Inertial Particle Behavior in a an Unsteady Separated Flow

A new inertial particle behavior is identified in a particle-laden, unsteady separated flow behind a backward-facing step. In a numerical investigation, it is shown that inertial particles eject away from the wall along a distinct material line that originates from a fixed wall location. The fixed separation location coincides with the zero averaged wall skin friction location of the carrier flow. At Stokes numbers larger than one, inertial particles separate at moderate angles. At Stokes numbers smaller than one, the inertial particle dispersion compares to the fluid particle traces showing a moving separation origin of the material line. The Saffman lift forces particles away from the wall and pollutes the distinct character of the separation material line.