Honeycomb-like materials to reduce aircraft engine noise developed

September 30th, 2008 - 2:16 pm ICT by ANI  

Washington, Sept 30 (ANI): Engineers from Georgia Tech Research Institute have developed a new honeycomb like materials that can reduce aircraft engine noise more effectively than conventional methods.
A honeycomb is a mass of hexagonal wax cells built by honey bees in their nests to contain their larvae and stores of honey and pollen.
The new microchanneled material developed by research engineer Jason Nadler can reduce engine noise by wearing it down 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.
The noise from commercial and military jet aircraft causes environmental problems for communities near airports, compelling the airplanes to follow often-complex noise-abatement procedures on takeoff and landing. It can also make aircraft interiors excessively loud.
The new material with honeycomb-like structures composed of many metallic nanotubes is capable of reducing noise in aircraft by up to 30 percent.
“This approach dissipates acoustic waves by essentially wearing them out,” said Nadler.
“It’’s a phenomenological shift, fundamentally different from traditional techniques that absorb sound using a more frequency-dependent resonance.”
According to Nadler, the technique 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.”
While 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 said. 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.
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. (ANI)

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