Visual Observation of the Second Characteristic Mode in a Quasiperiodic Flow

The flow between concentric cylinders with the inner cylinder rotating has been studied by visualization techniques. Velocity power spectra have shown that the flow is described by two characteristic frequencies before it becomes chaotic; the first frequency corresponds to traveling azimuthal waves. The second frequency is identified as a modulation of the waves and multiple values have been observed. These are believed to be the first such observations for any nonlinear nonequilibrium system.