HOUSING FOR COMPRESSOR OF A TURBOT ENGINE

Description

[0001] The invention relates to the design of a turbomachine, in particular an aircraft turbojet or an aircraft turboprop. The invention relates in particular to the casing of a high-speed compressor. Previous technique

[0002] In a turbomachine, and particularly in its compressor(s), the airflow is compressed by alternating rotor and stator blades. The stator blades extend radially inward from an external shell that defines the airflow path. Document EP 1 426 559 A1 describes an example of a compressor architecture for such a turbomachine. The shell that holds the stator blades has flanges upstream and downstream for attaching it to the upstream casing and the downstream inter-compressor casing. Thus, the shell acts as a vector, transmitting axial forces and torque between the various casings to which it is attached, and it also supports the forces exerted on the stator blades inside the compressor. These two sources of force generate areas of stress concentration, particularly at the blade attachment points in the shell.The usual response to ensure mechanical strength in these stress areas is to provide extra thickness or reinforcing parts, and therefore additional weight.

[0003] US patent 2,994,508 describes an arrangement in which ferrule elements are held by means of Y-shaped tabs that radially clamp the outer and inner sides of the crankcase flanges. This assembly is complex and expensive.

[0004] Document EP2896796A1 relates to the fixing of abradable material seals on a compressor shell by means of a strip resting on stator blade platform bearings, in accordance with the preamble of claim 1. Summary of the invention Technical problem

[0005] The invention aims to overcome the disadvantages described above and in particular to provide a lighter / lighter compressor and turbomachine without compromising their mechanical strength. Technical solution

[0006] The invention relates to a compressor casing for an aircraft turbojet engine equipped with a fan driven by a reduction gear according to claim 1, the casing comprising in particular: an outer shell made of composite material and optionally formed of several angular shell segments; and an annular row of platforms fixed to the shell, each platform supporting one or more stator blade(s); the casing being remarkable in that it comprises a ring, optionally formed of several angular ring segments, and having a layer of abradable material, the ring resting radially on bearing surfaces of the platforms so that no axial force can be transmitted between the ring and the platforms.

[0007] The ferrule can be a single-piece annular shell, featuring a taper compatible with the assembly of the various components to be attached to it. Alternatively, the ferrule can be composed of two half-shells. The composite material can be optimized with denser plies in areas subjected to greater mechanical stress. The composite material can be of the type of unidirectional thermosetting or thermoplastic pre-impregnated materials deposited by automated fiber placement (AFP) and consolidated in an autoclave or closed mold, or alternatively, 2D or 3D interlock fabrics consolidated by resin transfer molding (RTM).

[0008] The platforms and blades can form angular blade sectors with multiple blades. The layer of abradable material is intended to face the rotor blade tips of a rotor.

[0009] The design of the contact interface between the platforms and the ring prevents the transmission of axial force, thus avoiding stress concentration at the periphery of the platforms. In conventional assemblies, the blade platforms can be welded to each other or to the shell and rings. Weld beads create mechanically heterogeneous areas with a higher stress concentration coefficient (Kt). To ensure mechanical strength, particularly under fatigue, reinforcements or additional thicknesses are usually incorporated. Welds then present the dual disadvantage of a surface that is not entirely geometrically controlled for airflow guidance and of added weight due to structural reinforcement. With the design of the invention, the disadvantages associated with the presence of weld beads are eliminated.

[0010] This function is achieved by rounded or chamfered surfaces.

