Turbojet engine nozzle ring for an aircraft

Abstract

The turbomachine subassembly comprises: - at least one low-pressure nozzle ring, the nozzle ring comprising a root (38) integral with the nozzle ring; - a clamp (40) configured so as to fasten the root to a casing of the turbomachine; and - at least two pads (150) interposed between the root and the clamp, each pad being assembled in a form-fitting manner with one of either the root or the clamp.

Description

FIELD OF THE INVENTION

[0001] The invention relates to turbomachines such as aircraft turbojets. STATE OF THE ART

[0002] There are known aircraft turbojet engines with a double-flow system comprising a fan, a low-pressure compressor, a high-pressure compressor, a combustion chamber, a high-pressure turbine and a low-pressure turbine. The low-pressure turbine recovers part of the energy from the combustion of the gases to operate the fan, the compressor and the accessories.

[0003] The components of the low-pressure turbine include the moving blades and the low-pressure nozzles. The gases expand in the low-pressure nozzle. This accelerates the flow and deflects it. This flow turns the turbine rotor, which forms a moving wheel.

[0004] This invention is part of the solution to a recurring problem observed on the distributor located on the first stage of the low-pressure turbine. The distributor is formed by elements arranged in succession following the circumferential direction around the axis. Indeed, the particularity of each element is that it is held from above and below. The problem concerns its lower part (i.e. the underside of the lower platform), and more precisely, the foot or leg of the distributor element. This foot is used to hold the part by being pinched. However, on the one hand, this contact generates wear by friction (or fretting in English), on the other hand, the area is exposed during operation to a risk of type 2 corrosion by sulfur. Thus, the two combine to generate contact corrosion which can seriously degrade the part.

[0005] Numerous corrosion pustules were observed on the base of the distributor element, both in fleet and during an endurance test. In fleet, such a situation leads to the removal of the engine. In endurance testing, 17% of the parts showed cases of corrosion appearing at the base of the distributor element, after completing the equivalent of 6,200 endurance cycles.

[0006] To prevent corrosion, one may consider adding a coating to the part. However, this coating does not last long in the area due to friction.

[0007] Engine manufacturers want to ensure the functionality of parts and reduce engine removals. During engine inspections, wear and tear leads to the replacement of expensive parts. In addition, the time required for the operation is significant (for example, the need to disassemble an entire turbine module to replace a part, then reassemble it).

[0008] One aim of the invention is therefore to facilitate the maintenance of turbomachines and to reduce costs, in the face of this phenomenon of contact corrosion.

[0009] Documents FR-3 015 550, FR-3 011 270 and US 2015 0089957 present subassemblies in accordance with the preamble of claim 1. STATEMENT OF THE INVENTION

[0010] For this purpose, according to the invention, a turbomachine subassembly is provided, the subassembly comprising, at least one low pressure turbine distributor, the distributor comprising a single-piece foot with a distributor body, a clamp configured to fix the foot to a casing of the turbomachine, and at least two pads interposed between the foot and the clamp, each skate being assembled by form complementarity with one of the foot and the clamp.

[0011] Thus, it is the pad, and no longer the foot, which is in contact with the clamp. The pad therefore protects the foot from friction and contact corrosion. If the pad becomes damaged or worn, it simply needs to be replaced with a new pad, which is less expensive than replacing the distributor element itself. The invention therefore avoids the combined effect of wear and corrosion. If the foot is covered with an anti-corrosion coating, it protects the latter in the contact zone. The invention does not prevent wear, but ensures that it can be quickly controlled while avoiding the aggravating combination with corrosion, and quickly replace the worn part. It reduces maintenance costs since there are fewer parts to change and fewer turbine removals. It also improves the machine's performance because, during an inspection, the installation of a new pad ensures less leakage.It therefore makes it possible to control a phenomenon which was previously experienced on the blades.

[0012] It can be provided that each skate is assembled by complementarity of shape with the foot or with the clamp.

