BE1026460A1 - STRUCTURAL HOUSING FOR AXIAL TURBOMACHINE - Google Patents

Abstract

The invention relates to a structural casing (5) for an axial turbomachine (2), in particular for an aircraft turbojet engine, the casing (5) comprising a ring (50) having an internal surface (51), a hub (52) having an external surface (53), coaxial and fitted in the ring (50), and a plurality of arms (54) extending radially from the external surface (53) of the hub (52) to the internal surface (51) of the ring (50), the casing (5) being remarkable in that it further comprises, an annular row of covers (60) made of composite material covering at least partially the external surface (53) of the hub (52). The invention also relates to a turbomachine provided with such a casing (5) and to a method of manufacturing such a casing (5).

Description

Description

STRUCTURAL HOUSING FOR AXIAL TURBOMACHINE

Technical area

The invention relates to an assembly for an axial turbomachine. More specifically, the invention relates to a turbomachine housing and in particular a compressor housing.

Prior art

An axial turbomachine compressor casing may comprise a structural section essentially composed of an outer ring, a central hub and arms, called "struts", extending radially between the hub and the ring. The structural casing is generally in the form of a single piece obtained by foundry. The surface condition and in particular the roughness of the castings is not good enough to ensure optimal air flow guidance.

Alternatively, the document WO 2013/095211 A1 describes an example of a turbomachine stator made by an assembly of multiple elements. It is only by joining two adjacent angular sectors that the struts take shape. This casing is therefore particularly complex to assemble and the adjustments of the different angular sectors must be perfectly mastered so as not to disturb the air flow. Also, the general weight of the assembly is increased by the presence of numerous assembly elements, for example in the form of welds or fasteners.

Summary of the invention

Technical problem

The object of the invention is to solve at least one of the problems posed by the prior art. More specifically, the invention aims to improve the flow of air flow in a compressor, without making its assembly process more complex or compromising its weight.

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Technical solution

The invention relates to a structural casing for an axial turbomachine, in particular for an aircraft turbojet engine, the casing comprising: a ring having an internal surface, a hub preferably obtained by foundry and having an external surface, the hub being coaxial and fitted in the ring, and a plurality of arms extending radially from the external surface of the hub to the internal surface of the ring, the casing being remarkable in that it further comprises an annular row of covers made of composite material covering at least partially the outer surface of the hub.

The radial arms are also sometimes called "struts". They can be hollow.

The structural casing can form a bearing structure of the reactor.

The external surface is preferably substantially conical or so as to form a swan neck, that is to say a profile with an inflection point intended to connect a low-pressure compressor to a high-pressure compressor of a turbojet .

By “annular row of covers” is meant at least two covers of identical axial and radial position but angularly positioned differently around the external surface of the hub.

According to an advantageous embodiment of the invention, the covers have an external surface having an arithmetic roughness much less than 0.5 μm.

According to an advantageous embodiment of the invention, the covers are made of injected composite of PEI matrix with short carbon fibers.

According to an advantageous embodiment of the invention, the covers each comprise a flange enabling the covers to be assembled to the hub by fasteners. The flange can be upstream or downstream of the cover. The cover may have an L-shaped profile or a U-shaped profile, the flange closing inwards.

According to an advantageous embodiment of the invention, the covers have a variable thickness. It is thus possible to obtain during the manufacture of the covers shapes (in particular complex, or undercut) which it would be constraining to obtain by casting the hub. These shapes can minimize the risk of

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BE2018 / 5482 stall of the air flow, and thus limit aerodynamic losses for space and minimum weight.

According to an advantageous embodiment of the invention, the covers have a thickness which decreases from upstream to downstream.

According to an advantageous embodiment of the invention, the thickness of the covers varies circumferentially.

According to an advantageous embodiment of the invention, the thickness of the covers varies circumferentially, the maximum thickness being in the vicinity of the struts.

According to an advantageous embodiment of the invention, the thickness of the covers varies circumferentially, the minimum thickness being in the vicinity of the struts.

According to an advantageous embodiment of the invention, the set of covers forms a non-axisymmetric structure.

According to an advantageous embodiment of the invention, the hub, the arms and the ring have come from foundry material.

