| In recent years,the construction of road tunnel in our country has been vigorously developed,and the total length of tunnels has continued to increase.However,due to the closed tunnel structures,pollutants such as carbon monoxide,nitrogen oxides,and particulate matter emitted by vehicles during driving are likely to accumulate in the tunnel and are difficult to effectively eliminate.The air condition in the tunnel is usually poor,which may cause health problems for the people in the tunnel.Therefore,there are certain practical significance in the research of the flow field and pollutant diffusion in the tunnel.As far as road tunnels are concerned,the traffic wind generated by moving-vehicles is an important factor that affects the ventilation effect of the tunnel.Motor vehicle exhaust is the main source of pollutants in the tunnel.Therefore,it is necessary to focus on the impact of motor vehicle driving on the tunnel environment.In order to conduct a comprehensive analysis of the velocity field and concentration field distribution in the tunnel under the influence of different traffic conditions and environmental factors,this article mainly carried out the following work based on numerical simulation:(1)This study uses computational fluid dynamics software Fluent to establish a numerical calculation model that is in line with the reality,determines the appropriate mesh size and time step,uses dynamic mesh method to simulate the driving process of the vehicle,and conducts numerical simulation through the scale model experiment done by the predecessors And compare the data with it to complete the verification of the numerical simulation method.(2)The characteristics of the flow field caused by vehicles traveling in tunnels under different traffic conditions are studied,and the effects of vehicles velocities,vehicle spacing,vehicle flow and vehicle types on the piston wind speed in the tunnel and the flow field around the fleet are discussed,a total of 27 cases have been calculated.The results show that the influence of vehicles velocities and vehicle type on the tunnel flow field is greater than the distance between vehicles and traffic volume,and the piston wind speed is linearly related to vehicles velocities.(3)Based on the simulation analysis of the pollutant diffusion characteristics formed by the exhaust emissions of vehicles in the tunnel,the effects of vehicle velocities,ambient wind speed at the entrance of the tunnel and the types of vehicle on the distribution of pollutants in the vicinity of the vehicle fleet in the tunnel are studied,a total of 31 cases have been calculated.Within the variation range of the studied parameters,it is found that vehicle velocity and vehicle type have a greater impact on the distribution of pollutants in the tunnel;when the vehicle velocity is 10m/s,the pollutant distribution of the passenger car fleet is relatively uniform and the co concentration value is the highest,reaching 81.2ppm.About 1.3 times that of SUVs and 3.2 times that of cars.(4)Considering the distribution characteristics of pollutants in the vicinity of the fleet under extreme conditions when the tunnel is congested,two optimization schemes for the introduction of mechanical exhaust and natural ventilation in the tunnel are given,and the effects are compared with two optimization schemes for installing a jet fan and adding a shaft.The calculation results show that based on the conditions set in this paper,the two optimization schemes can enhance the tunnel ventilation,and the effect of adding a shaft is lower than that of installing a jet fan.After installing jet fans,the CO concentration around the bus fleet dropped from810.4ppm to 93.8ppm,a decrease of about 88%;after adding shafts in the tunnel,the CO concentration dropped to 430.1ppm,which was a decrease of about 47%compared with the condition of no shaft.The amplitude is 53% of that of the jet fan.Based on numerical simulation methods,this paper studies the impact of vehicle driving on the flow field and pollutant diffusion in road tunnels,analyzes the tunnel flow field and pollutant concentration distribution characteristics under different traffic conditions and environmental factors,and analyzes the characteristics of jet fan exhaust and shaft A comparative analysis of the two methods of ventilation was carried out.The study results can help workers and vehicle drivers avoid the hazards of pollutants,and at the same time can provide a certain reference for tunnel ventilation design. |
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