Selective withdrawal of polymer solutions: Computations

This paper reports numerical simulations of selective withdrawal of Newtonian and polymeric liquids, and complements the experimental study reported in the accompanying paper (Zhou and Feng 2]). We use finite elements to solve the Navier–Stokes and constitutive equations in the liquid on an adaptively refined unstructured grid, with an arbitrary Lagrangian–Eulerian scheme to track its free surface. The rheology of the viscoelastic liquids are modeled by the Oldroyd-B and Giesekus equations, and the physical and geometric parameters are matched with those in the experiments. The computed interfacial deformation is in general agreement with the experimental observations. In particular, the critical condition for interfacial rupture is predicted to quantitative accuracy. Furthermore, we combine the numerical and experimental data to explore the potential of selective withdrawal as an extensional rheometer. For Newtonian fluids, the measured steady elongational viscosity is within 47% of the actual value, apparently with better accuracy than other methods applicable to low-viscosity liquids. For polymer solutions, an estimated maximum error of 300% compares favorably with prior measurements.