On the quasiperiodic state in a moderate aspect ratio Taylor-Couette flow

The transition pathway leading to chaotic flow in a Taylor-Couette vessel of aspect ratio gamma=11.2 and radius ratio eta=0.81 with only the inner cylinder rotating has been studied using time-resolved particle image velocimetry. A hitherto unreported sequence of transitions, whereby the flow changes from wavy vortex flow to a quasiperiodic state of high modulation frequency, is identified using spatially resolved spectral analysis. The nature of the modulated wavy vortex flow is detailed using proper orthogonal decomposition, through which it is revealed that the modulation is similar to a fast moving azimuthal wave (FMAW). In contrast with previous observations of the FMAW at a much higher aspect ratio, the mode appears directly after wavy vortex flow and as a precursor to the CVF regime. The FMAW is also associated with codirectional vorticity fluctuations on each Taylor vortex core that diminish in strength close to the endwalls.