نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشجوی کارشناسی ارشد، گروه شهرسازی، واحد نجف آباد، دانشگاه آزاد اسلامی، نجف آباد، ایران

2 استادیار، گروه شهرسازی، واحد نجف آباد، دانشگاه آزاد اسلامی، نجف آباد، ایران

چکیده

همزمان با رشد سریع شهرنشینی و مطرح‌ شدن مباحث مربوط به گرمایش زمین، جزایر گرمایی و تغییرات اقلیمی، جریان باد به‌ عنوان یکی از تأثیرگذارترین عوامل در مناسب­سازی طراحی فضاهای باز شهری مرتبط با آسایش حرارتی مطرح‌ شده، به ‌طوری‌ که سرعت و نحوه حرکت باد برآسایش حرارتی انسان تأثیرگذار است. در نیم‌قرن اخیر، براثر تغییر شکل سازمان فضایی بافت­های شهری، الگوی جدیدی رواج یافته که با نیازهای اقلیمی شهر اصفهان مطابقت ندارد. با توجه به این که ضوابط شهرسازی و ساختمانی، سهم عمده­ای در شکل­دهی به بافت­های شهری و تنظیم شرایط آسایش حرارتی به همراه دارد، پژوهش حاضر سعی دارد که با در نظر گرفتن محوریت‌های موجود در سند یادشده، میزان تأثیرگذاری ضوابط شهرسازی و ساختمانی(سطح اشغال، ارتفاع، تراکم، تعداد طبقات و عرض گذر) در بافت جدید شهر اصفهان بر جریان باد را مورد ارزیابی قرار دهد. با توجه به ماهیت کاربردی این تحقیق، روش مورداستفاده در آن توصیفی_تحلیلی است و برای یافته اندوزی از روش‌های اسنادی و میدانی بهره جسته است. همچنین به ‌منظور تجزیه‌وتحلیل سناریوها­ی تعریف ‌شده، از مدل شبیه‌سازی پیچک‌های بزرگ استفاده گردیده است. در راستای دستیابی به اهداف پژوهش، مطالعه‌ حاضر در سه ‌گام متفاوت تعریف ‌شده، به‌ گونه‌ای که نخست با بررسی مبانی نظری مرتبط با آسایش حرارتی، شاخص‌های کالبدی تأثیرگذار استخراج گردیده سپس همپوشانی آنها با محورهای موجود در ضوابط شهرسازی و ساختمانی شهر اصفهان مورد بررسی قرار گرفته است. در گام پایانی نیز با تعریف سناریوهای محتمل براساس الگوهای مسکونی ردیفی غالب بافت جدید شهر اصفهان، شبیه‌سازی پیچک‌های بزرگ صورت پذیرفته است. تحلیل شبیه‌سازی سناریوهای مختلف مؤید این موضوع است که از میان شاخص‌های استخراج‌ شده، سطح اشغال تأثیرگذارترین پارامتر بر روی جریان هوای محدوده است و تراکم معیار مناسبی برای سنجش این موضوع به شمار نمی­آید. همچنین اثر تغییر سطح اشغال بر سرعت باد بیشتر از اثر تغییر ارتفاع ساختمان‌هاست. در ارتباط با عرض گذر، نوساناتی که سناریوهای مختلف بر نسبت سرعت در حیاط‌ها ایجاد می‌کنند، بسیار محدودتر از نوسانات ایجاد شده در کوچه‌ها و خیابان است. به طوری که در ابتدا و انتهای کوچه‌ها، سرعت بیشتر از بخش‌های میانی است. از این رو در سناریوهایی که ارتفاع ساختمان بین 10.5 تا 14 متر تعریف شده، شرایط مطلوبی به منظور تهویه هوای شهری و کاهش آلودگی هوا فراهم است.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Evaluating the effects of Urban planning Principles on Outdoor Thermal comfort with an emphasis on Wind flow through Large Eddy Simulation: the case study of row housing pattern in Isfahan

نویسندگان [English]

