Impeller and centrifugal compressor

Abstract

To suppress the influence of a centrifugal force which acts on a cover and to achieve a high peripheral speed of an impeller having a cover.SOLUTION: An impeller comprises: a disk in a disk shape centered on an axis; a cover arranged apart with respect to the disk in an axial direction, in which the axis extends; and a plurality of blades connecting the disk and the cover and arranged around the axis at intervals in a rotation direction. Each one of the blades has: a main wing extending further to a rear side in the rotation direction as it goes from the inner side in a radial direction centered on the axis toward the outer side; and a sub-wing arranged at an interval on a front side in the rotation direction with respect to the main wing, and whose front edge is located on the outer side in the radial direction relative to the front edge of the main wing. A lean angle of the main wing is equal to or larger than 0° and equal to or smaller than 20°. For the front edge of the main wing, axial positions of a tip part connected to the cover and a hub part connected to the disk coincide with each other when viewed from the rotation direction.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to an impeller and a centrifugal compressor. [Background technology]

[0002] As an impeller used in a centrifugal compressor, a type of impeller called a closed type is known. This type of impeller has a disk, blades, and a cover. The outer peripheral surface of the disk extends radially outward toward one side in the axial direction. A plurality of blades are arranged on this outer peripheral surface at intervals in the circumferential direction. The cover covers these blades from the radial outside. As a result, an impeller flow path is formed in the impeller, which is surrounded by a pair of adjacent blades, the disk, and the cover.

[0003] For example, a centrifugal compressor equipped with an impeller is disclosed in Patent Document 1. The impeller described in Patent Document 1 is a so-called closed impeller that includes a disk, a plurality of blades provided on the disk, and a cover provided to cover the plurality of blades. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-122516 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when trying to increase the peripheral speed of the impeller in order to improve the capacity of the centrifugal compressor, the centrifugal stress acting on the heavy cover increases. As a result, the centrifugal stress generated in the impeller becomes larger than that of an open impeller without a cover, making it difficult to increase the peripheral speed. Therefore, there is a demand for reducing the effect of the centrifugal force acting on the cover for impellers with a cover and increasing the peripheral speed of the impeller with a cover.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an impeller and a centrifugal compressor that can reduce the effect of centrifugal force acting on a cover and achieve a high peripheral speed of an impeller having a cover. [Means for solving the problem]

[0007] In order to solve the above problems, the impeller of the present disclosure comprises a disk having a disk shape centered on an axis, a cover arranged at a distance from the disk in the axial direction along which the axis extends, and a plurality of blades connecting the disk and the cover and arranged at intervals in the direction of rotation around the axis, each of the blades having a main wing extending to the rear side in the direction of rotation as it moves from the inside to the outside in the radial direction centered on the axis, and a sub-wing arranged at a distance forward in the direction of rotation relative to the main wing and whose leading edge is located radially outward relative to the leading edge of the main wing, the main wing having a lean angle of 0 degrees or more and 20 degrees or less, and when viewed from the direction of rotation, the axial positions of a tip portion connected to the cover and a hub portion connected to the disk are consistent.

[0008] A centrifugal compressor according to the present disclosure includes the impeller. Effect of the Invention

[0009] According to the impeller and centrifugal compressor of the present disclosure, the effect of centrifugal force acting on the cover can be suppressed, and the peripheral speed of the impeller having the cover can be increased. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view showing a configuration of a centrifugal compressor according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a cross-sectional view showing a meridian cross section of an upper half of an impeller provided in the centrifugal compressor. [Diagram 3] 3 is a view of the impeller blade as viewed from a first axial side. FIG. [Figure 4] FIG. 2 is a schematic diagram showing the shape of a blade of the impeller as viewed from the axial direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the impeller 40 and the centrifugal compressor 10 according to the present disclosure will be described with reference to the accompanying drawings. However, the present disclosure is not limited to only this embodiment.

