EP2060743B1 - Sealing of a stator guide vane ring in a turbine stage - Google Patents

Description

The present invention relates to the sealing of a rotor ring in a turbine stage of a turbomachine such as an airplane turbojet or turboprop engine as described in US Pat. EP 1538306A .

Typically, a turbomachine turbine comprises at least one stage comprising a distributor formed of an annular row of fixed vanes and followed by a rotor wheel mounted inside a sectorized ring. The distributor comprises at its downstream end an annular flange which extends radially outwards and which carries attachment means on a casing of the turbine. The downstream sectorized ring comprises an upstream cylindrical rim which is held radially on a rail of the turbine casing by means of an annular locking member with a C-shaped or U-shaped section axially engaged on the casing rail and on the cylindrical rim of the ring.

The cylindrical rim of the ring and the casing rail are generally thermally protected by an annular plate which is mounted between the outer rim of the distributor and the upstream end of the ring to limit the passage of gas from the vein of the ring. turbine radially outwardly in the annular housing space of the rim of the ring and crankcase rail.

However, the seal is not perfect and hot gas leaks from the vein of the turbine can increase the temperature of the crankcase hooks and cause the formation of cracks or cracks may destroy the hooks.

Moreover, the vanes of the distributor generally comprise cooling air flow channels taken upstream on the compressor of the turbomachine.

It is known to take a portion of the air circulating in the channels of these vanes and reinject this air into the annular housing space of the upstream edge of the ring and the casing rail to reduce their temperature. The injection of air into this space also makes it possible to maintain this space at a pressure greater than that of the combustion gases passing through the turbine, which limits the introduction of these gases into the annular space.

However, when the seal between the outer rim of the distributor and the upstream end of the ring is not sufficient, the cooling air injected into the annular housing space of the rim of the ring and the rail of casing, tends to pass radially from outside to inside in the turbine duct and therefore does not participate in the cooling of the housing and the ring.

The object of the invention is in particular to provide a simple, effective and economical answer to these problems of the prior art.

It relates to a turbine stage comprising sealing means between the distributor and the ring sectorized which are simple and effective to prevent the passage of gas in a radial direction between the outer rim of the distributor and the upstream end of the ring.

It proposes for this purpose a turbine stage of a turbomachine, comprising a rotor wheel mounted inside a sectorized ring carried by a turbine casing, a distributor located upstream of the wheel and formed of a row. annular fixed vanes, this distributor comprising at its downstream end an outer annular flange having fastening means on the turbine housing, sealing means being provided between the outer rim of the distributor and the upstream end of the ring for limiting the passage of gas radially between the outer rim of the distributor and the ring, characterized in that the sealing means comprise an annular plate which extends substantially radially between the outer rim of the distributor and the end upstream of the ring and which comprises, at its inner periphery and at its outer periphery, axial support means against a downstream face of the external rim of the distributor, the annular part e median of this sheet being axially spaced from the outer rim of the distributor and being in axial bearing against the upstream end of the ring, the sheet being resiliently biased in the axial direction by the upstream end of the ring.

The sealing plate according to the invention bears axially in the direction of the upstream, at its inner periphery and at its outer periphery, on the rim of the distributor, and its median annular portion bears elastically on the upstream end. of the ring. The three annular support areas of the sheet on the rim of the distributor and on the ring ensure a good seal between these elements, and thus prevent the passage of gas from the turbine duct outwards, in the annular space housing the rim of the ring and the crankcase rail, and the air leaks from this space inwards into the turbine duct.

The ring is in abutment at its upstream end on the middle part of the sheet, itself bearing on the rim of the distributor, which can result in a slight elastic deformation in bending of the sheet. This deformation is allowed by the axial space provided between the outer rim of the distributor and the sealing plate at the middle annular portion of this sheet.

This axial prestress is determined to make up the manufacturing tolerances of the various parts and, in operation, to maintain the three aforementioned supports, despite differential thermal expansions of the different parts. The bending deformation of the sheet may therefore be more or less important during the different operating speeds of the turbine.

Preferably, the sheet is fixed, by means of rivets for example, on the outer rim of the distributor. The sheet is for example fixed by its inner periphery on a radially inner end portion of the outer rim of the distributor.

In one embodiment of the invention, the sheet is substantially flat and is, in the mounting position, plated on the downstream face of the outer rim of the distributor, covering an annular groove of the downstream face.

