Centrifugal compressor

Abstract

A casing of a centrifugal compressor includes a diaphragm, an external casing that covers the diaphragm, a head that closes an opening at both ends of the external casing in the axial direction, and a discharge scroll that guides the working fluid discharged from the impeller to the discharge port. The discharge scroll is connected to the diffuser flow path on the outside in the radial direction, extends in a circumferential direction around the central axis, and is formed so that a gap in the radial direction when viewed from the axial direction is constant, and a gap in the axial direction gradually narrows the farther the gap is from the discharge port in the circumferential direction.

Description

centrifugal compressor

[0001] This application claims priority to Japanese Patent Application No. 2023-213861, filed on December 19, 2023, the contents of which are incorporated herein by reference.

[0002] A multi-stage centrifugal compressor, which has multiple stages of impellers that compress gas, is known as a type of centrifugal rotating machine. In a multi-stage centrifugal compressor, gas is drawn into a casing through a suction port, compressed sequentially by multiple stages of impellers, and discharged from the casing through a discharge port. A discharge scroll is connected to the discharge port, which maintains a constant flow rate of the gas discharged from the impeller through a diffuser passage and reduces its pressure.

[0003] For example, Patent Document 1 describes a discharge volute (discharge scroll) that is formed so that the radial spacing gradually increases toward the downstream side in the circumferential direction of gas flow. This discharge volute is formed by fixing volute pieces to a casing, the radial thickness of which gradually decreases toward the downstream side in the circumferential direction of gas flow.

[0004] EP 3239534

[0005] Incidentally, when forming a discharge scroll, it can be formed with a shape that changes the flow direction of the working fluid, such as gas, discharged from the diffuser passage radially outward and then flows in the discharge scroll radially inward, or a shape that allows the working fluid to flow in without changing its flow direction. A discharge scroll shaped to change the flow direction and then flow in the discharge scroll is prone to separation when the working fluid flows in the discharge scroll. On the other hand, a discharge scroll shaped to allow the working fluid to flow in without changing its flow direction is formed radially outward from the diffuser passage, resulting in an outer diameter that is too large for a centrifugal compressor. There is a demand for a compact discharge scroll that suppresses flow separation when the working fluid flows in.

[0006] The present disclosure provides a centrifugal compressor that can form a compact discharge scroll while suppressing flow separation when a working fluid flows in.

[0007] A centrifugal compressor according to the present disclosure includes a rotating shaft extending in an axial direction in which a central axis extends, and a casing having an inlet port formed on a first side in the axial direction and an outlet port formed on a second side in the axial direction, the rotating shaft having an impeller disposed within the casing, the impeller compressing and discharging a working fluid supplied from the first side in the axial direction outward in a radial direction relative to the central axis, the casing including a diaphragm formed in a cylindrical shape extending in the axial direction so as to cover the impeller, an outer casing formed in a cylindrical shape extending in the axial direction so as to cover the diaphragm, and an outer casing having a cylindrical shape extending in the axial direction so as to cover the outer casing. The casing includes a head that closes openings at both ends in the axial direction, a diffuser passage that guides the working fluid discharged from the impeller radially outward, and a discharge scroll that guides the working fluid discharged from the impeller to the discharge port, wherein the discharge scroll is connected to the diffuser passage on the radially outer side and extends in a circumferential direction around the central axis, and the radial spacing of the discharge scrolls is constant when viewed from the axial direction, and the axial spacing of the discharge scrolls is gradually narrowed as the scrolls move away from the discharge port in the circumferential direction.

[0008] According to the centrifugal compressor of the present disclosure, it is possible to form a compact discharge scroll while suppressing flow separation when the working fluid flows in.

[0009] 1 is a cross-sectional view of a centrifugal compressor according to an embodiment of the present disclosure; FIG. 2 is an enlarged cross-sectional view showing a configuration around a discharge scroll of the centrifugal compressor; FIG. 3 is a cross-sectional view taken along III-III in FIG. 1 showing the discharge scroll of the centrifugal compressor as viewed from the axial direction; FIG. 4 is an enlarged view of a main part taken along IV-IV in FIG. 3 showing a change in the axial width of the discharge scroll of the centrifugal compressor; FIG. 5 is an enlarged view of a main part taken along V-V in FIG. 3 showing a change in the axial width of the discharge scroll of the centrifugal compressor; FIG. 6 is an enlarged view of a main part taken along VI-VI in FIG. 3 showing a change in the axial width of the discharge scroll of the centrifugal compressor; FIG. 7 is an enlarged view of a main part taken along VII-VII in FIG. 3 showing a change in the axial width of the discharge scroll of the centrifugal compressor.

