EP4127408A1

EP4127408A1 - Intermediate casing for a turbomachine

Info

Publication number: EP4127408A1
Application number: EP21723322.0A
Authority: EP
Inventors: Paul Antoine FORESTO
Original assignee: Safran Aircraft Engines SAS
Current assignee: Safran Aircraft Engines SAS
Priority date: 2020-04-01
Filing date: 2021-04-01
Publication date: 2023-02-08
Anticipated expiration: 2041-04-01
Also published as: US20230220786A1; WO2021198624A1; EP4127408B1; FR3108937B1; FR3108937A1; CN115485454A

Abstract

The invention relates to an intermediate casing (1) for a turbomachine, comprising: o an inner wall (3) having an outer radial surface (30), o an outer wall (4) having an inner radial surface (40), and o a first arm (21), a second arm (22), a third arm (23), and a fourth arm (24), and - wherein: o the outer radial surface (30), the inner radial surface (40), the first arm (21) and the second arm (22) define a first space (6) therebetween having a first area (A1) in a first section plane (P1), o the outer radial surface (30) and the inner radial surface (40) are separated, in the first space (6) and in the first section plane (P1), by a radial distance from the first space (D1), o the outer radial surface (30), the inner radial surface (40), the third arm (23) and the fourth arm (24) define a second space (7) therebetween having a second area (A2) in the first section plane (P1), o the outer radial surface (30) and the inner radial surface (40) are separated, in the second space (7) and in the first section plane (P1), by a radial distance from the second space (D2), the intermediate casing (1) being characterised in that: - the first area (A1) and the second area (A2) are substantially identical, and - the radial distance from the first space (D1) and the radial distance from the second space (D2) are different.

Description

TURBOMACHINE INTERMEDIATE CASING

FIELD OF THE INVENTION

The invention relates to an intermediate casing of a turbomachine.

The invention relates more specifically to the profile of the radial surfaces of the walls of a turbomachine intermediate casing, and to a method of manufacturing a turbomachine intermediate casing.

STATE OF THE ART

Referring to Figures 1 to 3, an intermediate casing 1 known from the prior art is a structural part of a turbomachine, interposed between two rotors (not shown) of the turbomachine, said rotors being configured to be rotated at different speeds . Typically, an intermediate casing generally extends between the low pressure compressor and the high pressure compressor of a double-barrel, double-flow, direct-drive turbomachine. In a triple-barrel turbomachine or in a geared turbomachine, an intermediate casing generally extends between the fan and the low-pressure compressor.

In any case, the intermediate housing 1 slows down the air flow between the two rotors. To do this, as visible in Figures 1 and 2, it generally has a gooseneck structure ("gooseneck" or "swanneck" in English terminology), in which the passage section of the flow of air entering the intermediate casing 1 is smaller than the passage cross section of the air flow leaving the intermediate casing.

In addition, the intermediate casing 1 comprises a plurality of arms 2 extending between the inner radial wall 3 and the outer radial wall 4 of the intermediate casing 1, and having an aerodynamic profile. The arms 2 make it possible to transfer forces to the structural and stator parts of the turbomachine, typically from the bearings of the low pressure shaft to the fan casing (not shown). In addition, the arms 2 form an aerodynamic fairing for the passage of easements 5 (e.g. drain, mechanical drive shaft of the compressor, rotation sensor) extending between the internal radial part and the external radial part of the turbomachine.

However, the easements 5 do not all have the same size. Consequently, as particularly visible in FIG. 3, the arms 2 of the intermediate casing 1 do not all have the same thickness. Furthermore, the position of the maximum thickness, the along the chord of the aerodynamic profile, may also differ from one arm 2 to another. This position can moreover be determined during design in order to reduce the pressure losses induced by the arms 2 or to limit the distortion induced on one of the rotors.

Finally, the shape of the internal radial wall 3 and of the external radial wall 4 is identical, and symmetrical, over the entire intermediate casing 1. In fact, as can be seen in FIG. 3, the walls 3, 4 are generally designed in cross section. circular.

However, the heterogeneity of the aerodynamic profiles of the arms 2, in terms of maximum thickness and position of this maximum thickness, results in heterogeneity of the passage sections for the air flow between the different arms 2 of the intermediate casing 1. Thus, in FIG. 3, a first section has an area A1 greater than a second section, itself having an area A2 greater than the area A3 of a third section. However, such heterogeneities are detrimental to the aerodynamic quality of the air flow through the intermediate casing 1, in particular with regard to pressure losses.

