Abstract
We report an experimental observation of the transition in the circular Couette system for a fluid with stable stratification when the inner and the outer cylinders rotate in the same direction. The radius ration of our apparatus is 0.90 and the aspect ratio is 56.5. The density stratification is realized by the ‘double-bucket’ filling method with the Brunt-Väisälä frequency ranging from 0.69 to 2.90. We find several new flow regimes in addition to the T-regime (ordinary Taylor vortex flow), the S-regime (typical Taylor vortex flow for a stratified fluid with twice the wavenumber), and the x-regime (discontinuous at one meridian plane), which are found in the case with the outer cylinder at rest. In contrast to those found in the case with the outer cylinder at rest where the vortex boundaries are almost horizontal, the vortex flows of the new regime found in our case of the co-rotating cylinders can be wavy (the wavy-x regime), spiral (the spiral-x regime) and sometimes have discontinuities on two meridian planes (the xx-regime).