  • Samaneh Heidari 1
  • Golnaz Mortezaei 2

1 Master Student, Department Of Urban Planning, Najafabad Branch, Islamic Azad University, Najafabad, Iran

2 Assistant Professor, Department Of Urban Planning, Najafabad Branch, Islamic Azad University, Najafabad, Iran

چکیده [English]

Highlights
The effect of some urban planning criteria on wind flow has been evaluated through a new method called Large Eddy Simulation.
Simulation analysis of different scenarios confirmed that among density, lot coverage ratio and altitude, lot coverage ratio is the most influential parameter on the air flow.
Examining the effect of only density factor on air flow cant lead us to good conclusions about how wind flows.
Fluctuations in different scenarios indicate that at the beginning and the end of the streets, the wind speed is faster than the middle.
 
Introduction 
Along with the rapid growth of urbanization and the issues of global warming, environmental pollution, the urban heat island, and climate change, thermal comfort has turned into one of the most influential factors in adaptation of the design of climate-related urban open spaces. Today, the high temperature in human-made areas has doubled the need to consider thermal comfort in open urban spaces. Thus, wind flow is regarded as one of the most influential climatic parameters, where the speed and movement of the wind affect human thermal comfort.
Theoretical Framework 
The traditional architecture and urban planning applied in the city of Isfahan, Iran makes up a unique local examples of Iranian architecture, which has been forced to provide many climatic solutions due to the hot, dry climatic conditions. In the past half century, however, a new pattern has emerged in building massing models as a result of the changes in the forms of housing space into different types of dense multi-family housing. Due to their extension and pervasiveness in Iran, these terraced housing models can be considered as part of the new urban planning trend in the country. Because of the increase in density and building surface ratios, however, part of the self-purification capacity of the urban environment has vanished, and certain construction models have become common in different climates with unfavorable conditions. As many cities are looking for solutions to apply compression and massing as far as possible, the drawbacks of the previous model have become more prominent, and a need has arisen for solutions to the current situation, in order to reduce the probable adverse consequences in the future. The consequences that may arise from this trend include a lack of thermal comfort in open urban spaces, an increase in heat exchange between indoor and outdoor spaces, and a rise in energy loss as a result. A master plan and an auxiliary force to urban designers and planners, the Booklet for Urban Planning and Building Regulations of the city of Isfahan always seeks to modify this pattern in the current situation. In the present study, therefore, attempts are made to consider the existing directions in the booklet and examine the role of physical factors in wind flow and its extent in the new fabric of the city.
Methodology
Due to its applied nature, this research uses the descriptive-analytical method and documentary and field techniques for data collection. Moreover, the large eddy simulation (LES) model is used for analysis of the defined scenarios.
Results and Discussion. In order to achieve its purposes, the present study was designed in three phases. Thus, the effective physical indicators were first extracted through examination of the theoretical foundations related to thermal comfort, and their overlap with the directions in the Booklet for Urban Planning and Building Regulations of Isfahan was then studied. In the final step, LES was conducted through definition of the probable scenarios based on terrace housing models of the dominant line in the new fabric of Isfahan. An analysis of the simulation of different scenarios confirmed that an increase in lot coverage ratio, among the extracted indicators, caused a sharp decrease in speed ratio, while an increase in building height led to a decrease in speed ratio, and density exhibited a different effect, which could be interpreted along with the other criteria.
Conclusion
Based on the results, lot coverage ratio is the most effective parameter on air flow in the area, and density is not a suitable criterion for such measurement. Moreover, the effect of a change in lot coverage ratio on wind speed is greater than that of a change in building height. As for passage width, the fluctuations in speed ratio on narrow streets are far more limited than those on wide alleys and streets. Thus, speed is higher at the beginning and end of an alley than at the middle. In scenarios where building height is set between 10.5 and 14 meters, therefore, proper conditions are provided for urban air quality, ventilation, and air pollution.

کلیدواژه‌ها [English]

  • Architecture and Urban Planning Principles
  • Thermal comfort
  • Wind Flow
  • Large Eddy Simulation (LES)
  • Isfahan Terrace Housing Models
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