  Homogeneous polymer solutions are well-known to exhibit viscoelastic flow
instabilities: purely elastic when inertia is negligible, inertio-elastic
otherwise. Recently, shear-banding wormlike micelles solutions were also
discovered to follow a similar phenomenology. In the shear-banding regime,
inertia is usually negligible so only purely elastic flows have been reported.
Here, we investigate a non-shear-banding solution where inertia becomes
significant, leading to flow patterns akin to the inertio-elastic regime of
dilute polymer solutions. We show that the instability follows a supercritical
bifurcation and we investigate the structure of the inertio-elastic vortices
that develop above onset.
