Wind tunnel study on aerodynamic characteristics of shrubby specimens of three tree species

With the popularization of green roofing systems, their wind resistant performance is becoming more and more important especially in typhoon areas. A prerequisite study was carried out to determine the aerodynamic characteristics of suitable trees to provide basic scientific data. Shrubby specimens of three tree species appropriate for intensive green roofs with different aerodynamic forms were tested through a boundary layer wind tunnel experiment, including one deciduous tree, one coniferous tree and one broadleaf evergreen tree. Drags and overturning moments under different wind speeds were measured; wind-speed-specific frontal areas and tip displacements were recorded. After initial tests, trees were pruned to investigate the effect of crown porosity, and the effects of view angle and turbulence intensity were also considered. The results showed that even considering frontal area reduction due to increasing wind speeds, drag coefficients decreased with increase in wind speed for deciduous and coniferous trees. Drag coefficient characteristics for different trees agreed well with those obtained from previous researches. The effect of crown porosity varied among tree species, but view angle and turbulence intensity did not significantly affect it.