Patent Publication Number: US-2022228491-A1

Title: Assembly for turbomachine

Description:
FIELD OF THE INVENTION 
     The present invention relates to an assembly for a turbomachine. 
     The invention relates more specifically to an assembly for a turbomachine comprising a damper. 
     STATE OF THE ART 
     A turbomachine known from the state of the art comprises a casing and a fan capable of being rotated relative to the casing, around a longitudinal axis, by means of a fan shaft. 
     The fan comprises a disk centered on the longitudinal axis, and a plurality of blades distributed circumferentially at the outer part of the disk. 
     The range of operation of the fan is limited. More specifically, the evolution of a compression rate of the fan as a function of an air flow rate it draws when rotated, is restricted to a predetermined range. 
     Beyond this range, the fan is indeed subjected to aeroelastic phenomena which destabilize it. More specifically, the air circulating through the running fan supplies energy to the blades, and the blades respond in their eigenmodes at levels that may exceed the endurance limit of the material constituting them. This fluid-structure coupling therefore generates vibrational instabilities which accelerate the wear of the fan and reduce its service life. 
     A fan which comprises a reduced number of blades, and which is subjected to high aerodynamic loads, is very sensitive to this type of phenomena. 
     This is the reason why it is necessary to guarantee a sufficient margin between the stable operating range and the areas of instability, so as to spare the endurance limits of the fan. 
     To do so, it is known practice to equip the fan with dampers. Examples of dampers have been described in documents FR 2 949 142, EP 1 985 810 and FR 2 923 557, in the name of the Applicant. These dampers are all configured to be housed between the platform and the root of each blade, within the housing delimited by the respective stilts of two successive blades. 
     Furthermore, such dampers operate during a relative movement between two successive blade platforms, by dissipation of the vibration energy, for example by friction. Consequently, these dampers focus only on damping a first vibratory mode of the blades which characterizes a synchronous response of the blades to the aerodynamic loads. In this first vibratory mode, the inter-blade phase-shift is non-zero. 
     However, such dampers are totally ineffective for damping a second vibratory mode in which each blade flaps relative to the disk with a zero inter-blade phase-shift. Indeed, in this second vibratory mode, there is no relative movement between two successive blade platforms. This particular response of the blades to the aerodynamic loads, although asynchronous, still involves a non-zero moment on the fan shaft. In addition, this second vibratory mode is coupled between the blades, the disk and the fan shaft. The amplitude of this second vibratory mode is all the more important as the blades are large. 
     There is therefore a need to overcome at least one of the drawbacks of the state of the art described above. 
     DISCLOSURE OF THE INVENTION 
     One aim of the invention is to damp a mode of vibration of a rotor in which the phase-shift between the blades of said rotor is zero. 
     Another aim of the invention is to influence the damping of modes of vibration of a rotor in which the phase-shift between the blades of said rotor is non-zero. 
     Another aim of the invention is to propose a damping solution which is simple and easy to implement. 
     To this end, according to a first aspect of the invention, an assembly for a turbomachine is proposed, comprising:
         a casing,   a first rotor:   movable in rotation relative to the casing around a longitudinal axis, and   comprising:   a disk, and   a plurality of blades capable of flapping relative to the disk during a rotation of the first rotor relative to the casing,   a second rotor movable in rotation relative to the casing around the longitudinal axis, and   a damper configured to damp a movement of the first rotor relative to the second rotor, in a plane orthogonal to the longitudinal axis, the movement being caused by a flapping of at least one blade among the plurality of blades, the damper comprising:   a first bearing part:   bearing on the first rotor in a first bearing area extending over a first angular sector around the longitudinal axis,   being configured to apply a first centrifugal force on the first rotor, and   a second bearing part bearing on the first rotor in a second bearing area, different from the first bearing area, the second bearing area extending over a second angular sector around the longitudinal axis, the second angular sector being smaller than the first angular sector, and   a third bearing part:   bearing on the second rotor, and   being configured to apply a second centrifugal force on the second rotor.       

