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| Titel |
A simple one-dimensional model for urban canopy flows |
| VerfasserIn |
Wai Chi Cheng, Fernando Porté-Agel |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250134099
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| Publikation (Nr.) |
 EGU/EGU2016-14788.pdf |
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| Zusammenfassung |
| In urban canopy parameterizations, an urban canopy is usually modelled as a drag force on
the flow, and the turbulent shear stress is parametrized by various methods. One of the most
common methods to parametrize the turbulent shear stress in urban canopies is to use a
mixing length (lm) model. Different mixing length models have been proposed in the
literature, and recent direct numerical simulation and large-eddy simulation (LES) studies
have shown that these models underpredict the value of lm in urban canopies. The high value
of lm in the canopies is in fact related to the turbulence generated at the high-shear region
near the top of the canopy, which is similar to that in a plane mixing layer. By considering
this effect, a new simple mixing length model is proposed based on physical arguments.
The results of the new lm model and the previous models are compared with the
LES results of flows within and above uniform cube arrays of different densities.
The comparison clearly demonstrates the better performance of the new model in
predicting the wind profiles especially near the top of the urban canopies. For the
drag coefficient (Cd) representing an urban canopy, previous studies found that its
value depends on the building density. Here, a simple model for Cd is suggested by
considering the spatial distribution of mean wind within canopies of different building
densities. The model prediction is found to agree reasonably well with the LES results. |
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