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Добірка наукової літератури з теми "Airflow in street canyons"

Автор: Grafiati

Опубліковано: 13 квітня 2024

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Статті в журналах з теми "Airflow in street canyons"

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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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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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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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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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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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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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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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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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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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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Більше джерел

Дисертації з теми "Airflow in street canyons"

Glover, N. "Investigating the impact of trees on airflow within street canyons through the use of CFD and field measurements." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1472912/.

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The local wind climate within the urban environment plays a key role in the removal of heat and pollutants from pedestrian occupied areas as well as having an impact on pedestrian comfort and safety. One component of the urban landscape which is often neglected in the consideration of airflow is tree planting which can constitute a major component of the built environment. The aim of this research was therefore to gain a greater understanding into the effect of tree planting on airflow within street canyons and investigate the use of CFD modelling in predicting such effects. This aim was accomplished through the use of CFD modelling and field measurements of tree-lined and non tree-lined streets. Tree canopies were represented within the CFD model by porous subdomains containing momentum and turbulence sinks. This simple representation was found to offer favourable comparison against field measurements and would therefore provide a simple and effective method for the inclusion of trees within CFD models of the urban environment. Results of both the CFD models and field measurements found reduced wind speeds at pedestrian level as well as a significant reduction in vertical wind speeds at roof level within the tree-lined street. There was also seen to be a significant reduction in turbulence levels within the street containing trees. Based on these findings it can be concluded that trees are likely to be a useful aid in urban design helping to reduce high wind speeds and turbulence thus creating outdoor environments which are comfortable and safe for pedestrian use. However the results also indicate that the addition of trees to streets can reduce the amount of air exchange at roof top level that occurs and thus may lead to a reduction in natural ventilation and potential build-up of pollutants within pedestrian occupied areas.

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Maison, Alice. "Modélisation des impacts des arbres sur la qualité de l’air de l’échelle de la rue à la ville." Electronic Thesis or Diss., Marne-la-vallée, ENPC, 2023. http://www.theses.fr/2023ENPC0034.