The current design of the walls 3, 4 of the intermediate casing 1 is insufficient in this regard. In fact, it only makes it possible to control the slowing down of the air flow at the level of arms 2, the maximum thickness of which is close to the average of the maximum thicknesses. To do this, it provides for uniformly hollowing out the outer wall 4 of the intermediate casing 1, equidistant from the leading edges and the trailing edges of the arms 2, so as to avoid re-acceleration of the flow. The depth of this digging systematically depends on the average of the maximum thicknesses of the arms. Thus, the radius of the circular section of the walls 3, 4 depends on an average maximum thickness of the arms 2 of the intermediate casing 1.

But such a design does not take into account the arms 2 whose maximum thickness is far from the average of the maximum thicknesses. As a result, the flow is not controlled throughout the entire intermediate case 1.

There is therefore a need to overcome at least one of the drawbacks of the prior art described above.

DISCLOSURE OF THE INVENTION

One of the aims of the invention is to improve the aerodynamic behavior of the flow within an intermediate casing.

Another object of the invention is to improve the specific consumption of a turbomachine. Another object of the invention is to improve the operability of a rotor disposed downstream of an intermediate casing.

In this regard, the subject of the invention is an intermediate turbomachine casing, said intermediate casing: having a longitudinal axis, comprising: o an internal wall having an external radial surface with respect to the longitudinal axis, o an external wall having a inner radial surface with respect to the longitudinal axis, facing the outer radial surface, and o a first arm, a second arm, a third arm, and a fourth arm extending radially from the outer radial surface to the internal radial surface, and in which: the external radial surface, the internal radial surface, the first arm and the second arm define between them a first space having a first area in a first section plane of said intermediate casing, perpendicular to the longitudinal axis, where the outer radial surface and the inner radial surface are separated, in the first space and in the first section plane, by a radial distance of first space e, with respect to the longitudinal axis, o the outer radial surface, the inner radial surface, the third arm and the fourth arm define between them a second space having a second area in the first section plane, o the outer radial surface and the internal radial surface are separated, in the second space and in the first section plane, by a radial distance of second space, with respect to the longitudinal axis, the intermediate casing being characterized in that the internal radial surface and / or the outer radial surface have, in the first section plane, profiles adapted so that: the first area and the second area are substantially identical, and the radial distance of the first space and the radial distance of the second space are different.

In such an intermediate casing, each inter-arm surface has a profile adapted to the thickness of the adjacent arms, so that the flow is uniformly slowed down through the entire intermediate casing. This results in homogeneity in the aerodynamic behavior of the flow through the intermediate housing, which improves operability. of a rotor arranged downstream of the intermediate casing and, from there, the specific consumption of the turbomachine.

Advantageously, but optionally, the intermediate casing according to the invention can also include at least one of the following characteristics, taken alone or in combination:

^* in such an intermediate casing: the first arm, the second arm, the third arm, and the fourth arm each have: o a plurality of thicknesses along the longitudinal axis, and o a maximum thickness among said plurality of thicknesses, the first cutting plane passes through: o the first arm and the second arm at the level of a respective maximum thickness of the first arm and of the second arm, and / or o the third arm and the fourth arm at the level of a respective maximum thickness of the third arm and of the fourth arm,

^* in such an intermediate casing: the first space has a third area in a second section plane of said intermediate housing, perpendicular to the longitudinal axis, and offset from the first section plane along the longitudinal axis, the second space has a fourth area in the second section plane, the third area and the fourth area are substantially identical, and the inner radial surface and the outer radial surface have, in the second section plane, circular profiles,

^* the profile of the internal radial surface has, in the first section plane, an additional concavity compared to a circular profile,

^* the profile of the external radial surface has, in the first section plane, an additional concavity compared to a circular profile,

^* the second arm and the third arm are combined.

The subject of the invention is also a turbomachine comprising a turbomachine casing as described above.

Finally, a subject of the invention is a method of manufacturing an intermediate casing for a turbomachine, said intermediate casing: having a longitudinal axis, comprising: o an inner wall having an outer radial surface relative to the longitudinal axis, o an outer wall having an inner radial surface relative to the longitudinal axis, facing the outer radial surface, and o a first arm, a second arm, a third arm, and a fourth arm extending radially from the outer radial surface to the inner radial surface, and in which: the outer radial surface, the inner radial surface, the first arm and the second arms define between them a first space having a first area in a first section plane of said intermediate casing, perpendicular to the longitudinal axis, where the outer radial surface and the inner radial surface are separated, in the first space and in the first plane cutting, by a radial distance of first space, relative to the longitudinal axis, o the radial outer surface, the radial inner surface, the third arm and the fourth arm defined ssent between them a second space having a second area in the first section plane, where the external radial surface and the internal radial surface are separated, in the second space and in the first section plane, by a radial distance of second space, relative to the longitudinal axis, the manufacturing process being characterized in that it comprises a step of profiling the internal radial surface and / or the external radial surface so that, in the first section plane: the first area and the second area are substantially the same, and the radial distance of the first space and the radial distance of the second space are different.

