Spectral Analysis of Large-Eddy Simulations of the Convective Boundary Layer

Chin-Hoh Moeng National Center for Atmospheric Research,* Boulder, Colorado

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John C. Wyngaard National Center for Atmospheric Research,* Boulder, Colorado

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Abstract

To examine the fidelity of the simulated turbulent flow, we analyzed the spectra of 96×&96×96 large-eddy-simulation results. We derived expressions for the inertial-range spectra of a filtered wind field, compared our computed spectra with the theoretical predictions, and drew two main conclusions. First, the wave cutoff filter is more appropriate for our large-eddy-simulation model than the Gaussian filter. Second, only a certain combination of the subgrid-scale parameters for the dissipation rate and eddy viscosity provides good inertial-range spectra.

We offer an explanation for the unreasonably large sugrid temperature and moisture variances reported in Deardorff's 1974 lame-eddy-simulation results, and show that moment statistics up to third order are not sensitive to moderate changes in the subgrid-scale parameters.

Abstract

To examine the fidelity of the simulated turbulent flow, we analyzed the spectra of 96×&96×96 large-eddy-simulation results. We derived expressions for the inertial-range spectra of a filtered wind field, compared our computed spectra with the theoretical predictions, and drew two main conclusions. First, the wave cutoff filter is more appropriate for our large-eddy-simulation model than the Gaussian filter. Second, only a certain combination of the subgrid-scale parameters for the dissipation rate and eddy viscosity provides good inertial-range spectra.

We offer an explanation for the unreasonably large sugrid temperature and moisture variances reported in Deardorff's 1974 lame-eddy-simulation results, and show that moment statistics up to third order are not sensitive to moderate changes in the subgrid-scale parameters.

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