Acoustic treatment structure for an aircraft propulsion unit nacelle
A structure for the nacelle of an aircraft propulsion unit includes a first skin and stiffeners arranged to hold acoustic treatment modules against the first skin. Each acoustic treatment module includes a honeycomb core and a second skin, such that the honeycomb core is sandwiched between the first skin and the second skin. Such a structure allows the structural reinforcement function provided by the stiffeners to be separated from the acoustic treatment function performed by the acoustic treatment modules which are simply bearing on the first skin.
1. A structure for an aircraft propulsion unit nacelle comprising:
a first skin,
stiffeners fixed to the first skin to stiffen the first skin, and
acoustic treatment modules, each acoustic treatment module comprising a cellular core and a respective second skin fixed to the cellular core, each second skin of each acoustic treatment module separate from each other second skin of each other acoustic treatment module,
the first skin and the acoustic treatment modules being arranged so that the cellular core of each acoustic treatment module is clasped between the corresponding second skin and the first skin,
the first skin or the second skin of the acoustic treatment modules being acoustically permeable to attenuate power of acoustic waves in the cellular core of the acoustic treatment modules,
wherein each acoustic treatment module is embedded between at least two respective stiffeners, in that each acoustic treatment module is simply bearing on the first skin and comprises holding elements arranged to hold each acoustic treatment module against the first skin.
2. The structure according to claim 1 , wherein the holding elements cooperate with the respective second skin of each acoustic treatment module to exert a force for holding the acoustic treatment modules against the first skin.
3. The structure according to claim 1 , wherein each stiffener comprises a first element forming a stop for one or more acoustic treatment modules to limit displacement of the acoustic treatment modules in a direction tangential to the first skin, and a second element forming a stop for one or more acoustic treatment modules to limit displacement of the acoustic treatment modules in a direction normal to the first skin, the second element constituting at least one portion of the holding elements.
4. The structure according to claim 1 , wherein the stiffeners constitute at least one portion of the holding elements.
5. The structure according to claim 1 , wherein the holding elements comprise elastic blades fixed on the stiffeners.
6. The structure according to claim 1 , wherein the holding elements comprise one or more lateral elastic elements arranged to exert lateral pressure on the acoustic treatment modules against the respective stiffeners between which the acoustic treatment modules are embedded, to immobilize the acoustic treatment modules in a direction tangential to the first skin.
7. The structure according to claim 6 , wherein the lateral or transverse elastic elements are formed by at least one of the second skin and the cellular core of the acoustic treatment modules.
8. The structure according to claim 1 , wherein the holding elements comprise one or more transverse elastic elements arranged to exert transverse pressure of the acoustic treatment modules against the first skin, to immobilize the acoustic treatment modules in a direction normal to the first skin.
9. The structure according to claim 8 , wherein the lateral or transverse elastic elements are formed by at least one of the second skin and the cellular core of the acoustic treatment modules.
10. The structure according to claim 1 , wherein the first skin and the stiffeners comprise a composite material having a ceramic matrix.
11. The structure according to claim 1 , wherein the acoustic treatment modules comprise a metallic material.
12. The structure according to claim 11 , wherein the metallic material is selected from the group consisting of a titanium alloy and a nickel-based alloy.
13. An exhaust conduit of an aircraft propulsion unit nacelle comprising a structure according to claim 1 .
14. An aircraft propulsion unit nacelle comprising a structure according to claim 1 .
15. The aircraft propulsion unit nacelle according to claim 14 , wherein the stiffeners of the structure extend in respective directions parallel to a longitudinal axis of the aircraft propulsion unit nacelle.