Determine whether the inertialess elasto-viscoplastic instability is physical

Determine whether the complex dynamics generated by linear instability in inertialess elasto-viscoplastic flows governed by Saramito’s first, or Saramito–Bingham, constitutive model are physical phenomena or artefacts of that constitutive model.

Background

The paper finds that two-dimensional, zero-Reynolds-number circular Couette flow of an elasto-viscoplastic fluid described by Saramito’s Bingham model can become linearly unstable. The instability is strongest near pseudo-plug boundaries or low-shear-rate regions and can evolve into spatio-temporally complex nonlinear dynamics.

The authors emphasize that the instability is concentrated at increasingly short wavelengths, raising concerns about its physical interpretation and numerical sensitivity. They identify experiments with real yield-stress fluids and extensions to three dimensions as potentially necessary for determining whether the observed dynamics reflect physical behavior or a constitutive-model artefact.