A promising trend in subgrid-scale modeling consists in using transport equations for the subgrid-scale kinetic energy as e.g. in Ghosal et al. [1]. In the present work Direct Numerical Simulations (DNS) of forced homogeneous isotropic turbulence are used to analyze some of the assumptions often used in these models, and their dependence on the Reynolds number and implicit filter size. In particular, three key issues are analyzed: (a) the relative importance between production and diffusion of SGS kinetic energy; (b) the modeling of the viscous SGS dissipation and; (c) the acceleration statistics of the local and convective terms. Finally, the same analysis is applied to an equation for the evolution of the SGS scalar variance.
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