Advantageously, but optionally, the manufacturing process according to the invention can further include at least one of the following characteristics, taken alone or in combination:

^* the first arm, the second arm, the third arm, and the fourth arm of the intermediate casing each have: o a plurality of thicknesses along the longitudinal axis, and o a maximum thickness among said plurality of thicknesses, the method further comprising the steps of: performing a first digging in the outer wall and / or in the inner wall, so that the outer radial surface and the inner radial surface are separated, in the first space and in the first section plane, by: o a first radial distance of first space, with respect to the longitudinal axis, the first radial distance of first space extending from a point of the external radial surface and / or of the internal radial surface outside the first hollow, and o a second radial distance of first space, with respect to the longitudinal axis, the second radial distance of first space extending from a point of the outer radial surface and / or the inner radial surface in the first recess, such that the distance between the first radial distance of first space and the second radial distance of first space is a increasing function of the difference between: o the maximum thickness of the first arm and / or the second arm, and o the average of the respective maximum thicknesses of the first arm, the second arm, the third arm and the fourth arm as, and practice of a second digging in the outer wall and / or in the inner wall, so that the outer radial surface and the inner radial surface are separated, in the second space and in the first section plane, by: o a first radial distance of second space, relative to the longitudinal axis, the first radial distance of second space extending from a point on the external radial surface and / or from the internal radial surface outside the second excavation, and o a second radial distance from the second space, relative to the longitudinal axis, the second radial distance from the second space extending from a point on the external radial surface and / or from the internal radial surface passing through the second excavation, from so that the difference between the first radial distance of second space and the second radial distance of second space is an increasing function of the difference between: o the maximum thickness of the third arm and / or of the fourth arm, and o the mo yenne respective maximum thicknesses of the first arm, of the second arm, of the third arm and of the fourth arm, and ^* in such a process: the first digging is centered at a section plane passing through the first arm and the second arm at the level of the respective maximum thickness of the first arm and of the second arm, and the second digging is centered at a section plane passing through the third arm and the fourth arm at the level of the respective maximum thickness of the third arm and the fourth arm. DESCRIPTION OF FIGURES

Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and not limiting, and which should be read with reference to the accompanying drawings in which:

Figure 1, already described, is a perspective view of an intermediate casing known from the prior art.

Figure 2 is a longitudinal sectional view of the intermediate housing illustrated in Figure 1.

Figure 3 is another cross-sectional view perpendicular to the longitudinal axis of the intermediate housing shown in Figure 1.

FIG. 4 is a view in a first transverse sectional plane perpendicular to the longitudinal axis of a first embodiment of a turbomachine intermediate casing according to the invention.

Figure 5 is a circumferentially developed sectional view of a second embodiment of a turbomachine intermediate casing according to the invention,

FIG. 6 is a view in a second transverse sectional plane perpendicular to the longitudinal axis of a third embodiment of a turbomachine intermediate casing according to the invention.

FIG. 7 is a flowchart detailing the steps of a first example of implementation of a manufacturing process according to the invention.

FIG. 8 is a view in a first sectional plane of an intermediate casing produced with the aid of a second exemplary implementation of a manufacturing process according to the invention.

In all of the figures, similar elements bear identical references.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Intermediate casing

Referring to Figures 4 to 6, an intermediate casing 1 is a structural part of a turbomachine, interposed between two rotors (not shown) of the turbomachine, said rotors being configured to be rotated at different speeds. For example, the intermediate casing 1 can extend between a low pressure compressor and a high pressure compressor of a double-body, double-flow, direct-drive turbomachine. Alternatively, in a triple-barrel turbomachine or in a turbomachine with reducers, the intermediate housing 1 can extend between the fan and the low pressure compressor.

As visible in Figures 4 to 6, the intermediate casing 1 has a longitudinal axis X-X. The intermediate casing 1 further comprises:

- an inner wall 3 having an outer radial surface 30 relative to the longitudinal axis X-X,

- an outer wall 4 having an inner radial surface 40 relative to the longitudinal axis X-X, facing the outer radial surface 30, and

- a first arm 21, a second arm 22, a third arm 23, and a fourth arm 24 extending radially from the outer radial surface 30 to the inner radial surface 40.

The arms 21, 22, 23, 24 make it possible to transfer forces to structural and stator parts of the turbomachine (not shown), which are connected to the internal wall 3 and to the external wall 4. In addition, the arms 21 , 22, 23, 24 form an aerodynamic fairing for the passage of easements (not shown).

