THERMAL PROTECTION SHEET WITH RADIAL BARRIER, PARTICULARLY FOR TURBOMACHINE DISTRIBUTOR

Abstract

The invention relates to a thermal protection plate (10) suitable for use in a distributor (2) for a turbomachine, characterized in that it comprises at least one tab (16), called radial, adapted to come into axial stop against a first anti-rotation pin (40), and at least one tab (14), called axial, adapted to come into radial stop against a second anti-rotation pin (40).

Description

The invention relates generally to the field of turbomachinery, and more particularly to thermal protection elements adapted to be mounted in a distributor, for example an annular turbine distributor on a turbine housing. An example of a turbomachine is shown in Figure 5. A turbomachine typically includes a nacelle that forms an opening for the admission of a specific airflow to the engine itself. Generally, the turbomachine comprises one or more compression sections 4 for the air admitted into the engine (usually a low-pressure section and a high-pressure section) and a combustion chamber 5, in which the compressed air is mixed with fuel before being burned. The hot combustion gases from this combustion are expanded in the various turbine stages, including generally a high-pressure stage 6 immediately downstream of the chamber 5, which receives the gases at the highest temperature. After this initial expansion, the gases are expanded again as they are guided through the so-called low-pressure turbine stages 7. A low-pressure turbine 7 typically comprises one or more rows of turbine blades spaced circumferentially around the turbine rotor 7. It also includes a low-pressure distributor 2 that directs the gas flow from the combustion chamber 5 to the turbine blades at an appropriate angle and velocity to rotate the blades and the turbine rotor 7. The distributor 2 comprises a plurality of blades arranged radially about an axis of rotation of the turbomachine X, connecting an internal radial annular element and an external radial annular element. Together, these form an annular stream opposite the moving turbine blades. More specifically, the low-pressure distributor 3 consists of fixed blades arranged in a wheel divided into a plurality of segments, distributed circumferentially around the axis X of the turbomachine.Each segment comprises several adjacent fixed vanes attached to a ring-shaped element, as well as an upstream and a downstream retaining means. Here, upstream and downstream are defined by the direction of gas flow in the turbomachine. These retaining means are, for example, annular rails formed in the inner wall of the casing, against which bearing surfaces formed on the ring sectors of the distributor segments are directed. The assembly is arranged to allow for the relative expansion of the distributor with respect to the casing, which is a function of the machine's operating speed variations. However, due to the axial symmetry of the distributor wheels and the tangential forces resulting from the gas flow passing through them, it is necessary to provide means for locking the rotating sectors.To this end, French patent FR 2 743 603, registered in the name of the Applicant, describes a method of mounting such distributor segments inside a housing. The distributor segments comprise a peripheral outer rib, perpendicular to the axis of the distributor (and therefore of the turbomachine), bearing on corresponding upstream and downstream faces of the inner wall of the housing. A projection on the upstream face of the rib of each segment includes a notch in which an anti-rotation pin is housed. This pin comprises a head housed in the notch and a shaft inserted into a radial bore in the housing wall, thus preventing any rotation of the distributor segment around its axis. In order to protect the housing wall from the thermal radiation of the distributor, particularly the low-pressure distributor, a sheet metal plate is generally interposed between the distributor and the inner wall of the housing.This thermal protection plate rests upstream against a radial surface cut into the inner wall of the housing. The upstream edge of the protection plate is curved radially inwards to form a pin that also rests against an upstream edge of the distributor and helps to secure it against the upstream rail of the housing. Downstream, the protection plate includes a notch with a tab at the bottom of the notch. This assembly provides complete satisfaction in terms of securing the distributor inside the housing and protecting it thermally. It was observed, however, that the sheet metal was prone to dislodging from its contact with the anti-rotation pin. No longer held in place, the tab risks rubbing against the inner face of the housing wall, causing fretting (wear on the wall). It was therefore proposed to form, at the downstream end of the protective sheet metal, a radially inwardly curved edge to create a pin shape similar to its upstream end. This pin-shaped downstream edge would then create surface-to-surface contact at the interface between the thermal protection sheet metal and the housing. Nevertheless, this solution currently appears difficult to implement, as it requires the use of a permanently fixed circlip on the sheet metal to form the pin-shaped downstream edge, since this part of the sheet metal cannot be demolded. This solution is therefore costly in terms of both the final mass of the assembly and its manufacturing process.Document FR 2 960 591, also in the name of the Applicant and illustrated with reference to Figure 1, proposes modifying the anti-rotation pin 40 so that it acts as a stop for the tab in the event of radial movement of the sheet metal during the operation of the turbomachine. Indeed, by interposing a stop between the part of the sheet metal 10 that is likely to move during operation, the risk of contact with the inner wall 30 of the housing is eliminated. To achieve this, a shoulder 40a is formed on the anti-rotation pin 40, extending radially from the pin 40 between the tab 12a and the