According to an alternative embodiment, the arms are welded to the hub and to the external ring, the external ring preferably being formed from several angular sectors describing different angles. Thus, seen from the axis of the ring, the angles scanned, or the angles at which each sector extends, may be different. The hub may be provided with housings which can accommodate one end of the arms.

According to an advantageous embodiment of the invention, at least two of the angular sectors are manufactured at least in part by two different manufacturing processes, in particular additive manufacturing or foundry.

According to an advantageous embodiment of the invention, at least one of the covers surrounds at least one of the arms. It is thus possible to provide fewer covers than arms, the covers being threaded radially inward around the arm.

According to an advantageous embodiment of the invention, each radial arm is longer axially than high radially, preferably at least twice as long axially as high radially.

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The invention also relates to an axial turbomachine with a low-pressure compressor, a high-pressure compressor and an intermediate stream between the low-pressure compressor and the high-pressure compressor, remarkable in that the intermediate stream comprises a structural casing according to one of the embodiments set out above.

According to an advantageous embodiment of the invention, the low-pressure compressor comprises an internal ferrule and the covers partially cover the internal ferrule. Thus, the covers can overhang the ferrule and come to cover the junction between the ferrule and the hub.

According to an advantageous embodiment of the invention, the low-pressure compressor comprises a last stage of rectifier whose internal shroud is formed by the covers which extend from the structural casing. In this case, there is no junction between an internal ferrule and the housing at the axial level between the last stage of the compressor and the hub.

The invention also relates to a method of manufacturing a structural casing comprising a step of founding a hub with possibly arms and an external ring, the hub comprising an external surface, the method being characterized in that it comprises a step of mounting a plurality of covers made of composite material on the external surface of the hub.

According to an advantageous embodiment of the invention, the casing is according to one of the embodiments described above.

According to an advantageous embodiment of the invention, all the arms are assembled to the hub before the covers are installed on the external surface of the hub. Thus, the arms are first welded to the hub, then the covers are brought to the outer surface of the hub. Finally, the outer ring is assembled at the radial ends of the arms.

According to an advantageous embodiment of the invention, the covers are removed while they are in a malleable state and solidify by conforming to the shape of the external surface of the hub. The covers of composite material can be malleable during their manufacture, for example, before crosslinking. The outer surface of the hub can therefore serve as a mold on which the covers will take shape.

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According to an advantageous embodiment of the invention, the struts, the hub and the ring are either in one piece or assembled by welding, for example laser or electron beam welding.

The invention also relates to a method of assembling a turbomachine, the method comprising a manufacturing method as described above, the hub being assembled to the internal compressor shroud, then the covers being brought to the surface outer hub, at least partially covering the inner shroud of the compressor.

Benefits

The presence of covers in particular makes it possible to optimize the size of the pieces in function since the design possibilities of the internal guide surface of the vein are increased.

Also, the covers make it possible to "correct" inaccuracies in the dimensions produced, without discarding the casing. The casing can be a piece of several tens of kilograms with high added value and the presence of the covers makes it possible not only to impose a more flexible manufacturing tolerance on the external surface but also to potentially reform fewer parts.

Brief description of the drawings

FIG. 1 represents an axial turbomachine according to the invention;

Figure 2 is a diagram of a turbomachine compressor;

Figure 3 sketches a partial isometric view of the housing according to the invention;

Figure 4 depicts an isometric view of a cover;

Figures 5A and 5B illustrate a sectional view of the housing;

Figures 6A to 6C show three examples of embodiment of the housing according to the invention in axial section view;

Figure 7 shows a method of assembling a cover on the hub.

Description of the embodiments

In the following description, the terms interior and exterior refer to a positioning relative to the axis of rotation of an axial turbomachine. The

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BE2018 / 5482 6 axial direction is along the axis of rotation, and the radial direction is perpendicular to the axial direction. The lateral direction is heard along the circumference, and can be perpendicular to the axis.

FIG. 1 represents a double-flow turbojet engine 2. The turbojet engine 2 comprises a low-pressure compressor 4, a high-pressure compressor 6, a combustion chamber 8 and a turbine 10. In operation, the mechanical power of the turbine 10 transmitted via the central shaft to the rotor 12 sets in motion the two compressors 4 and 6.

