ACOUSTIC SANDWICH PANEL WITH IMPROVED MOUNTING

Abstract

An acoustic panel (30) comprising a first skin (31) and a second skin (32) extending on either side of an acoustic core (33), the acoustic panel (30) also comprising a side (34) connecting the first skin (31) and the second skin (32) and having an outer side face (34.1), the acoustic panel (30) comprising at least one threaded portion (45, 74) extending in a direction substantially orthogonal to a foreground (P1) containing the outer side face (34.1). Assembly comprising such a panel. Figure for the abbreviation: Fig. 5

Description

Title of the invention: ACOUSTIC SANDWICH PANEL WITH IMPROVED MOUNTING Technical field of the invention

[0001] The present invention relates to the field of acoustic insulation sandwich panels, and more specifically to the implementation of such panels in turbojet nacelles.

[0002] It relates more specifically to the junction of an air inlet on the nacelle housing, also called the blower housing in the case of a twin-flow turbomachine.

[0003] The invention applies to all turbomachine designs, for example turbojets with a fan driven directly by a low-pressure body, driven indirectly by a reducer, single-body, twin-body, single-flow and twin-flow turbojets. Prior art

[0004] In a turbomachine, here a central axis AX turbojet, air is admitted, following a longitudinal direction parallel to the AX axis, into an inlet sleeve to pass through a fan comprising a series of rotating blades before splitting into a central primary flow which circulates in a so-called primary airflow circulation channel and a secondary flow surrounding the primary flow.

[0005] The primary flow is compressed by stages of compressors before reaching a combustion chamber, after which it expands as it passes through turbines, before being discharged, generating thrust. The secondary flow, on the other hand, is propelled directly by the blower to generate the main thrust.

[0006] The turbofan engine also includes a nacelle that supports the turbofan engine components and provides the connection between the turbofan engine and the aircraft. The nacelle includes a fan casing on the upstream end of which is attached an air inlet—also called an air inlet lip. The air inlet conventionally comprises an annular structure and a substantially transverse rear bulkhead that connects an inner radial fairing and an outer radial fairing of the annular structure. Aircraft noise reduction requirements have led to the installation of acoustically treated panels to define the inner radial fairing (the one in contact with the inlet airflow) of the air inlet.

[0007] These sandwich-type panels are generally composite structures consisting of two rigid outer skin layers (most often made of aluminum or composite materials) and a lightweight central core, often made of materials such as foam or honeycomb. Acoustic treatments applied The aim of these panels is to improve their noise attenuation performance, which is crucial for passenger comfort and compliance with environmental regulations.

[0008] There are three main types of acoustically treated sandwich panels: SDOF (Single Degree of Freedom) panels, 2DOF (Double Degree of Freedom) panels, and multilayer panels.

[0009] Single-degree-of-freedom (SDOF) sandwich panels are designed with a single acoustic resonance mechanism. These panels consist of two skin layers and a homogeneous core. Their acoustic performance is determined primarily by the core density and the skin thickness. These panels are simple to manufacture and are often used in applications where moderate noise attenuation is sufficient.

[0010] 2DOF (double degree of freedom) sandwich panels incorporate two acoustic resonance mechanisms, thus offering improved attenuation performance over a wider frequency range. This type of panel generally comprises two layers of different cores separated by an intermediate layer, which allows for the effective treatment of low and high frequencies. 2DOF panels are more complex to manufacture but offer significant advantages in terms of noise reduction.

[0011] Multilayer sandwich panels comprise several layers of cores and skins, allowing for very fine acoustic control. These structures can be customized to meet specific noise attenuation needs at different frequencies. Their manufacturing complexity is high, but they offer the best acoustic performance among sandwich panel types.

[0012] The skins of sandwich panels are generally made from composite or metallic materials. Composite materials often consist of carbon or glass fibers impregnated with resin, while metallic skins are typically made of aluminum or titanium. Manufacturing the skins requires shaping processes such as vacuum molding, autoclaving, or thermoforming.

[0013] The cores, for their part, can be made from materials such as polymer foam, honeycomb structures, or cellular materials. Polymer foam is manufactured by molding or extrusion, while honeycomb structures are obtained by lamination and expansion. Cellular materials can be produced by extrusion or injection molding.