inner wall of the housing 30. However, the creation of this shoulder 40a increases the overall manufacturing cost of the anti-rotation pin 40, as well as its size. One objective of the invention is therefore to provide means for preventing the rotation of a segment of a valve, particularly a low-pressure valve of a turbomachine, relative to the turbine housing of the turbomachine. These means must also protect the housing from the valve's thermal radiation and prevent premature wear of the housing due to friction, and be of moderate cost and easy to manufacture. To this end, the invention provides a thermal protection plate suitable for use in a valve for a turbomachine, characterized in that it comprises at least one radial tab adapted to bear axially against a first anti-rotation pin, and at least one axial tab adapted to bear radially against a second anti-rotation pin.Some preferred but non-limiting characteristics of a thermal sheet according to the invention are as follows: - it comprises a plurality of radial tabs and axial tabs which alternate along said thermal protection sheet, and - the tabs are monobloc with said thermal sheet.The invention also proposes a distributor for a turbomachine, in particular a low-pressure distributor, adapted to be 20 mounted in a housing, comprising: - a plurality of segments distributed circumferentially around the axis of rotation of the turbomachine, - a plurality of anti-rotation pins, mounted both on a segment of the distributor and on the housing, and 25 - a thermal protection plate, disposed between the housing and the segments of the distributor), comprising a plurality of tabs, each being adapted to bear against an anti-rotation pin, the distributor being characterized in that the thermal protection plate comprises at least one axial tab adapted to come into radial contact 30 against a first anti-rotation pin, and at least one radial tab adapted to come into axial contact against a second anti-rotation pin. Some preferred but not limiting features of a distributor according to the invention are as follows: - the heat shield comprises a plurality of axial and radial tabs, - the heat shield comprises substantially as many radial tabs as axial tabs, - the radial and axial tabs alternate along the heat shield, around the axis of rotation of the turbomachine, and are separated by a notch, preferably with a material removal, - a circumferential width of at least one axial tab corresponds to the distance separating three adjacent anti-rotation pins, and - at least one axial tab is at a distance from the anti-rotation pin when the turbomachine is at rest. Finally, the invention proposes a turbomachine comprising a distributor as described above.Other features, objects and advantages of the present invention will become more apparent from the following detailed description, made with reference to the accompanying figures given by way of non-limiting example, in which: Figure 1 is a partial axial cross-sectional view of a turbine distributor mounted in a housing of a turbomachine according to the prior art, Figure 2 is a partial axial cross-sectional view of an example of a turbine distributor mounted in a housing of a turbomachine according to the invention, Figure 3a is a perspective view of an example of a thermal protection plate according to the invention, Figure 3b is a detailed view of a portion of the thermal protection plate of Figure 3a, Figure 4a is a first perspective view of the example of Figure 2, Figure 4b is a second perspective view of the example of Figure 2, and Figure 5 represents an example of a turbomachine to which the invention applies. The invention will be described particularly with reference to a low-pressure distributor 2 of a turbomachine 1, mounted in a low-pressure turbine housing 3 7. A low-pressure distributor 2 is formed of fixed blades arranged in a wheel divided into a plurality of segments 20, distributed circumferentially around a rotation axis X of the turbomachine 1. Each segment 20 comprises several adjacent fixed blades attached to a ring-shaped element, as well as an upstream retaining means and a downstream retaining means. These retaining means are, for example, the annular rails 32, 24 formed in an internal wall 30 of the casing 3, on which bearing surfaces 22, 24 formed on the ring sectors of the distributor segments 20 described above bear. In order to prevent the sectors from rotating, the distributor 2 includes a plurality of segment-locking devices, each comprising an anti-rotation pin 40, mounted both on a segment 20 of the distributor 2 and on the turbine casing 3.Similar to what is described in document FR 2 960 951, a projection on the upstream face of each segment 20 includes a notch in which the anti-rotation pin 40 is housed. This pin 40 includes a head 41 housed in the notch and a rod 42 slid into a radial bore of the wall 30 of the housing 3, and thus prevents any rotational movement of the distributor segment 20 around the axis of the latter (corresponding to the rotation axis X of the turbomachine). A thermal protection plate 10 is interposed between the segments 20 of the low-pressure distributor 2 and the inner wall 30 of the turbine housing 3, and is adapted to limit the thermal radiation from the distributor 2 onto the turbine housing 3. This thermal protection plate 10 bears upstream against a portion of a radial surface 33 formed in the inner wall of the housing. Conventionally, the upstream edge 12 of the protection plate 10 is radially curved inwards to form a pin. Optionally, the upstream edge can also bear against an upstream edge of the segment 20 of the distributor 2 and contribute to holding it against the upstream rail 32 of the housing 3. Downstream, the thermal protection plate 10 includes a plurality of tabs 14, 16, each adapted to bear against an anti-rotation pin 40 of the locking devices.To limit the risk of fretting caused by contact between the heat shield 10 and the housing 3, the plate 10 is modified at its downstream end. Specifically, the heat shield 10 includes