[0012] (Configuration of centrifugal compressor) Hereinafter, an impeller 40 and a centrifugal compressor 10 according to an embodiment of the present disclosure will be described with reference to Fig. 1 to Fig. 5. As shown in Fig. 1, the centrifugal compressor 10 mainly includes a casing 20, a rotating shaft 30, and an impeller 40.

[0013] (Casing configuration) The casing 20 accommodates a part of the rotating shaft 30 and the impeller 40. The casing 20 has a cylindrical shape extending in the direction in which the axis line O of the rotating shaft 30 extends (hereinafter, this direction will be referred to as the axial direction Da).

[0014] In the casing 20, a suction port 21 is formed near one end 20a of the first side Dau in the axial direction Da, through which the process gas (working fluid) flows from the outside into the casing 20. In addition, in the casing 20, a discharge port 22 is formed near the other end 20b of the second side Dad in the axial direction Da, through which the process gas flows out of the casing 20. That is, the one end 20a side of the first side Dau in the axial direction Da is the upstream side in the flow direction of the process gas in the centrifugal compressor 10. In addition, the other end 20b side of the second side Dad in the axial direction Da is the downstream side in the flow direction of the process gas in the centrifugal compressor 10.

[0015] A casing-side flow passage 25 is formed inside the casing 20 at a position between the impellers 40. The casing-side flow passage 25 passes the process gas flowing through the impeller 40 from an inlet 21 on one end 20a of the first side Dau in the axial direction Da in the casing 20 to an outlet 22 on the other end 20b of the second side Dad in the axial direction Da through an impeller flow passage 45 described later.

[0016] (Rotation shaft configuration) The rotating shaft 30 is rotatable about an axis O relative to the casing 20. Both ends of the rotating shaft 30 are supported rotatably about the axis O via journal bearings 28A and 28B. A thrust bearing 29 is disposed at one end 20a of the casing 20 in a position close to the journal bearing 28A. One end of the rotating shaft 30 is supported in the axial direction Da via the thrust bearing 29.

[0017] (Impeller configuration) Each of the multiple impellers 40 is attached to the rotating shaft 30 and compresses the process gas by utilizing centrifugal force. The multiple impellers 40 are housed inside the casing 20 at intervals in the axial direction Da. Note that in the embodiment of the present disclosure, although an example in which six impellers 40 are arranged is shown in FIG. 1, it is sufficient that at least one impeller 40 is arranged.

[0018] As shown in FIGS. 2 to 4, each impeller 40 is a so-called closed impeller that includes a disk 41, blades 50, and a cover .

[0019] (Disk configuration) The disk 41 is formed in a disk shape centered on the axis O. As shown in Fig. 2, the disk 41 is formed so as to gradually expand in diameter to an outer side Dro in a radial direction Dr centered on the axis O as it moves from a first side Dau in the axial direction Da to a second side Dad.

[0020] A circular through hole 411 penetrating in the axial direction Da is formed in the center of the disk 41. The impeller 40 is fixed integrally to the rotating shaft 30 with the inner surface of the through hole 411 fitted into the outer circumferential surface of the rotating shaft 30.

[0021] A disk main surface 412 is formed on a first side Dau in the axial direction Da of the disk 41. The disk main surface 412 expands to the outer side Dro in the radial direction Dr from the first side Dau to the second side Dad in the axial direction Da. The disk main surface 412 faces the outer side Dro in the radial direction Dr in the portion of the first side Dau in the axial direction Da. The disk main surface 412 faces the first side Dau in the axial direction Da in the portion of the second side Dad in the axial direction Da. That is, the disk main surface 412 curves to face the first side Dau in the axial direction Da from the first side Dau to the second side Dad in the axial direction Da. That is, the disk main surface 412 has a concave curved surface shape. The disk main surface 412 is one of the surfaces that form the impeller flow passage 45 described later. That is, the disk main surface 412 is a surface of the disk 41 through which the process gas flows.