[0014] The sandwich panel components are generally assembled by bonding, using structural adhesives capable of maintaining the mechanical and acoustic integrity of the structure. Assembly methods may include pressing. Hot bonding, vacuum bonding, and the use of mechanical fasteners are employed to enhance adhesion. Some panels may also incorporate a metallic honeycomb core brazed onto metal skins.

[0015] Traditionally, sandwich panels are joined together using specific bonding or welding techniques, ensuring structural and acoustic continuity. The adhesives used must offer excellent resistance to fatigue and to the operating environments of the aeronautics industry.

[0016] For connections between sandwich panels and non-sandwich elements (such as monolithic metal or composite structures), bonding, bolting, or riveting techniques can be used. For the latter two techniques, a flanged assembly is created, comprising a first flange and a second flange whose respective connecting faces are brought into contact. A bolt or rivet is inserted through aligned holes in the two flanges and then exerts a joining force on the bearing faces of each flange opposite the connecting faces.

[0017] For parts of revolution, shaping these flanges requires bending the outer radial skin to meet the inner radial skin, and, at a distance from this joint, bending the inner radial skin again at ninety degrees to create the flange. This creates an area devoid of acoustic core, the axial length of which corresponds at least to the length of the screw, rivet, or clamping or riveting tool. This area reduces the surface area of ​​the sandwich panel that is acoustically treated. Finally, shaping the flange and joining the skins involve complex and costly panel manufacturing techniques. Presentation of the invention

[0018] The present invention aims to improve the acoustic insulation of a composite panel structure assembled with an element of a different nature and to reduce the costs of such an assembly.

[0019] To this end, an acoustic panel is provided comprising a first skin and a second skin extending on either side of an acoustic core. The acoustic panel also includes a side connecting the first and second skins and having an outer side face. According to the invention, the acoustic panel includes at least one threaded portion extending in a direction substantially orthogonal to a first plane containing the outer side face.

[0020] According to other specific, non-exclusive and optional embodiments of the invention:

[0021] - the acoustic panel is in the shape of a sector of a piece of revolution;

[0022] - the acoustic panel includes an insert which carries the threaded portion;

[0023] - the insert extends through the side;

[0024] - the insert comprises an outer face of the insert extending into the foreground;

[0025] - the insert comprises an outer face of the insert which comes into contact with a face inner side of the side;

[0026] - the insert includes a housing for a barrel nut;

[0027] - the barrel nut extends through the first skin and / or the second skin;

[0028] -the flank extends orthogonally to the first skin and / or the second skin.

[0029] The invention also relates to an assembly of an acoustic panel as defined above on a flange of an element, in which the outer face of the side is in contact with a connecting face of the flange, a threaded body extending through the flange and the side to cooperate with the insert and apply a bearing force of the flange on the side.

[0030] Other features and advantages of the invention will become apparent from the following description of particular, non-limiting embodiments of the invention. Brief description of the figures

[0031] The invention will be better understood upon reading the following description, given by way of non-limiting example, and made with reference to the figures which represent:

[0032] [Fig-1] [Fig.1] is a schematic longitudinal sectional representation of a turbojet engine equipped with an acoustic panel according to the invention;

[0033] [Fig.2] [Fig.2] is a partial schematic representation in longitudinal section detail of an air inlet equipped with an acoustic panel according to a first embodiment of the invention;

[0034] [Fig.3] [Fig.3] is a schematic perspective representation of a panel acoustics according to a first embodiment of the invention;

[0035] [Fig.4] [Fig.4] is a partial schematic representation in longitudinal section detail of an assembly including the acoustic panel of [Fig.2] without the fixing screws;

[0036] [Fig.5] [Fig.5] is a partial schematic representation in longitudinal section detail of an assembly including the acoustic panel of [Fig.2] equipped with fixing screws;

[0037] [Fig.6] [Fig.6] is a partial schematic representation in longitudinal section detail of an assembly comprising an acoustic panel according to a second embodiment of the invention and which is devoid of fixing screws;

[0038] [Fig.7] [Fig.7] is a partial schematic representation in longitudinal section detail of an assembly comprising an acoustic panel according to the second embodiment of the invention provided with fixing screws;

