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  4. A Modulated-Gradient Parametrization for the Large-Eddy Simulation of the Atmospheric Boundary Layer Using the Weather Research and Forecasting Model
 
research article

A Modulated-Gradient Parametrization for the Large-Eddy Simulation of the Atmospheric Boundary Layer Using the Weather Research and Forecasting Model

Khani, Sina  
•
Porte-Agel, Fernando  
2017
Boundary-Layer Meteorology

The performance of the modulated-gradient subgrid-scale (SGS) model is investigated using large-eddy simulation (LES) of the neutral atmospheric boundary layer within the weather research and forecasting model. Since the model includes a finite-difference scheme for spatial derivatives, the discretization errors may affect the simulation results. We focus here on understanding the effects of finite-difference schemes on the momentum balance and the mean velocity distribution, and the requirement (or not) of the ad hoc canopy model. We find that, unlike the Smagorinsky and turbulent kinetic energy (TKE) models, the calculated mean velocity and vertical shear using the modulated-gradient model, are in good agreement with Monin-Obukhov similarity theory, without the need for an extra near-wall canopy model. The structure of the near-wall turbulent eddies is better resolved using the modulated-gradient model in comparison with the classical Smagorinsky and TKE models, which are too dissipative and yield unrealistic smoothing of the smallest resolved scales. Moreover, the SGS fluxes obtained from the modulated-gradient model are much smaller near the wall in comparison with those obtained from the regular Smagorinsky and TKE models. The apparent inability of the LES model in reproducing the mean streamwise component of the momentum balance using the total (resolved plus SGS) stress near the surface is probably due to the effect of the discretization errors, which can be calculated a posteriori using the Taylor-series expansion of the resolved velocity field. Overall, we demonstrate that the modulated-gradient model is less dissipative and yields more accurate results in comparison with the classical Smagorinsky model, with similar computational costs.

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Type
research article
DOI
10.1007/s10546-017-0287-5
Web of Science ID

WOS:000415143200001

Author(s)
Khani, Sina  
Porte-Agel, Fernando  
Date Issued

2017

Publisher

Springer

Published in
Boundary-Layer Meteorology
Volume

165

Issue

3

Start page

385

End page

404

Subjects

Atmospheric boundary layer

•

Large-eddy simulation

•

Subgrid-scalemodelling

•

Weather Research and Forecasting model

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
WIRE  
Available on Infoscience
December 4, 2017
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/142515
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