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Center for Nonlinear Studies |
At high Reynolds numbers, the Lagrangian-averaged Navier-Stokes Éø-model (LANS-Éø) is found to provide poor predictions of superfilter-scale energy spectra. By making the antithesis of a LES, we are able to study the subfilter-scale (SFS) physics responsible for these poor spectra. LANS-Éø's strong suppression of spectrally local SFS interactions and the conservation of small-scale circulation leads to the formation of rigid bodies. These contaminate the superfilter-scale energy spectrum with a k +1 scaling (instead of the predicted k -1 scaling for the H 1 norm). In comparison, the Clark-Éø and Leray-Éø models, truncations of LANS-Éø, do not conserve small-scale circulation and do not develop rigid bodies. These truncations, however, do not retain the good intermittency properties of LANS-Éø. In magnetohydrodynamics (MHD), the presence of the Lorentz force as a source (or sink) for circulation and as the restoring force for Alfven waves prevents the formation of rigid bodies in the MHD-Éømodel. MHD-Éø performs well as a predictor of superfilter-scale energy spectra and of intermittent current sheets at high Reynolds numbers. It may prove generally applicable as a MHD-LES.
Host: Todd Ringler, T-3, 7-7744,ringler@lanl.gov