[0039] [Fig-8] [Fig.8] is a partial schematic longitudinal sectional detail representation of an assembly comprising an acoustic panel according to a third embodiment of the invention and which is devoid of fixing screws;

[0040] [Fig.9] [Fig.9] is a partial schematic longitudinal sectional detail representation of an assembly comprising an acoustic panel according to the third embodiment of the invention provided with fixing screws;

[0041] [Fig. 10] [Fig. 10] is a partial schematic tangential sectional detail representation of an assembly comprising an acoustic panel according to the third embodiment of the invention and which is provided with fixing screws. Description of the implementation methods

[0042] With reference to Figures 1 and 2, a propulsion assembly 1000 comprises a turbomachine, here a turbojet generally designated 1, in which an airflow 100 is admitted, following a longitudinal direction parallel to the axis AX of rotation of the turbomachine 1, into an inlet sleeve 2 to pass through a fan comprising a series of rotating blades 3.

[0043] Part of the airflow 100 is compressed by compressor stages 4 and 5 before reaching a combustion chamber 6, after which it expands as it passes through turbines 7, before being discharged, generating thrust. The remainder of the airflow 100 is propelled directly by the fan to generate the main thrust.

[0044] In this text, the terms "internal" and "external" are used with reference to the position or orientation relative to the axis of rotation of the turbines 7.

[0045] In this text, the terms "upstream" and "downstream" are used with reference to the position or orientation of an element with respect to the direction of flow of the airflow 100 in the turbojet 1.

[0046] As a preliminary matter, an axial direction is defined, a radial direction which is orthogonal to the axial direction and a circumferential / tangential direction which is orthogonal to the axial and radial directions.

[0047] The turbojet 1 also includes a nacelle 8 which supports the turbojet 1 components and provides its connection to an aircraft (not shown). The nacelle 8 includes a fan casing 9, the upstream end of which includes, in particular, an upstream casing flange 20 to which an air inlet 10 is attached. The upstream flange 20 includes a web 21 which extends radially outwards from the casing 9. The web 21 has an upstream connecting face 22 and a downstream bearing face 23. A plurality of holes 24 extend through the web 21 to connect the connecting face 22 and the bearing face 23.

[0048] The air inlet 10 includes an annular structure 11 with longitudinal axis coinciding with the axis AX and which includes an internal fairing 12 and an external fairing 13.

[0049] As can be seen in [Fig. 2], the internal fairing 12 radially delimits a wall 15 external of a circulation vein 16 of the airflow 100. The internal fairing 12 is, here, made of a sandwich-type acoustic panel 30.

[0050] In the following description, the parts being parts of revolution or sectors of such parts, only a section will be described, it being understood that such a section is classically repeated according to a rotation about longitudinal axis AX.

[0051] With reference to Figures 2 to 5, the acoustic panel 30 is here in the shape of a right cylinder and comprises a first inner skin 31 and a second outer skin 32 extending on either side of an acoustic core 33. The panel 30 also comprises a downstream side 34 connecting the inner skin 31 and the outer skin 32. The side 34 has an outer face 34.1 of side 34 which extends in a first radial plane PL. An insert 40 extends into a cylindrical opening 35 made through the side 34 and into a housing 36 made in the core 33. The insert 40 is in the shape of a right cylinder and comprises an outer face 41 of insert 40 - here a downstream face - connected by a cylindrical wall 42 to an inner face 43 - here an upstream face. According to this first embodiment, the outer face 41 extends in the plane PL. The light 35 being, here, of a diameter substantially equal to the thickness of the core 33, the faces 41 and 43 each extend between an inner face 31.1 of the inner skin 31 and an inner face 32.1 of the outer skin 32. .

[0052] As can be seen in [Fig. 4], the insert 40 comprises a threaded portion—here a tapped bore 45—extending in a direction D45 substantially orthogonal to the first plane PI, i.e., an axial direction. The panel 30 comprises ten inserts identical to the insert 40 and spaced at thirty-six degrees from each other.

[0053] The manufacture of panel 30 can be carried out according to the following steps: a. internal skin forming 31; b. shaping of the external skin 32; c. forming of the acoustic core 33; d. Forming of the flank 34; e. assembly and joining of the skins 31 and 32 with the flank 34 and the core 33 according to methods known to a person skilled in the art; f. creation of light 35 and housing 36 by axial coring; g. application of glue in housing 36; h. mounting of the insert 40 in the housing 36 through the light 35. Operations f) to h) are repeated as many times as panel 30 contains inserts 40.

