centrifugal compressor

Abstract

To provide a centrifugal compressor which can suppress the lowering of efficiency caused by a power loss while reducing a surge point flow rate.SOLUTION: In a centrifugal compressor of the present disclosure, a casing has an introduction flow passage in which fluid flows, a discharge flow passage, and an impeller accommodation part for accommodating an impeller, and having an opposing face which forms an outside passage for making the introduction flow passage communicate with the discharge flow passage together with a cover. A pair of seal parts are provided at the outside passage. The cover has a communication part which penetrates the cover in a radial direction between the pair of seal parts in the outside passage. The communication part makes a region between a disc and the cover communicate with the outside passage. Also, the introduction flow passage has a limit point being a position in which a center angle of a circular arc of a chip-side flat face becomes 30° toward a downstream side from a standard point. The casing has a circulation flow passage for making a region between the pair of seal parts in the outside passage communicate with the introduction flow passage. An outlet-side opening on the introduction flow passage side in the circulation flow passage is located at an upstream side rather than the limit point.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to centrifugal compressors. [Background technology]

[0002] Patent Document 1 discloses a centrifugal compressor that uses centrifugal force to compress a gas fluid and is used in turbochargers, gas turbines, industrial air facilities, etc. This centrifugal compressor includes a disk fixed to a rotating shaft, an impeller having a plurality of blades attached to the disk, and a cover provided to surround these blades, and a casing that houses the impeller. The gap between the impeller cover and the casing forms a circulation channel. This circulation channel connects the outer channel of the impeller with an introduction channel that introduces fluid into the impeller. Furthermore, the cover is formed with an extraction channel that passes through the cover and communicates with the circulation channel.

[0003] Near the surge point flow rate, the difference in pressure (hereinafter referred to as wall pressure) that the fluid exerts on the wall surface of the circulation flow path between the inlet opening on the extraction flow path side and the outlet opening on the impeller suction port side becomes large. This wall pressure difference causes fluid to be supplied from the extraction flow path to the impeller suction port via the circulation flow path. This reduces the surge point flow rate. On the other hand, near the design flow rate, the wall pressure difference between the inlet and outlet openings of the circulation channel becomes small, making it difficult for the fluid to flow through the circulation channel. Therefore, near the design flow rate, power loss is reduced and the fluid can be efficiently flowed through the impeller. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6265000 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in a centrifugal compressor such as that disclosed in Patent Document 1, the outlet opening is located at the boundary between the casing and the impeller. Furthermore, the flow path formed inside the casing that introduces fluid into the impeller curves toward the impeller as it moves radially inward. This causes the flow velocity to increase and the wall pressure to decrease just before the fluid enters the impeller. Therefore, the outlet opening is located on a wall surface where the wall pressure decreases, resulting in a large difference in wall pressure between the inlet opening and the outlet opening. This causes the fluid to flow through the circulation flow path even near the design flow rate, resulting in increased power loss and reduced operating efficiency.

[0006] The present disclosure has been made to solve the above-mentioned problems, and an object of the present disclosure is to provide a centrifugal compressor that can reduce the surge point flow rate while suppressing a decrease in efficiency due to power loss. [Means for solving the problem]

[0007] In order to solve the above-described problems, a centrifugal compressor according to the present disclosure includes: a rotating shaft rotatable about an axis; an impeller arranged in the axial direction of the rotating shaft and compressing and feeding a fluid that flows in from one side in the axial direction radially outward, the impeller including a disk fixed to the rotating shaft, a plurality of blades provided on the disk, and a cover that covers the plurality of blades and extends radially outward toward the other side in the axial direction; a casing that surrounds the rotating shaft and the impeller, the casing having an impeller accommodating portion that has opposing surfaces that form an outer passage that accommodates the impeller and, together with the cover, communicates the introduction passage with the discharge passage; and a pair of seal portions that are provided in the outer passage and are arranged spaced apart in the axial direction. the cover has a communication portion that penetrates the cover in the radial direction between the pair of seal portions in the outer passage and communicates the outer passage with the area between the disk and the cover, the introduction flow path has, in a cross section including the axis, a straight portion with a tip-side flat surface that extends linearly in the radial direction, a curved portion with a tip-side curved surface that forms an arc from the radially inner end of the tip-side flat surface toward the impeller, a reference point that is the boundary between the tip-side flat surface and the tip-side curved surface, and a limit point that is a position from the reference point toward the downstream side where the central angle of the arc of the tip-side flat surface is 30°, and the casing has a circulation flow path that communicates the area between the pair of seal portions in the outer passage with the introduction flow path, and whose outlet-side opening on the introduction flow path side is located at the limit point or upstream of the limit point in the cross section. [Effects of the Invention]

