FASTENING OF AN ACOUSTIC SHIELDING TO A HOUSING SHELL OF AN AIRCRAFT ENGINE

Description

Technical field of the invention

[0001] The present invention relates to the making of a casing, in particular a fan casing, for an aircraft turbomachine, and in particular the attachment of an acoustic ferrule to a casing envelope. Technical background

[0002] Typically, a turbomachine comprises, from upstream to downstream, i.e. in the direction of gas flow, a blower, one or more compressors, a combustion chamber, one or more turbines, and a nozzle for ejecting the combustion gases exiting the turbine(s).

[0003] There figure 1 represents partially and schematically a fan 1 of an aircraft turbomachine.

[0004] The blower 1 includes a blade wheel 2 which is surrounded by a blower housing 3, also called a retention housing because of its function of retaining the blades in case of breakage of the blades, or in case of entry of debris into the blower.

[0005] The fan casing 3 typically includes an annular shell 9 with axis of revolution A that extends around the fan blades 2 of the turbomachine. This shell includes an annular mounting flange 3', 3" at each of its axial ends. These flanges 3', 3" are used to fix the casing 3 to annular walls of the turbomachine nacelle.

[0006] The blower housing 3 is linked, upstream, to an air inlet sleeve 5, and, downstream, to an intermediate housing ferrule 6.

[0007] The casing also includes an upstream acoustic ferrule 7 (also called OPB for One Piece Barrel) and downstream acoustic panels 8. The blower casing 3 also includes an annular layer 4 of abradable material, positioned on an internal annular surface of the casing, between the OPB 7 and the downstream panels 8.

[0008] In addition to its retention function, the blower housing 3 is also designed to: ensure mechanical continuity (of forces and moments) between the air inlet sleeve 5 and the intermediate casing ferrule 6; allow the fixing of the vein panels (OPB 7, acoustic panel 8 and layer of abradable material 4), allow the fixing of equipment and supports; meet the regulatory specifications for fire and leakage; allow continuity of electrical current for lightning resistance, etc.

[0009] OPB 7 for example is made of composite material while envelope 9 can be made of composite or metallic material.

[0010] THE figures 2a to 2h illustrate, for example, a known fastening system 10 of the OPB 7 to the casing 9 by bolted connection (screws 10a, nuts 10b, L-shaped connecting pieces 10c linked to each other in an S-shaped assembly, bores 10d intended to house the screws 10a). This fastening system 10 requires specific structural geometries and machining on each of the components to be assembled, such as counterbores 11 provided on the internal surfaces of the casing 9 ( Figures 2A And 2B ) and longitudinal grooves 12 in the OPB 7 to provide space for the connecting parts 10c ( figures 2C and 2D ). The assembled fastening system 10 is illustrated in a first standard version in figure 2Eand in a so-called positioning variant comprising, for example, a pin 13 / orifice 14 pair on the respective connecting parts 10c in figure 2F A schematic view of the linking system of the figure 2E is further illustrated in elevation and longitudinal section in figure 2G An example of such an existing OPB 7, on which grooves 12 are provided and elements 10a, 10b and 10c of the fastening system 10 are mounted, is further illustrated in figure 2H .

[0011] The particular geometries and machining alter the mechanical properties of the envelope 9 and the acoustic properties of the OPB 7. In addition, the fixing system 10 can be a source of stress concentrations since it is "highly" hyperstatic (the six degrees of freedom - translations and rotations - are eliminated several times), which weakens it.

[0012] To overcome this problem, it is necessary to simplify the geometries and the connection between OPB 7 and envelope 9.

[0013] Document FR 3059362 A1 describes a turbomachine housing comprising an annular sound insulation structure inside which an abradable element is fixed.

[0014] Document FR 3011033 A1 describes a method for manufacturing a turbomachine housing by individually manufacturing sectors, each provided with a support and an abradable element.

