Galleries / Turbulence: How to Visualize the Invisible

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Tyghe Trimble and Andrew Moseman; published August 13, 2008

3-D IMAGING

SHEAR SPEED

FLOWING HAIR

FORE!

MIXING GASES

MAGNETIC FIELDS

DIMENSIONAL TERRAIN

WIND BLOWN

ENGINEERING WITH FLOW

LONG WAY TO GO

<p>For most people, turbulence is an enemy that causes <a href="http://www.usatoday.com/weather/wturbwht.htm" target="blank">stomach-sinking moments</a> on a plane. For researchers, turbulence is the point where the interaction of flowing substances--including all liquids and gases--become violent and seemingly chaotic. </p><p>This image is a 3D representation of turbulence. The raw data itself is difficult to understand as anything but abstract numbers, so scientists use contour lines to give the idea of shape, like the purple seen here.</p>

<p>Full-fledged turbulence breaks out when gases with different densities move at a high speed relative to each other. In this case, one gas is 2.5 times denser than the other, and when they move at 380 miles per hour relative to each other, they become turbulent.</p><p>"Beyond a certain velocity, all things fluid get unstable--they will fluctuate and become turbulent," says <a href="http://www.me.vt.edu/MENewSite/Faculty/tafti/tafti.php" target="blank">Danesh Tafti</a>, an associate professor of mechanical engineering at Virginia Tech.</p>

<p>Companies looking to develop products like shampoo use simulations to see how long hair--and hair products--will flow in a stream of air and react to react to water, dust, and other factors. </p><p>Getting that perfect windswept look takes more hours of computer simulation than you might expect.</p>

<p>As a golf ball moves through the air, the pressure in front of it is higher than the pressure behind, increasing drag and decreasing a shot's distance. Dimples bring turbulent air flow closer to the ball, <a href="http://query.nytimes.com/gst/fullpage.html?res=9C04E6DA143EF934A35752C0A9659C8B63" target="blank">creating whirlpools of air</a> that lower drag and extend drives.</p>

<p>These colorful swirls depict the mixing of two distinct gases; the upper gas is three times as dense as the one below it. Small initial disturbances quickly turn violent along the unstable interface between the two gases. This test was run to help understand convection within the interiors of stars.</p>

<p>Turbulence is also a key ingredient in the growth of new stars.</p><p>Gases and matter swirl in a disk <a href="http://vis.lbl.gov/Vignettes/Incite4/index.html#NewImages" target="blank">around a newly forming star</a>, but the star's magnetic field causes turbulence that knocks matter free from the disk and lets it fall into the center. A simulation of magnetic field turbulence can be seen in this image, created at the University of Chicago.</p>

<p>Following even the simplest interactions of any turbulent phenomenon takes sophisticated computers thousands of hours to crunch through.</p><p>This image is from a research project that took nearly 1.2 million processor hours, all to study how turbulence dissipates energy in three dimensions.</p>

<p>Cooling towers at nuclear sites or chemical plants can release water droplets tainted with toxins, which the wind carries away. In an area where other tall buildings surround those towers, the movement of air becomes more complex, and predicting where the wind could carry droplets is difficult. </p><p>So researchers at <a href="http://www.windlab.colostate.edu/index.htm" target="blank">Colorado State University</a> and ANSYS created this simulation to show all the different paths of airflow. The cooling towers are located in the center, near the heaviest concentration of color.</p>

<p>Bulk air flow moves at about 70 miles per hour through the grille of a <a href="http://www.chevrolet.com/corvette/" target="blank">2008 Corvette Z06</a> in a virtual wind tunnel. Greater turbulent flow makes for a less aerodynamic ride, but it helps cool the engine when passing under the hood.</p>

<p>Even the researchers who created this image had a tough time interpreting its complex representation how of turbulent <a href="http://www.windows.ucar.edu/tour/link=/physical_science/physics/mechanics/fluids.html" target="blank">fluids</a> flow in three dimensions. And their high-powered supercomputers still struggle to outline something as common as airplane turbulence. </p><p>But as computers get faster and software more efficient, we may be able to see more clearly how the wind blows, how a faucet flows, and what happens in the universe when fluids move and collide.</p>

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