Статті в журналах: "Airflow in street canyons"

1

Wang, Le, Wenxin Tian, and Peilin Zheng. "Review of the Numerical Simulation of the Wind and Pollutant Diffusion in Urban Street Canyon under the Influence of Trees." Buildings 13, no. 4 (April 20, 2023): 1088. http://dx.doi.org/10.3390/buildings13041088.

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Tree is an essential factor affecting airflow and pollutant diffusion in the urban street canyon. The wind environment in the urban street canyon will be effectively improved by expounding the mechanism and implementing greening measures. Moreover, it will help decrease the pollutant concentration around the street canyon. This paper reviews the airflow and pollutant diffusion numerical simulation in the street canyon under the tree influence. Firstly, the numerical mathematical model used for pollutant diffusion and airflow in urban street canyons under the influence of trees is summarized. The representation of trees’ numerical mathematical model in the simulation domain is mainly proposed. Secondly, the wind environment and pollutant distribution factors influencing urban street canyons are elaborated and analyzed, including tree characteristics, layout, street canyon shape, and thermal. Furthermore, current research progress and deficiencies are discussed. Finally, the future research direction of wind environment and pollutant distribution simulation in urban streets under the influence of trees is pointed out.

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2

Parida, Yakup, Wen Rong He, Zhong Hua Zhou, and Deng Feng Fu. "A Numerical Study on Airflow and Particle Dispersion within an Urban Street Canyon with Different Wedge-Shaped Roofs." Advanced Materials Research 869-870 (December 2013): 213–17. http://dx.doi.org/10.4028/www.scientific.net/amr.869-870.213.

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This work presents a numerical study on airflow and particle dispersion within an urban street canyon with different wedge-shaped roof. A two-dimensional computational fluid dynamics (CFD) model for evaluating the airflow and particles dispersion within a street canyon was built up, which was based on the incompressible Reynolds Averaged Navier-Stokes equations, turbulence model and the particles transportation equation. It is revealed that: (1) particles dispersion inside an urban street canyon is mostly dominated by the in-canyon wind flow; (2) different wedge-shaped roof configurations causes a variety of particles distribution patterns; (3) air pollution levels are much higher in the step-down canyons relative to the step-up canyons; (4) the simulated result of FLUENT is reasonable, and the prospect of applying FLUENT to study atmospheric environment is very well. Key words: CFD; street canyon; particle dispersion; numerical simulation

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3

Wang, Peng, Dai Qing Zhao, Guo Tian Cai, and Cui Ping Liao. "Numerical Simulation of Traffic Emissions in Urban Street Canyon." Advanced Materials Research 168-170 (December 2010): 1548–51. http://dx.doi.org/10.4028/www.scientific.net/amr.168-170.1548.

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Dispersion of gaseous pollutant emissions in different street canyons was studied using two dimensional sections of canyon models airflow. Effects of building size, street width wind velocity and different turbulent model on the pollutant transport were examined. Depending on wind speed, building height, and street width, it was found that large recirculation regions in canyons may form. Under certain conditions, gaseous pollutants emitted from vehicle exhaust may trap inside the street canyon. It was shown that the amount of pollutants in street canyons reduces when the wind speed increases. The simulation results were compared with the available wind tunnel experiments and favorable agreement was found.

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4

Liu, Cheng-Wei, Shuo-Jun Mei, Di Liu, and Fu-Yun Zhao. "Convective dispersion of heat and airborne pollutants inside street canyons under the influence of urban ground heat flows." Indoor and Built Environment 28, no. 5 (April 26, 2017): 619–35. http://dx.doi.org/10.1177/1420326x17706186.

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This paper reports a computational fluid dynamics simulation of airflow and species dispersion inside street canyons and building blocks simultaneously. Urban thermal boundary flows could cause a profound effect on the dispersion of pollutant scalars and ventilation performance of street canyons. Nominal pollutant concentration differences between the urban street canyon and the countryside fresh air could be determined by a consideration of wind profile and ground vegetation. This study models the interaction of the fluid flow, thermal and pollutant dispersions based on the Reynolds number (Re), Grashof number (Gr) and their combinations – Archimedes number (Ar). The fluid, heat and pollutant dispersion performances were compared with the air, heat and pollutant removal efficiencies, indicated by the air change rate (ACR), heat removal rate (HRR) and pollutant removal rate (PRR). Numerical results indicate that Ar could promote fluid, heat and pollutant removals in street canyons. Transport function lines (contours of heat and mass functions) produced would illustrate the main recirculation developed inside these street canyons studied, to allow development of control strategies for dispersion of heat and pollutant species within these environments. The present work could contribute towards the understanding of the ventilation mechanism in street canyons surrounded by the residential buildings.

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5

Dai, Yuwei, Fuyao Zhang, and Dongmei Xu. "Experimental analysis of single-sided natural ventilation and interunit dispersion in scaled 2D street canyons." E3S Web of Conferences 356 (2022): 04037. http://dx.doi.org/10.1051/e3sconf/202235604037.

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Interunit dispersion problems have been studied previously mainly through on-site measurements, wind tunnel tests, and CFD simulations. In this study, a scaled outdoor experiment was conducted to examine the interunit dispersion characteristics in consecutive two-dimensional street canyons. Tracer gas (CO2) was continuously released to simulate the pollutant dispersion routes between the rooms in street canyons. The reentry ratio was analyzed to reveal the interunit dispersion of the rooms in the street canyons. This study provides authentic airflow and pollutant dispersion information in the street canyons in an urban environment.

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6

Zeng, Fanhao, David Simeja, Xinyi Ren, Zhonggou Chen, and Hanyi Zhao. "Influence of Urban Road Green Belts on Pedestrian-Level Wind in Height-Asymmetric Street Canyons." Atmosphere 13, no. 8 (August 12, 2022): 1285. http://dx.doi.org/10.3390/atmos13081285.

