Investigating vehicle effects on wind and pollutant fields in street canyon using the dynamic mesh and source term methods

Studying traffic pollution plays a key role in measuring urban sustainable development. The source term method (STM) and dynamic mesh updating method (DMM) are two methods used in CFD simulation to model vehicle-induced turbulence (VIT) and wind speed changes due to vehicle movements in street canyons. STM is a simple and computationally economical method that implicitly models the effects of moving vehicles on the wind field. In contrast, DMM explicitly models vehicle movements at a higher computational cost. The differences in wind speed and turbulence modeled by STM and DMM ultimately affect the modeling of air pollution dispersion in street canyons. This study investigates how STM and DMM model wind speeds and turbulent intensities differently in a two-dimensional street canyon with one-way and two-way traffic and how these differences subsequently affect air pollution dispersion. The results revealed that STM predicted 50 % higher turbulent kinetic energy up to a greater height in the street canyon than DMM. However, STM predicted about 23 % lower wind speeds, as it failed to replicate wind speed variations around moving vehicles. Moreover, STM modeled an asymmetric wind field with weak lateral and vertical wind speeds, which accumulated air pollutants in the street canyon. In contrast, DMM modeled intense lateral and vertical wind speeds following vehicle movements, prompting air pollutants to disperse along the street and in the vertical direction. All these differences ultimately led STM to predict about 60 % higher pollutant concentrations in the street canyon than DMM.