Abstract
The nature of the flow during impulsive spin-down to rest in a cylindrical cavity is studied experimentally. Flow visualization using reflective flakes and laser-Doppler velocimetry are the tools of this investigation. The velocimeter is configured to measure simultaneously the azimuthal velocity component at two arbitrarily separated locations within the cylinder. The Ekman number is about 10 −5 and the flow is unstable. The mean angular velocity decreases non-uniformly and monotonically. The velocity fluctuation amplitudes and frequencies decrease steadily. A novel data analysis is used to study the velocity fluctuations, which are neither stationary nor uniform. The assumptions of this analysis are the validity of Taylor's hypothesis of frozen-eddy transport and the ergodicity of the process following that rescaling. The fluctuations are equally dominant during all phases of the spin-down process when scaled with the current mean velocity. The root-mean-squared intensity measurements in the core (r/R r −1 dependence while a uniform value is observed in the buffer region (0.4 r/R k. The flow in the latter phases tends to a single vortex.
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