I³MS - Anderson Seminar
Prof. Dr. Patrick Anderson - Modeling Interfaces and Particles in Viscoelastic Fluids
Polymer Technology, TU Eindhoven
Fluids that contain particles and/or fluid-fluid interfaces are all around us. Some everyday example are paints and coatings containing particles, biological fluids such as blood, and oil-water emulsions found in many foods. In addition, the suspending fluids can be Newtonian or viscoelastic, where we focus on the latter case. Several numerical techniques will be presented for the simulation of these “complex fluids” in flow, which can be used to study idealized physical problems that involve particles and interfaces in viscoelastic fluids. One of such problems is particle migration in two-phase viscoelastic flows. Isolated, rigid particles suspended in viscoelastic fluids can migrate across streamlines, a phenomenon that does not occur if the suspending fluid is Newtonian. It is generally believed that this migration is due to an imbalance of normal stresses, which causes particles to migrate away from areas with high local shear rates (e.g. toward the outer cylinder in a wide-gap Couette device). We present simulations of particle migration in two-phase flows, where one of the fluids is viscoelastic, whereas the other is Newtonian. Particle migration can be induced due to an imbalance in normal stresses, which is a result of a contrast in viscoelastic properties of the two fluids. A second problem, is that of rigid spherical particles suspended in viscoelastic fluids under shear. Depending on the rheological properties of the suspending fluid, the particles are known to align in string-like structures in the flow direction. Although this phenomenon was first reported almost four decades ago by, the exact mechanism of particle alignment is not completely understood. Initially, it was believed that normal stress differences are responsible for the alignment of particles, but recent work showed particle alignment in a shear-thinning fluid without significant normal stress differences. To unravel the phenomenon of particle alignment, we present the first 3D direct numerical simulations of the alignment of three rigid, non- Brownian particles in a viscoelastic shear flow. In particular, we will systematically study the effect of the rheology of the suspending fluid, and will show that shear- thinning can promote alignment, but normal stress differences are essential for alignment to occur.