Identification of viscoelastic properties in non-rheometric flows by two-dimensional viscoelastic simulations with a rotating object

Abstract

The present study is aimed to investigate the underlying mechanisms for the successful viscoelastic identification via oscillatory shear in non-rheometric flows. To reduce computational cost, a two-dimensional (2D) oscillatory flow problem with a rotating object was selected. A complete set of rheometric analysis tools was developed to determine complex shear moduli in both linear and non-linear regimes. The analysis tools include 2D versions of flow quantification method based on energy dissipation rate, and expressions for shear stress from torque, shear rate, and strain from angular velocity and deflection angle, and complex shear moduli with respect to strain magnitude and oscillation frequency. The complex shear moduli from numerical simulations were compared with the theoretical Maxwell model with solvent viscosity under small-amplitude oscillatory shear conditions to validate the accuracy of the viscoelastic identification technique, and the effects of fluid inertia were quantitatively examined. Additionally, analyses of local stress behavior, in conjunction with the spectral decomposition of the total stress tensor, demonstrate that the synchronized pulsating stress field emerges even in non-rheometric flow. Analysis of the local flow fields confirmed that both the eigenvalues and eigenvector directions remained synchronized across the domain, which explains the physical basis for successful rheometric identification in non-rheometric flow systems. The limitations of viscoelastic measurement with a rotating object are also discussed in terms of the deviations in storage modulus