Turbine distributor

Abstract

This document describes a turbine distributor comprising: an inner and an outer shell; a plurality of blades arranged between the shells; a pocket (20) formed in an outer platform (16) of the outer shell, between two circumferentially adjacent blades (12), the pocket (20) having a bottom (22) and stiffeners (26) projecting from the bottom (22); a plate covering the pocket (20) at a radial distance from the stiffeners (26); and studs (28) projecting from the bottom (22) on which the plate rests. Abstract figure: Figure 3

Description

Title of the invention: Turbine distributor Technical field

[0001] The present disclosure relates to the design of a turbine distributor and more particularly to the maintenance of such a distributor. Prior art

[0002] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies both to new types of aircraft and those in circulation requiring the implementation of technological solutions in order to make them compliant with current regulations. Civil aviation has been mobilizing for several years now to make a contribution to the fight against climate change.

[0003] Technological research efforts have already made it possible to significantly improve the environmental performance of aircraft. The Applicant takes into consideration the impact factors in all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products whose integration and use in civil aviation result in moderate environmental consequences with the aim of improving the energy efficiency of aircraft.

[0004] In this context, engine efficiency is constantly being improved, which sometimes has an impact on the temperature of the gases or structural elements downstream of the combustion chamber. Controlling temperatures at the turbine level is essential for reasons of mechanical strength and control of expansion deformations.

[0005] Patent document FR 3 080 406 A1 describes a turbine distributor in which the blades are hollow and are adapted to receive a flow of air cooling the blades and taken from the compressor. In order to avoid the internal cavity of the blade becoming blocked, blocking elements such as pins or hoops are provided at the blade head.

[0006] To improve the cooling of turbine distributors, it may be necessary to further complicate their design, but in general, a complex design often leads to additional difficulties during engine manufacturing or maintenance operations.

[0007] The present application therefore aims to propose a design which makes it possible to better control the temperature rise of the distributor without presenting any disadvantages during maintenance. Summary

[0008] For this purpose, the present document relates to a turbine distributor forming a crown around an axis and comprising: an inner shroud comprising a plurality of inner platforms arranged circumferentially around the axis and an outer shroud comprising a plurality of outer platforms arranged circumferentially around the axis; a plurality of blades arranged radially between the inner shroud and the outer shroud; a pocket formed in an outer platform between two circumferentially adjacent blades, the pocket having a bottom as well as stiffeners extending projecting from the bottom; a sheet covering the pocket radially at a distance from the stiffeners; and pads extending projecting from the bottom and on which the sheet rests.

[0009] The pocket allows the structure to be refined and therefore heat to be evacuated more quickly. It also allows the circulation of a flow of cold air, for example taken from an upstream portion of the engine. The stiffeners mechanically reinforce the structure of the distributor to compensate for the loss of rigidity due to the presence of the pocket. The pocket is covered with a sheet metal which may need to be replaced during the life of the engine: the sheet metal or its brazing connection to the distributor may be damaged. In order to anticipate damage when removing the sheet metal, and positioning inaccuracies when installing a new sheet metal, the studs are designed to serve both as a reference for the operator removing the sheet metal (for example with an electrode debrazing process) and as a stop when installing a new sheet metal.

[0010] According to an advantageous embodiment, the stiffeners project from the bottom by a first height and the pads project from the bottom by a second height, the second height being at least three times greater than the first height. This safety factor of three times makes it possible to guarantee a minimum clearance in height above the stiffeners so that the pocket remains sufficiently spacious with respect to the stiffeners: stiffeners that are too large in relation to the total height of the pocket would hinder the circulation of air and / or reduce the efficiency of the heat exchange between the platform and the air.

[0011] According to an advantageous embodiment, the pocket comprises through-openings for fluid circulation and the sheet comprises through-orifices in fluid communication with the through-openings of the pocket, the pads comprising upstream pads in the vicinity of the through-openings and circumferentially offset from the through-openings, and downstream pads in the vicinity of the through-openings and circumferentially offset from the through-openings. The "neighborhood" here means as a distance between the studs and the orifices, or respectively the vents, which is less than 20% of the axial length of the pocket. These offsets prevent the studs from hindering the proper flow of air (and therefore heat dispersion) when air enters or escapes from the pocket at the vents and orifices.

