Formulation of an equivalent GNF model as an efficient approximation for flow of polymer solutions described by FENE-P

TL;DR

This paper develops a computationally efficient GNF-based approximation for the FENE-P model of polymer solutions, accurately capturing flow behavior while significantly reducing computation time, especially at higher flow rates.

Contribution

A novel GNF-XM model is proposed that closely approximates FENE-P flow predictions with much lower computational cost.

Findings

GNF-XM accurately predicts flow and stress profiles similar to FENE-P.

GNF-XM reduces computational time by about an order of magnitude.

GNF-XM successfully captures chain stretching effects near stagnation points.

Abstract

The molecular constitutive models, like FENE-P for polymer solutions, are known to have convergence issues at relatively larger flow rates. In this study, we investigate the possibility of a numerically efficient GNF-based approximation of FENE-P, which would closely approximate the flow field. Firstly, we compare the flow fields predicted by FENE-P and an equivalent GNF model. For these studies, we considered the flow around a sphere and selected the Carreau-Yasuda model as the representative GNF. This is made equivalent to the FENE-P by selecting parameters to equalize the viscosity-shear rate dependence. Our results show severe deficiencies of the GNF model, owing to its inability to account for chain stretching, particularly near the stagnation points. Next, the effect of extensional components on the local viscosity was added by formulating an equivalent GNF-X [Journal of Rheology 64, 493 (2020)] model. Even this failed to capture the asymmetry in the stress and flow profiles and predicted very large stresses at both stagnation points, relative to FENE-P. Hence, we proposed a novel modified formalism (denoted as GNF-XM) that was able to capture all trends successfully. The drag coefficients from GNF-XM agreed well with FENE-P predictions for all flow rates considered. Significantly, the computational times required to solve the flow field with GNF-XM is about an order of magnitude lower than that of FENE-P, especially at higher flow rates. Thus, we have successfully formulated a highly efficient GNF-based approximation to the FENE-P, whose formalism can be extended to other similarly complicated constitutive models.