EP3390783B1 - Turbine shroud assembly and corresponding turbine - Google Patents

Description

Background of the invention

The field of application of the invention is in particular that of aeronautical gas turbine engines. The invention is however applicable to other turbomachines, for example industrial turbines.

Ceramic matrix composite materials, or CMCs, are known to retain their mechanical properties at high temperatures, which makes them suitable for constituting hot structural elements.

In the case of all-metal turbine ring assemblies, it is necessary to cool all the elements of the assembly and in particular the turbine ring which is subjected to particularly hot flows. This cooling has a significant impact on the engine performance since the cooling flow used is taken from the main flow of the engine. In addition, the use of metal for the turbine ring limits the possibilities of increasing the temperature at the turbine, which would however improve the performance of aircraft engines.

Furthermore, a set of metal turbine ring deforms under the effect of heat flow, which changes the clearance at the flow path and, therefore, the performance of the turbine.

This is why the use of CMC for different hot parts of the engines has already been considered, especially since CMCs have the additional advantage of lower density than refractory metals traditionally used.

The use of ring segments in CMC significantly reduces the ventilation required to cool the turbine ring. However, maintaining the ring sectors in position remains a problem in particular with respect to the differential expansions that can occur between the metal support structure and the CMC ring sectors. In addition, another problem lies in controlling the shape of the vein both cold and hot without generating too much stress on the ring sectors.

The document is also known WO 2015/191186 which discloses a turbine ring assembly.

There is therefore a need to improve existing turbine ring assemblies employing a CMC material in order to maintain the ring sectors in position despite the differential expansions while limiting the intensity of the mechanical stresses to the sectors. CMC ring are subjected during operation.

Object and summary of the invention

For this purpose, the invention proposes, according to a first aspect, a turbine ring assembly according to claim 1.

In the ring assembly according to the invention, the ring sectors are kept cold due to the cooperation between the protruding portions and the housings present on the annular flanges opposite them. Maintaining ring areas by this relief cooperation may no longer be ensured hot due to the expansion of the annular flanges. When hot, the holding force is resumed by the expansion of the holding elements, which expansion does not entail significant stress on the ring sectors because of the presence of a cold clearance between the holding elements and the openings on the legs of the ring sector.

The housing of the annular flange has at least first and second inclined portions bearing on the projecting portion cooperating with said housing, said first and second inclined portions each forming, when observed in meridian section, a non-zero angle relative to in the radial direction and in the axial direction.

The radial direction corresponds to the direction along a radius of the turbine ring (straight connecting the center of the turbine ring to its periphery). The axial direction corresponds to the direction along the axis of revolution of the turbine ring and the flow direction of the gas flow in the vein.

The implementation of such inclined portions at the annular flanges of the ring support structure contributes to compensating for the differences in expansion between the annular flanges and the legs of the ring sectors and thus to reducing the mechanical stresses to which the sectors ring are subjected during operation.

In an exemplary embodiment, the first inclined portion may bear on the radially inner half of the projecting portion and the second inclined portion may be supported on the radially outer half of the projecting portion.

In an exemplary embodiment, said at least one inclined portion may form an angle of between 30 ° and 60 ° with the radial direction.

In an exemplary embodiment, the ratio (diameter of the part of the holding element present in said opening) / (diameter of said opening) can be between (1 + α _CMC ) / (1 + α _m ) and 1.1x (1 + α _CMC ) / (1 + α _m ) where α _m denotes the coefficient of thermal expansion of said part of the holding element and α _CMC denotes the coefficient of thermal expansion of the ceramic matrix composite material of the ring sectors, α _m and α _CMC being measured at 900 ° C. and expressed as
10 ^-6 ° C ^-1 .

Such values for the ratio between the diameter of the part of the holding element present in said opening and the diameter of said opening make it possible to obtain a maintenance of the optimum ring sectors when hot because of the integral or substantially integral filling. the game present between the opening and the holding member obtained by expansion of the holding member.

In an exemplary embodiment, each ring sector may have a shape in Pi (Π) in axial section.

The present invention also relates to a turbomachine comprising a turbine ring assembly as described above.

Brief description of the drawings

• la figure 1 est une vue en section radiale d'un exemple d'ensemble d'anneau de turbine selon l'invention,
• la figure 2 est un détail de la figure 1, et
• les figures 3 et 4 illustrent schématiquement le montage d'un secteur d'anneau dans la structure de support d'anneau de l'ensemble d'anneau de la figure 1.

