Physicists are one step closer to developing a complete mathematical theory that can predict how blood and other special fluids flow. This bizarre behavior has puzzled researchers for decades.
Not that we’ve tried it, but blood actually deforms a bit when it’s bumped, and strangely enough, it thickens when a strong, sudden force is applied to it – changing from a thin, watery substance to a viscous, almost solid substance .
Another (more hygienic) example of this is the classic trick you may remember from school science demonstrations: corn starch mixed with water. When you stir it slowly, nothing seems untoward, but squeeze out a handful of the mixture, and it solidifies into a rubbery ball. Open your hand and it will drip like liquid again.
What is actually happening is an example of a non-Newtonian fluid, a type of fluid that does not obey Newton’s law of viscosity and is instead characterized by its strange relationship between tension, the forces exerted on the fluid, and tension, how it deforms in response.
But that’s not the only strange thing about non-Newtonian fluids. They also exhibit a particularly chaotic fluid motion called elastic turbulence, which occurs only in these fluids, and not in obedient Newtonian fluids.
Turbulence of any kind turns an otherwise orderly laminar flow into a chaotic, swirling mess that makes mixing or pumping fluids difficult in industrial settings – or a boat ride on a fast-flowing river bumpy.
It usually happens at high flow velocities, and while it may be a well-known phenomenon, describing turbulence in its various forms remains “one of the last unsolved problems in classical physics,” claim the researchers behind this new study of elastic turbulence.
Researchers realized in the 1990s that in aqueous solutions containing polymers – which are long, repeating chains of molecules – the elasticity of the polymers stretching and contracting caused laminar flows to become unstable.
At the beginning of the 21st century, they discovered elastic turbulence, which is even more dramatic and manifests itself in slow laminar flows that are usually smooth.
Elastic turbulence is believed to arise in non-Newtonian fluids, which consist of ultrafine particles, polymers, or microscopic cells suspended in aqueous fluids, due to the way these particles interact and move. Without particles in the solution, the phenomenon disappears.
Scientists thought that elastic turbulence was completely different from the classical turbulence of Newtonian fluids, which behave much more predictably. But according to the team’s new models, the two phenomena may have more in common than previously thought.
Led by Marco Rosti, an aeronautical engineer who studies fluid dynamics at the Okinawa Institute of Science and Technology in Japan, the team measured the speed of non-Newtonian fluid flows and calculated the difference at three points, not the usual two used to measure and to study. classical turbulence.
They found that non-Newtonian fluids with elastic turbulence exhibit intermittent fluctuations in velocity at low flow rates, as Newtonian fluids do at high flows – a finding that helped them make statistical predictions about how the non-Newtonian fluid behaved.
“Our results show that elastic turbulence has a universal power-law decay of energy and a previously unknown intermittent behavior,” Rosti explains. “These findings allow us to look at the problem of elastic turbulence from a new angle.”
The study adds to other research efforts where physicists have made progress in describing non-Newtonian fluids, which have puzzled researchers with their strange properties since the 1930s — when they didn’t yet have the instruments or computers to analyze fluid flows to measure and simulate like we do. do today.
In 2019, researchers at the Massachusetts Institute of Technology (MIT) developed a 3D model that could describe how suspensions of ultrafine particles, such as a cornstarch mixture, change from a liquid to a solid and back again under different conditions.
The industrial applications of such a model are quite useful, allowing researchers, for example, to predict and optimize the behavior of slurries as they flow between vessels in industrial facilities.
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The new model developed by Rosti’s team could have similar practical applications.
“With a perfect theory” – if such a thing exists – “we can make predictions about flow and design devices that can change the mixing of fluids,” says Rosti. “This can be useful when working with biological solutions,” such as donated blood and lymphatic fluid.
Or, when the rest of us are messing around with ketchup, custard and toothpaste – three other fun examples of non-Newtonian liquids.
The research was published in Nature communication.