The annular groove of the downstream face of the outer rim of the distributor makes it possible to define an axial annular space between the rim of the distributor and the median annular portion of the sheet, thus allowing the bending elastic deformation of the sheet. This groove is sectorized as the distributor and can be substantially continuous 360 ° around the axis of the turbine and is closed by the sheet bearing on the outer rim of the distributor, radially inside and outside of this throat.

According to another embodiment of the invention, the annular plate is not flat, but curved with a concavity facing upstream. It comprises, for example, an annular portion having a U-shaped or V-shaped section whose opening is oriented upstream, this annular portion being in axial abutment against the upstream end of the ring and defining an annular space with the downstream face of the outer rim of the distributor.

The sealing plate is sectorized as the distributor and can extend over 360 ° around the axis of the turbine. It is preferably metallic.

The invention also relates to a turbomachine turbine, characterized in that it comprises at least one stage as described above.

The invention also relates to a turbomachine, such as an airplane turbojet or turboprop, characterized in that it comprises at least one turbine stage of the aforementioned type.

• la figure 1 est une demi-vue schématique partielle en coupe axiale d'une turbine de turbomachine ;
• la figure 2 est une vue à plus grande échelle d'une partie de la figure 1, et représente un étage de turbine selon la technique antérieure ;
• la figure 3 est une vue agrandie du détail I₃ de la figure 2 ;
• la figure 4 est une vue schématique partielle en coupe axiale d'un étage de turbine selon l'invention ;
• la figure 5 est une vue correspondant à la figure 4 et représentant une variante de réalisation de l'invention.

The invention will be better understood and other characteristics, details and advantages thereof will appear more clearly on reading the description which follows, given by way of non-limiting example with reference to the accompanying drawings in which:

• the figure 1 is a partial schematic half-view in axial section of a turbomachine turbine;
• the figure 2 is a larger-scale view of some of the figure 1 , and represents a turbine stage according to the prior art;
• the figure 3 is an enlarged view of detail I ₃ of the figure 2 ;
• the figure 4 is a partial schematic view in axial section of a turbine stage according to the invention;
• the figure 5 is a view corresponding to the figure 4 and representing an alternative embodiment of the invention.

We first refer to the figure 1 which represents a turbomachine low-pressure turbine 10 comprising four stages each comprising a distributor 12 formed of an annular row of fixed vanes 14 carried by an outer casing 16 of the turbine, and a wheel 18 located downstream of the distributor 12.

The wheels 18 comprise disks 20 assembled axially to each other by annular flanges 22 and carrying radial vanes 24. These wheels 18 are connected to a turbine shaft (not shown) via a drive cone 26 fixed on annular flanges 22 discs.

Each wheel 18 is surrounded externally with a small clearance by a ring 28 formed by sectors fixed circumferentially on the casing 16 of the turbine through locking members, as will be described in more detail in the following.

The distributors 12 comprise walls 30 of internal and external revolution 32, respectively, which delimit between them the annular flow vein of the gases in the turbine and between which radially extend the vanes 14.

The outer wall 32 of the distributor 16 of the upstream stage, better visible in figure 2 , comprises radially outer annular rims upstream 34 and downstream 36 having axial annular tabs 38 hooking, oriented upstream and intended to be engaged in corresponding axial annular grooves 40 of the casing 16 of the turbine.

The vanes 14 of this distributor 12 comprise cooling air circulation channels 42 coming from a supply enclosure 44 (arrows 46) located radially outside the wall 32 of the distributor. This air is partly discharged in the vein of flow of the turbine gases through orifices (not shown) formed near the trailing edge of the vanes 14 and opening into their channels 42, and partly discharged into a chamber 52 located radially inside the wall 30 of the dispenser (arrows 54). The cooling air is taken upstream on a compressor of the turbomachine and brought into the supply chamber 44 by appropriate means.

The ring 28 located downstream of the distributor 12 of the upstream stage comprises at its upstream end an annular hook 56 which is applied to a corresponding cylindrical rail 58 of the casing 16, and which is held radially on this rail by an annular member 60 with a C-shaped or U-shaped section which is axially engaged from upstream on the hook 56 and the rail 5 ( figure 3 ).

The member 60, the hook 56 and the rail 58 are housed in an annular space 62 which extends around the ring 28 between the housing 16 and the distributor 12. The member 60 bears at its upstream end on a downstream face 64 of the downstream annular rim 36 of the distributor.

