A grid nesting method for large-eddy simulation of planetary boundary-layer flows

Abstract

A method for performing nested grid calculations with a large-eddy simulation code is described. A common numerical method is used for all meshes, and the grid architecture consists of a single outer or coarse grid, and nested or fine grids, which overlap in some common region. Inter-grid communication matches the velocity, pressure and potential temperature fields in the overlap region. Resolved and sub-grid scale (SGS) turbulent fluxes and kinetic energy on the fine grid are averaged to the coarse grid using a conservation rule equivalent to Germano's identity used to develop dynamic SGS models.Simulations of a slightly convective, strong shear planetary boundary layer were carried out with varying surface-layer resolutions. Grid refinements in the (z, y, z) directions of up to (5, 5, 2) times were employed. Two-way interaction solutions on the coarse and fine meshes are successfully matched in the overlap region on an instantaneous basis, and the turbulent motions on the fine grid blend smoothly into the coarse grid across the grid interface. With surface-layer grid nesting, significant increases in resolved eddy fluxes and variances are found. The energy-scale content of the vertical velocity, and hence vertical turbulent fluxes, appear to be most influenced by increased grid resolution. Vertical velocity spectra show that the dominant scale shifts towards higher wavenumbers (smaller scales) and the magnitude of the peak energy is increased by more than a factor of 3 with finer resolution. Outside of the nested region the average heat and momentum fluxes and spectra are slightly influenced by the fine resolution in the surface layer. From these results we conclude that fine resolution is required to resolve the details of the turbulent motions in the surface layer. At the same time, however, increased resolution in the surface layer does not appreciably alter the ensemble statistics of the resolved and SGS motions outside of the nested region.

The Influence of Idealized Heterogeneity on Wet and Dry Planetary Boundary Layers Coupled to the Land Surface

“…Key variables in the SEB, such as heat and water vapor fluxes, are influenced by PBL concentrations of these quantities, which themselves are influenced by their surface fluxes, forming a negative feedback loop (McNaughton and Raupach 1996). We attempt to incorporate these important feedbacks in the study, by coupling our 3D, time-dependent LES code (Sullivan et al 1996) to the National Centers for Environmental Prediction/Oregon State University/ Air Force/Office of Hydrology (NOAH) LSM, version 2.0 (Chang et al 1999).…”

One‐Way Nested Large‐Eddy Simulation over the Askervein Hill

“…Two-way nesting has also been employed in the context of LES over flat surface with outer periodic boundary conditions. Sullivan et al (1996) developed a vertical nesting approach to refine a slice of the horizontal domain. Moeng et al (2007) designed two-way horizontally nested LESwithin-LES experiments using the Weather Research and Forecasting (WRF) model.…”

Finite-Difference, Time-Domain Simulation of Sound Propagation in a Dynamic Atmosphere

“…The main dynamic method of interest for FDTD calculations at Army tactical scales is large-eddy simulation, or LES (Moeng 1998). At present, LES is capable of providing inputs to an FDTD code at a resolution of several meters (e.g., Sullivan et al 1996). Conceivably the LES could be directly coupled with the acoustical calculation by simultaneously solving a single set of fluid equations.…”