TURBINE ANNULAR SHELL

Abstract

ANNULAR TURBINE SHELL One aspect of the invention relates to an annular turbine shroud (3) for a turbomachine, the shroud (3) extending along a longitudinal axis A and comprising: an annular base (11) with a longitudinal axis A; mounting elements (12) distributed circumferentially around the periphery of the base; an annular portion (13) extending axially and projecting from the base; a plurality of legs (14) distributed circumferentially on an inner surface of the shroud and spaced apart from each other so that a non-zero clearance exists between two consecutive legs; and an annular branch (15) extending radially and projecting from the base towards the longitudinal axis A. Figure to be published with the abstract: Figure 3

Description

Title of the invention: ANNULAR TURBINE SHELL TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of turbine shrouds for turbomachines such as a turbojet for aircraft.

[0002] The present invention relates to a ferrule comprising legs for improving the mechanical strength of the ferrule. The invention also relates to an assembly comprising this ferrule mounted in connection with turbine distributors. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Conventionally, a turbine shroud is a circular part, of large diameter, whose role is to ensure the positioning and maintenance of the distributors in a vein of the turbine. In [Fig.l], an example of a shroud 10 according to the prior art, mounted in the turbine of a turbomachine, is illustrated. The shroud 10 is a part mounted at the interface of numerous components of the turbine and which must satisfy a large number of functions linked to these components. The shroud 10 is in particular mounted at the interface of the distributors 20 of the turbine.

[0004] One of the functions of the ferrule 10 is to allow the centering of a low-pressure turbine on a high-pressure turbine. The ferrule 10 satisfies very precise assembly constraints and meets the mechanical strength requirements by supporting the forces transmitted between the different casings of the turbine.

[0005] Another function of the ferrule 10 is to ensure the axial stopping of the distributors 20.

[0006] Yet another function of the ferrule 10 is to allow a flow of cold air to pass through in order to supply fresh air to the hooks 30 of a turbine casing 40 which is in contact with the hooks 30' of a sealing sector 90. Indeed, in operation, two air flows 41, 51 pass over the shell 10. A cold air flow 41 coming from the inter-turbine casing 40', and a hot air flow 51 coming from a vein 50. At the time of takeoff, the shell 10 is in contact, on the one hand, with the cold air flow 41 with a temperature of approximately 400° and, on the other hand, with the hot air flow 51 with a temperature of approximately 900°. Currently, these two air flows are physically separated by the foot 70 of the shell 10 and a seal 60 positioned between the shell 10 and the distributor 20. The temperature difference between these two air flows imposes a high thermal gradient on the shell 10. The thermal constraints are such that current materials cannot withstand this environment for long.Indeed, under the effect of the thermal gradient, the ferrule 10 tends to compress on itself, which will cause local plasticization of the material, causing cracks to appear. These cracks are fissures which could propagate and end up joining, then being able to release a piece of the ferrule 10 into the vein 50.

[0007] An example of a foot having a crack is shown in [Fig. 2]. In this example, the crack 80 is located at the leg 71 of the foot 70 of the shell 10 which is the hottest zone of the shell 10. The initiation of the crack 80 generally occurs at the rear of the shell 10, in an angular zone 72 of the foot 70 of the shell 10, because this zone is in contact with the hot air flow 51 of the vein 50. The propagation of the crack 80 then generally occurs upstream of the shell 10, then goes back up towards the end 73 of the foot 70.

[0008] To solve this problem, it has been considered to reduce the temperature gradient to which the foot is subjected by cooling the shell, for example using a cooling device as described in patent document FR3000985. In this configuration, the shell is not in contact with the hot air flow because it is protected by the distributor. However, this solution is difficult to implement because it would require too significant a modification of the turbine and the parts of the turbine as illustrated in [Fig.l].

[0009] There is therefore a real need for an easy-to-implement solution to improve the mechanical strength of the shell and limit the risk of cracking. Summary of the invention

[0010] The invention offers a solution to the problems mentioned above, by modifying the geometry of the legs of the ferrule so as to improve the mechanical strength of the ferrule and to limit the risk of cracks appearing on said ferrule.

[0011] A first aspect of the invention relates to an annular shell of a turbomachine turbine, the shell extending along a longitudinal axis A and comprising: • an annular base of longitudinal axis A; • mounting elements distributed circumferentially around the perimeter of the base; • an annular portion extending axially projecting from the base; the ferrule further comprising: • a plurality of legs distributed circumferentially on an inner surface of the ferrule and spaced from each other so that a non-zero clearance exists between two adjacent legs; and • an annular branch extending radially in projection from the base towards the longitudinal axis A.