The member 60, the housing rail 58 and the hook 56 of the ring are thermally protected by an annular plate 66 which is mounted between the upstream end of the ring 28 and the downstream face 64 of the annular flange 36 of the distributor. , to limit the passage of gas from the vein of the turbine radially outwards in the annular space 62.

The housing rail 58 and the hook 56 of the ring are in operation subjected to high temperatures which can cause the formation of cracks or fissures likely to destroy them.

To remedy these problems, it has already been proposed to take a portion of the relatively cool air circulating in the channels 42 of the vanes of the distributor, and to bring this air into the annular space 62 to reduce the temperature inside. of this space.

For this, ducts 68 and 70 are respectively formed in the outer wall 32 and in the outer rim 36 of the distributor, to connect the Channels 42 of the vanes to the annular space 62. The ducts 68 formed in the outer wall 32 of the distributor communicate at one of their ends with a channel 42 of a blade and at the other of their ends with an annular passage 72 located radially outside the wall 32 of the distributor and defined axially by the outer annular flanges 34, 36 of the distributor. The ducts 70 formed in the outer rim 36 of the distributor 12 are oblique with respect to the axis of the turbine and oriented downstream towards the outside. They open at their upstream ends in the annular passage 72, and at their downstream ends on the downstream face 64 of the outer rim 36 of the distributor.

However, the annular plate 66 alone does not provide a sufficient seal between the distributor 12 and the ring 28, which results in leaks of the air injected into the annular space 62 radially inwards in the vein of the turbine.

The invention makes it possible to provide a simple solution to this problem by means of new sealing means.

The sealing means according to the invention comprise an annular plate 80 which extends radially between the outer rim 36 of the distributor and the upstream end of the ring 28 and which is axially prestressed by bearing on the upstream side, by its periphery. internal and its outer periphery, on the downstream face 64 of the flange 36 and by pressing the downstream side, at its median annular portion on the upstream end of the ring 28.

In the example shown in figure 4 , the annular sealing plate 80 is substantially flat and is fixed by rivets 82 on the outer flange 36 of the distributor. The rivets are substantially parallel to the axis of the turbine and pass through orifices 84 formed in a radially inner end portion of the sheet 80 and corresponding orifices 86 formed in a radially inner end portion of the rim 36 of the distributor.

The sheet 80 completely covers an annular groove 88 of the downstream face 64 of the flange 36. This groove 88 has a small axial depth, for example substantially equal to the thickness of the sheet, and has a radial dimension which is slightly smaller than that of the sheet. of the sheet 80. It is formed in the distributor areas over the entire angular extent of these sectors and can extend over 360 ° around the axis of the turbine. The sheet is formed of angular sectors each fixed on a distributor sector and can extend over 360 ° around the axis of the turbine.

The inner periphery of the sheet 80 extends over a circumference located radially inside the groove 88 and this inner periphery bears axially against a radially inner portion of the downstream face 64 of the flange 36. The outer periphery of the sheet extends over a circumference located radially outside the groove and this periphery bears axially on a radially outer portion of the downstream face 64 of the flange 36.

In the example shown, the orifices 84 and 86 for mounting the rivets 82 open at one of their ends into the annular groove 88 in the vicinity of its inner periphery, and are located radially inside the ring 28. upstream end of the ring 28 is in axial abutment on the sheet 80 in an area between the rivets and the outer periphery of the groove 88.

In the mounting position, the sheet 80 is elastically prestressed by the ring which exerts a sufficient force in the axial direction upstream on the sheet so that it undergoes a slight elastic deformation in bending. The axial prestressing of the sheet 80 is determined on the one hand to make up the manufacturing tolerances of the different parts, and to preserve the three annular sealing zones on the distributor flange and on the ring, despite the differential thermal expansions. parts in operation. The deformation of the sheet 80 may therefore vary during an operating cycle of the turbomachine.

The three bearing zones provide a good seal between the turbine duct and the annular space 62 for housing the upstream flange 56 of the ring and the casing rail 58. The supports C1, between the inner periphery of the sheet 80 and the flange 36 of the distributor, C2, between the sheet and the upstream end of the ring 28, and C3, between the outer periphery of the sheet 80 and the flange 36 of the distributor, prevent the passage of gas from the vein of the turbine to the outside in the annular space 62, and air leakage from the space 62 inward into the turbine duct.

