FR3117257A1 - Height-adjustable multi-cell acoustic attenuation panel - Google Patents

Abstract

Multi-cell acoustic attenuation panel with variable height A multicellular acoustic attenuation panel (220) comprises several rows of acoustic cells (240, 250, 260, 270, 280) each extending in a circumferential direction (DC), each acoustic cell being delimited by a wall (241, 251, 261, 271, 281) extending in height in a radial direction (DR). Acoustic cells (240, 280) of cell rows have a cross-sectional area greater than the cross-sectional area of acoustic cells of other cell rows (250, 260, 270) and a wall height less than the wall height acoustic cells from other rows of cells. Figure for abstract: Fig. 1.

Description

Height-adjustable multi-cell acoustic attenuation panel

The present invention relates to the general field of acoustic attenuation structures. It relates more particularly to acoustic attenuation structures or panels used to reduce the noise produced in aircraft engines such as in gas turbines or their exhaust.

In order to reduce the noise in the exhaust ducts of gas turbines, it is known to provide the surfaces of the elements delimiting these ducts with acoustic attenuation structures. These structures typically consist of a first multi-perforated skin permeable to the acoustic waves that it is desired to attenuate and of a second solid reflecting skin, a core, such as a honeycomb or a honeycomb structure, being placed between these two skins. In a well-known manner, the cores of such structures form Helmholtz-type resonators which make it possible to attenuate the acoustic waves produced in the conduit within a certain range of frequencies.

In technical fields where mass gain is a constant concern, such as aeronautics, acoustic attenuation structures are preferably made of composite material (fibrous reinforcement densified by a matrix) rather than metallic material.

Document US 9,631,519 describes an acoustic attenuation structure whose skins and core are formed from composite materials allowing a saving in mass compared to the metallic materials usually used.

However, in the acoustic attenuation structures of the prior art, the acoustic cells are limited to shapes of simple cells such as those of the cells of a classic structure of the NIDA® type.

In general, we seek to have a constant height of acoustic cells over the length of the room. This is possible for low heights (for example of the order of 20mm to 30mm), especially for metal parts. However, for significant heights (for example more than 50mm), the cells located upstream and downstream will be of variable height because it is necessary to manage the passage from the non-acoustic zones (monolithic skins) to the acoustic zone. . This is particularly true for parts made of composite materials where these zones of variable height are called chamfers. These bevels are short when the panel is thin (20mm to 30mm) but for significant heights (for example around 150mm to 250mm), the majority of the acoustic zone of the exhaust is made up of bevel zones. There is therefore only a short central zone at the desired constant height, the rest being of variable height experienced, and of height less than the nominal target acoustic height.

When the acoustic cells have variable heights between them, for example when the cells present at the level of a chamfer have a height lower than the height of the cells present outside the chamfer, a shift in the frequency range of the sound waves is observed. processed, this offset corresponding to an increase in the processed frequencies.

However, the acoustic emissions at the level of the exhaust part in the new architectures of aeronautical engines have frequencies included in the low frequencies. Combustion noises related to pressure fluctuations in the combustion chamber of the engine have frequencies typically between 400 Hz and 1000 Hz.

There is therefore a need to make it possible to control the frequency range of the sound waves to be attenuated, and this with acoustic cells of variable heights in the acoustic treatment zone.

To this end, the present invention proposes a multicellular acoustic attenuation panel comprising several rows of acoustic cells, each row extending in a circumferential direction, each acoustic cell being delimited by a wall extending in height in a radial direction,
characterized in that at least the acoustic cells of one or more first rows of cells have a cross-section greater than the cross-section of the acoustic cells of one or more second rows of acoustic cells and in that said acoustic cells of the first row or rows of acoustic cells have a wall height less than the wall height of the acoustic cells of the second row or rows of acoustic cells.

By “wall height”, we mean a height which can be constant for a given acoustic cell or an average height of an acoustic cell when the wall height of the cell varies.

By enlarging the section of the cells having a reduced wall height, the impact of the reduction in wall height on the overall volume of each cell is limited. This preserves for acoustic cells with a lower wall height the ability to attenuate low frequencies.

