Finite element numerical simulations are presented for two-dimensional creeping, planar and axisymmetric incompressible isothermal complex flows of both Newtonian and viscoelastic fluids. A number of constitutive equations are used to define fluid properties, including Newtonian, Oldroyd-B and Phan-Thien/Tanner (PTT) models. For viscoelastic flow, a modified semi-implicit Taylor-Galerkin method is presented with a consistent streamline upwind Petrov-Galerkin technique for the stress terms. Velocity gradient recovery is also employed. This multi-stage numerical solution algorithm implements a time marching, pressure-correction procedure. The significant influence of die-swell on the free surface flow development for wire-coating flows is reported and discussed in the results. The simulation of Poiseuille and annular flow of Newtonian and Oldroyd-B fluid for stick-slip and die-swell problems is presented. A planar- Newtonian stick-slip flow is compared with the analytical solution, whilst an axisymmetric die-swell case is compared against the theory and other numerical methods. Analysis for two free surface formulations is performed and results are shown for varying structure and mesh refinement. Investigation into the influence of elasticity and drag flow components on free surface location is performed for an Oldroyd-B fluid. The results indicate that, as elasticity increases, pressure and stresses do likewise. The swelling ratio, expressed in terms of extrudate swell, depends especially on this elastic influence. Newtonian fluid with slip effects and a viscoelastic analysis of PTT models are described for a low density, high speed wire-coating process on pressure-tooling and tube-tooling dies. Fluid coating flows such as these are especially useful in industrial wire coating processes for covering surface areas with one or more thin uniform layers of polymer melt. Pressure-tooling dies are used for coating narrow-gauge wires, whilst tube-tooling dies deal with wide-bore cables. The impact of variation in slip models at the die walls, and the effects of drag pressure driven flow are explored. Slip influence reduces swelling-ratio, but increases oscillations in the pre-die exit region. Comparison of pressure-tooling between PTT models are shown with variation in shear-thinning and stain-softening properties. The effects of deviation in polymeric viscosity and Weissenberg number are presented. The results have been confirmed through mesh refinement.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:638326 |
| Date | January 2000 |
| Creators | Ngamaramvaranggul, V. D. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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