The compressors have several rows of rotor blades associated with rows of stator blades. The rotation of the rotor around its axis of rotation 14 thus makes it possible to generate a flow of air progressively compressed up to the combustion chamber 8.

A fan 16 (also called a fan) is coupled to the rotor 12 via a reduction gear 13 and generates an air flow which is divided into a primary flow 18 and a secondary flow 20. The primary flow 18 and secondary 20 are annular flows, they are channeled using cylindrical partitions, or ferrules, which can be interior and / or exterior.

FIG. 2 is a sectional view of a compressor of an axial turbomachine such as that of FIG. 1. The compressor can comprise a low-pressure compressor 4. One can observe therein a portion of the fan 16 as well as the nozzle of separation 22 of the primary 18 and secondary 20 flows. The rotor 12 can comprise several rows of rotor blades 24.

The low-pressure compressor 4 comprises several rectifiers which each contain an annular row of stator vanes 26. Each rectifier is associated with the fan 16 or with a row of rotor vanes 24 to rectify the air flow.

The low-pressure compressor 4 comprises at least one compressor casing 28. The casing 28 may have a generally circular or tubular shape. It can be an external compressor casing and can be made of composite materials. The casing 28 may include fixing flanges 30, for example annular fixing flanges 30 for fixing the spout

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BE2018 / 5482 separation 22 and / or for fixing to an intermediate casing 5 of the fan of the turbomachine. The compressor casing 4 then performs a function of mechanical link between the separation nozzle 22 and the intermediate housing 5. The housing also provides a function of centering the separation nozzle 22 relative to the intermediate housing 5, for example using of its annular flanges 30. The annular flanges 30 may be made of composite and include fixing orifices (not shown) to allow fixing by bolts.

The casing 28 may comprise a wall 32 generally circular or in an arc, the axial edges of which may be delimited by the flanges 30. The wall 32 may have a profile of revolution around the axis of rotation 14. The wall 32 may be made of composite material, with a matrix and a reinforcement. The wall 32 may have the shape of an ogive, with a variation in radius along the axis 14.

The stator vanes 26 extend essentially radially from the wall 32, at the level of annular zones for receiving vanes. The stator vanes 26 each comprise a fixing platform 34, and possibly fixing pins 36 such as threaded rods. The wall may include annular layers of abradable material 38 between the platforms 34 of the blades.

Thanks to the use of composite materials, the casing 28 can measure between 3 and 5 mm thick for a diameter greater than 1 meter.

The stator vanes 26 are supported on their internal radial end by a ferrule 40.

Downstream of the low-pressure compressor 4 is a high-pressure compressor 6. The operation of the high-pressure compressor 6 is similar to the low-pressure compressor 4.

Between the two compressors 4, 6 is provided a support structure or structural casing 5. This casing 5 comprises an external ring 50, a central hub 52 and radial arms 54. The radial arms 54 extend in the air flow then that the external ring 50 and the central hub 52 respectively have an internal surface 51 and an external surface 53.

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The casing 5 can be provided with an upstream and / or downstream flange for connection with the compressors.

In the example illustrated in FIG. 2, the stator vanes of the compressors 4 and 6 are of variable orientation and the downstream flange of the casing 5 extends in axial superposition of the stator vanes of variable orientation of the compressor 6 so as to carry the actuation and the bearings of said blades. As described in FIG. 2, an annular row of rotor blades of the compressor 6 can optionally be interposed axially between the radial arms and such a row of stator blades of variable orientation.

Alternatively, the housing flanges can be brought closer to the ring 50.

According to the invention, the structural casing 5 has covers 60 which at least partially cover the external surface 53 of the central hub.

Each cover can be provided with a flange 62 facilitating its attachment to the casing. The flange 62 can be provided on the upstream side of the casing, on the downstream side, or both. Other means of assembly are naturally possible.

The covers 60 respectively have an external surface 61 which guides the air flow and an internal surface 63 facing the external surface 53 of the hub. At a given point on the cover 60, the thickness denoted “e” is the distance between the two surfaces 61 and 63.

