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Article

Efficacy of the Cell Perturbation Method in Large-Eddy Simulations of Boundary Layer Flow over Complex Terrain

1
Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA
2
Department of Applied Mathematics, University of Twente, 7522 NB Enschede, The Netherlands
3
Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
*
Author to whom correspondence should be addressed.
Atmosphere 2021, 12(1), 55; https://doi.org/10.3390/atmos12010055
Received: 12 November 2020 / Revised: 23 December 2020 / Accepted: 24 December 2020 / Published: 31 December 2020
A challenge to simulating turbulent flow in multiscale atmospheric applications is the efficient generation of resolved turbulence motions over an area of interest. One approach is to apply small perturbations to flow variables near the inflow planes of turbulence-resolving simulation domains nested within larger mesoscale domains. While this approach has been examined in numerous idealized and simple terrain cases, its efficacy in complex terrain environments has not yet been fully explored. Here, we examine the benefits of the stochastic cell perturbation method (CPM) over real complex terrain using data from the 2017 Perdigão field campaign, conducted in an approximately 2-km wide valley situated between two nearly parallel ridges. Following a typical configuration for multiscale simulation using nested domains within the Weather Research and Forecasting (WRF) model to downscale from the mesoscale to a large-eddy simulation (LES), we apply the CPM on a domain with horizontal grid spacing of 150 m. At this resolution, spurious coherent structures are often observed under unstable atmospheric conditions with moderate mean wind speeds. Results from such an intermediate resolution grid are often nested down for finer, more detailed LES, where these spurious structures adversely affect the development of turbulence on the subsequent finer grid nest. We therefore examine the impacts of the CPM on the representation of turbulence within the nested LES domain under moderate mean flow conditions in three different stability regimes: weakly convective, strongly convective, and weakly stable. In addition, two different resolutions of the underlying terrain are used to explore the role of the complex topography itself in generating turbulent structures. We demonstrate that the CPM improves the representation of turbulence within the LES domain, relative to the use of high-resolution complex terrain alone. During the convective conditions, the CPM improves the rate at which smaller-scales of turbulence form, while also accelerating the attenuation of the spurious numerically generated roll structures near the inflow boundary. During stable conditions, the coarse mesh spacing of the intermediate LES domain used herein was insufficient to maintain resolved turbulence using CPM as the flow develops downstream, highlighting the need for yet higher resolution under even weakly stable conditions, and the importance of accurate representation of flow on intermediate LES grids. View Full-Text
Keywords: large-eddy simulation; complex terrain; the Weather Research and Forecasting model; turbulence generation; cell perturbation method; the Perdigão large-eddy simulation; complex terrain; the Weather Research and Forecasting model; turbulence generation; cell perturbation method; the Perdigão
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MDPI and ACS Style

Connolly, A.; van Veen, L.; Neher, J.; Geurts, B.J.; Mirocha, J.; Chow, F.K. Efficacy of the Cell Perturbation Method in Large-Eddy Simulations of Boundary Layer Flow over Complex Terrain. Atmosphere 2021, 12, 55. https://doi.org/10.3390/atmos12010055

AMA Style

Connolly A, van Veen L, Neher J, Geurts BJ, Mirocha J, Chow FK. Efficacy of the Cell Perturbation Method in Large-Eddy Simulations of Boundary Layer Flow over Complex Terrain. Atmosphere. 2021; 12(1):55. https://doi.org/10.3390/atmos12010055

Chicago/Turabian Style

Connolly, Alex, Leendert van Veen, James Neher, Bernard J. Geurts, Jeff Mirocha, and Fotini K. Chow 2021. "Efficacy of the Cell Perturbation Method in Large-Eddy Simulations of Boundary Layer Flow over Complex Terrain" Atmosphere 12, no. 1: 55. https://doi.org/10.3390/atmos12010055

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