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This study was conducted to examine the effect on airflow of the shape of an urban road green belt in an asymmetrical street canyon. In this paper, the airflow field at pedestrian height in an asymmetrical street with different building height ratios (ASF) on both sides of the street is modeled and simulated using computational fluid dynamics (CFD) software, ANSYS FLUENT, and the flow rate characteristic distribution index and the average airflow intensity index are used to evaluate and analyze the airflow at the pedestrian level. The study shows that: (1) in an empty street scheme with different building ratios, the static wind area is located on the roof of the downstream building; the closer to the ground in a street with an ASF = 1/3, the lower the airflow rate. However, the situation is the opposite of that in other streets (2/3, 3/1, and 3/2). (2) The position of the green belt makes the windward side flow rate in the step-up street higher than that of the leeward side, and the flow rate of the leeward side in the step-down street is higher than that of the windward side. (3) Compared with other green belt forms, the use of two plates and three belts in the incremental street can increase the circumferential sinking at the roofs of the windward side of the street, thereby improving the wind environment in the entire street. The use of one plate, two-belt and three-plate, four-belt scenarios in the step-down street allows the two ends of the corner vortex to carry more airflow into the interior of the street and reduces both the “wind shadow effect” area in the middle of the street and the “air outlet effect” at both ends.

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7

Nguyen, Van Thinh, Thanh Chuyen Nguyen, and John Nguyen. "Numerical Simulation of Turbulent Flow and Pollutant Dispersion in Urban Street Canyons." Atmosphere 10, no. 11 (November 7, 2019): 683. http://dx.doi.org/10.3390/atmos10110683.

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In this study, we have developed a numerical model based on an open source Computational Fluid Dynamics (CFD) package OpenFOAM, in order to investigate the flow pattern and pollutant dispersion in urban street canyons with different geometry configurations. In the new model, the pollutant transport driven by airflow is modeled by the scalar transport equation coupling with the momentum equations for airflow, which are deduced from the Reynolds Averaged Navier-Stokes (RANS) equations. The turbulent flow calculation has been calibrated by various two-equation turbulence closure models to select a practical and efficient turbulence model to reasonably capture the flow pattern. Particularly, an appropriate value of the turbulent Schmidt number has been selected for the pollutant dispersion in urban street canyons, based upon previous studies and careful calibrations against experimental measurements. Eventually, the numerical model has been validated against different well-known laboratory experiments in regard to various aspect ratios (a relationship between the building height and the width of the street canyon), and different building roof shapes (flat, shed, gable and round). The comparisons between the numerical simulations and experimental measurements show a good agreement on the flow pattern and pollutant distribution. This indicates the ability of the new numerical model, which can be applied to investigate the wind flow and pollutant dispersion in urban street canyons.

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8

Nazridoust, Kambiz, and Goodarz Ahmadi. "Airflow and pollutant transport in street canyons." Journal of Wind Engineering and Industrial Aerodynamics 94, no. 6 (June 2006): 491–522. http://dx.doi.org/10.1016/j.jweia.2006.01.012.

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9

Gonzalez Olivardia, Franchesca, Qi Zhang, Tomohito Matsuo, Hikari Shimadera, and Akira Kondo. "Analysis of Pollutant Dispersion in a Realistic Urban Street Canyon Using Coupled CFD and Chemical Reaction Modeling." Atmosphere 10, no. 9 (August 21, 2019): 479. http://dx.doi.org/10.3390/atmos10090479.

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Studies in actual urban settings that integrate chemical reaction modeling, radiation, and particular emissions are mandatory to evaluate the effects of traffic-related air pollution on street canyons. In this paper, airflow patterns and reactive pollutant behavior for over 24 h, in a realistic urban canyon in Osaka City, Japan, was conducted using a computational fluid dynamics (CFD) model coupled with a chemical reaction model (CBM-IV). The boundary conditions for the CFD model were obtained from mesoscale meteorological and air quality models. Inherent street canyon processes, such as ground and wall radiation, were evaluated using a surface energy budget model of the ground and a building envelope model, respectively. The CFD-coupled chemical reaction model surpassed the mesoscale models in describing the NO, NO2, and O3 transport process, representing pollutants concentrations more accurately within the street canyon since the latter cannot capture the local phenomena because of coarse grid resolution. This work showed that the concentration of pollutants in the urban canyon is heavily reliant on roadside emissions and airflow patterns, which, in turn, is strongly affected by the heterogeneity of the urban layout. The CFD-coupled chemical reaction model characterized better the complex three-dimensional site and hour-dependent dispersion of contaminants within an urban canyon.

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10

Dai, Yuwei, Minzhang Hou, Haidong Wang, and Wanli Tu. "Source Location Identification in an Ideal Urban Street Canyon with Time-Varying Wind Conditions under a Coupled Indoor and Outdoor Environment." Buildings 13, no. 12 (December 15, 2023): 3121. http://dx.doi.org/10.3390/buildings13123121.

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Source location identification methods are typically applied to steady-state conditions under pure indoor or outdoor environments, but under time-varying wind conditions and coupled indoor and outdoor environments, the applicability is not clear. In this study, we proposed an improved adjoint probability method to identify the pollutant source location with time-varying inflows in street canyons and used scaled outdoor experiment data to verify the accuracy. The change in inflow velocity will affect the airflow structure inside the street canyons. Outdoor wind with a lower temperature will exchange heat with the air with a higher temperature inside the street canyon, taking away part of the heat and reducing the heat of the air inside the street canyons. Moreover, the room opening will produce some air disturbance, which is conducive to the heat exchange between the air near the opening and the outdoor wind. Furthermore, the fluctuations of the upper wind will influence the diffusion of the tracer gas. We conducted three cases to verify the accuracy of the source identification method. The results showed that the conditioned adjoint location probability (CALP) of each case was 0.06, 0.32, and 0.28. It implies that with limited pollutant information, the improved adjoint probability method can successfully identify the source location in the dynamic wind environments under coupled indoor and outdoor conditions.

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11

Qin, Hongqiao, Bo Hong, and Runsheng Jiang. "Are Green Walls Better Options than Green Roofs for Mitigating PM10 Pollution? CFD Simulations in Urban Street Canyons." Sustainability 10, no. 8 (August 9, 2018): 2833. http://dx.doi.org/10.3390/su10082833.