[0012] According to an advantageous embodiment, the bottom of the pocket is delimited by a contour formed by an upstream edge, a downstream edge and two lateral edges, the pads being arranged at a distance from all the edges and at a distance from a median line equidistant from the lateral edges. The air flow may undergo edge effects (boundary layer) in the vicinity of the lateral edges and the air flow may have a non-uniform flow rate over the entire section of the pocket, with in particular a greater flow rate along a median line, a line which “sees” more orifices and vents than the rest of the pocket. The arrangement of the pads set back from the lateral edges avoids an aerodynamic blocking effect and the arrangement of the pads set back from the median line prevents the line of greatest flow rate from hitting obstacles.

[0013] According to an advantageous embodiment, the pads have a circular or elliptical section. These sections are aerodynamic and therefore easily allow air to flow around the pads. In particular, the orientations of the ellipses can be aligned with the velocity field lines of the air flow in the pocket.

[0014] According to an advantageous embodiment, the distributor comprises three pairs of pads, including two upstream pads, two central pads and two downstream pads. This arrangement makes it possible to guarantee a constant radial height from upstream to downstream for the pocket (and therefore well-controlled cooling) and in particular when the sheet is curved (seen in a longitudinal plane). Without this arrangement, deformations of the sheet could alter the pocket.

[0015] According to an advantageous embodiment, the bottom of the pocket is delimited by a contour formed of an upstream edge, a downstream edge and two lateral edges, the stiffeners extending parallel to the upstream edge and / or to the downstream edge, from one lateral edge to the other lateral edge, the central pads being arranged between two adjacent stiffeners, the upstream pads being arranged between the upstream edge and a stiffener, and the downstream pads being arranged between the downstream edge and a stiffener. Thus, by offsetting the pads relative to the stiffeners, the latter are not subjected to mechanical stresses.

[0016] According to an advantageous embodiment, the studs are integral with the external platform which includes the pocket. According to an alternative, the studs are attached to the external platform which includes the pocket and are made of a harder material than the material constituting the external platform which includes the pocket. According to a variant, studs are attached to the external platform and are formed of the same material as the external platform. According to another variant, one or several studs are made in one piece (i.e. monobloc, formed with the platform) and one or more other studs are added to the pocket (for example by welding, or removable fixing).

[0017] The invention also relates to a method for replacing a distributor sheet, for a distributor according to one of the embodiments set out above, the method comprising removing the distributor sheet by means of a debrazing operation, placing a replacement sheet in contact with the pads and brazing the replacement sheet to the external platform which comprises the pocket.

[0018] As mentioned above, the presence of the studs makes it possible not to remove too much material during debrazing, and then to position the new sheet correctly.

[0019] The gain obtained by the design proposed by the invention in terms of cooling is therefore not accompanied by drawbacks linked to its maintenance. Brief description of the drawings

[0020] Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings, in which:

[0021] [Fig-1] is an isometric view of a distributor segment according to the present di popularization;

[0022] [Fig.2] is a front view and a cross-section of the sheet metal;

[0023] [Fig.3] is an isometric view of a pocket with the stiffeners and the pads, the sheet metal being illustrated in transparency;

[0024] [Fig.4] is a front view of the pocket;

[0025] [Fig.5] is a cross-section of the external platform and the sheet metal. Description of the embodiments

[0026] [Fig.l] shows a turbine distributor 10. The distributor 10 may be a high-pressure turbine distributor or a low-pressure turbine distributor. The distributor 10 is formed as a crown around an axis A, with an inner shroud 2 and an outer shroud 4. The distributor 10 is mainly composed of an annular row of blades 12 extending substantially in a radial direction R, between the inner shroud 2 and the outer shroud 4.

