Patent Publication Number: US-2022213810-A1

Title: Turbine for a turbomachine, such as an aeroplane turbofan or turboprop engine

Description:
TECHNICAL FIELD 
     The present disclosure relates to turbines for a turbomachine, such as a turbojet or aircraft turboprop engine. 
     PRIOR ART 
     As shown in  FIG. 1 , a low-pressure turbine of a turbomachine comprises annular rows  20  of moving blades  20   a  arranged axially alternating with annular rows  30  of stationary blades  30   a  and surrounded by a low-pressure turbine housing  10 . An annular row  20  of moving blades  20   a  and an annular row  30  of downstream stationary blades  30   a  together form a turbine stage. An annular row  30  of stationary blades  30   a  is also called a distributor. The distributor  30  is generally formed of a plurality of sectors arranged to be circumferentially abutting. 
     The radially outer end of each annular row  20  of moving blades  20   a  comprises tongues  22  which cooperate with an annularly shaped abradable material  24  carried by the radially inner face of a ring  26 . The ring is generally formed from a plurality of ring sectors arranged to be circumferentially abutting. The ring  26  is made integral with the housing  10  thanks to a means of support carried by the housing  10  and a means of attachment of a downstream distributor  30  as seen in  FIG. 2 . 
     Typically, the means of support comprises a cylindrical wall  12  connected to the housing  10  and extending axially downstream. The cylindrical wall  12  has a radially inner annular face  12   a  and a radially outer annular face  12   b.    
     The radially outer end of each annular row  30  of stationary blades  30   a  comprises an outer annular platform  32  carrying a means of attachment of the distributor  30 . This means of attachment comprises an inner annular spoiler  34  extending upstream from the upstream end of the platform  32 . In particular, the inner annular spoiler  34  has a radially outer annular face  34   b . The means of attachment of the distributor  30  further comprises a frusto-conical wall  36  extending upstream and radially outwards from the outer annular platform  32 . Lastly, the means of attachment comprises an outer annular spoiler  38  extending upstream from a radially outer end of the frusto-conical wall  36 . The outer annular spoiler  38  has a radially inner face  38   a.    
     The cylindrical wall  12  of the means of support is engaged in an annular groove  28  of a radially outer surface  26   b  of the ring  26 . The upstream  28   a  and downstream  28   c  annular faces of the annular groove  28  form axial stops on the upstream and downstream ends of the cylindrical wall  12 , thereby axially blocking the ring  26 . The annular bottom face  28   b  of the annular groove  28  forms a radial abutment with the radially inner face  12   a  of the cylindrical wall  12 , allowing radial attachment to the housing  10 . The form-fitting cooperation between the cylindrical wall  12  and the annular groove  28  of the ring  26  also provides a seal by limiting an outflow of hot air from the primary-air annular vein. 
     The distributor  30  is positioned with respect to the housing  10  so that the radially inner annular face  38   a  of the outer annular spoiler  38  of the means of attachment comes to bear on the radially outer annular face  12   b  of the cylindrical wall  12  of the means of support. The distributor  30  is also held relative to the ring  26  by the radially outer annular face  34   b  of the inner annular spoiler  34  of the means of attachment coming to bear on the radially inner face  26   a  of the ring  26 . A downstream end portion of the ring  26  is then engaged in an annular recess extending between the radially outer annular face  34   b  of the inner annular spoiler  34  and the radially inner annular face  38   a  of the outer annular spoiler  38 . This annular housing is thus delimited by the radially inner annular face  38   a  of the outer annular spoiler  38 , the outer annular face  34   b  of the inner annular spoiler  34  and an upstream face  36   a  of the frusto-conical wall  36 . 
     When the turbine is in use, the hot pressurised gases exiting the combustion chamber cause the temperature of the stationary blades  30   a , the moving blades  20   a  and the abradable material  24  to rise. 