FIG. 3 describes a partial isometric view of the structural casing 5, seen from the downstream. The hub 52 is covered with covers 60 over its entire periphery. In this example, each cover 60 has a flange 62 on its downstream side for its assembly with the hub 52. The external surfaces 61 of the covers 60 form the internal surface of the flow stream. In this embodiment, each cover 60 ends circumferentially by a notch 64 which makes it possible to cooperate with a circumferential half of the internal end of the arm 54.

The number of arms 54 can be between 2 and 20. They are preferably 8 in number, regularly distributed angularly around the hub.

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FIG. 4 shows a cover 60 with its two circumferential notches 64 which conform to the shape of the struts and its flange 62.

FIG. 5A is a sectional view in the direction V: V defined in FIG. 2. This example shows that the external ring can be produced from several angular sectors 50.1, 50.2, 50.3, 50.4. According to other embodiments, the ring is made in one piece, and possibly the ring, the arms and the hub are in one piece, from foundry.

Each of the parts can be made of a different material and those skilled in the art would be able to adapt the type of welding technology according to the materials present.

FIG. 5A illustrates the variations of the thickness e according to the circumferential direction. The dimensions here are exaggerated in order to make visible the variations in thickness e of the covers 60. The shape resulting from all the covers is not necessarily axisymmetric. In some cases it may indeed be advantageous not to have an internal guide surface of the vein which is axisymmetric in order to control the areas to which the greatest static or dynamic pressures are applied. Not all inter-strut spaces are necessarily covered with covers.

FIG. 5B is identical to FIG. 5A but shows another alternative for the shape of the covers 60. Here, the thicknesses are greater between two struts in order to guide the flow towards the feet of the struts 54. The reverse is also possible with extra thicknesses in the vicinity of the struts and a hollow in the circumferential medium of each cover 60.

According to an embodiment not illustrated, some covers 60 can be according to the example of FIG. 5A while others are according to the example of FIG. 5B.

FIGS. 5A and 5B show examples with 4 radial arms 54. The invention is naturally not limited in terms of the number of arms.

FIG. 6A illustrates a view in axial section of the casing 5 according to another embodiment. The hood 60 extends upstream beyond the casing in order to cover

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BE2018 / 5482 partly the ferrule 40. The junction between the ferrule 40 and the casing 5 is therefore covered by the cover 60 which can, at this location have a T-shaped profile. FIG. 6A also illustrates a configuration of a casing where the downstream flange does not extend beyond the casing, contrary to FIG. 2.

Figure 6B illustrates another aspect that the invention can take. In this example, the cover 60 has a variable thickness in the axial direction. It is for example possible to provide an upstream thickness greater than the downstream thickness. The reverse may also be conceivable.

The upstream thickness can be 1.5 to 20 times greater than the downstream thickness, preferably 2 to 6 times. Such variations in the thickness of the covers makes it possible to obtain the radial concentration of the flow over a shorter distance.

FIG. 6C illustrates yet another aspect of the covers 60, the flange 62 of which can close in the shape of a U or hook 65 to facilitate the centering of the covers on the hub 52. Again, this flange can be indifferently placed upstream or downstream of the housing.

FIG. 7 schematically describes a method of depositing a cover 60 on the hub in another embodiment of the covers 60. A cover 60 is here partially drawn. This has an orifice which cooperates with the strut. The cover 60 is removed while it is malleable, for example before crosslinking or before solidification. The cover 60 can therefore come into contact with the external surface 53 of the hub 52, by being inserted in the orientation of the arrow. Once deposited on the hub, the solidification of the cover 60 will ensure the maintenance of the cover 60 and its adhesion as close as possible to the surface 53.

According to an embodiment of the invention which is not illustrated, the structural casing 5 is an intermediate casing between a high-pressure turbine and a low-pressure turbine. A housing of substantially similar design, with the radial arms oriented aerodynamically opposite to that described in Figure 3, can be used. The materials will be chosen appropriately in order to withstand the higher temperatures in this part of the turbomachine.

The different details of the different embodiments set out in this application can be combined unless it is explicitly

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BE2018 / 5482 11 described as alternatives and that such a combination is made mechanically impossible. For example, the different thickness variations of the covers in the circumferential and axial directions can be combined.

