How to Parametrize Urban-Canopy Drag to Reproduce Wind-Direction Effects Within the Canopy

• Published in: Boundary-layer meteorology Vol. 149; no. 1; pp. 43 - 63
• Main Authors: Santiago, J. L., Coceal, O., Martilli, A.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.10.2013; Springer; Springer Nature B.V
• Subjects: Atmospheric Protection/Air Quality Control/Air Pollution; Atmospheric Sciences; Boundaries; Canopies; Computer simulation; Convection, turbulence, diffusion. Boundary layer structure and dynamics; Drag; Drag coefficients; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Meteorology; Navier-Stokes equations; Parameter estimation; Parametrization; Simulation; Wind; Wind direction; Drag coefficients; Wind direction; Reynolds-averaged Navier–Stokes (RANS); Direct numerical simulations (DNS); Urban-canopy parametrization; Urban structure; Wind effect; digital simulation; Urban atmosphere; parametrization; Reynolds-averaged Navier―Stokes (RANS); Drag; winds; Drag coefficient; Canopy(vegetation)
• ISSN: 0006-8314; 1573-1472
• DOI: 10.1007/s10546-013-9833-y

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.