Flow visualizations and numerical modeling of viscous fluids in rotational motions

Abstract

The paper presents experimental and numerical studies of viscous fluids involved in axisymmetric rotating motions: (i) the two immiscible fluids’ motion generated by the spinning disk in a cylindrical vessel, (ii) the Couette-Taylor motion between two concentric cylinders. The main objective of the research is the FLUENT code testing for the representation and modeling of the rotating motions, the numerical results comparison with the experimental visualizations and the validity limit determination of the axisymmetric solutions related to the 3D real configurations of the investigated cases. In the first studied case, the numerical solution obtained with the VOF (Volume of Fluids) solver is compared with the experimental visualizations. The evolution of the oil-water interface is investigated considering the upper disk spinning velocity, in contact with the oil. The numerical results are qualitatively similar to the experimental ones, but to the present it wasn’t possible a quantitative correspondence between them (the geometric congruent surfaces correspond at different Reynolds numbers). The analysis of the Taylor vortices’ appearance and evolution is made between two concentric cylinders; the inner cylinder has a rotation motion of constant velocity, the outer cylinder is at rest. The work fluid is composed by water with aluminum particles (the average characteristic diameter is smaller than 1 micron). The purpose of the experimental research is the study of the evolution of permanent and stable Taylor vortices toward the wavy Taylor regime. A point of interest is the amplitude of the wavy motion associated to the Taylor rings with the Reynolds number value, respectively the Taylor number, Ta. It was obtained a good qualitative and quantitative correlation between the axisymmetric numerical results and the experimental flow spectrum (in the Ta < Tacr = 1750 domain). The rotating motion modeling of pseudo-plastic fluids concerns both of the studies, along with the mixing process of the polymer immiscible solutions.