Visco-elastic analysis of polymer melts in complex flows

Numerical simulation of visco-elastic flows remains a subject of extensive investigations. For example, in regard to polymeric melt flows in industrial applications. Eventually, the objective is to perform simulations of visco-elastic flows in characteristic geometries under industrial processing conditions. This means, flows with a realistically rheological behaviour at high elasticity rates in three dimensional geometries. A mixed low-order finite element technique, based on the DEVSS/DG method, has been developed to analyse visco-elastic flows. The DEVSS/DG technique allows for efficient handling of multiple relaxation times using an implicit/explicit implementation. Especially for three dimensional calculations, this necessity becomes clear in regard to CPU time and memory requirement. In order to evaluate the predictive capabilities of constitutive equations, results of numerical simulations are compared with experimental results. In general, visco-elastic fluids are characterised in shear, and, in a lesser extent, also in elongation. The characterisation of polymer melts in complex flows, where combined shear/elongational regions occur, is investigated. For higher Weissenberg numbers, i.e. higher elasticity rates, the established constitutive equations, like the Giesekus and Phan-Thien Tanner models, are unable to describe the stress related experimental observations satisfactorily. These models mostly underpredict elongation. Alteration of the parameter sets of the models does not give any improvement. Therefore, a new constitutive equation has been developed. This Feta model is based on the PTT model, where the shear viscosity is fixed to experimental data, while still allowing for flexibility in describing extensional properties. Performances of the Feta model in complex flows is investigated.