The Impact Of Green Layout On The Flow Field And Pollutant Distribution Around Buildings

Currently,there are various problems about outdoor wind environment.For example, Winds in the residential area is so large that the pedestrians feel uncomfortable.While in the winter,cold air infiltration will increase building energy consumption;If wind speed is too low,it will cause local airflow dead zone,resulting in pedestrians sweltering,and it hinders the spread of pollutants;Urbanization,vehicle emissions,haze and so on lead to outdoor air quality declines,affect residents’ healthy life.Green can solve outdoor air environment problems.In summer,a rational combination of plants and buildings,can not only beautify the environment,but also improve and optimize the outside wind environment.On the one hand,trees shelter solar radiation,reduce the surface temperature of the building envelope,on the other hand,it can enhance natural ventilation;in the winter, a reasonable arrangement of green plants can not only block cold wind effectively and reduce building’s heat load,but also effectively reduce the wind speed outside the building to provide a comfortable pedestrian environment.Meanwhile,green around buildings also purify the air,absorb harmful gases,collect dust.Fine particulate matter pass through the tree canopy.by the effect of interception,impact,diffusion mechanism,it was trapped by leafs.Thereby,it reduces the air dust content to purifying air.This article is for the problem of city building outdoor wind environment, the use of CFD numerical simulation technology to explore for the presence of plants influence the flow field and the concentration field around the building.Firstly, single tree model was simulated, including 1.5m level flow field contours and comparison of wind profiles different from the positions after tree,leaf area density,to analysis flow field characteristics around a single tree.Then,design three different green layouts around the building,in the same amount of green, by the method of additional source term,analyzed from aspects of 1.5m level contours, wind profiles,wind speed distribution.On this basis,it was simulated concentration field to compare the three green layouts for the impact of the concentration field around the building.The simulation results show that the presence of plants improves the flow field around the building,in different green layouts, flow field and concentration distribution were different.The green layout of in front of the building at the corner portion has the most obvious effect,can notonly effectively suppress the corner of strong winds,but also has a certain influence on large areas in the rear of the building,in which region,the low wind was accelerated to avoid sweltering discomfort in summer.For the influence of plants on concentration field,the green layout of in front of the building has a good effect relatively,it can effectively reduce the concentration of particles in the air stream.Conclusions in this paper can provide the basis for future residential green belt design.In addition,the article also studied the improvement of plants presence in street canyon for flow field.In cases of two airflow directions of transverse and longitudinal,flow field of Street canyon has been studied to compared the impact of the plant.The results show that in longitudinal case the improving effect of plants for the flow field of the Street canyon is more obvious.