[0013] It can be provided that each skate is formed of a material different from a material of the foot, for example a stellite, or even of a material, such as carbon or graphite, less hard than a material of the foot.

[0014] It can also be provided that each skate is formed from a material identical to a material of the foot.

[0015] The subassembly may also have at least one of the following characteristics: the clamp is without jaws and has main faces in contact with the pads; the pads constitute jaws of the clamp; it comprises at least one relief, for example at least two reliefs, on one of the foot and the clamp configured to penetrate into a cavity of the other of the foot and the clamp; the or each relief has the shape of a rectangular parallelepiped; there are two pads; there are four pads, the foot having two faces, each face being in direct contact with two of the pads, the two pads in direct contact with each face being for example spaced from each other; each pad has a wear indicator; the clamp comprises jaws in contact with the pads; the pads are fixed directly to jaws of the clamp; each pad extends exclusively opposite the foot; and the foot has an anti-corrosion coating.

[0016] The invention also provides a turbomachine such as an aircraft turbojet, comprising a subassembly according to the invention.

[0017] The invention also provides a method of manufacturing a turbomachine such as an aircraft turbojet, in which: two pads are assembled by form fit with one of a foot of a low pressure turbine distributor and a clamp, the foot being in one piece with a body of the distributor, the clamp is fixed to the foot so that the pads are interposed between the foot and the clamp, and the clamp is fixed to a casing of the turbomachine.

[0018] Finally, according to the invention, there is provided a method of maintaining a turbomachine such as an aircraft turbojet, in which: a first pad interposed between a foot of a low-pressure turbine distributor and a clamp configured to fix the foot to a casing of the turbomachine is dismantled, the foot being in one piece with a body of the distributor, a second pad is assembled in place of the first by form complementarity with one of the foot and the clamp, and the clamp is fixed to the foot so that the second pad is interposed between the foot and the clamp. DESCRIPTION OF FIGURES

[0019] We will now present an embodiment of the invention by way of non-limiting example in support of the drawings in which: there figure 1 is an axial half-sectional view of an aircraft turbojet engine forming a machine according to the invention; figure 2 is a larger scale view of part of the turbojet engine of the figure 1 ; there figure 3 is a perspective view of a vending machine from the figure 1 ; THE figures 4 to 6 are views showing the attachment of the distributor of the figure 3 to the machine casing; the figures 7 and 8 are side and perspective views showing the attachment of the distributor foot to the casing in a first embodiment of the invention; figures 9 to 11 are similar views showing a second embodiment; the figure 12 illustrates an alternative embodiment; and the figures 13 to 16 are views analogous to the figures 7 and 8 illustrating two other embodiments.

[0020] There figure 1 illustrates an aircraft turbojet engine 1 according to the invention. This is a turbojet engine forming a double-flow, double-spool turbomachine. The turbomachine has a main axis XX.

[0021] It includes from upstream to downstream, so from left to right on the figure 1, a blower 2, a low pressure compressor 4, a high pressure compressor 6, a combustion chamber 8, a high pressure turbine 10 and a low pressure turbine 12. These components have moving parts rotating around the axis XX.

[0022] The compressors 4, 6, the combustion chamber 8 and the turbines 10, 12 define a main air flow vein. A nacelle 16 surrounds the fan 2 so as to form a fan compartment and to define a secondary air flow vein.

[0023] Conventionally, an air flow entering the turbomachine at an air inlet is compressed, then mixed with fuel and burned in the combustion chamber 8, the combustion gases enabling one or more turbine rotors to rotate around the axis. For example, the high-pressure turbine 10 drives the high-pressure compressor 6, and the low-pressure turbine 12 drives the low-pressure compressor 4 and the fan 2. The terms upstream and downstream refer to the general direction of air flow in the turbomachine from its inlet to its outlet.

[0024] The fixed part of the turbomachine notably comprises a casing, for example an inter-turbine casing 22, which is an intermediate casing interposed between the high pressure and low pressure turbines housed in their respective casings.

