in the free zones. The maximum velocity is observed in the middle section of the channel, below the leaf, and between the roots with the value of u=0.1158 m/s. Furthermore, the characteristics of turbulence in a channel are influenced by various factors such as channel geometry, flow velocity, and vegetation distribution. As a result, the presence of vegetation in a channel affects the flow and turbulence characteristics of the water significantly.