Diwen Zhou, Pengtao Yue & James J. Feng
J. Rheol. 52, 469-487 (2008)
Abstract - This paper reports
finite-element simulations of drop deformation in converging flows in
an axisymmetric conical geometry. The moving interface is captured
using a diffuse-interface model and accurate interfacial resolution is
ensured by adaptive refinement of the grid. We have explored the
effects of viscoelasticity on drop deformation when either the drop or
the matrix is a Giesekus fluid. Contrary to the popular belief that
viscoelasticity in the drop hinders deformation and that in the matrix
enhances deformation, we predict a more complex picture in which
viscoelasticity in either component may suppress or promote drop
deformation depending on the capillary number Ca and the drop-to-matrix
viscosity ratio β. Smaller Ca and β are conducive to the behavior
mentioned above, while large Ca and β may produce the opposite effect.
Both trends are explained by the reaction of the polymer stress to the
inhomogeneous and transient deformation in the converging flow field.
Finally, this understanding reconciles contradictory results in the
literature as opposite limits in the parameter space.