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To examine the effect of green roofs (GRs) and green walls (GWs) on coarse particle (PM10) dispersion in urban street canyons, a computational fluid dynamics (CFD) simulation was conducted with a Reynolds-averaged Navier-Stokes (RANS) model and a revised generalized drift flux model. Simulations were performed with different aspect ratios (H/W = 0.5, 1.0, and 2.0), greenery coverage areas (S = 300, 600, and 900 m2), and leaf area densities (LADs = 1.0, 3.5, 6.0 m2/m3). Results indicate that: (1) GRs and GWs all had the reduction ability of PM10 at the pedestrian level; (2) Averaged concentrations of PM10 in GWs and GRs varied little as LAD changed in H/W = 0.5 and 1.0. When H/W = 2.0, the aerodynamic effects of GRs increased since airflow was enhanced within street canyons, resulting in the increasing concentrations in GRs compared with non-greening scenarios; (3) Given equal greenery coverage area and aspect ratio, GWs are more effective in reducing street-canyon PM10, and the averaged concentrations declined with increasing LADs and greenery coverage areas, especially the H/W; (4) At the pedestrian level, the reduction ratio of GRs is greater than that of GWs with the maximum value of 17.1% for H/W = 0.5. However, where H/W = 1.0 and 2.0, the concentrations within GWs are lower than GRs, with maximum reduction ratios of 29.3% and 43.8%, respectively.

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12

Wang, Le, Junwei Su, Zhaolin Gu, and Qingxiang Shui. "Effect of Street Canyon Shape and Tree Layout on Pollutant Diffusion under Real Tree Model." Sustainability 12, no. 5 (March 9, 2020): 2105. http://dx.doi.org/10.3390/su12052105.

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Trees have a significant impact on the airflow and pollutant diffusion in the street canyon and are directly related to the comfort and health of residents. In this paper, OpenFOAM is used for simulating the airflow and pollutant diffusion in the street canyon at different height–width ratios and tree layouts. Different from the drag source model in the previous numerical simulation, this study focuses on the characterization of the blocking effect of tree branches on airflow by using more precise and real tree models. It is found that the airflow is blocked by the tree branches in the canopy, resulting in slower airflow and varying velocity direction; the air flows in the pore area between trees more easily, and the vortex centers are different in cases where the street canyon shape and tree layout are different. Low-velocity airflow distributes around and between two tree canopies, especially under the influence of two trees with different spacing. At the height of the pedestrian, the tree branches change the vortex structure of airflow, and thereby high pollutant concentration distribution on both sides of the bottom of the leeward side of the street canyon changes constantly. In the street canyon, the small change in tree spacing has a very limited influence on the pollutant concentration. The street canyon has the lowest average pollutant concentration at the largest y-axis direction spacing between two trees.

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13

Boumahdi, Meryeme, Chaker El Amrani, and Siegfried Denys. "An Innovative Air Purification Method and Neural Network Algorithm Applied to Urban Streets." International Journal of Embedded and Real-Time Communication Systems 10, no. 4 (October 2019): 1–19. http://dx.doi.org/10.4018/ijertcs.2019100101.

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In the present work, multiphysics modeling was used to investigate the feasibility of a photocatalysis-based outdoor air purifying solution that could be used in high polluted streets, especially street canyons. The article focuses on the use of a semi-active photocatalysis in the surfaces of the street as a solution to remove anthropogenic pollutants from the air. The solution is based on lamellae arranged horizontally on the wall of the street, coated with a photocatalyst (TiO2), lightened with UV light, with a dimension of 8 cm × 48 cm × 1 m. Fans were used in the system to create airflow. A high purification percentage was obtained. An artificial neural network (ANN) was used to predict the optimal purification method based on previous simulations, to design purification strategies considering the energy cost. The ANN was used to forecast the amount of purified with a feed-forward neural network and a backpropagation algorithm to train the model.

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14

Brimblecombe, Peter, Meng-Yuan Chu, Chun-Ho Liu, and Zhi Ning. "NOx and CO Fluctuations in a Busy Street Canyon." Environments 8, no. 12 (December 15, 2021): 137. http://dx.doi.org/10.3390/environments8120137.

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Busy street canyons can have a large flow of vehicles and reduced air exchange and wind speeds at street level, exposing pedestrians to high pollutant concentrations. The airflow tended to move with vehicles along the canyon and the 1-s concentrations of NO, NO2 and CO were highly skewed close to the road and more normally distributed at sensors some metres above the road. The pollutants were more autocorrelated at these elevated sensors, suggesting a less variable concentration away from traffic in the areas of low turbulence. The kerbside concentrations also showed cyclic changes approximating nearby traffic signal timing. The cross-correlation between the concentration measurements suggested that the variation moved at vehicle speed along the canyon, but slower vertically. The concentrations of NOx and CO were slightly higher at wind speeds of under a metre per second. The local ozone concentrations had little effect on the proportion of NOx present as NO2. Pedestrians on the roadside would be unlikely to exceed the USEPA hourly guideline value for NO2 of 100 ppb. Across the campaign period, 100 individual minutes exceeded the guidelines, though the effect of short-term, high-concentration exposures is not well understood. Tram stops at the carriageway divider are places where longer exposures to higher levels of traffic-associated pollutants are possible.

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15

Thravalou, S., A. Michael, M. Neophytou, and M. Philokyprou. "The Ventilation Capacity of Earthen Vernacular Buildings With Timber Projections (Sachnisi) in Dense Urban Canyons – Findings From a Field Study in the Mediterranean." IOP Conference Series: Earth and Environmental Science 1196, no. 1 (June 1, 2023): 012089. http://dx.doi.org/10.1088/1755-1315/1196/1/012089.

