Acoustic treatment device for turbine and combustion noises

1. An acoustic treatment device for an internal structure of a primary ejection duct from a turbojet pad, comprising:

an upstream zone and a downstream zone relative to an airflow direction in the primary ejection duct, the upstream zone including a perforated outside wall to allow acoustic waves to enter and the downstream zone including a solid outside wall, the upstream and downstream zones being located on each side of a separating wall with a first face on the side of the upstream zone and a second face on the side of the downstream zone,

wherein the separating wall has a perforation ratio of fifteen percent or less, and a micro-porosity of the separating wall and a honeycomb structure attenuate high frequency acoustic waves that cover the face of the separating wall in the downstream zone.

2. A device according to claim 1 , in which the honeycomb structure comprises at least one cellular layer and the cellular layer furthest from the separating wall is covered by an acoustic reflector.

3. A device according to claim 2 , in which the honeycomb structure comprises at least two layers of stacked cells, and two adjacent layers of stacked cells are separated from each other by a micro-porous separating wall like the separating wall which separates the upstream zone and the downstream zone.

4. A device according to claim 3 , in which the cells in the different cell layers have different thicknesses in different layers to attenuate acoustic waves from different frequency bands.

5. A device according to claim 1 , in which the honeycomb structure is made of a metal capable of resisting hot ejection temperatures.

6. A device according to claim 1 , further comprising:

a perforation in the outside wall of the structure;

an additional honeycomb structure capable of attenuating high frequency acoustic waves, and that covers an internal face of the outside wall; and

an acoustic reflector that covers the additional honeycomb structure, in the zone downstream from the structure.

7. A device according to claim 1 , in which the upstream zone comprises a plurality of Helmholtz resonators for attenuation of low frequency acoustic waves.

8. A device according to claim 1 , wherein the perforation ratio of the separating wall is five percent.

9. A device according to claim 1 , wherein the perforation ratio of the separating wall is fifteen percent.

10. A device according to claim 1 , wherein the perforation ratio of the separating wall is approximately five percent.

11. A device according to claim 1 , wherein the perforation ratio of the separating wall is approximately fifteen percent.