Effect of grid discontinuities on large-eddy simulation statistics and flow fields

Abstract

We have performed large-eddy simulations of spatially developing homogeneous isotropic turbulence advected past an interface where the grid is suddenly coarsened or refined by a factor of two in each direction. We have compared simulations in which the filter width is proportional to the grid size and is discontinuous at the coarse–fine grid interface, to others in which the filter width varies gradually between the values corresponding to the coarse and fine grids. The Smagorinsky and Lagrangian-dynamic eddy viscosity (LDEV) models were used to parameterize the unresolved subgrid scales. A sudden refinement of the grid does not result in significant flow perturbation: small scales are gradually generated and the flow is generally quite smooth across the interface. When the grid is suddenly coarsened, on the other hand, a considerable energy pileup at small scales is observed near the interface. At lower resolutions, the extent of this high-energy zone grows. Increasing the eddy viscosity upstream of the interface by smoothly increasing the filter width is beneficial. For fine-to-coarse interfaces, the LDEV model with a smoothly varying filter width yields more accurate results than other models. Explicit filtering of the advective term is also beneficial: by increasing the length scale of the turbulence upstream of the grid discontinuity, interpolation and aliasing errors are reduced and better agreement with single-grid results is obtained.

Keywords:

• large-eddy simulation
• adaptive mesh refinement
• discontinuous filters
• homogeneous turbulence

5. Acknowledgments

This research was supported by the Office of Naval Research under Grant No. N00014-06-1-0460, monitored by Dr. Ronald D. Joslin. The PARAMESH software used in this work was developed at the NASA Goddard Space Flight Center and Drexel University under NASA's HPCC and ESTO/CT projects and under Grant NNG04GP79G from the NASA/AISR project.