Study On The Measurement Of Water Flow In Compound Open Channel With Rigid Vegetation And Its Numerical Simulation By Lattice Boltzmann Method

Natural rivers are usually composed of main channels and floodplains,on which vegetation tends to grow.The aquatic vegetation on the floodplain will not only affect the water flow structure on the floodplain,but also have a great influence on the flow structure in the main channel.And then affect the sediment transport,bed deformation,water environment change and navigation,Therefore,it is of great practical value to study the problem of vegetated water flow in compound channels.In this thesis,the rigid vegetation(replaced by glass rods)arranged in different conditions on the floodplain in the compound channel with multistage floodplain.The flow velocity is measured by a three dimensional laser Doppler velocimeter(3D-LDV),and the measured data were analyzed.Furthermore,the D3Q27 model in the lattice Boltzmann method is used for the 3D numerical simulations of the flow in compound open channel with vegetation in the floodplain.The main results in this study are as follows:1.The D3Q27 model of lattice Boltzmann method is established through the development process of lattice Boltzmann method and its advantages compared with other traditional methods,and the boundary conditions of the model are deduced.Finally,the program code is compiled by MATLAB software.2.Rigid vegetation substituted by glass rods were arranged on the first and second floodplains in a laboratory compound channel,and 3D-LDV,water level meter and other instruments were employed to measure water level and 3D flow velocity under various cases.Finally,the changes of water level,flow velocity,hydraulic slope and turbulence intensity under different working conditions are compared and analyzed,and the distribution of vegetation velocity on the floodplain is serrated,the flow velocity is smaller when the vegetation is in staggered arrangement than when it is in parallel arrangement,the flow velocity is smaller when it is close to the vegetation in the main channel,the flow velocity is almost the same when it is far away from the vegetation as when there is no vegetation,and the flow velocity is smaller when the water depth is deeper at the same horizontal section etc flow characteristic.3.Using D3Q27 model for three dimensional lid driven flow are simulated,and the calculated results with the D3Q15 model and D3Q19 model comparison and analysis,get D3Q27 model is stable,so as to verify the reliability of the model.4.A number of typical case were set,and the 3d numerical simulation of water flow in a compound flume with vegetation on the floodplain is carried out by using the D3Q27 model,and the flow velocity distribution of the numerical simulation results under different case is compared and analyzed.The results obtained were consistent with the experimental results of water flow movement with rigid vegetation on the floodplain,which further verified the accuracy of the established model.