Large-Eddy Simulation of the Stable Atmospheric Boundary Layer using Dynamic Models with Different Averaging Schemes |
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| Authors: | Rob Stoll Fernando Porté-Agel |
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| Institution: | (1) Saint Anthony Falls Laboratory, Department of Civil Engineering, University of Minnesota, Minneapolis, 55414, MN, USA;(2) National Center for Earth-Surface Dynamics, Minneapolis, 55414, MN, USA |
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| Abstract: | Large-eddy simulation (LES) of a stable atmospheric boundary layer is performed using recently developed dynamic subgrid-scale
(SGS) models. These models not only calculate the Smagorinsky coefficient and SGS Prandtl number dynamically based on the
smallest resolved motions in the flow, they also allow for scale dependence of those coefficients. This dynamic calculation
requires statistical averaging for numerical stability. Here, we evaluate three commonly used averaging schemes in stable
atmospheric boundary-layer simulations: averaging over horizontal planes, over adjacent grid points, and following fluid particle
trajectories. Particular attention is focused on assessing the effect of the different averaging methods on resolved flow
statistics and SGS model coefficients. Our results indicate that averaging schemes that allow the coefficients to fluctuate
locally give results that are in better agreement with boundary-layer similarity theory and previous LES studies. Even among
models that are local, the averaging method is found to affect model coefficient probability density function distributions
and turbulent spectra of the resolved velocity and temperature fields. Overall, averaging along fluid pathlines is found to
produce the best combination of self consistent model coefficients, first- and second-order flow statistics and insensitivity
to grid resolution. |
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| Keywords: | Atmospheric boundary layer Dynamic subgrid-scale model Large-eddy simulation Stable boundary layer |
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