Subgrid-scale models of isotropic turbulence need not produce energy backscatter

This investigation questions the importance of inverse interscale energy fluxes, so-called backscatter, for modelling cascade in large-eddy simulations (LES) turbulent flows. The invariance filtered Navier–Stokes equations to divergence-preserving transformations subgrid-scale (SGS) stress tensor is exploited here explore alternative representations local SGS fluxes. Numerical optimisation procedures are applied – obtained by filtering isotropic turbulence flow fields find stresses that satisfy equations, but produce negligible backscatter. These show backscatter represents not a flux from subgrid resolved scales, conservative spatial and it need be modelled reproduce energetic exchange between scales LES. From perspective statistical mechanics, argued this consequence strong irreversibility inertial-range dynamics, which precludes cascades even sense. findings strongly unidirectional locally, can as an irreversible sink energy, justifying extended use purely dissipative models