Patent Publication Number: US-2023160313-A1

Title: Turbine rotor for a turbomachine and method for mounting the rotor

Description:
TECHNICAL FIELD OF THE INVENTION 
     The invention relates to the general field of turbomachines. 
     The invention relates more particularly to a high- or low-pressure turbine rotor, and to a turbomachine comprising said rotor. The invention also relates to a method for mounting said rotor. 
     TECHNOLOGICAL BACKGROUND OF THE INVENTION 
     Aeronautical turbomachines typically comprise several modules such as a low-pressure compressor, a high-pressure compressor, a combustion chamber, a high-pressure turbine followed by a low-pressure turbine, which drive the corresponding low-pressure or high-pressure compressor, and a gas ejection system. Each of the turbines is formed of one or more stages, each stage successively including a wheel of stationary vanes, called the guide vane, and a wheel of moving vanes, called the rotor. 
     In the present application, the terms “outer” and “inner”, “upper” and “lower”, “outside” and “inside” are used in reference to the position of a piece or surface relative to the longitudinal axis of the turbomachine. Furthermore, the terms “radial” and “axial” respectively correspond to an axial direction, parallel to the longitudinal axis of the turbomachine, and to a radial direction, that is, perpendicular to the longitudinal axis of the turbomachine. Furthermore, the terms “upstream” and “downstream” are used in reference to the flow direction of the airflow in the turbomachine, as illustrated in the figures by an arrow. 
       FIG.  1    is an axial cross-sectional view of a part of a turbine rotor according to prior art, taken at one of the vane roots mounted circumferentially around a rotor disc. 
     With reference to  FIG.  1   , the stationary vanes  11  of the guide vanes are joined together at their radially inner ends by annular sectors placed circumferentially end to end so as to form an inner shroud  12  and are mounted at their radially outer ends on a casing (not represented) of the turbine. 
     In addition, the rotor comprises a disc  3  comprising, at its outer periphery, teeth delimiting slots in which the moving vanes  4  are engaged by their respective roots  8 . Each moving vane  4  comprises a blade  5  fitted with a platform  6  connected to a stilt  7  which radially extends to a root  8 . The roots  8  of the moving vanes  4  are retained radially in the slots of the disc  3  by their bulbous section, called a dovetail section, and axially by an annular ring  14  which is in axial abutment against the upstream face of the roots  8  of the moving vanes  4 . The annular ring  14  is held radially in upstream grooves  6   c  formed at the inner faces of the platforms  6  and axially by an annular upstream clamp  15  fixed to the disc  3 . 
     In order to improve the performance of the turbomachine, and to avoid overheating of the disc  3  by the flow of hot gases coming from the upstream combustion chamber and flowing through the flow stream  9  of the turbine, it is important to limit as much as possible the circulation of these gases radially from the outside to the inside, that is from the stream  9  to the zone  10  located between the platforms  6  of the moving vanes  4  and the disc  3 . Indeed, the part of the gases of the stream  9  flowing radially under the platforms  6  does not contribute to the rotation of the moving vanes  40  and directly heats the teeth of the disc  3 . Moreover, the cooling of the disc  3  and of the roots  8  of the moving vanes  4  is ensured by ports (not illustrated) provided in the upstream clamp  15  which ensure the routing of a cold air flow towards the bottom of the slots of the disc  3 . Therefore, it is also necessary to limit the passage of the cold air flow radially from the inside to the outside. 
     To limit the circulation of gases between the stream  9  and the zone  10  located between the platforms  6  of the moving vanes  4  and the disc  3 , it is known to fit the platform  6  of each moving vane  4  with an upstream spoiler  6   a  and a downstream spoiler  6   b  which define a sealing baffle, respectively, with a downstream spoiler  13   b  and an upstream spoiler  13   a  formed axially projecting on the annular sectors of the inner shrouds  12  located, respectively, upstream and downstream of the rotor. 
