A geometric Volume-of-Fluid (VoF) approach to assessing geometric and thermal uncertainties in the extensional rheometry of viscoelastic fluids

Extensional rheology of viscoelastic polymer melts plays a pivotal role in optimizing key industrial processes such as thermoforming, blow molding, and film blowing. However, experimental uncertainties and the inherent complexity of viscoelastic flows make accurate characterization difficult. We present a novel computational framework that integrates advanced numerical modeling with rheological analysis to enable a deeper understanding of extensional flow phenomena: Our Eulerian-based rheoInterIsoFoam solver, realized within the OpenFOAM platform, employs the geometric Volume-of-Fluid (VoF) isoAdvector algorithm to improve interface tracking, thus overcoming the limitations of conventional, algebraic VoF methods. Applied to a commercial polycarbonate melt, our simulations allowed systematic evaluation of the impacts of key experimental uncertainties (i.e., in sample geometry and test temperature) on extensional viscosity. The results show that geometric uncertainties induced moderate, nearly proportional deviations in extensional viscosity, whereas temperature fluctuations had a more substantial impact. The validation against semi-analytical models supports the solver’s accuracy and numerical robustness in this case study, and corroborates that viscoelastic effects can play an important role in the materials' extensional behavior.