Impacts of Traffic Tidal Flow on Pollutant Dispersion in a Non-Uniform Urban Street Canyon

Abstract

A three-dimensional geometrical model was established based on a section of street canyons in the 2nd Ring Road of Wuhan, China, and a mathematical model describing the fluid flow and pollutant dispersion characteristics in the street canyon was developed. The effect of traffic tidal flow was investigated based on the measurement results of the passing vehicles as the pollution source of the CFD method and on the spatial distribution of pollutants under various ambient crosswinds. Numerical investigation results indicated that: (i) in this three-dimensional asymmetrical shallow street canyon, if the pollution source followed a non-uniform distribution due to the traffic tidal flow and the wind flow was perpendicular to the street, a leeward side source intensity stronger than the windward side intensity would cause an expansion of the pollution space even if the total source in the street is equal. When the ambient wind speed is 3 m/s, the pollutant source intensity near the leeward side that is stronger than that near the windward side (R = 2, R = 3, and R = 5) leads to an increased average concentration of CO at pedestrian breathing height by 26%, 37%, and 41%, respectively. (R is the ratio parameter of the left side pollution source and the right side pollution source); (ii) However, this feature will become less significant with increasing wind speeds and changes of wind direction; (iii) the pollution source intensity exerted a decisive influence on the pollutant level in the street canyon. With the decrease of the pollution source intensity, the pollutant concentration decreased proportionally.

Qualitative and Quantitative Investigation of Multiple Large Eddy Simulation Aspects for Pollutant Dispersion in Street Canyons Using OpenFOAM

“…Turbulence modelling is a core issue to address in CFD and it poses unique challenges for flows in the urban infrastructure [10]. The large size of buildings and high velocities of the atmospheric boundary layer result in highly turbulent flows [11], which are computationally expensive to concentration levels, exhibiting fair agreement with the experimental data, except from slight underestimation for the concentration fluctuations near the source. The same work suggests that the LES method could eventually replace wind tunnel experiments, although with the burden of extremely high grid resolution.…”

Recent Advances in Urban Ventilation Assessment and Flow Modelling

“…Ming et al [24] investigated flow and pollutant dispersion in a 3D geometrical model based on a street canyon section with a typical traffic tidal phenomenon in the 2nd Ring Road of Wuhan, China.…”

CFD Simulation of Pollutant Emission in a Natural Draft Dry Cooling Tower with Flue Gas Injection: Comparison between LES and RANS

“…The overbar in RANS represents time averaging, and the wavy line in LES represents filtering. The idea of RANS is to average the Navier-Stokes (NS) equation and transform the unsteady turbulence problem into a steady problem, at the cost of an additional unknown, called Reynolds stress, which is ρu i u j in Equation (1). The idea of LES is to filter the NS equation, use a direct numerical simulation for large scale turbulence, and describe the turbulence smaller than the filter scale with some model.…”

“…The coal-dominated energy conversion structure has caused the total emission of air pollutants in the thermal power industry to remain high for a long time. The total emission of SO 2 and NOx reaches about 60% of the national industrial emission every year, which makes the problem of air pollution become increasingly prominent [1][2][3][4].…”