     Furthermore, sealing between the platforms  6  is ensured by sealing plates  18 , also called “candies”, which are mounted between the moving vanes  4 , in side cavities  19  provided in the stilts  7  of the moving vanes  4 . In particular, each sealing plate  18  is mounted between two circumferentially adjacent moving vanes  4  and comprises a circumferential end part housed in the side cavity  19  of a moving vane  4  and an opposite circumferential end part housed in the side cavity  19  of the adjacent moving vane  4 . These sealing plates  18  fit snugly the inner shape of the side cavities  19  with small clearances. In operation, these sealing plates  18  are subjected to centrifugal forces and are radially pressed against the inner faces of the main walls of the platforms  6 , thus preventing the radial passage of hot gases from the stream to the zone  10  located radially below the platforms. 
     In addition, each moving vane  4  includes an upstream low wall  16   a  and a downstream low wall  16   b  extending radially between the root  8  and the platform  6  of each moving vane  4  which encompass and restrict the bypass of the gas flow flowing into the stream  9 . Furthermore, the upstream  16   a  and downstream  16   b  low walls limit the leakage of gas from the stream  9  that wants to bypass the moving vane  4  by passing through the root  6  of the moving vane  4 . 
     Moreover, in addition to ensuring sealing in the turbine, the reduction in the mass of the constituent elements of the turbomachine is a constant concern which has led to the development of vanes whose blades are made of a ceramic matrix composite material, called C.M.C. 
     While the use of C.M.C. material makes it possible to reduce the weight of the vanes and to increase their resistance to high temperatures, it also requires the geometry of the moving vanes  4  to be reviewed because of the restrictions of the method for manufacturing C.M.C. pieces. Indeed, it is complicated to make a moving vane fitted with a platform which has a structure similar to that described above, because such a structure generates especially problems of twisting of the fibres of the material during its manufacture. Of course, this problem of simplification of the structure of the platforms can also arise with other types of vanes. 
     SUMMARY OF THE INVENTION 
     The invention offers a solution to the above-mentioned problems by providing a turbine rotor including vanes, for example made of C.M.C., whose structure is simplified and sealing is ensured. 
     A first aspect of the invention relates to a turbine rotor extending about an axis and comprising:
         a disc centred on the axis of the rotor and including slots and teeth in an outer periphery of the disc, the slots being circumferentially distributed around the disc and the teeth each being delimited by two circumferentially adjacent slots,   a plurality of vanes, each vane comprising:
           a blade extending radially with respect to the rotor axis,   a root provided in radial extension of the blade, configured to be mounted in a respective slot of the disc,   a platform located between the blade and the root of the vane,
 
wherein, the disc comprises axial retention means configured to axially hold the roots of the vanes in the slots of the disc, the axial retention means including a first series and a second series of lamellae circumferentially distributed about the axis, the first series and the second series of lamellae being axially superimposed and arranged such that:
   
           at least two circumferentially adjacent lamellae of the first series are axially superimposed on a lamella of the second series and circumferentially offset,   each lamella of the first and second series is disposed facing a slot of the disc so as to axially block the root of a vane mounted in said slot of the disc.       

     By replacing the annular ring with the first series and second series of lamellae, the axial retention of the vanes is ensured as well as the sealing between the vanes by means of the lamellae of the first series overlapping the lamellae of the second series, which makes it possible to eliminate the upstream and downstream low walls. The elimination of the upstream and downstream low walls makes it possible to reduce the height of the stilt and therefore to reduce the mass of the vane. 
     Furthermore, due to the axial superposition of the lamellae of the first series and of the second series, such axial retention means are mechanically more resistant than the annular ring, to the stresses exerted by the hot gases during operation of the rotor. 
     Moreover, the replacement of the annular ring by the lamellae of the first and second series makes it possible to reduce the problems of differential expansion between the axial retention means and the vanes during operation of the rotor. Indeed, the increase in the total volume of the plurality of lamellae due to thermal expansion is less than the increase in the total volume of the annular ring. Also, the lamellae are less likely to stress adjacent pieces, that is, adjacent lamellae and vane platforms, thus limiting deformation or even breakage of these pieces during operation of the rotor. 
