Spatial Variability of Flow Statistics within Regular Building Arrays |
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Authors: | Omduth Coceal T Glyn Thomas Stephen E Belcher |
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Institution: | (1) Department of Meteorology, University of Reading, P.O. Box 243, Reading, RG6 6BB, UK;(2) School of Engineering Sciences, University of Southampton, Southampton, SO17 1BJ, UK |
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Abstract: | Turbulence statistics obtained by direct numerical simulations are analysed to investigate spatial heterogeneity within regular
arrays of building-like cubical obstacles. Two different array layouts are studied, staggered and square, both at a packing
density of . The flow statistics analysed are mean streamwise velocity ( ), shear stress ( ), turbulent kinetic energy (k) and dispersive stress fraction ( ). The spatial flow patterns and spatial distribution of these statistics in the two arrays are found to be very different.
Local regions of high spatial variability are identified. The overall spatial variances of the statistics are shown to be
generally very significant in comparison with their spatial averages within the arrays. Above the arrays the spatial variances
as well as dispersive stresses decay rapidly to zero. The heterogeneity is explored further by separately considering six
different flow regimes identified within the arrays, described here as: channelling region, constricted region, intersection
region, building wake region, canyon region and front-recirculation region. It is found that the flow in the first three regions
is relatively homogeneous, but that spatial variances in the latter three regions are large, especially in the building wake
and canyon regions. The implication is that, in general, the flow immediately behind (and, to a lesser extent, in front of)
a building is much more heterogeneous than elsewhere, even in the relatively dense arrays considered here. Most of the dispersive
stress is concentrated in these regions. Considering the experimental difficulties of obtaining enough point measurements
to form a representative spatial average, the error incurred by degrading the sampling resolution is investigated. It is found
that a good estimate for both area and line averages can be obtained using a relatively small number of strategically located
sampling points. |
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Keywords: | Direct numerical simulation Urban canopy layer Urban meteorology |
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