     Heat conduction occurs radially outwards from the abradable material  24  to the ring  26  carrying the abradable material. The heat is then transferred to the cylindrical wall  12  of the housing  10  coming to bear on the ring  26  through contacts between an upstream face  12   c  of the cylindrical wall  12  and the upstream face  28   a  of the annular groove  28  of the ring  26 , between the radially inner face  12   a  of the cylindrical wall  12  and the annular bottom face  28   b  of the groove  28  and between a downstream face  12   d  of the cylindrical wall  12  and the downstream face  28   c  of the groove  28 . This leads to an increase in temperature by heat conduction of the housing  10  and the cylindrical wall  12  supporting the distributor  30 . 
     The housing  10  and the means of support it comprises can thus reach a high temperature likely to embrittle them and reduce the life of the housing  10 , a part that is very large and expensive to produce. It is therefore important to find technical solutions to limit the heating of the means of support of the housing. 
     SUMMARY OF THE INVENTION 
     The invention aims at providing a simple, efficient and cost-effective solution to these problems. 
     For this purpose, it proposes a turbine for a turbomachine comprising:
         an annular row of moving blades surrounded by a support ring of abradable material carried by a housing, the ring defining a radially outer face,   a distributor mounted downstream of said annular row of moving blades and comprising a means of attachment to a means of support of the housing, the said means of attachment comprising a radially outer spoiler coming to bear radially inwards on a radially outer annular face of a cylindrical wall of said means of support, the said means of support further comprising an annular wall extending radially inwards from the cylindrical wall and engaged at its radially inner end in an annular groove of the ring, and in which a free annular space is formed between a radially outer face of the ring and the cylindrical wall of the means of support.       

     The distance between the cylindrical wall and the abradable material, as described with reference to the prior art, is thus extended from the radial annular wall into the means of support and the free annular space. This allows the cylindrical wall of the means of support to be moved radially away from the radially outer face of the ring and reduces the amount of heat transmitted by heat conduction through the ring to the cylindrical wall of the means of support. 
     Furthermore, the formation of this free space  40  induces a radial elongation of the means of attachment of the distributor  30  due to the arrangement of the means of support. In this way, the cylindrical wall of the means of support is less hot and transfers less heat to the housing by thermal conduction than in the prior art. 
     In one embodiment, the abradable material support ring is carried by the housing via the means of attachment of the distributor. 
     According to another embodiment, the cylindrical wall of the means of support extends in an axial direction of the turbine, i.e. a direction parallel to the turbine axis. 
     The free annular space advantageously extends axially between the radial annular wall of the means of support and a frusto-conical wall of the means of attachment, this frusto-conical wall being connected at its radially outer end to the radially outer spoiler. 
     This delimitation of the free annular space implies that the annular wall of the means of support extends radially inwards from the upstream end of the cylindrical wall or from an intermediate position between the upstream and downstream end of the cylindrical wall. This allows the frusto-conical wall of the means of attachment to be axially distanced from the radial annular wall of the means of support so as to limit heat transfer between these two elements. 
     Advantageously, the radial annular wall of the means of support extends radially inwards from an upstream end of the cylindrical wall. 
     This configuration of the radial annular wall of the means of support gives the means of support a compact and simple design. This also allows the prior-art ring to be adapted by making a minor modification to the annular groove of the ring cooperating with the means of support. This configuration also allows a maximum axial distance between the truncated wall of the means of attachment and the radial annular wall of the means of support, minimizing heat transfer between these two elements. 
     The turbine may also have the feature that the free annular space defines a radial distance between the radially outer face of the ring and the cylindrical wall, which radial distance is at least twice a radial depth of the annular groove of the ring. 
     Thus, the radial gap between the radially outer surface of the ring and the cylindrical wall is large enough to limit heat transfer between these two elements. 
     In a further feature of the invention, the means of attachment of the distributor comprises a radially inner spoiler connected to the upstream end of a radially outer platform of the distributor, the radially inner spoiler coming to bear on a radially inner face of the abradable material support ring. 
     The distributor is thus held relative to the ring by the radially outer face of the radially inner spoiler coming to bear on the radially inner face of the ring. Furthermore, the invention makes extremely local geometric modifications compared to the prior art: the holding of the distributor in relation to the ring is not modified compared to the prior art. This makes it possible to keep the surrounding elements that are not related to the technical problem solved by the present invention without modification. 
