CFD Simulation of Dense Cloud Dispersion in Urban Areas

The formation of toxic heavy clouds as a result of sudden accidental releases from mobile containers, such as road tankers or railway tanks, may well occur inside urban areas. Due to the semi-confined nature of the dispersion site simplified models are unsuitable. As an alternative, Computational Fluid Dynamics (CFD) has the potential to provide realistic simulations even or geometrically complex scenarios (Scargiali et. al., 2003) since the heavy gas dispersion process is described by basic conservation equations with a reduced number of approximations. In the present work a commercial general purpose CFD code (CFX 4.4 by Ansys) is employed for the simulation of dense cloud dispersion in urban areas. In order to try a generalization of results, the computational domain is modelled as a simple network of straight roads with regularly·distributed blocks mimicking the buildings. Results are compared with each other in order to assess the influence of the building fractional area coverage and normalize height on the dispersion phenomenon