[0027] The ferrules 2, 4 may be formed from several angular sectors assembled together (see right part of [Fig.l]), or they may be in one piece and extend over 360° around an axis of rotation A of a turbomachine. As illustrated in the left part of [Fig.l], the ferrule sectors 2, 4 comprise an internal platform 14, an external platform 16 as well as one or more blades 12. Thus, the assembly of blades 12 and platforms 14, 16 may be formed from a single piece, made in one piece by casting or plastic deformation.

[0028] The blades 12 and the platforms 14, 16 delimit a gas vein. Upstream of the dis tributor, the gas flows mainly in the axial direction A. Downstream of the distributor 10 the gas flow is deflected and its speed therefore has a tangential component allowing the rotation of the turbine (not shown) which is located downstream of the distributor 10.

[0029] Each blade 12 may be hollow and may have an internal cavity 13 which may extend over the entire radial height of the blade 12. This cavity 13 is in fluid connection with a source of cold air and thus makes it possible to control the temperature rise in the blade 12.

[0030] At the level of the external platform 16, the inter-blade spaces in a circumferential direction, identified by the arrow T, accommodate a pocket (20 in [Fig.3] and the following). [Fig.1] shows sheets 18 covering these pockets.

[0031] A sheet 18 is shown in detail in [Fig.2], in front view and in cross-section. The sheet 18 is in the form of a plate or a cover, with an upper surface 18.1 (visible in [Fig.l] also) and a lower surface 18.2 facing the pocket (number 20 in [Fig.3]). The thickness of the sheet 18 may be constant and the sheet 18 may be curved to follow the curvature of the external platform 16. The contour 18.3 of the sheet 18 may comprise an upstream edge and a downstream edge, both substantially rectilinear (in the front view, but arched to follow the curvature around the axis of the turbomachine, noted A in [Fig.l]). The contour 18.3 also includes lateral edges which essentially follow the shape of the extrados and intrados profiles of the blades 12. Thus, the sheet 18 occupies all the space between two circumferentially adjacent blades 12.

[0032] The contour 18.3 is intended to be brazed onto the external platform 16. It may happen that the sheet 18 or the brazing bonding it to the platform 16 deteriorates, the sheet 18 thus having to be replaced.

[0033] The sheet 18 also comprises orifices 18.4 allowing the circulation of air towards or outside the pocket. The orifices 18.4 may be regularly distributed in a circumferential direction and / or may be arranged in an upstream portion of the sheet 18.

[0034] [Fig. 3] shows a pocket 20 formed in the external platform 16, covered with a sheet 18 illustrated in transparency. This pocket 20 is blind in the sense that it opens radially towards the outside of the platform 16, but does not open internally. The pocket 20 can occupy a large part of the space between two adjacent blades (or between two cavities 13). A “large part” can be understood as the entire inter-blade space with the exception of a slight border allowing the brazing of the sheet 18 (see “B” in [Fig. 5]).

[0035] The pocket 20 has a bottom 22 which can be provided with openings 24 intended to bring or evacuate a flow of air into / from the pocket 20. The openings 24 can be distributed regularly circumferentially and / or can be arranged in a downstream part of the pocket 20. Advantageously, the openings 24 are arranged opposite the orifices 18.4 of the sheet 18, that is to say that some are arranged in the vicinity of a downstream end of the pocket and the others are arranged in the vicinity of an upstream end.

[0036] From the bottom 22, stiffeners 26 project. These may be parallel to each other and / or parallel to one of the sides of the pocket 20. In the example illustrated, the stiffeners 26 are mainly circumferential.

[0037] The pocket 20 also accommodates studs 28. These studs 28 have the dual function of keeping the sheet 18 at a distance from the bottom 22, to guarantee that the pocket 20 retains a certain volume in all circumstances (thermal and mechanical stresses), but also of serving as a reference for the operator during a maintenance operation and in particular an operation of debrazing the sheet 18 and repositioning a replacement sheet 18.

