Wind Tunnel Test Study On Wind Force Of Trees And Its Influence On Flow Field Behind Trees

China is a strong / typhoon prone country,trees are easy to break and fall under strong wind conditions,which will not only cause serious economic losses,but also may block traffic and threaten the safety of pedestrians.Therefore,it is necessary to study the mechanical characteristics and failure mechanism of trees under strong wind.In addition,trees will block the incoming flow and have a shielding effect.The sheltering effect of trees can effectively reduce the wind speed of the nearby flow field.If we can master the rules and make use of them,such as windbreak and sand fixation,farmland protection and improvement of local wind environment,it will be of great practical significance.Based on the summary of the existing research results,the following results hav e been achieved through systematic research and analysis:(1)In the wind tunnel laboratory,a set of measuring system and test method for measuring wind-induced forces and flow field behind trees are designed by using force balance and Cobra wind speed probe.The stress and flow field of trees under different crown shape,arrangement and porosity were measured.(2)Through the research,it is found that the stress of trees under different crown forms is quite different.The higher the tree height is,the large r the windward area of the crown is,the greater the wind force it receives.The relationship between the resistance and overturning moment of trees and wind speed is power function increasing,and the relationship between resistance coefficient and overtu rning moment coefficient and wind speed is power functio n decreasing.There will be mutual interference among trees under different arrangements,which will reduce the stress of trees,especially the stress of trees under a row arrangement will be significantly reduced,about 30% of that under a single arrangem ent.There is a positive correlation between tree porosity and wind force.With the increase of tree porosity,the wind force will gradually reduce.(3)It is found that the deformation of trees increa ses with the increase of wind speed,which results in the influence of trees on the flow field behind trees decreases slightly with the increase of wind speed.When a single tree is arranged,the influence of trees on the flow field is mainly concentrated in the range of tree crown,while a row of trees can form a relatively stable wind influence area behind the tree.And the influence of row arrangement on the flow field behind the tree is greater than that of single tree arrangement.The change of tree po rosity can significantly change the flow field characteristics in the area behind the tree.The larger the porosity is,the smaller the extent and range of its influence on the flow field in the area behind the tree is.