     In addition, the smaller lamellae are easier to mount and dismount than the annular ring. Furthermore, maintenance of the rotor is facilitated as it is sufficient to replace only the degraded lamella(s) and not the whole annular ring. 
     Furthermore, the lamellae are easier to manufacture than the annular ring, especially as it is easier to size the lamellae than the annular ring, 
     In addition to the characteristics just mentioned in the preceding paragraph, the turbine rotor according to the first aspect of the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations. 
     According to a non-limiting embodiment, each vane includes a stilt located between the root and the platform of said vane and having an upstream face and a downstream face and in that the lamellae of the first and second series have the general shape of a T, each of said lamellae including:
         a radially outer portion configured to face one face of at least two circumferentially adjacent stilts or to face at least two circumferentially adjacent lamellae ( 101 ,  102 ,  103 ),   a radially inner portion configured to face a root of a vane.       

     According to a non-limiting embodiment, the first series and the second series of lamellae include upstream lamellae mounted upstream of the disc, the upstream lamellae of the first series and of the second series being axially superimposed and arranged such that:
         at least two circumferentially adjacent upstream lamellae of the first series are axially superimposed on an upstream lamella of the second series and,   each upstream lamella of the first and second series is disposed facing a slot of the disc so as to axially block the root of a vane mounted in said slot of the disc.       

     According to a non-limiting embodiment, the axial retention means include an annular upstream clamp fixed on the one hand to the disc and holding on the other hand the upstream lamellae of the first series and of the second series against the disc. 
     According to a non-limiting embodiment, the upstream clamp has an upstream edge axially extending to an annular upstream spoiler. Thus, the upstream so spoiler of the platform of the moving vane is transferred to the upstream clamp, which simplifies the structure of the platform of the moving vanes and thus facilitates its manufacture, which is particularly interesting when the vanes are made of a ceramic matrix material. 
     According to a non-limiting embodiment, the platform of each vane includes a main wall having an upstream rim, each upstream lamella of the first series and of the second series bearing radially against at least one inner face of an upstream rim. 
     According to a non-limiting embodiment, the first series and the second series of lamellae include downstream lamellae mounted downstream of the disc, the downstream lamellae of the first series and of the second series being axially superimposed and arranged so that:
         at least two circumferentially adjacent downstream lamellae of the first series are axially superimposed on a downstream lamella of the second series and,   each downstream lamella of the first and second series is disposed facing a slot of the disc so as to axially block the root of a vane mounted in said slot of the disc.       

     According to a non-limiting embodiment, the axial retention means include radially inner holding means and radially outer holding means configured to hold axially and radially the downstream lamellae of the first and second series facing the slots of the disc. 
     According to a non-limiting embodiment, the radially inner holding means are formed by radial hooks of the disc, each radial hook extending radially from a downstream face of a tooth of the disc and being configured to receive a circumferential end of a radially outer portion of a downstream lamella. 
     In a non-limiting embodiment, the radially outer holding means are formed by radial grooves formed in the platforms of the vanes, each radial groove being provided in an inner face of a downstream rim of a platform and being configured to receive the radially outer portion of a downstream lamella. 
     According to a non-limiting embodiment, the vanes and lamellae are made of different materials. 
     According to a non-limiting embodiment, the vanes are made from a ceramic matrix material. 
     According to a non-limiting embodiment, the lamellae are made from a metal material. 
     A second aspect of the invention relates to a turbomachine comprising at least one turbine rotor according to the first aspect. 
     A third aspect of the invention relates to a method for mounting a turbine rotor according to the first aspect of the invention including the following steps:
         Inserting the roots of the vanes into the slots of the disc,   Positioning the first series and the second series of lamellae so that at least two circumferentially adjacent lamellae of the first series are axially superimposed on a lamella of the second series and each lamella of the first and second series is disposed facing a slot of the disc so as to axially block the root of a vane mounted in said slot of the disc.       

