scholarly journals The influence of aspect ratios and wall heating conditions on flow and passive pollutant exposure in 2D typical street canyons

2020 ◽  
Vol 168 ◽  
pp. 106536 ◽  
Author(s):  
Jian Hang ◽  
Xieyuan Chen ◽  
Guanwen Chen ◽  
Taihan Chen ◽  
Yuanyuan Lin ◽  
...  
Keyword(s):  
Street Canyons ◽  
Aspect Ratios ◽  
Wall Heating

Large-Eddy Simulation of Reactive Pollutant Dispersion Over Street Canyons of Different Aspect Ratios

2014 ◽  
Author(s):  
T. Z. Du ◽  
Chun-Ho Liu ◽  
Y. B. Zhao
Keyword(s):  
Aspect Ratio ◽  
Large Eddy Simulation ◽  
Chemical Reactions ◽  
Pollutant Dispersion ◽  
Pollutant Removal ◽  
Street Canyons ◽  
Eddy Simulation ◽  
Aspect Ratios ◽  
Large Eddy ◽  
Reactive Pollutant

In urban areas, pollutants are emitted from vehicles then disperse from the ground level to the downstream urban canopy layer (UCL) under the effect of the prevailing wind. For a hypothetical urban area in the form of idealized street canyons, the building-height-to-street-width (aspect) ratio (AR) changes the ground roughness which in turn leads to different turbulent airflow features. Turbulence is considered an important factor for the removal of reactive pollutants by means of dispersion/dilution and chemical reactions. Three values of aspect ratio, covering most flow scenarios of urban street canyons, are employed in this study. The pollutant dispersion and reaction are calculated using large-eddy simulation (LES) with chemical reactions. Turbulence timescale and reaction timescale at every single point of the UCL domain are calculated to examine the pollutant removal. The characteristic mechanism of reactive pollutant dispersion over street canyons will be reported in the conference.

scholarly journals Flow and Pollutant Transport in Urban Street Canyons of Different Aspect Ratios with Ground Heating: Large-Eddy Simulation

2011 ◽  
Vol 142 (2) ◽  
pp. 289-304 ◽  
Author(s):  
Xian-Xiang Li ◽  
Rex E. Britter ◽  
Leslie K. Norford ◽  
Tieh-Yong Koh ◽  
Dara Entekhabi
Keyword(s):  
Large Eddy Simulation ◽  
Pollutant Transport ◽  
Street Canyons ◽  
Urban Street ◽  
Eddy Simulation ◽  
Urban Street Canyons ◽  
Aspect Ratios ◽  
Large Eddy

scholarly journals Linear Error Dynamics for Turbulent Flow in Urban Street Canyons

2017 ◽  
Vol 56 (5) ◽  
pp. 1195-1208 ◽  
Author(s):  
K. Ngan ◽  
K. W. Lo
Keyword(s):  
Linear Theory ◽  
Free Atmosphere ◽  
Street Canyons ◽  
Urban Street ◽  
Eddy Simulation ◽  
Urban Street Canyons ◽  
Aspect Ratios ◽  
Large Eddy ◽  
Error Dynamics ◽  
Insight Into

AbstractThe ability to make forecasts depends on atmospheric predictability and the growth of errors. It has recently been shown that the predictability of urban boundary layers differs in important respects from that of the free atmosphere on the mesoscale and larger; in particular, nonlinearity may play a less prominent role in the error evolution. This paper investigates the applicability of linear theory to the error evolution in turbulent street-canyon flow. Using large-eddy simulation, streamwise aspect ratios between 0.15 and 1.50, and identical-twin experiments, it is shown that the growth rate of the error kinetic energy can be estimated from Eulerian averages and that linear theory provides insight into the spatial structure of the error field after saturation. The results should be applicable to cities with deep and closely spaced canyons. Implications for data assimilation and modeling are discussed.

Numerical Modeling of the Flow and Pollutant Dispersion in Street Canyons with Ground Thermal Effect

2014 ◽  
Vol 548-549 ◽  
pp. 601-606
Author(s):  
Ning Bo Zhang ◽  
Yan Ming Kang ◽  
Ke Zhong ◽  
Jia Ping Liu
Keyword(s):  
Thermal Effect ◽  
Street Canyon ◽  
Three Dimensional ◽  
Thermal Conditions ◽  
Pollutant Dispersion ◽  
Ambient Air ◽  
Street Canyons ◽  
Urban Street ◽  
Urban Street Canyons ◽  
Aspect Ratios

Thermal stratification affects the flow in and above urban street canyons. Such thermal effect is often not noticed, and can lead to pessimistic or optimistic results of the air quality in urban street canyons under calm conditions and low wind speeds. A three-dimensional CFD model is applied to simulate the flow patterns and particle concentrations in a street canyon under different aspect ratios and ground thermal conditions. The model is validated by the experimental data found in the literature. The simulation results are used to evaluate the flow and pollutant dispersion properties in the canyon. The results show that the ground thermal conditions can significantly affect the ventilation performance of the street canyon, which improves with the increased temperature difference (ΔT) between the ambient air and the ground of the canyon. The increased ΔT enhances the buoyancy induced secondary flow in the street canyon and hence reduce the particle concentrations in the canyon, with this influence more pronounced for small street widths.

scholarly journals Physical Modeling of Flow Field inside Urban Street Canyons

2008 ◽  
Vol 47 (7) ◽  
pp. 2058-2067 ◽  
Author(s):  
Xian-Xiang Li ◽  
Dennis Y. C. Leung ◽  
Chun-Ho Liu ◽  
K. M. Lam
Keyword(s):  
Numerical Modeling ◽  
Flow Pattern ◽  
Numerical Models ◽  
Flow Direction ◽  
Water Channel ◽  
Flow Characteristics ◽  
Street Canyons ◽  
Urban Street ◽  
Urban Street Canyons ◽  
Aspect Ratios

Abstract The flow characteristics inside urban street canyons were studied in a laboratory water channel. The approaching flow direction was horizontal and perpendicular to the street axis. The street width was adjusted to form street canyons of aspect ratios 0.5, 1.0, and 2.0. The velocity field and turbulent intensity were measured with a laser Doppler anemometer at various locations within the street canyons, which were used to elucidate the flow pattern inside the street canyons. It was found that the previous numerical modeling results are in good agreement with the current experimental results at most locations. For the street canyon of aspect ratio 0.5, which belongs to the wake interference flow regime, the mean and fluctuating velocity components were more difficult to measure as compared with the other two cases because of its more complicated flow pattern. Some guidelines for numerical modeling were developed based on the measurement results. The data presented in this paper can also be used as a comprehensive database for the validation of numerical models.

scholarly journals Detached eddy simulation of turbulent flow in isolated street canyons of different aspect ratios

2015 ◽  
Vol 6 (2) ◽  
pp. 351-364 ◽  
Author(s):  
Mauro Scungio ◽  
Fausto Arpino ◽  
Gino Cortellessa ◽  
Giorgio Buonanno
Keyword(s):  
Turbulent Flow ◽  
Detached Eddy Simulation ◽  
Street Canyons ◽  
Eddy Simulation ◽  
Aspect Ratios
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