Computational Simulation of Turbulent Flows and Pollution Dispersion in Complex Urban Canyons

Detailed computational simulations of turbulent flows and pollution dispersion in city canyons have been carried out using the computational fluid dynamics package CFX-5, which is capable of using unstructured meshes and a variety of turbulence closure schemes. The simulations have been done for city canyons with simple to complex structures. As a validation of CFX-5, a roof garden test is conducted. A comparison of the numerical results with observed data indicates that the simulations of turbulence and pollution dispersion are reasonable. The computational fluid dynamic approach is further applied to the canyon geometry typical to Hong Kong, using the area in the vicinity of Bank of China Tower as an example. It is shown that the characteristic of the circulation in city canyon is related not only to atmospheric conditions but also to the scaling parameters determined by the geometry of urban structure. It is shown that useful results for understanding of the mechanisms of pollution dispersion in urban atmospheric boundary layers can be obtained via a large number of simulations. Key word index: Turbulence, city canyon, dispersion .