Hurricanes, Other Vortices Seize Energy Via (shearing mechanism)

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Big whorls have little whorls
That feed on their velocity,
And little whorls have lesser whorls
And so on to viscosity.
-- Lewis F. Richardson

For decades, scientists who study hurricanes, whirlpools and other large fluid vortices have puzzled over precisely how these vast swirling masses of gas or liquid sustain themselves. How do they acquire the energy to keep moving? The most common theory sounded like it was lifted from Wall Street: The large vortices collect power as smaller vortices merge and combine their assets, in the same way that small companies join forces to create a mega-corporation.

But researchers from The Johns Hopkins University and Los Alamos National Laboratory now believe the better model is a much different business tactic: the hostile takeover. Working with theoretical analysis, computer simulations and lab experiments, the team has concluded that large fluid vortices raid their smaller neighbors in an energy grab and then leave their depleted victims either to wither away or to renew their resources by draining still smaller vortices.

(...)

"You have a large vortex spinning around, with a smaller one inside," Eyink said. "The large vortex has a shearing effect on the smaller one, like cake batter being stirred. The large-scale vortex acts like a giant mixer, stretching and thinning out the smaller one, transferring its energy into the larger vortex. The large-scale vortex actually acts like a vampire, sucking the energy out of the smaller one."

This phenomenon sustains a steady-state inverse energy cascade. "We end up with a group of large predator vortices preying on smaller ones, which in turn prey on smaller ones still, forming a food-chain of vortices," Eyink said.

http://www.sciencedaily.com/releases/2006/03/060306093402.htm

[htuttle]

1. It's just vortices, vortices, vortices, all the way down

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2. I once read it was turtles. Or vortices. Either one.