ارزیابی عملکرد تهویه طبیعی با استفاده از مدل سازی فرم های شهری در بافت قدیم کلان شهر شیراز (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
بیان مسئله: با توسعه شهرها در عصر حاضر، مشکلات و پدیده هایی مانند جزایر گرمایی شهری، کاهش کیفیت هوا در بافت شهرها و عدم آسایش حرارتی در فضاهای عمومی شهرها چالش های عمیقی برای زیست شهروندان به وجود آورده اند. از طرف دیگر، در مطالعات معماری و شهری، کمتر مطالعه ای به ویژگی های فرم و شکل شهرها به منظور افزایش تهویه طبیعی در خیابان ها به عنوان فضاهای عمومی پرتردد در شهرها پرداخته است.هدف: این مطالعه با در نظر گرفتن تراکم و ارتفاع ساختمان ها در جداره یک خیابان شهری در بافت میانی کلان شهر شیراز، به ارزیابی مدل های ممکن در جهت افزایش تهویه طبیعی و درنتیجه کاهش گرمای محیط شهری و خروج بهتر آلاینده ها می پردازد.روش: روش انجام تحقیق از نوع کمی و از ابزار شبیه سازی محاسبات دینامیک سیالات برای مدل سازی جریان باد در محیط شهری استفاده شده است. بر این اساس نرم افزار FloEFD پس از اعتبارسنجی در این مطالعه قرار گرفت و پس از مدل سازی در محیط داخلی نرم افزار سه مؤلفه دما، فشار، سرعت جریان هوا و الگوی حرکتی جریان هوا بین مدل های ایجادشده موردبررسی قرار گرفت.یافته ها: یافته های مطالعه نشان می دهد مدل دوم که با افزایش تدریجی تعداد طبقات از جداره خیابان به سمت بافت در نظر گرفته شده است، توزیع هوا و سرعت مناسب جریان هوای مناسب تری نسبت به دیگر مدل های بررسی شده، داشته است. بر اساس نتایج عددی، سرعت جریان در این مدل تا 2/2 متر بر ثانیه افزایش داشته است.نتیجه گیری: در ارتباط با الگوی جریان هوا در مدل بهینه، جریان با شدت سرعت بیشتر و در تمامی نقاط بافت و خیابان موردمطالعه پراکنده شده است که این امر منجر می تواند به خروج بهتر گرما و آلاینده ها از محیط خیابان منجر شود. مدل دوم یعنی افزایش تدریجی ارتفاع ساختمان ها از لبه خیابان به سمت بافت بهترین سرعت جریان هوا به منظور تهویه طبیعی در خیابان فراهم می کند. همچنین الگوی حرکتی جریان در مدل دوم نسبت به دو مدل دیگر بهتر می تواند در توزیع جریان در نقاط مختلف خیابان عمل کند به طوری که توزیع دما و فشار متوازن در نقاط مختلف منجر به افزایش کارایی تهویه در محیط خیابان گردیده است.Evaluation of Natural Ventilation Performance Using Modeling of Urban Forms in the Old Context of Shiraz Metropolis
Introduction: The rapid urbanization since the Industrial Revolution has significantly altered cities, replacing natural surfaces with buildings, which impacts near-ground meteorological conditions like temperature, wind, and humidity. This leads to pollution, urban heat islands, and higher energy demands. Urban ventilation, influenced by factors like urban design, can help mitigate these effects.Studies on urban ventilation focus on macro, meso, and micro scales, with micro-scale studies using CFD simulations and wind tunnel experiments to optimize airflow. In Shiraz, rapid development, destruction of greenery, and heavy traffic have made it the eighth most polluted city in Iran. This study examines the historical fabric of District 8 in Shiraz, focusing on building arrangement and its effect on airflow and pollution. The goal is to use CFD simulations and data to improve natural ventilation and address pollution, enhancing Shiraz’s environment and quality of life in the face of climate change and urban growth.Methodology: The historical fabric of Shiraz, covering an area of 395.90 hectares, houses a population of around 92,173 people, with a density of 199 people per hectare. It is located between Karim Khan Zand and Lotfali Khan Zand streets. According to cultural heritage regulations, building heights in this area should range from one to two stories; however, along the periphery of the fabric, particularly the ring surrounding it (between Qa'ani, Timuri, Saadi, and Tawhid streets), there are three- to four-story buildings, and even taller structures. In main streets such as Karim Khan Zand, Lotfali Khan Zand, and Ahmadi, there is also a trend towards taller buildings.For this research, an area of District 8 along Lotfali Khan Zand Street was selected due to its minimal changes and preservation of the original form and structure of buildings. However, within the old fabric, newly constructed buildings with varying heights have altered the original arrangement. This study uses a quantitative approach and simulation with the FloEFD software to assess airflow within the studied fabric. After library research and reviewing the existing site conditions, the initial model was created using the software . To evaluate the impact of research components on airflow and pollutant reduction on Lotfali Khan Zand Street, two additional models were created. In the first model, building heights increase from the street edge into the fabric, while in the second model, the height decreases as it approaches the street. The software uses the Navier-Stokes equations and the k-ε model to calculate wind direction and intensity, with advanced meshing techniques to improve computational accuracy. For simplification and to fit within system limitations, details like green spaces and intricate building features were excluded from the modeling.The models in FloEFD were designed using SolidWorks, integrated within the software. These models were based on existing maps and field data from buildings on Lotfali Khan Zand Street and the layers behind them. Irregularities in building heights cause air to be trapped in the fabric, hindering proper air exchange and ventilation. For fluid calculations, the computational domain was considered as a rectangular box around the model. Additionally, environmental data such as temperature, wind speed, and air pressure were input based on average meteorological data.This study evaluates three components: building heights (A), street widths (B), and urban block arrangements (C), by altering these parameters in the simulation software and analyzing their impacts on airflow, permeability, pressure, and temperature. Three different models were examined:Model 1: The existing situation with buildings scattered at irregular heights ranging from one to three stories.Model 2: Units with lower density and fewer stories (one to two stories) at the street edge, with taller buildings (three to six stories) behind them.Model 3: Taller buildings (three to six stories) at the street edge, with shorter units (one to two stories) behind them.In the simulation, parameters such as primary and secondary wind speeds, static and dynamic pressures, and the temperature of the incoming airflow were chosen as the objectives for analysis. All models were pre-meshed with advanced techniques before simulation.Results: Simulation model analysis: The simulation findings were reviewed using horizontal (Cut Plot), vertical (Surface Plot), and airflow trajectory (Flow Trajectories) distributions. The three models studied were:Existing fabric model: Irregular building dispersion.Lower floors at the street edge and higher floors behind: Relatively improved ventilation.Higher floors at the street edge and lower floors behind: The most effective model for proper airflow.Conclusion: In the studied area, creating diverse block arrangements and considering various building heights can enhance urban ventilation. The arrangement of buildings—lower heights near the street edge and taller ones behind—can improve wind flow, optimize natural ventilation, and significantly reduce pollutant levels. These findings offer valuable insights for urban planning, especially for areas in Shiraz, to help mitigate pollution and enhance the quality of life for residents.
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