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A centrifugal compressor according to the present invention will now be described with reference to the accompanying drawings. However, the present invention is not limited to this embodiment.

[0011] (Configuration of Centrifugal Compressor) As shown in Fig. 1, the centrifugal compressor 1 in this embodiment is a single-shaft multi-stage centrifugal compressor. The centrifugal compressor 1 mainly includes a rotating shaft 2 that rotates around a central axis O, and a casing 10 formed to surround the rotating shaft 2.

[0012] (Configuration of Rotating Shaft) The rotating shaft 2 extends in the axial direction Da. The rotating shaft 2 extends so as to penetrate the inside of the casing 10 along the central axis O. The rotating shaft 2 has a rotating shaft main body 21 and an impeller 22.

[0013] In this embodiment, the direction in which the central axis O extends is referred to as the axial direction Da. The axial direction Da of the rotating shaft 2 is along a horizontal plane. In other words, the central axis O extends horizontally. The radial direction based on the central axis O is simply referred to as the radial direction Dr. Furthermore, the direction around the rotating shaft 2 centered on the central axis O is referred to as the circumferential direction Dc.

[0014] The rotating shaft body 21 is formed in a cylindrical shape extending in the axial direction Da. An end of the rotating shaft body 21 on a first side Da1 in the axial direction Da is supported by the casing 10 by a journal bearing 32A and a thrust bearing 31 so as to be rotatable about the central axis O. An end of the rotating shaft body 21 on a second side Da2 in the axial direction Da is supported by the casing 10 by a journal bearing 32B so as to be rotatable about the central axis O.

[0015] The impeller 22 is disposed on the outer side Dro of the rotating shaft body 21 in the radial direction Dr based on the central axis O. A plurality of impellers 22 are disposed spaced apart in the axial direction Da within the casing 10. In this embodiment, for example, six impellers 22 are disposed at intervals in the axial direction Da.

[0016] Each impeller 22 compresses and discharges a working fluid (e.g., gas) supplied from a first side Da1 in the axial direction Da to an outer side Dro in the radial direction Dr. An impeller flow path 23 is formed inside each impeller 22. The cross-sectional area of ​​the impeller flow path 23 gradually decreases from the inner side Dri in the radial direction Dr to the outer side Dro in the radial direction Dr. As a result, the working fluid flowing through the impeller flow path 23 while the impeller 22 is rotating is gradually compressed and becomes highly pressurized. Note that each impeller 22 may be a closed impeller having a cover or an open impeller without a cover.

[0017] (Casing Configuration) The casing 10 is formed to surround the rotating shaft main body 21 and the plurality of impellers 22 from the outer side Dro in the radial direction Dr. The casing 10 includes an outer casing 11, a suction port 111, a discharge port 112, a plurality of diaphragms 15, and a head 17.

[0018] The outer casing 11 is formed in a cylindrical shape extending in the axial direction Da. The outer casing 11 is formed to cover the rotating shaft 2, the plurality of diaphragms 15, and the head 17 from the outer side Dro in the radial direction Dr. The outer casing 11 forms an inlet 111 and an outlet 112.

[0019] The suction port 111 is formed on a first side Da1 in the axial direction Da of the outer casing 11. The suction port 111 allows the working fluid to flow into the outer casing 11 from the outside.

[0020] The discharge port 112 is formed on the second side Da2 in the axial direction Da of the outer casing 11. The discharge port 112 discharges the working fluid compressed through all the impellers 22 inside the outer casing 11 to the outside of the outer casing 11. In other words, the discharge port 112 is disposed away from the suction port 111 on the second side Da2 in the axial direction Da.

[0021] The multiple diaphragms 15 are disposed on the inner side Dri of the outer casing 11 in the radial direction Dr. The multiple diaphragms 15 are formed as a whole in a cylindrical shape extending in the axial direction Da so as to cover the impellers 22 of each stage. Each diaphragm 15 is formed in a disk shape centered on the central axis O. The multiple diaphragms 15 are stacked in the axial direction Da, and adjacent diaphragms 15 are fixed to each other by welding or bolts. By being fixed to each other, the multiple diaphragms 15 cover the periphery of the rotating shaft 2 and form a casing flow path 40 therein that connects the multiple impellers 22. The multiple diaphragms 15, together with the rotating shaft 2, the head 17, the journal bearings 32A and 32B, and the thrust bearing 31, form a bundle. The bundle is housed within the outer casing 11. In the bundle, the plurality of diaphragms 15, the rotary shaft 2, the head 17, the journal bearings 32A and 32B, and the thrust bearing 31 are movable together to form a single unit.

