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作者

来源

URBAN FORESTRY & URBAN GREENING,Vol.35,P.230-239

语言

英文

关键字

Drag coefficient; Model trees; Natural trees; Particle image velocimetry; Wind tunnel; POROUS FENCES; WINDBREAK DRAG; VEGETATION; SHELTER; SIMULATION; DISPERSION; VELOCITY; POROSITY; SPRUCE; FOREST

作者单位

[Manickathan, Lento; Defraeye, Thijs; Allegrini, Jonas; Carmeliet, Jan] Swiss Fed Inst Technol, Dept Mech & Proc Engn, Chair Bldg Phys, Stefano Franscini Pl 1, CH-8093 Zurich, Switzerland. [Manickathan, Lento; Allegrini, Jonas; Derome, Dominique; Carmeliet, Jan] Swiss Fed Labs Mat Sci & Technol, Lab Multiscale Studies, Bldg Phys,Uberlandstr 129, CH-8600 Dubendorf, Switzerland. [Defraeye, Thijs] Swiss Fed Labs Mat Sci & Technol, Lab Biomimet Membranes & Text, Empa, Lerchenfeldstr 5, CH-9014 St Gallen, Switzerland. Manickathan, L (reprint author), Uberlandstr 129, CH-8600 Dubendorf, Switzerland. E-Mail: mlento@ethz.ch; thijs.defraeye@empa.ch; jonas.allegrini@empa.ch; dominique.derome@empa.ch; cajan@ethz.ch

摘要

The influence of trees in urban areas is typically assessed using urban microclimate models. These models rely on wind tunnel experiments using small-scale tree models to verify and validate their predictions of the flow field. However, it is not known sufficiently to which extent small model trees used in wind tunnel studies can recreate the behavior of large trees found in cities. In the present study, the drag coefficient and the turbulent flow downstream of model trees are compared with the ones of natural trees of a similar size to determine whether both types of tree provide similar aerodynamic characteristics. Therefore, measurements of the drag force and the flow field, using particle image velocimetry, are performed. The aerodynamic characteristics of the small trees are compared with the ones measured on larger mature trees from previous studies. The present study shows that the drag coefficients of model and natural trees are similar only if both types have a similar aerodynamic porosity and if the model tree can undergo an aerodynamic reconfiguration similar to that of a natural tree. Such reconfiguration implies the reorientation of the branches and leaves due to wind. A study on the influence of seasonal foliar density variation shows that the foliage configuration plays a critical role on the drag coefficient and the flow field. A defoliated tree, such as a deciduous tree in winter, is shown to have a substantially lower drag coefficient and a negligible influence on the flow.