Study On The Mitigation Measures Of Urban Air Pollution And Heat Island Effect Based On CFD Simulation

In recent years,China's rapid urbanization process has gradually intensified urban space,resulting in serious environmental problems such as urban air pollution and heat island effect,which not only endangers the health of people,increases the incidence of lung cancer,asthma,heart disease and other diseases,but also aggravates energy consumption,increases urban carbon emissions,and causes huge social and economic losses.Nowadays,China is shifting from the stage of high-speed development to the stage of high-quality development,to meet the growing needs of the people for a better life,to create a healthy,environmentally friendly,lowcarbon and sustainable urban environment,has become the focus of people's attention,and it is very important to explore an effective means that can alleviate urban air pollution and heat island effect.Based on the CFD method,this paper explores the mitigation methods of urban air pollution and heat island effect from the perspective of urban design,and then proposes a potential guidance scheme.This paper is divided into two parts:First,taking the typical building complex of the central business district(CBD)of the city as the research object,through experiments and numerical simulation methods,the air velocity,PM2.5 concentration and urban heat island intensity(UHII)distribution of the five mainstream wind directions in the building area are analyzed,and the orientation of the building array and the road orientation are optimized.Second,the spatial distribution of PM2.5 concentration around the road is studied in depth,and a prediction model(SDC)of PM2.5 concentration is proposed,which alleviates the air pollution around the building by controlling the distance between the building and the road.The main findings of the study are as follows.(1)It is recommended that the building array be built along the main urban wind direction with the main road of the city.When the prevailing wind direction is parallel or perpendicular to the building array alignment direction,the wind speed is 16.1-45.8%(0.09-0.44 m/s)higher than in other wind direction cases;the average concentration of PM2.5 is 28.9-56.8%(8.7627.66 ?g/m3)lower;the urban heat island intensity is 23.4-34.2%(0.8-1.15?)higher.(2)It is recommended to build urban residential areas and urban commercial areas in the upwind direction of the main roads.The average wind speed in the urban upwind area(UA)is 9.6-41.7%(0.04-0.5 m/s)higher than that in the downwind area(DA).the average PM2.5 concentration in UA is 12.9-37.9%(2.72-18.5 ?g/m3)lower than that in DA.the average urban heat island intensity in UA is 0.5-5.9%(0.02-0.15?)lower than that in DA.(3)It is proposed to build the building in an area 120 meters away from the road.Horizontally,within the distance range of 0 to 120 m(0<X<120 m)away from the road,the concentration of PM2.5 was relatively high nearest to the roadside and decreased from 75?g/m3 to 42 ?g/m3 at location further from the road.In the region with X>120 m,the concentration of PM2.5 was relatively low and maintained a steady variation trend of 40?g/m3 to 45 ?g/m3 concentration range.(4)Air purification measures are recommended for building spaces under 60 meters.Longitudinally,within the building height range of 0 to 60 m(0<Z<60 m),the concentration of PM2.5 was relatively high nearest to the ground floor and decreased from 73 ?g/m3 to 42 ?g/m3 on higher floors.In the region of Z>60 m,the concentration of PM2.5 was relatively low with a variation range of 40 ?g/m3 to 45 ?g/m3.This work can potentially provide a guide for future building/urban design to improve air quality in cities from the perspective of building zoning and main road construction,and reduce the human health risk of urban air pollution.And it can guide urban renewal for already built cities,optimize buildings in local areas of the city.It could also potentially contribute to the completion of China's Carbon Neutrality Plan.