     It is by damping a movement of the first rotor relative to the second rotor, in a plane orthogonal to the longitudinal axis, that it is possible to influence the second vibratory mode. Actually, unlike the first vibratory mode, the second vibratory mode is characterized by a zero inter-blade phase-shift. Consequently, placing a damper between two successive blades of a rotor, as it has already been proposed in the prior art, has no effect on the second vibratory mode. The damper of the assembly described above has, for its part, the advantage of influencing the second vibratory mode because it plays on an effect of the second vibratory mode: the movement of the first rotor relative to the second rotor, in the plane orthogonal to the longitudinal axis. By opposing this effect, the damper disrupts the cause thereof that is to say dampens the second vibratory mode. It should nevertheless be noted that the first vibratory mode also participates in the movement of the first rotor relative to the second rotor, in the plane orthogonal to the longitudinal axis. Consequently, by opposing this effect, the damper also participates in disrupting another cause thereof that is say damping the first vibratory mode. Furthermore, the second bearing part allows to improve the stability of the damper. 
     Advantageously, but optionally, the assembly according to the invention may further comprise one of the following characteristics, taken alone or in combination with one or several of the other of the following characteristics: 
     the first bearing part has a radially outer surface coming into contact with a radially inner surface of the first rotor,
         the third bearing part has a radially outer surface coming into contact with a radially inner surface of the second rotor,   the first bearing part is fixedly mounted on the first rotor,   the damper comprises a linking part:   connecting the first bearing part to the third bearing part, and   being thinned relative to the first bearing part and to the third bearing part,   in such an assembly:   the first bearing part has a first bearing surface arranged to apply a first force on the second rotor, the first force having a first longitudinal component in a first direction parallel to the longitudinal axis, and a first radial component in a second direction orthogonal to the longitudinal axis, the first longitudinal component being greater than the first radial component,   the third bearing part has a second bearing surface arranged to apply a second force on the second rotor, the second force having a second longitudinal component in the first direction, and a second radial component in the second direction, the second radial component being greater than the second longitudinal component,   it further comprises a sacrificial plate:   fixedly mounted on the third bearing part, and   bearing on the second rotor,   it further comprises:   a first sacrificial plate fixedly mounted on the first bearing part and having the first bearing surface, and   a second sacrificial plate fixedly mounted on the third bearing part and having the second bearing surface,   a slot is provided in the first bearing part, the assembly further comprising a metal insert inserted into the slot, the second sacrificial plate being fixedly mounted on the metal insert,   the second bearing part is configured to apply a third centrifugal force on the first rotor,   the second bearing part has a radially outer surface coming into contact with a radially inner surface of the first rotor,   the damper comprises:   a second bearing part:   bearing on the first rotor in a second bearing area, different from the first bearing area, the second bearing area extending over a second angular sector around the longitudinal axis, the second angular sector being smaller than the first angular sector, and   being configured to apply a third centrifugal force on the first rotor, and   another second bearing part:   bearing on the first rotor in a third bearing area, different from the first bearing area and from the second bearing area, the third bearing area extending over a third angular sector around the longitudinal axis, the third angular sector being smaller than the first angular sector, and   being configured to apply a fourth centrifugal force on the first rotor,   each of the second bearing parts has a radially outer surface, coming into contact with a radially inner surface of the first rotor,   at least one among the second bearing parts is fixedly mounted on the first rotor,   at least one among the second bearing parts comprises a portion thinned relative to the rest of said second bearing part,   at least one among the second bearing parts comprises a channel configured to promote a radial deformation of said second bearing part,   the second bearing parts form lateral sections extending on either side, in a circumferential direction, of the first bearing part,   it further comprises a flyweight fixedly mounted on the damper,   the flyweight is fixedly mounted on the first bearing part,   it further comprises a flyweight fixedly mounted on the third bearing part,   it further comprises:   a first flyweight fixedly mounted on the first bearing part, and   a second flyweight fixedly mounted on the third bearing part,   each of the blades among the plurality of blades comprises:   a blade root connecting the blade to the disk,   a profiled blading,   a stilt connecting the blading to the blade root, and   a platform connecting the blading to the stilt and extending transversely to the stilt, the first bearing part bearing on the platform of one blade among the plurality of blades,   at least one among the second bearing area and the third bearing area extends along an entire axial length of the platform, and   the second rotor comprises a shroud, the shroud comprising a circumferential extension, the third bearing part bearing on the circumferential extension.       

     According to a second aspect of the invention, there is proposed a turbomachine comprising an assembly as described above, and in which the first rotor is a fan and the second rotor is a low-pressure compressor. 
    
    
     
       DESCRIPTION OF THE FIGURES 
       Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and not limiting, and which should be read in relation to the appended drawings in which: 
         FIG. 1  schematically illustrates a turbomachine, 
         FIG. 2  comprises a sectional view of a part of a turbomachine, and a curve indicating a tangential movement of different elements of this turbomachine part as a function of the position of said elements along a longitudinal axis of the turbomachine, 
         FIG. 3  is a sectional view of part of an exemplary embodiment of an assembly according to the invention, 
         FIG. 4  is a perspective view of part of an exemplary embodiment of an assembly according to the invention, 
         FIG. 5  is a perspective view of part of an exemplary embodiment of an assembly according to the invention, 
         FIG. 6  is a perspective view of a damper of an exemplary embodiment of an assembly according to the invention, 
         FIG. 7  is a perspective view of a damper of an exemplary embodiment of an assembly according to the invention, 
         FIG. 8  is a perspective view of a damper of an exemplary embodiment of an assembly according to the invention, 
         FIG. 9  is a perspective view of part of an exemplary embodiment of an assembly according to the invention, 
         FIG. 10  is a perspective view of part of an exemplary embodiment of an assembly according to the invention, 
         FIG. 11  is a perspective view of a damper of an exemplary embodiment of an assembly according to the invention, 
         FIG. 12  is a perspective view of part of an exemplary embodiment of an assembly according to the invention, 
         FIG. 13  is a perspective view of part of an exemplary embodiment of an assembly according to the invention, 
         FIG. 14  is a perspective view of part of an exemplary embodiment of an assembly according to the invention, 
         FIG. 15  is a perspective view of a section of part of an exemplary embodiment of an assembly according to the invention, 
         FIG. 16  is a perspective view of part of an exemplary embodiment of an assembly according to the invention, and 
         FIG. 17  is a perspective view of part of an exemplary embodiment of an assembly according to the invention. 
     
