Computational Fluid Dynamical Modelling of Concentration Fluctuations in an Idealized Urban Area |
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| Authors: | Maya Milliez Bertrand Carissimo |
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| Institution: | (1) CEREA, Teaching and Research Center in Atmospheric Environment (ENPC/EDF R&D), 6-8 avenue Blaise Pascal, 77455 Champs-sur-Marne, France |
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| Abstract: | Turbulent mixing induces variability in concentration that is important in many applications, such as reactive plumes, risk
assessments or odour impact analyses (when the effects can have time scales on the order of a second). In urban canopies,
the variability may be modified by the presence of buildings. Our purpose is to study concentration fluctuation variance in
built-up areas using an Eulerian approach. We performed numerical simulations with the computational fluid dynamics model
Mercure_Saturne, which is a three-dimensional model adapted to atmospheric flow and pollutant dispersion. We use a k − ϵ turbulence closure and predict the concentration variance with a transport equation model. The model performance is evaluated
with the near-full scale experiment MUST (Mock Urban Setting Test), a field experiment conducted in Utah’s West Desert Test
Center. The modelled root-mean-square of the concentration fluctuations is compared to measurements for 20 of the MUST trials.
The model shows good agreement with the measurements, with the fraction of predictions within a factor of two of observations
of 60.1%, with better results for horizontal lines of detectors than for the detectors on vertical masts (with fractions of
predictions within a factor of two of observations of respectively 66.4% and 52.6%). The influence of different parameters
on the fluctuation variance is also studied and we show the importance of taking into account the stability of the stratification
when modelling the turbulent kinetic energy. |
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| Keywords: | Atmospheric pollutant dispersion Computational fluid dynamics modelling Concentration fluctuations Transport equation Urban canopy |
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