Furthermore, the intermediate casing 1 makes it possible to slow down an air flow which passes through it. To do this, it generally has a gooseneck structure (“gooseneck” or “swanneck” in English terminology), in which a section of passage of the air flow at the inlet of the intermediate casing 1 is smaller. that a section of passage for the air flow at the outlet of the intermediate casing 1. In addition, passages for the air flow are formed between the arms 21, 22, 23, 24. More precisely, the surface external radial 30, the internal radial surface 40, the first arm 21 and the second arm 22 define between them a first space 6, and the external radial surface 30, the internal radial surface 40, the third arm 23 and the fourth arm 24 define between them a second space 7.

In an advantageous embodiment, the second arm 22 and the third arm 23 are merged, so that the first space 6 and the second space 7 are adjacent in a circumferential direction around the longitudinal axis X-X.

In a first section plane P1 of the intermediate casing 1, perpendicular to the longitudinal axis XX, the first space 6 has a first area A1, and the second space 7 has a second area A2. This is particularly visible in Figure 4, which is a view of the intermediate casing 1 in the first section plane P1. In addition, the outer radial surface 30 and the inner radial surface 40 are separated, in the first space 6 and in the first section plane P1, by a radial distance from the first space D1, while the outer radial surface 30 and the surface internal radial 40 are separated, in the second space 7 and in the first section plane P1, by a radial distance from the second space D2. The concept of “radial” is here defined with respect to the longitudinal axis XX.

In addition, as can be seen in FIG. 4, the internal radial surface 30 and / or the external radial surface 40 have, in the first section plane P1, profiles adapted so that:

- the first area A1 and the second area A2 are substantially identical, and

the radial distance of the first space D1 and the radial distance of the second space D2 are different.

In this way, despite the difference in thicknesses of the arms 21, 22, 23, 24, the flow passage section within the intermediate casing 1 is identical throughout said intermediate casing 1, at least at the level of the first plane. cutting P1, which allows greater control of the slowing down of the flow flowing through the intermediate casing 1. Advantageously, only one of the two radial surfaces 30, 40, for example the internal radial surface 40, as visible in Figure 4, shows different inter-arm profiles around the longitudinal axis XX, and is dimensioned so that its profile is adapted to the different geometries of the arms 21, 22, 23, 24. Indeed, it s 'is an intermediate casing element 1 easy to design and / or to profile during the manufacture and / or maintenance of the turbomachine. In addition, this simplifies the manufacture of the intermediate casing 1, while making it possible to achieve the desired effect of homogenizing the flow.

In any event, as can be seen in FIG. 4, the thicker an arm 21, 22, 23, 24, the greater the radial distance D1 taken close to this arm 21, 22, 23, 24, and vice versa. More precisely, the loss of circumferential space caused by the size of an arm 21, 22, 23, 24, is compensated for by the radial profiling of the radial surfaces 30, 40, of the walls 3, 4 sufficiently close to said arm 21, 22 , 23, 24.

In one embodiment illustrated in FIG. 4, the profile of the internal radial surface 40 (illustrated in solid lines) has, in the first section plane P1, an additional concavity 401, 402, 403, 404 with respect to a profile circular (shown in dotted lines). This concavity 401, 402, 403, 404 forms a hollow, the depth of which depends on the thickness of the arm 21, 22, 23, 24 closest to said hollow. The greater the thickness of the arm 21, 22, 23, 24 compared to the average thickness of the arms 21, 22, 23, 24, the deeper the concavity 401, 402, 403, 404. Conversely, if the thickness of the arm 21, 22, 23, 24 is small compared to the average of the thicknesses of the arms 21, 22, 23, 24, the concavity 401, 402, 403, 404 is then opposed to the circular concavity, as visible in Figure 4. Advantageously, the profile of the outer wall 40 comprises several additional concavities 401, 402, 403, 404 relative to a circular profile, for example concavities 401, 402 of the same orientation, and deeper than the profile. circular, and concavities 403, 404 of orientation opposite to the circular profile. This is not, however, limiting since, in another embodiment, alternately or in combination, the profile of the outer radial wall 30 has, in the first section plane, an additional concavity 401, 402, 403, 404 relative to to a circular profile.