     The invention and its various applications will be better understood upon reading the following description and examining the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The figures are set forth by way of illustration and are by no means limiting. 
         FIG.  1    is an axial cross-sectional view of the part of a rotor, according to prior art, taken at a vane root mounted in a slot of the rotor disc. 
         FIG.  2    is a partial axial cross-sectional view of a turbomachine turbine. 
         FIG.  3    is an axial cross-sectional view of the part of a rotor, according to one embodiment of the invention, taken at a vane root mounted in a slot in the rotor disc. 
         FIG.  4    is a perspective view, from downstream of the turbine, of the rotor represented in  FIG.  3   . 
         FIG.  5    is a perspective view, from upstream of the turbine, of the rotor represented in  FIG.  3   . 
     
    
    
     DETAILED DESCRIPTION 
     Unless otherwise specified, a same element appearing in different figures has a single reference. 
     The invention relates to a rotor  20  of a turbine  1  for a turbomachine. 
     It is reminded that a turbomachine generally comprises, from upstream to downstream in the flow direction of gases, a fan, one or more compressor stages, for example a low-pressure compressor and a high-pressure compressor, a combustion chamber, one or more turbine stages, for example a high-pressure turbine and a low-pressure turbine, and a gas exhaust nozzle. 
       FIG.  2    is a partial axial cross-sectional view of a high- or low-pressure turbine of the turbomachine. 
     With reference to  FIG.  2   , the turbine  1  comprises a number of vane stages, each stage including a wheel of stationary vanes  110 , called the guide vane, and a wheel  20  of moving vanes  40 , called the rotor. 
     The wheels of stationary vane  110  are mounted via their radially outer ends to an outer casing  111  of the turbine  1  and are joined together at their radially inner ends by annular sectors of inner shroud  112  placed circumferentially end to end and carrying blocks of abradable material. 
     The wheels  20  of moving vanes  40  are axially assembled to each other by annular flanges and each include a disc  30  carrying individual moving vanes  40 . The rotor  20  is connected to the shaft of the turbine  1  via a drive cone  10 . 
     In operation, the stationary vanes  110  of the guide vane and the moving vanes  40  of the rotor  20  are exposed to hot gases flowing into the stream of the turbine  1  from the combustion chamber. 
     In the following description, the term “vane” will be used to refer to a rotor moving vane. 
       FIG.  3    is an axial cross-sectional view of the portion of the rotor  20 , according to one embodiment of the invention, taken at a vane root mounted in a slot  31  of the disc  30  of the rotor  20  of the turbine  1 . 
     With reference to  FIG.  3   , each vane  40  comprises a blade  50  connected by a platform  60  to a middle portion or stilt  70  which radially extends to a root  80 . 
     As can be seen in  FIGS.  4  and  5   , the roots  80  of the vanes  40  are engaged in slots  31  provided in the outer periphery of the disc  30 . The slots  31  are regularly distributed about the axis X of rotation of the rotor  20  and delimit teeth  32  between them. 
     Moreover, each platform  60  includes a main wall delimited by an upstream rim  61 , a downstream rim  62  and thus by two circumferential edges  64 . In order to limit gas leakage at the clearances between the circumferential edges  64  of the platforms  60 , each vane  40  comprises two side cavities  71  provided in the stilt  70 , inside which sealing members  90  called “candies” are positioned, Each sealing member  90  is mounted between two circumferentially adjacent vanes  40  and comprises a circumferential end part housed in the side cavity  70  of a vane  40  and an opposite circumferential end part housed in the side cavity  71  of a circumferentially adjacent vane  40 . These sealing members  90  are formed by a plate which fits snugly the inner shape of the side cavities  71  with small clearances. In operation, these sealing members  90  are subjected to centrifugal forces and are radially pressed against the inner faces of the side cavities  71  so as to prevent the radial passage of hot gases from the stream to the zone located between the platform  60  and the disc  30 . These sealing members  90  also provide damping of the vibrations to which the vanes  40  are subjected in operation. 
