ADVECTION BY POLYTROPIC COMPRESSIBLE TURBULENCE

Direct numerical simulation (DNS) is used to examine scalar correlatio n in low Mach number, polytropic, homogeneous, two-dimensional turbule nce (M(s) less than or equal to 0.7) for which the initial conditions, Reynolds, and Mach numbers have been chosen to produce three types of flow suggested by theory: (a) nearly incompressible flow dominated by vorticity, (b) nearly pure acoustic turbulence dominated by compressi on, and (c) nearly statistical equipartition of vorticity and compress ions. Turbulent flows typical of each of these cases have been generat ed and a passive scalar field imbedded in them. The results show that a finite-difference based computer program is capable of producing res ults that are in reasonable agreement with pseudospectral calculations . Scalar correlations have been calculated from the DNS results and th e relative magnitudes of terms in low-order scalar moment equations de termined. It is shown that the scalar equation terms. with explicit co mpressibility are negligible on a long time-averaged basis, A physical -space EDQNM model has been adapted to provide another estimate of sca lar correlation evolution in these same two-dimensional, compressible cases. The use of the solenoidal component of turbulence energy, rathe r than total turbulence energy, in the EDQNM model gives results close r to those from DNS in all cases. (C) 1995 American Institute of Physi cs.