The evolution of a localized vortex disturbance in external shear flows. Part 2. Comparison with experiments in rotating shear flows

The evolution of artificially generated localized disturbances in the shape of hairpin vortices, in laminar axisymmetric rotating shear flows, is inve stigated experimentally. The results are compared with the predictions of a theoretical model (Levinski & Cohen 1995) with respect to the growth of su ch disturbances. Hairpin vortices were generated at the surface of the inne r cylinder of an axisymmetric Couette apparatus, employing an injection-suc tion technique. The flow field was analysed from flow visualization using t op and side views and by measurements of the mean and instantaneous velocit y fields, carried out using laser Doppler anemometry and particle image vel ocimetry. An instability domain, within the range of base flow parameters w here the flow is known to be linearly stable, was found. The marginal ratio between the angular velocities of the inner and outer cylinders beyond whi ch the flow is stable to finite-amplitude localized disturbances agrees wit h the theoretical prediction based on the measured mean flow in the region of the disturbance. The dependence of the hairpin's inclination angle on th e ratio between the two angular velocities is fairly well predicted by the theoretical model.