[0012] Thus, the invention makes it possible to reduce tangential stresses on the legs and reduce the risk of cracks appearing.

[0013] In addition to the characteristics which have just been mentioned in the preceding paragraph, the ferrule according to one aspect of the invention may have one or more additional characteristics among those mentioned in the following paragraphs, considered individually or in all technically possible combinations.

[0014] According to one embodiment, the legs extend substantially radially from the base towards the longitudinal axis A. Thus, the legs close the inter-distributor spaces present between two side-by-side distributors.

[0015] According to one embodiment, each leg is L-shaped with a tab extending towards the longitudinal axis A and a hook extending axially from one end of the tab. The L-shape of the leg fits with at least one distributor and partially encompasses a portion of said distributor.

[0016] According to one embodiment, the tab of each leg comprises a width greater than a height, the width being measured in a direction tangential to a diameter of the ferrule, the height being measured in a radial direction. Thus, the tab width, large compared to the height, makes it possible to reduce shape defects, in particular tangential stresses, and to minimize the quantity of material directly in contact with the air of the vein.

[0017] According to one embodiment, the hook comprises a hook tooth projecting radially from one end of said hook. Thus, the hook tooth will be in contact with a distributor of the turbomachine.

[0018] A second aspect of the invention relates to a turbine assembly comprising: • a ferrule, and • a plurality of turbine distributors, positioned annularly next to each other and each carrying a plurality of turbine blades, each leg being positioned at the junction between two distributors. The ferrule makes it possible to position the distributors and to lock them axially.

[0019] According to one embodiment, the annular branch of the ferrule is in contact with each distributor, the annular branch of the ferrule forming, with the consecutive distributors, a sealed partition between a vein of the turbine where a flow of hot air circulates and a space of the turbine where a flow of cold air circulates.

[0020] According to one embodiment, each distributor comprises a second radially projecting wall on an outer face of the distributor, the annular branch of the ferrule being in contact with the second walls of two consecutive distributors.

[0021] According to one embodiment, each distributor comprises a first wall projecting axially relative to a downstream face of the distributor, each attachment of the ferrule being in contact with the first walls of two consecutive distributors.

[0022] A third aspect of the invention relates to a turbomachine comprising at least one shell as defined above.

[0023] The invention and its various applications will be better understood upon reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0024] The figures are presented for information purposes only and in no way limit the invention.

[0025] [Fig.l], already described, is a schematic view, in longitudinal section, of a part of a low pressure turbine comprising a shell according to the prior art.

[0026] [Fig. 2], already described, is a schematic view, in longitudinal section, of a foot of a ferrule according to the prior art.

[0027] [Fig. 3] is a schematic view, in longitudinal section, of a part of a turbine comprising a shell according to the invention.

[0028] [Fig.4] is an enlarged view of the dotted portion of [Fig.3].

[0029] [Fig.5] is a perspective view of a portion of the ferrule according to the invention.

[0030] [Fig. 6] is a perspective view of a portion of the ferrule according to the invention. mounted on turbine distributors. DETAILED DESCRIPTION

[0031] In the figures, identical elements are identified by identical references. For reasons of readability of the figures, the size scales between elements represented are not respected.

[0032] In the present application, the terms "upstream" and "downstream" are defined relative to the direction of flow circulation in the turbine, along the axis of a turbine. The terms "internal" or "interior" and "external" or "exterior" are defined radially relative to the axis of rotation, or longitudinal axis, of the shell, an internal (or interior) surface being radially closer to the axis of rotation than an external (or exterior) surface.

[0033] An example of a shroud according to the invention, mounted in a turbine of a turbomachine, is shown in [Fig. 3]. In this example, the shroud 3 is shown in connection with an inter-turbine casing 8, better known by its English designation TCF for "Turbine Center Frame", and with a turbine casing 5 by means of a bolted connection 100. The turbine casing 5 comprises a casing hook 52 in connection with a sealing sector hook 91 of a sealing sector 9. The shroud 3 and the sealing sector 9 are both in contact with a seal 7. The shroud 3 is connected to several distributors 2, only one of which is shown in [Fig. 3]. As shown in [Fig. 6], the distributors 2 are positioned annularly next to each other and each carry turbine blades. The ferrule 3 allows the positioning of the distributors 2 as well as their axial stop.

