Particle dispersion in a turbulent vortex core

Abstract

A study is performed using direct numerical simulation to examine the effect of turbulence on particle dispersion in a columnar vortex. A procedure is used to generate initial conditions in which turbulence external to the vortex has the wrapped, nearly azimuthal form characteristic of turbulence around a large-scale vortex structure. This approach enables control of the initial values of the external turbulence intensity and length scale for a given vortex size and strength. The effect of turbulence on dispersion of particles by the vortex flow is examined for a wide range of different values of the initial turbulence intensity. Cases both with zero mean axial flow and unstable vortices with nonzero mean axial flow are examined. The state of the external turbulence is determined by a balance between dissipation, stretching, and vorticity reorientation and stripping from the large-scale vortex core. We examine cases with peak initial turbulence kinetic energy differing by a ratio of up to 400, and for all cases we observe that the external turbulence has a dramatic effect on the particle dispersion. The results of the study have implications for large-eddy simulation of particulate flows for which the particle concentration in the region surrounding the coherent vortex structures will not be accurately predicted if the effect of smaller-scale turbulence surrounding these structures on particle dispersion is not resolved or appropriately modeled.