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Accueil > Seminars > Archives > Archives 2009

Purely elastic instabilities in free shear layers

Alexander Morozov, School of Physics, The University of Edinburgh, JCMB

published on , updated on

Free shear layers — 1D velocity profiles with a velocity jump across some
(imaginary) interface — are known to exhibit Kelvin-Helmholtz instability
which plays a crucial role in sustaining Newtonian turbulence close to the
onset. Addition of small amounts of polymer was previously shown to inhibit
Newtonian Kelvin-Helmholtz instability (large Reynolds number regime) and
was argued by some to be a possible explanation for the drag-reduction phenomenon.

Here we show that even though polymers do inhibit Newtonian Kelvin-Helmholtz
instability at large Reynolds numbers, there exists a purely elastic instability
of viscoelastic shear layers when Reynolds number is small or even zero. We
perform linear stability analysis of the Oldroyd-B equation and show that viscoelastic
shear layers become linearly unstable when normal stresses exceed a critical value.
We discuss the mechanism underlying this instability and argue that it might be connected
to purely elastic instabilities in parallel shear flows of viscoelastic fluids and
purely elastic turbulence.