Injecting Chaos Solve Decades of Fluid Mystery

fluid can Broadly divided into two categories: ordinary and weird. Common ones, like water and alcohol, perform more or less the desired effect when pumped through a pipe or stirred with a spoon. Various behavioral mysteries lurk in bizarre mysteries — including substances like paint, honey, slime, blood, ketchup and oobleck — that have puzzled researchers for centuries.

A longstanding conundrum that was first elucidated nearly 55 years ago is when certain liquids flow through cracks and holes in porous landscapes such as spongy soils. The fluid will flow normally at first. But as its flow rate increases, it passes a critical threshold at which it suddenly coalesces—its viscosity skyrockets like a martini turns to molasses.

One new research The effect is anchored to tiny molecules suspended in a fluid, which spin and stretch as the flow rate increases. At some point, molecular motion can cause the fluid flow to become chaotic, surging and rippling in swirling eddies. The chaotic start impedes the movement of the fluid. Applications for this discovery range from 3D printing to groundwater remediation and oil recovery.

“It’s a beautiful manuscript,” said Paul Alatia, who studies complex fluids at the University of Pennsylvania and was not involved in the work.

In the 1960s, when rheologist Arthur Metzner and his undergraduate student Ronald Marshall worked in the oil fields, engineers often injected water mixed with a so-called propellant into the ground to displace oil and help extract every drop of crude. The scientists noticed that when a propellant containing long-chain polymers was pumped into the ground at a certain rate, it seemed to become unexpectedly more viscous, an effect later found in many similar systems.

“Viscosity is one of the most important things you want to be able to predict, control and characterize,” says Sujit Dutta, a chemical engineer at Princeton University, who stumbled upon Metzner and Marshall’s 1967 paper on the subject during his graduate studies. “I was like, ‘This is kind of embarrassing, even after decades of intensive research, we still don’t know why the viscosity is the way it is and how to explain this increase.'”

It is well known that propulsion fluids and other viscoelastic fluids can contain long and complex molecules. At first, scientists thought the molecules might have built up in pores underground, like hair in a sewer. But they soon realized that these were not simple clogs. Once the flow rate dropped below the critical threshold, the blockage appeared to disappear completely.

The turning point came in 2015, when a group at the Schlumberger Gould Research Centre in Cambridge, UK, simplified the problem. The researchers constructed a 2D simulation of sandy soil with submillimeter-sized channels leading to a maze-like array of cross-shaped debris. They then pumped fluids containing different concentrations of molecules through the system. The team noticed that beyond a certain flow rate, the motion of the fluid in the space between the crosses became chaotic and disordered, greatly slowing the overall motion of the fluid.

In theory, such a thing should be nearly impossible. Conventional fluids are heavily influenced by inertia, and they tend to keep flowing. For example, water has a lot of inertia. As the water gets faster and faster, the small streams in the stream will begin to overtake the rest of the fluid, resulting in chaotic eddies.

By contrast, complex fluids like honey have little inertia. Once you stop stirring it will stop flowing. Because of this, it’s hard to create “inertial turbulence” — the normal turbulence that occurs in turbulent streams or under the wings of an airplane.

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