Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New Micro Honeycomb Materials Reduce Aircraft Noise

01.10.2008
Researchers at the Georgia Tech Research Institute (GTRI) are developing innovative honeycomb structures that could make possible a new approach to noise reduction in aircraft.

Noise from commercial and military jet aircraft causes environmental problems for communities near airports, obliging airplanes to follow often complex noise-abatement procedures on takeoff and landing. It can also make aircraft interiors excessively loud.

To address this situation, engineers at the Georgia Tech Research Institute (GTRI) are turning to innovative materials that make possible a new approach to the physics of noise reduction. They have found that honeycomb-like structures composed of many tiny tubes or channels can reduce sound more effectively than conventional methods.

“This approach dissipates acoustic waves by essentially wearing them out,” said Jason Nadler, a GTRI research engineer. “It’s a phenomenological shift, fundamentally different from traditional techniques that absorb sound using a more frequency-dependent resonance.”

The two-year project is sponsored by EADS North America, the U.S. operating entity of EADS.

Most sound-deadening materials – such as foams or other cellular materials comprising many small cavities – exploit the fact that acoustic waves resonate through the air on various frequencies, Nadler explains.

Just as air blowing into a bottle produces resonance at a particular tone, an acoustic wave hitting a cellular surface will resonate in certain-size cavities, thereby dissipating its energy. An automobile muffler, for example, uses a resonance-dependent technique to reduce exhaust noise.

The drawback with these traditional noise-reduction approaches is that they only work with some frequencies – those that can find cavities or other structures in which to resonate.

Nadler’s research involves broadband acoustic absorption, a method of reducing sound that doesn’t depend on frequencies or resonance. In this approach, tiny parallel tubes in porous media such as metal or ceramics create a honeycomb-like structure that traps sound regardless of frequency. Instead of resonating, sound waves plunge into the channels and dissipate through a process called viscous shear.

Viscous shear involves the interaction of a solid with a gas or other fluid. In this case, a gas – sound waves composed of compressed air – contacts a solid, the porous medium, and is weakened by the resulting friction.

“It's the equivalent of propelling a little metal sphere down a rubber hose when the sphere is just a hair bigger than the rubber hose,” Nadler explained. “Eventually the friction and the compressive stresses of contact with the tube would stop the sphere.”

This technique, Nadler adds, is derived from classical mechanical principles governing how porous media interact with gases – such as the air through which sound waves move. Noise abatement using micro-scale honeycomb structures represents a new application of these principles.

“You need to have the hole big enough to let the sound waves in, but you also need enough surface area inside to shear against the wave,” he said. “The result is acoustic waves don’t resonate; they just dissipate.”

In researching this approach, Nadler constructed an early prototype from off-the-shelf capillary tubes, which readily formed a low-density, honeycomb-like structure. Further research showed that the ideal material for broadband acoustic absorption would require micron-scale diameter tubes and a much lower structural density.

Creating such low-density structures presents an interesting challenge, Nadler says. It requires a material that’s light, strong enough to enable the walls between the tubes to be very thin, and yet robust enough to function reliably amid the high-temperature, aggressive environments inside aircraft engines.

Among the likely candidates are superalloys, materials that employ unusual blends of metals to achieve desired qualities such as extreme strength, tolerance of high temperatures and corrosion resistance.

Nadler has developed what could be the world’s first superalloy micro honeycomb using a nickel-base superalloy. At around 30 percent density, the material is very light – a clear advantage for airborne applications – and also very strong and heat resistant.

He estimates this new approach could attenuate aircraft engine noise by up to 30 percent. Micro-honeycomb material could also provide another means to protect the aircraft in critical areas prone to impact from birds or other foreign objects by dissipating the energy of the collision.

Technical Contact: Jason Nadler (404-407-6104)
E-mail: jason.nadler@gtri.gatech.edu

John Toon | Newswise Science News
Further information:
http://www.gtri.gatech.edu

More articles from Materials Sciences:

nachricht A new manufacturing process for aluminum alloys
19.06.2019 | DOE/Pacific Northwest National Laboratory

nachricht Innovative powder revolutionises 3D metal printing
19.06.2019 | Technische Universität Graz

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Successfully Tested in Praxis: Bidirectional Sensor Technology Optimizes Laser Material Deposition

The quality of additively manufactured components depends not only on the manufacturing process, but also on the inline process control. The process control ensures a reliable coating process because it detects deviations from the target geometry immediately. At LASER World of PHOTONICS 2019, the Fraunhofer Institute for Laser Technology ILT will be demonstrating how well bi-directional sensor technology can already be used for Laser Material Deposition (LMD) in combination with commercial optics at booth A2.431.

Fraunhofer ILT has been developing optical sensor technology specifically for production measurement technology for around 10 years. In particular, its »bd-1«...

Im Focus: The hidden structure of the periodic system

The well-known representation of chemical elements is just one example of how objects can be arranged and classified

The periodic table of elements that most chemistry books depict is only one special case. This tabular overview of the chemical elements, which goes back to...

Im Focus: MPSD team discovers light-induced ferroelectricity in strontium titanate

Light can be used not only to measure materials’ properties, but also to change them. Especially interesting are those cases in which the function of a material can be modified, such as its ability to conduct electricity or to store information in its magnetic state. A team led by Andrea Cavalleri from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg used terahertz frequency light pulses to transform a non-ferroelectric material into a ferroelectric one.

Ferroelectricity is a state in which the constituent lattice “looks” in one specific direction, forming a macroscopic electrical polarisation. The ability to...

Im Focus: Determining the Earth’s gravity field more accurately than ever before

Researchers at TU Graz calculate the most accurate gravity field determination of the Earth using 1.16 billion satellite measurements. This yields valuable knowledge for climate research.

The Earth’s gravity fluctuates from place to place. Geodesists use this phenomenon to observe geodynamic and climatological processes. Using...

Im Focus: Tube anemone has the largest animal mitochondrial genome ever sequenced

Discovery by Brazilian and US researchers could change the classification of two species, which appear more akin to jellyfish than was thought.

The tube anemone Isarachnanthus nocturnus is only 15 cm long but has the largest mitochondrial genome of any animal sequenced to date, with 80,923 base pairs....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

SEMANTiCS 2019 brings together industry leaders and data scientists in Karlsruhe

29.04.2019 | Event News

Revered mathematicians and computer scientists converge with 200 young researchers in Heidelberg!

17.04.2019 | Event News

First dust conference in the Central Asian part of the earth’s dust belt

15.04.2019 | Event News

 
Latest News

A new force for optical tweezers awakens

19.06.2019 | Physics and Astronomy

New AI system manages road infrastructure via Google Street View

19.06.2019 | Information Technology

A new manufacturing process for aluminum alloys

19.06.2019 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>