Other characteristics and advantages of the invention will emerge from the following description of a particular embodiment of the invention, which is not limiting, with reference to the appended drawings, in which:

• the figure 1 is a radial sectional view of an exemplary turbine ring assembly according to the invention,
• the figure 2 is a detail of the figure 1 , and
• the figures 3 and 4 schematically illustrate the mounting of a ring sector in the ring support structure of the ring assembly of the figure 1 .

Detailed description of embodiments

The figure 1 shows a high pressure turbine ring assembly comprising a turbine ring 1 made of a ceramic matrix composite material (CMC) and a ring support metal structure 3. The turbine ring 1 surrounds a set of rotary blades 5. The turbine ring 1 is formed of a plurality of ring sectors 10, the figure 1 being a radial sectional view along a plane passing between two sectors of consecutive rings. Ring sectors 10 present in the illustrated example a shape in Pi (Π) in axial section. The arrow DA indicates the axial direction with respect to the turbine ring 1 while the arrow DR indicates the radial direction with respect to the turbine ring 1.

Each ring sector 10 has a substantially P-shaped section (Π) inverted with an annular base 12 whose inner face coated with a layer 13 of abradable material defines the flow stream of gas flow in the turbine. Upstream and downstream tabs 14, 16 extend from the outer face of the annular base 12 in the radial direction DR. The terms "upstream" and "downstream" are used herein with reference to the flow direction of the gas flow in the turbine (arrow F).

The ring support structure 3 which is integral with a turbine casing 30 comprises an annular upstream radial flange 32 and an annular downstream radial flange 36. The lugs 14 and 16 of each ring sector 10 are held between the flanges. 32 and 36. Each of the annular flanges 32 and 36 defines a housing 320 and 360. The housings 320 and 360 cooperate with a respective projecting portion 140 and 160 to ensure the cold maintenance of the ring sectors 10 on the structure ring support 3. By "cold" is meant in the present invention, the temperature at which the ring assembly is located when the turbine does not run, that is to say at room temperature which may be for example about 25 ° C. The protruding portion 140 is located on the face 14a of the lug 14 facing the flange 32. The projecting portion 160 is, for its part, located on the face 16a of the lug 16 located opposite the flange 36 In the illustrated example, each tab 14 and 16 comprises a portion of extra thickness forming the projecting portion 140 or 160.

The housings 320 and 360 each have, in the illustrated example, two inclined portions. Thus, as illustrated in figure 2 , the housing 360 has a first inclined portion 360a and a second inclined portion 360b each forming a non-zero angle with the radial directions DR and axial DA. The first and second inclined portions 360a and 360b bear on the projecting portion 160 cooperating with said housing 360. The first 360a and second 360b inclined portions may not be parallel to each other, as illustrated. The housing 360 may furthermore have a radial portion 360c extending along the radial direction DR and located between the first inclined portion 360a and the second inclined portion 360b. In the illustrated example, the first 360a and second 360b inclined portions each form, when observed in meridian section, an angle of between 30 ° and 60 ° with the radial direction DR. On the figure 2 , α ₁ denotes the angle formed between the first inclined portion 360a and the radial direction DR, α ₂ denotes the angle formed between the first inclined portion 360a and the axial direction DA, α ₃ denotes the angle formed between the second portion inclined 360b and the radial direction DR and α ₄ designates the angle formed between the second inclined portion 360b and the axial direction DA. The first inclined portion 360a rests on the radially inner half Mi of the projecting portion 160 and the second inclined portion 360b bears against the radially outer half Me of the projecting portion 160. The housing 320 located on the upstream flange 32 has a structure similar to that just described for housing 360.

Furthermore, the ring sectors 10 are further maintained by holding elements, here in the form of locking bands 40a and 40b, for example in the form of pins 40a and 40b. A first set of locking shrouds 40a is engaged both in the annular upstream radial flange 32 and in the upstream lugs 14 of the ring sectors 10. For this purpose, each hoop 40a passes respectively through an orifice 35 formed in the radial flange. annular upstream 32 and an orifice 15 formed in each upstream lug 14, the orifices 35 and 15 being aligned during the assembly of the ring sectors 10 on the ring support structure 3. In the same way, a second set of frets 40b is engaged both in the annular downstream radial flange 36 and in the downstream lugs 16 of the ring sectors 10. For this purpose, each hoop 40b passes respectively through an orifice 37 formed in the annular downstream radial flange 36 and a orifice 17 formed in each downstream tab 16, the orifices 37 and 17 being aligned during assembly of the ring sectors 10 on the ring support structure 3.

