Patent Publication Number: US-11655728-B2

Title: Rotary machine

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present disclosure relates to a rotary machine. 
     Priority is claimed on Japanese Patent Application No. 2020-206795, filed Dec. 14, 2020, the content of which is incorporated herein by reference. 
     Description of Related Art 
     For example, a centrifugal compressor flows a working fluid inside a rotating impeller and compresses the working fluid, which is in a gaseous state, by using the centrifugal force generated when the impeller rotates. As disclosed in Japanese Unexamined Patent Publication No. 2019-173617, some such centrifugal compressors are provided with inlet guide vanes (inlet guide vanes) in order to adjust the flow rate of the working fluid introduced from the outside. In the configuration disclosed in Japanese Unexamined Patent Publication No. 2019-173617, the inlet guide vane (IGV) is disposed further upstream side in a flow direction with respect to an impeller of a stage where an inlet flow rate of the working fluid needs to be adjusted. The inlet guide vane extends from an inner peripheral surface of a housing toward an inner side of the housing in a radial direction. 
     SUMMARY OF THE INVENTION 
     However, in the configuration described in Japanese Unexamined Patent Publication No. 2019-173617, the inlet guide vane extends from the inner peripheral surface of the housing toward the inner side of the housing in the radial direction, and has a so-called cantilever shape. Therefore, when the length of the inlet guide vane in the radial direction is long, self-excited vibration (flutter) is likely to occur due to the flow of the working fluid in the housing. In the configuration described in Japanese Unexamined Patent Publication No. 2019-173617, a tip portion on the inner side of the inlet guide vane in the radial direction extends toward inner side in the radial direction rather than the outer peripheral surface of the rotary shaft. For this reason, the vane main body of the inlet guide vane becomes long, and the self-excited vibration is particularly likely to occur. 
     The present disclosure provides a rotary machine capable of suppressing self-excited vibration of an inlet guide vane. 
     A rotary machine according to the present disclosure comprises: a rotor that includes a rotary shaft that extends in an axial direction, in which an axis extends, about the axis, an impeller fixed to the rotary shaft, and an impeller cap that is disposed at an end portion of the rotary shaft and regulates the movement of the impeller in the axial direction; a housing that covers the rotor and has a suction port allowing a working fluid to flow inside the housing; and an inlet guide vane that is disposed inside the housing on a first side in the axial direction with respect to the impeller, and has a plurality of movable blades that extend from the housing toward an inner side in a radial direction around the axis and disposed at intervals in a circumferential direction about the axis, in which a blade tip portion, which is a tip end of each of the plurality of movable blades in the radial direction, is disposed on an outer side in the radial direction with respect to an outer peripheral surface of the impeller cap, and the position of at least a part of the blade tip portion in the axial direction overlaps the position of the impeller cap in the axial direction. 
     According to the rotary machine of the present disclosure, it is possible to suppress the self-excited vibration of the inlet guide vane and effectively suppress the generation of jet between the inlet guide vane and the impeller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram showing a schematic configuration of a rotary machine according to an embodiment of the present disclosure. 
         FIG.  2    is a cross-sectional view showing a configuration in which movable blades of an inlet guide vane are in a fully open state in the rotary machine. 
         FIG.  3    is an enlarged cross-sectional view of a main part of  FIG.  2   . 
         FIG.  4    is a cross-sectional view showing a configuration in which movable blades of the inlet guide vane are in a fully closed state. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, a mode for carrying out a rotary machine according to the present disclosure will be described with reference to the accompanying drawings. However, the present disclosure is not limited to only the embodiment. 
     (Configuration of Geared Compressor (Rotary Machine)) 
     As shown in  FIGS.  1  and  2   , a geared compressor (centrifugal compressor)  1  as a rotary machine according to the present embodiment mainly includes a rotor  3 , a housing  2  (refer to  FIG.  2   ), and an inlet guide vane  6  (refer to  FIG.  2   ), a radial bearing  12 , and a thrust bearing  17 . 
     (Configuration of Rotor) 
     The rotor  3  is rotatable about an axis O with respect to the housing  2 . The rotor  3  includes a rotary shaft  30 , an impeller  40 , and an impeller cap  38 . 
