Behavior of an elastic fluid in cylindrical swirling flow

The influence of the elastic properties of a 2.5% aqueous solution of polyacrylamide on the flow patterns in a cylindrical rig with a driven base has been studied experimentally. The flow structure as a function of Reynolds number (based on the cylinder radius, base circumferential velocity, and zero-shear viscosity) was studied using flow visualization. At very low Reynolds numbers (Re₀ ≈ 0.033), the flow along the cylinder axis is steady but in the opposite direction to that observed for Newtonian fluids. As the Reynolds number is increased (at Re₀ ≈ 0.132), an asymmetric, unsteady spiral vortex forms in the flow. Further increase in the Reynolds number (Re₀ ≈ 1.5) results in a highly unsteady flow pattern in the half of the cylinder closest to the rotating lid, while the other half is nearly stationary. The flow is observed to revert back to a steady Newtonian fluid-like flow pattern (i.e., fluid flows toward the rotating lid along the cylinder axis) at still higher Reynolds numbers. An analysis of the relative viscous, inertial, and elastic time scales as a function of Reynolds number provides further understanding of the observed flow regimes.