Patent Publication Number: US-10760441-B2

Title: Turbine for a turbine engine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of French Patent Application No. 1755821, filed Jun. 26, 2017, the contents of which is incorporated by reference herein. 
     TECHNICAL FIELD 
     The present invention relates to a turbine for a turbine engine, more particularly for a turbojet engine or a turboprop engine of an aircraft, as well as a method for mounting such a turbine. 
     BACKGROUND 
     A turbine engine, specifically a twin-spool turbine engine, conventionally includes, in the downstream direction, a fan, a low-pressure compressor, a high-pressure compressor, a combustion chamber, a high-pressure turbine and a low-pressure turbine. 
     Conventionally, in the present application, “upstream” and “downstream” are defined relative to the direction of the air flow in the turbine engine. Conventionally, in the present application, “internal” and “external”, “lower” and “higher” and “internal” and “external” are similarly defined radially relative to the axis of the turbine engine. 
     The low-pressure turbine of a turbine engine comprises a turbine shaft whereon several successive stages, each including an impeller and a guide vane are mounted. Each impeller comprises a disk, on the external periphery of which substantially radial blades are mounted, with the disks of the various impellers being coaxially connected together and to the driving shaft of the turbine rotor, using appropriate means. Each guide vane comprises an internal annular platform and an external annular platform between which substantially radial blades extend. The external platform of the guide vane comprises means for hooking and attaching on an external casing of the turbine. All the guide vanes form the stationary part of the engine called the stator. 
     The blades of each rotor wheel conventionally include lips at the radially external periphery thereof, and cooperate with a ring made of an abradable material so as to form sealing means of the labyrinth seal type. 
     Such a structure is known for instance from document FR 2 879 649. 
     In order to ensure high performances of the turbine engine, the clearances at the seals have to be checked and the leakage rate at the interface between the blade lips and the ring made of abradable material have to be limited. 
     Therefore the need exists for improving the efficiency of such labyrinth seals, while facilitating the mounting and the structure of the assembly. 
     The invention more particularly aims at providing a simple, efficient and cost-effective solution to this problem. 
     SUMMARY 
     For this purpose, the present invention relates to a turbine for a turbine engine, for instance a turbojet engine or a turboprop engine of an aircraft, having a stator and a rotor comprising a rotor wheel having vanes the radially external periphery of which comprises at least one lip which radially extends outwards, with sealing means radially extending about the vanes and comprising a sealing ring; with the radially external end of the lip cooperating with said sealing ring so as to form a seal of the labyrinth type, characterized in that said sealing ring comprises at least one first portion and one second portion axially offset relative to one another, with the first portion and/or the second portion defining a groove wherein the lip is inserted, with the first portion and/or the second portion each cooperating with at least one lip of the vanes axially located opposite said first and second portions, with the first portion comprising a first protruding zone engaged in a form-fitting manner in the axial direction into a first recessed zone of the second portion, with the stator comprising means for holding the first and second portions in position relative to the stator. 
     A first lip, which forms a seal of the labyrinth type with the groove walls is thus obtained, with said seal having a significant head loss, i.e. a substantially higher one than in the prior art solution. As a matter of fact, thanks to the mounting which is facilitated by the two-part structure of the ring, a first lip having a large radial dimension can be obtained, which is engaged into a groove having a large radial dimension too. Besides, the protruding and recessed zones are so configured as to engage with each other in the axial direction, which ensures sealing between the first and second portions of the sealing ring. 
     The above-mentioned assembling between the first and second portions is thus of the mortise-and-tenon joint type. 
     The means for holding same in position may comprise a stop for radially supporting the first portion and means for tightening the second portion against the stator, with the first portion being positioned upstream of the second portion. 
     Such characteristic makes it possible to facilitate the assembling of the ring on the stator. 
     The first portion can include a groove radially opening outwards and axially opening in the downstream direction, with the second portion including a groove radially opening outwards and axially opening in the upstream direction, opposite the groove of the first portion. The recesses of the first and second portions then form a groove. 
     In an alternative embodiment, only one of the first and second portions may comprise a recess, with the groove being defined by said recess and by one radial surface of the opposite portion. 
     The first portion may be radially held, upstream, by the stator, with the first portion being radially held, downstream, by the second portion. 
     The first portion and the second portion may comprise a block made of abradable material mounted on a support, with the first protruding and recessed zones of said first and second portions being formed on the supports. 
