Particle transport in a nonuniformly seeded mixing layer

The effect of nonuniform seeding on the dispersion of heavy particles in a temporally evolving mixing layer has been investigated using simulation of the two-dimensional, incompressible Navier-Stokes equations. Mean-square dispersion and particle concentration were obtained from the trajectories of 20,000 particles. Particle Stokes numbers (St) in the calculations were 0.05, 1, and 10 where St is defined as the ratio of the particle time constant to large scale fluid time scale. Particles were initially distributed along the centerline, nonuniformity achieved by locating a greater fraction of particles near the saddle point of the layer. Consistent with previous experimental and numerical studies, particle dispersion following the development of the large scale roller is largest for St = 1, though in general the maximum dispersion is a function of both time and Stokes number. More importantly, it is shown that substantial increases—as large as a factor of 10—in particle dispersion can be obtained using nonuniform seedings relative to that obtained for an initially uniform distribution. It is also demonstrated that particle concentrations are substantially less peaked along the center of the layer for initially nonuniform seedings relative to uniform distributions.