[0008] According to the centrifugal compressor of the present disclosure, it is possible to reduce the surge point flow rate while suppressing a decrease in efficiency due to power loss. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a longitudinal sectional view of a centrifugal compressor according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is an enlarged longitudinal cross-sectional view of a portion of the centrifugal compressor according to the embodiment of the present disclosure. [Figure 3] FIG. 3 is an enlarged view of the periphery of the circulation channel in FIG. 2. [Figure 4] 10A to 10C are diagrams illustrating the effects of the impeller according to the embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Configuration of centrifugal compressor) Hereinafter, a centrifugal compressor 100 according to an embodiment of the present disclosure will be described with reference to FIGS. 1 to 4. FIG. As shown in FIG. 1, the centrifugal compressor 100 includes a rotating shaft 1, an impeller 2, a casing 3, vanes 4, a seal portion 5 (see FIG. 2), and fin blades 6 (see FIG. 2).

[0011] The rotating shaft 1 is formed in a cylindrical shape extending in one direction. Hereinafter, the axis O of the rotating shaft 1 will be simply referred to as the axis O. The circumferential direction and the radial direction will be defined based on this axis O.

[0012] The impellers 2 are arranged in multiple stages in the direction of the axis O of the rotating shaft 1. In this embodiment, five stages of impellers 2 are arranged in the direction of the axis O. Each impeller 2 pressurizes the fluid G flowing in from one side in the direction of the axis O outward in the radial direction. The fluid G is a so-called working fluid. An example of the fluid G is air.

[0013] The casing 3 surrounds the rotating shaft 1 and the impeller 2 from the radial outside. The casing 3 is formed in a cylindrical shape extending in the direction of the axis O. The rotating shaft 1 is provided inside the casing 3. The rotating shaft 1 penetrates the casing 3 along the axis O. A journal bearing 7 is provided at each end of the casing 3 in the direction of the axis O. Furthermore, a thrust bearing 8 is provided on the other side of the casing 3 in the direction of the axis O. The rotating shaft 1 is supported by the journal bearing 7 and thrust bearing 8 so as to be rotatable around the axis O.

[0014] An intake port 9 for taking in fluid G from the outside is provided on one side of the casing 3 in the direction of the axis O. An exhaust port 10 for exhausting fluid G compressed inside the casing 3 is provided on the other side of the casing 3 in the direction of the axis O.

[0015] An internal space that repeatedly decreases and increases in diameter and that communicates with the intake port 9 and the exhaust port 10 is formed inside the casing 3. This internal space accommodates multiple impellers 2 and forms part of a flow path 11 for the fluid G. Hereinafter, the side of this flow path 11 where the intake port 9 is located will be referred to as the upstream side, and the side where the exhaust port 10 is located will be referred to as the downstream side. Therefore, the upstream side refers to the same direction as one side in the direction of the axis O, and the downstream side refers to the same direction as the other side in the direction of the axis O.

[0016] The vanes 4 are provided on the upstream side of each impeller 2. The vanes 4 include return vanes 4a and inlet guide vanes 4b. A plurality of return vanes 4a are provided in the flow passage 11 in each region between the impellers 2 adjacent to each other in the axial direction O. The inlet guide vane 4b is provided in the flow passage 11 on the upstream side of the first stage impeller 2. The seal portion 5 and the fin blades 6 are provided inside the casing 3 (see FIG. 2). The seal portion 5 and the fin blades 6 will be described in detail later.

[0017] (Impeller configuration) Next, the configuration of the impeller 2 will be described in detail with reference to Fig. 2. Fig. 2 illustrates one of the impellers 2 from the second stage onwards among the multiple stages of impellers 2. As shown in FIG. 2, the impeller 2 includes a disk 20 , blades 21 , and a cover 22 . Note that, in the following, the configuration of the present disclosure will be described using the impeller 2 in the second stage and thereafter as an example, but the configuration of the present disclosure described below can also be applied to the impeller 2 in the first stage.

