An Insight into Parameter Identifiability Issues in the Carreau-Yasuda Model: a More Consistent Rheological Formulation for Shear-thinning non-Newtonian Inelastic Fluids

Abstract: The Carreau-Yasuda rheological model is widely employed in both research and industrial applications to describe the shear-thinning behaviour of non-Newtonian inelastic fluids. However, its calibration against experimental data is often affected by intrinsic identifiability issues, which can lead to misleading physical interpretations of model parameters and unreliable flow predictions. In this paper, starting from the analysis of the identifiability challenges associated with the Carreau-Yasuda model, a novel rheological formulation for shear-thinning non-Newtonian inelastic fluids is proposed. Analytical results and exemplary numerical case studies demonstrate that the proposed formulation is based on physically meaningful model parameters, whose identifiability is not compromised by the key limitations of the Carreau-Yasuda model. Moreover, the new approach allows for effective parameter estimation through a straightforward direct identification strategy, eliminating the need for inverse calibration procedures based on optimization techniques.