The evolution of artificially generated localized disturbances
in the shape of hairpin
vortices, in laminar axisymmetric rotating shear flows, is investigated
experimentally.
The results are compared with the predictions of a theoretical model (Levinski
& Cohen 1995) with respect to the growth of such disturbances. Hairpin
vortices
were generated at the surface of the inner cylinder of an axisymmetric
Couette
apparatus, employing an injection–suction technique. The flow field
was analysed
from flow visualization using top and side views and by measurements of
the mean
and instantaneous velocity fields, carried out using laser Doppler anemometry
and
particle image velocimetry. An instability domain, within the range of
base flow
parameters where the flow is known to be linearly stable, was found. The
marginal
ratio between the angular velocities of the inner and outer cylinders beyond
which
the flow is stable to finite-amplitude localized disturbances agrees with
the theoretical
prediction based on the measured mean flow in the region of the disturbance.
The
dependence of the hairpin's inclination angle on the ratio between
the two angular
velocities is fairly well predicted by the theoretical model.