Numerical Simulation Of Flow Field Around Trees Under Strong Wind

With the development of urbanization,the "heat island effect" in cities has become more and more prominent.Tree planting has naturally become one of the most advantageous methods to solve the "heat island effect".Vegetation in coastal areas will be affected by strong winds from typhoons,and shelter forests in northwestern regions will be eroded by sandstorms.Guiding suggestions are provided for the preventio n and control of wind damage to trees.This paper studies the distribution of flow fields around trees under strong winds,and uses additional source term method for tree crowns.Simplified to porous media,a numerical simulation study was carried out on t he interference effect of trees on the wind field.The changes in the flow field of trees under different drag coefficients,different wind speeds,and different layout conditions were discussed.The specific results are as follows:First,a single tree model was established based on the Douban boxwood in the wind tunnel test to verify the reliability of the method and model.The results show that under the same wind speed,the numerical simulation results of the influence of trees on the flow field behind the trees are consistent with the results of wind tunnel experiments.In the downwind direction,the canopy is the center,and the contour is elliptical and expands radially around.The farther away from the center of the tree canopy,the smaller the attenuation effect of trees on wind speed and the smaller the impact on turbulence;in the cross-wind direction,the tree’s shadow area and the size of the canopy are within the plane of double tree height(X=1H)behind the tree Coincide.In the case of differe nt wind speeds,as the wind speed increases,the porosity of the trees will gradually increase,and the drag coefficient will decrease accordingly.The minimum wind speed at the relative reference point of the wind profile at twice the height of the tree t runk will gradually increase.,The maximum value of turbulence relative to the reference point gradually decreases.After considering the above conditions,the simulated wind field is similar to the wind field measured in the wind tunnel test.Secondly,based on the single tree model,the flow field distribution law behind a single row of trees is explored.The results show that the flow field distribution law of a single row of trees is consistent with that of a single tree on the whole.With the middle tree as the center,the contour is elliptical and expands radially around.The minimum wind speed and maximum turbulence behind the tree are consistent with the single tree area,but the shadow area behind the tree is farther than the single tree.For diffe rent downwind profiles,Y=0.5D,that is,the profile between two trees has the least interference to the flow field behind the tree,and Y=0D and Y=1D,that is,the canopy center profile has the largest interference to the flow field behind the tree.In th e case of different drag coefficients,as the drag coefficient increases,the wind speed behind the tree will decrease,the turbulence behind the tree will increase,and the center tree is more sensitive to the drag coefficient than the trees on both sides.That is,as the drag coefficient increases,the flow field changes more after the center tree.Finally,the additional source term method is also used to establish a double-row tree model to explore the distribution law of the flow field behind the doubl e-row tree under different arrangements.The results show that the overall flow field distribution of double-row trees is consistent with that of single-row trees and single-row trees.When arranged in parallel,the flow field distribution law behind the t ree is similar to that of the single-row tree,but the minimum wind speed and turbulence behind the tree are somewhat stronger than that of the single-row tree,and the sheltering distance behind the tree is also farther than that of the single-row tree.In different downwind sections,the Y=0.5D section has the least influence on the flow field,and Y=0D and Y=1D have the greatest influence on the flow field.When the staggered seams are arranged,the wind speed,turbulence and shielding distance behind th e trees are more affected than other arrangements,which shows that this arrangement has the best interference effect on the flow field.Under different downwind profiles,as the distance from the center tree is farther,the wind speed and turbulence of th e flow field behind the tree are less disturbed by the tree,and the sheltering distance behind the tree is also smaller.