    
    
     In all of the figures, the similar elements bear identical references 
     DETAILED DESCRIPTION OF THE INVENTION 
     Turbomachine  1   
     Referring to  FIG. 1 , a turbomachine  1  comprises a casing  10 , a fan  12 , a low-pressure compressor  140 , a high-pressure compressor  142 , a combustion chamber  16 , a high-pressure turbine  180  and a low-pressure turbine  182 . 
     Each of the fan  12 , of the low-pressure compressor  140 , of the high-pressure compressor  142 , of the high-pressure turbine  180  and of the low-pressure turbine  182  is movable in rotation relative to the casing  10  around a longitudinal axis X-X. 
     In the embodiment illustrated in  FIG. 1 , and as also visible in  FIGS. 2 and 3 , the fan  12  and the low-pressure compressor  140  are secured in rotation and are capable of being rotated by a low-pressure shaft  13  which is itself capable of being rotated by the low-pressure turbine  182 . The high-pressure compressor  142  is for its part capable of being rotated by a high-pressure shaft  15 , which is itself capable of being rotated by the high-pressure turbine  180 . 
     In operation, the fan  12  draws in an air stream  110  which separates between a secondary stream  112  circulating around the casing  10 , and a primary stream  111  successively compressed within the low-pressure compressor  140  and the high-pressure compressor  142 , ignited within the combustion chamber  16 , then successively expanded within the high-pressure turbine  180  and the low-pressure turbine  182 . 
     The upstream and the downstream are here defined relative to the direction of normal air flow  110 ,  111 ,  112  through the turbomachine  1 . Likewise, an axial direction corresponds to the direction of the longitudinal axis X-X, a radial direction is a direction which is perpendicular to this longitudinal axis X-X and which passes through said longitudinal axis X-X, and a circumferential or tangential direction corresponds to the direction of a planar and closed curved line, all the points of which are at equal distance from the longitudinal axis X-X. Finally, and unless otherwise specified, the terms “inner (or internal)” and “outer (or external)”, respectively, are used with reference to a radial direction such that the inner (i.e. radially inner) part or face of an element is closer to the longitudinal axis X-X than the outer (i.e. radially outer) part or face of the same element. 
     Fan  12  and Low-Pressure Compressor  140   
     Referring to  FIGS. 1 to 3 , the fan  12  comprises a disk  120  and a plurality of blades  122  circumferentially distributed at an outer part of the disk  120 . 
     Referring to  FIGS. 2 and 3 , each of the blades  122  of the plurality of blades  122  comprises:
         a blade root  1220  connecting the blade  122  to the disk  120 ,   a profiled blading  1222 ,   a stilt  1224  connecting the blading  1222  to the blade root  1220 , and   a platform  1226  connecting the blading  1222  to the stilt  1224  and extending transversely to the stilt  1224 .       

