New method simulates tens of thousands of bubbles in frothy streams


Bubbles aren’t just for bath time. Bubbles, especially bubbles in frothy streams, are essential for many industrial processes, including food and cosmetics production and drug development and delivery. But the behavior of these foamy flows is notoriously difficult to calculate due to the large number of bubbles involved.

Previous attempts to simulate foamy flows relied on the computationally expensive and time-consuming process of tracking bubbles by coating each individual bubble in the foam with color. This limited the simulations to a few dozen bubbles, instead of thousands or even millions of real foams.

Now, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a new way to simulate tens of thousands of bubbles in frothy flows, breaking the computational complexity of this long-standing process.

The research is published in Scientific advances.

“This new method allows us for the first time to study foams with many bubbles, opening the door to simulating a wide variety of micro to macro-scale flows, including wet foams, turbulent flows with bubbles, suspensions and emulsions in microfluidics.” said Petros Koumoutsakos, Herbert S. Winokur, Jr. Professor of Engineering and Applied Science at SEAS and lead author of the study.

Instead of coloring each individual bubble, the researchers broke the foam down into a grid, with each grid cell containing at most a portion of four bubbles. Each bubble inside the cell is colored either yellow, green, blue or red.

“If I have four partial bubbles inside a cell, then the remaining piece of the bubbles must be in neighboring cells,” said Petr Karnakov, a graduate student at SEAS and the paper’s first author. “We’ve developed an algorithm that can go into other cells and find the remaining pieces of the bubble, matching green to green, blue to blue, etc. So instead of needing millions of colors , you only need four.”

This capability enables predictive simulations at scales ranging from microfluidics to breaking waves. “Our new approach enables large-scale predictive simulations of flows with multiple interfaces,” said Sergey Litvinov, postdoctoral researcher at ETH Zurich.

The difference between all the previous approaches and the new approach developed by Koumoutsakos, Karnakov and Litvinov can be compared to the difference between a painting and a puzzle. A painting is painstakingly created stroke by stroke, while a puzzle relies on geometry and matching colors.

Next, the researchers aim to collaborate with experimentalists and industrial partners to see how the method can be applied in the medical field and the food industry as well as for membraneless electrolysis for energy applications.

The research was funded by the Swiss National Science Foundation under grant CRSII5_17386.


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