Particle Dispersion by Vortex Structures in Plane Mixing Layers

The dispersion of particles in a plane mixing layer between two air streams is investigated using experimental and numerical techniques. The results show that large-scale spanwise vortices strongly influence the particle dispersion process. Particles with aerodynamic response times on the order of the large scale vortex time scales are found to concentrate near the outer edges of the vortex structures. Time average velocity measurements also demonstrate that these particles tend to move away from the center of the mixing layer. Substantial changes in the lateral particle dispersion are producible by controlled forcing of the vortex structures. Comparisons between the experimental particle dispersion patterns and numerical simulations show striking similarities. A two-part model involving stretching and folding is suggested as a particle dispersion mechanism.