[0015] The invention therefore proposes, in particular, a method for manufacturing a housing for an aircraft turbomachine, as well as an improved aircraft turbomachine housing. The housing must, in particular, be simple in design and installation, economical, and easy to manufacture. Summary of the invention

[0016] The invention thus relates to a method for manufacturing an aircraft turbomachine casing, the casing comprising: an annular envelope extending around an axis A; an annular element, fixed on an inner surface of the envelope, the annular element comprising a body which is made of NIDA-type honeycomb material and which includes a downstream part having a first inner surface covered with a layer of abradable material, and an upstream part having a second inner surface free of abradable material, the body extending continuously from the upstream part to the downstream part.

[0017] According to the invention, the manufacturing process comprises: a manufacturing step of the annular element in the form of a continuous annular body, a cutting step of the continuous annular body into body sectors, a fixing step of the body sectors on the inner surface of the envelope, and a depositing step of a layer of abradable material on the inner surface of the downstream part of the body.

[0018] Thanks to this, the casing combines in a single annular element an acoustic attenuation function and an abradability function, which makes it possible for example to limit production costs thanks to a single part, where the prior art provides two parts (upstream acoustic ferrule and abradable support layer or cartridge).

[0019] Furthermore, the manufacturing process of the annular element in the form of a continuous annular body before cutting it into ring sectors offers the following advantages: the cost of manufacturing a single piece is limited compared to that of the individual production of several ring sectors, the gluing of ring sectors is simpler than that of an integral ring.

[0020] The method according to the invention may comprise one or more of the following features, considered independently of each other or in combination with each other: The step of installing the ring sectors on the inner surface of the envelope includes a step of filling gaps between the ring sectors with an abradable filling material; the filling material is a resin having a filler in the form of hollow beads, preferably a resin having a filler in the form of hollow glass beads, preferably even more preferably an epoxy resin loaded with hollow glass microspheres; the abradable gap-filling material is the same abradable material as the material composing the layer of abradable material; at the downstream part, the layer of abradable material becomes bonded with the filling material.

[0021] The invention also relates to an aircraft turbomachine casing manufactured according to the process of one of claims 3 to 6.

[0022] The housing according to the invention may comprise one or more of the following features, considered independently of each other or in combination with each other: The annular element is fixed by bonding to the inner surface of the casing; the layer of abradable material is disposed in a recess of the downstream part of the body; the abradable layer has an inner surface which extends in the axial continuation of the second inner surface; a film or fabric, for example laminate, based on fibers covers the first and second inner surfaces of the body in honeycomb material; the film itself being covered by the layer of abradable material at the level of the first inner surface; the downstream part of the body has an axial dimension greater than that of the upstream part; the abradable layer has a radial thickness measured with respect to said axis A which represents between 2 and 20% of the radial thickness of said body; the casing is made of a composite material comprising woven fibers embedded in a resin; the number of sectors of the body is between two and ten.

[0023] The bonding of the annular element to the casing is particularly simple, provides rigidity to the casing, eliminates the need for mechanical connections by metal parts and thus reduces the mass of the casing, and allows the upstream part of the annular element to be thickened in order to improve its acoustic attenuation properties.

[0024] The invention further relates to an aircraft turbomachine, comprising an aircraft turbomachine casing according to the preceding claim.

[0025] The following features can also be implemented in the invention: an outer surface of the body made of insulating material, radially opposed to the inner surfaces, is free of fibre-based film or fabric; the layer of abradable material is intended to be disposed opposite the ends of the blades of an aircraft turbomachine stator. Brief description of the figures

