Particle dispersion in the separation turbulent flow

Dispersion of particles in the separating flow behind a two-dimensional backward facing step is numerically studied attentively. Gas field is simulated by large eddy simulation (LES) and solid particle motion is traced by particle track model (PTM). It is shown that the dispersion of particles in the large eddy structures depends on particle parameters such as size and material density, as well as the fluid properties. The particles have represented three different dispersion modes when their Stokes numbers are different in magnitude. Large particles (St>>O(1)) is unaffected by the vortex flow filed because of their large inertia, called as the mode of inertial force. Very small particles (St<<O(1)), on the other hand, is in dynamic equilibrium with the carrier fluid and controlled by large eddy structures, defined as large eddy structure transportation mode. Whereas, there may be an intermediate particle size such that the particles tend to be centrifuged from the vortex cores and accumulate at the edges of the vortices. For this case the dispersion can lead to highly inhomogeneous particle concentration, identified as large eddy combined with centrifugal force mode. And then it is further discussed how particles enter the re-circulation region.