     The first portion and the second portion can be annular and consist of successive ring sectors, with each ring sector comprising slots at the circumferential ends thereof, with sealing tabs being mounted in said slots, between said sectors. 
     The first protruding zone and the first recessed zone can circumferentially extend over an angular range smaller than or substantially equal to the circumferential extension of one sector of the sealing ring. As mentioned above, the first protruding zone and the first recessed zone form a baffle which limits the rate of gas leakage flowing radially outwards in the jet, between the first and second portions. in order to optimize the efficiency of such baffle, same will preferably extend circumferentially on the whole or almost the whole of the circumferential extension of a sector of the ring. The above circumferential extension makes it possible to limit such leakage rate as much as possible. 
     The first portion, or the second portion respectively, can comprise a second protruding zone engaged in a form-fitting manner into a second recessed zone of the second portion, or the first portion respectively, with the first protruding and recessed zones being radially offset relative to the radially internal surface of the second protruding and recessed zones. 
     More particularly, the first protruding and recessed zones may be radially offset outwards relative to the second protruding and recessed zones. 
     The first protruding zone or the first recessed zone may be radially offset outwards relative to the second protruding zone or the second recessed zone. 
     Thanks to such axial shift, the baffle is larger in the axial direction, which optimizes the efficiency thereof by efficiently limiting the rate of gas leakage between the first portion and the second portion of the sealing ring. 
     The stator can comprise a turbine casing comprising an annular, for instance tapered wall, with at least one flange radially extending inwards from the annular wall of the turbine casing, with said flange axially bearing, upstream, on a radially external annular rim of the first portion, with said flange axially bearing, downstream, on a radially external annular rim of the second portion. 
     Said rims may be formed in the supports of the first and second portions. 
     The stator may comprise a downstream guide vane, with the downstream end of the second portion being engaged into a groove of the downstream guide vane. 
     The flange of the turbine casing may also be engaged into the groove of the downstream guide vane. 
     Each protruding zone may be attached to the first portion or to the second portion, at the base thereof, and may comprise a free end opposite the base. The first protruding zone may belong to the first portion, or to the second portion, respectively, with the second protruding zone possibly belonging to the second portion, or to the first portion, respectively. In this case, the free end of the first protruding zone may be axially offset relative to the base of the second protruding zone. Besides, the free end of the second protruding zone may be axially offset relative to the base of the first protruding zone. The base of the first protruding zone may be placed axially opposite the base of the second protruding zone. 
     The block made of abradable material of the first portion may comprise a radial downstream surface. The block made of abradable material of the second portion may comprise a radial upstream surface. The blocks made of abradable material of the first and second portions may be in mutual contact through their radial downstream and upstream surfaces. 
     The base of the second protruding zone may be axially offset, for instance in the downstream direction, relative to the downstream surface of the block of the first portion and/or relative to the upstream surface of the block of the second portion. 
     The first portion and/or the second portion comprise a radially external surface intended to support the flange of the casing. 
     Said external bearing surface comprises at least one annular groove. The contact area between the flange of the casing and the first and second portions is thus limited, so as to ensure a correct positioning. 
     The portion may comprise an attachment member, for instance having a U-shaped section, engaged in a form-fitting manner on the stator. The attachment member may be attached to the support of the first portion. 
     Each blade of the rotor wheel may comprise at least one first lip and one second lip, with the first lip extending radially outwards, beyond the second lip. The first lip may be engaged into the groove defined by the first and second portions. The second lips may cooperate with cylindrical or tapered radially internal surfaces of the first and second, portions. 
     The invention also relates to a method for assembling a turbine of the above-mentioned type, characterised in that it includes the following steps: 
     (a) mounting the first portion on a casing of the turbine, through an axial engagement in the upstream direction of said first portion relative to the casing, 
     (b) mounting the rotor wheel in the casing, 
     (c) mounting the second portion on the first portion, through an axial engagement in the upstream direction of said second portion relative to the first portion, 
     with the lip being introduced into the groove during step (b) and/or step (c). 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The invention will be better understood and other details, characteristics, and advantages of the invention will appear on reading the following description given by way of non-limiting example and with reference to the accompanying drawings, in which: 
         FIG. 1  is an axial view in perspective of a portion of a turbine according to one embodiment of the invention; 
         FIGS. 2 to 4  are exploded views in perspective of a part of the turbine according to the invention, 
         FIGS. 5 to 9  are views in axial section of a part of the turbine, which illustrates the successive steps of the assembling method according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     A low-pressure turbine  1  of a turbine engine according to a first embodiment is shown in  FIG. 1 . The turbine  1  includes a stationary casing  2 , having a tapered wall  3 , the axis of which matches the axis of the turbine engine and from which flanges  4 ,  5 , radially extend inwards. The casing  2  more particularly includes an upstream flange  4 , and a downstream flange  5 . Upstream and downstream are defined relative to the direction F of the gas flow inside the turbine  1 , i.e. from left to right in  FIG. 1 . 
