A theory on the ventilation over hypothetical urban areas

Abstract

Urban roughness is one of the major factors affecting the flows and turbulence structures in the bottom of the atmospheric boundary layer (ABL). Whereas, our understanding of their relation is limited. In this paper, we attempt to examine the interaction among aerodynamic resistance (friction factor f), ventilation (air exchange rate ACH), and pollutant removal (pollutant removal rate PCH). Using the method of characteristic, analytical solution shows that the turbulent ventilation of a hypothetical urban area is directly proportional to the square root of friction factor (ACH? f1-2) regardless of the building geometry. Next, a series of computational fluid dynamics (CFD) sensitivity tests are performed to verify the theory. In addition to the commonly employed rectangular building mod...