     The roots  80  of vanes  40  are retained radially in the slots  31  by their bulbous section, called dovetail section. Furthermore, the roots  80  of the vanes  40  are axially retained in the slots  31  of the disc  30  by axial retention means. 
     The axial retention means include upstream lamellae  101 ,  102  disposed upstream of the disc  30  and an upstream clamp  97  which holds said upstream lamellae  101 ,  102  against the disc  30 . 
     The upstream clamp  97  is fixed to the disc  30  of the rotor  20  and is in the form of a piece of revolution, whose axis of revolution is the same as the axis of rotation X of the rotor  20 . 
     The upstream clamp  97  has an upstream edge  97 - 1  axially extending to an annular upstream spoiler  97 - 2  which defines a sealing baffle with a downstream spoiler  113   b , visible in  FIG.  2   , provided in the annular sectors of the inner shroud  112  located upstream of the rotor  20 . The overlay of the upstream spoiler  97 - 2  provided in the upstream clamp  97  and the downstream spoiler  113   b  provided in the inner shroud  112  limits the passage of hot gases radially from the outside to the inside, that is from the annular flow stream of the hot gas flow to the zone located between the platform  60  of the vanes and the disc  30 , and conversely of a cold air flow radially from the inside to the outside. Furthermore, the downstream rim  62  of the main wall of the platform  60  axially extends to a downstream spoiler  62 - 1  which defines a sealing baffle with an upstream spoiler  113   a , visible in  FIG.  2   , provided in the annular sectors of the inner shroud  112  located downstream of the rotor  20 . 
     Moreover, the upstream clamp  97  has a downstream edge  97 - 3  which bears axially against the disc  30  and faces the upstream face of the roots  80  of the vanes  40 . Advantageously, the upstream clamp  97  includes sealing means formed by an O-ring  98  disposed, between the upstream clamp  97  and the disc  30 , in an annular groove  97 - 5  provided in a radially inner part of the downstream edge  97 - 3  of the upstream clamp  97 . 
     Moreover, in order to hold axially and radially the upstream lamellae  101 ,  102  against the disc  30 , the upstream clamp  97  includes an annular shoulder  97 - 4  provided in a radially outer part of its downstream edge  97 - 3 . Advantageously, the annular shoulder  97 - 4  forms a radial bearing surface and an axial bearing surface defining a housing for receiving the upstream lamellae  101 ,  102 . 
     The upstream lamellae  101   102  are disposed facing the slots  31  of the disc  30  so as to axially block the roots  80  of the vanes  40  in said slots  31 . In addition, each lamella  101 ,  102  has a radially inner end which bears radially against the radial bearing surface formed by the annular shoulder  97 - 4  and a radially outer end which bears radially against an inner face of the upstream rim  61  of a platform  60 . 
     The upstream lamellae  101 ,  102  consist of a first series and a second series circumferentially distributed about the axis X of the rotor  20  and axially superimposed. In particular, the upstream lamellae  101  of the first series are positioned between the axial bearing surface, formed by the annular shoulder  97 - 4  of the upstream clamp  97 , and the upstream faces of the upstream lamellae  102  of the second series. The upstream lamellae  102  of the second series are positioned between the upstream faces of the stilts  70  and the downstream faces of the upstream lamellae  101  of the first series. In addition, the upstream lamellae  101 ,  102  of the first and second series are arranged such that at least two adjacent upstream lamellae  101  of the first series are axially superimposed on an upstream lamella  102  of the second series. In other words, the upstream lamellae  101  of the first series and the upstream lamellae  102  of the second series overlap, that is, are circumferentially offset, so as to limit gas leakage via the gaps between two circumferentially adjacent upstream lamellae. 
     Advantageously, the upstream lamellae  101 ,  102  of the first and second series have the general shape of a T. 
