There are two categories of fluids: regular ones and weird ones. Water and alcohol act more or less as expected when pumped through pipes or stirred with a spoon. There are a lot of behavioral mysteries that have stumped researchers over the centuries.
A long-standing puzzle was first articulated nearly 55 years ago when certain liquids stream through cracks and holes in a porous landscape. The liquid will flow normally. It will pass a critical threshold as its flow rate increases, where it will suddenly coalesce, shooting up like a martini.
The manuscript is beautiful, according to a University of Pennsylvania researcher who wasn't involved in the work.
In the 1960s, the rheologist Arthur Metzner and his undergraduate student Ronald Marshall were working on oil fields, where engineers would often inject water mixed with so-called pusher fluids into the ground to displace the oil and help extract every drop of crude. The scientists noticed that when the pusher fluid was pumped into the ground above a certain rate, it seemed to suddenly become sticky.
One of the most important things you want to be able to predict and control isosity, according to Sujit Datta, a chemical engineer at Princeton University who came across the paper by Marshall and Metzner. Even after decades of research, we still don't know why the viscosity is what it is and how to explain the increase.
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Pusher fluids and other viscoelastic fluids can contain long, complex molecules. Scientists thought that the molecule might be piling up in the ground, like hair in the drain. They realized that these weren't easy to fix. The obstruction disappeared completely when the rate of flow fell below a critical threshold.
A group at the Gould Research Center in Cambridge, England, simplified the problem in 2015. The researchers built a two-dimensional analogue of sandy soil with sub millimeter-size channels leading into a labyrinth of cross-shaped pieces. They pumped the fluids into the system. The team noticed that the fluid movement became messy and disorganized in the spaces between the crosses, which slowed the motion of the liquid.
It should be almost impossible. inertia is the main influence on regular fluids' tendency to keep flowing. Water has a lot of inertia. As water moves faster and faster, small streams within the flow will start to overtake other sections of the fluid, leading to chaotic eddies.
A fluid like honey has very little inertia. It will stop flowing when you stop stirring it. It has trouble generatinginertial turbulence, which is the ordinary kind of turbulence that happens in a rushing stream or beneath an airplane's wings.
The Cambridge group did their experiments in fluids where inertia's effects were low. The researchers still found chaotic flow despite the fact that no turbulence should have appeared.
There was a second type of turbulence. When liquids with long molecular chains flow slowly, these polymers float along. As the flow rate increases, the molecule begin to twirl and tumble. Scientists still don't fully understand elastic turbulence, a phenomenon that occurs when the motion of the molecule pushes on the liquid.
The experimenters in Cambridge mixed bright fluorescent particles into their fluids to see how their fluids became disorganized in the spaces between the crosses. Datta said that researchers were able to connect elastic turbulence with the unexpected increase of liquids in porous landscapes.