The locking frets 40a and 40b are made of a material having a coefficient of thermal expansion greater than the coefficient of thermal expansion of the ceramic matrix composite material of the ring sectors 10. The locking frets 40a and 40b may for example be made of metal material, for example alloy AM1 or Inconel 718. A game J is present cold between the frets of block 40a, respectively 40b, and the orifices 15, 17 respectively, of the tabs 14, respectively 16. The expansion of the locking bands 40a and 40b in the orifices 15 and 17 contributes to the hot maintenance of the ring sectors 10 on the structure ring support 3 reducing or even filling the clearance J. By "hot" means here the temperatures to which the tabs of the ring sectors during the operation of the turbine, these temperatures can be understood between 600 ° C and 900 ° C. In the illustrated example, the ratio between the diameter d ₁ of the part of the frets 40b present in the orifice 17 and the diameter d _{2 of} said orifice 17 (ie d ₁ / d ₂ ) is between (1 + α _CMC ) / (1 + α _m ) and 1.1x (1 + α _CMC ) / (1 + α _m ) where α _m denotes the coefficient of thermal expansion of said portion of the frets 40b and α _CMC denotes the coefficient of thermal expansion of the material This characteristic can also be verified for the ratio (diameter of the portion of the hoop 40a present in the orifice 15) / (diameter of the orifice 15).

In addition, the inter-sector sealing is provided by sealing tabs housed in grooves facing in the opposite edges of two neighboring ring sectors. A tongue 22a extends over almost the entire length of the annular base 12 in the middle portion thereof. Another tab 22b extends along the tab 14 and on a portion of the annular base 12. Another tab 22c extends along the tab 16. At one end, the tab 22c abuts the tab 22a and on the tongue 22b. The tabs 22a, 22b, 22c are for example metallic and are mounted with cold clearance in their housings to ensure the sealing function at the temperatures encountered in operation.

Conventionally, ventilation orifices 33 formed in the flange 32 make it possible to bring cooling air to the outside of the turbine ring 1.

The assembly of an exemplary turbine ring assembly as shown in FIG. figure 1 .

Each ring sector 10 described above is made of a ceramic matrix composite material (CMC) by forming a fibrous preform having a shape close to that of the ring sector and densifying the preform with a ceramic matrix. For the realization of the fiber preform, it is possible to use ceramic fiber yarns, for example SiC fiber yarns, such as those marketed by the Japanese company Nippon Carbon under the name "Nicalon", or carbon fiber yarns. The fibrous preform is advantageously made by three-dimensional weaving, or multilayer weaving with the provision of debonding zones enabling the parts of preforms corresponding to the lugs 14 and 16 of the sectors 10 to be spaced apart. The weaving may be of the interlock type, as illustrated. Other weaves of three-dimensional weave or multilayer can be used as for example multi-web or multi-satin weaves. We can refer to the document WO 2006/136755 . After weaving, the blank can be shaped to obtain a ring sector preform which is consolidated and densified by a ceramic matrix, the densification can be achieved in particular by chemical vapor infiltration (CVI) which is well known in itself. A detailed example of manufacture of ring sectors in CMC is described in particular in the document US 2012/0027572 .

The ring support structure 3 is made of a metallic material such as a Waspaloy® or Inconel 718 alloy.

The realization of the turbine ring assembly is continued by mounting the ring sectors 10 on the ring support structure 3. The illustrated ring support structure 3 comprises at least one flange, here the flange radial downstream annular 36, which is elastically deformable in the axial direction DA of the ring. When mounting a ring sector 10, the annular downstream radial flange 36 is pulled in the direction DA as shown in FIG. figure 3 in order to increase the spacing between the flanges 32 and 36 and to allow the insertion of the ring sector 10 between the flanges 32 and 36 without risk of damage to the ring sector 10. In order to facilitate pulling apart the annular downstream radial flange 36, it comprises a plurality of hooks 39 distributed on its face 36b, which face is opposite the face 36a of the flange 36 opposite the downstream tabs 16 of the ring sectors 10. The traction in the axial direction DA exerted on the elastically deformable flange 36 is here carried out by means of a tool 50 comprising at least one arm 51 whose end comprises a hook 510 which is engaged in a hook 39 present on the outer face 36a of the flange 36. The number of square brackets 39 distributed on the face 36a of the flange 36 is defined according to the number of tensile points that one wishes to have on the flange 36. This number depends mainly on the elastic nature of the flange. Other forms and arrangements of means for exerting traction in the axial direction DA on one of the flanges of the ring support structure can of course be considered within the scope of the present invention.