[0038] The studs 28 may be integral with the platform 16 or attached thereto. When they are attached, the studs 28 may be made of a material distinct from that of the platform 16 and in particular a harder material. Thus, even when the sheet 18 is damaged, the studs remain intact and the distance between the bottom 22 and the sheet 18 remains unchanged.

[0039] The pads 28 can be distributed over the entire surface of the bottom 22. In the illustrated example, 6 pads are presented, grouped into 3 pairs of pads, the pads of each pair sharing the same axial position. A smaller or larger number of pads 28 is possible.

[0040] [Fig. 4] shows a top view of the pocket 20, the upstream being at the bottom of this figure, and the downstream at the top. The bottom 22 of the pocket 20 is delimited by a contour comprising an upstream edge 22.1, two lateral edges 22.2, 22.3 and a downstream edge 22.4. In the illustrated version, the upstream 22.1 and downstream 22.4 edges are substantially parallel and are oriented in the circumferential direction. The lateral edges 22.2, 22.3 follow the contours of the cavities 13 of the blades 12.

[0041] The sheet 18 and the bottom 22 have a substantially identical outline, with the difference that the sheet 18 is slightly larger. The sheet 18 can thus cover the entirety of the pocket 20 and be brazed to the platform 16, radially above, opposite the pocket 20.

[0042] [Fig.4] also shows the pads, including a pair of upstream pads 28.1, a pair of central pads 28.2 and a pair of downstream pads 28.3. The upstream pads 28.1 are arranged between the upstream edge 22.1 and a stiffener 26, the central pads 28.2 are arranged between two successive stiffeners 26 and the downstream pads 28.3 are arranged between a stiffener 26 and the downstream edge 22.4. Other distributions or another number of pads are naturally possible but this distribution and this number are particularly appropriate to properly support sheet 18 of [Fig.2].

[0043] The pads 28.1, 28.2, 28.3 are at a distance from the edges 22.1, 22.2, 22.3, 22.4 of the bottom as well as at a distance from a median line 30. This median line 30 is the average between the lateral edges 22.2, 22.3. Depending on the arrangement of the orifices 18.4 and the vents 24, and in particular when these are regularly distributed from one lateral edge to the other, the median line 30 is the line along which the air flow has the greatest speed, due to edge effects. It is therefore advisable to move the pads 28 away from this line. Similarly, it is advantageous to move the pads 28 away from the lateral edges to avoid aerodynamic blockage.

[0044] It is also visible in [Fig. 4] that the pads 28 have a circular section (they are cylinders with a fillet at the bottom 22). Other sections are possible, such as for example an elliptical section or a section with an intrados and an extrados. In this case, the pads are oriented to facilitate as much as possible the flow of the flow between the vents 24 and the orifices 18.4. It is also possible, when the pads are attached to the platform, to provide pads with controlled orientation, in order to regulate the flow in the pocket 20. A suitable mechanism (VSV synchronization ring type) could be envisaged. It is also possible to provide heat evacuation elements (for example fins which can be parallel to the bottom 22) on the pads 28, in order to increase the contact surface between the platform 16 and the air flow circulating in the pocket.

[0045] [Fig. 5] shows a cross-section of the pocket 20. It shows the stiffeners 26, the pads 28, the orifices and openings 18.4, 24 as well as a blade 12. The zones marked B are the brazing zones of the sheet 18 to the platform 16. [Fig. 5] also shows the heights H1 and H2 respectively of the stiffeners 26 and the pads 28. In the example illustrated, the stiffeners all have the same height and the pads all have the same height. But other designs are possible, in particular with a height increasing or decreasing from upstream to downstream.

[0046] The invention also relates to a maintenance method. In this method, a sheet metal requires replacement. The maintenance method comprises removing the sheet metal present on the platform, for example by means of an electrode debrazing method. The operator can use the pads 28 as an indicator of the limit of the material to be debrazed. A new sheet metal can then be placed, in contact with the pads 28.

