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Wind direction effects on urban flows

Wind direction effects on urban flows
Wind direction effects on urban flows
Practically all extant work on flows over obstacle arrays, whether laboratory experiments or numerical modelling, is for cases where the oncoming wind is normal to salient faces of the obstacles. In the field, however, this is rarely the case. Here, simulations of flows at various directions over arrays of cubes representing typical urban canopy regions are presented and discussed. The computations are of both direct numerical simulation and large-eddy simulation type. Attention is concentrated on the differences in the mean flow within the canopy region arising from the different wind directions and the consequent effects on global properties such as the total surface drag, which can change very significantly—by up to a factor of three in some circumstances. It is shown that for a given Reynolds number the typical viscous forces are generally a rather larger fraction of the pressure forces (principally the drag) for non-normal than for normal wind directions and that, dependent on the surface morphology, the average flow direction deep within the canopy can be largely independent of the oncoming wind direction. Even for regular arrays of regular obstacles, a wind direction not normal to the obstacle faces can in general generate a lateral lift force (in the direction normal to the oncoming flow). The results demonstrate this and it is shown how computations in a finite domain with the oncoming flow generated by an appropriate forcing term (e.g. a pressure gradient) then lead inevitably to an oncoming wind direction aloft that is not aligned with the forcing term vector.
0006-8314
265-287
Claus, J.
29dca742-3a5a-46cb-a274-a2e62900f3eb
Coceal, O.
da233575-2c0b-4e62-8aa8-32187bd2fbdd
Thomas, T.G.
bccfa8da-6c8b-4eec-b593-00587d3ce3cc
Branford, S.
b3cb17f7-3c04-47be-9b9e-2e9e1f102199
Belcher, S.E.
c834c272-81e1-4185-b5cd-5890a9a39ea0
Castro, I.P.
66e6330d-d93a-439a-a69b-e061e660de61
Claus, J.
29dca742-3a5a-46cb-a274-a2e62900f3eb
Coceal, O.
da233575-2c0b-4e62-8aa8-32187bd2fbdd
Thomas, T.G.
bccfa8da-6c8b-4eec-b593-00587d3ce3cc
Branford, S.
b3cb17f7-3c04-47be-9b9e-2e9e1f102199
Belcher, S.E.
c834c272-81e1-4185-b5cd-5890a9a39ea0
Castro, I.P.
66e6330d-d93a-439a-a69b-e061e660de61

Claus, J., Coceal, O., Thomas, T.G., Branford, S., Belcher, S.E. and Castro, I.P. (2012) Wind direction effects on urban flows. Boundary-Layer Meteorology, 142 (2), 265-287.

Record type: Article

Abstract

Practically all extant work on flows over obstacle arrays, whether laboratory experiments or numerical modelling, is for cases where the oncoming wind is normal to salient faces of the obstacles. In the field, however, this is rarely the case. Here, simulations of flows at various directions over arrays of cubes representing typical urban canopy regions are presented and discussed. The computations are of both direct numerical simulation and large-eddy simulation type. Attention is concentrated on the differences in the mean flow within the canopy region arising from the different wind directions and the consequent effects on global properties such as the total surface drag, which can change very significantly—by up to a factor of three in some circumstances. It is shown that for a given Reynolds number the typical viscous forces are generally a rather larger fraction of the pressure forces (principally the drag) for non-normal than for normal wind directions and that, dependent on the surface morphology, the average flow direction deep within the canopy can be largely independent of the oncoming wind direction. Even for regular arrays of regular obstacles, a wind direction not normal to the obstacle faces can in general generate a lateral lift force (in the direction normal to the oncoming flow). The results demonstrate this and it is shown how computations in a finite domain with the oncoming flow generated by an appropriate forcing term (e.g. a pressure gradient) then lead inevitably to an oncoming wind direction aloft that is not aligned with the forcing term vector.

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More information

Published date: February 2012
Organisations: Aerodynamics & Flight Mechanics Group

Identifiers

Local EPrints ID: 300664
URI: https://eprints.soton.ac.uk/id/eprint/300664
ISSN: 0006-8314
PURE UUID: 085e7b30-aec3-4d6c-a364-45eda0ddf158

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Date deposited: 28 Feb 2012 15:33
Last modified: 19 Oct 2017 14:16

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