[0022] The diaphragms 15 also have a casing flow path 40 that includes an introduction flow path 41 , a diffuser flow path 42 , and a return flow path 43 .

[0023] The inlet flow passage 41 guides the working fluid from the outer side Dro in the radial direction Dr toward the inner side Dri in the radial direction Dr. The inlet flow passage 41 changes the working fluid heading toward the inner side Dri in the radial direction Dr into a flow toward the second side Da2 in the axial direction Da, and guides it to the impeller 22. In this way, the inlet flow passage 41 changes the flow direction of the working fluid to the second side Da2 in the axial direction Da, and guides it to the impeller flow passage 23 of the impeller 22.

[0024] The diffuser passage 42 extends from the inner side Dri to the outer side Dro in the radial direction Dr. The end of the diffuser passage 42 on the inner side Dri in the radial direction Dr is connected to the end of the impeller passage 23 on the outer side Dro in the radial direction Dr. The diffuser passage 42 guides the working fluid compressed by the impeller 22 from the inner side Dri in the radial direction Dr to the outer side Dro in the radial direction Dr.

[0025] The return flow passage 43 reverses the flow direction of the working fluid that has passed through the diffuser flow passage 42 and flowed from the inner side Dri in the radial direction Dr to the outer side Dro in the radial direction Dr. The return flow passage 43 guides the working fluid flowing toward the outer side Dro in the radial direction Dr to the inner side Dri in the radial direction Dr. One end of the return flow passage 43 (a first side Da1 in the axial direction Da), which is upstream in the flow direction of the working fluid, is connected to the diffuser flow passage 42. The other end of the return flow passage 43 (a second side Da2 in the axial direction Da), which is downstream in the flow direction of the working fluid, is connected to the subsequent introduction flow passage 41.

[0026] A pair of heads 17 are arranged to close openings at both ends in the axial direction Da of the cylindrical outer casing 11. They are annular members centered on a central axis O. The pair of heads 17 are arranged inside the outer casing 11. The heads 17 of this embodiment have a first casing head 171 and a second casing head 172.

[0027] The first casing head 171 is disposed so as to close an opening on a first side Da1 in the axial direction Da of the outer casing 11. That is, the first casing head 171 is disposed adjacent to the first side Da1 in the axial direction Da of the plurality of diaphragms 15. An intake scroll that takes in external working fluid into the casing flow path 40 via the intake port 111 is formed between the first casing head 171 and the first-stage diaphragm 15, which is disposed furthest to the first side Da1 in the axial direction Da, among the plurality of diaphragms 15. The first casing head 171 is fixed to the plurality of integrated diaphragms 15 with bolts or the like. As a result, the first casing head 171 is integrated with the diaphragms 15.

[0028] The second casing head 172 is disposed so as to close an opening on the second side Da2 in the axial direction Da of the outer casing 11. In other words, the second casing head 172 is disposed adjacent to the second side Da2 in the axial direction Da relative to the plurality of diaphragms 15. Therefore, the second casing head 172 is adjacent to the final-stage diaphragm 15, which is disposed furthest on the second side Da2 in the axial direction Da, among the plurality of diaphragms 15. The second casing head 172 is fixed to the integrated plurality of diaphragms 15 with bolts or the like. As a result, the second casing head 172 is integrated with the diaphragms 15.

