On the local equilibrium of the subgrid scales: The velocity and scalar fields

Direct numerical simulations of homogeneous isotropic turbulence are used to analyze the local equilibrium assumption between large and small scales of motion in the context of large-eddy simulations. The local imbalance, between grid/subgrid scales transfer (of kinetic energy and scalar variance) and molecular dissipation, increases with the Reynolds and Schmidt numbers and with the filter size. It is shown that the correlations between SGS production and dissipation (for the velocity and scalar fields) are higher in regions dominated by strain and where vorticity and strain are comparably large, and smaller in regions where vorticity dominates. (c) 2005 American Institute of Physics.