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Atmosphere
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Computational Fluid Dynamics Simulations of Urban Airflow
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Computational Fluid Dynamics Simulations of Urban Airflow

A special issue of Atmosphere (ISSN 2073-4433). This special issue belongs to the section "Atmospheric Techniques, Instruments, and Modeling".

Deadline for manuscript submissions: closed (15 January 2023) | Viewed by 14468

Special Issue Editors

Dr. Mohammadreza Shirzadi

E-Mail Website
Guest Editor
PhD, Fine Particle Technology Laboratory, Graduate School of Advanced Science and Engineering Hiroshima University, 1-4-1, Kagamiyama, Higashi Hiroshima, Japan
Interests: computational fluid dynamics; multi-scale simulation; turbulence modeling; particle dynamics; industrial aerodynamic
Dr. Naoki Ikegaya

E-Mail Website
Guest Editor
Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Fukuoka, Japan
Interests: architectural environmental engineering; wind engineering; computational fluid dynamics; urban climate
Prof. Dr. Tsubasa Okaze

E-Mail Website
Guest Editor
Department of Architecture and Building Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8502, Japan
Interests: wind engineering; snow engineering; urban environmental engineering; computational fluid dynamics

Special Issue Information

Dear Colleagues,

One important part of scientific studies related to the atmosphere is the understanding of the physics and mechanisms of urban airflows, because it is essential for analyzing some key challenging issues in urban areas such as human health, pollution dispersion, indoor/outdoor comfort, heat islands, etc. Among the different assessment methods for urban airflows, including field measurements and reduced-scale wind tunnels and laboratory measurements, numerical simulation based on computational fluid dynamics (CFD) has shown great potential for scientific research and practical engineering applications.

Due to the increasing applications of CFD simulations in urban airflow studies, the open-access journal Atmosphere is hosting a Special Issue on CFD simulations of urban airflows aiming to represent the most recent findings of urban-related airflow studies based on CFD simulations. The purpose of this Special Issue is not only to highlight the capabilities of CFD simulations in urban airflow studies but also to discuss the limitations and the future possibilities of CFD modeling in this field. In addition, experimental studies are also welcome for demonstrating CFD datasets used for discussion of CFD accuracy. This Special Issue covers a wide range of CFD applications and aims to publish high-quality original research and review papers. In particular, the following topics are welcome:

  • Multi-scale/multi-physics CFD modeling of transport phenomena of urban airflows ;
  • Large-scale simulation of urban airflows using high-resolution CFD models;
  • Pollution dispersion/droplet dynamics in urban areas;
  • Indoor/outdoor air quality;
  • Infection risk modeling under urban microclimate interactions;
  • Urban heat islands;
  • Pedestrian wind environments;
  • Extreme gust and weak winds;
  • Urban ventilation;
  • Indoor and outdoor airflow interactions;
  • Turbulence model development for urban airflow;
  • Hybrid turbulence models for urban airflow modeling.

The emphasis of this Special Issue is to provide a forums in which to discuss the accuracy and uncertainty of CFD results as well as the validation of the numerical codes used in CFD simulations. Hence, authors are encouraged to provide details of these important aspects of CFD simulations that can enhance our understanding of the limitations, capabilities, and future possibilities of CFD simulations for urban studies.

Dr. Mohammadreza Shirzadi
Dr. Naoki Ikegaya
Prof. Dr. Tsubasa Okaze
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Atmosphere is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • computational fluid dynamics
  • numerical simulation
  • urban airflows
  • turbulence modeling
  • multi-scale simulation
  • microclimate
  • urban heat island
  • hybrid turbulence model
  • air quality and infection risk

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Published Papers (6 papers)

