The Building Of Pollutant Dispersion Model And Simulation Analysis In City Tunnel

With the constant improvement of the urban infrastructure, city tunnel is becoming more and more important in urban road traffic system,However, because the motor vehicle exhaust emissions produce a large number of poisonous and harmful material, it will be harmful for human health for a long time in this environment, so research of the diffusion of the pollutants from the tunnel get more and more attention of people.This paper, taking a look of Cheng du in the tunnel as the research object, according to the tunnel structure and geometry size pollutant diffusion model was constructed,using the application of computational fluid dynamics software FLUENT, using flow control equation of the navier-stokes equation, k-ε epsilon model, and also using finite volume method to analysis the internal tunnel pollution gas concentration distribution of CO and NO2.The thesis simulates the different ventilation speed and traffic conditions, inside the tunnel pollution gas concentration distribution of CO and NO2, wind speed and the ventilation traffic tunnel made a comparative analysis of the influence of the pollution gas concentration distribution of CO and NO2, research shows that:(1) ventilation velocity affect tunnel pollution gas maximum density in position, with the increasing of ventilation velocity, the farther the location of the maximum density distance tunnel entrance is. When ventilation speed v=0m/s,the maximum density of80-90m away from the entrance of the tunnel; When ventilation speed v=1m/s, appearing the location of the maximum density in100-110m away from the entrance of the tunnel; When ventilation speed v=2m/s, the location of the maximum density is located in the tunnel exit.(2) when the ventilation velocity v=0m/s, inside the tunnel concentration of pollution gas in various simulated point is greater than the concentration of the v=lm/s, when ventilation speed v=lm/s, inside the tunnel concentration of pollution gas in various simulated point is greater than the concentration of v=2m/s. Showing that with the increase of ventilation velocity, concentrations of pollution gas decreases, increasing ventilation tunnel wind speed is beneficial to control the internal density of CO and NO2pollution gas. (3) on the transverse section, close to the area around the tunnel wall,because of the air flow under the influence of the tunnel wall, tunnel wall surrounding air flow blockage, leading to greater concentration near the area around the tunnel wall (z=4m axis NO2concentration).So when setting up the tunnel ventilation shaft, vent can be set up in the tunnel wall or the top of the tunnel location, it is good to speed up the tunnel internal pollution gases to discharge the external, which has reference value for urban tunnel ventilation environmental protection design.(4) Concentration of CO gas is far greater than the concentration of Ndgas inside the tunnel. Simulation results show that the tunnel internal concentration of CO gas is the most about24times as the concentration of NO2gases, proportion of CO is far greater than other pollutants in motor vehicle exhaust, in the process of tunnel ventilation design, the CO should be used as the main factors.(5) in the same operating period, concentration of pollution gas simulated under the condition of peak hour traffic is obvious higher than the concentration under the condition of average hour traffic. The peak of city tunnel hours appeared in commuting time period (07:30-9:30,17:30-19:30), so during of this period, pollution gases (CO and NO2) is significantly higher than other period inside the tunnel, so as for tunnel set up a mechanical ventilation, tunnel managers can control the operation of ventilation according to the presence of the peak hour traffic time of the day, so that we can save energy resources, and guarantee the air quality in tunnel at the same time.