Abstract
In this study, we have developed a numerical model based on an open source Computational Fluid Dynamics (CFD) package OpenFOAM, in order to investigate the flow pattern and pollutant dispersion in urban street canyons with different geometry configurations. In the new model, the pollutant transport driven by airflow is modeled by the scalar transport equation coupling with the momentum equations for airflow, which are deduced from the Reynolds Averaged Navier-Stokes (RANS) equations. The turbulent flow calculation has been calibrated by various two-equation turbulence closure models to select a practical and efficient turbulence model to reasonably capture the flow pattern. Particularly, an appropriate value of the turbulent Schmidt number has been selected for the pollutant dispersion in urban street canyons, based upon previous studies and careful calibrations against experimental measurements. Eventually, the numerical model has been validated against different well-known laboratory experiments in regard to various aspect ratios (a relationship between the building height and the width of the street canyon), and different building roof shapes (flat, shed, gable and round). The comparisons between the numerical simulations and experimental measurements show a good agreement on the flow pattern and pollutant distribution. This indicates the ability of the new numerical model, which can be applied to investigate the wind flow and pollutant dispersion in urban street canyons.
Highlights
Pollution from industrial activities, vehicle exhaust, heating and cooling systems, etc. can cause fatal harms to humans in urban street canyons; the investigation of flow characteristics and pollution transports in urban street canyons is a vital task in the urban environment
We developed a numerical model based upon an open source Computational Fluid Dynamics (CFD) package
Before we can apply the model to investigate the effects of various geometry configurations, such as different roof shapes and aspect ratios, the model was carefully validated for different two-equation turbulence closure models and various Schmidt numbers
Summary
Pollution from industrial activities, vehicle exhaust, heating and cooling systems, etc. can cause fatal harms to humans in urban street canyons; the investigation of flow characteristics and pollution transports in urban street canyons is a vital task in the urban environment. The temporal steps have to be sufficiently small to resolve the period of the fastest fluctuations These calculations require a very strong capability of computer resources, and may exceed the available capacity of most powerful high performance computers in solving the three dimensional problems of wind flow and pollutant transport in urban street canyons with large Reynolds numbers. Designed as a numerical library of solvers for Partial Differential Equations, which can provide professional users an opportunity to build their own specific solvers, immerse them into the package Based on this advantage, we developed a new solver combing the wind flow calculation with a transport process together to facilitate the pollution transport simulation driven by the turbulent flows. A difference between the original and customized solvers is shown in Figure 1 below
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