     The rotary shaft  30  extends about the axis O in an axial direction Da where the axis O extends. As shown in  FIG.  1   , the rotary shaft  30  is rotatably supported around the axis O by a pair of radial bearings  12 . The pair of radial bearings  12  is disposed at intervals in the axial direction Da. The rotary shaft  30  is restrained from moving in the axial direction Da by a pair of thrust bearings  17 . The pair of thrust bearings  17  is disposed between the pair of radial bearings  12  at positions separated from each other on both sides in the axial direction Da with respect to a pinion gear  15  described later. 
     The rotary shaft  30  is connected to a driving source (not shown) such as an external motor via a speed increasing transmission portion  11 . The speed increasing transmission portion  11  includes the pinion gear  15  and a large-diameter gear  16 . The pinion gear  15  is fixed to the rotary shaft  30  between the pair of radial bearings  12 . The large-diameter gear  16  meshes with the pinion gear  15 . The large-diameter gear  16  is rotationally driven by the driving source. The large-diameter gear  16  is set to have a larger outer diameter than that of the pinion gear  15 . Therefore, the rotation speed of the rotary shaft  30  to which the pinion gear  15  is fixed is larger than the rotation speed of the large-diameter gear  16 . That is, the speed increasing transmission portion  11  accelerates the rotation speed of the large-diameter gear  16  by an external driving source via the pinion gear  15  and transmits the rotation speed to the rotary shaft  30 . 
     The impellers  40  are disposed at both end portions of the rotary shaft  30  in the axial direction Da. As shown in  FIG.  2   , each impeller  40  is a so-called closed impeller including a disk  41 , a blade  42 , and a cover  43  in the present embodiment. The impeller  40  may be an open impeller that does not have a cover  43 . 
     The disk  41  has a disk shape and is fixed to the rotary shaft  30 . 
     The disk  41  has a first surface  41   a  facing the cover  43  in the axial direction Da, and a second surface  41   b  facing the side opposite to the first surface  41   a  in the axial direction Da. The second surface  41   b  is the back surface of the impeller  40 . Here, as shown in  FIG.  1   , the geared compressor  1  is provided with one each impeller  40  at both end portions of the rotary shaft  30  in the axial direction Da in the present embodiment. Each impeller  40  is disposed in the axial direction Da such that the second surface  41   b  of the disk  41 , which is the back surface, faces the pinion gear  15  and the first surface  41   a  faces the end portion of the rotary shaft  30  on the side opposite to the pinion gear  15 . That is, in a first-stage impeller  40 A provided at a first end of the rotary shaft  30  and a second-stage impeller  40 B provided at a second end of the rotary shaft  30 , the disks  41  are disposed in opposite directions in the axial direction Da such that their back surfaces face each other. 
     In the following description, in each impeller  40 , the first surface  41   a  side of the disk  41  is referred to as the first side Da 1  in the axial direction Da, and the second surface  41   b  side is referred to as the second side Da 2  in the axial direction Da. That is, in the first-stage impeller  40 A and the second-stage impeller  40 B, the first side Da 1  in the axial direction Da and the second side Da 2  in the axial direction Da are opposite to each other. 
     As shown in  FIG.  2   , the blade  42  extends from the first surface  41   a  of the disk  41  to the cover  43 . A plurality of blades  42  are disposed at intervals in a circumferential direction Dc around the axis O. 
     The cover  43  is disposed on the first side Da 1  in the axial direction Da with respect to the disk  41  and the plurality of blades  42 . The cover  43  has a disk shape and is formed to cover the plurality of blades  42 . 
     The working fluid (for example, air) flows from the first side Da 1  in the axial direction Da toward the second side Da 2  in the axial direction Da with respect to the impeller  40 . In each impeller  40 , an impeller flow path  45  is formed between the disk  41  and the cover  43 . The impeller flow path  45  has an inflow port  45   i  and an outflow port  45   o . The inflow port  45   i  is open in the impeller  40  to face the first side Da 1  in the axial direction Da at the inner side Dri in the radial direction Dr. Here, the radial direction Dr is a direction around the axis O. The outflow port  45   o  is open toward an outer side Dro of the impeller  40  in the radial direction Dr. 