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Les arbres apportent de nombreux services écosystémiques en ville, ils permettent de diminuer certaines conséquences de l’urbanisation comme l’îlot de chaleur urbain et le ruissellement de l’eau. Leur effet thermo-radiatif améliore le confort thermique. Les arbres peuvent également impacter la qualité de l’air en ville via différents processus. Le dépôt de polluants gazeux et particulaires sur les feuilles des arbres peut contribuer à la diminution des concentrations. Cependant, l’effet aérodynamique des arbres modifie l’écoulement dans les rues canyons et limite la dispersion des polluants émis dans la rue. Par ailleurs, les arbres émettent des composés organiques volatils biogéniques (COVb) qui peuvent participer à la formation d’O3 et d’aérosols organiques secondaires. Les émissions de COVb varient selon l’espèce d’arbre, et sont influencées par des facteurs climatiques (température, rayonnement) mais aussi par le statut hydrique des arbres. Cette thèse a pour objectif de quantifier les impacts de ces différents processus sur la qualité de l’air en ville. Des simulations numériques sont réalisées sur la ville de Paris pendant l’été 2022 avec la chaîne de modèles CHIMERE/MUNICH afin de quantifier l’impact des arbres sur les concentrations atmosphériques de polluants à l’échelle locale et régionale. Les concentrations simulées sont comparées à des mesures. Les arbres urbains ne sont généralement pas pris en compte dans les modèles de qualité l’air, aussi bien à l’échelle régionale qu’à l’échelle de la rue. Pour intégrer les émissions de COVb dans le modèle régional CHIMERE, un inventaire est réalisé à partir de la base de données des arbres de la ville de Paris. Une méthode est développée afin d’estimer les caractéristiques des arbres qui sont utilisées en données d’entrée des différents modèles (surface de feuille, biomasse sèche, taille de la couronne, etc.). En moyenne sur les mois de juin et juillet 2022 à Paris, les émissions biogéniques locales des arbres induisent une augmentation de 1,0% d’O3, 4,6% de PM1 organiques et 0,6% de PM2.5. Les émissions biogéniques des arbres urbains augmentent très fortement les concentrations d’isoprène et de monoterpènes. Par comparaison aux mesures, les concentrations de terpènes ont tendance à être sous-estimées, compte tenu des incertitudes liées aux facteurs d’émissions et à la part de végétation manquante dans l’inventaire. Les émissions de terpène de la végétation urbaine et suburbaine influencent fortement la formation de particules organiques, il est donc important de bien les caractériser dans les modèles de qualité de l’air. Les différents effets des arbres urbains sur la qualité de l’air à l’échelle de la rue sont ensuite ajoutés dans le modèle de réseau de rue MUNICH. L’effet aérodynamique des arbres dans les rues est paramétré à partir de simulations de mécanique des fluides. Il induit une augmentation des concentrations des composés émis dans la rue. Cette augmentation peut atteindre +37% pour le NO2 dans les rues avec une surface de feuilles importante et un trafic élevé. Le dépôt sur les feuilles des arbres est calculé à partir d’une approche résistive adaptée à l’échelle de l’arbre urbain dans la rue. Cependant, son impact sur les concentrations reste limité sur les gaz et particules étudiés (< -3%).Pour finir, un couplage entre les modèles TEB (modèle de surface urbaine), SPAC (modèle de continuum sol-plante-atmosphère) et MUNICH a été mis en place. Ce couplage permet de mieux représenter les impacts des hétérogénéités du micro-climat urbain et de l’effet thermo-radiatif des arbres sur les concentrations de gaz et de particules. L’effet de ce micro-climat et du stress hydrique des arbres sur les émissions de COVb est aussi pris en compte afin d’affiner le calcul des émissions
Trees provide numerous ecosystem services in cities, helping to reduce some of the consequences of urbanization, such as the urban heat island and water run-off. Their thermo-radiative effect improves thermal comfort.Trees can also have an impact on urban air quality through various processes. The deposition of gaseous and particulate pollutants on tree leaves can help to reduce concentrations. However, the aerodynamic effect of trees modifies the airflow in street canyons and limits the dispersion of pollutants emitted in the street. Trees also emit biogenic volatile organic compounds (BVOCs), which can contribute to the formation of O3 and secondary organic aerosols. BVOC emissions vary depending on the tree species, and are influenced by climatic factors (temperature, radiation) and by the tree water status.The objective of this thesis is to quantify the impacts of these different processes on urban air quality. Numerical simulations are performed over the city of Paris during summer 2022 using the CHIMERE/MUNICH model chain in order to quantify the impact of trees on atmospheric concentrations of pollutants at the local and regional scales. The simulated concentrations are compared to measurements.Urban trees are not generally taken into account in air quality models, either at regional or street level. In order to integrate BVOC emissions into the CHIMERE regional model, an inventory is developed using the tree database of the city of Paris. A method is set up to estimate the characteristics of the trees, which are used as input data for the various models (leaf area, dry biomass, crown size, etc.). On average over the months of June and July 2022 in Paris, local biogenic emissions from trees lead to an increase of 1.0% in O3, 4.6% in organic PM1 and 0.6% in PM2.5. Biogenic emissions from urban trees strongly increase concentrations of isoprene and monoterpenes. Compared with measurements, terpene concentrations tend to be underestimated, given the uncertainties associated with emission factors and the missing part of the vegetation in the inventory. Terpene emissions from urban and suburban vegetation greatly influence the formation of organic particles, it is therefore important to characterize them properly in air quality models.The various effects of urban trees on air quality at street level are then added into the MUNICH street network model. The aerodynamic effect of street trees is parameterized using computational fluid dynamics simulations. It leads to an increase in the concentrations of compounds emitted into the street. This increase can reach +37% for NO2 in streets with a large leaf surface and high traffic. Deposition on tree leaves is computed using a resistive approach adapted to the scale of the tree in the street. However, its impact on concentrations remains limited for the gases and particles studied (< -3%).Finally, a coupling between the TEB (urban surface model), SPAC (soil-plant-atmosphere continuum model) and MUNICH models is developed. This coupling provides a better representation of the impacts of the urban micro-climate heterogeneities and of the thermo-radiative effect of trees on gas and particle concentrations. The effects of the micro-climate and of the tree water stress on BVOC emissions are also taken into account in order to refine the calculation of emissions

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Huang, Pong-Lai. "Modelling of air quality in street canyons /." View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?AMCE%202003%20HUANG.