[0054] Alternatively, the openings 35 can be made prior to the forming of the inner skin 31. The housings 36 can also be made in the core 33 prior to its assembly with the skins 31 and 32.

[0055] The assembly of the panel 30 onto the flange 20 of the housing 9 is achieved by bringing the outer face 34.1 of the side 34 into contact with the connecting face 22 of the flange 20. Screws 90 are then inserted into the holes 24 to extend through the flange 20 and engage with the tapped bores 45. The tightening of the screws 90 into the tapped bores 45 allows a bearing force to be applied by the side face 34.1 of the side 34 to the face 23 of the flange 20, thereby assembling the flange 20 onto the side 34 and connecting the air inlet 10 to the housing 9.

[0056] This results in a simple, reliable clamping assembly that is economical to implement and optimizes the acoustic protection surface area. Finally, using a reduced number of parts, the invention ensures continuity of the internal casing of the vein 16. Indeed, the outer face 31.2 of the inner skin 31 is continuous with the inner face 9.1 of the housing 9.

[0057] The identical or analogous elements to those previously described shall bear a numerical reference identical to that in the following description of a second and a third embodiment of the invention.

[0058] According to a second embodiment of the invention shown in figures 6 and 7, the outer face 41 of the insert 40 comes into contact with an inner face 34.2 of the side of the side 34. The insert 40 is then mounted in the core 33 prior to the assembly of the latter with the skins 31 and 32 as well as the side 34. The assembly of the panel 30 on the flange 20 is carried out in the same manner as described above.

[0059] According to a third embodiment shown in figures 8 to 10, the side 34 consists of ten side segments 50. Each segment 50 includes a side element 51 in the form of an annular sector with an amplitude of thirty-six degrees, which includes an outer face 51.1 extending in the plane PL. Each segment 50 includes an insert 60 which is attached to an inner face 51.2 of the side element 51.

[0060] The insert 60 is in the form of a straight cylinder and comprises an outer face 61 of the insert 60 - here a downstream face - connected by a cylindrical wall 62 to an inner face 63 - here an upstream face which comes into contact with the inner face 51.2. The faces 61 and 63 each extend between the inner face 31.1 of the inner skin 31 and the inner face 32.1 of the outer skin 32.

[0061] The insert 60 defines a cylindrical housing 65 for receiving a barrel nut 70. The housing 65 extends between the inner skin 31 and the skin 32 and opens onto each of the skins 31 and 32. The barrel nut 70 is, here, in the form of a straight cylinder and extends through the inner skin 31 and the outer skin 32. More precisely, the barrel nut 70 includes a head 71 that projects from the outer surface 32.2 of the outer skin 32. The body 72 of the barrel nut 70 extends into the housing 65 to pass through the inner skin 31. The end 73 of the barrel nut 70 is deformed by riveting to extend into a recess 31.3 in the inner skin 31. The body 72 includes a threaded portion 74 that extends in a direction D74 substantially orthogonal to the plane PL. The insert 60 also includes a bore 66, orthogonal to the housing 65, which extends in continuity with the threaded portion 74 to open onto the flank 34.

[0062] The assembly of the panel 30 onto the flange 20 of the housing 9 is achieved by bringing the outer face 34.1 of the flank 34 into contact with the connecting face 22 of the flange 20. Screws 90 are then engaged in the bores 24 to extend through the flange 20 and the bore 66 and to cooperate with the threaded portions 74.The screwing of the screws 90 into the threaded portions 74 allows a bearing force to be applied from the face 34.1 of the flank 34 on the face 23 of the flange 20 to achieve an assembly of the flange 20 on the flank 34, and thus link the air inlet 10 to the housing 9. The clamping force applied by the screws 90 is transmitted by the barrel nuts 70 directly to the inner skin 31 and the outer skin 32 without stressing the connection - generally made by gluing - of the insert 60 to the skins 31 and 32.

