Modeling and simulation of dense cloud dispersion in urban areas by means of computational fluid dynamics

Abstract

a b s t r a c tThe formation of toxic heavy clouds as a result of sudden accidental releases from mobile containers, such as road tankers or railway tank cars, may occur inside urban areas so the problem arises of their consequences evaluation.Due to the semi-confined nature of the dispersion site simplified models may often be inappropriate.As an alternative, computational fluid dynamics (CFD) has the potential to provide realistic simulations even for geometrically complex scenarios 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. The simulation strategy proposed involves a stationary pre-release flow field simulation followed by a dynamic after-release flow and concentration field simulations.In order to try a generalization of results, the computational domain is modeled as a simple network of straight roads with regularly distributed blocks mimicking the buildings. Results show that the presence of buildings lower concentration maxima and enlarge the side spread of the cloud. Dispersion dynamics is also found to be strongly affected by the quantity of heavy-gas released.

Modeling the Airflow and Particle Dispersion in Street Canyons under Unsteady Thermal Environment with Sinusoidal Variation

“…A two-dimensional (2D) street canyon is a simplification of an actual urban geometry. Numerous studies have focused on the impact of building characteristics (such as building heights, the shape roof of building, and the density of the building group) on the diffusion of pollutants in idealized and modeling urban street canyons (Li et al, 2008;Huang et al, 2009;Li et al, 2010;Buccolieri et al, 2011;Scargiali et al, 2011;Hang et al, 2012;Addepalli and Pardyjak, 2013;Scungio, 2013;Huang et al, 2015). Scungio et al (2015a) have used the detached eddy simulation to study the turbulent flow in isolated street canyons of different aspect ratios.…”

Evaluating Dust Particle Transport Performance within Urban Street Canyons with Different Building Heights

“…Numerous researchers have focused on gaseous pollutant diffusion mechanisms and impact factors in ideal urban street canyons. Such impact factors include the height difference of buildings (Li et al, 2008a;Liu et al, 2011), street length and width (Hang et al, 2010), building density (Scargiali et al, 2011), and vegetation covering both sides of a street (Buccolieriet al, 2011). Several studies have focused on the influence factors of atmospheric pollutant diffusion within high-rise buildings Hang et al, 2012), and the findings of these studies have provided suggestions for city planning.…”

Study of the consequences of CO2 released from high-pressure pipelines

“…Computational Fluid Dynamics (CFD) techniques (Pontiggia et al, 2011;Scargiali et al, 2011;Sun et al, 2013;Tauseef et al, 2011) as well as analytical models (Hanna et al, 2003;Koornneef et al, 2010;Mazzoldi et al, 2011;Witlox et al, 2014) have all been widely applied. Compared to analytical models, CFD models use more detailed mathematical descriptions of the conservation principles, allowing the simulation of complex physical processes involving heat and mass transport in complicated computational domains (Scargiali et al, 2011;Sun et al, 2013).…”

“…Compared to analytical models, CFD models use more detailed mathematical descriptions of the conservation principles, allowing the simulation of complex physical processes involving heat and mass transport in complicated computational domains (Scargiali et al, 2011;Sun et al, 2013). These techniques have also been used for the simulation of CO 2 dispersion in recent years, along with the increasing applications of CCS.…”