Referring to Figure 5, which is an unfolded view of the intermediate casing 1 in a circumferential three-dimensional surface of circular section, taken around the longitudinal axis XX, each of the arms 21, 22, 23, 24 has a plurality of thicknesses e1, e2, e3, e4 along the longitudinal axis XX. More precisely, each arm 21, 22, 23, 24 has a chord C1, C2, C3, C4 connecting a leading edge 210, 220, 230, 240 to a trailing edge 212, 222, 232, 242 of a aerodynamic profile of said arm 21, 22, 23, 24, in a plane substantially parallel to the average flow within the intermediate casing 1. Each thickness e1, e2, e3, e4 is therefore taken perpendicular to the chord C1, C2, C3 , C4, along the longitudinal axis XX, between a lower surface 211, 221, 231, 241 and an upper surface 213, 223, 233, 243 of the aerodynamic profile of the arm 21, 22, 23, 24. Among the plurality of thicknesses e1, e2, e3, e4, there is a maximum thickness em1, em2, em3, em4 whose position along the chord C1, C2, C3, C4 can be different from an arm 21, 22, 23, 24 to the other, as can be seen in FIG. 5. Now, in an advantageous embodiment of the intermediate casing, profiling of the walls 30, 40 as described above is carried out in the inter-arm space, at the level of the thick maximum urs em1, em2, em3, em4 respective arms 21, 22, 23, 24. In other words, the first section plane P1 previously described passes through:

- the first arm 21 and the second arm 22 at the level of a respective maximum thickness em1, em2 of the first arm 21 and of the second arm 22, and / or

- the third arm 23 and the fourth arm 24 at the level of a maximum thickness em3, em4 respectively of the third arm 23 and of the fourth arm 24.

Indeed, it is at the level of the maximum thickness em1, em2, em3, em4 of the arms 21, 22, 23, 24 that the reduction in the passage section of the flow is greatest. It is therefore at this level that it is most advantageous to profile the radial surfaces 30, 40 of the walls 3, 4 so as to ensure that the area A1, A2 of the first passage 6 and of the second passage 7 are identical, by modifying the radial distance D1, D2 separating the walls from one another.

Referring to Figures 5 and 6, in a second section plane P2 of the intermediate casing 1, perpendicular to the longitudinal axis XX, and offset from the first section plane P1 along the longitudinal axis XX, the first space 6 has a third area A3, and the second space 7 has a fourth area A4. In one embodiment, the third area A3 and the fourth area A4 are substantially identical, and the internal radial surface 30 as well as the external radial surface 40 have, in the second section plane P2, circular profiles. Indeed, as visible in Figure 5, it is not necessary to modify the profile of the radial surfaces 30, 40 of the walls 3, 4 over the entire length of the arms 21, 22, 23, 24, along the longitudinal axis XX. Indeed, the aerodynamic profiles of the arms 21, 22, 23, 24 are substantially identical at positions sufficiently far from the respective maximum thicknesses em1, em2, em3, em4 of the arms 21, 22, 23, 24, along the axis longitudinal XX. Consequently, the flow is homogeneous and uniform as the second section plane P2 passes, without it being necessary to modify the profile of the radial surfaces 30, 40 of the walls 3, 4.

Manufacturing process

Referring to Figures 7 and 8, a manufacturing process E of a turbomachine intermediate casing 1 will now be described.

The intermediate casing 1 has a longitudinal axis X-X, and further comprises:

Furthermore, the external radial surface 30, the internal radial surface 40, the first arm 21 and the second arm 22 define between them a first space 6, and the external radial surface 30, the internal radial surface 40, the third arm 23 and the fourth arm 24 define between them a second space 7. And, in a first section plane P1 of the intermediate casing 1, perpendicular to the longitudinal axis XX, the first space 6 has a first area A1, and the second space 7 has a second area A2. In addition, the outer radial surface 30 and the inner radial surface 40 are separated, in the first space 6 and in the first section plane P1, by a radial distance from the first space D1, while the outer radial surface 30 and the surface internal radial 40 are separated, in the second space 7 and in the first section plane P1, by a radial distance from the second space D2. In addition, each of the arms 21, 22, 23, 24 has a plurality of thicknesses along the longitudinal axis XX. More precisely, each arm 21, 22, 23, 24 has a chord connecting a leading edge to a trailing edge of an aerodynamic profile of said arm 21, 22, 23, 24, in a plane substantially parallel to the flow means within the intermediate casing 1. Each thickness is therefore taken perpendicular to the chord along the longitudinal axis XX, between an intrados and an extrados of the aerodynamic profile of the arm 21, 22, 23, 24. Among the plurality of thicknesses, there is a maximum thickness em1, em2, em3, em4, the position of which along the rope may be different from one arm 21, 22, 23, 24 to the other.

