How tiny plastic balls in turbulent water might one day result in improved weather forecasting

Think of scenes from the movie "Twister." Tornado chasers load up their trucks with ping-pong-ball-sized spheres and head for a twister. The spheres are then released into the storm's vortex, resulting in the transmission of valuable scientific information on tornadoes' actions to the chaser's computers.

Life imitates art: Cornell University researchers are releasing a myriad of tiny spheres, each about the size of a speck of dust, into flowing water. The information they get back explains how particles behave in a turbulent environment.

This basic understanding of turbulence can tell researchers much about our everyday world, reported Greg A. Voth, a Cornell graduate student, today (March 26) at the centennial meeting of the American Physical Society in Atlanta. "Perhaps it can be used for weather modeling, understanding how air and fuel mix in a combustion engine or the spreading of pollution in the air or the ocean," he said.

"It's a simple, idealized situation, where the world of physics could learn something fundamental about turbulence," Voth said.

The researchers look into the swirls and twists of turbulence by placing tiny polystyrene spheres, each about 50 microns across, into a water flow. The particles are then tracked as they move through a laser beam, using a silicon-strip measurement system from the Cornell Electron Storage Ring's CLEO II detector. As the particles cross the laser beam, the scientists can take as many as 70,000 images a second and follow the track, measuring speed and acceleration of the minuscule spheres.

To explain the tracking concept, Voth used the example of pointing a floodlight into a snowstorm on a dark night. "When you point the beam, you see the snowflakes go through their curved trajectories as they follow the wind," he said.

By tracking millions of particles, the Cornell researchers are learning about the fundamental nature of turbulent flows, which could lead to practical uses such as understanding how pollution particulates cross the oceans or how fuel mixes with air inside an engine, resulting in the development of more fuel-efficient engines.

Voth's faculty adviser, Eberhard Bodenschatz, Cornell associate professor of physics, explains that the particles behave the same way, whether in air or water, and the statistics and the dynamics are the same.

"The job of the physicist is to find general laws of nature. Right now, that's what we're doing. Applying those general laws comes later," Bodenschatz said.

Currently, the researchers are measuring turbulent flows in a two-dimensional projection. In April, they hope to add another imaging element, giving them a third dimension to study.

Other collaborators on the project include Arthur LaPorta, Cornell post-doctorate researcher, who also presented his findings on the research at the meeting, and James Alexander, Cornell associate professor of physics. The research is funded by the National Science Foundation.

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