DYNAMICS OF THE PASSIVE SCALAR IN COMPRESSIBLE TURBULENT-FLOW - LARGE-SCALE PATTERNS AND SMALL-SCALE FLUCTUATIONS

The work analyzes fluctuations of passive scalar and large-scale (mean field) effects in a turbulent compressible fluid how. It is shown tha t passive scalar transport can be accompanied by slow diffusion of sma ll-scale inhomogeneous fluctuating structures for large Peclet numbers , Pe much greater than 1. The origin of the inhibition of the diffusio n of small-scale fluctuations of the passive scalar is associated with compressibility (i.e., div u proportional to partial derivative rho/p artial derivative t not equal 0) of a surrounding fluid how. The condi tions for the slow diffusion of the passive scalar fluctuations in hom ogeneous and isotropic turbulent how are found. It is shown that the m agnitude of the fluctuations of the passive scalar generated in the pr esence of external gradient of the mean mass; concentration del Q in c ompressible fluid how can be fairly strong: root(q(2))similar to l(o)I n(Pe)\del Q\, where l(0) is the characteristic scale of the turbulent velocity field. The characteristic spatial scale of a localization of solutions is of the order of l(0)/root Pe. In addition, compressibilit y in the stratified turbulent inhomogeneous fluid how [i.e., div u = - (V rho . u)/rho not equal 0] results information of large-scale struct ures for large P6clet numbers. The formation of these patterns is caus ed by the instability of the uniform distribution of the mean passive scalar held whereby an additional nondiffusive component of the flux o f passive scalar particles results in a large-scale pattern. The condi tions for the excitation of the instability of the mean held are found . Possible environmental applications of these effects are discussed.