Visualizing the unseen forces of turbulence

Bringing bytes down to size
For a dataset running well into the trillions of bytes, it would be impractical to do a brute-force analysis, Bethel said.

Fortunately, researchers are turning to higher-capacity multicore platforms and graphics processing units, or GPUS, to lighten the load. Some of the muscular new graphics-processing chips have come courtesy of the video game industry, such as the GPUs in Sony’s PlayStation 3 supplied by Santa Clara, Calif.-based NVIDIA.

Engineers and scientists at NASA’s Ames Research Center at Moffett Field, Calif., for example, have developed a wall of 128 screens, called hyperwall-2, that uses GPUs and processor cores to render computer graphics with a resolution of 250 million pixels. Surpassing that level of detail would require the collective power of 600 video game consoles. Scientists also are implementing smarter programs like a new visual data exploration and mining application that “does in a few seconds formerly what took days or weeks of visualization time,” Bethel said. Other algorithms can track topological features of liquids in four dimensions, including time, thereby attaching solid numbers to the central question of how varying turbulence influences the degree of mixing.

P.K. Yeung, a professor of aerospace engineering at Georgia Institute of Technology in Atlanta, said his team’s simulations of fluid turbulence now incorporate eight times as many grid points as they did three years ago – from 8 billion to 64 billion. The increase, he said, has permitted him to examine much finer details of turbulent flow and how the mixing of fluids takes place in very small dimensions.

The team has had to rewrite computer codes to subdivide computational tasks into increasingly smaller pieces so the communication among fast-multiplying parallel processors can be properly managed. But that added flexibility has allowed Yeung to deal with more complex types of turbulent flow, like the turbulence encountered by fluids with significant variations in density. The work could have broad implications for natural phenomena like hurricanes, where air masses of different densities interact within a vertical column.

“And also in the ocean, we know that the water at the bottom is colder and denser and so there is interest in how the mixing takes place in a vertical dimension,” he said. “If the surface of the ocean gets warmed by 0.1 degrees, what is going to happen to the marine animals living closer to the bottom?”

Beyond climate and marine studies, aerospace applications stand to gain enormously from a more detailed look at turbulence.

A few years ago, NASA engineers lacked the computational power to model the potential impact of tile damage on a space shuttle re-entering the Earth’s atmosphere until after the fact, when the shuttle had landed. Now, those simulations are being run mid-flight, with realistic scenarios of the kind of turbulent forces — and their effects — on the shuttle’s tiles.

Similarly, software engineers at NASA’s Ames Research Center have developed a program called the Data-Parallel Line Relaxation to scrutinize the volatile environments that spacecraft and their occupants might encounter during high-speed entries into the atmosphere of Earth and other planets. 

The highly accurate computer simulation does for NASA’s spaceflight program what test facilities cannot, but wind tunnels may not go the way of the dinosaur just yet. Both NASA and Boeing have been able to sharply reduce the number of expensive wind tunnel tests for designing critical elements such as thermal materials and airplane wings.

Despite the enormous potential for computer modeling, however, researchers agree that sometimes there’s no substitution for a reality check in the form of a well-timed blast of turbulent air.

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