ADVECTION OF MASS FRACTION IN FORCED, HOMOGENEOUS, COMPRESSIBLE TURBULENCE

In nearly isothermal, compressible turbulence of a nondense gas the ma ss fraction of an embedded passive scalar satisfies the same formal co nservation equation as a passive scalar in incompressible turbulence. Direct numerical simulation of this system shows that the compressible turbulence modes are less efficient than the incompressible in transp orting scalar spectral content from large to small scales. It is argue d that the cause of this outcome is the reduced size of the integral l ength scale of the compressible velocity components vis a vis that of the incompressible velocity components, and this also explains the exp erimentally observed ineffectiveness of the dilatational velocity mode s in determining scalar flux in homogeneous, compressible turbulence w ith a uniform mean scalar gradient. (C) 1998 American Institute of Phy sics.