Study On The Dispersion Law Of Vehicle Pollutant In Urban Street Roundabouts

As an important part of the urban road traffic system,roundabouts carry a huge amount of traffic,and the operation characteristics of traffic flow are extremely complex,accompanied by a large number of vehicle exhaust pollutants,which have a serious adverse impact on the surrounding air environment and pedestrians.In order to reduce the adverse effects of exhaust pollutants,this paper comprehensively uses theoretical analysis,on-site measurement and numerical simulation methods,takes the roundabout of Dalian Digital Plaza as the engineering background,analyzes the traffic flow characteristics of the roundabout through traffic volume investigation,and simulates the change law of the wind environment and pollutant diffusion process of the roundabout by the influence of incoming wind speed,incoming wind direction,traffic volume,traffic flow speed and infrastructure layout based on traffic volume and meteorological data,and the main work and research results are as follows:(1)Through the traffic volume survey,it is concluded that the traffic volume of the roundabout at 7:00～8:00 in the morning rush hour is 5611pcu/h,and the traffic volume in the evening rush hour 17:00～18:00 is 4582pcu/h;The peak hour coefficient of 5 and 15 minutes is0.94～0.97,and the average time headway of some directional lanes during the morning flat peak hour is less than 2s,which is a potential safety hazard.Through meteorological investigation,it is concluded that the conventional wind direction in Dalian City is southwest wind,southeast wind and positive north wind,and the conventional wind level is 2～5.(2)Through the analysis of the pollutant concentration distribution of different wind speeds and directions,it is concluded that the greater the speed of the incoming wind,the greater the diffusion range of pollutants in the horizontal direction;The higher the height of the building on the windward side of the building group,the greater the diffusion range of pollutants in the vertical direction,and the larger the vertical contact area between the building and the incoming wind,the greater the diffusion range of pollutants in the vertical direction.(3)Through the analysis of the changes of the wind environment of different wind speeds and directions,it is concluded that the larger the vertical contact area between the building on the windward side of the building group and the incoming wind,the calmer the degree of vortex circling behind the building,the higher the height of the plane at the beginning of the highspeed vortex,and the smaller the impact on pedestrians at low altitudes.The incoming wind at the low altitude on the windward side of the high-rise building is diverted in advance when it touches the surface of the building,and as the horizontal height increases,the position of the diversion point gradually approaches the surface of the building until it is close to the surface of the building.(4)Through the analysis of the wind environment and pollutant concentration distribution around the infrastructure,it is concluded that the vehicles parked next to the roundabout have a protective effect on the wind environment and air environment in the pedestrian activity area,but when setting up parking lots next to the roundabout,the building layout and urban meteorological conditions should be comprehensively considered.When the bus stop is set up next to the roundabout,the bus reduces the utilization rate of the lane,and the pollutant concentration in the passenger waiting area exceeds the standard,and the statistical results of the bus line suggest that the bus stop be moved to the straight road south of Digital Road.