Viscoelastic Flow in Axisymmetric Contractions: the Effect of Contraction Ratio

Numerical simulations of PTT fluids in axisymmetric sudden contractions were carried out to investigate the effect of contraction ratio on the flow patterns under conditions of negligible inertia. The PTT model selected has a linear stress coefficient, and contraction ratios (CR) in the range 4:1 to 100:1 were investigated. The simulations are based on a finite volume methodology using very fine meshes and a purposely developed high-resolution scheme for the discretization of advective terms in the viscoelastic constitutive equation. In contrast to Newtonian fluids, where the contraction ratio has no significant influence for CR larger than 4, for these shear-thinning viscoelastic fluids the corner vortex increases with flow elasticity and, of more interest, a lip vortex is formed at large contractions ratios. This lip vortex also grows with elasticity, then merges and later engulfs the corner vortex, much like the situation for plane contraction flows. In this work, maps are presented outlining regions of different vortex behaviour.