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Abstract Vernacular architecture employs numerous elements for enhancing natural ventilation, especially in the Mediterranean climate. However, the cooling effectiveness of natural ventilation also relies on occupant behaviour and is highly determined by urban scale attributes. Still, airflow in real, inhomogeneous historic urban settings is rarely integrated in the thermal comfort studies of historic buildings. In this study, a multi-scale approach is adopted in order to assess the role of ventilation in establishing thermal comfort in earthen buildings, in real field conditions. This is achieved by addressing field monitoring of air velocity, temperature and relative humidity in: a) a dense (packing density λp=0.60) and inhomogeneous historic neighbourhood in Nicosia, Cyprus (measurement at a reference height); b) the street-canyon (measured at the mid-height of a narrow canyon with aspect ratio 2); and c) the interior of a typical adobe building with semi-open, pass-through spaces (portico) and closed timber projections with multiple openings, called sachnisi. Building ventilation was addressed as a function of in-street and rooftop airflow. Indoor thermal comfort was assessed in the case of specific ventilation patterns, comparing three adaptive comfort models. The results highlight the complexity of airflow in real inhomogeneous urban canopies and demonstrate that air velocity level in the street canyon is approximately one third of the reference free-stream wind velocity, while indoor air velocity remains at minimum levels. The study also reveals the contribution of night-time ventilation in cooling. Finally, spatial differentials of indoor environmental conditions in the portico were recorded for the first time, demonstrating the role of the sachnisi as a wind-capture element.

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16

Kuo, Chien-Yuan, Rong-Jing Wang, Yi-Pin Lin, and Chi-Ming Lai. "Urban Design with the Wind: Pedestrian-Level Wind Field in the Street Canyons Downstream of Parallel High-Rise Buildings." Energies 13, no. 11 (June 2, 2020): 2827. http://dx.doi.org/10.3390/en13112827.

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We are investigating how to use urban design approaches to conduct the layout and basic design of newly-built high-rise buildings to reduce wind obstruction and create effective urban ventilation. Few studies have addressed this issue. This study analyzes the effects of high-rise building on pedestrian-level wind in downstream street canyons based on wind tunnel test results, and examines the suitability of an urban design specification. The height (H) of high-rise buildings and the airflow passage width (S) between adjacent high-rise buildings are key control factors for this issue; H/D = 3 and S/D = 1.125 are critical parameters and recommended values (D is the height of the downstream street blocks).

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17

Dong, Jingliang, Zijing Tan, Yimin Xiao, and Jiyuan Tu. "Seasonal Changing Effect on Airflow and Pollutant Dispersion Characteristics in Urban Street Canyons." Atmosphere 8, no. 12 (February 23, 2017): 43. http://dx.doi.org/10.3390/atmos8030043.

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18

Longley, I. D., M. W. Gallagher, J. R. Dorsey, M. Flynn, and J. F. Barlow. "Short-term measurements of airflow and turbulence in two street canyons in Manchester." Atmospheric Environment 38, no. 1 (January 2004): 69–79. http://dx.doi.org/10.1016/j.atmosenv.2003.09.060.

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19

Fan, Xiaodan, Xuelin Zhang, Jian Hang, and A. U. Weerasuriya. "Numerical investigation of the effects of environmental conditions, droplet size, and social distance on interpersonal droplet transmission in a deep urban street canyon." E3S Web of Conferences 356 (2022): 04029. http://dx.doi.org/10.1051/e3sconf/202235604029.

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This study investigated the interpersonal droplet transmission between a healthy and an infected person in a deep and narrow street canyon using Computational Fluid Dynamics (CFD) simulation. The CFD simulations modelled various droplet sizes (Dp), background wind speeds (Uref), relative humidity (RH), and social distances (D) to estimate their effects on interpersonal droplet transmission. The results revealed noticeably opposite effects of these factors. For example, small background wind moved droplets upward and suspended them in the air for a longer time while high wind speeds distributed droplets in the street canyon with few of them retained in the air. Relative humidity had a trifling impact on dispersing small droplets (10μm, 25μm, 50μm), whereas it significantly modified the dispersion of large droplets, especially in small background wind speeds. Furthermore, small droplets travelled longer distances in dry air and were either deposited on the surrounding buildings’ walls or suspended in the air. In contrast, larger droplets in moist air rapidly deposited on the ground or the infected person’s body. In dry air, 45% of large droplets were inhaled or suspended in the air, exposing pedestrians to contaminated droplets. Large social distances significantly diluted the small droplets but increased the infection risk from large droplets because of the complex interaction of the ambient airflow and the gravity. It is recommended to keep social distances of 2 m and 4 m for pedestrians in deep urban street canyons in Windy condition and Calm-Wet condition, respectively.

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20

Huang, Yuandong, Xiaonan Hu, and Ningbin Zeng. "Impact of wedge-shaped roofs on airflow and pollutant dispersion inside urban street canyons." Building and Environment 44, no. 12 (December 2009): 2335–47. http://dx.doi.org/10.1016/j.buildenv.2009.03.024.

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Hassan, Sheikh, Umma Habiba Akter, Preetom Nag, Md Mamun Molla, Amirul Khan, and Md Farhad Hasan. "Large-Eddy Simulation of Airflow and Pollutant Dispersion in a Model Street Canyon Intersection of Dhaka City." Atmosphere 13, no. 7 (June 28, 2022): 1028. http://dx.doi.org/10.3390/atmos13071028.

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The atmospheric flow and dispersion of traffic exhaust were numerically studied in this work while considering a model street canyon intersection of a city. The finite volume method (FVM)-based large-eddy simulation (LES) technique in line with ANSYS Fluent have been used for flow and pollutant dispersion modelling through the consideration of the atmospheric boundary layer (ABL). Hexahedral elements are considered for computational domain discretization in order to numerically solve problems using FVM-LES. The turbulence parameters were superimposed through a spectral synthesizer in the existing LES model through ANSYS Fluent as part of ’damage control’ due to the unsteady k−ϵ simulation. Initially, the code is validated with an experimental study of an urban street canyon where the width and height ratio is in unity. After validation, a model urban street canyon intersection was investigated in this work. The model shows a high pollutant concentration in the intersecting corner areas of the buildings. Additionally, the study of this model intersection shows a high level of pollutant concentration at the leeward wall of downwind building in the case of increased height of an upwind building. Most importantly, it was realized from the street intersection design that three-dimensional interconnection between the dominating canyon vortices and roof level flow plays a pivotal role in pollutant concentration level on the windward walls. The three-dimensional extent of corner eddies and their interconnections with dominating vortices were found to be extremely important as they facilitate enhanced ventilation. Corner eddies only form for the streets towards the freeway and not for the streets towards the intersection. The results and key findings of this work offer qualitative and quantitative data for the estimation, planning, and implementation of exposure mitigation in an urban environment.

