Representations for the pressure-dilatation and dilatational dissipation covariances appearing in single-point moment closures for compressible turbulence are discussed. The representations have been obtained using simple scaling assumptions about the compressibility of the fluctuating components of a flow; the mathematical consequences of which are followed up using a simple singular perturbation idea and the methods of statistical fluid mechanics. In the limit of homogeneous turbulence with quasi-normal large scales the expressions derived are - in the low turbulent Mach number limit - asymptotically exact. While the results are expressed in the context of a single-point second-order closure theory they provide some interesting and very clear physical metaphors for the effects of compressibility on turbulence. The expressions obtained are functions of the rate of change of the turbulence energy, its correlation length scale, and the relative time scale of the cascade rate. The dilatational covariances are found to scale with the Mach numbers based on the mean strain and rotation rates. The physical implications of the analysis are discussed in the context of a few simple flows.
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