Effect of tunnel-shaped noise barriers on pollutant dispersion induced by continuous traffic flow by moving overset grid simulations

Modern urban roads are characterized by continuous high traffic flow rates and significant exhaust pollutants. Compared to traditional upright or cantilever noise barriers, tunnel-shaped noise barriers may pose stronger accumulating or shielding effects on vehicle induced pollutants, posing a more serious health threat to drivers, passengers, and pedestrians. Selecting fully-enclosed and semi-enclosed noise barriers as representative cases, this study employed large eddy simulation (LES) and the dynamic overset grid method to investigate the effect of tunnel-shaped noise barriers on pollutant dispersion characteristics under continuous traffic flow conditions. The research investigated the evolution and time-averaged characteristics of vehicle pollutants, and explored the characteristics of personal intake fraction, and the influence of traffic flow rate and vehicle speed. The underlying flow field mechanisms were revealed through instantaneous wind speed and vorticity field analysis. It was found that the pollutant concentration exhibits an accumulation stage and a stable stage inside a tunnel-shaped noise barrier. The accumulation time, time-averaged pollutant concentration, and mean personal intake fraction inside the fully-enclosed noise barrier are 2.52, 6.25, and 4.68 times those of the semi-enclosed noise barrier. The distribution characteristics of vehicle pollutants of the two types of tunnel-shaped noise barriers are also different. Compared to the semi-enclosed barrier, higher wind speeds and stronger air convection are present inside and outside the fully-enclosed noise barrier, leading to a longer duration of the accumulation stage. The open side of the semi-enclosed barrier results in higher downstream wind speeds and vorticity, promoting pollutant dispersion by convection and diffusion effects and decreasing pollutant concentrations inside the semi-enclosed barrier. The research results provide useful information for the noise barrier design and transportation planning in urban areas.

© 2025 The Author(s). Published by Elsevier Ltd.