According to a particular characteristic of the panel of the invention, the acoustic cells of the first row or rows of acoustic cells have an internal volume equivalent to the internal volume of the acoustic cells of the second row or rows of acoustic cells. The frequency shift between all the acoustic cells is thus reduced to a minimum. By "equivalent internal volume" is meant here a difference in volume of less than 30%, preferably less than 10%, and more preferably a difference in volume of zero.

According to another particular characteristic of the panel of the invention, each acoustic cell has a volume configured to capture sound waves having a frequency between 400 Hz and 1000 Hz.

According to another particular characteristic of the panel of the invention, the rows of acoustic cells are juxtaposed to each other from upstream to downstream in an axial direction, the row of acoustic cells present upstream of the plurality of rows of acoustic cells and the row of acoustic cells present downstream of the plurality of rows of acoustic cells have a lower wall height than the wall height of the acoustic cells of the other row(s) of cells.

The invention also relates to a sound attenuation structure of at least partially annular or semi-annular shape comprising an acoustic skin and a closing skin delimiting between them an annular or semi-annular volume comprising a multicellular acoustic attenuation panel according to the invention.

According to a particular characteristic of the structure of the invention, the acoustic skin, the closure skin and the multicellular acoustic attenuation panel are made of composite material comprising a fibrous reinforcement densified by a matrix.

According to another particular characteristic of the structure of the invention, the acoustic skin and the closure skin are made of a composite material comprising a fibrous reinforcement densified by a matrix, while the multicellular acoustic attenuation panel is made of a metallic material.

The invention also relates to:

- an ejection cone for an aeronautical engine comprising an acoustic attenuation structure according to the invention.

- an aeronautical engine exhaust nozzle comprising an acoustic attenuation structure according to the invention.

- an aeronautical gas turbine engine comprising an ejection cone according to the invention or an ejection nozzle according to the invention.

- an aircraft comprising at least one engine according to the invention.

There is a schematic perspective view of an exhaust cone of an aeronautical engine exhaust system in accordance with one embodiment of the invention,

There is a schematic sectional view of the acoustic attenuation structure present in the upstream part of the ejection cone of the ,

There is another schematic sectional view of the acoustic attenuation structure present in the upstream part of the ejection cone of the ,

There is a schematic top view showing the section of the acoustic cells of the acoustic attenuation structure present in the upstream part of the exhaust cone of the ,

There is a schematic perspective view of an exhaust cone of an aeronautical engine exhaust system according to another embodiment of the invention,

There is a schematic top view showing the section of the acoustic cells of the acoustic attenuation structure present in the upstream part of the exhaust cone of the .

A particular but non-exclusive field of application of the invention is that of the exhaust systems of aeronautical gas turbine engines such as those used in airplanes or helicopters. These exhaust systems comprise in particular a nozzle and an ejection cone defining between them an ejection channel for the exhaust gases.

There shows an exhaust cone 100 of a gas turbine engine exhaust system in accordance with one embodiment of the invention. The ejection cone 100 has a shape of revolution around an axial direction DA and comprises, from upstream to downstream in the axial direction DA, an upstream part 110 integrating an acoustic attenuation structure 200 and a downstream part 120 finalizing the aerodynamic line. The ejection cone is here made of a composite material, for example of a ceramic matrix composite (CMC) for temperature resistance reasons. The end of the upstream part 110 of the cone has a metal attachment flange 130 forming part of the motor casing (not shown in the ) or intended to be attached to it.

In a well-known way, parts in CMC material are formed by a fibrous reinforcement in refractory fibers (carbon or ceramic) which is densified by a ceramic matrix, in particular carbide, nitride, refractory oxide, etc. Typical examples of CMC materials are Oxide/Oxide materials (oxide fiber and oxide matrix such as alumina, mulite, alumino-silicate matrix), C-SiC (carbon fiber reinforcement and silicon carbide matrix), SiC-SiC and C-C/SiC materials (mixed carbon/silicon carbide matrix). The manufacture of CMC composite parts is well known.

The upstream part 110 of the ejection cone 100 comprises an acoustic attenuation structure 200 which is constituted in the example described here by a structural internal skin 210, a multicellular acoustic attenuation panel 220 and an acoustic external skin 230. The skin outer 230 delimits the inner surface of the exhaust gas flow path. The outer skin 230 also has perforations 231 to allow the entry of the acoustic waves to be attenuated into the attenuation structure while the inner skin 210 is solid so as to reflect these waves.

