Abstract
We experimentally study the propagation of vortex rings in aqueous solutions of polyethylene oxide (PEO400) and hydrolysed polyacrylamide (PAMH25). We study the canonical vortex ring as a caricature problem to the phenomenon of turbulent polymer drag reduction. PAMH25 has a similar infinite shear viscosity, ten times the zero shear viscosity and a thousand times the relaxation time of PEO400. We study the vortex rings generated by the trapezoidal motion of a piston-cylinder mechanism using PIV and PLIF at constant impulse. We see that PAMH25 drastically affects the propagation properties and the structure of the vortex ring, while PEO400 shows a behaviour similar to water. We conclude that PAMH25 retards the roll-up process of the ring, due to both the large range of plateau viscosities and large relaxation time. We surmise that the behaviour of the vortex ring observed might be used to unravel the mechanism of polymer drag reduction.
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