Once the annular flange 36 is spaced apart in the direction DA, the ring sector 10 is inserted between the annular flanges 32 and 36. During the insertion of the ring sector 10, the projecting portion 140 is engaged in the housing 120 and the orifices 15 and 35 are aligned. The flange 36 is then released in order to introduce the protruding portion 160 into the housing 360 and to align the orifices 17 and 37. The structure illustrated in FIG. figure 4 in which the ring sectors 10 are kept cold by cooperation of the projecting portions 140 and 160 and the housings 320 and 360. A band 40a is then engaged in the aligned orifices 35 and 15 respectively formed in the annular upstream radial flange 32 and in the upstream lug 14. In the same way, a hoop 40b is engaged in the aligned orifices 37 and 17 respectively formed in the annular downstream radial flange 36 and in the downstream lug 16. The frets 40a and 40b are forced into the annular flanges 32 and 36 to ensure their maintenance cold (mounting H6P6 for example or other tight fixtures). Each lug 14 or 16 of ring sector may comprise one or more orifices for the passage of one or more frets.

In cold, the ring sectors 10 are maintained by cooperation between the protruding portions 140 and 160 and the housings 320 and 360. When hot, the expansion of the annular flanges 32 and 36 may no longer make it possible to maintain the sectors ring 10 at the housing 320 and 360. The hot maintenance of the ring sectors 10 is then ensured by the expansion of the bands 40a and 40b in the orifices 15 and 17 which reduces or cancels the game J.

The expression "understood between ... and ..." must be understood as including boundaries.

Claims (6)

1. A turbine ring assembly comprising a plurality of ring sectors (10) made of ceramic matrix composite material forming a turbine ring (1), and a ring support structure (3) having two annular flanges (32; 36), each ring sector (10) having a portion forming an annular base (12) with an inner face defining the inside face of the turbine ring and an outer face from which there project at least two tabs (14; 16), the tabs (14; 16) of each ring sector (10) being retained between the two annular flanges (32; 36) of the ring support structure (3),
   each tab (14; 16) of the ring sectors (10) including a projecting portion (140; 160) on its face (14a; 16a) situated facing one of the two annular flanges (32; 36), this projecting portion (140; 160) co-operating with a housing (320; 360) present in the annular flange (32; 36), and
   each tab (14; 16) of the ring sectors (10) including at least one opening (15; 17) in which there is received a portion of a retention element (40a; 40b) secured to the annular flange (32; 36) situated facing said tab (14; 16), clearance (J) being present between the opening (15; 17) of said tab (14; 16) and the portion of the retention element (40a; 40b) present in said opening (15; 17), said retention element (40a; 40b) being made of a material having a coefficient of thermal expansion that is greater than the coefficient of thermal expansion of the ceramic matrix composite material of the ring sectors (10),
   characterized in that the housing (320; 360) in the annular flange (32; 36) presents at least first and second sloping portions (360a; 360b) bearing against the projecting portion (140; 160) co-operating with said housing (320; 360), said first and second sloping portions (360a; 360b), when observed in meridian section, each forming a non-zero angle (α₁; α₂; α₃; α₄) relative to the radial direction (DR) and relative to the axial direction (DA).
2. An assembly according to claim 1, wherein the first sloping portion (360a) bears against the radially inner half (Mi) of the projecting portion (140; 160), and wherein the second sloping portion (360b) bears against the radially outer half (Me) of the projecting portion (140; 160).
3. An assembly according to claim 1 or claim 2, wherein at least one of the first and second sloping portions (360a; 360b) forms an angle (α₁; α₃) relative to the radial direction (DR) that lies in the range 30° to 60°.
4. An assembly according to any one of claims 1 to 3, wherein the ratio of the diameter (d₁) of the portion of the retention element (40a; 40b) that is present in said opening (15; 17) divided by the diameter (d₂) of said opening (15; 17) lies in the range (1+α_CMC)/(1+α_m) to 1.1×(1+α_CMC)/(1+α_m), where α_m designates the coefficient of thermal expansion of said portion of the retention element and α_CMC designates the coefficient of thermal expansion of the ceramic matrix composite material of the ring sectors, α_m and α_CMC being measured at 900°C and being expressed as 10^-6×°C^-1.
5. An assembly according to any one of claims 1 to 4, wherein each ring sector (10) presents a Pi-shape (Π-shape)in axial section.
6. A turbine engine including a turbine ring assembly according to any one of claims 1 to 5.

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