[0047] In an alternative not shown, the sheet 18 may include blind holes intended to accommodate the head of the studs 28. This solution makes it possible to center the sheet when it is installed, or even to serve as a foolproofing device.

[0048] In an alternative not illustrated, the studs are integral with the sheet metal or attached to the sheet metal. They can then rest on the bottom 22 of the pocket 20. In this case, the bottom 22 of the pocket 20 may have wells receiving the head of the pads.

Claims

Claims

1. Turbine distributor (10) forming a crown (10) around an axis (A) and comprising: an inner shroud (2) comprising a plurality of inner platforms (14) arranged circumferentially around the axis (A) and an outer shroud (4) comprising a plurality of outer platforms (16) arranged circumferentially around the axis (A); a plurality of blades (12) arranged radially between the inner shroud (2) and the outer shroud (4); a pocket (20) formed in an outer platform (16) between two circumferentially adjacent blades (12), the pocket (20) having a bottom (22) as well as stiffeners (26) extending projecting from the bottom (22); a sheet metal (18) covering the pocket (20) radially at a distance from the stiffeners (26); and studs (28) extending projecting from the bottom (22) and on which the sheet metal (18) rests.

2. Dispenser (10) according to claim 1, characterized in that the stiffeners (26) extend projecting from the bottom (22) by a first height (H1) and the studs (28) extend projecting from the bottom (22) by a second height (H2), the second height (H2) being at least three times greater than the first height (H1).

3. Distributor (10) according to one of claims 1 or 2, characterized in that the pocket (20) comprises through openings (24) for fluid circulation and the sheet metal comprises through orifices (18.4) in fluid communication with the through openings (24) of the pocket (20), the studs (28) comprising upstream studs (28.1) arranged in the vicinity of the through orifices (18.4) and circumferentially offset from the through orifices (18.4), and downstream studs (28.3) arranged in the vicinity of the through openings (24) and circumferentially offset from the through openings (24).

4. Dispenser (10) according to one of claims 1 to 3, characterized in that the bottom (22) of the pocket (20) is delimited by a contour (22.1, 22.2, 22.3, 22.4) formed of an upstream edge (22.1), a downstream edge (22.4) and two lateral edges (22.2, 22.3), the studs (28) being arranged at a distance from all the edges (22.1, 22.2, 22.3, 22.4) and at a distance from a median line (30) equidistant to the lateral edges (22.2, 22.3).

5. Distributor (10) according to one of claims 1 to 4, characterized in that the studs (28) have a circular or elliptical section.

6. Distributor (10) according to one of claims 1 to 5, characterized in that it comprises three pairs of pads (28), including two upstream pads (28.1), two central pads (28.2) and two downstream pads (28.3).

7. Dispenser (10) according to the preceding claim, characterized in that the bottom (22) of the pocket (20) is delimited by a contour formed by an upstream edge (22.1), a downstream edge (22.4) and two lateral edges (22.2, 22.3), the stiffeners (26) extending parallel to the upstream edge (22.1) and / or to the downstream edge (22.4), from one lateral edge (22.2) to the other lateral edge (22.3), the central studs (28.2) being arranged between two adjacent stiffeners (26), the upstream studs (28.1) being arranged between the upstream edge (22.1) and a stiffener (26), and the downstream studs (28.3) being arranged between the downstream edge (22.4) and a stiffener (26).

8. Dispenser (10) according to one of claims 1 to 7, characterized in that the studs (28) are made in one piece with the external platform (16) which comprises the pocket (20).

9. Dispenser (10) according to one of claims 1 to 7, characterized in that the studs (28) are attached to the external platform (16) which comprises the pocket (20) and are made of a harder material than the material constituting the external platform (16) which comprises the pocket (20).

10. A method of replacing a distributor sheet metal (18), for a distributor (10) according to any one of claims 1 to 9, the method comprising removing the distributor sheet metal (18) by means of a debrazing operation, placing a replacement sheet metal (18) in contact with the pads (28) and brazing the replacement sheet metal (18) to the external platform (16) which comprises the pocket (20).

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