A FINITE-ELEMENT METHOD FOR COMPUTING THE FLOW OF MULTIMODE VISCOELASTIC FLUIDS - COMPARISON WITH EXPERIMENTS

The numerical computation of viscoelastic fluid flows with differentia l constitutive equations presents various difficulties. The first one lies in the numerical convergence of the complex numerical scheme solv ing the non-linear set of equations. Due to the hybrid type of these e quations (elliptic and hyperbolic), geometrical singularities such as reentrant corner or die induce stress singularities and hence numerica l problems. Another difficulty is the choice of an appropriate constit utive equation and the determination of rheological constants. In this paper, a quasi-Newton method is developed for a fluid obeying a multi -mode Phan-Thien and Tanner constitutive equation. A confined converge nt geometry followed by the extrudate swell has been considered. Numer ical results obtained for two-dimensional or axisymmetric flows are co mpared to experimental results (birefringence patterns or extrudate sw ell) for a linear low density polyethylene (LLDPE) and a low density p olyethylene (LDPE). (C) 1998 Elsevier Science B.V.