     The blade root  1220  may be integral with the disk  120  when the fan  12  is a one-piece bladed disk. Alternatively, as seen in  FIG. 3 , the blade root  1220  can be configured to be housed in a cell  1200  of the disk  120  provided for this purpose. 
     As seen in  FIGS. 2, 3 and 13 , the low-pressure compressor  140  also comprises a plurality of blades  1400  fixedly mounted at an outer part of a shroud  1402 , said shroud  1402  comprising a circumferential extension  1404  at the outer end from which radial sealing wipers  1406  extend. The radial sealing wipers  1406  face the platforms  1226  of the blades  122  of the fan  12 , so as to guarantee the inner sealing of the flowpath within which the primary stream  111  circulates. As more specifically visible in  FIG. 3 , the shroud  1402  of the low-pressure compressor  140  is fixed to the disk  120  of the fan  12 , for example by bolting. 
     Each of the blades  122  of the plurality of the blades  122  of the fan  12  is capable of flapping, by vibrating relative to the disk  120  during a rotation of the fan  12  relative to the casing  10 . More specifically, during the coupling between the air  110  circulating within the fan  12  and the profiled bladings  1222 , the blades  122  are the site of aeroelastic floating phenomena on different vibratory modes, and whose amplitude may be such that it exceeds the endurance limits of the materials constituting the fan  12 . These vibratory modes are furthermore coupled to the opposite compressive forces upstream of the turbomachine  1 , and to the expansion forces downstream of it. 
     A first vibratory mode characterizes a synchronous response of the blades  122  to the aerodynamic loads, in which the inter-blade phase-shift is non-zero. 
     A second vibratory mode characterizes an asynchronous response of the blades  122  to the aerodynamic loads, in which the inter-blade phase-shift is zero. The amplitude of the flapping of the second vibratory mode is moreover as large as the fan  12  blades  122  are large. 
     Furthermore, this second vibratory mode is coupled between the blades  122 , the disk  120  and the fan shaft  13 . The frequency of the second vibratory mode is in addition one and a half times greater than that of the first vibratory mode. Finally, the second vibratory mode has a nodal deformation at mid-height of the fan  12  blades  122 . 
     In vibratory modes, including the second vibratory mode, the flapping of the blades  122  involves a non-zero moment on the low-pressure shaft  13 . In particular, these vibratory modes cause intense torsional forces within the low-pressure shaft  13 . 
     The vibrations induced by the flapping of the blades  122  of the fan  12 , but also by the flapping of the blades  1400  of the low-pressure compressor  140 , lead to significant relative tangential movements between the fan  12  and the low-pressure compressor  140 . Indeed, the length of the blades  122  of the fan  12  is greater than the length of the blades  1400  of the low-pressure compressor  140 . Consequently, the tangential bending moment caused by the flapping of a blade  122  of the fan  12  is greater than the tangential bending moment caused by flapping of a blade  1400  of the low-pressure compressor  140 . The blading of the blades  122  of the fan  12  and of the blades  1400  of the low-pressure compressor  140  then have very different behaviors. Furthermore, the mounting stiffness within the fan  12  is different from the mounting stiffness within the low-pressure compressor  140 . 
     As seen more specifically in  FIG. 2 , this results in particular in a large-amplitude movement of the fan  12  relative to the low-pressure compressor  140 , in a plane orthogonal to the longitudinal axis X-X, at the interface between the platforms  1226  of the blades  122  of the fan  12  and the radial sealing wipers  1406  of the circumferential extension  1404  of the shroud  1402  of the low-pressure compressor  140 . The amplitude of this movement for the second vibratory mode is for example between 0.01 and 0.09 millimeter, typically on the order of 0.06 millimeter, or, in another example, on the order of a few tenths of a millimeter, for example 0.1 or 0.2 or 0.3 millimeter. 
     Damper  2   
     A damper  2  is used to damp these vibrations of the fan  12  and/or of the low-pressure compressor  140 . 
     The damper  2  is in particular configured to damp a movement of the fan  12  relative to the low-pressure compressor  140 , in a plane orthogonal to the longitudinal axis X-X, the movement being caused by a flapping of at least one blade  122  among the plurality of blades  122  of the fan  12   
     Referring to  FIGS. 3 to 17 , the damper  2  comprises:
         a first bearing part  21 :   bearing on the fan  12  in a first bearing area extending over a first angular sector A 1  around the longitudinal axis X-X, and   being configured to apply a first centrifugal force C 1  on the fan, and   a second bearing part  22 ,  24  also bearing on the fan  12 , but in a second bearing area, different from the first bearing area.       

     To apply the first centrifugal force C 1 , the first bearing part  21  has a radially outer surface, corresponding to the first bearing area, coming into contact with a radially inner surface of the fan  12 , typically a radially inner surface of the platform  1226 . 
     As visible in particular in  FIGS. 5 and 12 , the second bearing area extends over a second angular sector A 2 , A 4  around the longitudinal axis X-X, the second angular sector A 2 , A 4  being smaller than the first angular sector A 1 . 
     All or part of the blades  122  of the fan  12  may moreover be equipped with such a damper  2 , depending on the desired damping, but also the mounting and/or maintenance characteristics. 
     In one embodiment, the first bearing part  21  is fixedly mounted on the fan  12 , for example by gluing. This facilitates the integration of the damper  2  within the turbomachine  1 , and guarantees the bearing of the first bearing part  21  on the fan  12 . 
     Advantageously, referring to  FIGS. 4, 5, 12, 14, 16 and 17 , the first angular sector A 1  corresponds to the angular sector occupied by the platform  1226  of a blade  122  of the fan  12 . In other words, the first bearing part  21  extends over the entire the circumferential dimension of the platform  1226  of the blade  122 , at an inner surface of said platform  1226 . The bearing of the damper  2  on the fan  12  is thus improved. 
     In one embodiment, the damper  2  comprises a material from the range having the trade name “SMACTANE® ST” and/or “SMACTANE® SP”, for example a material of the type “SMACTANE® ST 70” and/or “SMACTANE® SP 50”. It has indeed been observed that such materials have suitable damping properties. 
     Referring to  FIGS. 3 to 17 , in one embodiment, the damper  2  comprises a third bearing part  23 :
         bearing on the low-pressure compressor  140 , and   being configured to apply a second centrifugal force C 2  on the low-pressure compressor  140 .       

     In order to apply the second centrifugal force C 2 , the third bearing part  23  has a radially outer surface coming into contact with a radially inner surface of the low-pressure compressor  140 , typically a radially inner surface of the circumferential extension  1404 , for example a radially inner surface of the sealing wipers  1406 . 
     As can be seen in  FIG. 4 , the third bearing part  23  bears on the low-pressure compressor  140  in a third bearing area extending over a third angular sector A 3  around the longitudinal axis X-X. 
     Alternatively, as for example illustrated in  FIG. 10 , the third bearing part  23  is fixedly mounted on the low-pressure compressor  140 , for example by gluing. The first bearing part  21  may then be mounted free to rub on the fan  12 . 
     In an advantageous variant of this embodiment, for example illustrated in  FIGS. 4, 6, 7, and 9 to 16 , the damper  2  further comprises a linking part  20 :
         connecting the first bearing part  21  to the third bearing part  23 , and   being thinned relative to the first bearing part  21  and to the third bearing part  23 .       

