wind flow

The purpose of this study is to investigate the role of vegetation in reducing nuisance wind speed on the Imam Street sidewalk. Imam Street is one of the main arteries in Tabriz, and the nuisance wind speed on its sidewalks disturbs the climate comfort for pedestrians, especially during the cold season.

A descriptive-analytical method is used in this study, and numerical simulations are performed using Dlubal RWIND 2.02 to evaluate the wind flow for the current condition and the proposed alternatives. In this context, the effect of vegetation height, spacing and arrangement (with tree bench) as independent variables on wind speed at pedestrian height as dependent variable was investigated. Spearman correlation test is used to evaluate the relationship between variables.

The studies have shown that trees with a height of 4 meters, distributed at a distance of 5 meters according to the pattern 1, can reduce the flow velocity on the pedestrian level by 52%.

The results show that the implementation of vegetation in appropriate spacing and pattern can significantly reduce wind speed. Placing tree benches on the sidewalk changes the airflow toward the street and reduces wind speed at the pedestrian level.

The development of wind energy in built environments is an old topic concerning sustainable urban residents, which has appealed to many researchers with the enhancement of new technologies and CFD techniques. This work seeks to study wind energy flows from the perspective of urban morphology.

In this research, the average numerical wind data have been collected from Isfahan meteorological station on the hottest day (21 July 2017) and the coldest day (20 January 2018) in the corresponding Iranian year for CFD studies on wind distribution in three urban configurations (traditional, gridded, and high-rise buildings) in local scale, which represents the overall structure of the morphological types in the city of Isfahan, Iran. The CFD have been numerically simulated and illustrated in the ENVI-met and DesignBuilder software to visualize the wind energy results obtained from each urban fabric.

The simulation results demonstrate the following. 1) The results for the traditional fabric based on the maximum value of wind speed and direction obtained from the software include 2.26 m/s on the hottest day and 2.68 on the coldest, lying in the category of gentle breeze based on the Beaufort scale. In terms of the comfort zone for activities such as sitting, standing, and walking, this does not cause problems for citizens, and the texture lies in the comfort zone. 2) The results involving the maximum value of wind speed and direction in the gridded fabric include 2.73 m/s on the hottest day and 2.80 on the coldest. For high-rise buildings, maximum wind speed is 4.26 m/s on the hottest day and 4.08 on the coldest. On the basis of the Beaufort scale, therefore, gridded and high-rise buildings lie in the medium breeze category. Moreover, the comfort zone for the sitting and standing activities in the gridded fabric is not a problem for citizens, but makes them feel a little uncomfortable with the walking activity. For high-rise buildings, however, there are many problems, and citizens feel plenty of discomfort based on the comfort range for the sitting, standing, and walking activities. 3) The results obtained from the study of the two pieces of software demonstrate that the power and accuracy of the numerical simulation made by ENVI-met is greater than that of DesignBuilder due to the focus and design of the former software in the field of urban planning, providing researchers with more accurate documentation.

The results of the analysis are as follows. 1) The traditional fabric has been designed entirely based on the principles of sustainability. The urban morphological parameters indicate the important role that urban architects and designers can play in optimal energy consumption with respect to wind flow by determining the morphological parametric criteria. 2) The overall analyses of the geometry of the two new fabrics (gridded and high-rise buildings) demonstrate that modern urban planning is in less accordance with the natural environment, including climatic conditions and indigenous culture. 3) The large differences between the three fabrics in terms of the different characteristics of urban morphology and the different effects of wind energy flow indicate the significant effect of urban morphology on potential wind flows, showing that the urban morphological indicators are significantly correlated with wind flow. 4) The results can be used as a practical guide for evaluation of the effects of urban wind flows and their interaction with urban morphology. The methods proposed in this study can be used as maximal analyses made for practical measures taken to reduce the negative effects of wind flow for urban management in Isfahan. Future extensions of this study, which is currently under investigation, will be aimed at a comprehensive examination of all climatic factors affecting urban morphology and, finally, achievement of an optimal, sustainable model for Isfahan and all climates in Iran along with the factors examined in this research.

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.

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.

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.

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.

The microclimate of urban open spaces is influenced by several factors such as urban morphology and geometry, urban density, vegetation, water level and surface characteristics. As more than a quarter of the urban areas are usually covered by streets, designing urban streets plays an important role in creating the urban climate. Among the influential and observable climatic elements in the thermal comfort of the streets, we can mention the wind flow.
The main goal of this study is to measure thermal comfort in the study area and to investigate the factors affecting the creation of thermal comfort with emphasis on wind flow, and for this purpose, strategies and solutions which are appropriate and applicable are presented in the area.
In this article, a part of Ferdowsi Street, between Ferdowsi Square and the intersection of Jomhuri Eslami, has been selected as a case study. Essential data were collected by field harvest in three days of June 1398 and modeled using ENVI MET software. In the results, we can see the effect of street geometry and vegetation on providing thermal comfort to pedestrians.