Numerical Simulation Of Vehicle Pollutant Dispersion In Urban Street Canyon

With the urbanization process in-depth and the growing of vehicle population, vehicle emissions have become a major source of urban air pollution. Especially to the canyon type street, the exhaust of motor vehicles accumulates in the street canyon, which do harm to the travelers who directly exposed in the atmosphere. In this paper, the author connects the knowledge of environment science, transportation engineering and hydrodynamics, and uses the numerical simulation method to study the dispersion of pollutants discharging from the motor vehicles in urban street canyons. This study can guide the planning and constructing of future urban roads, and can improve the quality of life for the urban residents, as well as can be of great significance to the sustainable development of future city and transportation.The author uses the numerical simulation method to study the pollutant effect on the pedestrians and bicyclists. In this study, the author combined the standard κ-ε turbulence model and component transport equation. The results show that the concentration of pollutants in leeward side is much higher than that in the windward side in street canyon. Therefore, the pedestrians and bicyclists in the leeward side suffered more serious emissions. The concentration of pollutants in the bike lane and sidewalk are almost the same as in the windward side. Near the road surface, the concentration of pollutants over the bike lane is higher than that over the sidewalk in leeward side. With altitude increases, the impact of the air flow field in street canyons comes out. The clockwise vortex takes the pollutants to the leeward side, resulting in pollutant concentrations over the sidewalk higher than that over the bike lane.The author also discussed the impact of the different location setting of bus lanes on the pedestrians and bicyclists. The results show that when the bus density is low, the emissions intensity over the bus lanes is lower than that over the vehicle lanes, setting the outside of bus lanes has less pollution to the pedestrians and bicyclists. When the density of bus is high, the emissions intensity over the bus lanes is higher than that over the vehicle lanes, setting the inside of bus lanes has smaller pollution to the pedestrians and bicyclists.Using the layering grid method and the slip interface dynamic mesh, the author achieved the driving of vehicle in three-dimensional typical isolated street canyon, and explored the interference to the original pollutant concentration field due to the parking or moving of a vehicle. The results found that roadside parking will obstruct the air flow which is closer to the ground, resulting in an increase in pollutant concentrations compared with no vehicle parking there. According to the simulation results, we can see that roadside parking in the street canyons will cause more serious harm to the travelers who exposed higher concentrations of pollutants. Vehicle driving will increase the disturbance, causing the pollutant concentration in a certain reduction nearby. But as the car shape tends to be streamline, and the air drag coefficient is generally lower than0.5, the process of car moving will not have a significant disturbance to the surrounding air, which resulted in the weak effect on the original concentration field in the street canyon.