     More specifically, as illustrated in  FIGS. 4, 6, 7, and 9 to 11 , the first bearing part  21  has a first radial thickness E 1  in a section plane which comprises the longitudinal axis X-X, the third bearing part  23  has a third radial thickness E 3  in the section plane, and the linking part  20  has a radial linking thickness E 0  in the section plane.  FIG. 3  provides an example of a view in such a section plane. As can be seen in  FIGS. 4, 6, 7, and 9 to 11 , the radial linking thickness E 0  is smaller than the first radial thickness E 1  and, than the third radial thickness E 3 . The linking part  20  is therefore thinned with respect to the first bearing part  21  and to the third bearing part  23 . 
     Thus, the first bearing part  21  and the third bearing part  23  are massive. Consequently, in operation, each of the first bearing part  21  and the third bearing part  23  exerts a respective centrifugal force C 1 , C 2  on the fan  12  and the low-pressure compressor  140 , on which bear said bearing parts  21 ,  23 . In this way, the bearing parts  21 ,  23  are each dynamically coupled respectively to a fan  12  and to the low-pressure compressor  140  on which each bears, so as to undergo the same vibrations as each of the fan  12  and the low-pressure compressor  140 . Furthermore, the bearing parts  21 ,  23  are stiffer than the linking part  20 , in particular in a tangential direction. Advantageously, as for example visible in  FIG. 4 , the third radial thickness E 3  is greater than the first radial thickness E 1 , so as to better guarantee the bearing of the third bearing part  23 . 
     The thinner linking part  20  is more flexible, in particular in a tangential direction. Therefore, it allows the fan  12  to transmit the vibrations to which it is subject to the low-pressure compressor  140  and, conversely, it allows the low-pressure compressor  140  to transmit the vibrations to which it is subject to the fan  12 . Indeed, for high vibration frequencies, damping is provided in particular by the shear operation of the linking part  20 , that is to say by viscoelastic dissipation. For low vibration frequencies, damping is in particular ensured by friction of either one of the first bearing part  21  or of the third bearing part  23  respectively against the fan  12  or against the low-pressure compressor  140 . 
     Furthermore, the third bearing part  23  bears on the circumferential extension  1404  of the shroud  1402  of the low-pressure compressor  140 , at an inner surface of the radial sealing wipers  1406 . Indeed, it is in this position that the movement of the fan  12  relative to the low-pressure compressor  140 , in the plane orthogonal to the longitudinal axis X-X, is of greater amplitude, typically a few millimeters. Consequently, the damper  2  is particularly effective there. Furthermore, the thinning of the linking part  20  ensures a clearance which allows the damper  2  to avoid to rub on one corner of the radial sealing wipers  1406 . 
     In one embodiment, for example illustrated in  FIGS. 12, 13, 15 and 17 , the second bearing part  22 ,  24  is configured to apply a third centrifugal force C 3 , C 4  to the fan  12 . For this purpose, the second bearing part  22 ,  24  has a radially outer surface coming into contact with a radially inner surface of the fan  12 . In an advantageous variant, the second bearing part  22  further bears on a downstream surface of the stilt  1224  of the blade  122 , as visible in  FIGS. 4 and 5 . In another variant, illustrated in  FIGS. 12 to 17 , the second bearing part  22 ,  24  bears under the platform  1226  of a blade  122  of the fan  12 , at an inner surface of the platform  1226 . 
     Referring to  FIG. 6 , in one embodiment, a sacrificial plate  230  bears on the low-pressure compressor  140 . The sacrificial plate  230  is fixedly mounted on the third bearing part  23 , for example by gluing, and/or by being housed within a groove  2300  of the third bearing part  23  provided for this purpose, as shown in  FIG. 6 . The sacrificial plate  230  is configured to guarantee the bearing of the third bearing part  23  on the low-pressure compressor  140 . Indeed, the mechanical stresses in operation are such that slight tangential, axial and radial movements of the damper  2  are to be expected. These movements are in particular due to the vibrations to be damped, but also to the centrifugal loading of the damper  2 . It is necessary that these movements do not wear out the low-pressure compressor  140 . In this regard, the sacrificial plate  230  comprises an anti-wear material, for example of the teflon type and/or any type of composite material. In an advantageous configuration, the sacrificial plate  230  is further treated by dry lubrication, in order to perpetuate the value of the coefficient of friction between the damper  2  and the low-pressure compressor  140 . This material with lubricating properties is for example of the MoS2 type. 
     Advantageously, the sacrificial plate  230  may also comprise an additional coating, configured to reduce the friction and/or wear of the low-pressure compressor  140 . This additional coating is fixedly mounted on the sacrificial plate  230 , for example by gluing. The additional coating is of the dissipative and/or viscoelastic and/or damping type. It may indeed comprise a material from the range having the trade name “SMACTANE® ST” and/or “SMACTANE® SP”, for example a material of the type “SMACTANE® ST 70” and/or “SMACTANE® SP 50”. It may also comprise a material chosen from those having mechanical properties similar to those of Vespel, Teflon or any other material with lubricating properties. More generally, the additional coating material advantageously has a coefficient of friction between 0.3 and 0.07. The sacrificial plate  230  is optionally combined by juxtaposition with its additional coating. Indeed, it allows to increase the friction, in particular tangential friction, of the damper  2  when, in operation, the sacrificial plate  230  is sufficiently constrained by the second centrifugal force C 2  so that the movement of the fan  12  with respect to the low-pressure compressor  140 , in the plane orthogonal to the longitudinal axis X-X, is damped by energy dissipation by means of a viscoelastic shear of the sacrificial plate  230 . 
     Referring to  FIGS. 7 and 16 , in one embodiment:
         the first bearing part  21  has a first bearing surface  2100  arranged to apply a first force F 1  on the low-pressure compressor  140 , the first force F 1  having a first longitudinal component F 1 L in a first direction parallel to the longitudinal axis X-X, and a first radial component F 1 R in a second direction orthogonal to the longitudinal axis X-X, the first longitudinal component F 1 L being greater than the first radial component F 1 R,   the third bearing part  23  has a second bearing surface  2320  arranged to apply a second force F 2  on the low-pressure compressor  140 , the second force F 2  having a second longitudinal component F 2 L in the first direction, and a second radial component F 2 R in the second direction, the second radial component F 2 R being greater than the second longitudinal component F 2 L.       