As visible in FIG. 7, the method E comprises a profiling step E1 of the internal radial surface 30 and / or the external radial surface 40 so that, in the first section plane P1:

- the first area A1 and the second area A2 are substantially identical, and

This profiling provides the intermediate casing 1 with the same advantages as those described above. Indeed, an air flow circulating through an intermediate casing 1 produced using such a manufacturing process E, exhibits a limited number of Mach number heterogeneities around the longitudinal axis X-X. In fact, the intermediate casing 1 no longer exhibits cross-section size disparities from one inter-arm flow channel to the other. The Mach number then decreases uniformly along the longitudinal axis X-X, at the level of the internal wall 3 and / or the external wall 4, regardless of the inter-arm flow channel considered.

As also visible in FIG. 6, in one embodiment, the manufacturing method E further comprises the steps of performing E2 of a first digging 401 and of performing E3 of a second digging 402 in the internal wall 3 and / or the outer wall 4 of the intermediate casing 1. More precisely, the first digging 401 is then carried out so that the external radial surface 30 and the internal radial surface 40 are separated, in the first space 6 and in the first section plane P1, by:

a first radial distance from the first space D11, relative to the longitudinal axis XX, the first radial distance from the first space D11 extending from a point on the external radial surface 30 and / or from the internal radial surface 40 outside of the first 401 digging, and

a second radial distance from the first space D12, relative to the longitudinal axis XX, the second radial distance from the first space D12 extending from a point on the external radial surface 30 and / or from the internal radial surface 40 in the first dig 401.

Furthermore, these radial distances D11, D12 are made such that the deviation between the first radial distance of first space D11 and the second radial distance of first space D12 is an increasing function of the deviation between:

- the maximum thickness em1, em2 of the first arm 21 and / or of the second arm 22, and the average of the respective maximum thicknesses em1, em2, em3, em4 of the first arm 21, of the second arm 22, of the third arm 23 and of the fourth arm 24.

Likewise, the second hollowing 402 is made so that the outer radial surface 30 and the inner radial surface 40 are separated, in the second space 7 and in the first section plane P1, by:

- a first radial distance of second space D21, relative to the longitudinal axis XX, the first radial distance of second space D21 extending from a point on the external radial surface 30 and / or from the internal radial surface 40 outside of the second excavation 402, and

a second radial distance from second space D22, relative to the longitudinal axis XX, the second radial distance from second space D22 extending from a point on the external radial surface 30 and / or from the internal radial surface 40 passing through the second dig 402.

Furthermore, these radial distances D21, D22 are made so that the difference between the first radial distance of second space D21 and the second radial distance of second space D22 is an increasing function of the difference between:

- the maximum thickness em3, em4 of the third arm 23 and / or the fourth arm 24, and

the average of the respective maximum thicknesses em1, em2, em3, em4 of the first arm 21, of the second arm 22, of the third arm 23 and of the fourth arm 24.

Thanks to these digging steps E2, E3, an intermediate casing 1 such as that illustrated in FIGS. 4 or 8 can be obtained. In these figures, the dotted lines represent a circular profile of internal radial surface 40, in the first section plane P1. The radius R of this profile depends on the average of the maximum thicknesses em1, em2, em3, em4 of the arms 21, 22, 23, 24 of the intermediate casing 1. More precisely, this radius R is determined so that, if the arms 21, 22, 23, 24 all had the same maximum thickness em1, em2, em3, em4 equal to the average of the maximum thicknesses em1, em2, em3, em4, then this circular profile of the internal radial surface would ensure that the Mach number decreases uniformly along the longitudinal axis XX, at the level of the internal wall and / or of the external wall 4, regardless of the channel d inter-arm flow considered. The solid line represents, for its part, the profile of the internal radial wall 40 obtained following the digging steps E2, E3 described above. As can be seen in these figures, the smaller the difference between the maximum thickness em1, em2, em3, em4 of an arm 21, 22, 23, 24 and the average of the maximum thicknesses em1, em2, em3, em4, or even negative if the maximum thickness of the arm em1, em2, em3, em4 is less than the average of the maximum thicknesses em1, em2, em3, em4, the smaller the radial distance of space D1, D2. Conversely, the greater the difference between the maximum thickness of an arm em1, em2, em3, em4 and the average of the maximum thicknesses em1, em2, em3, em4, the greater the radial distance of space D1, D2. . The profile of the internal radial surface 40 obtained is therefore non-symmetrical and has a plurality of additional concavities 401, 402, 403, 404 with respect to a circular profile. It should be noted that the profile of the outer radial wall 30 could be modified according to the same design logic, and with the same effects. However, it must be taken into account that the air flow speeds are different near the internal radial surface 40 and the external radial surface 30. In addition, the aerodynamic friction can be specific, in particular because of the shape in gooseneck. The depth of the recesses in the external radial surface 30 is therefore adapted accordingly.