The multicellular panel 220 comprises several rows of acoustic cells each extending along a circumferential direction (D _C ). In the example described here, the multicellular panel 220 comprises five rows of acoustic cells 240, 250, 260, 270 and 280 each extending in an annular manner in a circumferential direction D _C , the rows of acoustic cells 240, 250, 260 , 270 and 280 being juxtaposed with each other from upstream to downstream in the axial direction D _A , the row 240 being located the most upstream while the row 280 is located the most downstream of the rows of acoustic cells.

Each acoustic cell is delimited by a wall which extends in height in a radial direction D_R between the inner and outer skins 210 and 230 and in a circumferential direction D_VS. More precisely, the acoustic cells 240, 250, 260, 270 and 280 are each respectively delimited by a wall 241, 251, 261, 271 and 281 so as to form boxes capable of damping the acoustic waves which it is desired to attenuate. The wall delimiting the acoustic cells of a row, for example the wall 241, has a common portion with the wall of the acoustic cells of the adjacent row, for example with the wall 251.

As illustrated in FIGS. 2 and 3, the acoustic cells 240, 250, 260, 270 and 280 each have a wall height H ₂₄₁ , H ₂₅₁ , H ₂₆₁ , H ₂₇₁ and H ₂₈₁ respectively. More precisely, the most upstream acoustic cells 240 and the most downstream acoustic cells 280 respectively have wall heights H ₂₄₁ and H ₂₈₁ lower than the wall heights H ₂₅₁ , H ₂₆₁ and H ₂₇₁ respectively of the acoustic cells 250, 260 and 270 which are located between the acoustic cells 240 and 280.

In the example described here, the wall heights H₂₄₁, H₂₅₁, H₂₆₁, H₂₇₁and H₂₈₁ which are parallel to the radial direction D_R vary depending on whether one moves in the axial direction D_AT of the ejection cone 100 in particular because of the variable profile of the internal skins 210 and external skin 230 defining the shape of the acoustic attenuation structure 200.

Still in the example described here, the wall heights H ₂₄₁ and H ₂₈₁ are significantly lower than the wall heights H ₂₅₁ , H ₂₆₁ and H ₂₇₁ due to the presence of an upstream chamfer C _AM and a downstream chamfer C _AV . The acoustic attenuation structure 200 comprising the internal and external skins 210 and 230 being made of composite material, it is difficult to form sudden changes in slopes, in particular at the level of the internal skin, so as to form a recess making it possible to immediately obtain a housing depth suitable for acoustic cells. Indeed, unlike a metallic material, a sudden change in slope, for example by forming a 90° angle, leads to the formation of creases and/or local detachments in the composite material which reduce the mechanical resistance of the structure. This is why the changes in slope in the profile of a part of revolution made of composite material preferably include chamfers rather than marked angles.

The wall heights of each row of acoustic cells being variable depending on whether one moves in an axial direction D _A , in particular at the level of the chamfers C _AM and C _AV , the wall heights H ₂₄₁ , H ₂₅₁ , H ₂₆₁ , H ₂₇₁ and H ₂₈₁ described here correspond to an average wall height for each acoustic cell.

According to the invention, the acoustic cells of one or more rows of cells having a wall height lower than the wall height of the acoustic cells of one or more other rows have a cross-section greater than the cross-section of the acoustic cells of the other row(s) of cells. In the example described here, the rows of acoustic cells 240 and 280 which have wall heights H241 and H281 significantly lower than the wall heights H251, H261 and H271 of the rows of acoustic cells 250, 260 and 270 are formed so as to present S240 and S280 sections in cross section greater than the S250, S260 and S270 cross sections of the 250, 260 and 270 acoustic cells ( ). In the example described here, the section of the acoustic cells is enlarged by increasing their length in the axial direction DA, the width of the cells in the circumferential direction DC being constant between the rows of acoustic cells. In other words, the acoustic cells 240 and 280 have lengths L240 and L280 greater than the lengths L250, L260 and L270 of the acoustic cells 250, 260 and 270 in the axial direction DA. The section of the acoustic cells having a lower height can of course be adapted by increasing both the length and the width of the cells.

