Kinematics and dispersion characteristics of flows in asymmetric street canyons

Hoydysh, Walter G.; Dabberdt, Walter F.

doi:10.1016/0004-6981(88)90436-2

Cited by 160 publications

(84 citation statements)

References 2 publications

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“…Greatest concentrations along the boulevard and weakest vertical transport are observed when the longer sides of building blocks are parallel to the boulevard, which supports previous studies performed over idealised street canyons [63,67,68]. Non-uniform building height in V perHV is shown to decrease pc accumulation on the leeward side of the boulevard street canyon, especially under a southwesterly wind when the building height mainly increases downwind [65,69,70]. Apart from buildings, street trees can alter the flow field and canyon vortex, and thereby decrease pollutant ventilation.…”

Section: Discussionsupporting

confidence: 74%

Ventilation and Air Quality in City Blocks Using Large-Eddy Simulation—Urban Planning Perspective

et al. 2018

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Buildings and vegetation alter the wind and pollutant transport in urban environments. This comparative study investigates the role of orientation and shape of perimeter blocks on the dispersion and ventilation of traffic-related air pollutants, and the street-level concentrations along a planned city boulevard. A large-eddy simulation (LES) model PALM is employed over a highly detailed representation of the urban domain including street trees and forested areas. Air pollutants are represented by massless and passive particles (non-reactive gases), which are released with traffic-related emission rates. High-resolution simulations for four different city-block-structures are conducted over a 8.2 km 2 domain under two contrasting inflow conditions with neutral and stable atmospheric stratification corresponding the general and wintry meteorological conditions. Variation in building height together with multiple cross streets along the boulevard improves ventilation, resulting in 7-9% lower mean concentrations at pedestrian level. The impact of smaller scale variability in building shape was negligible. Street trees further complicate the flow and dispersion. Notwithstanding the surface roughness, atmospheric stability controls the concentration levels with higher values under stably stratified inflow. Little traffic emissions are transported to courtyards. The results provide urban planners direct information to reduce air pollution by proper structural layout of perimeter blocks.

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Section: Discussionsupporting

confidence: 74%

Ventilation and Air Quality in City Blocks Using Large-Eddy Simulation—Urban Planning Perspective

et al. 2018

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“…If the ambient wind is strong enough to drive the air circulation inside urban street canyon, the pollutants arising from vehicles will transport to the leeward wall, and then transport to the upper layer with the air circulations (Hoydysh and Dabberdt, 1988;Walton and Cheng, 2002;Chan et al, 2003;Li et al, 2009), which results in the higher pollutant concentration near the leeward side than the windward side (Walton and Cheng, 2002;Li et al, 2009). Traffic-induced turbulence also has significant effect on the pollutant distributions in urban street canyons (Depaul and Sheih, 1986;Qin and Kot, 1993).…”

Section: Main Affecting Factorsmentioning

confidence: 99%

Measurement Study of Diurnal Variations of PM2.5 Mass Concentrations and Affecting Factors on Pollutant Dispersion in Urban Street Canyons under Weak-Wind Conditions in Xi’an

Zhang

Cheng

et al. 2012

Aerosol Air Qual. Res.

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Daytime variations of PM 2.5 concentration in three street canyons in Xi'an were measured during June 11-15, 2010. Weather conditions, including the ambient wind condition and the street canyon air temperature, were also recorded. These measurements were conducted on weak-wind summer days, when the mean ambient wind velocity was 1.26 m/s. The results show that, under weak-wind conditions, there were no good correlation between PM 2.5 concentrations and vehicle flux inside the street canyons. The vehicle related PM 2.5 concentrations accumulated in the daytime inside the street canyons. The PM 2.5 concentrations at the pedestrian level were of near uniform horizontal distribution. These results indicate the absence of the typical primary air flow re-circulation inside the street canyons under weak-wind conditions, and that the dispersion and transportation of vehicle exhausts inside and/or outside the street canyons are influenced by vehicle induced air flow and thermal induced buoyancy.

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“…This velocity was found to vary between 0.15 and 0.8 m s −1 , and to be well correlated with the friction velocity at roof level. Hoydysh and Dabberdt (1988) argued that the transport of pollutants from the canyon to the upper air is achieved by the advection of the rotating vortex and the diffusion of sub-canyon-scale vortex turbulence.…”

Section: Introductionmentioning

confidence: 99%

A Scheme for Scalar Exchange in the Urban Boundary Layer

Yang

Shao

2006

Boundary-Layer Meteorol

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We present a scheme for parameterising scalar transfer in the urban boundary layer, which is divided into an inertial layer and a roughness layer. The latter is further divided into a shear layer and a canyon layer. In the inertial layer, scalar transfer is determined by turbulence related to canyon macroscopic features, while in the roughness layer, it is determined by shear-generated turbulence, canyon vortex and vortex-generated turbulence. We first describe a conceptual model for the canyon flow and the aerodynamic resistance network, and then estimate the resistances from the point of view of drag partition and vortex advection. The results are compared with the measurements from wind-tunnel experiments. It is found that for small canyon aspect ratio, σ c , the transfer velocity increases with σ c , reaching a maximum at around σ c = 0.5 and then decreases with σ c . We also show that the scheme is not sensitive to adjustable parameters.

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Kinematics and dispersion characteristics of flows in asymmetric street canyons

Cited by 160 publications

References 2 publications

Ventilation and Air Quality in City Blocks Using Large-Eddy Simulation—Urban Planning Perspective

Ventilation and Air Quality in City Blocks Using Large-Eddy Simulation—Urban Planning Perspective

Measurement Study of Diurnal Variations of PM2.5 Mass Concentrations and Affecting Factors on Pollutant Dispersion in Urban Street Canyons under Weak-Wind Conditions in Xi’an

A Scheme for Scalar Exchange in the Urban Boundary Layer

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