The closed form Adaptive Length Scale model in simple and complex flows

Zografos, K. (Speaker), Alexandre M. Afonso (Contributor), Robert J. Poole (Contributor)

Activity: Talk or presentation typesOral presentation

Description

In this paper we employ the closed form of the Adaptive Length Scale (ALS-C) model[1] and investigate its characteristics and potential use in numerical studies of dilute polymer solutions in general flows. The derivation of the ALS-C model was originally inspired by the ability of a Kramers chain to capture important properties of dilute polymer solutions in rapidly varying extensional flows, such as coil-stretch hysteresis.The model introduces two variable extensibility parameters which adapt to the flow changes that modify the developed stresses. The ALS-C can be considered as a generalised version of the Finitely Extensible Nonlinear Elastic model that follows the Peterlin approximation (FENE-P). In proposing the model it was hoped that it would be capable of predicting the enhanced pressure drop observed in many flows of dilute polymeric solutions, but this hypothesis has never been tested in complex flows.
The ALS-C model has not been yet considered in flows outside of simple homogeneous shear or extension and specifically not in any general computational fluid dynamics (CFD) simulations. The model has been implemented into an in-house CFD solver appropriate for viscoelastic fluids[2], while for enhanced stability the log-conformation approach[3] is employed within a finite-volume methodology. Here, we demonstrate the set of equations that need to be solved together with a modified approach that enhances the computational speed for evaluating the instantaneous changes in the adaptive length scale as a result of the instantaneous changes in the flow field. Initially, the performance of the model is illustrated for standard rheological and steady-state shear flows. Finally, its performance in flows within a range of complex geometries is presented, with particular emphasis placed on the estimation of the pressure drop and comparison with experimental data.

[1]I Ghosh et al, J Rheol 46(2002)
[2]PJ Oliveira et al, J Non-Newton Fluid Mech 79(1998)
[3]A Afonso et al, J Non-Newton Fluid Mech 157(2009)
Period14 Apr 2021
Event title14th Annual European Rheology Conference, AERC 2021
Event typeConference
Degree of RecognitionInternational