TRANSPORT OF HEAVY-PARTICLES IN A 3-DIMENSIONAL MIXING LAYER

Particle transport in a three-dimensional, temporally evolving mixing layer has been calculated using large eddy simulation of the incompres sible Navier-Stokes equations. The initial fluid velocity field was ob tained from a separate simulation of fully developed turbulent channel flow. The momentum thickness Reynolds number ranged from 710 in the i nitial field to 4460 at the end of the calculation. Following a short development period, the layer evolves nearly self-similarly. Fluid vel ocity statistics are in good agreement with both the direct numerical simulation results of Rogers and Moser (1994) and experimental measure ments of Bell and Mehta (1990). Particles were treated in a Lagrangian manner by solving the equation of motion motion for an ensemble of 20 ,000 particles. The particles have the same material properties as in the experiments of Hishida ct al. (1992), i.e., glass beads with diame ters of 42, 72, and 135 mu m. Particle motion is governed by drag and gravity, particle-particle collisions are neglected, and the coupling is from fluid to particles only. In general, the mean and fluctuating particle velocities are in reasonable agreement with the experimental measurements of Hishida et al. (1992). Consistent with previous studie s, the Stokes number (St) corresponding to maximum dispersion increase s as the flow evolves when defined using a fixed fluid timescale. Defi nition of the Stokes number using the time-dependent vorticity thickne ss, however, shows a maximum in dispersion throughout the simulation f or St approximate to 1.