[0026] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for an understanding of which reference should be made to the attached drawings in which: [ Fig.1 ] There figure 1 already described shows a partial cross-sectional view of a fan of an aircraft turbomachine according to the prior art; Fig. 2A ] There figure 2A already described shows a perspective view of a counterbore planned on an internal surface of a composite housing according to the prior art; Fig. 2B ] There figure 2B The already described shows an L-shaped fixing piece mounted in the counterbore illustrated in figure 2A according to the state of the art; [ Fig. 2C ] There figure 2C The already described shows a groove planned on an outer surface of the upstream acoustic ferrule according to the prior art; Fig. 2D ] There figure 2D The already described shows an L-shaped fixing piece mounted in the groove of the figure 2Cand must be attached to the L-shaped mounting piece of the figure 2B according to the state of the art; [ Fig. 2E ] There figure 2E The already described system shows a method for fixing L-shaped parts such as those of the Figures 2B And 2D , these being fixed to each other; Fig. 2F ] There figure 2F already described illustrates a so-called positioning variant of the fastening system of the figure 2E ; Fig. 2G ] There figure 2G The already described system shows the fastening system of the figure 2E in elevation and longitudinal section; [ Fig. 2H ] There figure 2H The already described shows an upstream acoustic ferrule equipped with grooves and elements of the fastening system of the figure 2E . [ Fig.3 ] There figure 3 shows in perspective a ferrule according to the invention, here free from a layer of abradable material; Fig. 4 ] There figure 4is a cross-sectional view partially showing a fan of an aircraft turbomachine, the fan including the ferrule according to the figure 3 ; Fig. 5 ] There figure 5 is an enlargement of a front part of the figure 4 ; Fig. 6 ] There figure 6 is a schematic cross-sectional view according to coordinates VI of the figure 4 . Detailed description of the invention

[0027] In the following description, the invention is applied to a blower housing 23, for example analogous to the blower housing 3 shown in figure 1 . The invention is not limited to this type of housing and can be applied to other housings of a turbomachine.

[0028] The housing 23 to which the invention applies has a generally annular shape around an axis A (see for example in figure 4). An arrow F represents a front-to-back orientation of the illustrated elements with regard to their orientation once installed in the turbomachine.

[0029] The crankcase 23 includes: an annular casing 29 extending around axis A and made of a composite material comprising woven fibers embedded in a resin, and a ferrule 24 provided and configured to be disposed inside the casing 29 in an installed state, and to cover an inner annular surface 29a of a front section of the casing 29 ( figure 4 ).

[0030] The ferrule 24 comprises a main body 25 of acoustic insulating material, forming an acoustic insulation module, or acoustic attenuation module, and a layer of abradable material 26.

[0031] The main body 25 comprises an upstream part 251 and a downstream part 252. The upstream parts 251 and downstream parts 252 extend continuously into one another. The downstream part 252 has a first internal surface 25a and the upstream part 251 has a second internal surface 25b.

[0032] The body 25 presents, continuously in this order, the first inner surface 25a, a shoulder 25e, the second inner surface 25b, an upstream annular edge 25c, an outer surface 25d.

[0033] The first and second inner surfaces 25a and 25b are annular and extend longitudinally around axis A. The second inner surface 25b is located in front of, or upstream of, the first inner surface 25a, depending on the intended front-to-back orientation F of the ferrule 24 once installed in the turbomachine 1. The transition from the first inner surface 25a to the second inner surface 25b is ensured by the shoulder 25e inwards; that is, this transition corresponds locally to a reduction in the diameter of the inner section of the body 25. The first inner surface 25a thus forms, with the shoulder 25e, a recess 250 outwards relative to the second inner surface 25b ( figures 3 and 4 ).

[0034] The layer of abradable material 26 is formed on the main body 25. More specifically, the layer of abradable material 26 is provided in the recess 250, so as to cover the first inner surface 25a of the main body 25. Preferably, the layer of abradable material 26 is shaped so that an inner surface 26a of it comes to the right of the second inner surface 25b, that is to say that the inner surface 26a of the abradable layer 26 extends in the axial continuation of the second inner surface 25b.

[0035] The main body 25 comprises a honeycomb material, the cells (not shown) being arranged in a honeycomb structure. Such a material is also known as NIDA. The main body 25 further comprises at least one film 27, or fabric, for example, laminated, made of fibers, preferably carbon fibers. Preferably, the body 25 comprises several films 27 layered by draping. For the sake of clarity, only one film 27 will be referred to below.

[0036] The fiber-based film 27 covers the first and second inner surfaces 25a and 25b of the body 25. The film 27 is itself covered by the abradable material layer 26 at the first inner surface 25a, i.e., in the recess 250. Preferably, the film 27 is folded upstream and also covers the upstream annular edge 25c of the body 25. Preferably, the outer surface 25d of the body 25, which is radially opposite the inner surfaces 25a, 25b, is free of the fiber-based film 27. This last feature can significantly contribute to limiting the mass of the ferrule 24 and reduces the draping time of the body 25.

