The present application relates to an axial turbomachine low-pressure compressor stator. The stator includes an outer annular casing made of organic matrix composite materials. The stator also has groups of vanes having an outer shroud, several rows of stator vanes spaced axially from one another, and segments of inner shrouds at the inner ends of the vanes. The rows of stator vanes are aligned along the circumference of the casing. Each outer shroud is pressed against the inside of the casing so it can be fastened by means of attachment pins. The outer shroud, and the rows of vanes of said group forming a one-piece assembly. The device of the present application reduces the number of vane attachment elements to a few attachment portions distributed on the shroud.

This application claims priority under 35 U.S.C. § 119 to Belgium Patent Application No. 2015/5394, filed 26 Jun. 2015, titled “Axial Turbomachine Compressor Casing,” which is incorporated herein by reference for all purposes.

BACKGROUND

1. Field of the Application

The present application relates to an axial turbomachine stator with a reduced number of attachments. The present application also relates to a stator with groups of axial turbomachine compressor vanes. The present application also proposes a turboprop or a turbojet engine of an aircraft.

2. Description of Related Art

An axial turbomachine compressor has a plurality of rows of vanes, at times rotor, at times stator. Their alternation gradually compresses the incoming flow while ensuring high throughput. The rows of stator vanes are supported by an external casing which also forms a mechanical link between the splitter fairing and the intermediate casing of the turbomachine. The outer casing plays a dual role in terms of sealing since it avoids secondary flows above the vanes and it receives the annular layers of abradable material to form annular seals around the rotor vanes.

The casing supports each vane individually, and thereby maintains them in a predetermined orientation and position to ensure optimum performance. In order to simplify the attachment of the vanes on the casing, it is known to group several stator vanes together by means of common platforms. They are then attached to the casing using a reduced number of screws.

Document EP 2 821 595 A1 discloses an axial turbomachine low-pressure compressor. The compressor comprises a composite outer casing supporting several rows of stator vanes between which the rows of rotor vanes move. The stator vanes are grouped together to form vane sectors, the platforms of which are linked together so as to form a common mounting bracket. The sector is attached by means of screws provided on the common mounting brackets. This configuration reduces the number of attachment pins in relation to the number of vanes, while favouring lightness and rigidity. However, the number of attachment pins remains high.

Although great strides have been made in the area of axial turbomachine compressor casing, many shortcomings remain.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present application aims to solve at least one of the problems of the prior art. More particularly, the present application aims to simplify the attachment of the vanes on an axial turbomachine stator. The present application also aims to stiffen an axial turbomachine stator.

The present application relates to an axial turbomachine stator, notably an axial turbomachine compressor, the stator comprising: an outer annular casing with an inner annular surface; and at least one group of vanes with: a row of stator vanes arranged in the circumference of the casing, and an outer shroud for attaching vanes to the casing, the shroud matching the inner surface of the casing; remarkable in that at least one or each group of vanes comprises a plurality of rows of axially-offset stator vanes, the outer shroud and the rows of vanes of said group being a single-piece assembly.

According to an advantageous embodiment of the present application, at least one or each vane group shroud extend axially over the entire length of the casing, and preferably forms a hermetic skin over the entire axial length of the casing.

According to an advantageous embodiment of the present application, the casing comprises an annular wall on which the inner surface is formed; and at least one, preferably two annular mounting flanges arranged at the axial ends of the annular wall.

According to an advantageous embodiment of the present application, the outer casing is made of a composite material, notably an organic matrix.

According to an advantageous embodiment of the present application, the composite casing comprises a fibre preform, preferably with a stack of woven plies and/or a three-dimensionally woven mattress.

According to an advantageous embodiment of the present application, at least one or each group of vanes is formed in one piece.

According to an advantageous embodiment of the present application, at least one or each outer shroud comprises a main outer surface with outer cavities closed by the casing.

According to an advantageous embodiment of the present application, at least one or each group of vanes comprises at least three rows of stator vanes, preferably at least four rows of stator vanes spaced axially from one another, preferably distributed axially along the casing.

