The purpose of this innovation is to reduce aircraft noise in the communities surrounding airports by significantly attenuating the noise generated by the turbomachinery, and enhancing safety by providing a containment barrier for a blade failure. Acoustic liners are used in today’s turbofan engines to reduce noise. The amount of noise reduction from an acoustic liner is a function of the treatment area, the liner design, and the material properties, and limited by the constraints of the nacelle or casement design. It is desirable to increase the effective area of the acoustic treatment to increase noise suppression. Modern turbofan engines use “wide-chord” rotor blades, which means there is considerable treatment area available over the rotor tip.

Turbofan engines require containment over the rotors for protection from blade failure. Traditional methods use a material wrap such as Kevlar integrated with rub strips and sometimes metal layers (sandwiches). It is possible to substitute the soft rub-strip material with an open-cell metallic foam that provides noise-reduction benefits and a sacrificial material in the first layer of the containment system.

An open-cell foam was evaluated that behaves like a bulk acoustic liner, serves as a tip rub strip, and can be integrated with a rotor containment system. Foams can be integrated with the fan-containment system to provide sufficient safety margins and increased noise attenuation. The major innovation is the integration of the foam with the containment.

The uniqueness of the innovation is the ability to reduce turbomachinery noise for aircraft engine applications while providing sufficient blade containment and minimal (if any) aerodynamic penalty. The innovation can be applied to compressors, turbines, and fans. Space is usually limited over the rotors due to the need for containment systems. The innovation replaces the first layer of the containment system with a foam that behaves like an acoustic bulk liner. The material properties of the foam can be tailored for temperature, density, porosity, and weight to suit the application. Existing turbofan engines do not use acoustic treatment placed directly over the rotor. The innovation enables this due to the foam behaving like a rub strip and an acoustic liner. Full-scale testing of production turbofan engine resulted in 5-dB total attenuation.

This innovation can be applied to other turbomachinery where noise reduction is needed from the rotors; for example, ground power systems, cooling/ventilating fans, and ducted propellers.

This work was done by Dennis L. Huff and Daniel L. Sutliff of Glenn Research Center; Michael G. Jones of Langley Research Center; and Mohan G. Hebsur of the Ohio Space Institute. For more information, download the Technical Support Package (free white paper) at under the Mechanics/Machinery category.

Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steve Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-18438-1.