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Research

19 pages, 8236 KiB  
Article
Heterogenous Canopy in a Lagrangian-Stochastic Dispersion Model for Particulate Matter from Multiple Sources over the Haifa Bay Area
by Eyal Fattal, Hadas David-Saroussi, Omri Buchman, Eran Tas and Ziv Klausner
Atmosphere 2023, 14(1), 144; https://doi.org/10.3390/atmos14010144 - 9 Jan 2023
Cited by 4 | Viewed by 1714
Abstract
The Haifa Bay area (HBA) is a major metropolitan area in Israel, which consists of high volume transportation routes, major industrial complexes, and the largest international seaport in Israel. These, which lie relatively near densely populated residential areas, result in a multitude of [...] Read more.
The Haifa Bay area (HBA) is a major metropolitan area in Israel, which consists of high volume transportation routes, major industrial complexes, and the largest international seaport in Israel. These, which lie relatively near densely populated residential areas, result in a multitude of air pollution sources, many of whose emissions are in the form of particulate matter (PM). Previous studies have associated exposure to such PM with adverse health effects. This potential consequence serves as the motivation for this study whose aim is to provide a realistic and detailed three-dimensional concentration field of PM, originating simultaneously from multiple sources. The IIBR in-house Lagrangian stochastic pollutant dispersion model (LSM) is suitable for this endeavor, as it describes the dispersion of a scalar by solving the velocity fluctuations in high Reynolds number flows. Moreover, the LSM was validated in urban field experiments, including in the HBA. However, due to the fact that the multiple urban sources reside within the canopy layer, it was necessary to integrate into the LSM a realistic canopy layer model that depicts the actual effect of the roughness elements’ drag on the flow and turbulent exchange of the urban morphology. This was achieved by an approach which treats the canopy as patches of porous media. The LSM was used to calculate the three-dimensional fields of PM10 and PM2.5 concentrations during the typical conditions of the two workday rush-hour periods. These were compared to three air quality monitoring stations located downstream of the PM sources in the HBA. The LSM predictions for PM2.5 satisfy all acceptance criteria. Regarding the PM10 predictions, the LSM results comply with three out of four acceptance criteria. The analysis of the calculated concentration fields has shown that the PM concentrations up to 105 m AGL exhibit a spatial pattern similar to the ground level. However, it decreases by a factor of two at 45 m AGL, while, at 105 m, the concentration values are close to the background concentrations. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics Simulations of Urban Airflow)
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19 pages, 3933 KiB  
Article
Identification of Wind-Induced Particle Resuspension in Urban Environment Using CFD Modelling
by Jakub Linda, Jiří Pospíšil and Klaudia Köbölová
Atmosphere 2023, 14(1), 57; https://doi.org/10.3390/atmos14010057 - 28 Dec 2022
Cited by 5 | Viewed by 2030
Abstract
Air pollution caused by particulate matter (PM) is a current problem in many cities. With the introduction of strict emission limits and electric cars, lower particle production is expected in the future. However, there are sources of particles that cannot be easily influenced. [...] Read more.
Air pollution caused by particulate matter (PM) is a current problem in many cities. With the introduction of strict emission limits and electric cars, lower particle production is expected in the future. However, there are sources of particles that cannot be easily influenced. These include resuspension, where particles deposited on surfaces re-enter the air, causing pollution multiple times. Resuspension can account for up to 18% of the total emissions in some cases. The present paper focuses on the use of the computational fluid dynamics (CFD) tools to describe the flow in a street canyon where resuspension by wind occurs. Based on the calculated flow, a resuspension model is applied to see where resuspension occurs and how far the particles can travel. The shear stresses on the surfaces and the character of the flow field in the boundary layer are evaluated. Different building configurations and flow parameters are tested using a simple 2D model. The model makes it possible to see in which parts of the street canyon resuspension can occur. It shows that the particles leave the street canyon only from the surfaces where the conditions are suitable for resuspension. These particles then enter the mainstream. However, most of the particles stay in the canyon, which can cause resuspension to pollute the air repeatedly. This effect can have a severe impact on human health. The total dispersion of particles in the urban environment is evaluated. The results may be useful for cities that clean the streets, as it is clear which areas will benefit most from the cleaning. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics Simulations of Urban Airflow)
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20 pages, 4830 KiB  
Article
High Resolution Modelling of Traffic Emissions Using the Large Eddy Simulation Code Fluidity
by Huw Woodward, Anna K. Schroeder, Clemence M. A. Le Cornec, Marc E. J. Stettler, Helen ApSimon, Alan Robins, Christopher Pain and Paul F. Linden
Atmosphere 2022, 13(8), 1203; https://doi.org/10.3390/atmos13081203 - 30 Jul 2022
Cited by 3 | Viewed by 1729
Abstract
The large eddy simulation (LES) code Fluidity was used to simulate the dispersion of NOx traffic emissions along a road in London. The traffic emissions were represented by moving volume sources, one for each vehicle, with time-varying emission rates. Traffic modelling software [...] Read more.