[0022] (Blade configuration) The blade 50 connects the disk 41 and the cover 42. The blade 50 extends from the disk main surface 412 toward the first side Dau in the axial direction Da. The blade 50 is connected to the cover 42 at a tip portion 51. The blade 50 is also connected to the disk 41 at a hub portion 52. A plurality of the blades 50 are arranged at intervals in the rotation direction R around the axis O. The plurality of blades 50 are arranged radially toward the outer side Dro in the radial direction Dr, centered on the axis O. In this embodiment, each blade 50 has a main wing 55 and a sub-wing 57 corresponding to the main wing 55. That is, a plurality of pairs of the main wing 55 and the sub-wing 57 (for example, six pairs, a total of twelve blades) are arranged.

[0023] The main wing 55 extends from the front side to the rear side in the rotation direction R from the inside Dri to the outside Dro in the radial direction Dr. The leading edge 551 of the main wing 55 is disposed in a position close to the end of the first side Dau in the axial direction Da of the cover 42. At the leading edge 551 of the main wing 55, the positions of the tip part 51 and the hub part 52 in the axial direction Da coincide with each other when viewed from the rotation direction R. The trailing edge 552 of the main wing 55 is disposed in the same position as the outer peripheral edge of the disk 41 in the radial direction Dr. That is, the trailing edge 552 of the main wing 55 extends to the outer peripheral edge of the disk 41 without leaving any gap therebetween. As shown in FIG. 4, the main wing 55 is curved so that the middle part is convex toward the front side (one side in the circumferential direction) in the rotation direction R. In the main wing 55, the surface facing the front side in the rotation direction R is a pressure surface 555 that is a convex curved surface. In the main wing 55, a surface facing the rear side in the rotation direction R (the other side in the circumferential direction) is a negative pressure surface 556 which is a concave curved surface. As shown in FIG. 3, the main wing 55 has a lean angle α of 0 degrees or more and 20 degrees or less. Here, the lean angle α is the angle of inclination toward the front in the rotation direction R with respect to the disk main surface 412. Preferably, the lean angle α of the main wing 55 is 0 degrees or more and 15 degrees or less. More preferably, the lean angle α of the main wing 55 is 0 degrees or more and 10 degrees or less.

[0024] As shown in FIG. 4, the sub-wings 57 are arranged at intervals on the front side of the rotation direction R with respect to the corresponding main wing 55. That is, one sub-wing 57 is arranged at intervals on the rear side of the rotation direction R with respect to another main wing 55 arranged at the front side of the rotation direction R with respect to the corresponding main wing 55. The sub-wings 57 are formed shorter than the main wing 55. The sub-wings 57 extend from the front side to the rear side in the rotation direction R as they move from the inner side Dri to the outer side Dro in the radial direction Dr. As shown in FIG. 2, the leading edge 571 of the sub-wing 57 is located on the outer side Dro in the radial direction Dr with respect to the leading edge 551 of the corresponding main wing 55. The tip portion 51 of the leading edge 571 of the sub-wing 57 is connected to a curved area in the disk main surface 412 when viewed from the rotation direction R. Also, the leading edge 571 of the sub-wing 57 is inclined at an inclination (inclination angle β) of 45 degrees or less with respect to a virtual line perpendicular to the axis O on a meridian section when viewed from the rotation direction R. Here, the meridian section is a cross section of a flow passage shape in which the shape of the blade 50 is rotated and projected along the axis O and superimposed on a longitudinal section passing through the axis O, rather than being a cut section of only the blade 50. Also, the trailing edge 572 of the sub-wing 57 is disposed at the same position as the outer circumferential edge of the disk 41 in the radial direction Dr. That is, the trailing edge 572 of the sub-wing 57 extends to the outer circumferential edge of the disk 41 without leaving any gap therebetween, similar to the trailing edge 552 of the main wing 55.