[0025] Each of the high and low pressure turbines comprises a plurality of stages each with a distributor fixed relative to the casing, receiving a gas flow and straightening it to apply it to a moving wheel rotating in a given direction.

[0026] We are interested in the following in the low pressure distributor 24 arranged at the inlet of the low pressure turbine 12, that is to say the upstream distributor of this turbine. It is arranged downstream of a rectifier of the fluid of the high pressure turbine 10 (or TCF casing for English Turbine center frame ) , for example directly downstream of the rectifier, or downstream of a wheel itself arranged downstream of the rectifier. The distributor 24 therefore corresponds to the first stage of fixed blades of the low pressure turbine. Alternatively, the distributor 24 can be arranged downstream of the low pressure turbine, or at the level of another turbine.

[0027] The distributor 24 has an annular shape centered on the axis XX. It is formed of distributor sectors or elements 25. With reference to the figure 3 , each element 25 comprises a body having an inner (or lower) platform 32 or inner shell, an upper (or outer) platform 34 or outer shell and several blades 36 extending in the radial direction between the platforms 32, 34 and connected thereto. The upper platform 34 is further from the axis than the lower platform 32.

[0028] On the outer side of the upper platform 34, the distributor element 25 is connected to the casing by conventional means which will not be detailed.

[0029] On the inner side of the inner platform 32, the distributor element 25 is extended by a foot 38 extending in projection from the platform in the radial direction. The foot has a flat shape located in a plane perpendicular to the axis, as shown in particular by figure 4 The foot is made of a single piece with the body of the distributor element 25. The foot has a known anti-corrosion coating.

[0030] The machine also includes for each distributor element 25 a clamp 40 configured to fix the foot 38 to the casing 22. As illustrated in particular in figure 6 , this clamp comprises two branches 42 having two main faces 44 facing each other. It is adapted to clamp the foot between the two branches in the direction of the axis XX.

[0031] The clamp 40 is connected to the inter-turbine casing by means of an annular flange 46. The flange is therefore configured to be securely connected to the fixed part of the turbomachine and to the foot 38 of the distributor element. By secure connection between two members, it is meant here that the connection is such that a movement of one of the members according to a degree of freedom implies the same movement of the other according to the same degree of freedom. The secure connection is for example a fixing. This connection ensures the maintenance of the foot 38 of the distributor element 25. This connection can also make it possible to separate the upstream and downstream of an area under the foot 38.

[0032] The flange 46 is thus configured to separate the upstream and downstream of an area under the foot 38 so as to prevent any fluid circulation under the foot. It extends so as to separate an upstream chamber and a downstream chamber arranged respectively upstream and downstream of the foot 38. The upstream chamber is arranged between the inter-turbine casing and the flange. Thus, the sealed flange makes it possible, for example, to prevent the circulation of hot air over certain members arranged downstream, typically turbine disks. The flange is adapted to limit heat transfer by convection, conduction and / or radiation from the upstream chamber, in particular from the flow fluid to the flange.

[0033] The clamp 40 forms a housing allowing relative radial movement of the clamp and the foot during operation without risking the foot being dislodged from the clamp 8. The clamp limits their relative translational movement along the axis XX.

[0034] We will now present several embodiments of the cooperation of the foot with the clamp. First embodiment

[0035] This embodiment is illustrated in the figures 7 and 8 .

[0036] The foot here carries four 150 skates. On the figure 7 , two of the skates are hidden by the skates in the foreground. On the figure 8 , two of the skates are hidden by the foot.

[0037] The runners here each have a strip or rail shape. The strips have their longitudinal directions which are parallel to each other and close to the radial direction.

[0038] The foot having two opposite faces 52. Each of them is in direct contact with two of the pads 150. On each face, the two pads in direct contact with the face are spaced from each other in the circumferential direction to the axis XX, as shown in the figure 8 .