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Yunkai, Yang. "Numerical study on flow and pollutant dispersion inside street canyons." Licentiate thesis, KTH, Installationsteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-118327.

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Анотація:

This thesis analyzes the characteristics of flow pattern and vehicle-emitted pollutant dispersion in roughness surface layer. In an urban environment, wind flow and transported-pollutant source interfere strongly with buildings and other roughness elements on the surface ground, which results in complex characteristics of flow pattern and pollutant dispersion in 3D circumstances. The present study intends to simplify the research domain and investigate the fundamental modeling problems that exist in the field. The current physical research topic is restricted to 2D street canyon in equilibrium conditions. The study is motivated by the fact that characteristics of flow pattern and pollutant distribution inside street canyons are important for public health. The research has applied the computational fluid dynamics (CFD) methodology. To date, insights have typically focused on idealized street canyons without strictly limited boundary conditions and turbulence models. Those approaches face challenges related to their applicability to real urban scenarios or the reliability of prediction results. The thesis examines the influence of grid density, turbulence models and turbulent Schmidt number on pollutant distribution at windward and leeward surfaces of street canyon. Since numerical results usually are validated with wind-tunnel measurement data, the results between full-size model and wind-tunnel model are compared in order to test the Reynolds number effect. The lack of measurement data means that the morphometric method is used to generate upcoming wind profile, including the mean vertical velocity and turbulence parameters. The thesis also analyzes the potential errors brought by the method (Scenario A). Based on the evaluated numerical model, the thesis continues to study the impacts of surrounding buildings and geometry of street canyon on flow and pollutant distribution inside street canyons. The effect of wind on pollutant distribution inside street canyons was also investigated (Scenario A). Furthermore, the influence of roof shape and configuration of street canyon on characteristics of flow and pollutant distribution is also systematically studied, with the results shown in scenario B. The main conclusions of the thesis are that the uncertainty of numerical results derives from different aspects. Wind profile in the inlet profile generated by morphometric method brings major error to the simulation results. Current turbulence models cannot compromise the simulation results between flow field and pollutant distribution field. Ignored small-scale obstacles also need to be handled carefully. Numerical results revealed that flow and pollutant distribution inside street canyons are mainly dominated by the geometry of the street canyon itself. Medium-spaced surrounding buildings are also better able to transport pollutant out of the street canyon. Through systematic analysis, roof shape is proven to have a significant effect on flow and pollutant distribution inside a street canyon. The major impact is altered turbulence intensity depth and strength of shear layer inside the street canyon, which is important for pollutant removal process out of the street canyon. In the future, advanced turbulence models accompanied by small-obstacle effect models need to be developed in order to reliably simulate flow and pollutant dispersion simultaneously. Based on the advanced turbulence model, simulation of flow and pollutant dispersion in a complex 3D environment is essential in the next steps for the purpose of engineering application. Accurate vertical wind profile provided for inlet profile is another interesting direction for further development. Keywords: Flow; Pollutant dispersion; CFD; Street canyon; Reliability

QC 20130215

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Stachitas, Tucker Flagg. "Evaluation of 3-D radiant heat transfer in street canyons." [Gainesville, Fla.] : University of Florida, 2009. http://purl.fcla.edu/fcla/etd/UFE0041302.

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Wong, Ching-chi, and 黃精治. "Flow and pollutant dispersion over idealized urban street canyons using large-eddy simulation." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/206698.

