Experiments on the onset of instability in unsteady circular Couette flow

Experiments have been performed to study the hydrodynamic stability of unsteady circular Couette flow generated by monotonic time-dependent inner-cylinder motions. The onset of instability was determined by measuring the axial component of velocity using laser-Doppler velocimetry; deviations from the pure-swirl value of zero are indicative of the initiation of Taylor vortices. The measurement technique was found to have an ‘intrusive’ effect on the flow stability, which was eliminated by the design of the experimental procedure. Significant enhancement of stability was found, in qualitative, but not quantitative, agreement with earlier theoretical predictions.