To Predict Turbulence, Just Count the Puffs – Issue 25: Water

The water is always running in Björn Hof’s laboratory.

Like a Zen water fountain, it gently flows over the top of a reservoir into a tube, and from there into a glass pipe 15 meters long, but thinner than a glass thermometer. To keep the flow as smooth and serene as possible, Hof, of the Institute of Science and Technology Austria in Klosterneuberg, controls conditions such as temperature and sterility of the tube as meticulously as might a biologist trying to breed a particular strain of bacteria.

And in a way, Hof is trying to breed a strain of reproducing creatures, just not living ones. Into the Zen-like perfection, he occasionally adds a pinprick of confusion: a tiny amount of water injected through the side of the tube. As each “puff” of swirling water travels down the pipe, it may divide into two puffs like a self-replicating bacterium, or it may just as suddenly die out.

The dynamics of this population of puffs, Hof believes, holds the key to a problem that has vexed physicists for over a century: How does turbulence get started, and what is it, anyway?

It’s been more than 130 years since an English…

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