[0029] (Configuration of Discharge Scroll) Furthermore, the casing 10 of the centrifugal compressor 1 has a discharge scroll 50 and a flow path forming portion 57. The discharge scroll 50 guides the working fluid discharged from the final-stage impeller 22 among the multiple impellers 22 to the discharge port 112. As shown in FIG. 2 , the discharge scroll 50 is connected to the diffuser flow path 42 at an outer side Dro in the radial direction Dr. As shown in FIG. 3 , the discharge scroll 50 extends in a circumferential direction Dc about the central axis O. The discharge scroll 50 is a flow path formed in a spiral shape over one circumference in the circumferential direction Dc about the central axis O. The discharge scroll 50 is connected to the diffuser flow path 42 at an inner side Dri in the radial direction Dr over the entire circumference. The discharge scroll 50 is connected to the discharge port 112 at an outer side Dro in the radial direction Dr in a part of the circumferential direction Dc. The discharge scrolls 50 are formed with a constant interval in the radial direction Dr when viewed from the axial direction Da. As shown in Figures 4 to 7, the discharge scroll 50 is formed so that the spacing in the axial direction Da gradually narrows as the distance from the discharge port 112 increases in the circumferential direction Dc. That is, as shown in Figure 4, the discharge scroll 50 is formed so that the spacing in the axial direction Da is widest at the position closest to the discharge port 112 in the circumferential direction Dc. Then, as shown in Figures 5 to 7, the spacing in the axial direction Da of the discharge scroll 50 gradually narrows as the distance from the discharge port 112 increases in the circumferential direction Dc. In the discharge scroll 50 of this embodiment, the spacing in the axial direction Da gradually narrows so that the flow velocity of the working fluid flowing inside the discharge scroll 50 is constant in the circumferential direction Dc.

[0030] 2, the discharge scroll 50 is defined by a space formed in the second casing head 172 and the outer casing 11. The discharge scroll 50 is surrounded by a scroll inner peripheral surface 51 on the inside Dri in the radial direction Dr, a scroll outer peripheral surface 52 on the outside Dro in the radial direction Dr, a first flow path forming surface 53 disposed on the second side Da2 in the axial direction Da, and a second flow path forming surface (flow path forming surface) 54 disposed on the second side Da2 in the axial direction Da.

[0031] The scroll inner circumferential surface 51 is located at the innermost position Dri in the radial direction Dr of the discharge scroll 50. The scroll inner circumferential surface 51 is a surface that faces the outer side Dro in the radial direction Dr. The scroll inner circumferential surface 51 is formed by the second casing head 172. When viewed from the circumferential direction Dc, the scroll inner circumferential surface 51 is disposed on the outer side Dro in the radial direction Dr with respect to the diffuser flow path 42. When viewed from the circumferential direction Dc, the scroll inner circumferential surface 51 is disposed on the inner side Dri in the radial direction Dr with respect to the boundary between the second casing head 172 and the diaphragm 15 and the outer casing 11.

[0032] The scroll outer peripheral surface 52 is located at the outermost position Dro in the radial direction Dr of the discharge scroll 50. The scroll outer peripheral surface 52 faces the inner peripheral surface Dri in the radial direction Dr. The scroll outer peripheral surface 52 faces the scroll inner peripheral surface 51 in the radial direction Dr. The distance between the scroll outer peripheral surface 52 and the scroll inner peripheral surface 51 in the radial direction Dr is constant in both the axial direction Da and the circumferential direction Dc. The scroll outer peripheral surface 52 is formed by the outer casing 11. The scroll outer peripheral surface 52 is located on the inner side Dri in the radial direction Dr with respect to the outer peripheral surface of the external casing 11. When viewed from the circumferential direction Dc, the scroll inner peripheral surface 51 is located on the outer side Dro in the radial direction Dr with respect to the boundary between the second casing head 172 and the diaphragm 15 and the external casing 11.

[0033] The first flow passage forming surface 53 is located closest to the first side Da1 in the axial direction Da of the discharge scroll 50. The first flow passage forming surface 53 is a surface facing the second side Da2 in the axial direction Da. The first flow passage forming surface 53 is formed by the outer casing 11 and the diaphragm 15. The first flow passage forming surface 53 is formed in a flat shape so as to be integrally connected to the surface that forms the diffuser flow passage 42 at the same position in the axial direction Da.

[0034] The second flow passage forming surface 54 is located closest to the second side Da2 in the axial direction Da in the discharge scroll 50. The second flow passage forming surface 54 faces the first flow passage forming surface 53 in the axial direction Da. The distance between the first flow passage forming surface 53 and the second flow passage forming surface 54 in the axial direction Da gradually increases in the circumferential direction Dc as the discharge port 112 approaches. The second flow passage forming surface 54 is a surface facing the first side Da1 in the axial direction Da. The second flow passage forming surface 54 is formed by the second casing head 172 and a flow passage forming portion 57, which will be described later. The second flow passage forming surface 54 extends from the scroll inner circumferential surface 51 to the outer side Dro in the radial direction Dr.