The large eddy simulation (LES) code Fluidity was used to simulate the dispersion of NOx traffic emissions along a road in London. The traffic emissions were represented by moving volume sources, one for each vehicle, with time-varying emission rates. Traffic modelling software was used to generate the vehicle movement, while an instantaneous emissions model was used to calculate the NOx emissions at 1 s intervals. The traffic emissions were also modelled as a constant volume source along the length of the road for comparison. A validation of Fluidity against wind tunnel measurements is presented before a qualitative comparison of the LES concentrations with measured roadside concentrations. Fluidity showed an acceptable comparison with the wind tunnel data for velocities and turbulence intensities. The in-canyon tracer concentrations were found to be significantly different between the wind tunnel and Fluidity. This difference was explained by the very high sensitivity of the in-canyon tracer concentrations to the precise release location. Despite this, the comparison showed that Fluidity was able to provide a realistic representation of roadside concentration variations at high temporal resolution, which is not achieved when traffic emissions are modelled as a constant volume source or by Gaussian plume models. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics Simulations of Urban Airflow)
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24 pages, 12025 KiB  
Article
Large-Eddy Simulation of Airflow and Pollutant Dispersion in a Model Street Canyon Intersection of Dhaka City
by Sheikh Hassan, Umma Habiba Akter, Preetom Nag, Md. Mamun Molla, Amirul Khan and Md Farhad Hasan
Atmosphere 2022, 13(7), 1028; https://doi.org/10.3390/atmos13071028 - 28 Jun 2022
Cited by 14 | Viewed by 3013
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics Simulations of Urban Airflow)
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24 pages, 4695 KiB  
Article
Performance Evaluation of the RANS Models in Predicting the Pollutant Concentration Field within a Compact Urban Setting: Effects of the Source Location and Turbulent Schmidt Number
by Mohammad Reza Kavian Nezhad, Carlos F. Lange and Brian A. Fleck
Atmosphere 2022, 13(7), 1013; https://doi.org/10.3390/atmos13071013 - 23 Jun 2022
Cited by 5 | Viewed by 2118
Abstract
Computational Fluid Dynamics (CFD) is used to accurately model and predict the dispersion of a passive scalar in the atmospheric wind flow field within an urban setting. The Mock Urban Setting Tests (MUST) experiment was recreated in this work to test and evaluate [...] Read more.
Computational Fluid Dynamics (CFD) is used to accurately model and predict the dispersion of a passive scalar in the atmospheric wind flow field within an urban setting. The Mock Urban Setting Tests (MUST) experiment was recreated in this work to test and evaluate various modeling settings and to form a framework for reliable representation of dispersion flow in compact urban geometries. Four case studies with distinct source locations and configurations are modeled using Reynolds-Averaged Navier–Stokes (RANS) equations with ANSYS CFX. The performance of three widely suggested closure models of standard k−ε, RNG k−ε, and SST k−ω is assessed by calculating and interpreting the statistical performance metrics with a specific emphasis on the effects of the source locations. This work demonstrates that the overprediction of the turbulent kinetic energy by the standard k−ε counteracts the general underpredictions by RANS in geometries with building complexes. As a result, the superiority of the standard k−ε in predicting the scalar concentration field over the two other closures in all four cases is observed, with SST k−ω showing the most discrepancies with the field measurements. Additionally, a sensitivity study is also conducted to find the optimum turbulent Schmidt number (Sct) using two approaches of the constant and locally variable values. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics Simulations of Urban Airflow)
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18 pages, 8007 KiB  
Article
Evaluation of the Wind Environment around Multiple Urban Canyons Using Numerical Modeling
by Minu Son, Jeong-In Lee, Jae-Jin Kim, Soo-Jin Park, Daegi Kim and Do-Yong Kim
Atmosphere 2022, 13(5), 834; https://doi.org/10.3390/atmos13050834 - 19 May 2022
Cited by 2 | Viewed by 2412
Abstract
This study aimed to evaluate the wind environment in step-up and step-down urban canyons through a computational numerical experiment using the computational fluid dynamics (CFD) model. Spatial structural conditions were considered according to the location of high-rise buildings, and the changing wind patterns [...] Read more.
This study aimed to evaluate the wind environment in step-up and step-down urban canyons through a computational numerical experiment using the computational fluid dynamics (CFD) model. Spatial structural conditions were considered according to the location of high-rise buildings, and the changing wind patterns inside canyons were compared and analyzed by varying the building heights. Under the step-up to step-down condition, wind velocity inside the canyon weakened, a vertical vortex formed, and vertical air flow separated; additionally, in shallow and deep canyons, wind velocity and detailed flow differed slightly according to each additional condition. For the step-down to step-up condition, the building located in the center appeared to be isolated, and a general wind environment phenomenon consistent with the step-up and step-down structures was observed. However, depending on the isolated area, an additional roof-top canyon was formed, and the wind field in the canyon was found to affect the wind velocity and detailed flow in other canyons. The wind velocity components of the inflow and outflow winds into the canyon differed based on the step-up to step-down or step-down to step-up conditions, and according to the conditions in the first and second canyons. Furthermore, the vertical wind velocity components were greatly affected by the step-up and step-down structures. Accordingly, the height and structural location of the building could affect various phenomena, such as the separation of vortices and air currents inside the canyon, and a variable wind environment was formed according to a series of conditions for the building. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics Simulations of Urban Airflow)
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