     The shaft end  30   s , which is the end portion of the rotary shaft  30  in the axial direction Da, projects to the first side Da 1  in the axial direction Da with respect to the impeller  40 . An impeller cap  38  is fixed to the shaft end  30   s . The impeller cap  38  rotates together with the rotary shaft  30 . The impeller cap  38  forms a rotor end portion  3   e , which is an end portion in the axial direction Da of the rotor  3 . The impeller cap  38  regulates the movement of the impeller  40  in the axial direction Da. That is, the impeller cap  38  restrains the position of the impeller  40  in the axial direction Da so as not to fall off from the rotary shaft  30 . 
     As shown in  FIGS.  2  and  3   , the impeller cap  38  of the present embodiment has a tubular portion  38   a  and a cap tip portion  38   b . The tubular portion  38   a  is formed in a cylindrical shape extending with a constant diameter in the axial direction Da about the axis O. The shaft end  30   s  of the rotary shaft  30  is inserted in the inner side of the tubular portion  38   a . The cap tip portion  38   b  closes the end portion of the first side Da 1  in the axial direction Da of the tubular portion  38   a . That is, the cap tip portion  38   b  is disposed on the first side Da 1  in the axial direction Da with respect to the tubular portion  38   a . The cap tip portion  38   b  is formed such that the diameter gradually increases from the first side Da 1  to the second side Da 2  in the axial direction Da. The cap tip portion  38   b  of the present embodiment is formed, for example, in a hemispherical shape. The cap tip portion  38   b  is integrally formed with the tubular portion  38   a.    
     (Configuration of Housing) 
     As shown in  FIG.  2   , the housing  2  is formed to cover the rotor  3 . The housing  2  is formed of metal and forms an outer shell of the geared compressor  1 . The housing  2  has a shaft insertion hole  21  through which the rotary shaft  30  is inserted on the second side Da 2  in the axial direction Da with respect to the position where the impeller  40  is disposed. The housing  2  includes an intake nozzle  22  and an exhaust flow path  23  around each impeller  40 . 
     The intake nozzle  22  causes the working fluid to flow into the housing  2 . The intake nozzle  22  is formed in a tubular shape to extend in the axial direction Da. Inside the intake nozzle  22 , a suction port  22   a  around the axis O is formed. The intake nozzle  22  communicates with the outside of the housing  2  and the inflow port  45   i  of the impeller flow path  45  opened to the inner side Dri in the radial direction Dr of the impeller  40  through the suction port  22   a . When the impeller  40  rotates in the circumferential direction Dc around the axis O, the working fluid is sucked from the outside to the inside of the housing  2  through the suction port  22   a.    
     The exhaust flow path  23  causes the working fluid inside the housing  2  to flow out to the outside of the housing  2 . The exhaust flow path  23  is formed on the outer side Dro of the outflow port  45   o  of the impeller flow path  45  in the radial direction Dr. The exhaust flow path  23  has a spiral shape that is continuous in the circumferential direction Dc. 
     (Configuration of Inlet Guide Vane) 
     An inlet guide vane  6  controls the flow rate of the working fluid passing through the suction port  22   a . The inlet guide vane  6  is disposed on the inner side of the intake nozzle  22  of the housing  2 . That is, the inlet guide vane  6  is disposed inside the housing  2  on the first side Da 1  in the axial direction Da with respect to the impeller  40 . The inlet guide vane  6  has a plurality of movable blades  60 . The plurality of movable blades  60  are disposed so as to project into the suction port  22   a  having a circular cross section when viewed from the axial direction Da. The plurality of movable blades  60  are disposed along the inner peripheral surface of the intake nozzle  22  at equal intervals in the circumferential direction Dc around the axis O. 
