Viscous Multiphase: Two-Layer Pipe Co-Extrusion
In industry, co-extrusion is a process in which multiple materials are simultaneously extruded and combined to form one final product. This process is particularly widespread in polymer processing as a method to combine different polymers into multi-layered products, such as coatings, pipes, and films. These polymers are typically non-Newtonian fluids that require special material laws to describe their complex rheological behaviour. Moreover, when multiple non-Newtonian phases are present, the interface between these phases requires tracking. To simulate multi-layer extrusion or co-extrusion applications, Simcenter STAR-CCM+ provides the Viscous Multiphase model, which, in conjunction with the Conservative Level Set method, handles the tracking of the interface between the non-Newtonian phases. The Conservative Level Set method determines the location of each phase, and consequently the location of the interface, by solving an additonal transport equation for the phase field.
The Viscous Multiphase model is specifically designed to simulate liquid non-Newtonian phases modeled by either generalized Newtonian or viscoelastic fluid models, and does not support gas phases.
In this tutorial, you simulate the co-extrusion of two immiscible non-Newtonian liquids through a circular die, which join to form a two-layer pipe. The objective of the simulation is to achieve a specific thickness of the inner layer, where the outer layer serves merely as coating. Therefore, you analyze the position of the interface between the inner and outer phase.
The following diagram shows the tutorial geometry:

The die consists of two concentric inlets: one for the outer phase; one for the inner phase. The phases interact and then exit through a single pressure outlet. The inner and outer phase travel slowly through the die, at average speeds of 5.5 and 5.0 mm/s respectively. Both phases are modelled as generalized Newtonian Power Law liquids with different model parameters for each phase.
Due to symmetry, only a quarter of the die geometry is modelled.