Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Fluid flow technology takes a cue from fast-swimming sharks

17.12.2002


This diagram depicts the arrangement of riblets on the inside surface of a pipe, for a study conducted by Ohio State University chemical engineer Konrad Koeltzsch and his colleagues from the Dresden University of Technology in Germany. [Graphic courtesy of Ohio State University.]


Ohio State University chemical engineer Konrad Koeltzsch and his colleagues from the Dresden University of Technology in Germany studied how the angle of small grooves, called riblets, affect the flow of fluids such as air or water. The researchers lined a pipe with this grooved film, which was created by technology company 3M. Each V-shaped groove measures 150 micrometers across -- approximately twice the width of a human hair. [Photo courtesy of Ohio State University.]


A study of airflow in pipes may help solve a mystery concerning the ears of fast-swimming sharks. The results could also lead to new audio technologies, according to an engineer at Ohio State University.

Konrad Koeltzsch, a postdoctoral researcher in chemical engineering and the Alexander von Humboldt Fellow at Ohio State, and his colleagues investigated grooves in sharkskin called riblets.

Koeltzsch began to study sharkskin while he was a postdoctoral researcher at the Dresden University of Technology in Germany. He worked with Albrecht Dinkelacker, a German researcher who pioneered the study of riblets, and Dresden professor Roger Grundmann. The three published their results in a recent issue of the journal Experiments in Fluids.



Some 20 years ago, engineers found that lining a pipe with riblet-like grooves could speed flow through a pipe by as much as 10 percent.

The very idea that a textured surface could speed fluid flow appears counterintuitive at first, Koeltzsch said. "We normally think that smooth surfaces cause the least drag," he explained. A fundamental point in fluid mechanics is that rough surfaces increase drag, and sharkskin is considered rough. If such a rough surface reduces drag, that doesnt seem to make sense.

The answer still lies in fluid mechanics, Koeltzsch said, in a phenomenon called "wall-bounded turbulence" that hasn’t been well understood until now.

The reason that riblets work the way they do is complex, Koeltzsch said. The most promising explanation comes from researchers at Seoul National University in Korea, who suggested that the size of the riblets and the rotation of spiraling areas of fluid known as vortices are both important factors. The optimal arrangement, Koeltzsch said, is when the distance between the peaks of the riblets is half the diameter of the vortices. In this case, the fluid caught by the vortices only contacts the peaks of the riblets and not the walls of the pipe, so friction is reduced and the fluid moves faster.

Other researchers previously determined that riblets could be used to speed the flow of fluids such as water and air. NASA, for instance, has been developing riblet technology for airplanes, sea vessels, and even swimsuits since the 1980s.

Koeltzsch said it is now well understood that the riblets running along a shark’s body from head to tail help the shark swim faster. But very fast-swimming sharks, such as the silky shark and blue shark, also have special arrangements of riblets, the function of which is a mystery.

The riblets converge or diverge in a "V" pattern on the skin surrounding the shark’s sensory organs. One set angles in toward the shark’s pit organ, and other angles away from the lateral-line organ. The function of the pit organ is a matter of controversy in biology, Koeltzsch said, but scientists believe the lateral-line organ functions similarly to the human ear. Scientists have debated the exact purpose of the converging and diverging riblets for a decade.

Koeltzsch and his coauthors suspected that the diverging riblets drew water away from a shark’s "ears" to prevent the noisy sound of rushing water, which inhibits the sharks hearing. If that were true, the riblets could enable sharks to better hear signs of prey.

To simulate riblets in the lab, the engineers lined their pipe with the textured film by technology company 3M so that the ridges made an angle of 45 degrees with the length of the pipe. The ridges on one side of the pipe formed a converging pattern, and the other side formed a diverging pattern.

In tests, the converging riblets slowed airflow near the pipe wall by as much as 15 percent, and the diverging riblets sped up airflow by the same amount. This means diverging riblets reduce turbulence, making water flow more quietly past the shark’s ear.

"Everybody might have had that experience, when on a windy day we hear the noisy sound of air rushing past our ears," Koeltzsch said. "A fast-swimming shark listens to that noise constantly, only the fluid rushing past its ears is water, not air. The faster it swims, the louder the noise. This study suggests that fast-swimming sharks evolved diverging riblets to speed water past their lateral-line organ and reduce background noise in just the right way to aid their sense of hearing.

"Since the function of the pit organ is still not clear, these findings could help biologists solve that mystery, too," he added.

Koeltzsch suspects that diverging riblets could also be used to improve the performance of microphones, where the flow of air or water over the equipment affects audio quality.

This work was funded by Deutsche Forschungsgemeinschaft, the German equivalent to the U.S. National Science Foundation. Koeltzsch is continuing his investigations at Ohio State, using the funds from his von Humboldt fellowship.

With Robert Brodkey, professor of chemical engineering, Koeltzsch has now turned his attention away from sharks, to penguins and seals. He hopes to determine whether hair makes these aquatic mammals more hydrodynamic. Initial studies by other scientists have shown that natural and artificial fibers can reduce drag by amounts that vary from 1.5 to 50 percent.

Continued research could show whether hair would improve the design of boat hulls and even airplanes, Koeltzsch said. Airplanes wouldnt need to use as much high-cost fuel if they experienced less friction as they cut through the air.

"Wouldn’t it be something if, in the future, airplanes had hairy surfaces?" he asked.

Contact: Konrad Koeltzsch, (614) 688-3210; Koeltzsch.1@osu.edu
Written by Pam Frost Gorder, (614) 292-9475; Gorder.1@osu.edu

Pam Frost Gorder | EurekAlert!
Further information:
http://www.osu.edu/researchnews/archive/riblets.htm

More articles from Process Engineering:

nachricht New manufacturing process for SiC power devices opens market to more competition
14.09.2017 | North Carolina State University

nachricht Quick, Precise, but not Cold
17.05.2017 | Fraunhofer-Institut für Lasertechnik ILT

All articles from Process Engineering >>>

The most recent press releases about innovation >>>

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

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...

Im Focus: Fast, convenient & standardized: New lab innovation for automated tissue engineering & drug

MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems Holding GmbH about commercial use of a multi-well tissue plate for automated and reliable tissue engineering & drug testing.

MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems...

Im Focus: Silencing bacteria

HZI researchers pave the way for new agents that render hospital pathogens mute

Pathogenic bacteria are becoming resistant to common antibiotics to an ever increasing degree. One of the most difficult germs is Pseudomonas aeruginosa, a...

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

Molecular Force Sensors

20.09.2017 | Life Sciences

Producing electricity during flight

20.09.2017 | Power and Electrical Engineering

Tiny lasers from a gallery of whispers

20.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>