Optimal placement of buildings rows in residential areas to Reduce sand deposit of Sadobistrozeh wind in Sistan

The drought has caused a kind of wind that is called as Sadobistroze wind in Sistan. This wind has accumulated sand and gravel. Due to the severity of these winds and the volume of very fine particles of sand, it is very difficult to control their flow. Creating an appropriate urban form can help reduce these problems. wind erosion causes problems such as the influx of sand grains, which can lead to severe dust and air pollution, reduced public health, reduced immune system against diseases, children's asthma, threats of sensitive electronic power transfer systems, damage to agricultural land, rural settlements, roads and increaseaccidents. Sistan area with 15197 square kilometers is located latitude 31 ° 2 'north longitude and 61 ° 29' east longitude and 489 meters high in the north of Sistan and Baluchestan province and east of Iran. This area is bordered by the north and east with Afghanistan, the border with the Southern Khorasan province and the south with the city of Zahedan. The average number of sunspots per annum for more than 260 days of sunshine, the range of high temperature changes overnight, an average annual rainfall of 64 mm with inappropriate dispersion, high temperature and sunny hours Sistan is one of the windy areas in eastern Iran. In fact, the wind has three main characteristics: direction, speed and frequency. According to estimates of the number of days with storm and dust for a period of 10 years, the Sistan region has more than 1500 days, the highest proportion at the national level. Drought is a dominant phenomenon in the Sistan region, which has also had a profound negative impact not only on the biodiversity of the communities (plant-animal) but also on the physical environment of urban and rural residential areas. Although in Sistan (due to the presence of 120 days of winds and the existence of a soil susceptible to wind erosion in this area), erosion has already occurred in the past, but after drought, due to the provision of wind erosion conditions, Dust storms have been formed and reached their maximum intensity. In addition to the incorrect management of the drought in the area, it seems that problems such as inappropriate physical shape and inappropriate building patterns in accordance with the existing climatic conditions and the lack of planting of climate-friendly plants in the area seems to have increased the severity of these damages. The statistical data (wind speed and direction) is derived from the statistics of the synoptic meteorological station in Zabul. Subsequently, using computational fluid dynamics (CFD), using simulation to understand the behavior of the wind in urban form. Flow3D software is used for simulation. In this software, the k-standard model is selected, this model is mostly used to simulate the mean flow characteristics in turbulent flow conditions. Modeling was done using 3D drawing software. Boundary conditions and direction of flow and speed were determined. Due to the nature of the wind, the most important factor in controlling the flow of air on a city scale is space geometry. All spaces between buildings, both horizontal distances, the relationship of the building with its height, are the parameters that, when exposed to the wind, affect wind in terms of pressure distribution, average speed and etc. This paper focuses on modeling the airflow associated with natural disasters, Specially sandstorms. Article focus on the modeling of airflow related to natural disasters, such as sand accumulation, with urban form studies. The goal is to understand Which kind of urban form can speed up the flow of sand and prevent sand deposits in the building area (streets, alleys, open spaces). Urban design was studied through simulation of airflow using Flow 3D software. Initially, a flat surface was selected with an initial configuration for the model. Each time the flow of air was tested in different models. In this study, the relationship between urban wind speed and morphological parameters such as dimensions, building geometry and building density were investigated. By creating an appropriate geometric form of the buildings, this research is looking for solutions to reduce this accumulation. For this purpose, simulations were first performed to find the threshold velocity for sand particles, and it was concluded that the wind carries sand particles with a diameter of 50 microns at speeds greater than 2 to 4 m/s and Able to move them. So, to prevent sand accumulation, the wind speed should not be less than 2 m/s. Since sand is more near the surface of the earth and during the winds are not much off the ground due to heavy loads, the study of the airflow at the ground connection to the building was tested in various cases. According to the simulations performed in four urban models, it is observed that the highest proportion for achieving this goal is for buildings clinging together in a column with an urban length of 80 meters and building buildings in a row. It was concluded that the maximum urban length is 80 meters when the buildings are 1 meter above the ground. It was concluded that urban wind speed could help reduce the depression of sand, taking into account the proper values of these parameters. Therefore, the study of the shape of the city can be avoided by studying the urban form and choosing relationships such as placing a building at a distance of more than one meter from the ground, and an urban length of eighty meters, and connected buildings.