Investigation of subfilter models and scalar-scalar covariances for supercritical mixing*

The applicability of the conventional large eddy simulation (LES) simplifications and subfilter models for simulation of supercritical mixing and combustion has been uncertain and questioned in recent studies. The majority of modeling efforts are typically focused on the unclosed velocity-velocity and velocity-scalar covariance terms in the conservation equations for momentum and energy. There has been a lack of studies examining the relevance of other subfilter terms, for example, in the equation of state. This is especially important in the context of turbulent flows at supercritical conditions, where thermodynamic nonidealities play a dominant role. In this work, a three-dimensional direct numerical simulation of a binary species, supercritical spatial mixing layer at high Reynolds number is performed. The database is used to perform a priori analyses of the underlying LES assumptions and the subfilter models used for the unclosed velocity-velocity and velocity-scalar covariance terms. We then investigate the relevance of subfilter scalar-scalar covariance terms associated with the filtered equation of state and internal energy and an approximate deconvolution model is developed to accurately model these terms.