     The movable blade  60  is rotatable around the center axis Ar extending in the radial direction Dr. Each movable blade  60  has a blade main body  61  and a shaft portion  62 . As shown in  FIG.  3   , each blade main body  61  extends so as to project from the inner peripheral surface of the intake nozzle  22  to a blade height direction D 1 , which is the extending direction (radial direction Dr) of the center axis Ar. The blade main body  61  has a blade profile in a cross-sectional shape when viewed from the radial direction Dr. Here, a blade chord direction D 2 , which is the direction connecting a front edge portion  611  and a rear edge portion  612  of the blade main body  61  having a blade cross-sectional shape, is orthogonal to the blade height direction D 1  (radial direction Dr). The blade main body  61  is formed such that the length (chord length) of the blade chord direction D 2  gradually decreases from the outer side Dro to the inner side Dri in the radial direction Dr. 
     The blade main body  61  has a blade tip portion  61   s  on the inner side Dri in the radial direction Dr. The blade tip portion  61   s  is a plane parallel to the axis O. That is, the blade tip portion  61   s  extends linearly so as to be parallel to the axis O in a cross-sectional view parallel to the axis O. Therefore, the blade tip portion  61   s  is not formed at an acute angle, and the chord length L in the blade chord direction D 2  is formed as a surface having a constant length. 
     The blade tip portion  61   s  is disposed at a minute interval on the outer side Dro in the radial direction Dr with respect to the impeller cap  38 . In the present embodiment, when viewed from the axial direction Da, an entire area of the movable blade  60  is disposed on the outer side Dro in the radial direction Dr rather than the position where the tubular portion  38   a  is disposed. That is, when viewed from the axial direction Da, the blade main body  61  and the impeller cap  38  do not overlap each other. Further, the position of the blade tip portion  61   s  in the radial direction Dr is preferably as close to the outer peripheral surface of the tubular portion  38   a  as possible within a range in which the movable blade  60  does not come into contact with the impeller cap  38  even when the movable blade  60  rotates. 
     The shaft portion  62  is formed so as to project from the blade main body  61  to the outer side Dro in the radial direction Dr. The shaft portion  62  is formed integrally with the blade main body  61 . The shaft portion  62  is inserted into the shaft support hole  22   h  formed in the intake nozzle  22 . The shaft portion  62  is rotatable around the center axis Ar by a blade driving device (not shown) in a state of being inserted into the shaft support hole  22   h . As a result, the blade main body  61  can rotate around the center axis Ar integrally with the shaft portion  62 . In each movable blade  60 , the angle of the blade main body  61  with respect to the flow direction (axial direction Da) of the working fluid flowing through the suction port  22   a  is adjusted by rotating about the center axis Ar. The inlet guide vanes  6  are opened and closed by rotating each of the plurality of movable blades  60  about the center axis Ar. 
     Here, as shown in  FIGS.  2  and  3   , the state in which the blade chord direction D 2  of the movable blade  60  is disposed to be parallel to the flow direction (axial direction Da) of the working fluid is defined as the fully open state of the movable blade  60 . That is, the fully open state is a state in which the movable blade  60  (blade main body  61 ) is rotated to be the thickest in the cross-sectional view orthogonal to the axis O. When the movable blade  60  is in the fully open state, the flow rate of the working fluid passing through the suction port  22   a  is maximized. On the other hand, when the movable blade  60  is rotated around the center axis Ar from the fully open state and the blade chord direction D 2  intersects the flow direction (axial direction Da) of the working fluid, the suction port  22   a  is gradually blocked by the blade main body  61 . As a result, the flow rate of the working fluid flowing into the impeller  40  from the suction port  22   a  through the inlet guide vane  6  is reduced. In the present embodiment, as shown in  FIG.  4   , the state in which the blade chord direction D 2  is orthogonal to the flow direction (axial direction Da) of the working fluid is defined as the fully closed state of the movable blade  60 . That is, the fully closed state is a state in which the movable blade  60  (blade main body  61 ) is rotated to be the thinnest in the cross-sectional view orthogonal to the axis O. 
     The position of at least a part of the blade tip portion  61   s  in the axial direction Da overlaps the position of the impeller cap  38  in the axial direction Da. That is, when viewed from the radial direction Dr, a part of the blade tip portion  61   s  overlaps the impeller cap  38 . In the present embodiment, the position of an entire area of the blade tip portion  61   s  in the axial direction Da overlaps the position of the impeller cap  38  in the axial direction Da. 