[0037] The ferrule 24 is glued into the casing 29, that is to say on an inner surface 29a of the casing 29. A layer of glue 28 is thus arranged between the ferrule 24 and the casing 29 ( figure 4The adhesive layer 28 is, for example, but not limited to, applied as a film to the outer surface 25d of the body sectors 253, 254 or ring sectors composing the ferrule 24 (see below for details of sectors 253, 254). The ferrule 24 is then placed in the casing 29 and the assembly is heated, for example in an autoclave, to cause the body sectors 253, 254 to bond to the surface 29a. Pressure is preferably applied to the ferrule 24 to ensure that it is firmly pressed against the surface 29a during heating.

[0038] Preferably, the ferrule 24 is manufactured as a continuous annular body, meaning that the ferrule 24 is a single piece extending 360 degrees after its manufacture. The ferrule 24 is then preferably cut into ring sectors which can subsequently be installed on the inner surface 29a of the casing 29.

[0039] The number of ring sectors can, for example, be between two and ten. The ferrule illustrated in figures 3 And 6 presents, for example, but not limited to, two ring sectors 253 and 254. Such a manufacturing process for a ferrule in the form of a continuous annular body before cutting it into ring sectors offers the following advantages: the cost of manufacturing a single piece is limited compared to that of the individual production of several ring sectors, the gluing of ring sectors is simpler than that of an integral ring.

[0040] Once the ring sectors 253, 254 are glued against the surface 29a, gaps 30 may appear between the sectors 253, 254, more precisely between the ends 25f of each sector 253 and 254 ( figures 3 And 6). These gaps 30 are both the result of the division of sectors 253, 254 and of a desired play for the easy installation of sectors 253, 254 in the envelope 29.

[0041] The gaps 30 are preferably filled with a filling or covering material 33 ( figure 6 ). The filling material 33 is preferably an abradable material, such as the abradable material composing layer 26, including at the level of the sound insulation or attenuation module in front of layer 26.

[0042] The abradable material of layer 26 and / or the filler material 33 is / are a resin containing a filler in the form of hollow beads (e.g., glass). The abradable material may be an epoxy resin filled with hollow glass microspheres (e.g., that marketed under reference DMR76-059, Scotch-Weld EC-3524 B / A Black).

[0043] It is noted that in figure 6, and more generally at the level of the downstream part 252, the layer of abradable material 26 comes into contact with the filling material 33.

[0044] The invention offers advantages on several levels. From a technical point of view, particularly from a mechanical point of view: the crankcase casing does not undergo machining, for example of the type of counterbores of the prior art.The integrity of the composite material of the casing is therefore not altered and the continuity of the fibers within it is preserved, which avoids the concentration of stresses in the casing; the interface generating aerodynamic disturbances between the OPB and the abradable material layer of the prior art is eliminated; the bonding of the shell to the casing increases the overall stiffness of the casing and improves the general vibration behavior of the casing and the turbomachine; the aforementioned bonding is of the surface type, unlike the point bonds of the prior art, which limits mechanical stresses during operation; the elimination of the metallic bonds, the carbon ply of the outer face of the acoustic insulation module, the downstream edge of the OPB and the upstream edge of the abradable material support layer are accompanied by a mass reduction.

[0045] From an acoustic point of view: The elimination of the metal connections makes it possible to do away with the associated grooves in the body of the acoustic attenuation module, thus allowing the acoustic insulation material comprising the honeycomb structure to have a constant height azimutally, that is to say over the entire circumference of the acoustic insulation module in a plane perpendicular to the longitudinal axis of the shell and the turbomachine; all the cells of the honeycomb structure are thus of the same height azimutally, which eliminates the azimuthal perturbation of the prior art and allows the acoustic insulation module to offer better acoustic insulation efficiency; the acoustically treated surface is increased.