[0025] As shown in FIG. 4, the leading edge 571 of the sub-wing 57 is at least partially located upstream of the throat position S between a pair of adjacent main wings 55 in the rotation direction R. Here, the throat position S is the position where the flow passage cross-sectional area is the smallest in the impeller flow passage 45 formed between the negative pressure surface 556 of the main wing 55 arranged on the front side of the rotation direction R and the pressure surface 555 of the main wing 55 arranged on the rear side of the rotation direction R among the pair of adjacent main wings 55 in the rotation direction R. The throat position S in this embodiment is the position where the imaginary line connecting the negative pressure surface 556 of the main wing 55 arranged on the front side of the rotation direction R and the leading edge 551 of the pressure surface 555 of the main wing 55 arranged on the rear side of the rotation direction R is the shortest in a cross section perpendicular to the blade height direction. The leading edge 571 of the sub-wing 57 is located upstream of the throat position S in the entire area from the tip portion 51 to the hub portion 52. Here, the upstream side refers to the upstream side in the flow direction of the process gas flowing through the impeller flow passage 45, and is the side (position) closer to an inlet 451 of the impeller flow passage 45 described later. In other words, the leading edge 571 of the sub-blade 57, in the entire region from the tip portion 51 to the hub portion 52, is disposed at a position closer to the inlet 451 of the impeller flow passage 45 with respect to the throat position S.

[0026] The sub-wing 57 is curved so that the middle part is convex toward the forward side in the rotation direction R. In other words, the sub-wing 57 is curved in the same direction as the main wing 55. In the sub-wing 57, the surface facing the forward side in the rotation direction R is a pressure surface 575 that is a convex curved surface. In the sub-wing 57, the surface facing the rear side in the rotation direction R is a negative pressure surface 576 that is a concave curved surface. Also, as shown in FIG. 3, the sub-wing 57 has a lean angle α of 0 degrees or more and 20 degrees or less, similar to the main wing 55. Preferably, the lean angle α of the sub-wing 57 is 0 degrees or more and 15 degrees or less. More preferably, the lean angle α of the main wing 55 is 0 degrees or more and 10 degrees or less. In other words, it is preferable that the lean angle α of the sub-wing 57 is the same as that of the main wing 55.

[0027] (Cover composition) As shown in FIG. 2, the cover 42 is disposed away from the disk 41 on a first side Dau in the axial direction Da. The cover 42 covers the blades 50 from the first side Dau in the axial direction Da. The end of the blade 50 opposite to the end connected to the disk main surface 412 is fixed to the cover 42. The cover 42 is disposed facing the disk 41 so as to sandwich the main wing 55 and the sub-wing 57 between the cover 42 and the disk 41. The cover 42 is formed so as to gradually increase in diameter from the first side Dau in the axial direction Da to the second side Dad on the outer side Dro in the radial direction Dr. The cover 42 is formed so as to become thinner toward the outer side Dro in the radial direction Dr. The cover 42 has a cover facing surface 421 formed on the second side Dad in the axial direction Da of the cover 42, which faces the disk main surface 412.

[0028] The cover opposing surface 421 expands to the outer side Dro in the radial direction Dr as it moves from the first side Dau to the second side Dad in the axial direction Da. The cover opposing surface 421 faces the outer side Dro in the radial direction Dr in the portion on the first side Dau in the axial direction Da. The cover opposing surface 421 faces the second side Dad in the axial direction Da in the portion on the second side Dad in the axial direction Da. In other words, the cover opposing surface 421 curves to face the second side Dad in the axial direction Da as it moves from the first side Dau to the second side Dad in the axial direction Da. In other words, the cover opposing surface 421 has a convex curved surface shape. The tip portions 51 of the main wing 55 and the sub-wing 57 are joined to the cover opposing surface 421.

[0029] Between the disk 41 and the cover 42, an impeller flow passage 45 is formed, which is partitioned in the rotation direction R by a plurality of blades 50. The impeller flow passage 45 extends while curving from the inside Dri to the outside Dro in the radial direction Dr as it moves from the first side Dau to the second side Dad in the axial direction Da. The impeller flow passage 45 has an inlet 451 that opens in the radial direction Dr and on the first side Dau in the axial direction Da, and an outlet 452 that opens on the outside Dro in the radial direction Dr and on the first side Dau in the axial direction Da. The inlet 451 opens toward the first side Dau in the axial direction Da so that the process gas that has flowed through the casing side flow passage 25 can flow in. The outlet 452 opens toward the outside Dro in the radial direction Dr so that the process gas flows out to the casing side flow passage 25.