[0063] Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0064] In particular,

[0065] - although here the acoustic panel is in the shape of a straight cylinder and thus describes a sector of a cylinder of three hundred and sixty degrees, the invention also applies to other configurations of the acoustic panel such as for example an acoustic panel in the shape of a sector of a cylinder of ninety degrees, four sectors then being necessary to define the complete cylindrical envelope of the air inlet;

[0066] - although here the light is circular light, the invention also applies to other forms of light such as, for example, a square or polygonal light;

[0067] - although here the housing is in the shape of a straight cylinder and made by core drilling, The invention also applies to other forms of housing such as, for example, a polygonal or non-circular housing to be able to block a rotation of the insert on itself around an axial axis, the housing being able to be made by machining, laser cutting etc.;

[0068] - although here the insert is fixed by gluing in the panel, the invention applies also to other means of fixing the insert to the panel such as fixing by screwing or riveting through the inner or outer skin, or by resin coating during the impregnation of the skins;

[0069] - although here the insert includes a threaded bore cooperating with a screw, the invention also applies to other types of threaded portions cooperating with a threaded body such as for example a threaded stud integral with the insert and which cooperates with a nut;

[0070] - although here the panel according to the invention has been described in application to an entrance air, the invention also applies to other types of structures such as for example a downstream portion of the vein;

[0071] - although here the internal fairing defines the internal wall of a circulatory vein of air, the invention also applies to an internal fairing which would partially define such a vein, such as for example an internal fairing connected to another element which would also contribute to the definition of the vein;

[0072] - although here the crankcase and air intake flanges are described as being circular elements of revolution, the invention also applies to flanges composed of a plurality of crown sectors;

[0073] - although here the assembly of the air inlet onto the crankcase is carried out using two flat flanges bolted or riveted together, the invention also applies to other flanged type assemblies such as screwed flanges or flanges with conical sides;

[0074] - although here the invention has been described in application to a propulsion system including a twin-spool turbojet engine, the invention also applies to propulsion assemblies comprising other types of turbomachinery such as for example a propulsion assembly comprising a single-spool turbojet engine;

[0075] - although here the flank comprises ten flank segments, the invention applies also to a different number of flank segments such as between one and nine or more than ten;

[0076] - although here the insert is integral with the side, the invention also applies to a insert attached to the side which may, or may not, pass through the side;

[0077] - although here the barrel nut is fixed to the panel by riveting, the invention also applies to other methods of attaching the barrel nut to the panel such as screwing or gluing.

Claims

Demands

1. Acoustic panel (30) comprising a first skin (31) and a second skin (32) extending on either side of an acoustic core (33), the acoustic panel (30) also comprising a side (34) connecting the first skin (31) and the second skin (32) and having an outer side face (34.1), characterized in that the acoustic panel (30) comprises at least one threaded portion (45, 74) extending in a direction substantially orthogonal to a first plane (PI) containing the outer side face (34.1).

2. Acoustic panel (30) according to claim 1, wherein the acoustic panel (30) is in the shape of a sector of a part of revolution.

3. Acoustic panel (30) according to claim 1 or 2, comprising an insert (40, 60) which carries the threaded portion (45, 74).

4. Acoustic panel (30) according to claim 3, wherein the insert (40) extends through the side (34).

5. Acoustic panel (30) according to claim 4, wherein the insert (40, 60) comprises an outer face of insert (41) extending into the first plane (PI).

6. Acoustic panel (30) according to claim 3, wherein the insert (40) comprises an outer face of insert (41, 61) which comes into contact with an inner face of flank (34.2) of the flank (34).

7. Acoustic panel (30) according to any one of claims 3 to 6, wherein the insert (60) includes a housing (65) for receiving a barrel nut (70).

8. Acoustic panel (30) according to claim 7, wherein the barrel nut (70) extends through the first skin (31) and / or the second skin (32).

9. Acoustic panel (30) according to any one of the preceding claims, wherein the side (34) extends orthogonally to the first skin (31) and / or the second skin (32).

10. Assembly of an acoustic panel (30) according to any one of claims 3 to 9 on a flange (20) of an element (9), wherein the outer face (34.1) of the side (34) is in contact with a connecting face (22) of the flange (20), a threaded body (90) extending through the flange (20) and the side (34) to cooperate with the insert (40, 70) and apply a support force from the flange (20) on the side (34).