[0046] From an industrial perspective: the fusion of the acoustic insulation module with the abradable layer module, separate in the prior art, generally reduces industrial costs (one part to produce, to transport, etc.instead of two); eliminating machining on the inner surface of the casing reduces the manufacturing cycle time; eliminating mechanical linking parts reduces the number of components to be purchased, stored and managed (brackets, screws, rivets, washers, nuts, gasket at the interface between the acoustic insulation module and the abradable material support layer); the manufacturing of the acoustic insulation module and, more generally, of the combined shell is simplified (uniformity of the honeycomb material which does not require specific machining, elimination of folds on the outer face of the acoustic insulation module, simplified draping of the folds) and the number of three-dimensional checks is significantly reduced; there is no longer a need for specific tooling for the assembly and disassembly of the connections, unlike the screw connections of the prior art (e.g., torque wrenches, wrench extensions).

[0047] In addition, the disappearance of angle bracket connections is accompanied by the disappearance of the problems and constraints inherent in them: cracking and residual tensile stresses (resulting from bending), the need for numerous visual checks, adjustment of assembly clearances (static stresses), the risk of imbalances and related vibration problems.

Claims

1. A method for manufacturing an aircraft turbine engine housing, the housing (23) comprising: - an annular shell (29) extending about an axis A; - an annular element (24; 253, 254), attached to an inside surface (29a) of the shell (29), the annular element (24; 253, 254) comprising a body (25) which is made of a NIDA-type cellular material and which comprises a downstream portion (252) having a first inside surface (25a) covered with a layer of abradable material (26), and an upstream portion (251) having a second inside surface (25b) without abradable material, the body (25) extending continuously from the upstream portion (251) to the downstream portion (252), the manufacturing method comprising: - a step of manufacturing the annular element (24; 253, 254) as a continuous annular body, - a step of cutting the continuous annular body into body segments (253, 254), - a step of attaching the body segments (253, 254) to the inside surface (29a) of the shell (29), and - a step of depositing a layer of abradable material (26) on the inside surface (25a) of the downstream portion (252) of the body (25).

2. The manufacturing method according to the preceding claim, wherein the abradable material of the abradable material layer (26) is a resin comprising a filler in the form of hollow beads, preferably a resin comprising a filler in the form of hollow glass beads, more preferably an epoxy resin filled with hollow glass microspheres.

3. The manufacturing method according to one of the preceding claims, wherein the step of installing the ring segments on the inside surface (29a) of the shell (29) comprises a step of filling gaps (30) between the ring segments (253, 254) with an abradable filling material (33).

4. The manufacturing method according to the preceding claim, wherein the filling material (33) is a resin comprising a filler in the form of hollow beads, preferably a resin comprising a filler in the form of hollow glass beads, more preferably an epoxy resin filled with hollow glass microspheres.

5. The manufacturing method according to claim 3 or 4, wherein the abradable filling gaps material (30) is the same abradable material as the material making up the abradable material layer (26).

6. The manufacturing method according to the preceding claim, wherein at the downstream portion (252) the abradable material layer (26) is integral with the filling material (33).

7. A housing for an aircraft turbine engine manufactured by the method of one of claims 3 to 6.

8. The housing according to the preceding claim, wherein the annular element (24; 253, 254) is attached by adhesion to the inside surface (29a) of the shell (29).

9. The housing according to claim 7 or 8, wherein the abradable material layer (26) is disposed in a recess (250) of the downstream portion (252) of the body (25).

10. The housing according to one of claims 7 to 9, wherein the abradable layer (26) has an inside surface (26a) which extends in the axial extension of the second inside surface (25b).

11. The housing according to one of claims 7 to 10, wherein a film (27) based on fibres covers the first and second inside surfaces (25a, 25b) of the body (25) made of cellular material, the film (27) itself being covered by the abradable material layer (26) at the first inside surface (25a).

12. The housing according to one of claims 7 to 11, wherein the downstream portion (252) of the body (25) has a greater axial dimension than the upstream portion (251).

13. The housing according to one of claims 7 to 12, wherein the abradable layer (26) has a radial thickness measured with respect to said axis A which is between 2 and 20 % of the radial thickness of said body (25).

14. The housing according to any one of claims 7 to 13, wherein the shell (29) is made of a composite material comprising woven fibres embedded in a resin.

15. The housing according to one of claims 7 to 14, wherein the number of segments of the body (25) is between two and ten.