Development and decay of vortex flows in viscoelastic fluids between concentric cylinders

TL;DR

This study investigates the development and decay of vortex flows in viscoelastic fluids between concentric cylinders through experiments and numerical simulations, revealing oscillatory behaviors influenced by fluid elasticity and shear-thinning effects.

Contribution

It combines experimental and numerical approaches to analyze vortex dynamics in viscoelastic fluids, highlighting the roles of elasticity and shear-thinning in transient vortex behavior.

Findings

Vortex development exhibits oscillations before reaching steady state.

Overshoot and undershoot parameters characterize vortex growth and decay.

Elasticity number influences the magnitude of overshoot and undershoot.

Abstract

We study the development and decay of vortex in viscoelastic fluids between coaxial cylinders by means of experiments with solutions of polyacrylamide and glycerin and numerical simulations. The transient process is triggered when the inner cylinder is either abruptly started or stopped while the outer is kept fixed. The azimuthal velocity, obtained by means of digital particle velocimetry, exhibits oscillations before reaching the stationary state. The development of the vortex is characterized by means of the overshoot, i.e. the difference between the maximum and the stationary velocity. Analogously, in the decay of the vortex, the azimuthal velocity changes its direction and the relevant parameter is the undershoot defined as the maximum reversed transient velocity. To get a deeper insight into this phenomenon, the experimental results are supplemented with numerical simulations of rheological models as the Oldroyd-B and White-Metzer. The results obtained with the first model reveal the dependence of the overshoot and undershoot with the elasticity number of the fluid. Using the White-Metzer model we explain the increase of the overshoot produced by the reduction of the solvent viscosity in terms of the shear-thinning effects.