Rheological characterization and flow reconstruction of polyvinylpyrrolidone aqueous solutions by means of velocity profiling-based rheometry

A method for reconstructing velocity fields of non-Newtonian fluids is proposed, which ensures consistency with experimentally evaluated rheological properties. A polyvinylpyrrolidone (PVP) aqueous solution for the test fluid is generally assumed as Newtonian, while it is viscoelastic in limited conditions of unsteady shear flows. Comprehensive evaluation for figuring out the dependence of viscoelasticity on applied shear deformation and its timescale was conducted by rheology mapping [Ohie et al., “Effective rheology mapping for characterizing polymer solutions utilizing ultrasonic spinning rheometry”, Exp. Fluids, 63, 2 (2022)], which is based on a velocity profiling-based rheometry. It revealed the conditions of shear rate and oscillation frequency where the viscoelasticity emerges. A newly proposed convergence calculation method was adapted to this PVP solution as a demonstration for reconstructing velocity fields from the experimentally obtained data set. The proposed calculation scheme is designed not to need a separate rheological model for each complex fluid. The predicted oscillatory shear flows between double concentric cylinders were clearly different with and without the non-Newtonian characteristic. The predicted velocity profiles considering the non-Newtonian characteristic were in good agreement with verification experimental results. This indicates validity of the proposed convergence calculation method combined with the experimentally evaluated rheological properties.