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Mei, Dan, Yan Wang, and Qihong Deng. "Modeling the Airflow and Particle Dispersion in Street Canyons under Unsteady Thermal Environment with Sinusoidal Variation." Aerosol and Air Quality Research 17, no. 4 (2017): 1021–32. http://dx.doi.org/10.4209/aaqr.2016.12.0559.

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23

Zhang, Yunwei, Zhaolin Gu, and Chuck Wah Yu. "Impact Factors on Airflow and Pollutant Dispersion in Urban Street Canyons and Comprehensive Simulations: a Review." Current Pollution Reports 6, no. 4 (November 18, 2020): 425–39. http://dx.doi.org/10.1007/s40726-020-00166-0.

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24

Huang, Yuan-dong, Ming-xia Jin, and Ya-nan Sun. "Numerical Studies on Airflow and Pollutant Dispersion in Urban Street Canyons Formed by Slanted Roof Buildings." Journal of Hydrodynamics 19, no. 1 (February 2007): 100–106. http://dx.doi.org/10.1016/s1001-6058(07)60034-1.

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25

Mei, Dan, and Xuemei Xu. "The influence of vapor on the particle transport in high humid neighborhood environment." Journal of Physics: Conference Series 2076, no. 1 (November 1, 2021): 012043. http://dx.doi.org/10.1088/1742-6596/2076/1/012043.

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Abstract The particle transport characteristics have a significant effect on the exposure of residents and pedestrians to traffic pollutants in the street canyon. Around the lakeside environment, the diffusion of water vapor affects the flow characteristics of the gas mixture, which has a considerable influence on particle transport in the street canyon. A computational domain containing water bodies from which droplets were emitted by evaporation, a lakeside avenue and architectural groups were constructed. The RNG k-ε turbulence model and discrete phase model were applied to study the velocity, pressure, density of the airflow and particle transport characteristics in the street canyon with the absolute humidity increase (AHI) of 0, 3.8×10-4 g/kg, 1.7×10-3 g/kg, 3.1×10-3 g/kg. The saturated vapor pressure on the surface of droplets was modified by the pressure correction equation, which can limit the evaporation rate of the droplets. The simulation results demonstrated that, the diffusion of vapor could reduce the airflow velocity and increase the air pressure and density. The particle concentration in the street canyon increased with the AHI. Most of the pathogens in the air are transmitted with the flow of particle, and the study has some guiding significance to prevent the transmission of viruses.

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26

Liang, Qian, Yucong Miao, Gen Zhang, and Shuhua Liu. "Simulating Microscale Urban Airflow and Pollutant Distributions Based on Computational Fluid Dynamics Model: A Review." Toxics 11, no. 11 (November 13, 2023): 927. http://dx.doi.org/10.3390/toxics11110927.

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Urban surfaces exert profound influences on local wind patterns, turbulence dynamics, and the dispersion of air pollutants, underscoring the critical need for a thorough understanding of these processes in the realms of urban planning, design, construction, and air quality management. The advent of advanced computational capabilities has propelled the computational fluid dynamics model (CFD) into becoming a mature and widely adopted tool to investigate microscale meteorological phenomena in urban settings. This review provides a comprehensive overview of the current state of CFD-based microscale meteorological simulations, offering insights into their applications, influential factors, and challenges. Significant variables such as the aspect ratio of street canyons, building geometries, ambient wind directions, atmospheric boundary layer stabilities, and street tree configurations play crucial roles in influencing microscale physical processes and the dispersion of air pollutants. The integration of CFD with mesoscale meteorological models and cutting-edge machine learning techniques empowers high-resolution, precise simulations of urban meteorology, establishing a robust scientific basis for sustainable urban development, the mitigation of air pollution, and emergency response planning for hazardous substances. Nonetheless, the broader application of CFD in this domain introduces challenges in grid optimization, enhancing integration with mesoscale models, addressing data limitations, and simulating diverse weather conditions.

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Shui, Tao Tao, Jing Liu, and Fei Ma. "Numerical Simulation of Cross-Ventilation in Buildings Affected by Surrounding Buildings with Different Separation Distances." Applied Mechanics and Materials 353-356 (August 2013): 2993–96. http://dx.doi.org/10.4028/www.scientific.net/amm.353-356.2993.

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In order to investigate natural cross-ventilation in buildings, computational fluid dynamics (CFD) with the DES model is applied. The aim of this paper is to investigate the influence of surrounding buildings on natural ventilation in target building under different separation distances. The simulation results indicate that surrounding buildings has a significant impact on airflow structure and airflow rate of the target building. The flow characteristics in target building is determined by the flow regime in street canyon.

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Zhang, Yunwei, Zhaolin Gu, and Chuck Wah Yu. "Review on Numerical Simulation of Airflow and Pollutant Dispersion in Urban Street Canyons under Natural Background Wind Condition." Aerosol and Air Quality Research 18, no. 3 (2018): 780–89. http://dx.doi.org/10.4209/aaqr.2017.09.0303.

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Mouzourides, Petros, Costas Marakkos, and Marina K. A. Neophytou. "Urban street canyon flows under combined wind forcing and thermal buoyancy." Physics of Fluids 34, no. 7 (July 2022): 076606. http://dx.doi.org/10.1063/5.0090642.

