Gaetano DA attended the 85th Annual Meeting of the Society of Rheology in Montréal (Québec, CANADA) giving the talk:”Rotation of an ellipsoidal particle in a viscoelastic liquid in an unconfined shear flow by numerical simulations”.
ABSTRACT – The flow of non-spherical particles suspended in fluids is relevant in several applications such as injection moulding, extrusion, etc. In many processes, the suspending liquid exhibits non-Newtonian properties. The available theories dealing with dynamics of anisotropic objects in sheared viscoelastic liquids are limited to infinitely elongated particles and to asymptotically small or large Deborah numbers. Recent experiments in shear flow showed that the aspect ratio and the fluid rheology strongly affects the particle motion. A systematic study relating the particle dynamics to the geometrical and fluid properties is missing. In this work, the rotation of an ellipsoidal particle in an unconfined sheared viscoelastic liquid is investigated by 3D finite element simulations. To highlight different rheological properties, the suspending fluid is modeled by using two constitutive equations. The particle dynamics is studied by varying the aspect ratio and the Deborah number. Fluid viscoelasticity slows down the particle rotation rate as compared to a Newtonian fluid. In agreement with previous theories and recent experiments, a drift away from the Jeffery orbit and orientation towards the vorticity direction is found for low Deborah numbers. By increasing the Deborah number, a transition towards flow alignment is found. Higher aspect ratios reduce the critical Deborah number for flow alignment. The observed dynamics is qualitatively unaffected by the presence of second normal stress differences.