tabs 14, 16 adapted so that the plate is radially butted 15 and axially butted against the anti-rotation pins 40. The heat shield is thus held in position against the anti-rotation pins 40, while its movement is limited towards the inner wall 30 of the housing 3. Here, radial means a direction extending substantially transversely with respect to the X-axis of the turbomachine, and axial means a direction extending substantially parallel to the X-axis of the turbomachine.For example, the tabs 14, 16 of the thermal protection 10 may include axial tabs 14, adapted to radially bear against the corresponding anti-rotation pin 40, and 25 radial tabs 16, adapted to axially bear against the corresponding anti-rotation pin 40. Thus, the radial tabs 16 extend transversely with respect to the X-axis of the turbomachine 1, and allow the thermal protection plate 10 to be held in axial position relative to the distributor 2. These 30 radial tabs 16 therefore form axial stops. For this purpose, the radial tabs 16 are arranged for example so as to extend opposite an upstream face 46 of the anti-rotation pins 40, this upstream face 46 corresponding to the face of the anti-rotation pins directed upstream of the turbomachine 1, facing the gas flow.The axial tabs 14 extend substantially parallel to the X-axis of the turbomachine 1, and prevent the thermal protection plate 10 from moving towards the turbine housing 3, i.e., in a radial direction. Therefore, these axial tabs act as radial stops. The axial tabs 14 are arranged, for example, to extend opposite a lower face 44 of the anti-rotation pins 40, this lower face 44 corresponding to the face of the anti-rotation pins 40 directed towards the axis of rotation X of the turbomachine 1, opposite the distributor 2. According to one embodiment, the thermal protection plate 10 comprises substantially as many axial tabs 14 as radial tabs 16. Thus, if the distributor 2 comprises twenty-six anti-rotation pins 40, the thermal protection plate 10 can, for example, comprise thirteen axial tabs 14 and thirteen radial tabs 16.The radial tabs 16 and axial tabs 14 can also be alternately distributed along the periphery of the thermal protection plate 10, in order to maintain the symmetry of the turbomachine 1 and to balance the distributor 2. The thermal protection plate 10 is preferably annular in shape and can be monolithic, i.e., a single piece, or obtained by joining several interconnected annular segments. The tabs 14, 16 can be formed integrally with the rest of the thermal protection plate 10. For example, they can be obtained by cutting the downstream edge of the thermal protection plate 10 to form notches 18, with or without material removal.In the embodiment illustrated in figures 7 to 4b, the notches 18 are made with material removal, in order to avoid possible friction of the axial tabs 14 against the anti-rotation pin 40 during the expansion of the distributor 2. Furthermore, the thermal protection plate 10 may include a tab 14, 16 for each anti-rotation pin 40, so that for a given anti-rotation pin 40, the thermal protection plate 10 has either a radial tab 16 or an axial tab 14 opposite it. Alternatively, the thermal protection plate 10 may include a radial tab 16 and an axial tab 14 for each anti-rotation pin 40. The same anti-rotation pin 40 may then be radially abutted against an axial tab 14 and axially abutted against a radial tab 16. The axial tabs 14 may be wider (along the circumference of the thermal protection plate 10) than the radial tabs 16. For example, a circumferential width of an axial tab 14 may correspond to the distance separating three adjacent anti-rotation pins 40.A given axial tab 14 can therefore extend not only opposite the corresponding anti-rotation pin 40, but also on either side of this pin 40 up to the adjacent anti-rotation pins 40, the adjacent anti-rotation pins 40 each being opposite another tab, preferably radial 16. This embodiment makes it possible to simplify the making of the thermal protection plate 10, to strengthen the resistance to the radial forces of the axial tab 14 applied by the anti-rotation pin 40, and to prevent the plate 10 from coming into contact with the turbine housing 3 despite the vibrations suffered by the latter, and also makes it possible to obtain better protection against thermal radiation. The radial tabs 16, for their part, then have a width (along the circumference of the thermal protection sheet 10) corresponding approximately to the width of the upstream face 46 opposite the anti-rotation pin 40.Alternatively, the radial tabs 16 are wider than the axial tabs 14, and extend between three adjacent anti-rotation pins 40, the axial tabs 14 then being of width substantially equal to the width of the lower face 44 opposite the anti-rotation pin 40. According to yet another variant, the axial tabs 14 and the radial tabs 16 are of equal width and extend on either side of each anti-rotation pin 40, over a width globally equal to the distance between two adjacent anti-rotation pins 40. Optionally, the radial tabs 16 can be inserted into a groove formed in the face opposite the corresponding anti-rotation pin 40. Furthermore, in its rest position, i.e., when the turbomachine 1 is not operating, the axial tabs 14 can extend relative to and away from the lower face 44 of the corresponding anti-rotation pins 40, in order to allow a specific radial displacement of the thermal protection plate 10 in the event of its expansion. This radial displacement is, however, limited, as the axial tab 14 acts as a radial stop when it comes into contact with the lower face 44 of the anti-rotation pin. Therefore, there is a gap 19 between the axial tabs 14 and the lower surface 44 of the anti-rotation pins 40 when the distributor 2 is at rest. The radial tabs 16, on the other hand, are in contact with the upstream face 46 of the anti-rotation pins 40, whether the turbomachine 1 is at rest or in operation, to maintain the thermal protection plate 10 in position relative to the distributor 2 and the turbine housing 3.25