[0039] Each pad 150 is assembled by form fit with the foot 38. For example, each pad comprises three reliefs extending in projection from a face of the pad in contact with the foot, as illustrated in figure 11 in support of the second mode. The reliefs are configured to penetrate into respective cavities of the foot provided for this purpose. It is also possible to provide conversely that the reliefs are located on the clamp and the cavities in the foot.

[0040] Each pad 150 is interposed between the foot and the clamp, as illustrated. Each branch of the clamp is therefore supported on the foot by a jaw of the branch while being in contact exclusively with the two feet.

[0041] The pads therefore form an additional material on either side of the foot to accommodate the clamp. Friction therefore occurs on these bands which can wear out and are subsequently repairable.

[0042] Each shoe 150 may be formed from the same material as the distributor element 25, for example a metal alloy. It may also be formed from a material different from a material of the foot, for example a stellite. A stellite is a metal alloy whose principal component is cobalt and the principal alloying element is chromium. It may also contain a small amount of tungsten or molybdenum and a small but significant amount of carbon. A stellite offers good resistance to contact friction.

[0043] During the manufacture of the turbojet, the pads 150 are assembled by form fit with the clamp. Then the latter is fixed to the foot so that the pads are interposed between the foot and the clamp and the clamp is fixed to the casing 22 by means of the flange. The tight assembly with the force of the clamp on the pads ensures that they are held on the foot.

[0044] During turbojet maintenance, if the 150 pads are worn, they are dismantled by separating them from the foot. Then new pads are assembled in their place by form fit with the foot, and the clamp is fixed to the foot so that the new pads are interposed between the foot and the clamp. The replacement can also concern only one of the pads, or several of them without it being all of them.

[0045] Each pad may be provided with a wear indicator, for example in the form of a 53 marking on the sidewall or field of the pad. When this marking is damaged or disappears, it is a sign that the pad must be replaced. Such a wear indicator quickly and effectively shows whether the wear is acceptable or not. In the event that the pad is too worn, it is sufficient to replace it by unseating it and fitting a new pad, as explained.

[0046] Thanks to the invention, the base of the distributor element keeps its anti-corrosion coating intact, and friction is controlled.

[0047] In the following embodiments and variants, the common components will not be described again. The description will only concern the characteristics that differ. Second embodiment

[0048] This embodiment is illustrated in the figures 9 to 11 .

[0049] This time, there are two 250 skates. This feature, independently of those that follow, could be applied to the first embodiment.

[0050] Each 250 skate is this time assembled by form complementarity with the 40 clamp, more precisely in the jaws of the branches of the clamp. figure 11 shows the reliefs 60 of one of the pads 250 opposite the cavities 62 intended to receive them in the clamp.

[0051] Additionally, but independently of this, each pad 250 is formed of a material that is less hard than a material of the foot, such as carbon or graphite, a stellite. This material can thus wear or crumble during friction occurring in operation, thereby reducing the contact friction force.

[0052] This method has the advantage of being easier to implement because the amount of material required on the clamp is lower. In addition, no modification to the base of the distributor element 25 is required, and there is no risk of problems with the application of the anti-corrosion coating on the distributor. In addition, the geometry of the base is simplified since it is not necessary to provide one or more cavities. Variant

[0053] This variant is illustrated in the figure 12 .

[0054] It is based on the second mode.

[0055] Here, the relief 60 is unique and has, independently of this, an elongated rectangular parallelepiped shape. The cavity 62 has a female shape complementary to this male shape. Third embodiment

[0056] This embodiment is illustrated in the figures 13 And 14 .

[0057] In this embodiment, there are two pads 350 located on the foot. Each face 52 of the foot carries a single pad in the form here of a strip extending in the circumferential direction to the axis. The strip has a shape and a position which correspond to the support zone of the clamp on each face 52.

[0058] Independently of this, the clamp is without jaws. The main faces 44 of its branches 42 are in direct contact with the pads. It is understood that in such an arrangement the jaws of the clamp become useless.

