Beautiful patterns of water flow
The flow of water in nature displays beautiful patterns. Water placed in the space between two rotating concentric cylinders produces multiple donut shaped vortices (right image) at lower rotation rates and at higher rotation rates these donuts get wavy along their periphery (left image).
Micron-sized mica flakes are added to water and illuminated with a bright light source at an angle to visualize the flow patterns. Alignment of these flakes along the fluid streamlines results in brighter upward rotating vortices and darker downward rotating vortices. The outer cylinder is transparent to show the flow patterns.