Three-dimensional numerical simulation of viscoelastic contraction flows using the Pom-Pom differential constitutive model

A three-dimensional finite element method is applied for analyzing the viscoelastic flow of branched LDPE through 3D planar contraction geometry. For describing the viscoelastic properties of the flowing material, a recently proposed eXtended Pom-Pom model is used. The main purpose of our study is to evaluate the ability of this model to capture some specific 3D effects in the case of converging entry flow of relatively high strain-hardening polyethylene melts. A special attention is paid to the vortex region. Like in our previous study [I. Sirakov, A. Ainser, J. Guillet, Three-dimensional numerical simulation of viscoelastic planar contraction flow, in: Proceedings of the Fourth International ESAFORM Conference, Liege, 23-25 April 2001] (where the Phan-Thien Tanner (PTT) model was used), the calculations predict an open vortex in which the material is involved in a complicated spiral motion, directed from the vertical plane of symmetry to the side wall of the contraction. Quantitative comparisons with experiments are done on the vortex size in the width direction (contraction z-axis).