     According to a preferred embodiment of the invention, the free annular space extends over an axial distance between the radial annular wall of the means of support and the frusto-conical wall of the means of attachment which is greater than an axial dimension of the cylindrical wall of the means of support. 
     According to another preferred embodiment of the invention, the free annular space extends over an axial distance between the radial annular wall of the means of support and the frusto-conical wall of the means of attachment which is greater than an axial dimension of the radially outer spoiler of the means of attachment. 
     These features may be considered together or alternatively and advantageously with the aim of maximising the axial dimension of the free annular space so that the axial spacing between the frusto-conical wall of the means of attachment and the annular wall radially inwards of the means of support is sufficient to limit heat transfer from the frusto-conical wall of the means of attachment to the cylindrical wall and the annular wall inwardly of the means of support. 
     In one embodiment of the invention, the turbine described above is a low-pressure turbine. 
     The invention also relates to a turbomachine such as a turbojet or an aircraft turboprop engine comprising a turbine as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features, details and benefits will emerge from reading the detailed description below, and from the analysis of the attached drawings, on which: 
         FIG. 1 , already described above, shows a partial schematic half-view in axial section of a low-pressure turbine of the prior art; 
         FIG. 2 , already described above, is a larger scale schematic view of the zone outlined in dotted lines in  FIG. 1 ; 
         FIG. 3  is a schematic view similar to  FIG. 2  illustrating an embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     A turbomachine turbine according to a preferred embodiment of the invention is shown in  FIG. 3  and comprises annular rows  20  of moving blades  20   a  arranged axially alternating with annular rows  30  of stationary blades  30   a , also known as blades, said annular rows  20  of moving blades  20   a  and the annular rows  30  of stationary blades  30   a  being surrounded by a low-pressure turbine housing  10 . The term “ring” as used herein refers to circumferentially extending parts, which parts may be in the form of a ring or ring sectors arranged to be circumferentially abutting. For example, the distributor  30  may be formed from a plurality of sectors arranged to be circumferentially abutting. 
     In a manner similar to the prior art, the radially outer end of each annular row  20  of moving blades  20   a  comprises tongues  22  sealingly engaging an annularly shaped abradable material  24  carried by the radially inner face  26   a  of a ring  26 . The ring  26  is preferably sectorised, i.e. formed from a plurality of ring sectors arranged to be circumferentially abutting. The abradable material  24  support ring  26  is made integral with the housing  10  thanks to a means of support carried by the housing  10  and a means for attaching a downstream distributor  30  to the housing  10 . 
     The means of support comprises a cylindrical wall  12  connected to the housing  10  and extending axially downstream. The cylindrical wall  12  has a radially inner annular face  12   a  and a radially outer annular face  12   b . The means of support further comprises an annular wall  14  extending radially inwards from the cylindrical wall  12 . In a preferred embodiment of the invention as shown in  FIG. 3 , the annular wall  14  extends radially inwards from an upstream end of the cylindrical wall  12  of the means of support. The radially inner end of the radial annular wall  14  engages in an annular groove  28  of the ring  26 . In the example shown in  FIG. 3 , the means of support has a general “L” shape with two legs formed by the cylindrical wall  12  and the radial annular wall  14 , or a general “T” shape formed by the cylindrical wall  12 , the annular wall  14  and considering a connection  13  to the housing. 
     The radially outer annular face  26   b  of the ring  26  comprises a radially outwardly directed annular groove  28  in which the radially inner end of the radial annular wall  14  of the means of support is engaged. This annular groove  28  comprises an upstream annular face  28   a  and a downstream annular face  28   c  forming axial stops on the upstream face  14   a  and the downstream face  14   c  of the radially inner end of the radial annular wall  14  of the means of support, thereby axially blocking the ring  26 . The annular bottom face  28   b  of the annular groove  28  forms a radial abutment with the cylindrical face  14   b  of the radially inner end of the radial annular wall  14 , limiting the radially outward movement of the ring  26  relative to the housing  10 . The form-fitting cooperation between the radial ring wall  14  and the annular groove  28  of the ring  26  also seals off the hot air in the vein. 
