On the effects of nonequilibrium on the subgrid-scale stresses

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Description/Abstract

An a priori study of the subgrid-scale (SGS) stresses and dissipation in two nonequilibrium, wall-bounded flows is carried out. The velocity fields were computed by direct simulations of two- and three-dimensional boundary layers obtained, respectively, by a sudden change in the Reynolds number and by an impulsive motion in the spanwise direction of the lower wall of a plane channel in fully developed turbulent flow conditions. Several realizations of the transient period of the flow were examined. The SGS stresses react to the imposition of the secondary shear more rapidly than the large-scale ones, and return to equilibrium before the resolved stresses do. In general, the subgrid scales are less sensitive than the large ones to the near-wall and nonequilibrium effects. Scale-similar and dynamic models appear well-suited to reproduce the correlation between resolved Reynolds stress production and events with significant production of SGS energy