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

Detailed computational simulations of turbulent flows and pollution dispersion in citycanyons have been carried out using the computational fluid dynamics package CFX-5, which iscapable of using unstructured meshes and a variety of turbulence closure schemes. The simulationshave been done for city canyons with simple to complex structures. As a validation of CFX-5, a roofgarden test is conducted. A comparison of the numerical results with observed data indicates that thesimulations of turbulence and pollution dispersion are reasonable. The computational fluid dynamicapproach is further applied to the canyon geometry typical to Hong Kong, using the area in thevicinity of Bank of China Tower as an example. It is shown that the characteristic of the circulationin city canyon is related not only to atmospheric conditions but also to the scaling parametersdetermined by the geometry of urban structure. It is shown that useful results for understanding ofthe mechanisms of pollution dispersion in urban atmospheric boundary layers can be obtained via alarge number of simulations.