     The heat transmitted radially outward from the ring  26  to the means of support is first transmitted through the radial annular wall  14  before being received by the cylindrical wall  12  due to the “T” shape of the means of support which ensures that the cylindrical wall  12  is radially spaced from the ring  26 . The amount of heat received by the cylindrical wall  12  from the ring  26  is therefore reduced. 
     The inner end of the radial annular wall  14  engaged in the annular groove  28  of the ring  26  has an axial dimension which is smaller than the axial dimension of the cylindrical wall  12  engaged in the annular groove  28  in the case of the turbine of the prior art. This results in a decrease in the radial bearing surface between the ring  26  and the means of support. Heat exchanges take place between the ring  26  and the means of support through the bearing surfaces. This reduction in the bearing surface between the ring  26  and the means of support therefore promotes a reduction in heat exchange between the ring  26  and the means of support. 
     This reduction in the axial dimension of the annular groove  28  results in a reduction in the clamping loss of the ring  26  in operation at the supports between the upstream face  14   a  of the annular wall  14  and the upstream annular face  28   a  of the annular groove  28  and between the downstream face  14   b  of the annular wall  14  and the downstream face  28   c  of the annular groove  28 . This results in a reduction in stresses, thus improving the low cycle fatigue life of the ring  26 . 
     The radially outer end of each annular row of stationary blades  30   a  comprises an outer annular platform  32  comprising a means of attachment of the distributor  30  to the means of support of the housing  10  and a means of attachment to the support ring  26  of the abradable material support  24 . This means of attachment comprises a spoiler or an inner annual lug  34  extending upstream from the upstream end of the platform  32 . In the case of a distributor formed of a plurality of sectors, each sector comprises an inner spoiler. In particular, the inner annular spoiler  34  has a radially outer annular face  34   b . The means of attachment of the distributor  30  further comprises a frusto-conical wall  36  extending upstream and radially outwards from the outer annular platform  32 . In other words, the frusto-conical wall  36  has a cross-section contained in an axial plane which increases in an upstream direction. Finally, the means of attachment comprises a spoiler or an outer annular lug  38  extending upstream from an outer radial end of the frusto-conical wall  36 . In the case of a distributor formed of a plurality of sectors, each sector comprises an outer spoiler. In particular, the outer annular spoiler  38  has a radially inner annular face  38   a.    
     The distributor  30  is positioned with respect to the housing  10  so that the radially inner annular face  38   a  of the outer annular spoiler  38  of the means of attachment rests on the radially outer annular face  12   b  of the cylindrical wall  12  of the means of support. The distributor  30  is also held relative to the ring  26  by the radially outer annular face  34   b  of the inner annular spoiler  34  of the means of attachment coming to bear on the radially inner face  26   a  of the ring  26 . 
     A free annular space  40  is formed between the cylindrical wall  12  of the means of support and a radially outer face  26   b  of the ring  26 . The free annular space  40  is devoid of any solid heat-conducting elements, including any fasteners. In this way, the radially inner face  12   a  of the cylindrical wall  12  is arranged directly opposite the radially outer face  26   b  of the ring  26 . The free annular space  40  extends radially between the radially outer face  26   b  of the ring  26  and the radially inner annular face  12   a  of the cylindrical wall  12 . The radial distance between the outer face  26   b  of the ring  26  and the radially inner annular face  12   a  of the cylindrical wall  12  is at least greater than a radial depth of the annular groove  28  of the ring  26 . Advantageously, the radial distance between the outer face  26   b  of the ring  26  and the radially inner annular face  12   a  of the cylindrical wall  12  is at least twice the radial depth of the annular groove  28  of the ring  26 . The cylindrical wall  12  of the means of support is thus radially distanced from the radially outer face  26   b  of the ring  26  compared to the prior art. 
