Research On Numerical Simulation Measurement Of Open Channel Flow With Flexible Vegetation

Aquatic vegetation in rivers,reservoirs and lakes has large influence on flow characteristics,and further affects sediment transport,irrigation,draining,water environment,etc.In order to study the influence of flexible vegetation on water flow,an series of measurements have been conducted on the water flow with reflective vegetation in a laboratory flume,using three dimensional laser Doppler velocimeter(LDV)and other instruments,and analyzed the characteristics of water flow based on the measurement results.A multiple relaxation lattice Boltzmann equation(MRT-LBE)has been established based on lattice Boltzmann method(LBM),and its numerical algorithm has been analyzed.Finally,numerical simulations are conducted on the water flow characteristics of laboratory flume with flexible vegetation using the MRT-LBE.The main content of this paper includes the following several aspects:First,the fundamental ideas and development history of computational fluid dynamics(CFD)and the development of lattice Boltzmann method(LBM)are introduced.The introduction focuses on the theories of LBM,the construction of discrete velocity model.A typical three deimensional(3D)model,i.e.D3Q15 is suggested and its boundary conditions are derived.Next,a series of experiments are carried out in a laboratory flume,and the flexible vegetation is substituted by plastic plants.Two plant arrangements(dense and sparse),three plant heights(6cm,8cm and 13cm),three water discharges(high,medium and low)are chosen and there 18 typical cases in total.LDV and other relevant instruments have been employed to measure the water level,3D velocities,vegetation tilt angles,turbulent strength and other data in vegetation area under different cases.The relationships between flow velocity and vegetation submergence,plant density,flow discharge.The flow characteristics were concluded based on the analysis and comparison of measurement results.In the end,a LBM was designed for the laboratory flume flow with flexible vegetation and 3-dimensional numerical simulation carried out.Due to the comparatively high Reynolds number,the single relaxation time model(SRT)will cause the numerical simulation process into divergence.Therefore,the MRT-LBE is chosen for numerical simulation,and the drag force of plant and gravity force are took into considered.The D3Q15 MRT-LBE model is developed and is applied to numericalsimulate the flow characteristics in a flume with flexible vegetation under several typical cases and the numerical results are analyzed and compared.