A study of various factors affecting Newtonian extrudate swell

Mitsoulis, Evan; Georgiou, Georgios C.; Kountouriotis, Zacharias

doi:10.1016/j.compfluid.2011.12.019

Cited by 38 publications

(53 citation statements)

References 32 publications

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“…We will give detailed information about the pressure and velocity in the vicinity of the singularity for a wide range of Reynolds numbers (0 6 Re 6 100) and for slip along the die wall. We demonstrate that our method predicts swell ratios and exit pressure loss corrections in excellent agreement with a recent numerical study of Mitsoulis et al [3] for our coarsest approximation P ¼ 10. Mitsoulis et al [3] used a low order finite element method with a high mesh refinement around the singularity.…”

Section: Introductionsupporting

confidence: 85%

“…Fig. 4 and Table 3 shows the comparison of the swelling ratios obtained with our algorithm with the results of Mitsoulis et al [3], which are in excellent agreement. Fig.…”

Section: Resupporting

confidence: 76%

“…Comparison of swell ratios for Newtonian fluid from the current study (P ¼ 10) with Mitsoulis et al[3].…”

mentioning

confidence: 74%

“…We start by computing the extrudate swell for Re ¼ 0 and initialise this computation with the solution of the corresponding stick-slip problem. The stick-slip problem corresponds to the Table 3 Comparison of Newtonian die swell ratio for increasing Reynolds number with Mitsoulis et al [3].…”

Section: Impact Of Inertiamentioning

confidence: 99%

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Spectral/hp element methods for plane Newtonian extrudate swell

2015

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a b s t r a c tSpectral/hp element methods and an arbitrary Lagrangian-Eulerian (ALE) moving-boundary technique are used to investigate planar Newtonian extrudate swell. Newtonian extrudate swell arises when viscous liquids exit long die slits. The problem is characterised by a stress singularity at the end of the slit which is inherently difficult to capture and strongly influences the predicted swelling of the fluid. The impact of inertia (0 6 Re 6 100) and slip along the die wall on the free surface profile and the velocity and pressure values in the domain and around the singularity are investigated. The high order method is shown to provide high resolution of the steep pressure profile at the singularity. The swelling ratio and exit pressure loss are compared with existing results in the literature and the ability of high-order methods to capture these values using significantly fewer degrees of freedom is demonstrated.

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Section: Introductionsupporting

confidence: 85%

“…Fig. 4 and Table 3 shows the comparison of the swelling ratios obtained with our algorithm with the results of Mitsoulis et al [3], which are in excellent agreement. Fig.…”

Section: Resupporting

confidence: 76%

“…Comparison of swell ratios for Newtonian fluid from the current study (P ¼ 10) with Mitsoulis et al[3].…”

mentioning

confidence: 74%

Section: Impact Of Inertiamentioning

confidence: 99%

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Spectral/hp element methods for plane Newtonian extrudate swell

2015

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“…When n < 0.3, we obtain a swell ratio below one, meaning that the extrudate shrinks slightly. The influence of n in the swell ratio seems to be qualitatively similar to the inertia effects observed for Newtonian fluids elsewhere [95,96]. Furthermore, the extrudates display non-monotonic free-surface profiles for 0 < n < 0.5, similarly to the regime of delayed extrudate swell observed for 6 ≤ Re ≤ 10 [96].…”

Section: Numerical Results For the Carreau Fluidsupporting

confidence: 56%

Numerical simulation of the planar extrudate swell of pseudoplastic and viscoelastic fluids with the streamfunction and the VOF methods

Comminal

Pimenta

Hattel

et al. 2018

Journal of Non-Newtonian Fluid Mechanics

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. Numerical simulation of the planar extrudate swell of pseudoplastic and viscoelastic fluids with the streamfunction and the VOF methods. Journal of Non-Newtonian Fluid Mechanics, 252, 1-18. DOI: 10.1016/j.jnnfm.2017 A B S T R A C TWe present an Eulerian free-surface flow solver for incompressible pseudoplastic and viscoelastic non-Newtonian fluids. The free-surface flow solver is based on the streamfunction flow formulation and the volume-of-fluid method. The streamfunction solver computes the vector potential of a solenoidal velocity field, which ensures by construction the mass conservation of the solution, and removes the pressure unknown. Pseudoplastic liquids are modelled with a Carreau model. The viscoelastic fluids are governed by differential constitutive models reformulated with the log-conformation approach, in order to preserve the positive-definiteness of the conformation tensor, and to circumvent the high Weissenberg number problem. The volume fraction of the fluid is advected with a geometric conservative unsplit scheme that preserves a sharp interface representation. For the sake of comparison, we also implemented an algebraic advection scheme for the liquid volume fraction. The proposed numerical method is tested by simulating the planar extrudate swell with the Carreau, Oldroyd-B and Giesekus constitutive models. The swell ratio of the extrudates are compared with the data available in the literature, as well as with numerical simulations performed with the open-source rheoTool toolbox in OpenFOAM ® . While the simulations of the generalized Newtonian fluids achieved mesh independence for all the methods tested, the flow simulations of the viscoelastic fluids are more sensitive to mesh refinement and the choice of numerical scheme. Moreover, the simulations of Oldroyd-B fluid flows above a critical Weissenberg number are prone to artificial surface instabilities. These numerical artifacts are due to discretization errors within the Eulerian surface-capturing method. However, the numerical issues arise from the stress singularity at the die exit corner, and the unphysical predictions of the Oldroyd-B model in the skin layer of the extrudate after the die exit, where large extensional deformations occur.

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Numerical and experimental studies for gas assisted extrusion forming of molten polypropylene

Ren

Huang

Liu

et al. 2015

J of Applied Polymer Sci

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In this study, the experiments of gas-assisted extrusion (GAE) for molten polypropylene were carried out under different gas pressures, the different extrudate deformations and sharkskin defects of melt were observed. To ascertain the effects of gas on melt extrusion, non-isothermal numerical simulation of GAE based on gas/melt two-phase fluid model was proposed and studied. In the simulations, the melt extruded profile, physical field distributions (velocities, pressure drop, and first normal stress difference) were obtained. Numerical results showed that the deformation degree of melt increased with increasing gas pressure, which was in good agreement with experimental results. It was demonstrated that the influence of gas pressure on the melt extrusion could be well reflected by GAE simulation based on gas/melt two-phase fluid model rather than simplified-GAE (SGAE) based on full-slip wall boundary condition used in the past time. Experimental and numerical results demonstrate that the gas pressure induced first normal stress difference is the main reason of triggering flow behavior changes, extrudate deformations, and sharkskin defects of melt. Therefore, the reasonable controlling of gas pressure is a key in practice of GAE, and the gas layer and its influence should be considered in GAE numerical simulation.

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A study of various factors affecting Newtonian extrudate swell

Cited by 38 publications

References 32 publications

Spectral/hp element methods for plane Newtonian extrudate swell

Spectral/hp element methods for plane Newtonian extrudate swell

Numerical simulation of the planar extrudate swell of pseudoplastic and viscoelastic fluids with the streamfunction and the VOF methods

Numerical and experimental studies for gas assisted extrusion forming of molten polypropylene

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