flow visualization | Water Calendar

Umbrella shaped ink droplet — Slowly sinking umbrella shaped ink droplet, like a primitive octopus. Photo(s): Lasse Johansson

Like an octopus. The ink pattern slowly takes on a distinct resemblance in my mind. Evolving slowly, from the ink droplet I sent into the water. Sinking, second by second, the shape is shifting, now taking this form, now that. Another shot, and I see a jellyfish.

Water’s inherent tendency to form patterns can be observed as simply as with ink droplets falling into water. Preferably in a container with flat walls. The impact of the droplet creates vaulting toroidal forms, vortexes resembling jellyfish, and finally, when the motion slows down, settles into sinking octopus-like forms.

Karman vortex street - fully developed — Kármán vortex street, generated by a paddle and captured on paper with dye. The inrolling motion, clockwise at left, counter-clockwise at right, has developed more fully, and the alternating vortexes are clearly discernible. Paddle movement is downwards. From a workshop with Nigel Wells. Archives of Institute of Ecological Technology.

Flip, flap, flip, flap, the tail fin of the trout swishes to and fro, thrusting the fish forward in the still water. Silently it speeds away under the surface. Seemingly without effort it moves, leaving a series of wakes behind. As a contrast, our propeller thrusts water backwards indiscriminately, creating a white foam of turbulent water behind the boat. How can the fish swim so fast and elegant, almost effortlessly? Continue reading “The fish and the propeller”

Tag: flow visualization

January 2026 – Ink droplets falling in water

The fish and the propeller