[0030] (Action and effect) The impeller 40 and the centrifugal compressor 10 of the above configuration have a main wing 55 with a lean angle α of 0 degrees or more and 20 degrees or less, and a sub-wing 57 with a leading edge 571 located on the outer side Dro in the radial direction Dr of the leading edge 551 of the main wing 55. Furthermore, the leading edge 551 of the main wing 55 is arranged so that the positions of the axial direction Da of the tip portion 51 and the hub portion 52 coincide when viewed from the rotation direction R. Since the lean angle α of the main wing 55 is small and the positions of the axial direction Da of the tip portion 51 and the hub portion 52 of the leading edge 551 coincide, the main wing 55 is connected to the disk main surface 412 and the cover facing surface 421 in a state close to perpendicular. As a result, the cover 42 is firmly supported by the multiple main wings 55 to the disk 41. Furthermore, the cover 42 is firmly supported by the sub-wing 57 to the disk 41 at a position on the outer side Dro in the radial direction Dr of the impeller 40. Therefore, it is possible to suppress the effect of centrifugal force acting on the cover 42 while increasing the rigidity of the cover 42 by the multiple main blades 55 and sub blades 57. This makes it possible to achieve high speed rotation of the impeller 40.

[0031] In addition, the lean angle α of not only the main wing 55 but also the sub-wing 57 is set to be equal to or greater than 0 degrees and equal to or less than 20 degrees. Therefore, not only the main wing 55 but also the sub-wing 57 are connected to the disk main surface 412 and the cover facing surface 421 in a state close to perpendicular. As a result, the cover 42 is firmly supported on the disk 41 not only by the multiple main wings 55 but also by the multiple sub-wings 57. Therefore, the rigidity of the cover 42 can be further increased by the multiple sub-wings 57.

[0032] In addition, at least a part of the leading edge 571 of the sub-wing 57 is located upstream of the throat position S between the pair of main wings 55. Therefore, between the leading edges 551 of the pair of main wings 55, the sub-wing 57 acts on the disk main surface 412 and the cover opposing surface 421 like a support. In other words, the cover 42 is firmly supported on the disk 41 near the leading edge 571 of the sub-wing 57. Therefore, the rigidity of the cover 42 can be further increased by the multiple sub-wings 57. In particular, in this embodiment, the entire area of ​​the leading edge 571 of the sub-wing 57 is located upstream of the throat position S between the pair of main wings 55. Therefore, the rigidity of the cover 42 can be further increased by the multiple sub-wings 57.

[0033] Furthermore, the leading edge 571 of the sub-blade 57 is inclined at an angle of 45 degrees or less with respect to a virtual line perpendicular to the axis O on a meridian cross section. Therefore, the leading edge 571 of the sub-blade 57 can support the cover 42 against the disk 41 while suppressing loss of the process gas flowing through the impeller flow passage 45 when it collides with the leading edge 571 of the sub-blade 57. Furthermore, since the inclination angle β of the leading edge 571 of the sub-blade 57 is within 45 degrees, the workability of the impeller flow passage 45 (inside of the impeller 40) can be ensured.

[0034] In addition, the trailing edge 552 of the main wing 55 and the trailing edge 572 of the sub-wing 57 are disposed at the same position. Specifically, the trailing edge 552 of the main wing 55 and the trailing edge 572 of the sub-wing 57 extend to the outer peripheral edge of the disk 41 in the radial direction Dr. Therefore, the flow straightening effect of the main wing 55 and the sub-wing 57 can be maintained up to the outlet 452 of the impeller flow path 45. Therefore, by guiding the process gas to the outer peripheral edge of the disk 41 with the main wing 55 and the sub-wing 57, it is possible to suppress the occurrence of loss greater than the loss caused by the position and shape of the leading edge 571 of the sub-wing 57.

