Simulations of flow and dispersion around buildings

Physical and numerical simulations of the flow of atmospheric boundary laye rs around a number of building configurations, with pollutant releases from them, are described. Attention is concentrated on the issues that face the numerical modeler. Some inferences are drawn about the likely degree of un certainty in the use of computational fluid dynamics for such cases, by usi ng comparisons between the results obtained using different modeling choice s, and between these results and experimental data. It is demonstrated that decisions concerning the precise details of the turbulence model may often be less important than those concerning details of the specifications of b oundary conditions, the mesh construction, and the numerical schemes used t o solve the modeled equations. All these factors lead to inevitable uncerta inty about the quantitative accuracy of the calculation. The degree of unce rtainty depends greatly on the particular quantity of interest and may or m ay not be significant in a practical case.