Study On Vehicle Pollutants Dispersion Characteristics Of The City Tunnel By Numerical Simulation

In this paper, more popular in the world of computational fluid dynamics (CFD) softwareFluent was used to simulate the dispersion characteristics of urban tunnel vehiclepollutants.Firstly, by reference to other references known Nanjing Gulou tunnel measured data toverify the credibility of the results calculated by Fluent.Then calculate the critical length of thetunnelwithoutexternal ventilationmeet the tunnel inside ventilation requirements.Analysis therelationship between the amount of the tunnelventilation requirements with speed, slope, trafficflow, and identified the tunnel emissions program and its emission concentration of pollutants inthe different scenarios depending on the size of the wind ventilation.Then analyzed the diffusioncharacteristics and excessive rangeunder different wind direction, wind speed, tunnel length,tunnel exit mode and other conditions of pollutants.Finally, a comparative analysis by directdischarge in the tunnel mouth, emissions and set via the shaft wall of the tunnel barrier wallsurrounding the environmental impact of the case in three different ways,and analyzes theventilation shaft in the high-impact features with different shafts and external wind speed, theretaining wall influence pollutant dispersion characteristics in different length and height of thesurrounding environment.Through the above analysis we draw the following conclusions:1．Tunnel Ventilation1) When the tunnel length is less than1500m, natural ventilation inside the tunnel to meetthe environmental requirements. When1500to3000m, can be vertical ventilation mode and fulljet ventilation, but the full jet ventilation for fire relief unfavorable, and therefore should be usedlongitudinal ventilation scheme.When3000to6000m, while vertical ventilation should set aventilation shaft. Greater than6000m, two ventilation shafts should be set at the same timeusing longitudinal ventilation.2. The effects of different wind direction, wind speed, the tunnel length of the tunnelVehicle Pollutants Dispersion.1) When the wind tunnel exit wind direction consistent with external natural wind, directionalong the tunnel exit exceeded scope increases, but smaller increases range.When the naturalwind (2.5m/s) direction relative to the tunnel exit, along the tunnel exitdirection exceeded scopenarrow, both sides of the road exceeded scope increased.By comparingthe COwithNO2exceeded scope can be found, NO2exceeded scope largerthan CO. So the tunnel NO2pollution should bepaied attention.2) The wind for lateral wind (article westerly), when the wind speed is less than2.0m/s,wind speed each additional0.5m/s CO and NO2the maximum distanceincreases5m inthedownwindroad. When the wind speed increases from2.0m/s to2.5m/s, the maximum lateralexceeded distance increases10m. When the wind speed increases from2.5m/s to3.0m/s,themaximum lateral exceeded distance basically unchanged, the main impact of it is theconcentration along the axis of the tunnel exit.When the wind speed increases from3.0m/s to3.5m/s, mean maximum exceeded lateral distance18m approximately.3) When the tunnel length is less than1500m, CO and NO2exceeded the maximum lateraldistance, both with increasing length of the tunnel in the direction of increasing the rangeexceeding the tunnel axis; when the tunnel length of more than1500m, CO and NO2exceededthe maximum lateral distance with the length of the tunnel increased slightly decreases.3．Effects of different ways on the surrounding environment Emissions1) When the vehicle pollutant generated within the tunnel emissions directly from the tunnelmouth, it is detrimental to the surrounding environment, you need to take certain measures toreduce pollution. Pollutant emissions calculated by this article, the impact on the environmentNO2slightly larger than the CO, therefore NO2on the tunnel issue should be taken seriouslyenough.2) When the shaft height is20m, the lateral wind speed each additional0.5m/s, COexceeded distance decreases18m along the axis of the shaft, the maximum lateral distanceincreases exceeding7m. The maximum lateral distance increases exceeding7m of NO2. Whenthe shaft height is50m, the lateral wind speed each additional1m/s, CO exceeded distancedecreases18m along the axis of the shaft, the maximum lateral distance increases exceeding7m.The exceeded distance decreases18m along the axis of the shaft,the maximum lateraldistance increases exceeding5m of NO2. When the shaft height is100m, the lateral wind speedeach additional1m/s, CO exceeded distance decreases14m along the axis of the shaft, themaximum lateral distance increases exceeding5m.The exceeded distance decreases19m alongthe axis of the shaft, the maximum lateral distance increases exceeding6m of NO2.3) When the tunnel pollutant emissions or setting the shaft wall can reduce the impact onthe surrounding environment, the measures taken in accordance with the conditions selectedgeographical location, using exhaust shaft when no tall buildings on both sides of the road. When the tunnel set the retaining wall, retaining wall height of the wall should be higher than theheight of the tunnel, and the retaining wall length should be longer possiblely.