It is well-known that, increasing the flow rate in polymer extrusion, the flow becomes unstable
and the smooth extrudate surface becomes wavy and disordered to an increasing degree. In order
to investigate the mechanisms responsible for these instabilities we perform a linear stability
analysis of the steady extrusion of a viscoelastic fluid flowing through a planar die under creeping
flow conditions. We consider the Phan-Thien-Tanner (PTT) model to account for the
viscoelasticity of the material. We employ the mixed finite element method combined with an
elliptic grid generator to account for the deformable shape of the interface. The generalized
eigenvalue problem is solved using Arnoldi’s algorithm. We perform a thorough parametric study
in order to determine the effects of all material properties and rheological parameters. We
investigate in detail the effect of interfacial tension and the presence of a deformable interface. It
is found that the presence of a finite surface tension destabilizes the flow as compared to the case
of the stick-slip flow. We recognize two modes which are found to become unstable beyond a
critical value of the Weissenberg number and perform an energy analysis to examine the
mechanisms responsible for the destabilization of the flow and compare against the mechanisms
that have been suggested in the literature. / --
| Identifer | oai:union.ndltd.org:upatras.gr/oai:nemertes:10889/8697 |
| Date | 02 June 2015 |
| Creators | Πέττας, Διονύσιος |
| Contributors | Τσαμόπουλος, Ιωάννης, Pettas, Dionisios, Τσαμόπουλος, Ιωάννης, Δημακόπουλος, Ιωάννης, Μαυραντζάς, Βλάσης |
| Source Sets | University of Patras |
| Language | gr |
| Detected Language | English |
| Type | Thesis |
| Rights | 0 |
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