[0035] (Other embodiments) Although the embodiments of the present disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like that do not depart from the gist of the present disclosure are also included.

[0036] The lean angle α of the sub-wing 57 is not limited to being 0 degrees or more and 20 degrees or less. In other words, only the lean angle α of the main wing 55 may be 0 degrees or more and 20 degrees or less, and the lean angle α of the sub-wing 57 may be 20 degrees or more.

[0037] Furthermore, the leading edge 571 of the sub-wing 57 is not limited to the structure in which the entire area is located upstream of the throat position S between the pair of main wings 55 as in this embodiment. Therefore, the rigidity of the cover 42 can be further increased by using a plurality of sub-wings 57. It is sufficient that at least a portion of the leading edge 571 of the sub-wing 57 is located upstream of the throat position S between the pair of main wings 55.

[0038] Furthermore, the blade 50 is not limited to a structure having only the main wing 55 and the sub-wing 57 as in this embodiment. For example, the blade 50 may have a second sub-wing.

[0039] <Additional Notes> The impeller 40 and the centrifugal compressor 10 described in the embodiment can be understood, for example, as follows.

[0040] (1) The impeller 40 according to the first aspect includes a disk 41 having a disk shape centered on an axis O, a cover 42 arranged apart from the disk 41 in an axial direction Da along which the axis O extends, and a plurality of blades 50 connecting the disk 41 and the cover 42 and arranged at intervals in a rotation direction R around the axis O. Each of the blades 50 extends from an inner side Dri to an outer side Dro in a radial direction Dr about the axis O toward a rear side in the rotation direction R. and a sub-wing 57 arranged at a distance forward of the main wing 55 in the direction of rotation R and having a leading edge 571 positioned outward in the radial direction Dr than a leading edge 551 of the main wing 55, the main wing 55 having a lean angle α of 0 degrees or more and 20 degrees or less, and when viewed from the direction of rotation R, the position in the axial direction Da of a tip portion 51 connected to the cover 42 and a hub portion 52 connected to the disk 41 coincide with each other.

[0041] As a result, the lean angle α of the main wing 55 is small, and the positions of the axial direction Da of the tip portion 51 and the hub portion 52 of the leading edge 551 are aligned, so that the main wing 55 is connected to the disk 41 and the cover 42 in a nearly perpendicular state. As a result, the cover 42 is firmly supported to the disk 41 by the multiple main wings 55. Furthermore, the cover 42 is firmly supported to the disk 41 by the sub-wing 57 at a position on the outer side Dro of the radial direction Dr of the impeller 40. Therefore, the rigidity of the cover 42 can be increased by the multiple main wings 55 and the sub-wing 57, while the effect of the centrifugal force acting on the cover 42 can be suppressed. As a result, it is possible to achieve high rotation speed of the impeller 40.

[0042] (2) The impeller 40 according to a second aspect is the impeller 40 of (1), wherein the auxiliary blades 57 have a lean angle α of 0 degrees or more and 20 degrees or less.

[0043] As a result, not only the main wings 55 but also the sub-wings 57 are connected to the disk 41 and the cover 42 in a nearly perpendicular state. As a result, the cover 42 is firmly supported to the disk 41 not only by the multiple main wings 55 but also by the multiple sub-wings 57. Therefore, the rigidity of the cover 42 can be further increased by the multiple sub-wings 57.

[0044] (3) The impeller 40 of the third aspect is the impeller 40 of (1) or (2), wherein the leading edge 571 of the sub-wing 57 is at least partially located upstream of the throat position S between a pair of adjacent main wings 55 in the rotational direction R.

[0045] As a result, the sub-wings 57 act on the disk 41 and the cover 42 like a support pillar between the leading edges 551 of the pair of main wings 55. That is, the cover 42 is firmly supported on the disk 41 near the leading edges 571 of the sub-wings 57. Therefore, the rigidity of the cover 42 can be further increased by the multiple sub-wings 57.