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In this work, we investigate buoyancy-driven flows within urban street canyon cavities of three aspect ratios under simultaneous inertial wind forcing. The main aim of this work is to enhance the understanding of induced urban airflow patterns under non-isothermal conditions through experimental investigation, which to date are relatively scarce. The experimental results can be used for corresponding computational fluid dynamics simulations. Scaled-down models of typical street-canyon cavity geometries were deployed inside a water channel, where different ambient atmospheric conditions were simulated using dimensional analysis and similarity criteria. Three model street-canyon cavities were examined with height-to-width (aspect) ratios of 2/3, 1, and 2. The thermal buoyancy forcing was applied by means of differential heating between the two canyon side antagonistic walls for a given background flow velocity well-above the canyon height. The non-dimensional parameter B was used to quantify the influences of buoyancy and inertial forcing on the urban-canyon flow, as well as factoring in the geometrical aspect of the street canyon. The particle image velocimetry technique was used to acquire velocity vector fields across the middle vertical planar cross section of the urban street canyon. The results showed that the canyon aspect ratio affects the resulting flow field; however, a main vortical structure is present in all the visualized flow patterns with flow direction always being consistent with that of an uprising flow along the canyon heated wall.

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Zhao, Yi, Ruibin Li, Lu Feng, Yan Wu, and Naiping Gao. "Boundary layer wind tunnel tests of outdoor airflow field around urban buildings: A review of methods and status." E3S Web of Conferences 356 (2022): 04031. http://dx.doi.org/10.1051/e3sconf/202235604031.

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Outdoor airflow fields have received increasing attention in the building aerodynamics community due to that the airflow distributions around outdoor buildings are closely related to issues such as thermal comfort, building ventilation, and pollutant dispersion. The focus of this paper is on the airflow distributions around buildings obtained through wind tunnel tests, and such studies are mostly conducted in boundary layer wind tunnel with long test section. This paper reviews current techniques for boundary layer wind tunnel tests of airflow distributions in urban outdoor environments. Then, the characteristics of airflow distributions around buildings in three typical configurations from previous studies (i.e. isolated building, street canyon, and building complexes) are reviewed. This review highlights that the proposed building models should be carefully assessed in combination with wind tunnel tests at the design stage. In addition, it is important to obtain wind tunnel test data for buildings with thermal effects, and the importance of arranging the underlying surfaces during the test is also emphasized.

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31

Pospisil, Jiri, Miroslav Jicha, Katerina Niachou, and Matheos Santamouris. "Computational modelling of airflow in urban street canyon and comparison with measurements." International Journal of Environment and Pollution 25, no. 1/2/3/4 (2005): 191. http://dx.doi.org/10.1504/ijep.2005.007666.

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32

Li, Haiwei, Yongling Zhao, Ronita Bardhan, Aytac Kubilay, Dominique Derome, and Jan Carmeliet. "Time-evolving Impact of Trees on Street Canyon Microclimate." Journal of Physics: Conference Series 2654, no. 1 (December 1, 2023): 012145. http://dx.doi.org/10.1088/1742-6596/2654/1/012145.

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Abstract Nowadays, cities are frequently exposed to heatwaves, worsening outdoor thermal comfort and increasing cooling energy demand in summer. Urban forestry is seen as one of the viable and preferable solutions to combat extreme heat events and urban heat island (UHI) in times of climate change. While many cities have initiated tree-planting programs in recent years, the evolving impact of trees on street microclimate, in a time span of up to several decades, remains unclear. This study focuses on the cooling effects of a common type of street trees, linden trees, in five age groups, i.e., 10-20, 20-30, 30-40, 40-60, and 60-100 years old, while the diversity of trees is present in nature, that is, various species and crown geometries, The leaf area index (LAI) and leaf area density (LAD) of linden trees vary nonlinearly as they grow, peaking at different ages. Computational fluid dynamics (CFD) simulations were performed for an idealized street canyon with linden trees of various age groups. Turbulent airflow, heat and moisture transport, shortwave and longwave radiation, shading, and transpiration were fully coupled and solved in OpenFOAM. Meteorological data, including air temperature, wind speed, moisture, and shortwave radiation of the heatwave in Zurich (June 2019), were applied as boundary conditions. The results show that young trees in the age group of 10-20 years old provide little heat mitigation at the pedestrian level in an extreme heat event. Optimal heat mitigation by trees is observed for the group of 30-60 years old linden trees. Finally, the potential impact of growing trees on air ventilation in streets is evaluated.

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Wu, Mei, Guangwei Zhang, Liping Wang, Xiaoping Liu, and Zhengwei Wu. "Influencing Factors on Airflow and Pollutant Dispersion around Buildings under the Combined Effect of Wind and Buoyancy—A Review." International Journal of Environmental Research and Public Health 19, no. 19 (October 8, 2022): 12895. http://dx.doi.org/10.3390/ijerph191912895.

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With the rapid growth of populations worldwide, air quality has become an increasingly important issue related to the health and safety of city inhabitants. There are quite a few factors that contribute to urban air pollution; the majority of studies examining the issue are concerned with environmental conditions, building geometries, source characteristics and other factors and have used a variety of approaches, from theoretical modelling to experimental measurements and numerical simulations. Among the environmental conditions, solar-radiation-induced buoyancy plays an important role in realistic conditions. The thermal conditions of the ground and building façades directly affect the wind field and pollutant dispersion patterns in the microclimate. The coupling effect of wind and buoyancy on the urban environment are currently hot and attractive research topics. Extensive studies have been devoted to this field, some focused on the street canyon scale, and have found that thermal effects do not significantly affect the main airflow structure in the interior of the street canyon but strongly affect the wind velocity and pollutant concentration at the pedestrian level. Others revealed that the pollutant dispersion routes can be obviously different under various Richardson numbers at the scale of the isolated building. The purpose of this review is therefore to systematically articulate the approaches and research outcomes under the combined effect of wind and buoyancy from the street canyon scale to an isolated building, which should provide some insights into future modelling directions in environmental studies.

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34

Huang, Yuan Dong, Yue Jiao Peng, Jian Wei Jiang, Zhong Hua Zhou, and Jing Gu. "A Comparative Study of Various Turbulence Models for Simulating Pollutant Dispersion within an Isolated Street Canyon." Advanced Materials Research 356-360 (October 2011): 766–70. http://dx.doi.org/10.4028/www.scientific.net/amr.356-360.766.