     Specifically, when the movable blade  60  is in the fully open state, a front edge portion  611   s  of the blade tip portion  61   s  is disposed on the second side Da 2  in the axial direction Da with respect to the tip end  38   s  on the first side Da 1  in the axial direction Da of the cap tip portion  38   b  in the axial direction Da. When the movable blade  60  is in the fully open state, the rear edge portion  612   s  of the blade tip portion  61   s  is disposed at a position overlapping the tubular portion  38   a  in the axial direction Da. 
     Further, as shown in  FIG.  4   , even when the movable blade  60  is in the fully closed state, the position of at least a part of the blade tip portion  61   s  in the axial direction Da overlaps the impeller cap  38  in the axial direction Da. In the present embodiment, when the movable blade  60  is in the fully closed state, the position of the entire area of the blade tip portion  61   s  in the axial direction Da overlaps the position of the cap tip portion  38   b  in the axial direction Da. 
     In such a geared compressor  1 , the working fluid is sucked into the intake nozzle  22  of the housing  2  from the suction port  22   a  by rotating the impeller  40  integrally with the rotary shaft  30 . In the suction port  22   a , the flow rate of the working fluid is adjusted by an opening of the inlet guide vane  6  when the working fluid passes through the inlet guide vane  6 . The working fluid passing through the inlet guide vane  6  is taken into the impeller flow path  45  from the intake nozzle  22  through the inflow port  45   i.    
     The working fluid flows from the inflow port  45   i  toward the outflow port  45   o  due to the centrifugal force generated by the impeller  40  that rotates integrally with the rotary shaft  30 . The working fluid is compressed while flowing from the inflow port  45   i  to the outflow port  45   o . The compressed working fluid flows out from the outflow port  45   o  to the outer side Dro in the radial direction Dr, and is sent to the exhaust flow path  23  on the outer side Dro in the radial direction Dr. The working fluid is further compressed while swirling around the axis O along the exhaust flow path  23 . 
     (Operational Effects) 
     According to the geared compressor  1  as described above, the position of the blade tip portion  61   s  of each of the plurality of movable blades  60  configuring the inlet guide vane  6  overlaps the position of the impeller cap  38  in the axial direction Da. Thereby, a blade height H, which is the length in the blade height direction D 1  of the blade main body  61  in the radial direction Dr, can be shortened. The vibration of the blade main body  61  can be suppressed by shortening of the blade main body  61 . Specifically, a non-dimensional frequency F of the blade main body  61  is represented by:
 
 F=L·ω/V   (1)
 
L is a chord length at the blade tip portion  61   s  in the blade chord direction D 2  of the blade main body  61 , ω is a natural frequency of the blade main body  61 , and V is a flow velocity of the working fluid. The natural frequency ω of the blade main body  61  is increased by shortening the blade height H of the blade main body  61 . Therefore, when the blade height H of the blade main body  61  is shortened and the natural frequency ω of the movable blade  60  is increased, the non-dimensional frequency F is increased. As the non-dimensional frequency F of the movable blade  60  increases, the self-excited vibration (flutter) caused by the flow of the working fluid is less likely to occur. Therefore, since the position of the blade tip portion  61   s  overlaps the position of the impeller cap  38  in the axial direction Da, the self-excited vibration of the movable blade  60  can be suppressed due to the working fluid flowing into the housing  2  from the suction port  22   a.  
 
     Further, the position of the blade tip portion  61   s  in the radial direction Dr is formed at the position close to the impeller cap  38  with a gap so as not to contact even when the movable blade  60  rotates. As a result, the space between the blade tip portion  61   s  and the outer peripheral surface of the impeller cap  38  becomes considerably narrow. In a case where the movable blade  60  is in the fully closed state, when viewed from the axial direction Da, although many areas of the suction port  22   a  is blocked by the blade tip portion  61   s , an annular gap is formed between the blade tip portion  61   s  and the outer peripheral surface of the impeller cap  38 . As a result, the jet may be generated by the working fluid that passes through the annular gap. When the flow velocity of the working fluid is suppressed so as to such jet does not occur, an increase in the flow rate of the centrifugal compressor is prevented. However, it is possible to prevent the working fluid from passing between the inlet guide vane  6  and the rotor end portion  3   e  by making the gap minute. Therefore, it is possible to effectively suppress the generation of the jet between the inlet guide vane  6  and the rotor end portion  3   e.    
