At Cornell's Laboratory of Atomic and Solid State Physics and Laboratory of Elementary Particle Physics, researchers have been tracking the paths of the tiny polystyrene "snowflakes" in the cylinder in an effort to shed light on the behavior of turbulent flows. But current technology only allows observers to follow a few particles at a time, making it nearly impossible to gather enough data to accomplish the task. Now, with a $1.4 million, three-year grant from the National Science Foundation (NSF), a group of Cornell physicists and engineers are developing an instrument that will allow them to track hundreds of particles simultaneously.
With it, they believe they will dramatically advance scientists' understanding of turbulence -- and, perhaps, even begin to tackle the long-unsolved problem of predicting how turbulent fluid flows behave.
Turbulence affects how pollutants disperse in air or water, how far pollen from crops will spread and how fast chemicals mix in industrial processes. Understanding how warm clouds form in turbulent air currents could improve the global circulation models that climatologists use to predict global warming.
"There are a lot of fundamental turbulence questions that can be attacked with this new technology," says Eberhard Bodenschatz, professor of physics and principal investigator on the NSF grant. Co-principal investigators on the project are physics professor Sol Gruner and professors of mechanical and aerospace engineering Lance Collins and Zellman Warhaft.
Turbulent fluid flows are among the most mathematically complex phenomena in nature. Capricious and chaotic, they present a formidable challenge to the researcher seeking to form abstract theory from empirical observation. "At a small enough scale, all turbulence behaves the same way," says Bodenschatz. "Whether I do an experiment and study turbulence, or whether I take a car engine and there's some exploding gasoline in there, the mixing properties should be the same."
The problem is an extremely complicated one, says Bodenschatz. "Say you want to predict where the next swirl will be -- you cannot say that. They're unpredictable. They're the most chaotic thing you can imagine. That's why when an airplane approaches possible air turbulence, pilots will say, 'most likely we will get turbulence.' They don't know when it will happen."
One challenge in turbulence research lies in tracking the erratic paths of the particles as they dip and swirl. Currently available technology, like the silicon strip detectors used in Bodenschatz's laboratory, captures only a few particles at a time.
With the NSF grant, the Cornell scientists will construct an array of four digital cameras that will take pictures of the tiny, flying polystyrene spheres in three dimensions. The device will capture up to 100,000 frames per second -- compared with 30 frames per second for an ordinary video camera. A 64-processor computer cluster will then analyze the photos and construct three-dimensional flight trajectories for each individual particle.
The instrument will allow researchers to follow not just a few, but many hundreds of particles, in flows with Reynolds numbers (a measure of the intensity of the turbulence) hundreds of times higher than those previously observable.
This release was prepared by Lissa Harris, a Cornell graduate student and Cornell News Service science-writing intern.
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