How to Parametrize Urban-Canopy Drag to Reproduce Wind-Direction Effects Within the Canopy
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.
KeywordsDirect numerical simulations (DNS) Drag coefficients Reynolds-averaged Navier–Stokes (RANS) Urban-canopy parametrization Wind direction
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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