Numerical simulations of pollutant dispersion in an idealized urban area, for different meteorological conditions

Abstract

In order to estimate the impacts of buildings on air pollution dispersion, numerical simulations are performed over an idealized urban area, modelled as regular rows of large rectangular obstacles. The simulations are evaluated with the results of the Mock Urban Setting Test (MUST), which is a near full-scale experiment conducted in Utah's West Desert area: it consists of releases of a neutral gas in a field of regularly spaced shipping containers. The numerical simulations are performed with the model Mercure_Saturne, which is a three-dimensional computational fluid dynamics code adapted to atmospheric flow and dispersion simulations. It resolves complex geometries and uses, in this study, a k-closure for the turbulence model. Sensitivity studies focus on how to prescribe the inflow conditions for turbulent kinetic energy. Furthermore, different sets of coefficients available in the literature for the k-closure model are tested. Twenty MUST trials with different meteorological conditions are simulated and detailed analyses are performed for both the dynamical variables and average concentration. Our results show overall good agreement according to statistical comparison parameters, with a fraction of predictions for average concentration within a factor of two of observations of 67.1%. The set of simulations offers several inflow wind directions and allows us to emphasize the impact of elongated buildings, which create a deflection of the plume centerline relative to the upstream wind direction.

Influence of urban morphology on air flow over building arrays

“…Building aspect ratios are expected to play a significant role in so-called 'topological dispersion' , Jerram et al 1995, Belcher 2005, where the presence of the obstacle (building) enhances the lateral dispersion of the plume. This effect is greatly enhanced for some wind directions when the building has a form other than the classic cuboid, as evidenced in the few studies involving such types of buildings (see, e.g., MacDonald, 1998b;Yee and Biltoft, 2004;Milliez and Carissimo, 2007).…”

Verification of Computational Fluid Dynamics Model Using Observation Data in Artificial Street Canyon

“…그러나 이를 위해서는 매우 작은 크기의 격 자가 요구되기 때문에 매우 긴 계산 시간을 필요로 한다 (Cheng et al, 2003;Yakhot et al, 2006). RANS 모델은 난류 종결 방법을 이용하여 아격자 규모의 난 류 효과를 모수화하기 방법을 사용하기 때문에, 비교 적 큰 격자 크기를 사용할 수 있는 장점이 있다 (Milliez and Carissimo, 2007;Santiago et al, 2007). (Fig.…”

Dispersion modeling of air pollutants in the atmosphere: a review

“…Despite its huge computational cost, LES has become a popular tool for planetary boundary layer case studies, and its results are often used as a verification dataset for other models [13,135]. CFD-based street canyon models are widely used to predict air quality in urban and industrial areas [59,[134][135][136][137][138][139]. However, several weaknesses were pointed out that made CFD results less reliable as the scale increased [132,133].…”