[0011] According to advantageous embodiments of the invention, the casing may comprise one or more of the following features, taken individually or in all technically possible combinations: The ring is held radially externally by the ferrule and internally by the platforms. Preferably, only a radially internal surface of the ring is in contact with the platform, and conversely, the contact between the platform and the ring is made on only a radially external surface of the platform; each platform includes a circumferential end abutted to a circumferential end of a circumferentially adjacent platform, and the opposite ends of the two circumferentially adjacent platforms each include a housing portion, the two housing portions together forming a housing receiving an element for fixing the platforms to the ferrule.This design has the advantage of combining the fastening elements of the different platforms, thus reducing the overall weight. The fastening element is a screw or a bolt, with a head that fits into the housing and a shaft, possibly threaded, extending radially through and outside the ferrule. A nut and washer can be used to tighten the screw or bolt on the outside of the ferrule. The opening in the ferrule through which the screw passes can be significantly larger than the head of the screw or bolt to prevent any axial or circumferential force from being transmitted between the platform and the ferrule via the screw. The ring is made of a metallic material, comprising an internal groove filled with the abradable layer and an external groove forming a radial clearance between the ring and the ferrule.This geometry allows the ring to deform, particularly radially, under the effect of thermal expansion (its own or that of the bladed disk arranged radially inside the ring), without mechanical stresses appearing on the platforms. The ring can be equipped with axial grooves, regularly or irregularly distributed at angles, to allow for treatment (as in the example disclosed in EP 2 202 385 A1); the surfaces of the ring in contact with the platforms and the surfaces of the platforms in contact with the ring are chamfered or have a rounded profile.This type of arrangement allows the ring to deform or slide axially relative to the platform, the deformations or sliding allowing the contact between the platforms and the ring to be maintained, and therefore the continuity of the air guiding surface, without generating mechanical stress at the interface between the platforms and the ring; each platform includes an upstream bearing and / or a downstream bearing which have radial and / or circumferential contact surfaces with the ring; the ring has an upstream lip and / or a downstream lip, cooperating with the platform; a flexible seal, in particular made of silicone, is arranged axially between the platforms and the ring so that no axial force can be transmitted between the platforms and the ring; the ring is mounted floating in the ferrule.It is thus free to deform under the action of thermal expansion without generating mechanical stresses on the platform or the shell; the row of platforms is a first row and the casing includes a second and possibly a third row of platforms, and the ring is a first ring and the casing includes a second and possibly a third ring, each of the rings being arranged upstream of a respective row of platforms. Each ring receives a layer of abradable material arranged upstream of one or each row of stator blades and positioned on the inner surface of the ring.The abradable material is suitable for cooperating with the external radial ends of a rotor wheel; the blades are one piece with their respective platform, the whole being made of metal or composite material; the blades are made of composite material and / or the platforms are made of composite material, possibly one piece with the ferrule; the housing comprises a row of variable-pitch blades.

[0012] The invention also relates to a turbomachine comprising a blower driven by a reducer, a low-pressure compressor, a high-pressure compressor and an intermediate casing, disposed between the low-pressure compressor and the high-pressure compressor, the turbomachine being remarkable in that the low-pressure compressor has a casing according to one of the embodiments described above.

[0013] According to an advantageous embodiment, the ferrule comprises an upstream flange and a downstream flange, for fixing it respectively - directly or indirectly - to an upstream housing and to the intermediate housing, the housing comprising an upstream flange and a downstream flange, fixed to the respective flanges and ensuring continuity of the airflow guidance surface with an upstream ring and a downstream platform.

[0014] The invention also relates to a method for assembling a casing according to one of the embodiments described above or a turbomachine according to one of the embodiments described above, the method comprising a step of placing compressor stages in the shell, possibly by alternately stacking an annular row of platforms and a ring.

[0015] Alternatively, the process includes a step of assembling platforms to a first half-shell of the ferrule, a step of positioning axially bladed discs between two adjacent annular rows of platforms, a step of assembling platforms to a second half-shell of the ferrule, and finally a step of assembling the second half-shell to the first half-shell.

[0016] In general, the various objects and embodiments of the invention can be combined with each other in all possible technical combinations, unless otherwise explicitly stated. Additional benefits

[0017] The composite material ferrule and the absence of welding and especially the reinforcements it requires allows for a weight saving.

[0018] The rings, preferably metallic, allow for passive control of the clearance between the blade heads and the abradable material through thermal expansion. An abradable material is more easily deposited (or redeposited during maintenance) onto these rings. These rings also limit booster casing deformation under engine thrust.

[0019] Another advantage of using different parts (ferrule, platform, ring) is that it is possible to replace only one of the parts involved in case of manufacturing or usage failure rather than discarding the entire housing.

