A database of Direct Numerical Simulations (DNS) representing mixing of species under supercritical pressure (supercritical-p) conditions has been created for the purpose of understanding the modelling of ▽p(Φ), ▽ • q(Φ) and ▽ • j_α(Φ) in the context of Large Eddy Simulation (LES). The analysis consists of two separate parts. The activities of all terms appearing in the LES equations are first evaluated, and the dominant terms for each of the transport equations are identified. These data are used to check whether the standard LES assumptions ▽p(Φ) = ▽p(Φ), ▽·q(Φ) = ▽·q(Φ) and ▽·j_α(Φ) = ▽·j_α(Φ), which are routinely used for atmospheric-p flows, continue to be valid also in the realm of supercritical-p conditions. Having found that these assumptions do not hold under supercritical-p conditions, alternative modelling strategies for these terms are proposed, and their accuracy with respect to the standard LES assumptions is assessed through a priori and a posteriori analyses.
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