(237c) Purely Elastic Instabilities in Parallel Shear Flows

It is a common assumption that, in the absence of inertia and curvature, the flow of viscoelastic fluids is linearly stable to flow perturbations. A recent theoretical analysis [1], however, has shown that viscoelastic flows may be unstable to a finite amplitude perturbation even in the absence of curvature and inertia. In this talk, the flow stability of a viscoelastic solution is investigated in a parallel shear geometry at low Reynolds numbers. The experimental setup is a microchannel that is 2.5 cm long and 100 um wide, and consists of two regions. The first region contains an array of cylinders designed to produce a perturbation in viscoelastic flows. The second region is a long (2.2 cm), square channel devoid of cylinders, in which the spatio-temporal behavior of the perturbation are monitored using particle tracking velocimetry. Velocimetry data shows strong velocity fluctuations far (200 x width) from the initial perturbation. These fluctuations increase as the Wissenberg number or flow rate is increased.

[1] Morozov, A.N. and W. van Saarloos, Subcritical finite-amplitude solutions for plane Couette flow of viscoelastic fluids. Physical Review Letters (95), 2005