[0035] The flow passage forming portion 57 forms at least a portion of the second flow passage forming surface 54. In this embodiment, the flow passage forming portion 57 forms a portion of the second flow passage forming surface 54 at a position overlapping with the external casing 11 in the radial direction Dr. That is, the flow passage forming portion 57 forms a region on the outer side Dro of the second flow passage forming surface 54 in the radial direction Dr instead of the external casing 11. Note that the region on the inner side Dri of the second flow passage forming surface 54 in the radial direction Dr is formed by the second casing head 172. The flow passage forming portion 57 is fixed to the external casing 11 at the outer side Dro in the radial direction Dr relative to the second casing head 172. The flow passage forming portion 57 is disposed in a recess 113 formed in the external casing 11. The recess 113 is recessed from the inner circumferential surface of the external casing 11 toward the outer side Dro in the radial direction Dr. The recess 113 also forms a space in the external casing 11 for forming the discharge scroll 50. The recess 113 is formed with a constant width in the axial direction Da. The flow path forming portion 57 is a surface that forms the recess 113, and is disposed in contact with a space forming surface 114 that faces the first side Da1 in the axial direction Da in the outer casing 11. As shown in Figures 4 to 7, the flow path forming portion 57 is formed so that the spacing in the axial direction Da gradually increases as it becomes farther away from the discharge port 112 in the circumferential direction Dc.

[0036] As shown in Fig. 4, the flow path forming portions 57 are not disposed at the positions closest to the discharge port 112 in the circumferential direction Dc. In other words, the flow path forming portions 57 are formed so that the spacing in the axial direction Da is narrowest at the positions closest to the discharge port 112 in the circumferential direction Dc. Then, as shown in Figs. 5 to 7, the spacing in the axial direction Da of the flow path forming portions 57 gradually increases with increasing distance from the discharge port 112 in the circumferential direction Dc. In this way, the flow path forming portions 57, together with the surface of the second casing head 172 facing the second side Da2 in the axial direction Da, form the second flow path forming surface 54.

[0037] (Operation and Effect) In the centrifugal compressor 1 configured as described above, the working fluid discharged from the final-stage impeller 22 passes through the final-stage diffuser passage 42 and flows into the discharge scroll 50. The discharge scroll 50 is connected to the final-stage diffuser passage 42 at the outer side Dro in the radial direction Dr. Therefore, the flow direction of the working fluid is not changed when flowing from the diffuser passage 42 into the discharge scroll 50. As a result, separation of the working fluid when flowing from the diffuser passage 42 into the discharge scroll 50 can be suppressed. Furthermore, the discharge scrolls 50 have a constant spacing in the radial direction Dr when viewed from the axial direction Da. In other words, the spacing of the discharge scrolls 50 in the radial direction Dr is constant regardless of the position in the circumferential direction Dc. Furthermore, the discharge scrolls 50 are formed such that the spacing in the axial direction Da gradually narrows as the distance from the discharge port 112 increases in the circumferential direction Dc. Therefore, in the discharge scroll 50, by changing the spacing in the axial direction Da, it is possible to ensure a flow path area through which the working fluid flows from the diffuser flow path 42 to the discharge port 112. As a result, it is possible to ensure the required performance of the discharge scroll 50 while suppressing expansion of the discharge scroll 50 in the radial direction Dr. In this way, it is possible to form a compact discharge scroll 50 while suppressing flow separation when the working fluid flows in.

[0038] In particular, the scroll inner peripheral surface 51 is disposed on the outer side Dro in the radial direction Dr with respect to the diffuser passage 42. Therefore, there is no need to change the flow direction of the working fluid from the outer side Dro to the inner side Dri in the radial direction Dr when the working fluid flows from the diffuser passage 42 into the discharge scroll 50. Therefore, flow separation when the working fluid flows into the discharge scroll 50 can be suppressed with high precision.

[0039] Furthermore, the spacing in the axial direction Da of the discharge scroll 50 gradually narrows so that the flow velocity of the working fluid flowing inside the discharge scroll 50 is constant in the circumferential direction Dc. This makes it possible to reduce stall and pressure loss of the working fluid flowing through the discharge scroll 50 while suppressing expansion of the discharge scroll 50 in the radial direction Dr. In this way, stable performance can be ensured even with a compact discharge scroll 50.