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Flows and pollutant dispersion over flat rural terrain have been investigated for decades. However, our understanding of their behaviours over urban areas is rather limited. Most cases have either focused on street level or in the roughness sub-layer (RSL) of urban boundary layer (UBL). Whereas, only a handful of studies have looked into the coupling between street-level and UBL-core dynamics, and their effects on pollutant dispersion. In this thesis, computational fluid dynamics (CFD) is employed to examine the flows and pollutant transport in and over urban roughness. Idealised two-dimensional (2D) street canyons are used as the basic units fabricating hypothetical urban surfaces. A ground-level passive and chemically inert pollutant source is applied to simulate the flows and pollutant dispersion over rough surfaces in isothermal condition. Large-eddy simulation (LES) with the one-equation subgrid-scale model is used to solve explicitly the broad range of scales in turbulent flows. Arrays of idealized street canyons of both uniform and non-uniform building height are used to formulate a unified theory for the flows and pollutant dispersion over urban areas of different morphology. The geometry of roughness elements is controlled by the building-height-to-street-width (aspect) ratio (0.083 ≤ AR ≤ 2) and/or the building height variability (BHV = 0.2, 0.4 and 0.6), in which the characteristic regimes of skimming flow, wake-interference and isolated roughness are covered. A detailed analysis on the roof-level turbulence structure reveals parcels of low-speed air masses in the streamwise flows and narrow high-speed down-drafts in the urban canopy layer, signifying the momentum entrainment into the street canyons. The decelerating streamwise flows in turn initiate up-drafts carrying pollutants away from the street canyons, illustrating the basic pollutant removal mechanism in 2D street canyons. Turbulent transport processes, in the form of ejection and sweep, are the key events governing the exchanges of air and pollutant of street canyon. Air exchange rate (ACH) along the roof level is dominated by turbulent transport, in particular over narrow street canyons. The LES results show that both the turbulence level and ACH increase with increasing aerodynamic resistance defined in term of the Fanning friction factor. At the same AR, BHV greatly increases the friction factor and the ACH in dense built areas (AR ≤ 0.25). The turbulence intensity is peaked on the windward side of street canyons that does not overlap with the maximum velocity gradient near the leeward building corners, suggesting the importance of background turbulence in street-level ventilation. Over the building roughness, pollutant plume dispersion after the ground-level area source in cross flows resumes the self-similar Gaussian shape in the vertical direction in which the vertical plume coverage is proportional to the square root of downwind distance in the streamwise direction. Moreover, the vertical dispersion coefficient is proportional to the one-fourth power of friction factor over idealised street canyons. Conclusively, friction factor can be used to parametrise ventilation and pollutant dispersion over urban areas.
published_or_final_version
Mechanical Engineering
Doctoral
Doctor of Philosophy

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Hall, Terianne C. "Predicting velocities and turbulent exchange in isolated street canyons and at a neighborhood scale." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61867.

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Анотація:

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 127-130).
Urban planners need a fast, simple model to assess the impact of early design phase iterations of neighborhood layout on the microclimate. Specifically, this model should be able to predict the expected urban heat island intensity and the locations in neighborhood layouts that are prone to pollutant retention. Current models are inadequate for this purpose because they use computationally intensive techniques to solve for flow through a neighborhood and often require a strong technical background for effective use of the models. In this thesis, we use analytical equations and empirical relationships to calculate the expected wind speeds in isolated, idealized street canyons. We demonstrate that flow in street canyons is driven by momentum exchange with the air above. We discuss the importance of flow separation and turbulent exchange between the urban canopy layer and the urban boundary layer for removing heat and pollutants from street canyons. Next, we introduce a method to parameterize this exchange and extend this work to more realistic street canyons and idealized neighborhoods. We evaluate this work using computational fluid dynamics and comparison to experimental results and models from the literature. We examine cases where the flow is influenced by buoyancy effects and assess the applicability of our work in these situations. Finally, we address how this work could be further developed into generalized planning guidelines and incorporated into a comprehensive model for urban planners.
by Terianne Catherine Hall.
S.M.

