Large eddy simulation of flow structures and pollutant dispersion in the near-wake region of the studied ground vehicle for different driving conditions

In the present study, a three-dimensional large eddy simulation (LES) of the flow structure, and pollutant dispersion and concentration field in the near-wake region of the studied ground vehicle [Dong, G., Chan, T.L., 2006. Large eddy simulation of flow structures and pollutant dispersion in the near-wake region of a light-duty diesel vehicle. Atmospheric Environment 40, 1104–1116] for different rear slant angles (i.e., α=25° and 60°), stationary (i.e., low and high idling modes) and moving (i.e., vehicle speed modes) vehicle conditions, vehicular exhaust jet exit conditions, and ambient wind conditions (i.e., wind speed and direction) within the urban road microenvironment was investigated comprehensively. Time-averaged flow and pollutant concentration fields behind the studied ground vehicle are calculated. The vehicular exhaust jet plume condition behind the studied ground vehicle dominates the flow pattern and pollutant dispersion at lower vehicle speed and low idling conditions. The vortices and turbulent mixing induced by the interaction between the vehicular exhaust jet plume, and the ambient wind flow condition behind the studied ground vehicle plays an important role in dispersing the pollutant concentration at higher vehicle speed and high idling conditions. The increasing of the studied ground vehicle speed restrains the development of the vehicular exhaust jet plume along the downstream direction and quickens the diluting rate of the pollutant concentration behind the studied ground vehicle. The oblique ambient wind flow condition enhances the dilution of pollutant concentration behind the studied ground vehicle along its vehicular exhaust jet plume in the downstream direction. However, a more evident effect of oblique ambient wind flow on dispersing the pollutant concentration behind the studied ground vehicle is found for the lower vehicle speed and low idling cases. The results provide a better understanding of the three-dimensional flow structures, and pollutant dispersion and concentrating field in the near-wake region of the studied ground vehicle for different driving conditions in urban road microenvironments.