| In recent years the urban climate has been changing frequently and the wind environment has been deteriorating.As an important part of the urban space,the creation of a comfortable,healthy and sustainable living environment is beginning to attract attention with the introduction of the concept of habitat.With its flexible configuration,urban green space has become an important initiative to improve the local microclimate.Therefore,within the framework of landscape garden planning and design research,this paper considers the response of trees under natural wind,combines field measurements and numerical simulations to gain a comprehensive understanding of the change pattern of the surrounding wind environment after the wind response of trees,based on which the impact of the spatial layout of trees in residential areas on the wind environment is further studied and tree layout optimisation strategies are proposed.The specific research work is as follows:Considering the response of trees to wind speed,the fitted relationship between porosity and wind speed was established by field measurement of tree porosity at different wind speeds VP=0.02u+0.36;a numerical model of tree wind response was established,and the drag coefficient at different wind speeds was simulated using the additional source term method,and the feasibility of the model was verified by field measurement of the wind environment behind the trees.In order to investigate the effect of wind response on the wind environment,the surrounding flow field and flow velocity distribution characteristics of vertically fixed trees（T-S）and wind-responsive trees（T-D）were compared and analysed at different wind speeds and spacings to quantify the effect of wind response-induced changes in porosity and aspect ratio on the wind environment.It was found that:1)the effective shading distance after wind response of trees was 2.4H,which was 0.3H less compared to vertically fixed trees;2)As the wind speed increases,the tree porosity gradually increases,and the minimum wind speed behind the tree increases accordingly.The relationship between porosity and minimum wind speed is umin=0.00762VP-0.19653;3)The relationship between tree height to width ratio and the location of minimum wind speed occurrence and wind speed recovery distance are x0=-1.92651H/W+2.37383,l=-15.42323H/W+17.31669;In order to study the influence of tree spatial layout on the wind environment in residential areas,the wind environment at pedestrian breathing height under different planting spacing,layout forms and tree heights were analyzed,and tree spatial layout optimization strategies were proposed.The study shows that 1)the wind velocity developed along the central axis of the trees in response to wind at different spacing produces an intersection point at a distance of 3H behind the trees,which increases1H compared with the vertical fixed trees;before 3H,the spacing is more efficient in reducing wind;after 3H,the spacing is less efficient in reducing wind;2)the column layout has a significant wind blocking effect and the comfort zone area accounts for the largest proportion,while the row layout has a wind guiding effect parallel to the wind direction;3)different tree heights The obstructive effect on wind speed at pedestrian breathing height is from small to large 10m,8m and 6m.Based on the resulting optimisation strategy,an application study was carried out with an actual residential area as an example.Through simulation,the problem of wind environment at the pedestrian breathing height of the district was found,its greening space layout was optimised and enhanced,and the wind environment before and after optimisation was compared and analysed through wind speed evaluation indicators. |
