Acoustically attenuating sandwich panel constructions
An aircraft engine assembly comprising a nacelle configured to surround the aircraft engine having an inlet open to ambient air and an annular acoustic panel provided within the nacelle. Sound emitted from the aircraft engine is attenuated by the annular acoustic panel. The annular acoustic panel comprises an open framework, made from a first material, forming a plurality of cells.
1. An aircraft engine assembly comprising:
an aircraft engine;
a nacelle configured to surround the aircraft engine and having an inlet open to ambient air;
an annular acoustic panel, comprising an open framework, made from a first material, forming a plurality of cells, and a surface treatment provided on the open framework to increase the sound attenuation of the open framework relative to the open framework without the surface treatment, the surface treatment comprising a surface modification including at least one of a nanostructure comprising filaments projecting away from the open framework, a coating, a particulate layer, a fabric, or a cellular solid body;
wherein at least one of the length, angle of projection, and porosity of the filaments may be selected to attenuate one or more predetermined frequencies of sound, and the annular acoustic panel is provided within the nacelle and sound emitted from the aircraft engine is attenuated by the annular acoustic panel.
2. The aircraft engine assembly of claim 1 wherein the nacelle comprises an inlet section defining the inlet and the acoustic panel is mounted to the inlet section and defines an inner surface.
3. The aircraft engine assembly of claim 1 wherein the aircraft engine comprises a fan section and the acoustic panel is mounted to the fan section.
4. The aircraft engine assembly of claim 1 wherein at least some of the cells form a portion of a Helmholtz resonator, and the open framework comprises a honeycomb structure.
5. The aircraft engine assembly of claim 4 further comprising an impervious backing sheet located on a rear side of the honeycomb structure and a perforated front sheet located on a front side of the honeycomb structure.
6. The aircraft engine assembly of claim 1 wherein the surface treatment has a geometry that at least disperses or attenuates sound waves.
7. The aircraft engine assembly of claim 1 wherein the coating comprises at least one of a deposition coating or a polymer coating.
8. The aircraft engine assembly of claim 1 wherein the particular layer comprises particles of a size selected to attenuate one or more predetermined frequencies.
9. The aircraft engine assembly of claim 1 wherein the surface modification comprises at least one of at etching the surface of the open framework and texturing the surface of the open framework.
10. The aircraft engine assembly of claim 9 wherein the texturing comprises an additive manufacturing applied texture, stamping, or rolling.
11. The aircraft engine assembly of claim 1 wherein the surface treatment is applied only to a portion of the open framework or to the impervious backing sheet.