According to an advantageous embodiment of the present application, at least one or each outer shroud comprises attachment portions such as attachment pins, possibly threaded, the portions preferably extending radially.

According to an advantageous embodiment of the present application, at least one or each attachment portion comprises plastically deformed branches so as to integrally secure the corresponding shroud to the casing.

According to an advantageous embodiment of the present application, the stator comprises an annular space separating two consecutive rows of vanes of the same group of vanes, the space being adapted to receive an annular row of rotor vanes of the turbomachine.

According to an advantageous embodiment of the present application, the stator comprises several groups of vanes, and vanes with attachment platforms connected to the casing, the platforms of vanes being arranged between groups of vanes, preferably in the circumferential direction.

According to an advantageous embodiment of the present application, at least one or each group comprises inner shrouds integral with the inner ends of the vanes of said group.

According to an advantageous embodiment of the present application, the stator comprises several groups of vanes and at least one or more angular segments of inner shrouds arranged between the groups of vanes, the inner shroud segments are possibly connected to the inner ends of said vanes or to the inner shrouds of the groups.

According to an advantageous embodiment of the present application, at least one or each group comprises one or more annular zones for receiving seals, notably layers of abradable material, intended to ensure sealing with the rows of rotor vanes; said zones possibly comprising a surface with a roughness Ra greater than 10 μm, and/or a mesh.

According to an advantageous embodiment of the present application, the stator vanes of at least one or each row of vanes of at least one or each group are arranged in the circumference of the casing.

According to an advantageous embodiment of the present application, the outer casing comprises a main inner surface, at least one or each outer shroud comprises a main outer surface in contact with the main inner surface, possibly matching the main inner surface, preferably pressed against the main inner surface. The main aspect may be associated to the area.

According to an advantageous embodiment of the present application, the casing comprises openings through which the attachment portions of the outer shrouds pass.

According to an advantageous embodiment of the present application, at least two consecutive rows of vanes of the same group are spaced apart by a distance greater than or equal to the axial length of one of said rows of vanes.

According to an advantageous embodiment of the present application, the stator comprises several groups of vanes; the outer shrouds cover the entire internal surface of the casing.

According to an advantageous embodiment of the present application, at least one or each group comprises an outer shroud in the shape of a quadrilateral with corners, said group comprising an attachment portion at each corner of the quadrilateral, preferably the attachment portions of each group are joined at the corners.

According to an advantageous embodiment of the present application, at least one or each group comprises at least ten times more, preferably at least fifteen times more, and even more preferably at least twenty times more stator vanes than attachment portions.

The present application also relates to an axial turbomachine primary airflow compressor, the compressor comprising a stator provided with an outer annular casing with an inner annular surface; and at least one group of vanes with: a row of stator vanes arranged along the circumference of the casing, and an outer shroud for attaching vanes to the casing, the shroud matching the inner surface of the casing and being in contact with the primary flow, preferably axially guiding the primary flow; remarkable in that at least one or each group of vanes comprises a plurality of rows of axially-offset stator vanes, the outer shroud and the rows of vanes of said group being a single-piece assembly.

The present application also relates to a turbomachine comprising a stator, remarkable in that the stator is in compliance with the present application; preferably the turbomachine comprises a low-pressure compressor, the stator being the stator of said low-pressure compressor.

According to an advantageous embodiment of the present application, the turbomachine comprises a one-piece rotor, the casing comprising two half-shells united together around said one-piece rotor.

Generally speaking, the advantageous modes of each object of the present application also apply to the other objects of the present application. As far as possible, each object of the present application can be combined with the other objects.

The vanes are reunited in wedge-shaped segments forming the casing of the compressor. The present application considerably reduces the resources required to attach the stator vanes. Each attachment pin contributes to the fastening of several rows of stator vanes. In this way, the number of fastening openings to be provided in the casing is reduced. This preserves the mechanical strength of the casing and limits the risk of leaks.

The present application also enables a hermetic barrier to be formed along the casing. It forms a lining with continuity of material preventing recirculations from bypassing the vane platforms along the inner surface of the casing.

