Abstract
In order to assess the predictive capability of the S–MDCPP model, which may describe the viscoelastic behavior of the low-density polyethylene melts, a planar contraction flow benchmark problem is calculated in this investigation. A pressure-stabilized iterative fractional step algorithm based on the finite increment calculus (FIC) method is adopted to overcome oscillations of the pressure field due to the incompressibility of fluids. The discrete elastic viscous stress splitting (DEVSS) technique in combination with the streamline upwind Petrov-Galerkin (SUPG) method are employed to calculate the viscoelastic flow. The equal low-order finite elements interpolation approximations for velocity-pressure-stress variables can be applied to calculate the viscoelastic contraction flows for LDPE melts. The predicted velocities agree well with the experimental results of particle imagine velocity (PIV) method, and the pattern of principal stress difference calculated by the S-MDCPP model has good agreement with the results measured by the flow induced birefringence (FIB) device. Numerical and experimental results show that the S-MDCPP model is capable of accurately capturing the rheological behaviors of branched polymers in complex flow.
Highlights
During the past two decades with the developments of numerical algorithm and constitutive model, computational rheology has achieved great progress as an important tool
It can be seen that our experimental result agrees well with the principal stress difference (PSD) patterns measured by Verbeeten [15,27]
Because the channel contraction ratio of the experimental device used by Verbeeten is 3.29:1, but the contraction ratio of this study is 4:1, the size of the PSD pattern has a slight difference in the contraction region
Summary
During the past two decades with the developments of numerical algorithm and constitutive model, computational rheology has achieved great progress as an important tool. Wang et al [16] evaluated the performance of the double-convected Pom-Pom mode (DCPP) model using the particle imagine velocity (PIV) method They observed that the LDPE melt appears as large corner vortex in the contraction entrance, which has good agreement with the numerical results predicted by Polyflow software. Similar contraction flows widely appear in industrial polymer processing, such as extrusion flow, injection molding, fiber spinning process, etc By means of this complex flow field, the rheological responses of the constitutive model may be computed in a numerical way and verified by stress and velocity fields using the birefringence experiment and PIV measurement respectively.
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