[0040] Furthermore, the discharge scroll 50 has a scroll inner peripheral surface 51 formed by the second casing head 172 and a scroll outer peripheral surface 52 formed by the outer casing 11. Therefore, the space on the inner side Dri in the radial direction Dr of the discharge scroll 50 is formed in the second casing head 172. On the other hand, the space on the outer side Dro in the radial direction Dr of the discharge scroll 50 is formed in the outer casing 11. In this way, by forming a part of the discharge scroll 50 in the external casing 11, the size in the radial direction Dr of the second casing head 172 can be reduced. As a result, the size in the radial direction Dr of the external casing 11 that covers the second casing head 172 can also be reduced. This makes it possible to form a discharge scroll 50 that can ensure stable performance while reducing the size in the radial direction Dr of the centrifugal compressor 1.

[0041] Furthermore, a portion of the second flow path forming surface 54 is formed by a flow path forming portion 57. The flow path forming portion 57 is formed so that the spacing in the axial direction Da gradually increases with increasing distance from the discharge port 112 in the circumferential direction Dc. By arranging such a flow path forming portion 57 in the outer casing 11 or the second casing head 172, it is possible to easily form the discharge scroll 50 in which the spacing in the axial direction Da gradually decreases with increasing distance from the discharge port 112 in the circumferential direction Dc.

[0042] In particular, as in this embodiment, the flow path forming portion 57 is fixed within the recess 113 of the outer casing 11 at the outer side Dro in the radial direction Dr relative to the second casing head 172. Therefore, the flow path forming portion 57 forms the outer side Dro region of the second flow path forming surface 54 in the radial direction Dr at a position overlapping with the outer casing 11, instead of the outer casing 11. The outer casing 11 is a massive and heavy member that is not only larger in the radial direction Dr than the diaphragm 15 and the second casing head 172, but also very long in the axial direction Da. Machining a three-dimensional recess 113 on the inner circumferential surface of such an outer casing 11, in which the spacing in the axial direction Da varies with the circumferential direction Dc, is an extremely difficult task. However, by arranging the flow path forming portion 57, the width of the recess 113 itself in the axial direction Da can be made constant. This facilitates machining of the outer casing 11 and facilitates the production of the discharge scroll 50.

[0043] Furthermore, the region Dri on the inside of the second flow passage forming surface 54 in the radial direction Dr is formed by the second casing head 172. In other words, the flow passage forming portion 57 is not disposed in the second casing head 172, and a portion of the discharge scroll 50 is formed so as to be recessed from the outer peripheral surface of the second casing head 172. The second casing head 172 is not only a smaller member than the outer casing 11, but also has its machined portion on its outer peripheral surface rather than its inner peripheral surface. Therefore, even a three-dimensional recess in which the spacing in the axial direction Da changes in the circumferential direction Dc can be formed relatively easily. Therefore, the size of the flow passage forming portion 57 can be reduced, and the discharge scroll 50 can be manufactured at low cost.

[0044] (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 within the scope that does not deviate from the gist of the present disclosure are also included.

[0045] The centrifugal compressor 1 is not limited to a structure in which the discharge scroll 50 is formed via the flow path forming portion 57. In other words, the centrifugal compressor 1 does not have to have the flow path forming portion 57. In that case, the second flow path forming surface 54 may be formed by the outer casing 11 and the second casing head 172.

[0046] Furthermore, the flow path forming portion 57 is not limited to a structure in which it is fixed to the external casing 11 and forms an area on the outer side Dro of the second flow path forming surface 54 in the radial direction Dr, instead of the external casing 11. For example, the flow path forming portion 57 may be fixed to the second casing head 172. In this case, the flow path forming portion 57 may form an area on the inner side Dri of the second flow path forming surface 54 in the radial direction Dr, instead of the second casing head 172. Furthermore, the flow path forming portion 57 may be fixed to both the external casing 11 and the second casing head 172. In that case, the flow path forming portion 57 may form the entire area of ​​the second flow path forming surface 54, instead of the external casing 11 and the second casing head 172.

[0047] Furthermore, the flow path forming portion 57 may have any structure as long as it can form at least a part of the second flow path forming surface 54. That is, the flow path forming portion 57 may be formed as a solid block structure, or may be formed as a hollow structure. When the flow path forming portion 57 is formed as a hollow shape, it may have a structure including, for example, a plate material that forms a part of the second flow path forming surface 54 and a support member that supports this plate material on the space forming surface 114.

[0048] Furthermore, the discharge scroll 50 is not limited to a structure formed as a space spanning the outer casing 11 and the second casing head 172. The discharge scroll 50 may be formed only in the outer casing 11, or only in the second casing head 172.

