Formation of inhomogeneities in two-phase low-Mach-number compressible turbulent fluid flows

A new phenomenon of turbulent thermal diffusion is discussed. This effect i s related to the dynamics of small inertial particles in low-Mach-number co mpressible turbulent fluid flows. Turbulent thermal diffusion is caused by the correlation between temperature and velocity fluctuations of the surrou nding fluid and leads to relatively strong nondiffusive mean flux of inerti al particles in regions with mean temperature gradients. It is shown that t urbulent thermal diffusion under certain conditions can cause a large-scale instability of spatial distribution of particles. Particles are concentrat ed in the vicinity of the minimum (or maximum) of the mean temperature of t he surrounding fluid depending on the ratio of material particle density to that of the surrounding fluid. At large Reynolds and Peclet numbers the tu rbulent thermal diffusion is much stronger than the molecular thermal diffu sion. Turbulent thermal diffusion can be important in various naturally occ urring and industrial multiphase flows. In particular, this effect may caus e formation of inhomogeneities in spatial distribution of fuel droplets in internal combustion engines. It is conceivable to suggest that the effect o f turbulent thermal diffusion can play an important role in a process of so ot formation in flames and in atmospheric dynamics of pollutants, e.g. smog and aerosol clouds formation. (C) 1998 Elsevier Science Ltd. All rights re served.