     In other words, the first bearing surface  2100  ensures the axially positioned bearing of the damper  2  since it is a downstream axial surface of the damper  2  coming into contact with an upstream axial surface of the low-pressure compressor  140 . Furthermore, the second bearing surface  2320  ensures the radially positioned bearing of the damper  2  since it is a radially outer surface of the damper  2  coming into contact with a radially inner surface of the low-pressure compressor  140 . In addition, in operation, the second bearing surface  2320  participates in the application of the second centrifugal force C 2  on the low-pressure compressor  140 . 
     Referring to  FIG. 8 , in an advantageous variant of the embodiment illustrated in  FIGS. 7 and 16 :
         a first sacrificial plate  210  is fixedly mounted on the first bearing part  21 , for example by gluing, and has the first bearing surface  2100 , and   a second sacrificial plate  232  is fixedly mounted on the third bearing part  23 , for example by gluing, and has the second bearing surface  2320 .       

     The first sacrificial plate  210  and the second sacrificial plate  232  advantageously have the same characteristics as those described with reference to the sacrificial plate  230  of the embodiment illustrated in  FIG. 6 , with the same benefits for the damping of a movement of the fan  12  with respect to the low-pressure compressor  140 , in the plane orthogonal to the longitudinal axis X-X. 
     Still with reference to  FIG. 8 , also advantageously, a slot  213  is formed in the first bearing part  21 , a metal insert  233  being inserted into the slot  213 , the second sacrificial plate  232  being fixedly mounted on the metal insert  233 , for example by gluing. The metal insert  233  allows to stiffen the damper  2 . Furthermore, the metal insert  233  facilitates the deformation of the first sacrificial plate  210  and of the second sacrificial plate  232 . 
     With reference to  FIGS. 9 to 11 , in one embodiment, a flyweight  3  is fixedly mounted on the damper  2 , for example by gluing. The flyweight  3  allows to adjust the centrifugal forces C 1 , C 2 , C 3 , C 4  exerted by the damper  2  on the fan  12  and on the low-pressure compressor  140 , so as to improve the dynamic coupling between the first bearing part  21  and the fan  12 , and between the third bearing part  23  and the low-pressure compressor  140 . Advantageously, the flyweight  3  comprises an elastomeric material. With reference to  FIG. 9 , the flyweight  3  may then be fixedly mounted both on the first bearing part  21  and on the third bearing part  23 , for example by gluing. 
     Referring to  FIG. 10 , in an advantageous variant, the flyweight  3  is fixedly mounted on the first bearing part  21 , for example by gluing, preferably only on the first bearing part  21 . Advantageously, as can be seen in  FIG. 10 , the flyweight is offset upstream of the first bearing part  21 , so as to leave the linking part  20  free so that, in operation, it can effectively operate in shear mode to damp a movement of the fan  12  with respect to the low-pressure compressor  140 , in a plane orthogonal to the longitudinal axis X-X. Alternatively, the flyweight  3  is fixedly mounted on the third bearing part  23 , for example by gluing, preferably only on the third bearing part  23 . Advantageously, and for the same reasons as those mentioned with reference to the first bearing part  21 , the flyweight  3  is offset downstream from the third bearing part  23 . Preferably, the flyweight  3  is fixedly mounted only on the first bearing part  21  if the third bearing part  23  is fixedly mounted on the low-pressure compressor  140 . 
     In another advantageous variant, with reference to  FIG. 11 :
         a first flyweight  31  is fixedly mounted on the first bearing part  21 , for example by gluing, and   a second flyweight  32  is fixedly mounted on the third bearing part  23 .       

