Three-dimensional features of particle dispersion in a nominally plane mixing layer

Navier-Stokes simulations of a temporally growing mixing layer are employed to investigate three-dimensional mechanisms for the dispersion and accumulation of small, heavy, spherical particles. It is found that in particular the presence of the streamwise braid vortices gives rise to additional dynamical effects that modify the concentration, dispersion, and suspension patterns observed in two-dimensional situations. Intense stretching and folding by the evolving three-dimensional vorticity field, when combined with inertial effects such as ejection by the concentrated streamwise vortices, strongly distorts the geometry of both clear fluid and particle laden regions. Different time scales can be associated with the spanwise and streamwise vortices, so that these distinct vortical systems can selectively affect different classes of particles. (C) 1996 American Institute of Physics.