Chunfeng Zhou, Pengtao Yue & James J. Feng
J. Fluid Mech. 593, 385-404 (2007)
Abstract - We simulate the rise
of Newtonian drops in a nematic liquid crystal parallel to the
far-field molecular orientation. The moving interface is computed in a
diffuse-interface framework, and the anisotropic rheology of the liquid
crystal is represented by the Leslie-Ericksen theory, regularized to
permit topological defects. Results reveal interesting coupling between
the flow field and the orientational field surrounding the drop,
especially the defect configuration. The flow generally sweeps the
point and ring defects downstream, and may transform a ring defect into
a point defect. The stability of these defects and their transformation
are depicted in a phase diagram in terms of the Ericksen number and the
ratio between surface anchoring and bulk elastic energies. The nematic
orientation affects the flow field in return. Drops with planar
anchoring on the surface rise faster than those with homeotropic
anchoring, and the former features a vortex ring in the wake. These are
attributed to the viscous anisotropy of the nematic. With homeotropic
anchoring, the drop rising velocity experiences an overshoot, owing to
the transformation of the initial surface ring defect to a satellite
point defect. With both types of anchoring, the drag coefficient of the
drop decreases with increasing Ericksen number as the flow-alignment of
the nematic orientation reduces the effective viscosity of the liquid
crystal.