Flow and Dispersion Phenomena in a Simplified Urban Square

Abstract

The paper deals with wind conditions and air pollutant dispersion in urban squares. We focus on the phenomenological description of principal flow phenomena appearing in squares and on the understanding of basic transport mechanisms. For this purpose a simplified square with rectangular layout was investigated by means of wind tunnel tests applying sand erosion technique and tracer gas concentration measurements. The MISKAM CFD model was used to simulate flow and dispersion at various wind directions. The analysis of results allowed the identification of flow structures appearing in the square, the interaction of which is responsible for the inhomogeneous wind speed and concentration distribution in the square. Most importantly, separation zones of buildings located on the upstream side of the square cause low local wind speeds and strong vertical pollutant transport. Separation zones in front of the downstream building blocks induce higher local wind speeds and improve the removal of pollutants.