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CFD calculations are carried out using the standard, RNG and realizable κ-ε turbulence models to simulate the airflow and pollutant dispersion inside an isolated street canyon. The computed air velocity vector fields and pollutant concentration contours show that all the three studied κ-ε models produce a very similar clockwise vortex structure that carries the pollutants released from the line source on the street floor towards the leeward side of the canyon. The calculated non-dimensional pollutant concentration distributions on both the leeward and windward walls of the canyon are compared with the wind tunnel measured data. It is revealed that (1) on the windward wall of the canyon, the calculated pollutant concentrations using the standard, RNG and realizable κ-ε models are all in perfect agreement with the experimental observations, (2) the RNG and realizable κ-ε models provide almost the same results for pollutant concentration distributions on the leeward wall of the canyon, (3) the RNG and realizable κ-ε models overestimate greatly the pollutant concentration values on the leeward wall of the canyon, whereas the concentration distributions predicted by the standard κ-ε model on the leeward wall are in reasonable agreement with the wind tunnel data.

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35

Zajic, D., H. J. S. Fernando, R. Calhoun, M. Princevac, M. J. Brown, and E. R. Pardyjak. "Flow and Turbulence in an Urban Canyon." Journal of Applied Meteorology and Climatology 50, no. 1 (January 1, 2011): 203–23. http://dx.doi.org/10.1175/2010jamc2525.1.

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Abstract A better understanding of the interaction between the built environment and the atmosphere is required to more effectively manage urban airsheds. This paper reports an analysis of data from an atmospheric measurement campaign in Oklahoma City, Oklahoma, during the summer of 2003 that shows wind flow patterns, turbulence, and thermal effects in the downtown area. Experimental measurements within a street canyon yielded airflow patterns, stability conditions, and turbulence properties as a function of the incoming wind direction and time of the day. Air and surface temperatures at two different sites, one within the downtown urban canyon and the other in a nearby park, were measured. A study of the stability conditions within the urban canyon during the campaign indicates that dynamically stable conditions did not occur within the canyon. This provides evidence that the built environment can strongly influence the thermal characteristics in cities. Mean flow patterns close to the street level are analyzed for two different ranges of incoming wind directions and are compared with those obtained from a previous field experiment featuring idealized building configurations. This paper presents an approach allowing the estimation of wind direction in an urban canyon, given inflow conditions, that shows good agreement with wind patterns in the Oklahoma City street canyon. Turbulence statistics were calculated and normalized using different velocity scales to investigate the efficacy of the latter in specifying turbulence levels in urban canopies. The dependence of turbulence quantities on incoming wind direction and time of the day was investigated.

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36

Niachou, K., I. Livada, and M. Santamouris. "Experimental study of temperature and airflow distribution inside an urban street canyon during hot summer weather conditions. Part II: Airflow analysis." Building and Environment 43, no. 8 (August 2008): 1393–403. http://dx.doi.org/10.1016/j.buildenv.2007.01.040.

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37

Carlos, Jorge S. "Window assessment at different level height on a Portuguese typical street canyon." WEENTECH Proceedings in Energy 4, no. 2 (January 2, 2019): 143–59. http://dx.doi.org/10.32438/wpe.0218.

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This paper presents the results of a study investigating the ventilation mode, the solar heat gain and daylight performance via vertical fenestration on a street canyon. In recent years there has been a growing awareness in energy-efficient building design and operation of the building stock. Dynamic envelope/window systems have potential to optimize the performance of the building, between airing, solar heat gain and daylight admission. However, higher thermal resistance glazing implies a reduction of solar transmittance. A typical street canyon in Portugal was used for the present study. Three different room ratios and two types of windows at two different floors were used for comparison. Different simulation tools were used during this study. To be comparable with other studies several ratios were present, as the window/wall, the glazing/wall ratios, the window/floor and the glazing/floor ratios as well as the window opening area. This paper presents the obtained airflow and solar gains on both heating and cooling season in addition to the level of daylight factor. It was found that specific adaptive actions to improve indoor environmental quality and reduce the need of energy consumption are needed.

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38

Huang, Yuan-Dong, Ren-Wei Hou, Ze-Yu Liu, Ye Song, Peng-Yi Cui, and Chang-Nyung Kim. "Effects of Wind Direction on the Airflow and Pollutant Dispersion inside a Long Street Canyon." Aerosol and Air Quality Research 19, no. 5 (2019): 1152–71. http://dx.doi.org/10.4209/aaqr.2018.09.0344.

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39

Zheng, Bin, Afang Jin, Shuzhi Zhang, and Hao Peng. "Numerical Simulation of Pollutant Spread in a Double-Deck Viaduct." Sustainability 15, no. 21 (October 25, 2023): 15244. http://dx.doi.org/10.3390/su152115244.

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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.

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Xiong, Sheng Yi, Hong Yan Zhang, Li Hui Jiao, and Yao Zhang. "Field Monitoring of PM₁₀ Dispersion at Street-Canyon Road Intersection." Applied Mechanics and Materials 71-78 (July 2011): 4095–98. http://dx.doi.org/10.4028/www.scientific.net/amm.71-78.4095.

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In order to research the harm of particle matter to human health, the TSI dust instrument, particle counter and miniature meteorological instrument were used in this paper to monitor the PM10 concentration of one typical cross road in Xi’an city. The affect factors of the PM10 concentration were also discussed. The results provided that: there is weak linear relationship between sample concentration of PM10 and wind velocity because of the complex shape of the buildings. The fine particles (<1.0μm) mainly come from vehicle emission in the cross road,and the sample concentration of PM10 has a significant relationship with the fine particles under high humidity conditions, while it has weak correlation with traffic flow. The fine particles from vehicle emission and the high humidity condition is the primary cause of the high PM10 concentration, while the temperature and airflow caused by the building shape affect the diffusion and distribution of the PM10.

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41

Liu, Jiarui, Yujie Zhao, Cho Kwong Charlie Lam, Jie Liang, Hong Ling, and Qun Wang. "Integrated impacts of solar heating and water evaporation on urban airflows and thermal environments in 2D street canyons." Urban Climate 48 (March 2023): 101411. http://dx.doi.org/10.1016/j.uclim.2023.101411.