     In this way, it is possible to independently adjust the first centrifugal force C 1  and the second centrifugal force C 2 . This improves the damping of vibrations by targeting the vibration modes specific to the fan  12  and specific to the low-pressure compressor  140 . 
     With reference to  FIGS. 12 to 17 , in one embodiment, the damper  2  comprises:
         a second bearing part  22 :   bearing on the fan  12  in a second bearing area, different from the first bearing area, the second bearing area extending over a second angular sector A 2  around the longitudinal axis X-X, the second angular sector A 2  being smaller than the first angular sector A 1 , and   being configured to apply a third centrifugal force C 3  to the fan  12 , and   another second bearing part  24 :   bearing on the fan  12  in a third bearing area, different from the first bearing area and from the second bearing area, the third bearing area extending over a third angular sector A 4  around the longitudinal axis X-X, the third angular sector A 4  being smaller than the first angular sector A 1 , and   being configured to apply a fourth centrifugal force C 4  to the fan  12 .       

     To apply the third centrifugal force C 3 , and the fourth centrifugal force C 4 , each of the second bearing parts  22 ,  24  has a radially outer surface, coming into contact with a radially inner surface of the fan  12 , typically a radially inner surface of the platform  1226 . 
     As visible in  FIGS. 12 to 17 , the two second bearing parts  22 ,  24  form lateral sections extending on either side, in a circumferential direction, of the first bearing part  21 . Thus, the two second bearing parts  22 ,  24  promote coupling with the fan  12 , and the damping of a movement of the fan  12  relative to the low-pressure compressor  140 , by increasing the overall stiffness of the first bearing part  21 . Moreover, the rigidity of the first bearing part  21  is increased at its circumferential ends. The damping of the damper  2 , in particular in a tangential direction, is then generally improved. 
     In an advantageous variant of this embodiment, at least one among the first bearing part  21  and the two second bearing parts  22 ,  24 , is fixedly mounted on the fan  12 , for example by gluing. This facilitates the integration of the damper  2  within the turbomachine  1 , and guarantees the bearing of said bearing parts  21 ,  22 ,  24  on the fan  12 . 
     In an equally advantageous variant, as can be seen in  FIGS. 12, 13, 14, 16 and 17 , each of the first bearing part  21 , and the two second bearing parts  22 ,  24  bears on the blade platform  122  of the fan  12 , at an inner surface of the platform  1226 . 
     With reference to  FIGS. 14 and 17 , in a variant of this embodiment, at least one among the two second bearing areas  22 ,  24  extends along an entire axial length of the platform  1226 . In other words, at least one among the two second parts  22 ,  24  extends all along the platform  1226 . Advantageously, as also visible in  FIGS. 14 and 17 , at least one among the two second bearing parts  22 ,  24  is flush with one edge of the platform  1226 . In other words, a radial surface of the platform  1226  at a circumferential end of said platform  1226  is extended by a radial surface of the second bearing part  22 ,  24  at a circumferential end of said second bearing part  22 ,  24  which corresponds to the circumferential end of the platform  1226 . In this way, the second bearing parts  22 ,  24  of the circumferentially adjacent dampers  2  within the fan  12  bear against each other. This participates in the damping by friction of the vibrations of the fan  12 . Furthermore, these bearings of the second bearing parts  22 ,  24  of the dampers  2  circumferentially adjacent to one another improve the sealing of the air flowpath  110 . In an advantageous variant, for example illustrated in  FIG. 17 , only one among the second bearing parts  22 ,  24  extends all along the platform  1226 , flush with one edge of the platform  1226 , while the other among the second bearing parts  22 ,  24  extends only along a portion of the platform  1226 . Thus, only the second bearing part  22 ,  24  which is the longest axially participates in the sealing while the other participates rather in damping. 
     With reference to  FIG. 15 , in another variant of this embodiment, at least one among the second bearing parts  22 ,  24  comprises a portion thinned relative to the rest of said second bearing part  22 ,  24 . More specifically, as visible in  FIG. 15 , a first circumferential thickness e 1  of the second bearing part  22 ,  24  is different from a second circumferential thickness e 2  of the second bearing part  22 ,  24 , said second circumferential thickness e 2  being taken at a radial position different from a radial position of the first circumferential thickness e 1 . Advantageously, as visible in  FIG. 15 , at least one among the second bearing parts  22 ,  24  is thicker at an inner surface of the platform  1226  than at a distance from the inner surface distance of the platform  1226 . This allows to stiffen said second bearing part  22 ,  24  in order to promote the application of the corresponding centrifugal force C 3 , C 4  to the fan  12 . Furthermore, the presence of the first circumferential thickness e 1  facilitates the holding, for example by gluing, of the second bearing part  22 ,  24  on the inner surface of the platform  1226 . Finally, the presence of the second circumferential thickness e 2  improves the sealing between the second bearing parts  22 ,  24  which are circumferentially adjacent. 
     Still with reference to  FIG. 15 , but as also visible in  FIGS. 14 and 16 , in an advantageous variant of this embodiment, at least one among the second bearing parts  22 ,  24  comprises a channel  241 . The channel  241  is configured to promote a radial deformation of said second bearing part  22 ,  24  during the application of the corresponding centrifugal force C 3 , C 4 . This in particular promotes the sealing between the platforms  1226  of the successive blades  122  of the fan  12 . 
     In this embodiment, it can also be seen that the bearing parts  21 ,  22 ,  23 ,  24  are massive. Consequently, in operation, each of the first bearing parts  21 ,  22 ,  23 ,  24  exerts a respective centrifugal force C 1 , C 2 , C 3 , C 4  on the fan  12  and the low-pressure compressor  140 , on which bear said bearing parts  21 ,  22 ,  23 ,  24 . In this way, the bearing parts  21 ,  22 ,  23 ,  24  are each dynamically coupled respectively to a fan  12  and to the low-pressure compressor  140  on which each bears, so as to undergo the same vibrations as each of the fan  12  and the low-pressure compressor  140 . Furthermore, in the variant of this embodiment where the damper  2  comprises a linking part  20 , the bearing parts  21 ,  22 ,  23 ,  24  are stiffer than the linking part  20 , in particular in a tangential direction. 
     In all that has been described above, the damper  2  is configured to damp a movement of the fan  12  relative to the low-pressure compressor  140 , in the plane orthogonal to the longitudinal axis X-X. 
     This is however not limiting, since the damper  2  is also configured to damp a movement of any first rotor  12  relative to any second rotor  140 , in a plane orthogonal to the longitudinal axis X-X, as long as the first rotor  12  is movable in rotation relative to the casing  10  around the longitudinal axis X-X and comprises a disk  120  as well as a plurality of blades  122  capable of flapping by vibrating relative to the disk  120  during a rotation of the first rotor  12  relative to the casing  10 , and as the second rotor  140  is also movable in rotation relative to the casing  10  around the longitudinal axis X-X. 
     Thus, the first rotor  12  can be a first stage of the high-pressure compressor  142  or of the low-pressure compressor  140 , and the second rotor  140  can be a second stage of said compressor  140 ,  142 , successive to the first stage of compressor  140 ,  142 , upstream or downstream thereof. Alternatively, the first rotor  12  can be a first stage of a high-pressure turbine  180  or of low-pressure turbine  182 , and the second rotor  140  can be a second stage of said turbine  180 ,  182 , successive to the first stage of turbine  180 ,  182 , upstream or downstream thereof. 
     In any event, the damper  2  has a small space requirement. Consequently, it can be easily integrated into the existing turbomachines. 
     In addition, by being configured to exert centrifugal forces C 1 , C 2 , C 3 , C 4  on the first rotor  12  and, optionally, on the second rotor  140 , the damper  2  ensures a significant tangential stiffness between the first rotor  12  and the second rotor  140 . It thus differs from an excessively flexible damper which would only deform during a movement of the first rotor  12  relative to the second rotor  140 , in the plane orthogonal to the longitudinal axis X-X. On the contrary, the damper  2  dissipates such a movement:
         either by friction and/or oscillations between a state where the damper  2  is bonded on the rotors  12 ,  140  and a state where the damper  2  slides on the rotors  12 ,  140 , which allows damping in particular the low frequencies,   or by viscoelastic shear within the damper  2 , which allows damping in particular the high frequencies.       