[0020] Also, planning the abradable layer on a ring makes it easier to deposit compared to depositing abradable on a ferrule, which is more restrictive and cumbersome to handle.

[0021] The two-half-shell design allows the mounting of a rotor consisting of a bladed drum ("blum") and a one-piece annular ferrule that can receive one-piece moving wheels (blisks) assembled in a non-permanent manner. Brief description of the drawings

[0022] There figure 1 represents a turbomachine according to the invention; The figure 2 represents a schematic cross-sectional view of part of a state-of-the-art compressor; The figure 3 represents a cross-sectional view of a compressor housing according to the invention; The figures 4 And 5 illustrate two design examples for a blade mounting platform according to the invention; The figure 6 shows two examples of a fastening element used to attach the platform to the ferrule. Description of the implementation methods

[0023] In the following description, the terms "internal" (or "inside") and "external" (or "outside") refer to radial positioning relative to the axis of rotation of a turbomachine. The axial direction corresponds to the direction along the turbomachine's axis of rotation. The radial direction is perpendicular to the axis of rotation. Upstream and downstream refer to the main flow direction within the turbomachine. The term "solid" is understood as rotationally fixed, and specifically rigidly connected. The term "monobloc" is equivalent to "made from a single block of material" and designates different elements produced from the same block of material, as opposed to "added," which means that an element is attached to another element after its fabrication. The figures represent the elements schematically, notably without all assembly or sealing components.Certain dimensions, and in particular the radial thickness of the different parts, are exaggerated in order to facilitate understanding of the figures.

[0024] There figure 1 This simplified diagram represents a turbomachine 2 comprising a low-pressure compressor 4 and a high-pressure compressor 6, a combustion chamber 8, and two turbines 10. In operation, the mechanical power of the turbines 10 drives the two compressors 4 and 6 by means of their respective shafts 12 and 13. The compressors 4 and 6 have several rows of rotor blades (or rotors) associated with rows of stator blades (or statorics). The rotation of the rotor 15 around its axis of rotation 14 thus generates an airflow and progressively compresses this air until it enters the combustion chamber 8.

[0025] A blower 16 is coupled to the shaft 12 and generates an airflow which splits into a primary flow 18 and a secondary flow 20 passing through an annular duct (partially shown) along the machine and then joining the primary flow at the turbine outlet.

[0026] Gear reduction means, such as a reducer 17, for example epicyclic, can reduce the rotational speed of the blower 16 relative to the associated turbine.

[0027] An upstream housing 22, equipped with support arms (or "struts"), holds the gearbox 17 and supports the upstream part of the turbomachine. A compressor housing 24 supports the compressor 4. An inter-compressor housing 5, including support arms, is located between the low-pressure compressor 4 and the high-pressure compressor 6.

[0028] During operation, the various casings are subjected to significant loads. The fan tends to pull the entire aircraft forward. The casings are mechanical components that must therefore each support at least a portion of the thrust generated by the fan. The outer shell contributes to the rigidity of the structure and bears some of these stresses, schematically represented by the arrow labeled F on the diagram. figure 1 Stress concentration points are also illustrated, particularly at the downstream structural arms. By attaching the blades directly to the shell, they also experience some of the mechanical stresses of the shell. The idea of ​​the invention, as described below, is to decouple the blades from the shell's forces and thus separate the functions of flow guidance, abradable attachment, and casing treatment integration from the shell itself.

[0029] There figure 2This is a cross-sectional view of the compressor 4 in a known turbomachine. Part of the fan 16 and the primary 18 and secondary 20 flow separation nozzle 28 can be seen. The rotor 15 may comprise several rows of rotor blades 30.

[0030] The low-pressure compressor 4 includes at least one rectifier which contains an annular row of stator blades 32 intended to rectify the airflow deflected by the rotating blades.

[0031] The low-pressure compressor 4 includes a housing 34. The housing 34 generally has an axisymmetric shape and may incorporate reinforcements, grooves, or stiffening ribs. The housing 34 includes a ferrule 35 whose axial ends have mounting flanges 36, for example, annular mounting flanges 36 for attaching the separation nozzle 28 and / or for attaching to an intermediate housing 5 of the turbomachine.