     The head  101 - 1 , or radially outer portion, of the upstream lamellae  101 ,  102  is configured to face the upstream face of at least two circumferentially adjacent stilts  70  or to face the upstream face of at least two circumferentially adjacent upstream lamellae  101 ,  102 . In particular, the head  101 - 1  of the upstream lamellae  101  of the first series bears axially against the upstream face of at least two circumferentially adjacent upstream lamellae  102  of the second series. The head  102 - 1  of the upstream lamellae  102  of the second series bears axially against the upstream faces of at least two circumferentially adjacent stilts  7 . 
     Furthermore, the root  101 - 2 ,  102 - 2 , or radially inner portion, of the upstream lamellae  101   102  of the first and second series face at least one root  50  of a vane  40  mounted in a slot  31  of the disc  30 . Moreover, the roots  101 - 2 ,  102 - 2  of the upstream lamellae  101   102  of the first and second series form a lug for rotationally blocking said upstream lamellae  101 ,  102 . In particular, the root  101 - 2 ,  102 - 1  of the upstream lamellae  101 ,  102  of the first and second series is in circumferential abutment against an upstream rim  32 - 1  of a tooth  32  of the disc  30 . 
     In addition, the axial retention means include downstream lamellae  103 ,  104  disposed downstream of the disc  30  and radially outer and inner holding means for holding said downstream lamellae  103 ,  104  radially and axially facing the slots  31  of the disc  30 . 
     Advantageously, the radially outer holding means are formed by radial grooves  62 - 2  provided in the inner faces of the downstream rims  62  of the platforms  60 . Thus, when the platforms  60  are arranged circumferentially end to end, the radial grooves  62 - 2  placed end to end form an annular radial groove. Moreover, the radially inner holding means are formed by radial hooks  33  extending radially from the downstream face of each tooth  32  of the disc  30 . Thus, the head  103 - 1 ,  104 - 1  of each downstream lamella  103 ,  104  is held, at its radially outer end, by at least one radial groove  62 - 2  and, at its radially inner end, by at least two adjacent radial hooks  33 . 
     Moreover, similarly to the upstream lamellae  101 ,  102 , the downstream lamellae  103 ,  104  are disposed facing the slots  31  of the disc  30  so as to axially block the roots  80  of the vanes  40  in said slots  31 . In addition, the downstream lamellae  103 ,  104  consist of a first series and a second series circumferentially distributed about the axis X of the rotor  20 . In addition, the downstream lamellae  103  of the first series and the downstream lamellae  104  of the second series are axially superimposed. In particular, the downstream lamellae  104  of the second series are positioned between the downstream faces of the stilts  70  of the vanes  40  and the upstream faces of the downstream lamellae  103  of the first series. In addition, the downstream lamellae  103 ,  104  of the first and second series are arranged such that at least two circumferentially adjacent downstream lamellae  103  of the first series are axially superimposed on a downstream lamella  104  of the second series. In other words, the downstream lamellae  103  of the first series and the downstream lamellae  104  of the second series overlap, that is, are circumferentially offset, so as to limit gas leakage via the gaps between two circumferentially adjacent downstream lamellae. 
     Advantageously, the downstream lamellae  103 ,  104  of the first and second series have the general shape of a T. 
     The head  103 - 1 , or radially outer portion, of the downstream lamellae  103 ,  104  are configured to face the downstream face of at least two circumferentially adjacent stilts  70  or to face the downstream face of at least two circumferentially adjacent downstream lamellae  103 ,  104 . In particular, the head  103 - 1  of each downstream lamella  103  of the first series bears axially against the downstream faces of at least two downstream lamellae  104  of the second series while the head  104 - 1  of each downstream lamella  104  of the third series bears axially against the downstream faces of at least two stilts  7 . Each head  103 - 1 ,  104 - 1  of the downstream lamellae  103 ,  104  of the first and second series bears radially against two adjacent radial hooks  33 . 
     Furthermore, the root  103 - 2 ,  104 - 2  of the downstream lamellae  103 ,  104  of the first and second series is positioned between two adjacent radial hooks  33 , facing a root  80  of a vane  40 . Thus, the root  103 - 2 ,  104 - 2  of each of said downstream lamellae  103 ,  104  forms a lug which is in circumferential abutment against a radial hook  33  of the disc  30  so as to rotationally block said downstream lamella  103 ,  104 . 
