Abstract:

Objective: The relationship between wind load and wind speed of trees under different arrangement modes was studied,and the flow field characteristics behind trees were analyzed in order to find out the wind load and flow field characteristics when there is mutual interference among trees,and then provide a basis for tree protection and wind resistance. Method: The relationship between wind load and wind speed of a single tree,a row of trees and a column of trees was studied through wind tunnel test. At the same time,the flow field characteristics of specific plane behind a single tree and a row of trees were studied. Result: The resistance and overturning moment of the trees in the three arrangements increase with wind speed in a power way; The force of trees under a row arrangement was slightly less than that under a single arrangement,but the difference between the two decreased with the increase of wind speed; The force of the trees in a column is significantly reduced,and the resistance value is only 1/3 of the single arrangement; The resistance coefficient and the overturning moment coefficient of trees under the two arrangement modes of a single tree and a row decrease with wind speed in a power way; The resistance coefficients of trees in a column arrangement are almost independent of wind speed,while the overturning moment coefficients increase approximately linearly with the increase of wind speed; Under the incoming wind speed of 10 m·s^-1,the minimum relative wind speed in the cross-wind planebehind the tree is 0.47,and the maximum relative turbulence is 2.1. The isolines of relative wind speed and relative turbulence are radial distribution centered on the tree crown. The minimum value of relative wind speed and maximum value of relative turbulence are 0.42 and 2.2 in the cross-wind direction plane behind a row of trees. The isolines of relative wind speed and relative turbulence are parallel zonal distribution centered on the tree crown. The isolines of relative wind speed and relative turbulence in the downwind plane behind the tree under the two arrangements are elliptical centered on the tree crown. Conclusion: The wind load of trees increases as a power function with the increase of wind speed,but different arrangements will affect the wind load of trees. When the wind speed is the same,the resistance and overturning moment of trees under the three arrangement modes of a single tree,a row and a column decrease in turn. There is a wind-affected zone on the leeward side of the tree,and the flow field characteristics of this zone will change significantly,which is reflected by the decrease of wind speed and the increase of turbulence. When a single tree is arranged,the wind-affected area of the tree is a radial area centered on the canopy,and the wind-affected zone of the tree is a relatively continuous zone when arranged in a row.

Key words: trees, wind load, drag coefficient, overturning moment coefficient, flow field, wind tunnel test