In the following description, the terms interior or internal and exterior or external refer to a position in relation to the axis of rotation of an axial turbomachine. The axial direction corresponds to the direction along the rotational axis of the turbomachine. The terms upstream and downstream refer to the main direction of flow in the turbomachine.

FIG. 1is a simplified representation of an axial turbine engine. In this case, it is a double-flow turbojet engine. The turbojet engine2comprises a first compression level, designated low-pressure compressor4, a second compression level, designated high pressure compressor6, a combustion chamber8and one or more turbine levels10. In operation, the mechanical power transmitted to the turbine10via the central shaft to the rotor12moves the two compressors4and6. The latter comprise several rows of rotor vanes associated with rows of stator vanes. The rotation of the rotor about its axis of rotation14thus generates a flow of air and gradually compresses the latter up to the inlet of the combustion chamber8. Gearing-down means can increase the speed of rotation transmitted to the compressors.

An intake fan16is coupled to the rotor12and generates an air flow which is divided into a primary flow18passing through the various abovementioned levels of the turbomachine, and a secondary flow20passing through an annular conduit (shown in part) along the machine that then joins the primary flow at the turbine outlet. The secondary flow can be accelerated so as to generate a thrust reaction. The primary flow18and secondary flow20are annular flows; they are guided by the casing of the turbomachine. For this purpose, the casing has cylindrical walls or shrouds which may be internal and external.

FIG. 2is a sectional view of a compressor of an axial turbomachine such as that ofFIG. 1. The compressor may be a low-pressure compressor4. One can observe a portion of the fan16and the splitter fairing22of the primary flow18and the secondary flow20. The rotor12comprises several rows of rotor blades24, in this case three. At least one or each row of rotor blades24may form a one-piece assembly with a rotor disk or spool12.

The low-pressure compressor4comprises a plurality of rectifiers, in this case four, each of which contain a row of stator vanes26. The rectifiers are associated with the fan16or a row of rotor blades for rectifying the airflow, so as to convert the flow velocity into static pressure. The rectifiers are secured to an outer casing28formed by several groups of vanes30distributed about the rotational axis14of the turbomachine.

The groups of vanes30can each have attachment portions32to the casing28. They extend axially over the entire axial length of the casing. There may be attachment pins, such as screws or lockbolts. These attachment portions32may include deformed or deformable elements to ensure integral blockage. They may be of split shank fastener type, that is to say with two tabs folded back against the outer surface of the casing. Additionally or alternatively, the groups of vanes can be bonded to the casing.

The casing28has an annular wall34with an inner surface receiving each outer surface of the outer shroud36of the group of vanes30. The wall34is limited axially by the outer annular flanges38. These can be used to secure the casing28of the compressor to the intermediate casing40of the turbomachine, and to support the splitter fairing22at the inlet of the compressor4.

The stator can form a composite structure in more than one respect. The casing28and in particular its wall34can be made of an organic matrix composite material reinforced by a fibrous preform. This preform may have a stack of woven carbon fibre plies. Additionally, the outer shroud36of the group can be made of metal, such as titanium, aluminum or their alloy. Associating a metal with an organic material makes it possible to benefit from the mechanical, chemical, thermal strength of the former and the lightness of the latter.

The compressor4can have several internal shrouds42that are connected to inner ends of the stator vanes26. These shrouds42form seals that cooperate with sets of sealing members, or outer annular ribs, of the rotor12. The shrouds42can include annular layers of abradable material44to cooperate through abrasions with these sealing members, to ensure dynamic sealing. The shrouds can be formed by angular segments of internal shrouds. Each segment is integral with a group of vanes30, each group30may thus comprise several inner shroud segments distributed axially along said group30.

Still from the point of view of sealing, the compressor can have seals46around the annular rows of rotor vanes24. These seals46can be formed on each group of rotor vanes40, in a plurality of annular bands axially separated by the rows of stator vane. These seals46can be layers of abradable material46.

