In this study, we conduct a parametric analysis to evaluate the sensitivities of wall-modeled
large-eddy simulation (LES) with respect to subgrid-scale (SGS) models, mesh resolution, wall
boundary conditions and mesh anisotropy. While such investigations have been conducted for
attached/flat-plate flow configurations, systematic studies specifically targeting turbulent flows
with separation are notably sparse. To bridge this gap, our study focuses on the flow over a
two-dimensional Gaussian-shaped bump at a moderately high Reynolds number, which involves
smooth-body separation of a turbulent boundary layer under pressure-gradient and surface-
curvature effects. In the simulations, the no-slip condition at the wall is replaced by three different
forms of boundary condition based on the thin boundary layer equations and the mean wall-shear
stress from high-fidelity numerical simulation to avoid the additional complexity of modeling the
wall-shear stress. Various statistics, including the mean separation bubble size, mean velocity
profile, and dissipation from SGS model, are compared and analyzed. The results reveal that
capturing the separation bubble strongly depends on the choice of SGS model. While simulations
approach grid convergence with resolutions nearing those of wall-resolved LES meshes, above this
limit, the LES predictions exhibit intricate sensitivities to mesh resolution. Furthermore, both wall
boundary conditions and the anisotropy of mesh cells exert discernible impacts on the turbulent
flow predictions, yet the magnitudes of these impacts vary based on the specific SGS model chosen
for the simulation.
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Large-Eddy Simulation of Conditionally Neutral Boundary Layers: A Mesh Resolution Sensitivity Study
Large-eddy simulation (LES) is used to model turbulent winds in a nominally neutral atmospheric boundary layer at varying mesh resolutions. The boundary layer is driven by wind shear with zero surface heat flux and is capped by a stable inversion. Because of entrainment the boundary layer is in a weakly stably stratified regime. The simulations use meshes varying from 1282× 64 to 10242× 512 grid points in a fixed computational domain of size (2560, 2560, 896) m. The subgrid-scale (SGS) parameterizations used in the LES vary with the mesh spacing. Low-order statistics, spectra, and structure functions are compared on the different meshes and are used to assess grid convergence in the simulations. As expected, grid convergence is primarily achieved in the middle of the boundary layer where there is scale separation between the energy-containing and dissipative eddies. Near the surface second-order statistics do not converge on the meshes studied. The analysis also highlights differences between one-dimensional and two-dimensional velocity spectra; differences are attributed to sampling errors associated with aligning the horizontal coordinates with the vertically veering mean wind direction. Higher-order structure functions reveal non-Gaussian statistics on all scales, but are highly dependent on the mesh resolution. A generalized logarithmic law and a k−1spectral scaling regime are identified with mesh-dependent parameters in agreement with previously published results.
more » « less- PAR ID:
- 10155294
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of the Atmospheric Sciences
- Volume:
- 77
- Issue:
- 6
- ISSN:
- 0022-4928
- Page Range / eLocation ID:
- p. 1969-1991
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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