The ducts 70 of the figure 3 which provide the fluidic communication between the annular passage 72 and the annular space 62 are here replaced by axial holes 90 formed in the flange 36 of the distributor and axial grooves 92 formed in the annular tabs 38 of this flange. The holes 90 open at their downstream ends radially outside the sheet 80. In a variant, the flange 36 of the dispenser may comprise ducts 70 similar to those of FIG. figure 3 these ducts opening at their ends downstream radially outside the sheet.

Before mounting the ring 28 on the turbine casing 16, the plate 80 can already be plated by means of the rivets on the downstream face 64 of the distributor flange. The ring 28 is then mounted on the housing rail 58 and abuts on the sheet 80 to preload axially.

Alternatively, before mounting the ring 28, the sheet 80 is held by the rivets and extends from upstream to downstream to the outside so that only its inner periphery is in contact with the downstream face of the flange 36 Fixing the ring on the casing then makes it possible to press the outer periphery of the sheet onto the external rim of the distributor.

In yet another variant represented in figure 5 , the annular plate 80 'is not flat but curved with a concavity oriented axially upstream. In the example shown, the sheet 80 'comprises in the vicinity of its outer periphery a curved annular portion V-shaped section or U whose opening is oriented upstream. This sheet 80 'is mounted in the same manner as the sheet 80 described above, and its curved portion delimits an annular space 94 with the downstream face 64 of the outer flange 36 of the distributor. It is therefore not necessary to provide an annular groove on this face 64, as is the case in the embodiment of the figure 3 . The curved portion of the sheet 80 'bears against the upstream end of the ring (at C3), this ring exerting a sufficient force in the axial direction upstream on the sheet 80' so that it undergoes a slight elastic deformation in flexion, as described with reference to figure 3 .

The sealing plate 80, 80 'is made of metal alloy, and has a relatively small thickness of about one to a few millimeters.

Although the sheet 80, 80 'according to the invention is associated in the example shown with a distributor whose outer rim 36 comprises means for fluid communication between the annular passage 72 and the annular space 62, this sheet could be associated to a distributor without such means. The sheet could also be fixed on the distributor by other fastening means than the rivets 82. It could possibly be fixed on the upstream end of the ring 28.

Claims (8)

1. A turbine stage of a turbomachine, the stage comprising a rotor wheel (18) mounted inside a sectorized ring (28) carried by a turbine casing (16), and a nozzle (12) situated upstream from the wheel and made up of an annular row of stator vanes (14), the nozzle including at its downstream end an outer annular rim (36) having fastener means (38) for fastening to the turbine casing, sealing means being provided between the outer rim of the nozzle and the upstream end of the ring to limit the passage of gas in a radial direction between the outer rim of the nozzle and the ring, the stage being characterized in that the sealing means comprise an annular sheet (80, 80') extending substantially radially between the outer rim of the nozzle and the upstream end of the ring, and comprising at its inner periphery and at its outer periphery means for bearing axially against a downstream face (64) of the outer rim of the nozzle, the middle annular portion of said sheet being axially spaced apart from the outer rim of the nozzle and bearing axially against the upstream end of the ring, the sheet being elastically prestressed in the axial direction by the upstream end of the ring.
2. A turbine stage according to claim 1, characterized in that the sheet (80, 80') is fastened to the outer rim (36) of the nozzle, e.g. by means of rivets (82).
3. A turbine stage according to claim 1, characterized in that the sheet (80, 80') is fastened via its inner periphery to a radially inner end portion of the outer rim (36) of the nozzle.
4. A turbine stage according to claim 1, characterized in that the sheet (80) is substantially plane and, in the assembled position, is pressed against the downstream face (64) of the outer rim (36) of the nozzle, covering an annular groove (88) in the downstream face (64) of the outer rim (36).
5. A turbine stage according to claim 1, characterized in that the sheet (80') comprises an annular portion of U-shaped or V-shaped section with its opening facing upstream, said annular portion bearing axially against the upstream end of the ring and co-operating with the downstream face (64) of the outer rim (36) of the nozzle to define an annular space (49).
6. A turbine stage according to claim 1, characterized in that the sealing sheet (80, 80') is made up of sheet sectors, each fastened to a nozzle sector.
7. A turbine stage according to claim 1, characterized in that the sheet (80, 80') is made of metal.
8. A turbomachine such as an airplane turbojet or turboprop, characterized in that it includes at least one turbine stage according to claim 1.

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