Evaluation of the ventilation and pollutant exposure risk level inside 3D street canyon with void deck under different wind directions

Abstract

With continuous global warming, growing urban population density and increasing compactness of urban buildings, VD (void deck) street design has become increasingly popular in city planning, especially in tropical countries. However, understanding on traffic pollutant dispersion in the VD street canyons is still at early stage. This paper quantitatively evaluates the effects of VD location and wind direction on the ventilation and traffic pollutant exposure inside the street canyon with VDs.The results show that the VD location and wind direction have significant effects on the flow field and pollutant dispersion inside the canyon. When VDs are located at the upwind building, downwind building, and both buildings, the wind directions with maximum ACH (air exchange rate) are 60°, 30° and 60°, respectively. Under seven wind directions (0°, 15°, 30°, 45°, 60°, 75°, and 90°), the VD provides higher ACH than that of the regular canyon, especially at high α (angle between the approaching wind and the canyon axis). When α = 90°, regular canyon has the lowest ventilation capacity, but ACH values of canyons with both VDs or the leeward VD are 189.1% and 177.6% of regular canyon, respectively. Also, mean K (dimensionless pollutant concentration) values of the canyon wall and pedestrian respiration plane on one side where VD is located are significantly reduced compared to the regular canyon. Therefore, when VDs are at both buildings, both pedestrian respiration planes and walls have the lowest K values, thus providing the best living environment for pedestrians and near-road residents. As α increases, the K values on both respiration planes significantly decrease except for the leeward respiration plane of the canyon with the windward VD.These findings can help to design urban street canyons for mitigating traffic pollution risk and improving ventilation in tropical cities with frequently changing wind directions.

Modelling of Deep Street Canyon Air Pollution Chemistry and Transport: A Wintertime Naples Case Study

“…The boundary conditions for MBM-FleX are established based on these CFD assumptions, specifically accounting for the effects of perpendicular wind on canyon ventilation. Parallel wind has been posited to exert a larger influence on street canyon ventilation [47] but the focus here was on scenarios where the ambient wind blows perpendicular to the canyonaxis, as detailed in Section 3.2. Drawing from prior research [48,49], it was assumed that a linear relationship exists between vertical mixing velocities and the perpendicular velocity of the wind above the roof level.…”

Research on the Impact of Air Temperature and Wind Speed on Ventilation in University Dormitories under Different Wind Directions (Northeast China)

“…It is widely known that in real-world scenarios, the natural ventilation efficiency of a room is typically determined by multiple factors. These primarily include outdoor wind direction [23][24][25], wind speed [26][27][28], air temperature [29][30][31], and so on. However, current research on indoor natural ventilation tends to analyze the impact of specific single variables on indoor ventilation efficiency.…”

Numerical Simulation of Pollutant Spread in a Double-Deck Viaduct

“…The shape of the roof also affects the diffusion of pollutants in street valleys, and the researchers carried out numerical simulation studies for different roof shapes, and found that the shape of the roof is an important influencing factor, and the airflow velocity is higher in pitched roofs than in other roof forms, and pollutant accumulation near the leeward side of pitched roofs is higher than that of flat roofs [26,27]. Wind environment, wind speed and direction: the greater the wind speed, the more conducive to the diffusion of pollutants; when the wind direction is parallel to the street valley, the stronger the purification capacity of the wind [28][29][30][31]. Seasonal variations significantly alter the microclimate of the street canyon, with relatively high concentrations of pollutants during summer mornings and winter nights [32].…”