Abstract
The mean wind direction within an urban canopy changes with height when the incoming flow is not orthogonal to obstacle faces. This wind-turning effect is induced by complex processes and its modelling in urban-canopy (UC) parametrizations is difficult. Here we focus on the analysis of the spatially-averaged flow properties over an aligned array of cubes and their variation with incoming wind direction. For this purpose, Reynolds-averaged Navier–Stokes simulations previously compared, for a reduced number of incident wind directions, against direct numerical simulation results are used. The drag formulation of a UC parametrization is modified and different drag coefficients are tested in order to reproduce the wind-turning effect within the canopy for oblique wind directions. The simulations carried out for a UC parametrization in one-dimensional mode indicate that a height-dependent drag coefficient is needed to capture this effect.
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Notes
Here, and in the following, we continue to use the term drag coefficient to indicate the ratio between the force exerted by the obstacles on the flow and the product of the square of the wind speed and the vertical surface building density.
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Acknowledgments
This study has been partially supported by the project Modelización de la Influencia de la Vegetación Urbana en la Calidad del Aire y Confort Climático (CGL2011-26173) funded by Spanish Ministry of Economy and Competitiveness and by the Project Supercomputation and E-Science (SyeC) from the Spanish CONSOLIDER Programme.
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Santiago, J.L., Coceal, O. & Martilli, A. How to Parametrize Urban-Canopy Drag to Reproduce Wind-Direction Effects Within the Canopy. Boundary-Layer Meteorol 149, 43–63 (2013). https://doi.org/10.1007/s10546-013-9833-y
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DOI: https://doi.org/10.1007/s10546-013-9833-y