By way of non-limiting example, the acoustic cells 240 and 280 have wall heights H ₂₄₁ and H ₂₈₁ of 95 mm while the acoustic cells 250, 260 and 270 have wall heights H ₂₅₁ , H ₂₆₁ and H ₂₇₁ 150mm. In addition and in accordance with the invention, the acoustic cells 240 and 280 have lengths L ₂₄₀ and L ₂₈₀ twice as large as the lengths L ₂₅₀ , L ₂₆₀ and L ₂₇₀ of the acoustic cells 250, 260 and 270 in the axial direction. D _A. Thus, in the illustrated embodiment, the acoustic cells 240 and 280 have a volume of approximately 3.7 liters while the acoustic cells 250, 260 and 270 have a volume of approximately 2.9 liters. The frequency shift of the attenuation peak between the acoustic cells 240 and 280, on the one hand, and the acoustic cells 250, 260 and 270, on the other hand, is only 100Hz.

The acoustic cells may have different geometries from those shown on the . The cells can in particular have polygonal, rectangular, spherical, etc. shapes. The choice of the dimension or dimensions to be increased in order to adapt the section of cells having a lower height depends on the geometry of the cells.

There shows another example of an exhaust cone 400 of a gas turbine engine exhaust system according to one embodiment of the invention which comprises as previously described has a shape of revolution about a direction DA and comprises from upstream to downstream along the axial direction DA an upstream part 410 incorporating an acoustic attenuation structure 300 and a downstream part 420 finalizing the aerodynamic line. The ejection cone is here made of a composite material, for example of a ceramic matrix composite (CMC) for temperature resistance reasons.

The upstream part 410 of the ejection cone 400 comprises an acoustic attenuation structure 300 which is constituted in the example described here by a structural internal skin 310, a multicellular acoustic attenuation panel 320 and an acoustic external skin 330 delimiting the internal surface of the exhaust gas flow path and also having perforations 331 in order to allow the entry of the acoustic waves to be attenuated into the attenuation structure while the internal skin 310 is solid so as to reflect these waves.

The multicellular panel 320 comprises several rows of acoustic cells each extending along a circumferential direction (D _C ). In the example described here, the multicellular panel 320 comprises five rows of acoustic cells 340, 350, 360, 370 and 380 each extending in an annular manner in a circumferential direction D _C , the rows of acoustic cells 340, 350, 360 , 370 and 380 being juxtaposed with each other from upstream to downstream in the axial direction D _A , the row 340 being located the most upstream while the row 380 is located the most downstream of the rows of acoustic cells.

The 340, 350, 360, 370 and 380 acoustic cells differ from the 240, 250, 260, 270 and 280 acoustic cells previously described in that they have a rectangular shape.

Each acoustic cell is delimited by a wall which extends in height in a radial direction D _R between the inner and outer skins 310 and 330 and in the circumferential direction D _C . More precisely, the acoustic cells 340, 350, 360, 370 and 380 are each respectively delimited by two adjacent walls 341, 351, 361, 371, 381 and 391 in the circumferential direction D _C and by two adjacent walls 321 in the axial direction D _A so as to form boxes capable of damping the acoustic waves which it is desired to attenuate.

According to the invention, the acoustic cells of one or more rows of cells having a wall height lower than the wall height of the acoustic cells of one or more other rows have a cross-section greater than the cross-section of the acoustic cells of the other row(s) of cells. In the example described here, the rows of acoustic cells 340 and 380 which have wall heights significantly lower than the wall heights of the rows of acoustic cells 350, 360 and 370 are formed so as to present cross-sections S340 and S380 greater cross section than the S350, S360 and S370 cross sections of the 350, 360 and 370 acoustic cells ( ). In the example described here, the section of the acoustic cells is enlarged by increasing their length in the axial direction DA. In other words, the acoustic cells 240 and 280 have lengths L240 and L280 greater than the lengths L250, L260 and L270 of the acoustic cells 250, 260 and 270 in the axial direction DA. The section of the acoustic cells having a lower height can of course be adapted by increasing both the length and the width of the cells.

