Joint PDF Modelling of Turbulent Flow and Dispersion in an Urban Street Canyon |
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| Authors: | J Bakosi P Franzese Z Boybeyi |
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| Institution: | (1) Los Alamos National Laboratory, Los Alamos, NM 87545, USA;(2) College of Science, George Mason University, Fairfax, VA 22030, USA |
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| Abstract: | The joint probability density function (PDF) of turbulent velocity and concentration of a passive scalar in an urban street
canyon is computed using a newly developed particle-in-cell Monte Carlo method. Compared to moment closures, the PDF methodology
provides the full one-point one-time PDF of the underlying fields containing all higher moments and correlations. The small-scale
mixing of the scalar released from a concentrated source at the street level is modelled by the interaction by exchange with
the conditional mean (IECM) model, with a micro-mixing time scale designed for geometrically complex settings. The boundary
layer along no-slip walls (building sides and tops) is fully resolved using an elliptic relaxation technique, which captures
the high anisotropy and inhomogeneity of the Reynolds stress tensor in these regions. A less computationally intensive technique
based on wall functions to represent the boundary layers and its effect on the solution are also explored. The calculated
statistics are compared to experimental data and large-eddy simulation. The present work can be considered as the first example
of computation of the full joint PDF of velocity and a transported passive scalar in an urban setting. The methodology proves
successful in providing high level statistical information on the turbulence and pollutant concentration fields in complex
urban scenarios. |
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| Keywords: | Langevin equation Monte-Carlo method Probability density function method Scalar dispersion Urban-scale turbulence |
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