     Each flange  4 ,  5 , includes a first annular portion  6  which extends radially inwards from the tapered wall  3 , and a second cylindrical portion  7  which extends in the downstream direction. 
     The upstream flange  4  further includes an annular radial rim  8  which extends radially inwards from the downstream end of the second portion  7 . 
     The stator of the turbine  1  specifically includes two stages of guide vanes, which will be respectively referred to as the upstream guide vane  9  and the downstream guide vane  10 , with each guide vane  9 ,  10  including a radially internal platform (not visible), a radially external platform  11   a ,  11   b  and stationary blades  12   a ,  12   b  connecting said platforms. 
     The external platform  11   a  of the upstream guide vane  9  includes a globally tapered wall  13 , the downstream end of which comprises a bearing area  14  including a first portion  15  which extends radially outwards and a second portion  16  which extends axially in the downstream direction. 
     The downstream end of the second portion  16  of the bearing area  14  axially bears onto the rim  8  of the upstream flange  4  of the casing  2 , with the second portion  16  of the bearing area  14  further bearing onto the second portion  7  of the upstream flange  4 . 
     The upstream end of the external platform  11  of the downstream guide vane  10  includes a radially internal rim  17 , and a radially external rim  18  which axially extend in the upstream direction, which are radially separated from each other. The radially internal rim  18  radially bears onto the radially external surface of the second portion  7  of the downstream flange  5 . The function of the radially internal rim  17  will be described in greater details hereunder. 
     The turbine  1  further includes a sealing ring  19  rigidly mounted on the casing  2  and formed in two portions  20 ,  36 , i.e. an upstream portion  20  and a downstream portion  36 . The sealing ring  19  consists of several contiguous angular sectors  21  on the whole circumference, which are also shown in  FIGS. 2 to 4 . 
     The upstream portion  20  specifically includes an upstream block  22  made of abradable material, having an annular shape. The upstream block  22  includes a recess  23 A at the downstream end thereof, with said recess  23 A opening radially inwards and axially in the downstream direction. 
     The external surface of the upstream block  22  is attached to an upstream support  24 , having an annular shape. The upstream support and the upstream block are then divided into sectors. The downstream support  24  comprises a rim  25  located in a median zone of the support  24  and radially extending outwards. The rim is able to axially bear on the downstream flange of the casing. 
     The radially external surface of the upstream support  24  further comprises an annular groove  26  directly located downstream of the rim  25 . The downstream end of the upstream support  24  forms an annular bearing zone  27  having a limited surface, able to radially bear on the downstream flange  5  of the casing  2 . 
     The upstream support  24  comprises a recessed zone  28  on its radially internal portion, with said recessed zone  28  opening radially inwards and axially in the downstream direction. 
     The upstream support  24  further comprises a protruding zone  29  which axially extends in the downstream direction and circumferentially extends on almost the whole sector  21  concerned. 
     The protruding zone  29  comprises a base  30  located upstream and a free end  31  opposite the base, located downstream. 
     The protruding zone  29  is radially offset outwards relative to the recessed zone  28 . Besides, the base  30  of the protruding zone  29  is axially offset in the downstream direction relative to the upstream end  32  of the recessed zone  28 . 
     An annular attachment member  33  with a U-shaped section, is attached at the upstream end of the upstream support  24  radially inside said upstream support  24 . Said upstream attachment member  33  includes a radially external branch  34 , able to radially bear onto the external surface of the second portion  7  of the upstream flange  4 , and a radially internal branch  35  able to radially bear onto the second portion  16  of the bearing area  15  and onto the rim of the upstream support  4 . A radial mounting clearance can be provided for. 
     The upstream guide vane  9  is thus attached to the upstream flange  4  through said upstream attachment member  33 . Such member  33  also makes it possible to attach the upstream support  24  on the upstream flange  4 . 
     The downstream part  36  specifically includes a downstream block  37  made of abradable material, having an annular shape. The downstream block  37  includes a recess  23 B at the upstream end thereof, with said recess  23 B opening radially inwards and axially in the upstream direction. The recesses  23 A,  23 B of the upstream  22  and downstream  37  blocks define a groove  39 . 