FIG. 3illustrates a profile view of a group of vanes30. The group30comprises three rows of vanes26. Although only one vane per row is visible, each row may comprise a plurality of vanes. Similarly, a group can have two, four or more rows of vanes26.

The stator vanes26essentially extend radially from the outer shroud36. The outer shroud36, the attachment portions32and the vanes23, preferably each vane26and each attachment portion32of the group30form a one-piece assembly, preferably formed in one piece.

The group30has annular passages48such as annular spaces48intended to receive an annular row of rotor vanes. These spaces48allow a rotor row to be mounted between two successive rows of stator vanes26. Their axial length is greater than the majority of the axial length of a row of stator vanes26, preferably greater than or equal to said length. The spaces48can also define and/or axially separate the inner shrouds42.

FIG. 4outlines a plan view of a group of vanes30observed from the inside. For clarity, the optional inner shrouds are not shown. The number of vanes26per row is figurative. Each row may comprise at least two vanes26, preferably at least ten vanes26, and possibly at least thirty vanes26.

The vanes26can form a grid. Due to the reduction in diameter of the primary flow path that passes through the compressor, the outer shroud36narrows downstream. The outer shroud36has seal receiving zones50. These zones50can be circular arcs and arranged between the rows of vanes26. Their inner surface can be essentially rough, of roughness Ra greater than or equal to 10 μm, preferably greater than or equal to 50 μm. The zones50may be covered with anchoring mesh.

The stator vanes26of each row are evenly spaced, and have the same angular orientation in the flow. They are immovable relative to each other. Advantageously, the vanes of the same row are identical. Optionally, the spacing between the vanes can vary locally as well as their angular orientation. Some vanes may be different from the rest of the vanes of their row.

FIG. 5represents a sectional view of the stator of the compressor according to a first embodiment of the present application. The cross section is made along the axis5-5plotted inFIG. 2. Only half of the stator is shown. The attachment portions32pass through the wall34of the casing28via the fastening openings.

The compressor includes a casing28formed from half-shells joined by means of axial flanges extending radially. It also has several groups of vanes30, the combination of which forms a closed circle. Here, the half-shell supports three groups of vanes30, six groups distributed around the axis of rotation14can form a closed loop. However, the circumference of the casing can be formed by four, eight, or any other number of groups. The outer shrouds36cover the entire circumference of the inner surface of the casing28.

The groups30have inner shroud segments42. These may be one-piece with their respective group, preferably integral with the vanes and the outer shroud of the associated group. They receive the annular seals which seal the sealing members of the rotor. These seals can be applied to the group30before or after they are mounted on the casing. The joining of the inner shroud segments forms at least one circle, preferably several circles. A group of vanes30can be achieved by additive manufacturing; powder-based for example. It is contemplated to produce a group by the lost wax casting process.

According to an alternative, the segments of inner shrouds are attached to the inner ends of the vanes of the groups.

FIG. 6represents a sectional view of the stator of the compressor according to a second embodiment of the present application. The section is made along the axis5-5plotted inFIG. 2. ThisFIG. 6reflects the numbering of the previous figures for the identical or similar elements, although the numbering is incremented from 100. Specific numbers are used for elements specific to this embodiment.

The compressor has a mixed configuration in that it has groups of vanes130secured in a group to the casing128, and vanes152secured in an individual manner. The separate vanes152can each comprise individual platforms154with attachment pins156. According to an option, the vanes152may be combined into rows of vane sub-groups. These sub-groups can contain a single row of vanes. The vanes, that is to say the radial parts passing through the primary flow, of the separated vanes152can be similar to the vanes126of groups130.

Segments of attached internal shrouds160can be secured to the inner ends of the separated vanes152outside the groups of vanes130. These attached internal shrouds160can be secured to the inner shrouds142of the groups130. Such a composite assembly increases the stiffness of the assembly owing to the groups130, which can be metallic, and the lightness by inserting attached inner shrouds160made of composite material.

The foregoing description is described in relation to a casing. However, the groups of vanes can be adapted to any part of a turbomachine, including a turbine. The shapes of the vanes can be re-engineered; the use of Inconel type metals or ceramic materials is possible.