[0032] The stator blades 32 extend essentially radially from the housing 34 to internal ferrules 38. One of the rows of stator blades 32 may have variable orientation around its axis 40. The stator blades 32 are fixed to the housing 34 by means of platforms 42. A layer of abradable material 44 is generally provided opposite the rotor blades 30. In such a configuration, the anchoring areas of the stator blades – the housings (gaps, “bathtubs”) accommodating the platforms 42 – form stress concentration zones because they concentrate both the forces experienced by the stator blades induced by the straightening of the airflow 18 and the forces transmitted from the blower 16 or the gearbox 17. These zones are therefore generally reinforced with additional thicknesses of material. In addition to this, there are the weld beads from the platforms 42 to the ferrule 35. All of this represents a considerable weight.

[0033] There figure 3 describes a housing 34 according to the invention. The ferrule 35 is generally tubular in shape and may be made up of several angular sections, such as two half-shells joined in a plane including the axis 14. The ferrule includes two flanges 36 for its attachment to an upstream housing (22 on the figure 1 and partially represented on the figure 3 ), and to an intermediate casing (5 on the figure 2 ).

[0034] The ferrule 35 has an outer surface 35.1 and an inner surface 35.2.

[0035] The stator blades 32 extend radially inwards from the ferrule 35. The blades 32 are fixed to the ferrule 35 by means of platforms 42. The platforms 42 may be integral with the blades 32. The platforms 42 are fixed to the ferrule 35 by means which are described below extending along the axis A.

[0036] The rotor blades 30 are partially shown. They can be positioned opposite a layer of abradable material 44. The latter is supported by a ring 46.

[0037] The inner ends of the blades 32 are supported by an internal ferrule 38 under which a layer of abradable material 48 can be attached, which can cooperate with the blades of a rotor (15 on the figure 2 ).

[0038] There figure 3 illustrates three compression stages, each formed of a pair of rows of rotor blades 30 and stator blades 32. It should be noted that the invention is not limited to this number of compression stages.

[0039] Flanges 50, 52 can ensure the continuity of the air stream upstream and downstream of these three stages.

[0040] An enlarged portion of the figure 3 shows in detail the contact between a ring 46 and a platform 42.

[0041] The platform 42 includes an external surface 42.1 which is in contact with the ferrule 35. Sealing can be achieved by means of a gasket such as the one illustrated in document WO 2019 / 105610 A1. The internal surface 42.2 of the platform is an air guide surface.

[0042] The ring 46, for its part, includes an external surface 46.1 which can bear against the ferrule 35 and an internal surface 46.2 which defines an internal groove which accommodates the layer of abradable material 44.

[0043] In this example, a surface 42.3, 46.3 with an "S" profile, provided on the platform 42 and on the ring 46, ensures linear contact between the platform 42 and the ring 46. The surface 42.3 is provided on one or more spans 42.4 of the platform 42. The surface 46.3 is provided on a lip 46.4 of the ring 46.

[0044] When the ring 46 - preferably metallic - deforms during operation under the action of thermal expansion (its own or that of the rotor), the point of contact between the ring 46 and the platform 42 can move because the lip 46.4 deforms.

[0045] Similarly, the point of contact between the external surface 46.1 of the ring 46 and the internal surface 35.2 of the ferrule 35 can move, the ring 46 being mounted floating in the ferrule 35. The design of the various surfaces (profiles and clearances) is suitably chosen to allow expansion of the ring even under the maximum temperature conditions generally permissible in operation.

[0046] The ring 46 finally has an external groove 46.5 allowing its free deformation without contact constraints with the ferrule 35. This groove 46.5 also forms a plenum which can be used to integrate a casing treatment.

[0047] There figure 4shows a first example of a platform 42, with, at the top an isometric view, in the middle a front view (circumferentially viewed) and at the bottom a top view (radially viewed).

[0048] The platform 42 comprises an external surface 42.1 substantially conforming to the internal surface 35.2 of the ferrule 35, and an internal surface 42.2 from which the blade 32 extends. The platform 42 can be monobloc with the blade 32.