Claims

DEMANDS 1. Distributor (2) for a turbomachine (1), in particular a low-pressure distributor, adapted for mounting in a housing (3), comprising: - a plurality of segments (20) distributed circumferentially around an axis of rotation (X) of the turbomachine (1), - a plurality of anti-rotation pins (40), mounted both on a segment (20) of the distributor and on the housing (3), and - a thermal protection plate (10), disposed between the casing (3) and the segments (20) of the distributor (2), comprising a plurality of tabs (14, 16), each adapted to bear against an anti-rotation pin (40), the distributor (2) being characterized in that the thermal protection plate (10) includes at least one axial tab (14) adapted to come into radial contact against an underside face (44) of a first anti-rotation pin (40), and at least one radial tab (16) adapted to come into axial contact against an upstream face (46) of a second anti-rotation pin (40).

2. Distributor (2) according to claim 1, wherein the thermal protection sheet (10) comprises a plurality of axial tabs (14) and radial tabs (16).

3. Distributor (2) according to any one of claims 1 or 2, wherein the thermal protection sheet (10) comprises substantially as many radial tabs (16) as axial tabs (14).

4. Distributor (2) according to any one of claims 1 to 3, wherein the radial tabs (16) and the axial tabs (14) alternate along the thermal protection plate (10), around the axis of rotation (X) of the turbomachine, and are separated by a notch (18), preferably with material removal.

5. Distributor (2) according to any one of claims 1 to 4, wherein a circumferential width of at least one axial tab (14) corresponds to the distance separating three adjacent anti-rotation pins (40).

6. Distributor (2) according to any one of claims 1 to 5, wherein at least one axial tab (14) is at a distance from the anti-rotation pin (40) when the turbomachine (1) is at rest.

7. Turbomachine comprising a distributor according to any one of claims 1 to 6.

8. Thermal protection plate (10) suitable for use in a distributor (2) according to any one of claims 1 to 6, characterized in that it comprises at least one tab (16), referred to as radial, adapted to come into axial contact against an upstream face (46) of a first anti-rotation pin (40), and at least one tab (14), referred to as axial, adapted to come into radial contact against an inferior face (44) of a second anti-rotation pin (40).

9. Thermal protection plate (10) according to claim 8, comprising a plurality of radial tabs (16) and axial tabs (14) which alternate along said thermal protection plate (10).

10. Thermal protection sheet (10) according to any one of claims 8 or 9, wherein the tabs (14, 16) are one piece with said thermal sheet (10).

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