Structure of modulated wavy vortical flows in the circular Couette system

Results of experimental studies are presented on the evolution of the circular Couette flow with the outer cylinder at rest. In particular, several modes of modulated wavy vortical flows have been identified in a consistent way both from flow visualization and from signals of scattered laser beam. The latter technique has been extended to measure the spatial correlation between fluctuations as a function of the azimuthal separation of the points. It has been found that the two-point angular correlation reflects the pattern of modulation, and falls off as (R_d — R)^σ when the ‘disorder Reynolds number’ R_d is approached. The value of the exponent σ has been estimated to be about 1/3 in the experiment.