شبيه سازي عددي پخش آلودگي در محيط خيابان

چكيده انگليسي :

Numerical Simulation for Dispersion of Air Pollution in Canyon Street Reza Babaei r babaee@me iut ac ir February 5 2011 Department of Mechanical engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Ahmad sedaghat sedaghat@cc iut ac ir Abstract Keeping the air quality acceptable has become an important task for decision makers as well as for non governmental organizations Particulate and gaseous emissions of pollutants from auto exhausts are responsible for rising discomfort increasing airway diseases decreasing productivity and the deterioration of artistic and cultural patrimony in urban centers Air quality limit values which are aimed at protecting public health are frequently exceeded especially in streets and other urban hotspots Within these streets pedestrians cyclists drivers and residents are likely to be exposed to pollutant concentrations exceeding current air quality standards Increased emissions and reduced natural ventilation cause accumulation of high pollution levels in urban street canyons Nutural ventilation in urban streets canyons is restricted because the bulk of flow does not enter inside and pollutions are trapped in the lower region In this project a two dimensional time independent flow model has been applied to the evaluation of pollutant dispersion properties in urban street canyons The processes by which pollutants emitted at street level are transported and diffused from street canyons are examined to determine the exchange rates of pollutants between street canyons and the upper air under variable flow conditions and different aspect ratios the ratio of the building height to the street width the wind flow and pollutant dispersion phenomena in different street canyons for different aspect ratios and height ratios and different velocities are studied and is simulated by Fluent With rapid development in computer hardware and numerical algorithms computational fluid dynamics CFD techniques are widely utilized to study the wind field and pollutant transport in urban street canyons Model equations developed from statistical analysis of field data generalize to the three dimensional air quality aspects of the particular urban roadway section studied and to those displaying similar characteristics and weather conditions The standard k epsilon and RNG k epsilon turbulence closure schemes are for solving the most commonly used Reynolds averaged Navier Stokes RANS equations The studies were conducted on the effects of street canyon aspect ratio building configuration ambient wind direction inflow turbulence intensities Turbulence model of RNG k epsilon with species transport without reaction was developed to investigate the flow field and pollutant dispersion inside street canyons The domain of numerical solution is discretised by Gambit software Aspect ratios of varied from 1 to 4 were employed in the study These street canyon aspect ratios covered a range of basic flow regimes including skimming flow wake interference flow and isolated roughness flow that was mentioned by Oke and Nakamura 1988 A pollutant line source located in the middle of the street was used to simulate vehicular emissions Power law was implemented for velocity inlet profil In low velocities results presented agree with the generally obtained threshold values for different flow regimes mentioned by oke and Nakamura 1988 But increase in velocity has smeared the flow regimes boundry In higher velocities pollutant dispersion is mainly promoted by better mixing inside the canyons Results is showed that the flow regime and pollution dispersion pattern is depend on both the canyon geometry and velocity inlet the objective this work is to demonstrate the various flow regimes in different canyon geometries and velocities inlet Wind tunnel modeling technique has been extensively used to investigate air pollution dispersion phenomena in the urban street canyon s The simulation results we

بابايي اسبوئي، رضا

شبيه سازي عددي پخش آلودگي در محيط خيابان

مجراي خيابان شهري , نسبت منظري خيابان , مدل توربولانس 4-K , مدل انتقال گونه ها