CFD evaluation of mean pollutant concentration variations in step-down street canyons

Abstract

Atmospheric pollution became a big issue in densified urban areas where the ventilation in streets is not sufficient. It is particularly the case for street surrounded by high buildings socalled street canyons. The ventilation and, thus, the concentrations in this kind of street are highly relying on geometric properties of the street (width of the street, heights of the buildings, etc.). Reynolds-averaged Navier-Stokes equations are used to investigate the impact of two geometric street ratios on pollutant dispersion: the ratio of the leeward to the windward building height (H1/H2) and the ratio of the street width to the windward building height (W/H2). The aim is to quantitatively assess the evolution of mean pollutant concentrations in the case of stepdown street canyons with H1/H2 ranging from 1.0 to 2.0 and street width ratios W/H2 ranging from 0.6 to 1.4. Three types of recirculation regimes could be established, depending on the number and the direction of the vortices occurring inside and outside the canyon. Evolution of pollutant concentrations as a function of both ratios is provided as well as the recommended regimes in the perspective of reducing pollutant concentration in step-down street canyons at pedestrian level and near building faces.

Methodologies to assess mean annual air pollution concentration combining numerical results and wind roses

“…A Reynolds-Averaged Navier-Stokes (RANS) methodology was used to solve the Navier-Stokes equations with the RNG k-ε turbulence model, and the transport of particulate matter was performed using a transport equation. This solver was validated previously in Reiminger et al (2020).…”

Impacts of the side ratio of isolated buildings on airflows and pollutant dispersion under different temperature stratifications: Numerical investigations

“…Various single factors were studied by researchers. For example, the influence of uniform and nonuniform building height [1][2][3][4][5][6] and building layout [3,[7][8][9], building spacing with an aspect ratio of a street canyon [10][11][12][13], building shapes [14,15], and fixed or time-varying meteorological conditions [8,[16][17][18] were investigated.…”

A multi-fidelity framework for the estimation of the turbulent Schmidt number in the simulation of atmospheric dispersion

“…However, the literature does not report clear guidelines on the definition of this parameter [14,15,16,17]. Nevertheless, the importance of Sc t was largely demonstrated [18,19,20,21]. For Atmospheric Boundary Layer (ABL) flows, typical values range between 0.2 and 1.3 [22].…”