Preferential concentration vs. clustering in inertial particle transport by random velocity fields

摘要

The concept of preferential concentration in the transport of inertialparticles by random velocity fields is extended to account for the possibilityof zero correlation time and compressibility of the velocity field. It is shownthat, in the case of an uncorrelated in time random velocity field,preferential concentration takes the form of a condition on the field historyleading to the current particle positions. This generalized form ofpreferential concentration appears to be a necessary condition for clusteringin the uncorrelated in time case. The standard interpretation of preferentialconcentration is recovered considering local time averages of the velocityfield. In the compressible case, preferential concentration occurs in regionsof negative divergence of the field. In the incompressible case, it occurs inregions of simultaneously high strain and negative field skewness.