Recent results on instabilities and turbulence in couette flow

The evolution of spatial and temporal order of a fluid contained between concentric cylinders with the inner cylinder rotating has been investigated by flow visualization and laser Doppler velocimetry, and by measuring spatial correlations in the scattered intensity. Various states and transitions have been observed, depending on the Reynolds number history of the flow. A transition sequence observed when the Reynolds number is slowly increased is the following: to (time-independent) Taylor vortex flow, which, with its axial periodicity, breaks the axial translational symmetry; to wavy vortex flow, which is periodic in time and can have four-fold axial rotational symmetry; to modulated wavy vortex flow, which is quasiperiodic in time (with two frequencies) and can have two-fold axial rotational symmetry; and to weakly turbulent wavy vortex flow, where the power spectrum of the time series has two sharp peaks and one broad component, and the flow no longer has complete spatial periodicity in the axial direction.