[0034] The ferrule 3 is an annular element mounted around a longitudinal axis A corresponding to the axis of rotation of the turbine and shown solely for information purposes in [Fig. 3] (the longitudinal axis A normally being further away from the ferrule 3). The ferrule 3 comprises a ring of axis A forming a base 11. Mounting elements 12 extend from the base 11 in a radial direction and opposite to the axis A. With reference to [Fig.5], the mounting elements 12 are characterized by notches distributed circumferentially on an outer surface of the base 11. In the example of [Fig.5], the notches are flat, square in shape and are perforated in their middle in order to each receive an axis of the bolted connection 100. According to an alternative, the notches can be in the shape of a circle, a triangle or any other shape allowing a bolted connection 100.

[0035] The shell 3 comprises at least one opening 1 passing through the base 11 so as to allow a flow of cold air (at a temperature of approximately 400°C) to pass from the inter-turbine casing 8 and heading towards the casing hook 52 in order to cool it. The shell may comprise, for example, twenty-two openings 1 distributed circumferentially on the shell 3 relative to the axis A of the shell 3. In another cavity, a flow of hot air (at a temperature of approximately 900°C) coming from a vein 6 of the turbine circulates and licks the shell 3.

[0036] The ferrule 3 further comprises an annular portion 13 extending axially from the base 11, from downstream to upstream. This annular portion 13 is between the distributor 2 and the inter-turbine casing 8.

[0037] According to the invention, the ferrule 3 comprises a plurality of legs 14 distributed circumferentially on an inner surface of the ferrule 3, as shown in [Fig. 5]. For example, the ferrule 3 comprises twenty-two legs. As seen in [Fig. 3], where only one leg 14 is shown, each leg 14 has an L shape and comprises a tab 142 and a hook 141. The tab 142 of the leg 14 extends radially from the base 11 towards the axis A. The hook 141 extends axially at one end of the tab 142, from downstream to upstream, said end being the part of the leg 14 closest to the axis A.

[0038] With reference to [Fig.5], the leg 142 is trapezoidal in shape with a width that reduces from the base 11 to the end of the leg 142. The height of the leg 142 is less than the width of said leg 142, the height being measured in a radial direction and the width in a direction tangential to a diameter of the ferrule 3. This geometry of the legs 14 makes it possible to avoid the appearance of cracks on said legs 14. Indeed, with such a geometry, the legs 14 can deform more easily (than in the state of the art) in order to withstand the mechanical stresses created by the temperature difference between the flow of cold air and the flow of hot air. This deformation is possible in particular thanks to the clearances existing between two adjacent legs 14.The tangential stresses applied to the legs 14 are then less significant than in the case of the ferrule feet of the prior art, subjected to strong tangential stresses.

[0039] In certain embodiments, the legs 14 of the ferrule 3 are made in a relatively deformable flexible material so as to facilitate their deformation and thus avoid the appearance of cracks. For example, the material of the legs 14 of the ferrule 3 may be a nickel-chromium alloy, such as Waspaloy ®.

[0040] With reference to [Fig.6], each leg 14 of the ferrule 3 is positioned astride two consecutive distributors 2. In other words, each leg 14 is positioned at the junction of two distributors 2 so that it contributes to maintaining each of these distributors 2 and closes the space between the two consecutive distributors so as to limit the passage of air. The geometry of the legs 14 also makes it possible to reduce (compared to the prior art) the quantity of material directly in contact with the hot air flow of the vein 6. Indeed, the legs 14 have less surface area in contact with the hot air flow (compared to the foot 70 of the prior art). Thus, all the spaces between two distributors 2 are closed by one of the legs 14 of the ferrule.

[0041] As shown in [Fig.6], the distributor 2 comprises, at its external end: • a base 23, • a first wall 21 extending axially from the base 23, from upstream to downstream, and • a second wall 22 extending radially from the base 23 in a direction opposite to the axis A.

