3D Viscoelastic analysis of a polymer solution in a complex flow

Abstract

A mixed low-order finite element technique based on the Discrete Elastic Viscous Stress Splitting (DEVSS)/Discontinuous Galerkin (DG) method has been developed for the analysis of three-dimensional viscoelastic flows in the presence of multiple relaxation times. In order to evaluate the predictive capabilities of some established nonlinear constitutive relations like the Giesekus and the Phan-Thien–Tanner (PTT) model results of 3D calculations are compared with experimental results in a cross-slot flow geometry. Moreover, the performance of a new viscoelastic constitutive equation that provides enhanced independent control of the shear and elongational properties is investigated. Steady shear flows and a combined shear/elongational flow are analyzed for a polyisobutylene solution. A general method is introduced to compare calculated stresses along the depth of the flow with birefringence measurements using the stress optical rule. In particular at and downstream of the stagnation point in the cross-slot flow geometry, the numerical/experimental evaluation shows that the multi-mode Giesekus and the PTT model are unable to describe the stress-related experimental observations. The new viscoelastic constitutive relation proves to perform significantly better for this stagnation flow.