Partition selection in multiscale turbulence modeling

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Abstract
The variational multiscale (VMS) method for large-eddy simulation (LES) is a promising new approach that employs variational projection to achieve a priori scale separation in lieu of traditional spatial filtering. However, depending on the numerical method used, VMS may not be convenient in all spatial directions. We apply the VMS methodology to a numerical method that does not support explicit scale separation in the wall-normal direction for turbulent channel flow. Similar to the common LES practice of filtering only in the planes, variational projection is performed only in the planes and this strategy is found to be as successful as the full VMS method. However, in all VMS approaches, the partition between the large and small scales and the overall resolution are crucial parameters for obtaining quality solutions. By applying scale separation in just one of the coordinate directions, we have developed a consistent method for partition and resolution selection in channel flow that is related to the physical structures in the near-wall region. The idea behind this approach can, potentially, be extended for informed VMS parameter selection in other flows.