     Further, the blade tip portion  61   s  is formed as a surface parallel to the axis. As a result, the chord length L of the blade tip portion  61   s  can be longer. As a result, the non-dimensional frequency F can be increased in the above Expression (1). This can also suppress the vibration of the blade main body  61 . 
     Further, in the inlet guide vane  6 , even in the fully closed state where the blade main body  61  is the thinnest in the cross-sectional view orthogonal to the axis O, at least a part of the blade tip portion  61   s  overlaps the impeller cap  38  in the axial direction Da. That is, no matter how the movable blade  60  rotates, a part of the blade tip portion  61   s  always overlaps the impeller cap  38 . As a result, the blade main body  61  is accommodated between the housing  2  and the impeller cap  38  in the radial direction Dr. As a result, the blade height H of the blade main body  61  in the radial direction Dr can be further shortened. The vibration of the blade main body  61  can be further suppressed by shortening the blade main body  61  in this manner. 
     Further, in the present embodiment, the position of the entire area of the blade tip portion  61   s , not a part of the blade tip portion  61   s , overlaps the position of the impeller cap  38  in the axial direction Da. As a result, the blade height H, which is the length in the blade height direction D 1  of the blade main body  61  in the radial direction Dr, can be considerably shortened. Therefore, the blade main body  61  is shortened, and the vibration of the blade main body  61  can be effectively suppressed. 
     Further, when viewed from the axial direction Da, the entire area of the movable blade  60  is disposed on the outer side Dro in the radial direction Dr with respect to the impeller cap  38 . That is, the entire blade main body  61  is disposed on the outer side Dro in the radial direction Dr with respect to the impeller cap  38  so as not to overlap the impeller cap  38  when viewed from the axial direction Da. As a result, the blade height H of the blade main body  61  in the radial direction Dr can be shortened. Therefore, the natural frequency of the movable blade  60  can be increased. As a result, in the above Expression (1), the non-dimensional frequency F is increased, and self-excited vibration is less likely to occur. 
     Other Embodiments 
     While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the gist of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims. 
     In the above embodiment, as an aspect of the geared compressor  1 , a so-called uniaxial two-stage configuration has been described as an example. However, the aspect of the geared compressor  1  is not limited thereto, and a biaxial four-stage, or more axes and stages may be provided depending on the design and specifications. 
     Further, the rotary machine of the present invention is not limited to the geared compressor  1 , but may be an uniaxial multi-stage flow type centrifugal compressor, or the like, a gas turbine, a steam turbine, or the like in which the rotary shaft  30  is directly rotationally driven by an external driving source. 
     APPENDIX 
     The rotary machine  1  described in the embodiment is comprehended, for example, as follows. 
     (1) The rotary machine  1  according to a first aspect includes a rotary machine  1  including a rotor  3  that includes a rotary shaft  30  that extends in an axial direction Da, in which an axis O extends, about the axis O, an impeller  40  fixed to the rotary shaft  30 , and an impeller cap  38  that is disposed at an end portion of the rotary shaft  30  and regulates movement of the impeller  40  in the axial direction Da; a housing  2  that covers the rotor  3  and has a suction port  22   a  allowing a working fluid to be flowed inside; and an inlet guide vane  6  that is disposed inside the housing  2  on a first side Da 1  in the axial direction Da with respect to the impeller  40 , and has a plurality of movable blades  60  that extend from the housing  2  toward an inner side Dri in a radial direction Dr around the axis O and disposed at intervals in a circumferential direction Dc about the axis O, in which a blade tip portion  61   s , which is a tip end of each of the plurality of movable blades  60  in the radial direction Dr, is disposed on the outer side Dro in the radial direction Dr with respect to an outer peripheral surface of the impeller cap  38 , and the position of at least a part of the blade tip portion  61   s  in the axial direction Da overlaps the position of the impeller cap  38  in the axial direction Da. The rotary machine is, for example, a geared compressor, an axial centrifugal compressor, a gas turbine, a steam turbine, or the like. 
