3D simulation of the Hierarchical Multi-Mode Molecular Stress Function constitutive model in an abrupt contraction flow

A recent development of the Molecular Stress Function constitutive model, the Hierarchical Multi-Mode Molecular Stress Function (HMMSF) model has been shown to fit a large range of rheometrical data with accuracy, for a large range of polymer melts. We develop a 3D simulation of the HMMSF model and compare it to experimental data for the flow of Lupolen 1840H LDPE through an abrupt 3D contraction flow. We believe this to be the first finite element implementation of the HMMSF model. It is shown that the model gives a striking agreement with experimental vortex opening angles, with very good agreement to full-field birefringence measurements, over a wide range of flow rates. A method to give fully-developed inlet boundary conditions is implemented (in place of using parabolic inlet boundary conditions), which gives a significantly improved match to birefringence measurements in the inlet area, and in low stress areas downstream from the inlet. Alternative constitutive model parameters are assessed following the principle that extensional rheometer data actually provides a ‘lower bound’ for peak extensional viscosity. It is shown that the model robustly maintains an accurate fit to vortex opening angle and full-field birefringence data, provided that both adjustable parameters are kept such that both shear and extensional data are well fitted.

URI

http://hdl.handle.net/10454/18929

Version

Published version

Citation

Olley P, Gough TD, Spares R and Coates PD (2022) 3D simulation of the Hierarchical Multi-Mode Molecular Stress Function constitutive model in an abrupt contraction flow. Journal of Non-Newtonian Fluid Mechanics. 304: 104806.

Link to Version of Record

https://doi.org/10.1016/j.jnnfm.2022.104806

Type

Article