Numerical simulation of particle transport in planar shear layers

Numerical simulations of particle dispersion in a planar shear dominated by large scale vortical structures are reported. The shear layer is formed by two co-flowing streams past a splitter plate. The emphasis of this work is on examining how the particle dynamics are affected by the large-scale coherent structures in the initial development of the instabilities in a spatially-developing mixing layer. The two-dimensional time-dependent gas-phase equations are solved numerically using the explicit flux corrected transport (FCT) algorithm in the low-Mach-number regime. The dispersion of particles is studied by following their trajectories in the shear layer. A detailed visualization of the Bow field, dominated by the large structures, and of the particle dynamics is performed to obtain qualitative as well as quantitative information on the particle dispersion. The visualization clearly reveals the capturing of the small and intermediate size particles by the vortical structures. The small size particles, however, remain captured in the vortical structures, whereas the intermediate size particles are flung our of them, leading to their enhanced dispersion. The large particles remain mostly unaffected by the large eddies. The quantitative results obtained indicate that the above behavior can be well correlated with the Stokes number (S-t) values; the optimal dispersion corresponds to the Stokes numbers in the range 0.1 < S-t < 5.0. This is in qualitative agreement with previously reported experimental as well as numerical results. The results also indicate that the particles injected in the faster stream exhibit higher dispersion compared to those injected in the slower stream. This divergence in the dispersion behavior is related to the asymmetric entrainment as reported by some earlier experimental and numerical studies.