     As shown in  FIG. 3 , the free annular space  40  may extend axially between the radial annular wall  14  of the means of support and the frusto-conical wall  36  of the means of attachment. To this end, the radial annular wall  14  of the means of support may extend from the upstream end of the cylindrical wall  12  or from an intermediate position between the upstream end and the downstream end of the cylindrical wall  12 . This allows the radial annular wall  14  and the frusto-conical wall  36  to be moved axially away from each other, thus limiting the heat transfer between them. 
     The annular space is thus delimited radially by the radially outer face  26   b  of the ring  26  and the radially inner face  12   a  of the cylindrical wall  12  and it is delimited axially by the upstream face  14   c  of the radial annular wall  14  and the upstream face  36   a  of the frusto-conical wall  36  of the means of attachment. The annular space contains a volume of hot air whose flow is considered static. This reduces heat exchange by thermal convection by reducing the heat exchange coefficients between the hot air contained in the annular space  40  with the radially inner face  12   a  of the cylindrical wall  12 , the downstream face  14   c  of the radial annular wall  14  of the means of support, the radially outer face  26   b  of the ring  26  and the radially inner face  38   a  of the outer annular spoiler  38  of the means of attachment. 
     In the practical embodiment shown in  FIG. 3 , the radial annular wall  14  extends from the upstream end of the cylindrical wall  12  so that the axial distance between the radial annular wall  14  and the frusto-conical wall  36  is maximised, minimising heat transfer between these elements. 
     According to a preferred embodiment of the invention, an axial distance between the radial annular wall  14  of the means of support and the frusto-conical wall  36  of the means of attachment is chosen which is greater than the axial dimension of the cylindrical wall  12 . 
     According to another preferred embodiment of the invention, which may be independent of or associated with the preceding one, an axial distance is chosen between the radial annular wall  14  of the means of support and the frusto-conical wall  36  of the means of attachment which is greater than an axial dimension of the outer annular spoiler  38  of the means of attachment. 
     These two preferred embodiments of the invention allow sufficient axial spacing between the radial annular wall  14  and the frusto-conical wall  36  to optimally limit heat transfer between these two elements. 
     The presence of the free annular space  40  also implies that the radial distance between the radially inner face  26   a  of the ring  26  and the radially outer annular face  12   b  of the cylindrical wall  12  is greater than the same axial distance between these same two faces of the prior art. Thus, the radial dimension of the frusto-conical wall  36  is increased compared to the prior art to increase the radial spacing between the inner annular spoiler  34  and the outer annular spoiler  38 . In this way, the supports of the means of attachment of the distributor  30  on the means of support and on the ring  26  are advantageously maintained. 
     A thermal protection sheet  42  is positioned between the outer annular spoiler  38  of the means of support and the housing  10 . The sheet is at least held against a radially outer face  38   b  of the outer annular spoiler  38 . This sheet reduces heat transfer from the outer annular spoiler  38  to the housing  10 . 
     Heat conduction takes place radially outwards from the abradable material  24  heated by the hot gases flowing through the vein to the ring  26  supporting it. The heat is then transferred to the radial annular wall  14  of the means of support which is in contact with the ring  26  by the following points of contact, namely the contact between the upstream face  14   a  of the radial annular wall  14  and the upstream face  28   a  of the groove, the contact between the radially inner face  14   b  of the radial annular wall  14  and the bottom face  28   b  of the groove and the contact between the downstream face  14   c  of the radial annular wall  14  and the downstream face  28   c  of the groove. The radial annular wall  14  finally transfers the heat to the cylindrical wall  12  of the means of support and to the housing  10 . As a result, the distance between the abradable material  24  and the cylindrical wall  12  is lengthened by the radial annular wall  14  compared to the prior art, which limits the amount of heat received by the cylindrical wall  12  from the means of support. 
     The free annular space  40  formed between the cylindrical wall  12  of the means of support and the ring  26  also makes it possible to limit the heat flow transmitted by the ring  26  to the cylindrical wall  12  of the means of support in that air is a less good thermal conductor than the metal parts generally constituting the various elements of the turbine and the housing  10 . 
     Due to these effects, the cylindrical wall  12  of the means of support receives less heat and is therefore less hot. This increases the life of the housing  10  and the cylinder wall  12  and reduces maintenance costs.