[0049] <Additional Notes> The centrifugal compressor 1 described in the embodiment can be understood, for example, as follows.

[0050] (1) A centrifugal compressor 1 according to a first aspect includes a rotating shaft 2 extending in an axial direction Da along which a central axis O extends, and a casing 10 having an inlet 111 formed on a first side Da1 in the axial direction Da and an outlet 112 formed on a second side Da2 in the axial direction Da, the rotating shaft 2 being disposed within the casing 10 and including an impeller 22 that compresses and discharges a working fluid supplied from the first side Da1 in the axial direction Da to an outside Dro in a radial direction Dr based on the central axis O, the casing 10 including a diaphragm 15 formed in a cylindrical shape extending in the axial direction Da to cover the impeller 22, and an outer casing 10 that is formed in a cylindrical shape extending in the axial direction Da to cover the diaphragm 15. the discharge scroll 50 is connected to the diffuser passage 42 at the outside Dro in the radial direction Dr, extends in a circumferential direction Dc around the central axis O, and is formed so that the spacing in the radial direction Dr is constant when viewed from the axial direction Da, and the spacing in the axial direction Da gradually narrows as the discharge scroll 50 moves away from the discharge port 112 in the circumferential direction Dc.

[0051] With this configuration, the working fluid discharged from the final-stage impeller 22 passes through the diffuser passage 42 and flows into the discharge scroll 50. The discharge scroll 50 is connected to the diffuser passage 42 at the outer side Dro in the radial direction Dr. This prevents the working fluid from separating when it flows from the diffuser passage 42 into the discharge scroll 50. Furthermore, the discharge scrolls 50 have a constant spacing in the radial direction Dr when viewed from the axial direction Da. That is, the spacing in the radial direction Dr of the discharge scrolls 50 is constant regardless of the position in the circumferential direction Dc. Furthermore, the discharge scrolls 50 are formed such that the spacing in the axial direction Da gradually narrows as they move away from the discharge port 112 in the circumferential direction Dc. Therefore, the discharge scroll 50 can ensure a flow path area for the working fluid to flow from the diffuser passage 42 to the discharge port 112 by changing the spacing in the axial direction Da. As a result, the required performance of the discharge scroll 50 can be ensured while preventing the discharge scroll 50 from expanding in the radial direction Dr. In this way, the discharge scroll 50 can be formed compactly while suppressing flow separation when the working fluid flows in.

[0052] (2) A centrifugal compressor 1 according to a second aspect is the centrifugal compressor 1 of (1), in which the spacing of the discharge scroll 50 in the axial direction Da gradually narrows so that the flow rate of the working fluid flowing inside the discharge scroll 50 in the circumferential direction Dc is constant.

[0053] This configuration makes it possible to reduce the expansion of the discharge scroll 50 in the radial direction Dr while reducing stall and pressure loss of the working fluid flowing through the discharge scroll 50. In this way, stable performance can be ensured even with a compact discharge scroll 50.

[0054] (3) A centrifugal compressor 1 according to a third aspect is the centrifugal compressor 1 of (1) or (2), wherein the discharge scroll 50 has a scroll inner peripheral surface 51 on the inner side Dri in the radial direction Dr formed by the head 17, and a scroll outer peripheral surface 52 on the outer side Dro in the radial direction Dr facing the scroll inner peripheral surface 51 in the radial direction Dr formed by the outer casing 11.

[0055] According to this configuration, the space on the inner side Dri in the radial direction Dr of the discharge scroll 50 is formed in the head 17. On the other hand, the space on the outer side Dro in the radial direction Dr of the discharge scroll 50 is formed in the external casing 11. In this way, by forming a part of the discharge scroll 50 in the external casing 11, the size of the head 17 in the radial direction Dr can be reduced. As a result, the size of the external casing 11 that covers the head 17 in the radial direction Dr can also be reduced. This makes it possible to form a discharge scroll 50 that can ensure stable performance while reducing the size of the centrifugal compressor 1 in the radial direction Dr.

[0056] (4) A centrifugal compressor 1 according to a fourth aspect is the centrifugal compressor 1 according to any one of (1) to (3), wherein the casing 10 has a flow path forming portion 57 in the discharge scroll 50, the flow path forming portion 57 being arranged on the second side Da2 in the axial direction Da and forming at least a part of a flow path forming surface facing the first side Da1 in the axial direction Da, and the flow path forming portion 57 is formed so that the spacing in the axial direction Da gradually increases as it moves away from the discharge port 112 in the circumferential direction Dc.

