A NOVEL UTILITY TO CALCULATE THE FORCE AND TORQUE FOR VISCOELASTIC MATERIALS

Viscoelastic fluids, which exhibit both viscous and elastic behavior, play a crucial role in a wide range of engineering and industrial processes, including polymer and food processing, additive manufacturing and biomedical applications.
A comprehensive understanding of the mechanical interactions between these fluids and the boundaries of such flow systems is essential for accurately predicting performance, optimizing equipment and processes, and validating constitutive models. Specifically, the evaluation of forces and torques exerted by viscoelastic fluids on surfaces is critical for interpreting flow-induced stresses, assessing mechanical loads, and deriving rheological properties under complex flow conditions.
This work presents the development and implementation of an innovative force and torque computation utility specifically designed for viscoelastic materials within the open-source computational fluid dynamics (CFD) framework OpenFOAM. Unlike existing force utilities, which are primarily intended for inelastic fluids and neglect the non-linear stress contributions characteristic of viscoelastic fluids, the proposed tool incorporates the complete extra stress tensor derived from user-specified viscoelastic constitutive models for two-phase flows. This enhancement facilitates the precise calculation of hydrodynamic forces and torques in simulations involving viscoelastic behavior.
To verify the accuracy and applicability of the implementation, a benchmark case was conducted simulating a polymer melt undergoing extensional deformation. The setup utilized corresponds to a Sentmanat Extension Rheometer (SER), in which a parallelepiped polymer sample is elongated between two counter-rotating drums, and the torque was computed using the newly developed utility. The torque data obtained were employed to calculate the transient extensional viscosity of the polymer melt. The resulting extensional viscosity evolution, illustrated in Figure 1,
demonstrates strong agreement between numeric predictions and semi-analytical results, thereby validating the accuracy of the implementation and confirming the physical consistency of the computed stress contributions.