In one embodiment, as visible in FIG. 5, the previously described recesses 401, 402 can be made so that:

- the first hollowing 401 is centered at a section plane P1 passing through the first arm 21 and the second arm 22 at the level of the maximum thickness em1, em2 respectively of the first arm 21 and of the second arm 22, and

- The second excavation 402 is centered at a section plane P1 passing through the third arm 23 and the fourth arm 24 at the level of the respective maximum thickness em3, em4 of the third arm 23 and the fourth arm 24.

It is then possible to obtain an intermediate casing 1 such as that illustrated in FIG. 5. As visible in this figure, the recesses 401, 402 are made on either side of a line connecting the positions of the maximum thicknesses em1, em2, em3, em4 of the arms 21, 22, 23,24 along the longitudinal axis XX. Advantageously, the recesses 401, 402 are made in a substantially rectangular zone of the internal radial surface 30 and / or of the external radial surface 40, as visible in FIG. 5. Even more advantageously, this rectangular zone has a width equal to about 10% of the chord C1, C2, C3, C4 of an adjacent arm 21, 22, 2324, taken in a plane substantially parallel to the average flow within the intermediate casing 1. In this way, the manufacturing process E implies a limited modification of the walls 3, 4 of the intermediate casing 1. In addition, the position of the recesses 401, 402 is optimized as a function of the position of the maximum thicknesses em1, em2, em3, em4, along the longitudinal axis XX.

Claims

1. Intermediate casing (1) of a turbomachine, said intermediate casing (1): having a longitudinal axis (XX), comprising: o an internal wall (3) having an external radial surface (30) relative to the longitudinal axis (XX) , o an outer wall (4) having an inner radial surface (40) relative to the longitudinal axis (XX), facing the outer radial surface (30), and o a first arm (21), a second arm (22), a third arm (23), and a fourth arm (24) extending radially from the outer radial surface (30) to the inner radial surface (40), and in which: o the outer radial surface (30), the internal radial surface (40), the first arm (21) and the second arm (22) define between them a first space (6) having a first area (A1) in a first section plane (P1) of said intermediate casing (1), perpendicular to the longitudinal axis (XX), o the outer radial surface (30) and the inner radial surface (40) are separated, in the first space (6) and in the first section plane (P1), by a radial distance from the first space (D1), with respect to the longitudinal axis (XX), o the external radial surface (30), the surface radial internal (40), the third arm (23) and the fourth arm (24) define between them a second space (7) having a second area (A2) in the first section plane (P1), o the external radial surface (30) and the internal radial surface (40) are separated, in the second space (7) and in the first section plane (P1), by a radial distance of second space (D2), with respect to the longitudinal axis (XX), the intermediate casing (1) being characterized in that the internal radial surface (40) and / or the external radial surface (30) have, in the first section plane (P1), profiles adapted so that : the first area (A1) and the second area (A2) are substantially identical, and the radial distance of first space (D1) and the radial distance of second space (D2) are different.

2. Intermediate casing (1) according to claim 1, wherein: the first arm (21), the second arm (22), the third arm (23), and the fourth arm (24) each have:

O a plurality of thicknesses (e1, e2, e3, e4) along the longitudinal axis (XX), and o a maximum thickness (em1, em2, em3, em4) among said plurality of thicknesses (e1, e2, e3, e4), the first section plane (P1) passes through: o the first arm (21) and the second arm (22) at the level of a respective maximum thickness (em1, em2) of the first arm (21) and of the second arm (22), and / or o the third arm (23) and the fourth arm (24) at the level of a respective maximum thickness (em3, em4) of the third arm (23) and of the fourth arm (24).

3. Intermediate casing (1) according to one of claims 1 and 2, wherein: the first space (6) has a third area (A3) in a second section plane (P2) of said intermediate casing (1), perpendicular to the longitudinal axis (XX), and offset from the first section plane (P1) along the longitudinal axis (XX), the second space (7) has a fourth area (A4) in the second plane of section (P2), the third area (A3) and the fourth area (A4) are substantially identical, and the internal radial surface (40) and the external radial surface (30) have, in the second section plane (P2), circular profiles.

4. Intermediate casing (1) according to one of claims 1 to 3, wherein the profile of the internal radial surface (40) has, in the first section plane (P), an additional concavity (401, 402, 403 , 404) with respect to a circular profile.

5. Intermediate casing (1) according to one of claims 1 to 4, wherein the profile of the outer radial surface (30) has, in the first section plane (P1), an additional concavity (401, 402, 403 , 404) with respect to a circular profile.