     However, the damper  2  remains flexible enough to maximize the contact surfaces between said damper  2  and the rotors  12 ,  140  on which it bears. To do so, the damper  2  has a tangential rigidity greater than an axial rigidity and a radial rigidity. 
     The contact forces between the damper  2  and the rotors  12 ,  140  can in particular be adjusted by means of flyweights  3  and/or sacrificial plates  230 ,  210 ,  232  and/or additional coatings on said sacrificial plates  230 ,  210 ,  232 . At low frequencies, it is indeed necessary to ensure that the centrifugal forces C 1 , C 2 , C 3 , C 4  exerted by the damper  2  on the rotors  12 ,  140  are not too large, in order to guarantee that the damper  2  can oscillate between a bonded state and a slippery state on the rotors  12 ,  140 , and thus damp by friction. At high frequencies, on the other hand, it is necessary to ensure that the centrifugal forces C 1 , C 2 , C 3 , C 4  exerted by the damper  2  on the rotors  12 ,  140  are sufficiently large for the pre-stress of the damper  2  on the rotors  12 ,  140  to be sufficient, in order to ensure that the damper  2  can be the viscoelastic shear seat. 
     The wear of the rotors  12 ,  140  is in particular limited by the treatment of the surfaces of the damper  2  bearing on the rotors  12 ,  140 , for example to equip them with a coating with a low coefficient of friction.