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Barbano, Francesco <1991&gt. "Characterization of turbulent exchange processes in real urban street canyons with and without vegetation." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amsdottorato.unibo.it/9452/1/barbano_francesco_tesi.pdf.

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Recent studies on turbulent exchange processes between the urban canopy layer and the atmosphere above have focused primarily on mechanical effects and less so on thermal ones, mostly by means of laboratory and numerical investigations and rarely in the real environment. More recently, these studies have been adopted to investigate city breathability, urban comfort and citizen health, with the aim to find new mitigation or adaptation solutions to air pollution and urban heat island, to enhance the citizen wellness. To investigate the small-scale processes characterizing vegetative and non-vegetative urban canopies, two field campaigns have been carried out within the city of Bologna, Italy. New mechanical and thermal time scales, and their ratios (rates), associated with inertial and thermal flow circulations, have been derived to this scope. In the non-vegetated canopy, mechanical time scales are found to describe fast exchanges at the rooftop and slow within the canopy, while thermal ones to describe fast mixing in the whole canopy. Faster processes are found in the vegetative canopy, with rapidly mixed mechanical time scales and varying thermal ones. The exchange rates are found to identify favorable mixing conditions in the 50−75% of the investigated period, but extreme disadvantageous events can totally suppress the exchanges. The exchange rates are also found to drive the pollutant removal from vegetated and non-vegetated canopies, with an efficacy which depends on the in-canyon circulation. The impacts of real trees in a real neighborhood of the city is tackled with a simplified fluid-dynamics model, where mean flow and turbulence are studied with different vegetation cofigurations, topological and morphological characteristics. Vegetation is found to increase both blocking and channeling effects on the mean flow and to modify the production/dissipation rate of turbulence, depending on the wind direction and topology. Nevertheless, buildings maintain a predominant impact on the atmospheric flows.

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Rusticali, Valeria. "Confronto tra distribuzioni dimensionali di particelle misurate in due street canyons della città di Bologna." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16780/.

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Il particolato atmosferico è uno degli inquinanti atmosferici principali in quanto esercita effetti importanti su clima, tempo meteorologico, visibilità, salute umana, ambiente e beni culturali. Nonostante i numerosi studi, la conoscenza dei processi fisici che lo governano risulta ancora limitata. L'obiettivo della presente tesi è stato quello di analizzare le distribuzioni dimensionali di particelle di aerosol raccolte tramite due contatori ottici di particelle nel periodo Gennaio-Febbraio 2018 in due diverse aree urbane (street canyons) di Bologna, al fine di confrontarne l'andamento temporale e di analizzare l'importanza dei processi di rimozione dall'atmosfera. Lo studio si colloca all'interno del progetto H2020 `iSCAPE' (Improving the Smart Control of Air Pollution in Europe", GA n. 689954), avente come oggetto il controllo della qualità dell'aria tramite lo sviluppo di tecniche innovative di controllo sostenibile e passivo. Dopo aver introdotto i concetti generali, si passa a descrivere l'area di studio ed infine i dati raccolti. Questi ultimi sono stati analizzati sviluppando appositi codici MatLab per la visualizzazione grafica, nonchè per effettuare calcoli sulle distribuzioni ottenute. I risultati mostrano che entrambi i siti sono caratterizzati da fluttuazioni rapide del numero di particelle, con andamenti medi simili, soprattutto per quanto riguarda le particelle più piccole. Il confronto tra i due siti in varie condizioni meteorologiche (nebbia, cielo sereno, pioggia e neve) ha messo in evidenza i valori particolarmente elevati nelle giornate di nebbia e l'efficacia della rimozione umida tramite precipitazioni, soprattutto di quelle nevose, nella diminuzione delle concentrazioni di particelle di aerosol.

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Polito, Martina. "Mean flow and turbulent exchange characteristics in real urban street canyons: the Lazzaretto case study." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.

