One piece acoustic liner – reduces engine noise by up to 4 dB

Citation

(2009), "One piece acoustic liner – reduces engine noise by up to 4 dB", Aircraft Engineering and Aerospace Technology, Vol. 81 No. 1. https://doi.org/10.1108/aeat.2009.12781aad.010

One piece acoustic liner – reduces engine noise by up to 4 dB

Article Type: Materials From: Aircraft Engineering and Aerospace Technology: An International Journal, Volume 81, Issue 1

Technologists at GKN Aerospace have developed an all-composite one-piece acoustic liner for the aero-engine intake. In trials, this liner is reported to be demonstrating a 3-4 dB reduction in the noise levels experienced with the traditional two piece engine intake design.

This one piece liner is expected to enter full production in the next 2 years.

Noise regulations and public concern over noise pollution from aircraft operating to and from heavily populated areas mean engine manufacturers have challenging targets to reduce the noise output of their engines as well as to cut fuel consumption and emissions for environmental and operating cost reasons.

In order to reduce engine noise, cylinders of material are created like organ pipes tuned to respond to the frequencies that we hear. These tubes are contained in the acoustic liner in the engine intake. The pressure waves bounce around in the tubes and the vibrations cancel themselves out. The most effective acoustic design has many tubes aligned at right angles to the intake wall with individual holes of different sizes.

However, any joins in the liner introduce a beat to the sound pressure waves and this limits noise reduction.

The new design combines one piece “zero splice construction” with a cell-aligned double layer honeycomb core. Together, the elimination of the joints and the use of the honeycomb material with a dividing septum makes the liner far more effective – able continuously to absorb noise across a wide frequency range whilst offering a significant weight reduction.

Phil Grainger, Senior Technical Director and Chief Technologist at GKN Aerospace comments: “Our development work targeted noise reduction as our first goal and has achieved significant benefits in this area. In addition, the low weight of these liners means they also offer valuable weight and performance benefits for the aircraft operator”.

GKN Aerospace has long experience in the design and manufacture of passive sound insulation systems for the air intakes and bypass ducts of aircraft engine nacelles and is the world’s largest producer of noise reducing, resistance welded honeycomb sandwich structures.