[0057] With this configuration, by arranging the flow path forming portion 57 in the outer casing 11 or the head 17, it is possible to easily form an ejection scroll 50 in which the spacing in the axial direction Da gradually narrows as it moves away from the ejection port 112 in the circumferential direction Dc.

[0058] (5) A centrifugal compressor 1 according to a fifth aspect is the centrifugal compressor 1 of (4), wherein the flow path forming portion 57 is fixed to the external casing 11 on the outer side Dro of the radial direction Dr relative to the head 17, and forms a part of the flow path forming surface at a position overlapping with the external casing 11 in the radial direction Dr.

[0059] With this configuration, the flow path forming portion 57 forms the outer region Dro of the second flow path forming surface 54 in the radial direction Dr at a position overlapping the external casing 11, instead of the external casing 11. The external casing 11 is a huge and heavy member that is not only larger in the radial direction Dr than the diaphragm 15 and the head 17, but also very long in the axial direction Da. Machining a three-dimensional recess 113 on the inner peripheral surface of such an external casing 11, in which the spacing in the axial direction Da varies with the circumferential direction Dc, is an extremely difficult task. However, by providing the flow path forming portion 57, the width of the recess 113 in the external casing 11 itself in the axial direction Da can be made constant. This simplifies the machining of the external casing 11, and facilitates the production of the discharge scroll 50.

[0060] According to the centrifugal compressor of the present disclosure, it is possible to form a compact discharge scroll while suppressing flow separation when the working fluid flows in.

[0061] REFERENCE SIGNS LIST 1 Centrifugal compressor O Central shaft 2 Rotating shaft 21 Rotating shaft body 22 Impeller 23 Impeller flow path 10 Casing 11 Outer casing 111 Suction port 112 Discharge port 113 Recess 114 Space forming surface 15 Diaphragm 40 Casing flow path 41 Inlet flow path 42 Diffuser flow path 43 Return flow path 17 Head 171 First casing head 172 Second casing head 50 Discharge scroll 51 Scroll inner peripheral surface 52 Scroll outer peripheral surface 53 First flow path forming surface 54 Second flow path forming surface 57 Flow path forming portion 31 Thrust bearing 32A, 32B Journal bearing Da Axial direction Da1 First side Da2 Second side Dr Radial direction Dro Outer side Dri Inner side Dc Circumferential direction

Claims

1. A compressor comprising: a rotating shaft extending in an axial direction along which a central axis extends; and a casing having an inlet port formed on a first side in the axial direction and an outlet port formed on a second side in the axial direction, wherein the rotating shaft is disposed within the casing and has an impeller that compresses and discharges a working fluid supplied from the first side in the axial direction radially outward relative to the central axis, the casing having: a diaphragm formed in a cylindrical shape extending in the axial direction so as to cover the impeller; an outer casing formed in a cylindrical shape extending in the axial direction so as to cover the diaphragm; a head that closes openings at both ends in the axial direction of the outer casing; a diffuser passage that guides the working fluid discharged from the impeller toward the radially outward direction; and a discharge scroll that guides the working fluid discharged from the impeller to the discharge port, the discharge scroll being connected to the diffuser passage on the radially outer side and extending in a circumferential direction around the central axis, A centrifugal compressor in which the radial spacing when viewed from the axial direction is constant, and the axial spacing is gradually narrowed as the distance from the discharge port increases in the circumferential direction.

2. A centrifugal compressor as set forth in claim 1, wherein the interval between said discharge scrolls in the axial direction gradually narrows so that the flow velocity of said working fluid flowing inside said discharge scrolls is constant in the circumferential direction.

3. A centrifugal compressor as described in claim 1 or 2, wherein the discharge scroll has a radially inner scroll inner surface formed by the head, and a radially outer scroll outer surface facing the scroll inner surface in the radial direction formed by the outer casing.

4. A centrifugal compressor as claimed in claim 1 or 2, wherein the casing has a flow path forming portion disposed on the second axial side of the discharge scroll and forming at least a part of a flow path forming surface facing the first axial side, and the flow path forming portion is formed such that the axial spacing gradually increases with increasing distance from the discharge port in the circumferential direction.

5. A centrifugal compressor according to claim 4, wherein the flow passage forming portion is fixed to the outer casing on the radially outer side relative to the head, and forms a part of the flow passage forming surface at a position overlapping with the outer casing in the radial direction.

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