Numerical Simulation Of The Effect Of Construction Activities On Solid Particles In Street Canyon

The problem of environmental pollution caused by particulate matter has become the common concern of the world,the real estate construction and the rail transit construction of infrastructure is going with the flourishing in the developing country.Dust produced in the construction contributes much to the particulate matter,at the same time the street canyon in the city is more and more popular,the particles in which are more likely to accumulate and cause serious pollution problems,bringing the health threat to the surrounding residents and the pedestrian in the street canyon.At present in China,the form of the residential equipped with the commercial functional areas is more mature,so it has an important significance to study the particle distribution in the street canyon.Therefore this paper selects a street canyon as the research object,in which Metro line 2 extension cord is under construction,in the GuangGu commercial area of HongShan district in Wu Han city,HuBei province.The particles is PM10,so the paper discusses the effect of three aspects to particle distribution,such as the height ratio of the street canyon,the direction of wind and the location of the pollution source,through the actual measurement and numerical simulation.It provides the theory basis for the layout of the street canyon buildings and the prevention measures of particulate matter.In this paper,the case of street canyon can be simplified as increasing street canyon model.Meshing uses ICEM software,and post-processing with FLUTNT software of CFD.The air flow field in street canyon with the standard turbulence model,particles uses Lagrange method of the discrete phase model to track particle tracks.The governing equations are discretized by finite volume method,and TECPLOT for graphics processing.The concentration value of particles PM10 obtained by measured adding up to the particulate matter produced by motor vehicle exhaust in the street canyon is close to the results by the numerical simulation.The results show that the numerical simulation is reliable,and the main conclusions of numerical simulation are summarized as follows:(1)When the pollution is located in the north,under the west wind,for the descending street canyon,particles mainly gathered in the middle of the canyon.For the symmetric and decreasing street canyon,the aggregation of particulate matter is more dispersed.The influence height of the increasing canyon in the whole canyon is much uniform,about 20m.For the symmetrical and decreasing canyon,from 15m in the front of the canyon to 30m at the end of the canyon,showing a gradual upward trend.Under the north wind,the high concentration area of particles in the canyon is obviously increased.In the front and rear sides of canyon,and in the pedestrian area of the north side of the three types of canyon,the pollution of the particulate matter is serious.Under the south wind,the location and size of the particles aggregation in the increasing and symmetrical street canyon are the same,which is concentrated in the middle of the street.It can be seen that if there is a large spacing on the south side,the pollution level of particulate matter can be appropriately slowed down,and the concentration level of particulate matter in the leeward area of the north side is related to the ability of the airflow in the spacing to take out the particulate matter.Under south wind,we should pay special attention to the particulate pollution in the building concave area and larger area.(2)For the mean value of the particles concentration in the breathing plane of the street canyon,the pollution is the most serious in the descending canyon under north wind,and the much slight in the descending canyon under north wind.For the mean value of the particles concentration change rule in the north-south direction,under west wind for three types canyon,the distribution rule and the concentration level of particles in the north-south direction is almost the same.In the north wind,the particulate matter concentration grad ?ally increased from the south side to the north side of the canyon,and the concentration level of the descending canyon,the symmetrical canyon,the increasing canyon grad ? ally decreased.Under south wind,in the middle plane Y = 0m reach the highest value,the concentration level of the north side is lower than the south side,the rankings of the north and south sides of three types canyon are not the same.For the mean value of the particles concentration change r?le in the height direction,under different height ratio and winds,the diffusion rule of the particles in the vertical height is very similar,showing a gradual decline trend.On the whole,below 5 meters,With the increase of vertical height,the concentration declined faster,followed by a slow decline.(3)when the pollution source is located in the south,for the symmetrical canyon,the particulate pollution all became serious under three kinds of winds.For the increasing and descending canyon,particulate matter accumulation had a slight change in the location.For the mean value of the particles concentration change rule in the depth direction,canyon height ratio has little effect on the particle distribution in the depth direction of parallel wind,under the vertical wind,for the descending and symmetric canyon,the distribution of particles in the depth direction is similar,and the unevenness and spacing of the building will change the level of particulate matter.