Effect of tissue density on speed of the wind flow in part of Tehran Elahiyeh

Wind on land is an important factor for the exchange of heat and transportation of microscopy and non-microscopic particles from one point to another. So it has important role in reducing pollutants entering the urban spaces. The physical elements of the urban tissue, such as orientation of the streets and distribution of high-rise buildings have important role in secondary patterning the wind flow. Because of Tehran Elahiyeh is one from the densest of urban tissues in north of Tehran city, so wind features was evaluated in this part because of showing this tissue role in weather pollutants increasing. For this purpose, hourly data of wind velocity and orientation of North Tehran meteorological station (Aghdasiyeh) in period 1988-2009 was used. Wind speed changes in the Elahiyeh area tissue were evaluated in heights of 2 and 10 meter because of different features of station around tissue. The wind speed of threshold was calculated to remove the heat island effect, then the predominant wind directions and theirs frequency was evaluated. Accordingly, the district tissue was simulated using the Arc Scene of ArcGIS software. Also, the effects of high-rise buildings on wind flow patterns were studied for samples buildings by the Reynolds Law. Results are indicator important decrease of wind velocity in Elahiyeh area tissue in compared to station tissue due to high-rise buildings in this tissue. Annual and seasonal frequency of wind velocity indicated that more of % 60 from winds frequency is calm and dominate wind directions are west north-east south and north-south. Simulation of area tissue showed that the highest tissues are exactly in direct of dominate wind. Theses tissues prevent from flow of wind that consequently increase pollution and Thermal Island at area. Amount of threshold wind in three of statistical periods indicated that threshold wind velocity is low so it prevents from weather suitable ventilation in area. Calculation of Reynolds number for samples buildings in area showed that Reynolds number is more of 200000 that is indicator random whirlwind in cannon trail area.