Numerical Simulation of Pollutant Spread in a Double-Deck Viaduct

Abstract

This study uses the computational fluid dynamics (CFD) method to investigate the effects of the depth-width ratio of a three-dimensional street valley and wind velocity on the flow field and pollutant spread in street valleys with double-deck elevated bridges. The simulation results indicate that when there is no viaduct, there is only one vortex in the gorge when the depth-width ratio (H/W) is less than 1.5; when it is equal to 1.5, multiple vortices appear. With a double-deck viaduct, the viaduct changes the airflow field and turbulence structure in the valley, creating a primary vortex and multiple secondary vortices. Aiming at the diffusion of pollutants, the changing trend in the horizontal and vertical direction was quantitatively analyzed. The study found that when the aspect ratio increased from 0.8 to 1.5, the CO concentration on the leeward side increased by 40%, and the CO concentration on the windward side increased by four times. When the street width increased from 20 m to 37.5 m, the CO concentration decreased by 30%. The increase in wind speed reduced the CO concentration by 28% on the lee side and 33% on the windward side. This study reveals the general pattern of pollutant dispersion in viaduct-street canyon structures, providing insights into the construction of viaducts.