Two types of intermittency of passive scalar fluctuations

Turbulent transport of passive scalar (e.g., number density of particles) advected by an incompressible fluid flow in the case U = v was studied in a large number of publications. Here U is the particle velocity and v is the velocity of fluid. Interesting features in turbulent transport of passive scalar appear when U ≠ v. In this case new phenomena, e.g., turbulent thermal diffusion and turbulent barodiffusion [1], and self-excitation, i.e., exponential growth of fluctuations of the number density of inertial particles [2] occur. These effects are caused by inertia of particles which results in a divergent velocity field of particles. The self-excitation of the fluctuations results in the intermittency in spatial distribution of inertial particles [2].