Claims (21)

claims 1. Structural casing (5) for an axial turbomachine (2), in particular for an aircraft turbojet engine, the casing (5) comprising: - a ring (50) having an internal surface (51), a hub (52) preferably obtained by foundry and having an external surface (53), the hub (52) being coaxial and fitted in the ring (50), and a plurality of arms (54) extending radially from the external surface (53) of the hub (52) to the internal surface (51) of the ring (50), the casing (5) being characterized in that it further comprises an annular row of covers (60) made of composite material covering at least partially the external surface (53) of the hub (52). 2. Housing (5) according to claim 1, characterized in that the covers (60) have an external surface (61) having an arithmetic roughness much less than 0.5 μm. 3. Housing (5) according to one of claims 1 or 2, characterized in that the covers (60) are made of composite material with PEI matrix injected with short carbon fibers. 4. Housing (5) according to one of claims 1 to 3, characterized in that the covers (60) each comprise a flange (62) allowing the assembly of the covers (60) to the hub (52) by elements of hardware. 5. Housing (5) according to one of claims 1 to 4, characterized in that the covers (60) have a variable thickness (e). 6. Housing (5) according to the preceding claim, characterized in that the covers (60) have a thickness (e) which decreases from upstream to downstream. 7. Housing (5) according to the preceding claim, characterized in that the thickness (e) is 1.5 to 20 times greater upstream of the covers than downstream, preferably 2 to 6 times. 2018/5482 BE2018 / 5482 8. Housing (5) according to one of claims 5 to 7, characterized in that the thickness (e) of the covers (60) varies circumferentially, the maximum thickness being in the vicinity of the struts. 9. Housing (5) according to one of claims 5 to 7, characterized in that the thickness (e) of the covers (60) varies circumferentially, the minimum thickness being in the vicinity of the struts. 10. Housing (5) according to one of claims 5 to 9, characterized in that the set of covers (60) forms a non-axisymmetric structure. 11. Housing (5) according to one of claims 1 to 10, characterized in that the ring (50), the hub (52) and the arms (54) have come from foundry material. 12. Housing (5) according to one of claims 1 to 11, characterized in that the arms (54) are welded to the hub (52) and to the ring (50), the ring (50) being preferably formed several angular sectors (50.1, 50.2, 50.3, 50.4) describing different angles. 13. Housing (5) according to one of claims 1 to 12, characterized in that at least one of the covers (60) surrounds at least one of the arms (54). 14. Axial turbomachine (2) with a low-pressure compressor (4), a high-pressure compressor (6) and an intermediate flow (5) between the low-pressure compressor (4) and the high-pressure compressor (6) , characterized in that the intermediate vein comprises a structural casing (5) according to one of claims 1 to 13. 15. Turbomachine (2) according to claim 14, characterized in that the low pressure compressor (4) comprises an internal ferrule (40) and the covers (60) partially cover the internal ferrule (40). 16. Turbomachine (2) according to claim 14, characterized in that the internal shroud (40) of the low pressure compressor (4) is formed by the covers (60). 2018/5482 BE2018 / 5482 17. Method for manufacturing a structural casing (5) comprising a step of founding a hub (52) possibly with arms (54) and a ring (50), the hub (52) comprising an external surface (53 ), the method being characterized in that it comprises a step of mounting a plurality of covers (60) made of composite material on the external surface (53) of the hub. 18. Method according to claim 17, characterized in that the casing is according to one of claims 1 to 13. 19. Method according to one of claims 17 or 18, characterized in that all the arms (54) are assembled to the hub (52) before the covers (60) are installed on the external surface (53) of the hub ( 52). 20. Method according to one of claims 17 to 19, characterized in that the covers (60) are deposited on the external surface (53) while they are in a malleable state and solidify by conforming to the shape of the surface outer (53) of the hub (52). 21. A method of assembling a turbomachine (2) according to claim 15, comprising a manufacturing method according to one of claims 17 to 20, the hub (52) being assembled to the internal shroud (40) of the compressor ( 4), then the covers (60) being brought to the external surface (53) of the hub (52), covering at least partially the internal shroud (40) of the compressor (4).