6. Intermediate casing (1) according to one of claims 1 to 5, wherein the second arm (22) and the third arm (23) are merged.

7. Turbomachine comprising an intermediate casing (1) according to one of claims 1 to 6.

8. A method of manufacturing (E) an intermediate casing (1) of a turbomachine, said intermediate casing (1): having a longitudinal axis (XX), comprising: o an inner wall (3) having an outer radial surface (30) relative to the longitudinal axis (XX), o an outer wall (4) having an inner radial surface (40) relative to the longitudinal axis (XX) ), facing the outer radial surface (30), and o a first arm (21), a second arm (22), a third arm (23), and a fourth arm (24) extending radially from the surface external radial (30) to the internal radial surface (40), and in which: o the external radial surface (30), the internal radial surface (40), the first arm (21) and the second arm (22) define between them a first space (6) having a first area (A1) in a first sectional plane (P1) of said intermediate casing (1), perpendicular to the longitudinal axis (XX), o the external radial surface (30) and the internal radial surface (40) are separated, in the first space (6) and in the first section plane (P1), by a radial distance of first space (D1), with respect to the axis e longitudinal (XX), o the outer radial surface (30), the inner radial surface (40), the third arm (23) and the fourth arm (24) define between them a second space (7) having a second area ( A2) in the first section plane (P1), where the external radial surface (30) and the internal radial surface (40) are separated, in the second space (7) and in the first section plane (P1), by a radial distance of second space (D2), relative to the longitudinal axis (XX), the manufacturing process (E) being characterized in that it comprises a profiling step (E1) of the internal radial surface (40) ) and / or of the outer radial surface (30) so that, in the first section plane (P1): the first area (A1) and the second area (A2) are substantially identical, and the radial distance of the first space (D1) and the radial distance of second space (D2) are different.

9. A method of manufacturing (E) an intermediate casing (1) according to claim 8, wherein the first arm (21), the second arm (22), the third arm (23), and the fourth arm (24) ) of the intermediate casing (1) each have: o a plurality of thicknesses (e1, e2, e3, e4) along the longitudinal axis (XX), and o a maximum thickness (em1, em2, em3, em4) among said plurality of thicknesses (e1, e2, e3, e4), the method (E) further comprising the step of: performing (E2) a first digging (401) in the outer wall (4) and / or in the inner wall (3), so that the outer radial surface (30) and the inner radial surface (40) are separated, in the first space (6) and in the first section plane (P1), by: o a first radial distance of first space (D11), with respect to the longitudinal axis (XX), the first radial distance of first space (D11) extending from a point of the outer radial surface (30) and / or the surface internal radial (40) outside the first recess (401), and o a second radial distance of first space (D12), relative to the longitudinal axis (XX), the second radial distance of first space (D12) s' extending from a point of the outer radial surface (30) and / or the inner radial surface (40) in the first recess (401), so that the gap between the first radial distance of first space (D11) and the second radial distance of first space (D12) is an increasing function of the difference between: o the maximum thickness (em1, em2) of the first arm (21) and / or of the second arm (22), and o the average of the respective maximum thicknesses (em1, em2, em3, em4) of the first arm (21), of the second arm (22), of the third arm (23) and of the fourth arm (24) , and practice (E3) of a second hollowing (402) in the outer wall (4) and / or in the inner wall (3), so that the outer radial surface (30) and the inner radial surface (40) are separated, in the second space (7) and in the first section plane (P1), by: o a first radial distance of second space (D21), with respect to the longitudinal axis (XX), the first radial distance of second space (D21) extending from a point of the external radial surface (30) and / or of the internal radial surface (40) outside the second recess (402), and o a second radial distance of second space ( D22), with respect to the longitudinal axis (XX), the second radial distance of second space (D22) extending from a point of the outer radial surface (30) and / or the inner radial surface (40 ) passing through the second excavation (402), so that the difference between the first radial distance of second space (D21) and the second radial distance of second space (D22) is an increasing function of the difference between: o l 'maximum thickness (em3, em4) of the third arm (23) and / or of the fourth arm (24), and o the average of the respective maximum thicknesses (em1, em2, em3, em4) of the first arm (21), of the second arm (22), third arm (23) and fourth arm (24).

10. The manufacturing method (E) according to claim 9, wherein: the first hollow (401) is centered at a section plane (P1) passing through the first arm (21) and the second arm (22) at the level of the respective maximum thickness (em1, em2) of the first arm (21) and of the second arm (22), and the second hollow (402) is centered at level of a section plane (P1) passing through the third arm (23) and the fourth arm (24) at the level of the respective maximum thickness (em3, em4) of the third arm (23) and of the fourth arm (24) ).