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42

Shevchenko, O., and S. Snizhko. "BIG CITY WIND REGIME." Bulletin of Taras Shevchenko National University of Kyiv. Geography, no. 72 (2018): 13–20. http://dx.doi.org/10.17721/1728-2721.2018.72.3.

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Big city wind regime is an important factor which influences on air pollution level and bioclimate of the territory. It forms as a result of climatic conditions influence and the impact of various objects (height and density of construction, road network, green zones, water bodies etc.) within the city. The article is devoted to the study and analysis of big city wind regime, as well as generalizing of the basic knowledge about air flow transformation in urban areas for future using this information in scientific research and for the correction of aeration regime of different territories. Wind speed reduction is the main feature of urban areas wind regime. Usually, wind velocity in the city is approximately 30 % lower compared to its neighbourhoods. Not only the mean wind speed is lower in urban areas, but also the vertical wind profile is characterized by some differences. Urban heat island existence leads to the formation of a mesoscale thermal circulation in the city – a rural breeze which is the most pronounced under conditions without wind or with weak wind speed. Transformation of air flow in an urban street canyon depends on the wind direction – when the wind is directed parallel to the canyon axis, wind within canyon has a higher velocity (according to the Venturi effect). In a street canyon which is oriented with its axis perpendicular to the wind direction, when air flows across the cross-section of a canyon, a vortex is formed and accordingly wind velocity is getting lower. Depending on the characteristics of the canyon (its height/width and length/width ratio) three distinct wind regimes may be identified in the canyon – isolated roughness flow regime, wake interference regime and skimming flow regime. Thus, the wind field has a very complex structure in the urban areas, because on airflow in the city influence a lot of factors.

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43

Huang, Yuandong, and Zhonghua Zhou. "A Numerical Study of Airflow and Pollutant Dispersion Inside an Urban Street Canyon Containing an Elevated Expressway." Environmental Modeling & Assessment 18, no. 1 (July 27, 2012): 105–14. http://dx.doi.org/10.1007/s10666-012-9332-4.

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Nardecchia, Fabio, Annalisa Di Bernardino, Francesca Pagliaro, Paolo Monti, Giovanni Leuzzi, and Luca Gugliermetti. "CFD Analysis of Urban Canopy Flows Employing the V2F Model: Impact of Different Aspect Ratios and Relative Heights." Advances in Meteorology 2018 (July 29, 2018): 1–16. http://dx.doi.org/10.1155/2018/2189234.

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Computational fluid dynamics (CFD) is currently used in the environmental field to simulate flow and dispersion of pollutants around buildings. However, the closure assumptions of the turbulence usually employed in CFD codes are not always physically based and adequate for all the flow regimes relating to practical applications. The starting point of this work is the performance assessment of the V2F (i.e., v2¯ − f) model implemented in Ansys Fluent for simulating the flow field in an idealized array of two-dimensional canyons. The V2F model has been used in the past to predict low-speed and wall-bounded flows, but it has never been used to simulate airflows in urban street canyons. The numerical results are validated against experimental data collected in the water channel and compared with other turbulence models incorporated in Ansys Fluent (i.e., variations of both k-ε and k-ω models and the Reynolds stress model). The results show that the V2F model provides the best prediction of the flow field for two flow regimes commonly found in urban canopies. The V2F model is also employed to quantify the air-exchange rate (ACH) for a series of two-dimensional building arrangements, such as step-up and step-down configurations, having different aspect ratios and relative heights of the buildings. The results show a clear dependence of the ACH on the latter two parameters and highlight the role played by the turbulence in the exchange of air mass, particularly important for the step-down configurations, when the ventilation associated with the mean flow is generally poor.

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Huang, Yuan-dong, Cui Long, Ji-tong Deng, and Chang-Nyung Kim. "Impacts of Upstream Building Width and Upwind Building Arrangements on Airflow and Pollutant Dispersion in a Street Canyon." Environmental Forensics 15, no. 1 (January 2, 2014): 25–36. http://dx.doi.org/10.1080/15275922.2013.872714.

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46

Huang, Yuan-Dong, Xuan Xu, Ze-Yu Liu, Ji-Tong Deng, and Chang-Nyung Kim. "Impacts of shape and height of building roof on airflow and pollutant dispersion inside an isolated street canyon." Environmental Forensics 17, no. 4 (October 2016): 361–79. http://dx.doi.org/10.1080/15275922.2016.1230912.

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47

Huang, Yuan-dong, Wen-rong He, and Chang-Nyung Kim. "Impacts of shape and height of upstream roof on airflow and pollutant dispersion inside an urban street canyon." Environmental Science and Pollution Research 22, no. 3 (August 30, 2014): 2117–37. http://dx.doi.org/10.1007/s11356-014-3422-6.

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48

Huang, Yuan-dong, Meng-zhen Li, Su-qi Ren, Meng-jie Wang, and Peng-yi Cui. "Impacts of tree-planting pattern and trunk height on the airflow and pollutant dispersion inside a street canyon." Building and Environment 165 (November 2019): 106385. http://dx.doi.org/10.1016/j.buildenv.2019.106385.

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HATAYA, Naoko, Yoshiki JUNIMURA, Tatsuaki IWATA, Akashi MOCHIDA, Hironori WATANABE, Hiroshi YOSHINO, and Kiyotaka SAKAIDA. "EFFECTS OF ROADSIDE TREES ON TURBULENT AIRFLOW, AIR POLLUTANT DIFFUSION AND PEDESTRIAN THERMAL COMFORT WITHIN STREET CANYONS : Field measurements of summer thermal environment and air quality in the central part of Sendai (Part 1)." Journal of Environmental Engineering (Transactions of AIJ) 72, no. 613 (2007): 95–102. http://dx.doi.org/10.3130/aije.72.95_1.

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50

Niachou, K., I. Livada, and M. Santamouris. "Experimental study of temperature and airflow distribution inside an urban street canyon during hot summer weather conditions—Part I: Air and surface temperatures." Building and Environment 43, no. 8 (August 2008): 1383–92. http://dx.doi.org/10.1016/j.buildenv.2007.01.039.

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