[0049] In this example, the platform includes a single bearing surface 42.4 on each axial side, presenting a contact surface 42.3 with the rings 46. The bearing surface is radially on the inner side of the platform 42. The ring is thus radially "wedged" between the ferrule and the platform, making any means of attaching the ring to the platforms or the ferrule optional. While the bearing surface 42.4 is shown here as extending circumferentially over the entire platform 42, alternatively, the bearing surface 42.4 may be only on a portion of the platform and may therefore present circumferential contact surfaces with the ring (see figure 5 A lug 42.4' can be arranged on one or both of the 42.4' bearing surfaces so as to cooperate with a notch in a ring and thus limit or even prevent the circumferential movement of the ring. The ring 46 and its notch 46.6 are partially shown in dashed lines.

[0050] The platform has two faces at its circumferential ends 42.5, 42.6 which can be partially or fully curved. The continuity of the airflow guidance surface is ensured by the continuity of the surfaces of the platforms arranged end-to-end.

[0051] A housing 42.10 for receiving a latch (or screw) is arranged on the outer face 42.1. In this example, it is made of two parts 42.7, 42.8, each at one end 42.5, 42.6 of the platform. These two parts can be substantially cylindrical. One of the parts, preferably on the convex side 42.5, includes an outer portion with a flat 42.9 that forms a radial stop for the latch. Alternatively, the radial stop can be a cover attached to the outer face 42.1. By assembling the platforms against each other, parts 42.7, 42.8 form a substantially cylindrical housing 42.10.

[0052] Additional housing (not shown) may also be provided on the platform to accommodate additional assembly elements.

[0053] Some or all surfaces of platform 42 may remain as cast.

[0054] There figure 5 This shows a variant for the geometry of platform 42. In this example, several 42.4 spans are arranged on each side of platform 42. The number of 42.4 spans can differ between sides, as can their positions. In this example, they are arranged in a staggered pattern, which can facilitate the placement of platforms 42 on ring 46 or vice versa.

[0055] Two circumferentially adjacent platforms 42 can be identical or different.

[0056] The surface marked 42.3' can serve as a circumferential stop for the ring 46, having corresponding notches to fit into the spans 42.4 of the platform 42.

[0057] The variant of the figure 5 is therefore certainly a platform 42 more complex to manufacture but it can present advantages on the indexing in position of the ring 46.

[0058] There figure 6 shows two examples of a fastener 54 whose head 54.1 can penetrate the housing and whose stem 54.2, optionally threaded, can extend through and beyond the ferrule 35.

[0059] The example on the left shows a screw 54. In one step of assembling the housing, the head 54.1 is inserted into a half-recess of a platform 42, and then an adjacent platform encloses the head 54.1 under the flat 42.9. A nut is then screwed onto the threaded rod 54.2 from the outside. This technique can be repeated for each platform, on two half-shells of the ferrule 35 (180°), and then the half-shells are assembled together. Alternatively, when the ferrule is a single-piece annular ferrule, all the platforms in the same annular row are assembled to the ferrule before a ring is stacked on top of the platforms.

[0060] The example on the right shows a latch 54. This includes a head 54.1 which is a radial protrusion of the rod 54.2. The assembly is identical to that performed with the screw. The latch is lighter than the screw, although it requires precise angular positioning around the axis A to ensure that the head 54.1 remains securely in the housing.

[0061] The invention has been described by means of examples of embodiments but is not limited to them. Elements of each embodiment can be combined with elements of other embodiments. The invention is limited only by the scope of the joined claims.

[0062] The number of compression stages can be adapted to the requirements and thus be 1, 2, 3, or 4, or even more. One of the stages can include a row of variable-pitch blades. Alternatively, this row of variable-pitch blades can be located upstream. of crankcase 34 ( figure 3 ofdocument WO 2019 / 105610 A1).

[0063] If the preferred application area of The casing according to the invention relates to architectures in which the outer shell absorbs significant stresses, such as on the figure 2 , where the housing is interposed between two structural housings (5 and 22), the invention is not limited to that.

