Application of Ecological CFD on 3-D Free-Surface Flow with Plant Canopy

The main objective of this study is to investigate the 3-D free-surface flow with plant canopies from an ecological viewpoint, and analyze the flow field within plants so as to research how the plant canopy affect the outflow in downstream of the study field. We select the finite volume method to discretize the governing equations of our model. PISO scheme is used to adjust flow field to satisfy the continuity equation. The κ-ε model is adopted to simulate the 3-D turbulence flow field in the study, and apply the volume of fluid concept in modeling multiphase flow with water and air through porous media to procure the water-damping effect of the plant .
The κ-ε turbulence model is firstly verified by the experimental measurement given by Nepf and Vivoni (2000). The numerical results are in good agreement with the experimental data for the mean velocity, turbulent root-mean-square velocity, and eddy viscosity. Since the canopy density is different for various plants and plant densities, a series of experiments of the canopy density in paddy field for different rice growth periods are carried out. The experimental results are further input into the CFD model.
Our study includes two cases, one is single paddy field and the other is tri-paddy field. The simulated result shows that the field of no paddy has good flood detention function, and delays the time to peak over 20%. And the higher of the plant is, the well water-damping effect of the plant is. For the paddy field having the height of rice over 30cm, it reduces the flood flow rate about 10% ~26%, and holds the time to peak over 21% compared to the field without paddy. Furthermore, paddy field redistributes flow discharge distribution. Therefore the paddy field indeed provides flood mitigation and detention function.