[0042] [Fig. 4] is an enlarged view of [Fig. 3] showing the connection between the distributor 2 and the ferrule 3. [Fig. 4] is in particular an enlargement of the dotted frame of [Fig. 3]. This [Fig. 4] shows in more detail the lug 142 of the leg 14. It shows in particular that the lug 142 comprises a first bearing surface 143 perpendicular to the axis A. The hook 141 comprises a hook tooth 144 projecting radially from the end of the hook 141. The hook tooth 144 comprises a second bearing surface 145 parallel to the axis A. The first and second bearing surfaces 143, 145 are in contact with the first wall 21 of the distributor 2. The distributor 2 and the leg 14 are thus made integral by means of the hook 141.

[0043] A thickness of the first wall 21 of the distributor 2 is less than a distance between the base 11 and the second bearing surface 145, the thickness of the first wall 21 and the distance between the base 11 and the second bearing surface 145 being measured in a radial direction. Thus, the leg 14 of the ferrule 3 fits the first wall 21 of the distributor 2.

[0044] The ferrule 3 also comprises an annular branch 15 extending radially from the base 11 towards the axis A. This annular branch 15 comprises a third bearing surface 151 perpendicular to the axis A in contact with the second wall 22 of the distributor 2. The annular branch 15 in contact with the second wall 22 of the distributor 2 makes it possible to create a sealed partition between the flow of cold air and the flow of air hot air circulating in the ferrule 3. In fact, the flow of hot air circulates in the vein 6 and comes to lick the hook 141 as well as the tab 142 of the leg 14 and the annular branch 15. This partition, the function of which is identical to that of the seal 60 of the prior art (illustrated [Fig.l]), makes it possible to do without a seal and therefore to do without a seal assembly step.

[0045] Thus, thanks to the invention, the service life of the ferrule 3 is increased. It will no longer be necessary to replace the part as often as before. The invention therefore also allows a saving on the downtime of the turbine necessary for changing the ferrule 3.

[0046] Although described through a certain number of examples, variants and embodiments, the ferrule 3 according to the invention comprises various variants, modifications and improvements which will be obvious to those skilled in the art, it being understood that these variants, modifications and improvements are part of the scope of the invention.

Claims

Claims

1. Annular shell (3) of a turbomachine turbine, the shell (3) extending along a longitudinal axis A and comprising: - an annular base (11) of longitudinal axis A; - mounting elements (12) distributed circumferentially around the periphery of the base (11); - an annular portion (13) extending axially in projection from the base (11); characterized in that the shell (3) further comprises: - a plurality of legs (14) distributed circumferentially on an inner surface of the shell (3) and spaced from each other so that a non-zero clearance exists between two adjacent legs (14); and - an annular branch (15) extending radially in projection from the base (11) towards the longitudinal axis A.

2. Ferrule (3) according to claim 1, characterized in that the legs (14) extend substantially radially from the base (11) towards the longitudinal axis A.

3. Ferrule (3) according to one of claims 1 or 2, characterized in that each leg (14) is L-shaped with a tab (142) which extends towards the longitudinal axis A and a hook (141) which extends axially from one end of the tab (142).

4. Ferrule (3) according to claim 3, characterized in that the tab (142) of each leg (14) comprises a width greater than a height, the width being measured in a direction tangential to a diameter of the ferrule (3), the height being measured in a radial direction.

5. Ferrule (3) according to claim 3 or 4, characterized in that the hook (141) comprises a hook tooth (144) projecting radially from one end of said hook (141).

6. Turbine assembly comprising: - a ferrule (3) according to any one of claims 1 to 5, and - a plurality of turbine distributors (2), positioned annularly next to each other and each carrying a plurality of turbine blades, characterized in that each leg (14) of the ferrule (3) is positioned at the junction between two distributors (2).

7. Assembly according to claim 6, characterized in that the annular branch (15) of the ferrule (3) is in contact with each distributor, the annular branch of the ferrule forming, with the consecutive distributors (2), a watertight partition between a vein (6) of the turbine where a flow of hot air circulates and a space of the turbine where a flow of cold air circulates.

8. Assembly according to any one of claims 6 or 7, characterized in that each distributor (2) comprises a second wall (22) projecting radially on an outer face of the distributor (2), the annular branch (15) of the ferrule (3) being in contact with the second walls (22) of two consecutive distributors (2).

9. Assembly according to any one of claims 6 to 8, characterized in that each distributor (2) comprises a first wall (21) projecting axially relative to a downstream face of the distributor (2), each hook (141) of the ferrule (3) being in contact with the first walls (21) of two consecutive distributors (2).

10. Turbomachine comprising at least one shell (3) according to any one of claims 1 to 5.

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