[0064] When a ring is formed from several angular segments, these segments can be in circumferential floating contact with each other, or assembled by snap-fit ​​joints (mortise and tenon, dovetail, etc.). Platform assembly (with locks or screws) can also be applied to ring segments. This technique can complement or replace bearing surfaces and lugs on the platforms that circumferentially and radially secure the ring segments.

Claims

1. A compressor casing (34) for an aircraft jet engine (2) equipped with a fan driven by a gearbox, the casing (34) comprising: - an external shroud (35) made of composite material and optionally formed of several angular segments of the shroud; and - an annular row of platforms (42) attached to the shroud (35), each platform (42) supporting one or more stator blades (32); the casing (34) being characterized in that it comprises: - a ring (46), optionally formed of several angular segments of the ring, and having a layer of abradable material (44), characterized in that: the ring (46) rests radially on support portions (42.4) of the platforms (42) such that no axial force can be transmitted between the ring (46) and the platforms (42), and in that the surfaces (46.3) of the ring (46) in contact with the platforms (42) and the surfaces (42.3) of the platforms (42) in contact with the ring (46) are chamfered or rounded surfaces (42.3, 46.3).

2. The casing (34) according to claim 1, characterized in that the ring (46) is radially maintained externally, preferably exclusively, by the shroud (35) and internally, preferably exclusively, by the platforms (42).

3. The casing (34) according to claim 1 or 2, characterized in that each platform (42) comprises a circumferential end (42.5) abutted against a circumferential end (42.6) of a circumferentially adjacent platform (42), and the facing ends (42.5, 42.6) of the two circumferentially adjacent platforms (42) each comprise a housing portion (42.7, 42.8), the two housing portions (42.7, 42.8) together forming a housing (42.10) receiving a fixing element (54) for attaching the platforms (42) to the shroud (35).

4. The casing (34) according to claim 3, characterized in that the fixing element (54) is a screw or lock, provided with a head (54.1) received in the housing (42.10) and a shaft (54.2), optionally threaded, extending radially through and outside the shroud (35).

5. The casing (34) according to any one of the preceding claims, characterized in that the ring (46) is made of metallic material, comprising an internal groove (46.2) filled with the layer of abradable material (44) and an external groove (46.5) forming a radial clearance between the ring (46) and the shroud (35).

6. The casing (34) according to any one of the preceding claims, characterized in that each platform (42) comprises an upstream and / or downstream support portion (42.4) which has the contact surfaces (42.3) radially and / or circumferentially with the ring.

7. The casing (34) according to one of the preceding claims, characterized in that the ring (46) has an upstream lip and / or a downstream lip (46.4), cooperating with the platform (42).

8. The casing (34) according to one of the preceding claims, characterized in that the ring (46) is mounted floating within the shroud (35).

9. The casing (34) according to one of the preceding claims, characterized in that the row of platforms (42) is a first row and the casing (34) comprises a second and optionally a third row of platforms (42), and in that the ring (46) is a first ring and the casing (34) comprises a second ring and optionally a third ring, each of the rings (46) being disposed upstream of a respective row of platforms (42).

10. A turbine engine (2) comprising a fan (16) driven by a gearbox (17), a low-pressure compressor (4), a high-pressure compressor (6) and an intermediate casing (5), disposed between the low-pressure compressor (4) and the high-pressure compressor (6), the turbine engine being characterized in that the low-pressure compressor (4) has a casing (34) according to one of claims 1 to 9.

11. The turbine engine (2) according to claim 10, characterized in that the shroud (35) comprises an upstream flange (36) and a downstream flange (36), for respectively fastening it - directly or indirectly - to an upstream casing (22) and to the intermediate casing (5), the casing (34) comprising an upstream flange (50) and a downstream flange (52), attached to the respective flanges (36) and ensuring a continuity of the surface guiding the airflow with an upstream ring (46) and a downstream platform (42).

12. A method of assembling a casing (34) according to one of claims 1 to 9 or a turbine engine (2) according to claim 10 or 11 comprising a step of placing compressor stages within a shroud (35), optionally by alternately stacking an annular row of platforms (42) and a ring (46).