3-DIMENSIONAL FEATURES OF PARTICLE DISPERSION IN A NOMINALLY PLANE MIXING LAYER

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