     In the rotary machine  1 , the position of at least a part of each blade tip portion  61   s  of the plurality of movable blades  60  configuring the inlet guide vane  6  overlaps the position of the impeller cap  38  in the axial direction Da. As a result, the blade height H, which is the length in the blade height direction D 1  of the movable blade  60  in the radial direction Dr, can be shortened. The vibration of the movable blade  60  can be suppressed by shortening the movable blade  60 . 
     (2) The rotary machine  1  according to a second aspect may be the rotary machine  1  of (1), and the blade tip portion  61   s  may be a plane parallel to the axis O. 
     As a result, the chord length L of the blade tip portion  61   s  can be longer. As a result, the non-dimensional frequency F can be increased in the above Expression (1). Thereby, the vibration of the movable blade  60  can be suppressed. 
     (3) The rotary machine  1  according to a third aspect is the rotary machine  1  of (1) or (2), and each of the plurality of movable blades  60  is rotatable around a shaft portion  62  that extends in the radial direction Dr, and when the movable blade  60  is rotated to be the thinnest in a cross-sectional view orthogonal to the axis O, the position of at least a part of the blade tip portion  61   s  in the axial direction Da overlaps the position of the impeller cap  38  in the axial direction Da. 
     As a result, no matter how the movable blade  60  rotates, a part of the blade tip portion  61   s  always overlaps the impeller cap  38 . As a result, the blade height H of the movable blade  60  in the radial direction Dr can be shorter. The vibration of the movable blade  60  can be further suppressed by shortening the movable blade  60  in this manner. 
     (4) The rotary machine  1  according to a fourth aspect is any one of the rotary machines  1  from (1) to (3), and a position of an entire area of the blade tip portion  61   s  in the axial direction Da overlaps the position of the impeller cap  38  in the axial direction Da. 
     As a result, the blade height H, which is the length in the blade height direction D 1  of the movable blade  60  in the radial direction Dr, can be considerably shortened. Therefore, the movable blade  60  is shortened, and the vibration of the movable blade  60  can be effectively suppressed. 
     (5) The rotary machine  1  according to a fifth aspect is any one of the rotary machines  1  from (1) to (4), and when viewed from the axial direction Da, the entire area of the movable blade  60  is disposed on the outer side Dro in the radial direction Dr with respect to the impeller cap  38 . 
     As a result, the entire movable blade  60  is disposed on the outer side Dro in the radial direction Dr with respect to the impeller cap  38  so as not to overlap the impeller cap  38  when viewed from the axial direction Da. Thereby, the blade height H of the movable blade  60  in the radial direction Dr can be shortened. As a result, the self-excited vibration is less likely to occur. 
     EXPLANATION OF REFERENCES 
     
         
           1  Geared compressor (rotary machine) 
           2  Housing 
           3  Rotor 
           3   e  Rotor end portion 
           6  Inlet guide vane 
           11  Speed increasing transmission portion 
           12  Radial bearing 
           15  Pinion gear 
           16  Large-diameter gear 
           17  Thrust bearing 
           21  Shaft insertion hole 
           22  Intake nozzle 
           22   a  Suction port 
           22   h  Shaft support hole 
           23  Exhaust flow path 
           30  Rotary shaft 
           30   s  Shaft end 
           38  Impeller cap 
           38   a  Tubular portion 
           38   b  Cap tip portion 
           38   s  Tip end 
           40  Impeller 
           40 A First-stage impeller 
           40 B Second-stage impeller 
           41  Disk 
           41   a  First surface 
           41   b  Second surface 
           42  Blade 
           43  Cover 
           45  Impeller flow path 
           45   i  Inflow port 
           45   o  Outflow port 
           60  Movable blade 
           61  Blade main body 
           61   s  Blade tip portion 
           611 ,  611   s  Front edge portion 
           612 ,  612   s  Rear edge portion 
           62  Shaft portion 
         Ar Center axis 
         D 1  Blade height direction 
         D 2  Blade chord direction 
         Da Axial direction 
         Da 1  First side 
         Da 2  Second side 
         Dc Circumferential direction 
         Dr Radial direction 
         Dri Inner side 
         Dro Outer side 
         H Blade height 
         L Chord length 
         O Axis