     Advantageously, the upstream clamp  15  and/or the upstream lamellae  101 ,  102  and/or the downstream lamellae  103 ,  104  include(s) ports (not illustrated) which ensure the routing of a cold air flow, illustrated by arrows, towards the bottom of the slots of the disc  3  so as to ensure the cooling of the disc  30  and the roots  80  of the moving vanes  40 . 
     Advantageously, the vanes  40  and the upstream and downstream lamellae  101 ,  102 ,  103 ,  104  are made of different materials. Thus, the vanes  40  are for example made of a ceramic matrix composite material while the upstream and downstream lamellae  101 ,  102 ,  103 ,  104  are for example made of metal material. In an alternative embodiment, the vanes  40  and the lamellae  101 ,  102 ,  103 ,  104  are made of the same material, for example of ceramic matrix composite type. 
     The invention also relates to a method for mounting the rotor  20  described above, 
     In a first step, the sealing members  90  are positioned in the side cavities  71  provided in the stilts  70  of the vanes  40 . 
     In a second step, the roots  80  of the vanes  40  are partially inserted into the slots  31  of the disk  30 , preferably over half the width of the disk  30 . 
     In a third step, the downstream lamellae  103 ,  104  of the first and second series are positioned inside the radial hooks  33 . In particular, the downstream lamellae  103 ,  104  are arranged so that the head  103 - 1 ,  104 - 1  of said downstream lamellae  103 ,  104  is held by two adjacent radial hooks  33  and their root  103 - 2 ,  104 - 2  is positioned between these two radial hooks  33 . Moreover, the downstream lamellae  103 ,  104  of the first and second series are axially superimposed such that at least two circumferentially adjacent downstream lamellae  103  of the first series are axially superimposed on a downstream lamella  104  of the second series. 
     In a fourth step, the downstream lamellae  103 ,  104  of the first and second series are placed obliquely in the radial hooks  33  so as to bring the radially outer ends of said lamellae  103 ,  104  closer to the downstream rim  62  of the platforms  60  of the vanes  40 . 
     In a fifth step, the roots  80  of the vanes  40  are fully inserted into the slots  31  of the disc  30  and the radially outer ends of the downstream lamellae  103 ,  104  of the first and second series are positioned inside the radial grooves  62 - 1  provided in the downstream rims  62  of the platforms  60  of the vanes  40 . 
     In a sixth step, the upstream lamellae  101 ,  102  of the first and second series are placed in the housing formed by the annular shoulder  94 - 4  of the upstream clamp  97 . In particular, the upstream lamellae  101 ,  102  of the first and second series are arranged so that at least two circumferentially adjacent upstream lamellae  101  of the first series are axially superimposed on an upstream lamella  102  of the second series. The head  101 - 1  of the upstream lamellae  101  of the first series then bears axially against the upstream faces of at least two upstream lamellae  102  of the second series while the head  102 - 1  of the upstream lamellae  102  of the second series bears axially against the upstream faces of at least two circumferentially adjacent stilts  7 . Furthermore, the root  101 - 2 ,  102 - 2  of the upstream lamellae  101 ,  102  of the first and second series is in circumferential abutment against an upstream rim  32 - 1  of a tooth  32  of the disc  30 . 
     In a seventh step, the upstream clamp  97  is fixed to an upstream flange of the disc  30  of the rotor  20  so that the radially outer ends of the upstream lamellae  101 ,  102  of the first and second series bear radially against the inner face of the upstream rims  61  of the platforms  60  and so that the radially inner ends of the upstream lamellae  101 ,  102  of the first and second series bear radially against the radial bearing surface formed by the annular shoulder  97 - 4  of the upstream clamp  97 . 
     Of course, the invention is not limited to the different embodiments described, and alternative embodiments are possible.