Analysis of subgrid-scale eddy viscosity with use of results from direct numerical simulations

Without resort to any modeling, subgrid-scale eddy viscosity is computed from the results of high-resolution (${64}^3$ and ${128}^3$ grid points) direct numerical simulations of three-dimensional homogeneous, isotropic, decaying turbulence. In these simulations the eddy viscosity peaks sharply at the cutoff wave number, in rough agreement with the results of Kraichnan. In addition, in the low–wave-number range the eddy viscosity may be negative, contrary to the generally accepted concept of a subgrid-scale eddy viscosity. Some possible explanations of this behavior are discussed.