Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Earth’s turbulence stirs things up slower than expected

06.03.2006


In a simple world rivers would flow in straight lines, every airplane ride would be smooth, and we would know the daily weather 10 years into the future. But the world is not simple -- it is turbulent.



That’s good news, since turbulence helps drive natural processes essential for life. Unfortunately it also means we are never 100 percent sure it won’t rain on Saturday.

"Turbulence is the last major unsolved problem of classical physics," explains Eberhard Bodenschatz, professor of physics who studies turbulence with his research group at Cornell and the Max Planck Institute (MPI) for Dynamics and Self-Organization, Germany.


The group recently moved closer to a solution by measuring how two tiny polystyrene spheres in turbulent water separate based on how far apart they initially are from each other. The results were published in the Feb. 10 issue of Science.

The findings suggest that, for almost every turbulent flow on Earth, including violent volcanic eruptions, particles separate more slowly than expected. This discovery could help improve models of dispersion of pollutants and bioagents and even help explain how crustaceans find food, mates and predators by sensing odors in the ocean depths.

Turbulence occurs when a gas or fluid, like air or water, is pushed at high speeds or on large scales, and is characterized by chaotic, seemingly random, flow patterns. Because of its complexity, turbulence is very efficient at mixing: a solution of two liquids, such as cream and coffee, will mix much more quickly if the flow is turbulent than if it is not.

As a white-water rafter might toss a stick into rapids to observe its behavior before jumping in, physicists watch particles in turbulence to understand the flow. A key measurement is how quickly two particles will separate, or "pair dispersion."

In the 1920s, British scientist L.F. Richardson predicted that pair dispersion should grow quickly, as time multiplied by itself twice (time cubed), independent of the initial separation of the pair -- a statement known as the Richardson-Obukhov law. In the 1950s, Australian-born Cambridge mathematician G.K. Batchelor added the amendment that for short timescales, pair dispersion is not independent of initial separation and should grow more slowly, as time multiplied by itself (time squared).

Until recently, the difficulty of photographing tiny particles at high speeds made direct measurements of these predictions impossible.

"When we first planned these experiments, fast enough cameras didn’t exist," said Cornell graduate student Nicholas Ouellette, a co-author of the Science article. The final experiment used three high-tech digital cameras able to record up to 27,000 pictures per second of several hundred polystyrene spheres simultaneously in 8 cubic inches of water. The diameter of the spheres was about one-fourth the thickness of a human hair -- a thickness needed because it matched the smallest eddies in the turbulent water.

The experiment showed that when the initial separation of the spheres is large relative to the turnover time of the eddies, they will obey Batchelor dispersion, independent of the turbulence’s severity. However, if the initial separation is smaller, then the particles will only exhibit Batchelor dispersion initially before transitioning to behavior consistent with the Richardson-Obukhov law.

"Right now new technology -- like our fast cameras -- is making experiments possible that just 10 years ago were considered impossible. It’s a very exciting time to be in the field," Ouellette said.

The other authors of the Science paper are Haitao Xu, Cornell and MPI for Dynamics and Self-Organization, lead author Mickal Bourgoin, Laboratoire des Écoulenments Géophysiques et Industriels, France, and Jacob Berg, Ris National Laboratory, Denmark.

Press Relations Office | EurekAlert!
Further information:
http://www.cornell.edu

More articles from Earth Sciences:

nachricht In times of climate change: What a lake’s colour can tell about its condition
21.09.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)

nachricht Did marine sponges trigger the ‘Cambrian explosion’ through ‘ecosystem engineering’?
21.09.2017 | Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

NASA'S OSIRIS-REx spacecraft slingshots past Earth

25.09.2017 | Physics and Astronomy

MRI contrast agent locates and distinguishes aggressive from slow-growing breast cancer

25.09.2017 | Health and Medicine

Rainbow colors reveal cell history: Uncovering β-cell heterogeneity

22.09.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>