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Research in Turbulence
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Affiliated Faculty:
Dave Caughey,
Lance Collins,
Al George,
Sid Leibovich,
John Lumley,
Steve Pope,
Zellman Warhaft,
Charles Williamson
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Billowing smoke stacks, cumulous clouds and waterfalls are visible everyday examples of turbulent flows. Though less visible, turbulent flows are ubiquitous in our transportation systems, process industries and natural environment (the atmosphere, oceans, rivers and even stars). In contrast to laminar flows–exemplified by honey pouring from a jar–turbulent flows have inherent instabilities leading to chaotic, three-dimensional unsteady motions with a large range of scales. A bumpy aircraft flight may be caused by eddies of atmospheric turbulence which are larger than the aircraft, whereas the drag on the wing and fuselage are caused by eddy motions smaller that a millimeter.
Turbulence is a particular strength of the Fluids Group at Cornell. We have three graduate courses on turbulence and turbulent flows, and our faculty are authors of two of the leading textbooks on the subject: A First Course in Turbulence, Tennekes & Lumley (1972) and Turbulent Flows, Pope (2000).
Our research covers experimental, theoretical and computational approaches. We have a dozen wind tunnels, including ones with active grids for generating high-Reynolds number turbulence.
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Aerosol particles cluster in turbulent flows. Green surfaces are
vortex tubes where fluid circulates rapidly, centrifuging particles
out into the interstitial straining regions. White surfaces are
particle-rich regions with more than ten times the nominal particle concentration.
(Courtesy Lance Collins) |
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False-color image of the chemical species OH in a
turbulent mixing layer bewteen cold hydrogen and hot air. From
large-eddy simulations performed by Lu, Ren & Pope (2004).
(Courtesy Steve Pope)
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Our work on the computational side includes direct numerical simulations (DNS), large-eddy simulations (LES) and probability density function (PDF) methods especially for reactive flows. These studies are greatly facilitated by the use of our own clusters (up to 64 processors) and by the clusters at the Cornell Theory Center (which has over 1500 processors). A current focus of interest is the behavior of small particles in turbulence, which is directly related to: the formation of rain droplets in warm clouds; the dispersion of dust, pollen, spores and biological agents; and fuel sprays in gasoline, diesel and aircraft gas-turbine engines.
Turbulent flows are characterized by extremely high rates of mixing. In the mixing of fuel and air in all types of engines (e.g., for cars, aircraft and ships) turbulent flow is essential, and devising means of enhancing the turbulent mixing rates would yield significant benefits in fuel economy and reduced pollutant emissions. On the other hand, the drag on these vehicles is largely due to the effectiveness–unwanted in this context–of turbulent flows to mix momentum. Similarly, the cost of pumping oil and gas through pipelines is directly proportional to the frictional losses due to turbulence. In these latter examples, devising ways to reduce friction and drag in turbulent flows has very significant economic pay-off.
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