In the cover article of the July 31 issue of the journal Science, a team headed by Julio M. Ottino, professor and chair of chemical engineering at Northwestern's Robert R. McCormick School of Engineering and Applied Science, has provided the first experimental realization of a 3-D chaotic flow, showing all the intricacies of the regular islands and the chaotic regions in the flow. Cross-section of doughnut shapes traced by red, green and yellow dye streams injected under a spinning disk. The dyes fluoresce as they pass through a laser sheet slicing down the middle of a cylindrical tank. In many cases, you would like to get rid of chaos, but in the case of mixing, we would often like to enhance it, and we would certainly like to understand it. The experimental device Ottino's group created in Northwestern's Laboratory for Fluid Dynamics, Chaos, and Mixing, is a clear Plexiglas cylindrical tank filled with glycerin.
Chaotic flow is created by a nearly vertical shaft spinning a nearly horizontal flat disk.
Needles immersed in the whirling glycerin inject streams of fluorescent dyes that glow red, green and yellow when they pass through a laser beam. The laser is the key to visualizing the chaos in this complicated 3-D system. When you light the whole thing, it looks like a mess. A flat circular dye stream would appear as just two dots where the stream crosses the sheet. There are these near-misses, and the dye path traces a doughnut region around the tank.