Implementation of a viscoelastic fluid model considering transition to plastic regime and polymer rupture
Name: EDUARDO MARQUES VIEIRA
Publication date: 23/08/2024
Examining board:
Name |
Role |
|---|---|
| EMANUEL NEGRÃO MACÊDO | Examinador Externo |
| MARCIO FERREIRA MARTINS | Examinador Interno |
| RAMON SILVA MARTINS | Coorientador |
Summary: Viscoelastic fluid is a non-Newtonian kind of fluid. They can be represented by a damper (that controls the viscosity behavior) associated with a spring (that controls the elastic behavior), Generally, viscoelastic fluids are obtained by adding polymer molecules in a Newtonian solvent fluid. Due to the stress field promoted by the flow, the polymer scission is experimentally observed. The polymer breakage phenomenon is not visualized numerically because all the viscoelastic fluid models do not
consider it.
In this thesis, first, we give a friendly review of the viscoelastic fluid models, explaining the linear and the nonlinear models. All the models were submitted to a transient simulation in a Cross-Slot Channel to present some behavior differences between the models.
After showing the limitations of some models, we take the FENE spring model and remove its singularity. This results in a spring that is not limited by a maximum length but now is able to break.
Our model, which we called EPTRA – Elastic to Plastic Transition and Rupture Analysis – model, is the only model that considers that the spring can suffer damage, i.e., have a plastic regime. By achieving a spring function that can suffer a scission, we go from one polymer molecule to a continuum medium by applying the Fokker-Planck equation. Furthermore, we show the steps in the implementation at OpenFOAM®, which is a Computational Fluid Dynamics (CFD) software with the RheoTool®solver package, which is a solver package for non-Newtonian fluids simulations. We simulate a laminar flow in a Cross-Slot channel and a 4:1 Contraction. We observed more breaks in the Cross-Slot, thus, we also demonstrated the transient difference between our model and the other ones.
Lastly, it is implemented the Log-Conformation tensor formulation for the EPTRA model. This formulation deals with numerical instabilities and allows the simulation of cases with higher Weissenberg numbers.