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In the context of the European iSCAPE project (Improving the Smart Control of Air Pollution in Europe) an experiment was set up in order to test photocatalytic coatings effectiveness in reducing the concentration of pollutants. Further analysis on various aspects of the urban environment have been possible thanks to the experiment. The measurements collected during the experimental field campaign have been used to study the differences in the atmospheric phenomena due to the different morphology of two street canyons. Data in time periods characterized by non-synoptic conditions have been selected and then compared. The first part of the study is dedicated to the characterization of the mean flow. Subsequently, turbulent fluxes have been studied for both canyons with the Eddy Covariance method, in order to appreciate the different behaviour of the two canyons. In the end, the data collected have been elaborated with the Quadrant Analysis. This latest study has made possible to compare the results obtained by the measurements in a real urban canopy layer with the results obtained in a controlled environment and in a vegetated canopy layer. The study has examined the intensity of sweep and ejection effects in an urban canopy layer. The results show that in both canyons sweep effects prevail for the downwind case. Instead, for an upwind flow the dominant effects are those of ejection. For parallel wind directions the two canyons behave differently, due to their different morphology. Furthermore, the intensity of both effects is not as strong as in the perpendicular cases. The behaviour of the fluctuations of CO2 and H2O concentration with respect to the temperature fluctuations has been compared to the results obtained in a vegetated canopy layer. The analysis has shown that in the downwind and parallel cases the trends are in agreement with the ones obtained in the vegetated environment. For an upwind flow, however, the expected trends are not found.

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Книги з теми "Airflow in street canyons"

Kalsoom, Nazia. Study of the process of pollution dispersion within street canyons by CFD methods. 1999.

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Engine Airflow: A Practical Guide to Airflow Theory, Parts Testing, Flow Bench Testing and Analyzing Data to Increase Performance for Any Street or Racing Engine. Penguin Publishing Group, 2011.

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Частини книг з теми "Airflow in street canyons"

Louka, P., G. Vachon, J. F. Sini, P. G. Mestayer, and J. M. Rosant. "Thermal Effects on the Airflow in a Street Canyon — Nantes’99 Experimental Results and Model Simulations." In Urban Air Quality — Recent Advances, 351–64. Dordrecht: Springer Netherlands, 2002. http://dx.doi.org/10.1007/978-94-010-0312-4_25.

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Meroney, Robert N., Stillianos Rafailidis, and Michel Pavageau. "Dispersion in Idealized Urban Street Canyons." In Air Pollution Modeling and Its Application XI, 451–58. Boston, MA: Springer US, 1996. http://dx.doi.org/10.1007/978-1-4615-5841-5_48.

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Ming, Tingzhen, Chong Peng, Tingrui Gong, and Zhengtong Li. "Heat Transfer and Pollutant Dispersion in Street Canyons." In Pollutant Dispersion in Built Environment, 17–56. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-3821-1_2.

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Fuka, Vladimír, and Josef Brechler. "Large Eddy Simulation of Coherent Structures in Street Canyons." In Air Pollution Modeling and its Application XXII, 709–15. Dordrecht: Springer Netherlands, 2013. http://dx.doi.org/10.1007/978-94-007-5577-2_120.

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Mensink, C., N. Lewyckyj, and L. Janssen. "A New Concept for Air Quality Modelling in Street Canyons." In Urban Air Quality — Recent Advances, 339–49. Dordrecht: Springer Netherlands, 2002. http://dx.doi.org/10.1007/978-94-010-0312-4_24.

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Kim, Hyoung-June, Joon-Yong Yoon, and Nak-Won Sung. "Experimental Modeling of Polluted Air Dispersion in Street Canyons of Metropolitan." In Fluid Machinery and Fluid Mechanics, 167–72. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-540-89749-1_22.

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Crowther, John M., and Abdel Galeil A. A. Hassan. "Three-Dimensional Numerical Simulation of Air Pollutant Dispersion in Street Canyons." In Urban Air Quality — Recent Advances, 279–95. Dordrecht: Springer Netherlands, 2002. http://dx.doi.org/10.1007/978-94-010-0312-4_20.