[0059] The advantage of this solution is that the geometry of the gripper is simplified. It also increases the gripping surface of the gripper on each face and makes it more difficult for the distributor to slide against the flange. It therefore reduces friction, delaying the time required to change the pads. Fourth embodiment

[0060] This embodiment is illustrated in the figures 15 And 16 .

[0061] This time, the two 450 skates are fixed to the clamp and constitute its jaws, extending out from the branches towards the foot.

[0062] Numerous modifications may be made to the invention defined by the appended claims without departing from the scope thereof.

[0063] The solution is interesting for all contact interfaces between two parts. Because this then leads to wear of at least one of the two parts and potentially the appearance of corrosion. For example, this type of solution could be considered instead of stellites in the heels of moving wheels. The invention has the particular advantage of allowing the pads to be replaced easily over time.

Claims

1. A turbomachine subassembly such as a turboreactor of an aeronef, the subassembly comprising: - at least one low-pressure turbine (12) nozzle ring (24), the nozzle ring comprising a root (38) integral with a body of the nozzle ring, - a clamp (40) configured to attach the root to a casing (22) of the turbomachine, and - at least two pads (150-450) interposed between the root and the clamp, the turbomachine subassembly being characterized in that each pad is assembled in a form-fitting manner with one among the root and the clamp.

2. The subassembly according to the preceding claim, wherein each pad (150; 350) is assembled to the root (38) in a form-fitting manner.

3. The subassembly according to the preceding claim, wherein each pad (150; 350) is formed from a material different from a material of the root (38), for example a stellite.

4. The subassembly according to any one of claims 2 to 3 wherein the clamp (40) has no jaw and has main faces (44) in contact with the pads (350).

5. The subassembly according to claim 1 wherein each pad (250; 450) is assembled in a form-fitting manner to the clamp (40).

6. The subassembly according to the preceding claim wherein each pad (250; 450) is formed from a material, such as carbon or graphite, that is less hard than a material of the root (38).

7. The subassembly according to any one of claims 5 or 6 wherein the pads (450) constitute the jaws of the clamp (40).

8. The subassembly according to any one of the foregoing claims which comprise at least one protrusion (60), for example at least two protrusions, on one among the root (38) and the clamp (40) configured to penetrate into a cavity (62) of the other among the root and the clamp.

9. The subassembly according to the preceding claim wherein the or each protrusion (60) has the shape of a rectangular parallelepiped.

10. The subassembly according to any one of the preceding claims wherein the pads (250-450) are two in number.

11. The subassembly according to any one of claims 1 to 9 wherein the pads (150) are four in number, the root (38) having two faces (52), each face being directly in contact with two of the pads, the two pads in direct contact with each face being for example spaced away from one another.

12. The subassembly according to any one of the preceding claims, wherein each pad (150-450) has a wear indicator (53).

13. A turbomachine, such as an aircraft turbojet engine (1), comprising a subassembly according to any one of the preceding claims.

14. A method for manufacturing a turbomachine such as an aircraft turbojet engine (1), comprising: - assembling two pads (150-450) in a form-fitting manner to one among a root (38) of a low-pressure turbine (12) nozzle ring (24) and a clamp (40), the root being integral with a body of the nozzle ring, - attaching the clamp (40) to the root so that the pads are interposed between the root (38) and the clamp (40), and - attaching the clamp (40) to a casing (22) of the turbomachine.

15. A method for maintaining a turbomachine such as an aircraft turbojet engine (1), comprising: - disassembling a first pad (150-450) interposed between a root (38) of a low-pressure turbine (12) nozzle ring (24) and a clamp (40) configured to attach the root to a casing (22) of the turbomachine, the root being integral with a body of the nozzle ring, - assembling a second pad (150-450) in place of the first pad in a form-fitting manner with one among the root (38) and the clamp (40), and - attaching the clamp to the root so that the second pad is interposed between the root and the clamp.

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