Large-eddy simulation for flow and dispersion in urban streets

Abstract

Large-eddy simulations (LES) with our recently developed inflow approach (Xie &
Castro, 2008a) have been used for flow and dispersion within a genuine city area -
the DAPPLE site, located at the intersection of Marylebone Rd and Gloucester Pl
in Central London. Numerical results up to second-order statistics are reported for
a computational domain of 1.2km (streamwise) x 0.8km (lateral) x 0.2km (in full
scale), with a resolution down to approximately one meter in space and one second
in time. They are in reasonable agreement with the experimental data. Such a comprehensive
urban geometry is often, as here, composed of staggered, aligned, square
arrays of blocks with non-uniform height and non-uniform base, street canyons and
intersections. Both the integrative and local effect of flow and dispersion to these
geometrical patterns were investigated. For example, it was found that the peaks
of spatially averaged urms, vrms, wrms and < u0w0 > occurred neither at the mean
height nor at the maximum height, but at the height of large and tall buildings. It
was also found that the mean and fluctuating concentrations in the near-source field
is highly dependent on the source location and the local geometry pattern, whereas
in the far field (e.g. >0.1km) they are not. In summary, it is demonstrated that
full-scale resolution of around one meter is sufficient to yield accurate prediction of
the flow and mean dispersion characteristics and to provide reasonable estimation
of concentration fluctuations

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Identifiers

ORCID for Zheng-Tong Xie: orcid.org/0000-0002-8119-7532

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