Numerical scale separation in large-eddy simulation

Abstract

Large-eddy simulation (LES) seeks to predict the dynamics of spatially filtered turbulent flows. The essence of a scale-separation LES model is that it stops the nonlinear production of smaller scales of motion at the scale set by the filter: there the modeled eddy dissipation has to balance the production. Numerical discretization changes both the nonlinear production and dissipation of sub-filter scales. Therefore, the discrete balance between production and dissipation can deviate from the continuous balance, in particular if a balance is imposed near the scale set by the numerical grid. This paper demonstrates that a scale-separation LES model should attain a production-dissipation balance in the numerical setting. Eddy-viscosity models based on this requirement are derived and successfully applied in simulations of decaying isotropic turbulence and channel flow.

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