Experimental investigation of vortex ring evolution in polymer solutions

Results on formation and propagation of vortex rings, in water and different concentration of the turbulent-drag reducing polymer (PAMH hydrolyzed polyacrylamide) solutions are presented. Adding PAMH changes solvent viscosity, elasticity and relaxation time. Vortex-ring properties such as ring velocity, circulation, enstrophy, kinetic energy and vorticity are measured using Particle Image Velocimetry (PIV). We show that, at constant impulse, vortex ring properties in PAMH solution deviate from that in Newtonian-fluid, water. We further perform experiments in water by matching the limiting Reynolds numbers of the PAMH solution corresponding to zero-shear and infinite-shear viscosities. While the circulation of PAMH solutions lie between the circulation of the two limiting Reynolds numbers of water experiments, however, enstrophy and peak vorticity do not follow this trend. We attribute the deviation of PAMH-rings to the modification of vorticity distribution. PLIF experiments show the phenomenon of ring-reversal, we attribute this to the elastic properties of the polymer-solution. (C) 2020 Elsevier Ltd. All rights reserved.