| Summary: |
Polymeric fluids usually manifest non-Newtonian behavior in flow, and in particular viscoelastic character. These types of fluids are used in several industries, such as petrochemical, foods, pharmaceutical, plastics, paints or detergents.
In the 1950s, less than 5 million tonnes of plastic products were produced per year worldwide. This year about 80 million tonnes of plastic products will be manufactured worldwide, illustrating the growing importance of polymeric materials in our life.
Viscoelastic flows are very complex and sometimes the flow patterns observed are completely unexpected, as illustrated in the excellent album of photographs collected by Boger and Walters (1993) ["Rheological Phenomena in Focus", Elsevier].
Most of the published works on visualization of viscoelastic flows refer to situations that are approximately two-dimensional. However, under practical situations viscoelastic fluids are processed in complex geometries where the flow patterns are truly 3D.
The aim of this project is the study of viscoelastic flows in complex geometries that originate truly three-dimensional flows. 3D sudden contractions and the flow past a cylinder placed in cross flow in the middle of a square duct will be investigated. Both geometries are relatively simple, but the resulting flow patterns are complex due to the 3D nature of the flow and to the nonlinear rheological behavior of the viscoelastic fluids. Experimental techniques will be used to characterize the hydrodynamics, such as LDA (laser Doppler Anemometry), streakline photography techniques and pressure drop measurements. These flows will also be investigated numerically using a computational rheology code that has been successfully developed within our research group during the past eight years.
The use of numerical and experimental methods in this study is complimentary. While the numerical methods enable the analysis of certain flow details that cannot be measured, the experimentat  |
Summary
Polymeric fluids usually manifest non-Newtonian behavior in flow, and in particular viscoelastic character. These types of fluids are used in several industries, such as petrochemical, foods, pharmaceutical, plastics, paints or detergents.
In the 1950s, less than 5 million tonnes of plastic products were produced per year worldwide. This year about 80 million tonnes of plastic products will be manufactured worldwide, illustrating the growing importance of polymeric materials in our life.
Viscoelastic flows are very complex and sometimes the flow patterns observed are completely unexpected, as illustrated in the excellent album of photographs collected by Boger and Walters (1993) ["Rheological Phenomena in Focus", Elsevier].
Most of the published works on visualization of viscoelastic flows refer to situations that are approximately two-dimensional. However, under practical situations viscoelastic fluids are processed in complex geometries where the flow patterns are truly 3D.
The aim of this project is the study of viscoelastic flows in complex geometries that originate truly three-dimensional flows. 3D sudden contractions and the flow past a cylinder placed in cross flow in the middle of a square duct will be investigated. Both geometries are relatively simple, but the resulting flow patterns are complex due to the 3D nature of the flow and to the nonlinear rheological behavior of the viscoelastic fluids. Experimental techniques will be used to characterize the hydrodynamics, such as LDA (laser Doppler Anemometry), streakline photography techniques and pressure drop measurements. These flows will also be investigated numerically using a computational rheology code that has been successfully developed within our research group during the past eight years.
The use of numerical and experimental methods in this study is complimentary. While the numerical methods enable the analysis of certain flow details that cannot be measured, the experimentation is very important in the validation of the mathematical models used in the numerical code.
Another goal of the numerical work is the development of an efficient methodology for the computation of 3D viscoelastic flows, and particularly to produce a working program capable of analyzing 3D complex flows of polymer melts, with application in polymer processing industries. The significance for the field of computational rheology is twofold: (i) the ability to simulate realistic 3D melt flow processes such as extrusion; (ii) a better understanding of problematic high-stress regions at separation points, including the setting of appropriate boundary conditions for practical applications, which will lead to improved process design. |
| Results: |
The output of this project will consist of accurate experimental results for complex viscoelastic flows in three-dimensional geometries using streakline photography and Laser-Doppler anemometry (LDA) techniques. Pressure drop measurements will also be available, which can be used to correlate the excess pressure drop in the 3D contractions with the Weissenberg (We) and Reynolds numbers (Re). The selected test-cases are the flow in square/square contractions, for various contraction ratios, and the flow past a cylinder in a square duct.
For the 3D contraction flow we will analyze the influence of fluid rheology and of the contraction ratio in the flow patterns for low Re conditions. For the viscoelastic flow past a cylinder in a duct the effect of the fluid rheology will be analyzed for the cases when the cylinder is placed in the middle of the square duct and when it is misaligned. A Newtonian fluid, a constant viscosity elastic (Boger) fluid and a shear-thinning viscoelastic fluid will be used in both test-cases in order to understand the influence of elasticity and shear-thinning effects on the flow patterns.
The numerical simulations will be done using a viscoelastic finite-volume code developed during the past eight years within our group. The comparisons between experimental results and numerical simulations will be used to assess the quality of the numerical code and will also be used to improve its quality, both in terms of precision and robustness.
Actually there is a lack of experimental data for 3D complex viscoelastic flows. Thus, we believe this contribution may have a great value in the understanding of the behavior of complex fluids in 3D geometries. These results will also be very valuable for other researchers in the field, for use in code validation for truly 3D complex flow calculations. Actually the available benchmark flow problems in computational rheology are only for two-dimensional geometries, thus we expect that these results may be used to define two new benchmark flow problems, for assessment of 3D viscoelastic codes.
In this project we will optimize our numerical method, in order to develop a robust and accurate software particularly suitable for viscoelastic flow predictions in polymer processing industries.
This project will also train one young researcher in the field of experimental and computational rheology. |