Thesis /

ROMDOC-THESIS-2016-285

Modelarea curgerii fluidelor vâscoase aditivate cu polimeri în geometrii complexe

Călin, Andreea
2008-10-28

Abstract: In the general context of non-newtonian fluid dynamics, this work assumes the objective of characterizing viscoelastic polymer solutions and their flow in complex geometries (with immediate application in microfluidics and biofluid mechanics). Starting with rheometric studies (in shear and extensional tests, within the linear and the nonlinear regime) focused on the influence of polymer molecular weight and concentration on the rheology of the solutions, the analyzed fluids are constitutively modeled, using to this purpose a new method for the determination of the Giesekus parameters. This method allows a better prediction of nonlinear effects manifested by fluids of weak and medium elasticity (verified herein for large amplitude oscillatory shear). Two complex flow applications are studied through experiments and numerical simulations. The first case is the flow of polymer solutions in a microbifurcation with a closed branch (where flow separation occurs). Interest is invested in the influence of elasticity and shear-dependent viscosity on the flow topology in the vicinity of the bifurcation and on the stress distribution at the wall. The second application is the flow of polymer solutions in the presence of an interface with a purely viscous fluid, taking place in a Hele-Shaw type geometry. The evolution and dynamic of the interface is studied as a function of polymer concentration (rheological properties) and inflow velocity. An important observation is that vortical structures appear in the immediate vicinity of the interface (in the less viscous fluid) and they can be used for a better spatial recognition of the separation surface between the two fluids. The original contributions of this work are related to: (i) complete characterization (experimentally and through constitutive modeling) of the aqueous polyacrylamide solutions, as a function of molecular weight and concentration; (ii) constitutive modeling of fluids with weak and medium elasticity, by developing a new method for describing nonlinear behavior; (iii) qualitative characterization of the influence of elasticity and shear-thinning viscosity on the flow topology in microbifurcations and stress distribution on the wall; (iv) identification of interfacial vortices and their correlation to the exact position of the interface between two immiscible fluids (in the presence of surface tension), through the vorticity number.

Keyword(s): Mecanica fluidelor ; Hidrodinamică -- Modele matematice -- Teză de doctorat ; Polimeri -- Aditivi -- Teză de doctorat
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