Document Type : Original Article
Authors
1
Ph.D. Candidate, Department of Architecture, Faculty of Art and Architecture, Shiraz Branch, Islamic Azad University, Shiraz, Iran
2
Associate professor, Department of Architecture, School of Architecture, College of Fine Arts, University of Tehran, Tehran, Iran
3
Associate professor, Department of Architecture, Faculty of Art and Architecture, Shiraz Branch, Islamic Azad University, Shiraz, Iran
Abstract
Air pollution has negative effects on people's health and the economy of countries. Air pollutants can be categorized into three groups, including particulate matter, Volatile Organic Compounds, and microorganisms. Particulate Matter is the most important air pollutant, especially in the big cities of the world. Particulate Matter is classified into three groups according to their size, including large (with a diameter between 2.5-10 microns), fine particles (with a diameter between 0.1-2.5 microns), and ultrafine particles (with a diameter between 0.1 microns and less). The wind flow behavior is an important factor in determining the particle concentrations in urban spaces. On the other hand, the urban geometry affects the wind velocity and consequently the outdoor air quality. Therefore, the proper design of urban context can be beneficial in reducing the effects of air pollution. However, less attention has been paid to this influence in the guidelines. The outdoor air quality is monitored by measuring particle concentrations and atmospheric parameters and the effect of the context on the dispersion of pollutants is not taken into account. Besides, the number of urban air quality monitoring locations is few. The concentration of some pollutants (including Particulate Matter) is determined in these monitoring stations. Therefore, they do not provide sufficient and comprehensive data to control urban air pollution. The Computational fluid dynamics analysis can be used to evaluate the wind flow behavior and pollutant dispersion and as a result, predict the urban air quality. This research aimed to study the behavior of wind flow and PMs around buildings at different heights, street canyons, and building sides in a part of the residential context of Asalouyeh City. Accordingly, the effect of wind flow behavior on particle dispersion was investigated. Besides, the effect of height, and street and building orientation on the wind flow behavior and PM dispersion were investigated. A part of the residential context in the high-density area was selected as the case study. The wind velocity, pressure, turbulence, flow pathlines, PM velocity and concentration, and particle tracks were defined at ground level, different heights, streets aligned with the wind direction and perpendicular to it, and windward and leeward side faces using CFD simulation in Ansys-Fluent 2021. An area of 129276 square meters and a length of 378 meters were simulated as a wind tunnel. Findings showed that the buildings act as a windbreak and cause wind velocity to decrease significantly in the leeward side face. With the increase in height and as a result, increase in the velocity and turbulence of the wind, the length of the wind shadow decreased in the leeward side face. At higher altitudes, as the wind joined the free stream, the flow turbulence was reduced. Accumulation of massless particles was observed in the leeward side face in the wind shadow area. The highest and lowest PM concentrations were observed in the windwards and the wind shadow, respectively. Therefore, the PM concentrations follow the wind velocity. Findings can be useful in studying outdoor air quality, as well as evaluating thermal comfort and choosing materials according to wind loads in urban spaces.
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