A new method for determining pressures in complex fluids

Fluid dynamics researchers use many techniques to study turbulent flows such as ocean currents, or the swirling atmospheres of other planets. Arezzo Adricani’s team discovered that the mathematical construction used in these areas provides valuable information about stress in complex flow geometries.

Ardekani, a professor of mechanical engineering at Purdue University, studies complex flows: from transport processes related to biopharmaceuticals, to Behavior of microorganisms around an oil spill. “Newtonian fluids like water are easy to understand, because they don’t have a microscopic structure,” she said. “But complex fluids have massive molecules that expand and relax, changing many properties of the fluid, resulting in very interesting fluid dynamics.”

Viscoelastic flows occur frequently in nature, in biomedical environments, and in industrial applications – such as solutions used to treat groundwater. “When groundwater becomes contaminated, the treatments use some polymer-based solutions to disperse chemicals designed to break down the pollutants,” said Ardakany. “But what kind of polymer should they use, how much, and where should it be injected? The only way to answer these questions is by understanding the behavior of these flows, which goes back to measuring strains.”

Currently the only way to determine the pressures of polymeric fluids is a technique called refraction, which measures the specific optical properties of a fluid. But it is very difficult to implement, often imprecise, and not applicable to all types of macromolecules.

Ardkany team discovered a new technology. The researchers created a file sports framework It takes the input from the flow velocity, obtained from particle image velocity measurement (a common technique in fluid dynamics), output strain and extending domain topologies for complex fluids. Their research has appeared in Proceedings of the National Academy of Sciences (PNAS).

in Measurement of particle image velocity (PIV), tracer particles are injected into a liquid. Using the movement of those particles, the researchers can extrapolate information about the kinetics of the aggregate flow. While this could easily be used to assess stress in Newtonian fluids, Ardekani’s team discovered a mathematical correlation between these measurements and stresses in viscoelastic flows.

Everything connects through something called Lagrangian coherent structures (LCSs). “Lagrangian coherent structures are mathematical constructs used to predict the dynamics of fluid flows,” Ardakani said. “Oceologists use them to predict how currents will move; biologists who track microorganisms; and even astrophysicists, who monitor turbulent clouds in places like Jupiter.”

While disordered LCSs are often used by researchers, they have not been applied to polymeric stress yet. “We’ve united two disparate branches of continuity mechanics,” Ardakani said. “Using Lagrange stretching, and its application to Eulerian stress fields. This applies over a wide range of scales, from medium scale all the way up to industry scale measurements.”

The paper is a collaboration between Ardekani, Ph.D. Student Manish Kumar and Jeffrey Guasto, Professor of Mechanical Engineering at Tufts University. They presented their findings in November at the 75th annual meeting of the (American Physical Society) Fluid Dynamics Division in Indianapolis, which Ardakany co-organised.

While the research is largely mathematical, Ardakany is excited to see how experimentalists will use the technology in the lab and in the real world. “Let’s use the example of groundwater treatment again,” Ardakany said. Researchers typically use tracking analysis on injected fluids to measure the velocity field. But now, they can also determine Stress So they can more accurately predict the transport of this fluid.”