Field Measurement On The Water Flow Movement With Flexible Vegetation In A Multistage Floodplain Flume And Numerical Simulation By Lattice Boltzmann Method

The natural river channel is generally composed of an main channel and floodplains.Some plants,such as shrubs,trees,aquatic plants and reeds,usually grow on the floodplain,which not only affect the flow movement of the floodplain,but also affect the flow characteristics in the main channel.In order to study the influence of flexible vegetation on river flow,using the flume with multi-stage floodplain on one side in the laboratory,some typical cases are set for the flow with flexible vegetation(replaced by plastic grass)or rigid vegetation(replaced by glass rod).The D3Q15 model of three-dimensional lattice Boltzmann method is used for numerical simulation.The main research work includes the following aspects.Firstly,for the D3Q15 model in the three-dimensional lattice Boltzmann method,the single relaxation and multiple relaxation forms and the boundary treatment format of the model are derived,and a series of algorithm designs are carried out.Finally,the MATLAB software is used to program and calculate.Secondly,the flow velocity and other physical quantities of vegetation in the compound open channel are measured using 3D laser Doppler velocimeter(LDV)and other instruments.The flexible plants are replaced by plastic grasses,and the rigid plants are replaced by glass rods.A series of cases are designed.The measured results are analyzed,and the flow characteristics of vegetation floodplain in the compound open channel are obtained.The results show that along the Y direction,the velocity distribution near the vegetation on the floodplain is serrated,and the velocity distribution in the main channel is relatively uniform;along the Z direction,the velocity on the floodplain fluctuates,but the velocity in the main channel and floodplain increases gradually.Finally,the D3Q15 multi-relaxation model is used to simulate the three-dimensional flow in the compound flume with vegetation,and several typical cases are designed.The results are compared and analyzed,and some flow laws are obtained: along the X direction,the vegetation makes the flow velocity on the floodplain smaller;along the Y direction,the velocity distribution is parabolic except that of the floodplain.Along the Z direction,the velocity of the main channel and floodplain increases with the increasing of Z.Then,the numerical simulation results are compared with the measured results for a certain condition,and the results show that they are basically consistent,which proves the reliability of the established model.