Experiment Research And Numeical Simulation On The Flow Structure Of The Open Channel With Rigid Submerged Plants

Plants are an essential part of the aquatic ecosystem,and it is necessary to study the influence of plants on the flow structure.More and more researchers are paying attention to this basic research.This paper systematically expounds the research progress of physical experiment and numerical simulation of open channel water flow with plants at home and abroad.On this basis,the Particle Image Velocimetry(PIV)was used to study the flow structure of the open channel with rigid submerged plants through laboratory model test.The distribution characteristics of flow velocity,turbulence intensity,Reynolds stress and vorticity intensity under different plant densities,flow rates and relative water depths were analyzed.In this paper,the two-dimensional flow field with rigid submerged plants is numerically simulated by using fluid computational software FLUENT with the Reynolds stress turbulence model is selected,the free water surface is captured by VOF method,and the vegetation zone is genealized into porous media region.The main research results are as follows:(1)In the absence of plants,the average velocity distribution along the vertical line was logarithmic,while in the presence of plants,the velocity distribution along the vertical line showed obvious zonal distribution characteristics.The regional distribution characteristics are related to planting density,relative water depth and inflow rate.When the relative depth of water is large,the distribution law of the average velocity along the vertical line is suitable for the distribution in two regions.When the water depth is relatively small,the distribution law of the average velocity along the vertical line is more suitable for the distribution of the three regions.The velocity distribution characteristics of each zone are different.The velocity in the first zone is a relatively small value,the velocity in the second zone increases with the increase of water depth,and the velocity in the third zone maintains a relatively large value almost unchanged.The greater the relative depth,the greater the range of the three zones,and the greater the maximum velocity.The velocity gradient in the two zones and the maximum velocity achieved increase with the increase of density or flow rate.In this paper,according to the characteristics of velocity zoning distribution and previous research results,a new empirical expression is proposed for the velocity above the plant.The velocity calculated by the empirical formula is in good agreement with the measured value.(2)In the absence of plants,the turbulent intensity changes little along the direction of water depth.In the presence of plants,the turbulence intensity in the canopy is the most intense and the turbulence intensity value is the largest.The larger the incoming flow rate or plant density is,the greater the turbulence intensity will be.When the relative water depth is small,the turbulence intensity decreases to the surface gradually after reaching its maximum value at the canopy of the plant.When the relative water depth is large,the turbulence intensity decreases to the minimum value at a certain distance below the water surface,and then keeps this value a little change.The distribution of Reynolds shear stress is similar to that of turbulent intensity.(3)With the increase of flow rate,the vorticity intensity in the canopy increases.The vorticity intensity near the canopy is greatly affected by the flux,while the vorticity intensity near the water surface and within the plant zone is less affected by the flux.The effect of plant density on vorticity is not obvious.When the relative water depth is small,the vorticity intensity reaches its maximum value in the reverse direction at the canopy of the plant,and then decreases to the water surface.When the relative water depth is large,the vorticity intensity decreases to its minimum value at a certain distance below the water surface,and then the value of the vorticity intensity does not change much.(4)In this paper,porous media region is used to replace rigid submerged plants,Reynolds stress turbulence model is selected and VOF method is adopted to capture free water surface.The established mathematical model is reliable and can well simulate the water flow movement of rigid submerged plants.