Viscous and Viscoelastic Fingering

The displacement of a more viscous fluid by a lower viscosity fluid in quasi-two dimensional flows created in the so-called Hele Shaw cell creates complex fingering patterns. For Newtonian fluids, the shape and shape evolution for fingering patterns are influenced by the viscosity ratio of inner to outer fluid. In this contribution, we examine the influence of viscoelasticity on the onset and the evolution of fingering instabilities, by utilizing model viscoelastic fluids with rate-independent shear viscosity, measurable first normal stress difference, and known extensional rheology response. We show that the analysis of viscoelastic fingering provides a representative experimental system for characterizing the influence of nonlinear viscoelasticity on interfacial and nonlinear flows commonly encountered in many real processing operations.