     The external surface of the downstream block  37  is attached to a downstream support  38 , having an annular shape. 
     The downstream support  38  and the downstream block  37  are then divided into sectors. The downstream support  38  comprises a rim  40  located in a downstream zone of the support  38  and radially extending outwards. The rim  40  is able to axially bear on the downstream flange  5  of the casing  2 . 
     The radially external surface of the downstream support  38  further comprises an annular groove  41  located upstream of the rim  40 . The upstream zone of the downstream support  38  forms two annular bearing zones  42  having limited surfaces and axially located on either side of the groove  41 . Said bearing zones  42  are able to radially bear on the downstream flange  5  of the casing  2 . 
     The downstream support  38  comprises a protruding zone  43  on its radially internal portion, with said protruding zone  43  axially extending in the upstream direction and being engaged in a form-fitting manner into the recessed zone  28  of the upstream support  24 . 
     The downstream support  38  further comprises a recessed zone  44  which circumferentially extends on almost the whole sector  21  concerned. The protruding zone  29  of the upstream support  24  is engaged in a form-fitting manner into the recessed zone  44  of the downstream support  38 . 
     The protruding zone  43  of the downstream support  38  comprises a base  45  located downstream and a free end  46  opposite the base  45 , located upstream. 
     The protruding zone  43  is radially offset inwards relative to the recessed zone  44 . Besides, the base  45  of the protruding zone  43  is axially offset in the upstream direction relative to the downstream end of the recessed zone  47 . 
     Besides, the downstream support  38  radially bears on the radially external surface  48  of the internal rim  17  of the external platform  11   b  of the downstream guide vane  10 . The downstream block  37  axially bears on the upstream radial surface of the internal rim  17  of the external platform  11   b  of the downstream guide vane  10 . 
     The turbine  1  further includes a rotor wheel  51  including vanes  52 , with the radially external periphery  53  of each vane  52  including a first, axially central, lip  54  and two second lips  55  axially offset on either side of the first lip  54 . The first and second lips  54 ,  55  extend radially outwards, with the first lip  54  extending radially outwards relative to the second lips  55 . The first lip  54  is engaged into the recesses  23 A,  23 B of the upstream and downstream portions  20 ,  36  of the ring  19 . The second lips  55  extend opposite the radially internal surfaces of the upstream and downstream blocks  22 ,  37 . 
     The cumulative axial dimension of the recesses  23 A,  23 B, i.e. the axial dimension of the groove  39 , enables a displacement or an uncertain axial positioning of the rotor wheel  51 , and thus of the first lip  54 , relative to the casing  2 , with such uncertainty possibly resulting from the manufacturing and mounting tolerances as well as from the mechanical and/or thermal constraints in operation. 
     The mounting of the turbine  1  will now be described while referring to  FIGS. 5 to 9 . 
     The upstream guide vane  9  is first mounted inside the casing  2  ( FIG. 5 ), the upstream portion  20  of the ring  19  is then axially engaged in the upstream direction into the casing  2  ( FIG. 6 ), on the upstream flange  4  of the casing  2 . The upstream attachment member  33  is engaged in the upstream flange  4  and in the part  16  of the upstream guide vane  9  so as to provide the attachment of the upstream guide vane  9  on the upstream flange  4 . The rotor wheel  51  including the vanes  52  is then axially engaged into the casing  2 , in the upstream direction ( FIG. 7 ), with the first lip  54  being, at least partially, positioned in the recess  23 A of the upstream abradable block  22 . The downstream portion  36  of the ring  19  is then axially engaged into the casing  2 , in the upstream direction, so that the protruding  29  and recessed  28  zones of the upstream portion can engage, in a form-fitting manner, into the recessed  44  and protruding  43  zones of the downstream portion  36  ( FIG. 8 ). The downstream portion  36  is thus attached to the upstream portion  20 . 
     The downstream guide vane  10  is then axially engaged into the casing  2 , in the upstream direction ( FIG. 10 ). The rim  17  of the external platform  11  of the downstream guide vane  10  radially bears onto the downstream flange  5 . The internal rim  17  of the external platform  11   b  of the downstream guide vane  10  radially bears onto the radially internal surface of the downstream support  38  and axially bears on the downstream block  37 , as mentioned above. The downstream support  38  thus bears onto the downstream flange  6  of the casing  2 , using the downstream guide vane  10 .