Element for sound absorption mounted on aircraft components
An element ( 26 ) for sound absorption is intended for being mounted on components of aircrafts, such as engine nacelles. The element includes a face-sheet ( 28 ), which is, at least in a region thereof, acoustically permeable, a substantially sound-reflective back-sheet ( 30 ) and a honeycomb layer ( 32 ), “sandwiched” between the face-sheet ( 28 ) and the back-sheet ( 30 ) and defining a mesh structure which has hollow cells ( 34, 34 ′) laterally neighboring one another. The cells ( 34, 34 ′) are adapted to make the sound waves that enter through the face-sheet ( 28 ) and are reflected by the back-sheet ( 30 ) resonate inside their side walls. The element ( 26 ) has a passage ( 36 ) that connects together a group of the cells ( 34, 34 ′), thereby causing the cells to acoustically cooperate with one another.
1. An engine nacelle comprising:
a cowling having a substantially barrel shape, said cowling having a through cavity extending in a substantially axial direction; said cowling has an outer barrel facing outward and an inner barrel surrounding said through cavity; said cowling having an air intake located at one end of said through cavity for conveying external air into said cowling;
a first single element for sound absorption forming an inlet ring, the inlet ring comprising the inner barrel in an inlet region of said cowling; and
a second single element for sound absorption forming an outlet ring, the outlet ring comprising the inner barrel in an outlet region of said cowling;
each of said first and second single elements for sound absorption comprising:
a face-sheet, which is, at least in a region thereof, acoustically permeable;
a substantially sound-reflective back-sheet;
a honeycomb layer interposed between said face-sheet and said back-sheet and defining a mesh structure which has a plurality of hollow cells laterally adjacent one another, wherein mutually opposite open axial ends of said cells are covered by the face sheet and the back-sheet; said cells being adapted to make sound waves that enter through said face-sheet and are reflected by back-sheet resonate inside side walls;
at least one notch formed on a bottom of said honeycomb layer and positioned between said cells, said bottom resting on said back-sheet; said notch connecting together a group comprising a pair of said cells that are laterally adjacent in said mesh structure and passing through at least one delineating wall, thereby causing said cells to acoustically cooperate with one another; and
an intermediate divider positioned in the honeycomb layer and housed in one of said acoustically cooperating cells, wherein said intermediate divider divides said one of said acoustically cooperating cells;
wherein said face-sheet has at least one acoustically permeable portion capable of being passed through by a prevalent portion of the incident sound waves, and at least one acoustically reflective portion; said group of acoustically cooperating cells including at least one cell facing said acoustically permeable portion and at least one other cell facing said acoustically reflective portion.
2. The nacelle according to claim 1 , wherein said intermediate divider is substantially sound-absorbing.
3. The nacelle according to claim 1 , wherein said intermediate divider is substantially sound-reflective.
4. Aircraft comprising a nacelle according to claim 1 .
5. An engine nacelle comprising: a cowling having a substantially barrel shape, said cowling having a through cavity extending in a substantially axial direction; said cowling has an outer barrel facing outward and an inner barrel surrounding said through cavity; said cowling having an air intake located at one end of said through cavity for conveying external air into said cowling; a first single element for sound absorption forming an inlet ring, the inlet ring comprising the inner barrel in an inlet region of said cowling; and a second single element for sound absorption forming an outlet ring, the outlet ring comprising the inner barrel in an outlet region of said cowling; each of said first and second single elements for sound absorption comprising: a face-sheet, which is, at least in a region thereof, acoustically permeable; a substantially sound-reflective back-sheet; a honeycomb layer interposed between said face-sheet and said back-sheet and defining a mesh structure which has a plurality of hollow cells laterally adjacent one another, wherein mutually opposite open axial ends of said cells are covered by the face sheet and the back-sheet; said cells being adapted to make sound waves that enter through said face-sheet and are reflected by back-sheet resonate inside side walls; at least one notch formed on a bottom of said honeycomb layer and positioned between said cells, said bottom resting on said back-sheet; said notch connecting together a group comprising a pair of said cells that are laterally adjacent in said mesh structure and passing through at least one delineating wall, thereby causing said cells to acoustically cooperate with one another; and an intermediate divider positioned in the honeycomb layer and housed in one of said acoustically cooperating cells, wherein said intermediate divider divides said one of said acoustically cooperating cells; wherein said group of acoustically cooperating cells includes at least one cell in which there is a first substantially sound-absorbing intermediate divider, and at least one other cell in which there is a second substantially sound-reflective intermediate divider.