Study Of Plants' Influence On Flow Characteristics

With the improvement of awareness of ecological river construction, plants in the river bank protection and restoration ecology projects has been applied more and more widely. Aquatic plants growing in the river could promote water purification and beautify the environment. Floodplain trees in favor of solid beach revetment. But they could also increase the flow resistance and reduce the flood discharge capacity of the river. So, the study on flow characteristics of river with aquatic plants is necessary.In this paper, research achievements and problems of domestic and foreign scholars about river flow with aquatic plants are analyzed. The river flow containing flexible plants and rigid plants are all studied with two methods of theory analysis and numerical simulation.The main research contents and results are as follows:(1) The general formula of plants' effect on the river flow drag force has been deduced.The empirical and analytical formulas about vertical distrib ution of river flow velocity have been summarized. Through formula derivations, influence factors of plants on the river flow resistance have been found out. The general formula of plants' effect on the river flow drag force has been deduced with the establishment of general channel model.(2) The three dimensional hydraulic characteristics of open channel with the submerged flexible vegetation was studied by use of RNG k-? turbulence model and VOF method tracking the free surface.The submerged flexible vegetation area is simplified as porous medium region,the porous medium model is selected to simulate the influence of flexible plants to water flow, there are some assumptions that the permeability of porous media is determined by the pressure difference and the porosity is determined by flexible plant space volume ratio. Simulation results are given for the curve of water level and vertical distribution of flow parameters such as turbulence intensity.The research shows that numerical simulation results and testing results are in good agreement by comparison.(3)The unilateral double channel is considered as the research object. The effect of trees on the beaches on the double river flow characteristics has been studied through three-dimensional numerical simulation.The river flow is studied by using RNG k-? turbulence model and VOF method tracking on the water surface, only considering the influence of tree trunk to flow and simplifying t he tree trunk to straight cylinder without deformation and swing under the action of water flow, analyze the river flow characteristics by three-dimensional numerical simulation. Results are given water level variation on beaches and main channel and floodplain curve, beach groove junction region along the vertical velocity distribution, the river cross-section along the transverse velocity distribution.The results show that, coupling RNG k-? turbulence model and VOF model can well simulate the variation law of the containing plant river flow characteristics. The research results can be applied to the river ecological restoration project, have certain guidance value to the engineering practice and application.