Wind Tunnel Test Study On The Interaction Between The Wind-sand Flow Field And Trees

In the boundary layer wind tunnel,the sandstorm climate were simulated by the method of falling sand at the top of the tunnel.The characteristics of wind-sand flow field under different wind tunnel wind speeds and falling sand amounts were discussed,including the distribution law of wind velocity,sand consistency and turbulence intensity.Taking the Buxus sinica with typical canopy characteristics as test trees,under the simulated wind-sand flow field,the influence of the trees on the wind-sand flow field behind the tree was studied.At the same time,the change of windward area of tree under static state and different wind speed is discussed.The force balance was used to measure the stress of the tree under the wind-sand flow field,and the influence of wind-sand on the stress was analyzed.After systematic research,the following results have been achieved:(1)Based on the measured net wind field information obtained from the observation field in a typical desert area,a variety of wind-sand flow field environments were simulated in the wind tunnel,and the flow field characteristics were analyzed.The results show that,compared with the net wind field,moving sand particles have a significant reduction effect on wind speed,but have an increase effect on the turbulence intensity.This reduction effect and increase effect are significant as the concentration of sand increases,and the degree of influence on the wind speed and turbulence intensity at different heights is related to the vertical distribution characteristics of the sand concentration.At the same wind speed,the sand concentration increases with the increase of the amount of falling sand.When the wind speed is small,the sand concentration decreases with increasing height.When the wind speed is high,the sand concentration at the lower height decreases,the sand concentration at the upper height increases,and the sand concentration profile decreases first and then increases along the height direction.(2)In the simulated sand and dust storm flow field,the wind-sand flow field at the three kinds of distance behind trees was measured and compared with that without trees.The results show that: under the same wind speed,the wind speed and sand concentration under the canopy behind the tree are slightly increased,and the wind speed and sand concentration above the tree top are basically unchanged,and the wind speed and sand concentration in the canopy height decreased significantly.The wind speed and the sand concentration in the middle of the tree have the highest reduction ratio compared to when there is no tree.The reduction degree increases with the increase of the amount of falling sand,and decreases with the increase of the distance between the trees.The degree of turbulence intensity behind the trees has increased significantly,and the law of the increase is similar to that of the former two.When the amount of falling sand is three,the decrease in wind speed and sand concentration at the canopy position behind the trees increases with the increase in wind speed,and the increase in the degree of turbulence intensity increases with the increase of wind speed.(3)The change of windward area of trees under different wind speeds was studied,and the influence of wind-sand action on tree stress was analyzed.The results show that the windward area of the test tree decreases with increasing wind speed.The average resistant force and average overturning moment of the trees measured by the balance under falling sand conditions are both less than the net wind field result,and the pulsation resistant force and pulsation overturning moment are greater than the net wind field result.At the same wind speed,the average drag coefficient and the average overturning moment coefficient of the test tree under the action of wind and sand are greater than the net wind field result,and increase with the increase of the amount of falling sand.