Effect of External Forcing on Droplet Dispersion in a Developing Shear Layer

The dynamics and dispersion of nonevaporating droplets in a forced transitional shear layer are studied. The shear layer is formed by two coflowing parallel streams downstream of a splitter plate. The effects of periodic forcing on the dynamics of large-scale vortical structures and on the dispersion characteristics of droplets in a spatially and temporally developing shear layer are investigated. Results indicate that by forcing the shear layer at the first subharmonic of the fundamental mode, the droplet dispersion can be enhanced significantly. The forcing at the fundamental mode increases droplet dispersion in the initial part, but then decreases dispersion farther downstream. These results are consistent with the previously published experimental and numerical results on the effect of forcing on the shear layer growth. It is also observed that the forcing causes a relatively larger gain in dispersion for intermediate size particles compared to that for gas particles, implying that the centrifugal mechanism may be strengthened by forcing. The dispersion enhancement is more pronounced in the initial part of the shear layer, which is perhaps the more important region for improved droplet dispersion and mixing in spray applications.