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Pavlidis, Dimitrios, Elsa Aristodemou, Jefferson L. M. A. Gomes, Christopher C. Pain, and Helen ApSimon. "Numerical Simulation of Air Flows in Street Canyons Using Mesh-Adaptive LES." In Direct and Large-Eddy Simulation VII, 485–89. Dordrecht: Springer Netherlands, 2010. http://dx.doi.org/10.1007/978-90-481-3652-0_72.

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Schwarze, Tobias, and Martin Lauer. "Geometry Estimation of Urban Street Canyons Using Stereo Vision from Egocentric View." In Informatics in Control, Automation and Robotics, 279–92. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-10891-9_16.

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Hoshiko, Tomomi, Fumiyuki Nakajima, Tassanee Prueksasit, and Kazuo Yamamoto. "Health Risk of Exposure to Vehicular Emissions in Wind-Stagnant Street Canyons." In Springer Geography, 59–95. Dordrecht: Springer Netherlands, 2011. http://dx.doi.org/10.1007/978-94-007-2771-7_4.

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Тези доповідей конференцій з теми "Airflow in street canyons"

Du, T. Z., Chun-Ho Liu, and Y. B. Zhao. "Large-Eddy Simulation of Reactive Pollutant Dispersion Over Street Canyons of Different Aspect Ratios." In ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting collocated with the ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/fedsm2014-21252.

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Анотація:

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.

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Najeeb, Doa M., and Susan A. Hassan. "The Effect of Urban Fabric Type on the Street Canyon Airflow." In 2019 4th Scientific International Conference Najaf (SICN). IEEE, 2019. http://dx.doi.org/10.1109/sicn47020.2019.9019360.

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Huang, Jianxiang, Anqi Zhang, and Rong Peng. "Evaluating the Multizone Model for Street Canyon Airflow in High Density Cities." In 2015 Building Simulation Conference. IBPSA, 2015. http://dx.doi.org/10.26868/25222708.2015.2978.

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O'Driscoll, Stephen, John G. Murphy, and Niall J. Smith. "Computed tomography of air pollutants in street canyons." In OPTO Ireland, edited by Thomas J. Glynn. SPIE, 2003. http://dx.doi.org/10.1117/12.463985.

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Patania, F., A. Gagliano, F. Nocera, and A. Galesi. "Air quality in street canyons: a case study." In AIR POLLUTION 2009. Southampton, UK: WIT Press, 2009. http://dx.doi.org/10.2495/air090011.

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"Wall Estimation from Stereo Vision in Urban Street Canyons." In 10th International Conference on Informatics in Control, Automation and Robotics. SciTePress - Science and and Technology Publications, 2013. http://dx.doi.org/10.5220/0004484600830090.

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Tang, SK, and K. E. Piippo. "Sound fields inside street canyons with inclined flanking building façades." In 161st Meeting Acoustical Society of America. Acoustical Society of America, 2011. http://dx.doi.org/10.1121/1.3624578.

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Suter, I., C. Maksimovic, and Maarten van Reeuwijk. "LES study of a mixed layer above urban street canyons." In THMT-15. Proceedings of the Eighth International Symposium On Turbulence Heat and Mass Transfer. Connecticut: Begellhouse, 2015. http://dx.doi.org/10.1615/ichmt.2015.thmt-15.1470.

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Pulvirenti, B., S. Di Sabatino, and R. Buccolieri. "Thermal effects on flow and pollutant dispersion within street canyons." In Turbulence, Heat and Mass Transfer 6. Proceedings of the Sixth International Symposium On Turbulence, Heat and Mass Transfer. Connecticut: Begellhouse, 2009. http://dx.doi.org/10.1615/ichmt.2009.turbulheatmasstransf.1550.

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Zhu, Sirui, and Lup Wai Chew. "Flows across 3D urban street canyons: Reynolds number independence revisited." In 2023 Building Simulation Conference. IBPSA, 2023. http://dx.doi.org/10.26868/25222708.2023.1526.

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