A new way to identify stresses in complex flu

Fluid mechanics researchers use many techniques to study turbulence like ocean currents and the swirling atmospheres of other planets. Arezoo Adrekani’s team discovered that the mathematical structures used in these fields provide valuable information about stresses in complex flow geometries.

AldecaniPurdue University Professor of Mechanical Engineering, Research complicated flow: from transport processes related to biopharmaceuticals, Microbial behavior around oil spills“Newtonian fluids, like water, are easy to understand because they have no fine structure,” she said. “But complex fluids have stretchable macromolecules that change many properties of the fluid, leading to very exciting fluid dynamics.”

Viscoelastic flow occurs frequently in nature, in biomedical settings, and in industrial applications (such as solutions used in groundwater remediation). “When groundwater becomes contaminated, remediators use certain polymer-based solutions to disperse chemicals designed to break down the contaminants,” Ardekani said. “But what type of polymer should we use, how much, and where should we inject it? will have to.”

Currently, the only way to quantify stress in polymer fluids is through a technique called birefringence, which measures certain optical properties of fluids. However, it is very difficult to implement, often imprecise, and not applicable to all types of macromolecules.

Ardekani’s team discovered a new technology. Researchers have created a mathematical framework that takes input from flow velocities obtained from particle image velocimetry (a common technique in fluid mechanics) and outputs stress and stretch field topologies of complex fluids. their research Proceedings of the National Academy of Sciences (PNAS).

In particle image velocimetry (PIV), tracer particles are injected into the fluid. By using the motions of these particles, researchers can infer information about the overall flow kinematics. While this can be readily used to assess stresses in Newtonian fluids, Ardekani’s team found a mathematical correlation between these measurements and stresses in viscoelastic flows.

All are connected via what is called a Lagrangian coherent structure (LCS). “A Lagrangian coherent structure is a mathematical structure used to predict the dynamics of fluid flow,” Ardekani said. “It’s used by oceanographers to predict how ocean currents move; biologists tracking microbes; even astrophysicists observing turbulent clouds in places like Jupiter. ”

LCS is often used by turbulence researchers, but has never been applied to macromolecular stresses. “We combined his two different disciplines of continuum mechanics,” Ardekani said. “Lagrange he uses stretching and applies it to the Eulerian stress field, which applies to a wide range of scales, from mesoscale to industrial-scale measurements.”

This paper is a collaboration between Ardekani and her PhD student Manish Kumar. Jeffrey GustAssociate Professor of Mechanical Engineering Tufts UniversityThey are in November APS (American Physical Society) Fluid Mechanics Division 75th Annual Meeting at Indianapolis, co-hosted by Aldecani.

Although the research is largely mathematical, Ardekani is excited to see how experimenters will use the technique in the lab and in the real world. “Let’s use the groundwater remediation example again,” Ardekani said. “Researchers typically use tracer analysis of injected fluids to measure velocity fields. But now we can also identify stress fields, so we can predict the transport of that fluid more accurately.”

Writer: Jared Pike, Communications Specialist, Purdue School of Mechanical Engineering

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