The acoustic attenuation structure and, consequently, the multicellular panel that composes it has an at least partially annular or semi-annular shape.

By enlarging the section of the cells having a reduced wall height, the impact of the reduction in wall height on the overall volume of each cell is limited so as to have acoustic cells which have an equivalent internal volume in order to reduce as much as possible the frequency shift between all the acoustic cells. By "equivalent internal volume" is meant here the volume difference between the acoustic cells of one row relative to another row, this volume difference being less than 30%, preferably less than 10%, and more preferably zero. or close to 0%. This preserves for acoustic cells with a lower wall height the ability to attenuate low frequencies.

According to a particular characteristic of the invention, the acoustic cells of upper cross-sectional section and lower wall height have an internal volume equivalent to the internal volume of the other acoustic cells. In this case, the frequency shift in the acoustic attenuation between the different rows of acoustic cells is minimized.

The acoustic attenuation structure according to the invention can correspond to a part of revolution and be made in a single part or from a plurality of annular sectors assembled with each other.

The acoustic attenuation structure of the invention may in particular be integrated into an aero engine exhaust cone as described above and/or even into an exhaust nozzle of an aero engine exhaust system.

Claims (11)

Multicellular acoustic attenuation panel (220) comprising several rows of acoustic cells (240, 250, 260, 270, 280), each row extending in a circumferential direction (D _C ), each acoustic cell being delimited by a wall ( 241, 251, 261, 271, 281) extending in height in a radial direction (D _R ),
characterized in that the acoustic cells (240, 280) of one or more first rows of acoustic cells have a cross-sectional section (S ₂₄₀ , S ₂₈₀ ) greater than the cross-sectional section (S ₂₅₀ , S ₂₆₀ , S ₂₇₀ ) of the acoustic cells of one or more second rows of acoustic cells (250, 260, 270) and in that said acoustic cells of the first row or rows of acoustic cells have a wall height (H ₂₄₁ , H ₂₈₁ ) less than the wall height (H ₂₅₁ , H ₂₆₁ , H ₂₇₁ ) of the acoustic cells of the second row or rows of acoustic cells. Panel according to Claim 1, in which the acoustic cells (240, 280) of the first row or rows of acoustic cells have an internal volume equivalent to the internal volume of the acoustic cells of the second row or rows of acoustic cells (250, 260, 270). Panel according to claim 1 or 2, in which each acoustic cell (240, 250, 260, 270, 280) has a volume configured to pick up sound waves having a frequency between 400 Hz and 1000 Hz. Acoustic attenuation panel according to any one of claims 1 to 3, in which the rows of acoustic cells (240, 250, 260, 270, 280) are juxtaposed to each other from upstream to downstream in an axial direction ( D _A ) and wherein the row of acoustic cells (240) present upstream of the plurality of rows of acoustic cells and the row of acoustic cells (280) present downstream of the plurality of rows of acoustic cells have a wall height (H ₂₄₁ , H ₂₈₁ ) lower than the wall height (H ₂₅₁ , H ₂₆₁ , H ₂₇₁ ) of the acoustic cells of the other row(s) of cells. Acoustic attenuation structure (200) comprising an acoustic skin (230) and a closure skin (210) delimiting between them an annular or semi-annular volume comprising a multicellular acoustic attenuation panel (220) according to any one of claims 1 to 4. Structure according to Claim 5, in which the acoustic skin (230), the closing skin (210) and the multicellular acoustic attenuation panel (220) are made of a composite material comprising a fibrous reinforcement densified by a matrix. Structure according to claim 5, in which the acoustic skin (230) and the closing skin (210) are made of a composite material comprising a fibrous reinforcement densified by a matrix, while the multicellular acoustic attenuation panel (220) is made of a metallic material. . Ejection cone (100) of an aeronautical engine comprising an acoustic attenuation structure (200) according to any one of claims 5 to 7. Aero engine exhaust nozzle comprising an acoustic attenuation structure according to any one of claims 5 to 7. Aero gas turbine engine comprising an exhaust cone according to claim 8 or an exhaust nozzle according to claim 9. Aircraft comprising at least one engine according to claim 10.