Instabilities in viscoelastic flow through an axisymmetric sudden contraction

Experimental study of the volume defects in polystyrene extrusion

“…The fringes displacements are getting more rapid and more complex: it seems that several successive modes occur and are superimposed to the first one. These results are qualitatively similar to those reported by Yesilata et al [16] concerning pressure drop fluctuations in an abrupt contraction during elastic instabilities. It is also interesting to investigate the time evolution of the instability frequency along the die channel.…”

“…However, this critical stress depends on the die length, the temperature and also the molecular weight [9]. Moreover, upstream die flow visualizations during the instability, using either flow birefringence [10][11][12][13], tracers [6,[13][14][15][16][17][18], or laser Doppler velocimetry [17,18] proved that the region upstream the contraction was the site of the defect initiation. Nigen et al [19] have recently carried out investigations using particle image velocimetry and confirmed the link between entry flow destabilization and gross melt fracture.…”

“…The vortices would oscillate, above a critical size, and then burst into the main convergent flow, destabilizing it. Vortex instabilities have been clearly demonstrated in recent works on Boger fluids polymer solutions [16,17]. However, applications to molten polymers remain less common.…”

Flow patterns in 4:1 micro-contraction flows of viscoelastic fluids

“…In the studies where macro-size contraction geometry was used, the flows with high Weissenberg numbers could not be reached due to the limitation of the shear rate, and flow dynamics has been studied mostly in steady states. There were some reports on the vortex oscillation that arises due to elasticity (Alves et al, 2005;Kwon, 2012;Kwon and Park, 2012;Yesilata et al, 1999). However, detailed characteristics or the flow patterns in the unsteady region has never been explored yet.…”

The Finite Volume Method in Computational Rheology

“…This sequence of events has been seen as early as the late seventies by Cable and Boger (1978a, 1978b and Nguyen and Boger (1979) and has been studied in detail by Lawler et al (1986), McKinley et al (1991 and Yesilata et al (1999).…”