MARK BUCHANAN: A physics breakthrough that could change the world
'Even the hardest problems can succumb to persistent investigation, as two recent discoveries demonstrate'
If humans want to avoid boiling the oceans, we’ll have to find ways to use energy more efficiently. This, in turn, requires solving a problem that people don’t typically connect to climate change: the turbulence created when we pump air, water, oil, gas and other substances through countless miles of ducts and pipes. Thanks to its confounding effects, fully 10 percent of all the electrical energy produced on Earth gets wasted.
Fortunately, some recent breakthroughs in the realm of physics might point the way to a solution.
Physicists have long been perplexed by turbulence - the way fluids and gases, if moving fast enough, inevitably dissolve into a messy chaos of whirls and eddies. It’s theoretically tricky because it's erratic and intermittent, and often can't be captured with the smooth mathematics used in most of science. Even the concept of velocity makes little sense: Movements grow so tangled and mixed up that any tiny parcel will have parts flowing in different directions. When, back in the 1920s, weather prediction pioneer Lewis Richardson wrote a paper titled “Does the wind have a speed?” he asked the question seriously.
Yet even the hardest problems can succumb to persistent investigation, as two recent discoveries demonstrate. One clarifies how smooth flows fall apart into turbulence. The other shows how that undoing can sometimes be avoided in clever and somewhat bizarre ways.
There seems to be a fairly sharp threshold at which fluid flowing smoothly in a pipe becomes turbulent, yet the precise mechanics have long been a mystery. Does it happen all at once, or in stages? In a series of landmark experiments, German physicist Bjorn Hof and colleagues offer new insight: Turbulence emerges in the form of little puffs - tiny regions of confused, disorganized flow - which can then split, creating more puffs. Below a certain speed of flow, the puffs die out more quickly than they split: Even if you create some turbulence by putting your finger in the flow, it will soon subside. But above a critical speed, the splitting happens faster than the dying out, causing the turbulence to spread. Weirdly, it seems to grow following precisely the same mathematics as diseases.
This discovery alone is a major breakthrough. But Hof and colleagues went further, exploring how turbulence might be controlled. They investigated, for example, the effect of extra stirring from rotors placed inside a pipe, or by the injection of jets of fluid along the pipe walls. Intuition suggests that these would increase turbulence, and they do, but in both cases the flow downstream quickly returns to the smooth state. More important, the interventions can reduce the overall friction associated with turbulence by as much as 90 percent, something few researchers would have expected.
These experiments, addressing a classic problem in physics, are some of the coolest science I’ve seen in a while. Esoteric as they might seem, they can have big practical consequences -- eventually helping engineers avoid turbulence, and energy losses linked to it, in anything from household plumbing and city sewers to transcontinental pipelines. Such breakthroughs are more than just thrilling to see. They may be necessary for the survival of the human race.