[0046] (4) The impeller 40 according to the fourth aspect is any one of the impellers 40 of (1) to (3), in which the leading edge 571 of the sub-wing 57 is inclined at an angle of 45 degrees or less with respect to a virtual line perpendicular to the axis O on a meridian cross section.

[0047] This allows the leading edge 571 of the sub-blade 57 to support the cover 42 against the disk 41 while suppressing loss of the working fluid flowing through the flow passage of the impeller 40 when it collides with the leading edge 571 of the sub-blade 57. Furthermore, since the inclination angle β of the leading edge 571 of the sub-blade 57 is within 45 degrees, the workability of the inside of the impeller 40 can be ensured.

[0048] (5) The impeller 40 according to the fifth aspect is any one of the impellers 40 of (1) to (4), in which the trailing edge 552 of the main wing 55 and the trailing edge 572 of the sub-wing 57 are arranged at the same position in the radial direction Dr.

[0049] This allows the flow straightening effect of the main blades 55 and the sub-blade 57 to be maintained up to the outlet 452 of the impeller flow path 45. Therefore, by guiding the process gas up to the outer circumferential edge of the disk 41 with the main blades 55 and the sub-blade 57, it is possible to prevent loss greater than that caused by the position and shape of the leading edge 571 of the sub-blade 57.

[0050] (6) A centrifugal compressor 10 according to a sixth aspect includes the impeller 40 of any one of (1) to (5). [Explanation of symbols]

[0051] 10...Centrifugal compressor O…Axis line 20…Casing 20a...One end 20b...Other end 21…Suction port 22…Discharge port 25…Casing side flow passage 30…Rotation axis 40…Impeller 41…Disc 411...Through hole 412…Disc main surface 50…Blade 51…Tip section 52…Hub section 55…Wing 551…leading edge (wing) 552…trailing edge (wing) 555…Pressure surface (main wing) 556…Suction surface (wing) 57…Secondary wing 571…Leading edge (auxiliary wing) 572… Trailing edge (secondary wing) 575…Pressure surface (auxiliary wing) 576…Negative pressure surface (secondary wing) S…Throat position α…Lean angle β…Inclination angle 42…Cover 421…Cover facing surface 45…Impeller passage 451...Inlet 452...Outlet 28A and 28B...Journal bearings 29...Thrust bearing Da…Axial direction Dau…first side Dad…Second side Dr…Radial direction Dro…Outside Dri…inside R…Rotation direction

Claims

1. a disk having a disk shape centered on an axis; a cover disposed apart from the disk in an axial direction in which the axis extends, with respect to the disk; a plurality of blades connecting the disk and the cover and disposed at intervals in a rotational direction around the axis; each of the blades includes: a main blade extending toward a rear side in the rotational direction as it goes from an inner side to an outer side in a radial direction centered on the axis; a sub-blade disposed at an interval from the main blade on a front side in the rotational direction, and having a leading edge located on an outer side in the radial direction than a leading edge of the main blade; the main blade has a lean angle of 0 degrees or more and 20 degrees or less; when viewed from the rotational direction, a leading edge of the main blade has an axial position that coincides with a tip portion connected to the cover and a hub portion connected to the disk; an impeller in which at least a part of a leading edge of the sub-blade is located upstream with respect to a throat position between a pair of adjacent main blades in the rotational direction.

2. The impeller according to claim 1, wherein the sub-blade has a lean angle of 0 degrees or more and 20 degrees or less.

3. The impeller according to claim 1 or 2, wherein a leading edge of the sub-blade is inclined at an angle of 45 degrees or less with respect to a virtual line orthogonal to the axis in a meridian plane cross section.

4. The impeller according to claim 1 or 2, wherein a trailing edge of the main blade and a trailing edge of the sub-blade are disposed at the same position in the radial direction.

5. A centrifugal compressor including the impeller according to claim 1 or 2.