[0018] (disk) The disk 20 is fixed to the outer peripheral surface of the rotating shaft 1. The disk 20 has a substantially circular cross section when viewed in the direction of the axis O. The disk 20 is formed so that, in a cross section including the axis O, the radial dimension gradually increases from one side to the other side in the direction of the axis O. Therefore, the disk 20 is formed in a roughly conical shape.

[0019] (blade) A plurality of blades 21 are arranged side by side in the circumferential direction on a conical surface facing the upstream side of both sides of the disk 20 in the direction of the axis O. Each blade 21 extends radially outward in the radial direction with the axis O as the center. More specifically, the blade 21 is formed by a thin plate that stands from the upstream surface of the disk 20 toward the upstream side. When viewed from the direction of the axis O, each blade 21 is curved from one side to the other side in the circumferential direction.

[0020] (cover) The cover 22 is a cylindrical member that covers the plurality of blades 21. The cover 22 extends radially outward as it moves toward the other side in the direction of the axis O. From another perspective, the cover 22 is provided on the edge of the blade 21. Therefore, the plurality of blades 21 are sandwiched between the cover 22 and the disk 20 in the direction of the axis O. As a result, a space is formed between the cover 22, the disk 20, and a pair of adjacent blades 21. This space forms a part of the flow path 11 inside the casing 3.

[0021] The cover 22 has a cylindrical portion 23 and a tapered portion 24. The cylindrical portion 23 forms the upstream side of the cover 22. The cylindrical portion 23 extends linearly in the direction of the axis O. The tapered portion 24 forms the downstream side of the cover 22. The tapered portion 24 extends from the end of the cylindrical portion 23 toward the downstream side (the rear-stage impeller 2 side) in the direction of the axis O, and is formed so as to gradually increase in diameter toward the downstream side in the direction of the axis O. The cover 22 also has a communication portion 25 that penetrates in the radial direction.

[0022] (Communication part) The communicating portion 25 is formed at the boundary between the cylindrical portion 23 and the tapered portion 24. The communicating portion 25 is a slit formed around the entire circumferential direction of the cover 22. That is, the communicating portion 25 is formed in a ring shape when viewed from the direction of the axis O. The communicating portion 25 is formed on the upstream side (throat side) of the impeller 2 that sucks in the fluid G. Furthermore, the communicating portion 25 penetrates the cover 22 in the radial direction and, in a cross section including the axis O, is formed linearly so as to gradually incline toward the other side in the direction of the axis O as it extends radially inward. Furthermore, the communicating portion 25 extends along the flow path cross section of the compression flow path 26 in the impeller 2. Furthermore, a radially inner end 25a of the communicating portion 25 is formed in a tapered shape that gradually increases in diameter in the direction of the axis O as it goes radially inward in a cross-sectional view including the axis O. Furthermore, the inner circumferential surface of the communicating portion 25 on the side of the end 25a is formed in a curved shape and smoothly connected to the inner circumferential surface of the cover 22.

[0023] Hereinafter, a part of the flow passage 11 formed between adjacent blades 21 in the impeller 2 will be referred to as a compression flow passage 26. The compression flow passage 26 curves radially outward along the outer circumferential surface of the disk 20 toward the other side (downstream side) in the direction of the axis O.

[0024] (Impeller peripheral configuration) Next, the configuration around each impeller 2 will be described in detail. As shown in FIGS. 2 and 3, the casing 3 has an inlet flow path 30, a discharge flow path 40, a return flow path 41, an impeller housing portion 42, and a circulation flow path 70 therein.

[0025] (Inlet flow path) The introduction flow passage 30 is a flow passage 11 through which the fluid G flows into the impeller 2. The introduction flow passage 30 constitutes a part of the flow passage 11 inside the casing 3. The introduction flow passage 30 is provided on the upstream side of each impeller 2.

[0026] (Straight section) The introduction flow path 30 has, in a cross section including the axis O, a straight portion 31, a curved portion 32, a reference point 33, and a limit point .

[0027] A pair of wall surfaces that constitute the straight portion 31 and face each other in the direction of the axis O extend linearly in the radial direction in a cross section including the axis O. Hereinafter, of the pair of wall surfaces that constitute the straight portion 31, the wall surface on the other side in the direction of the axis O will be referred to as the "tip side flat surface 35," and the wall surface on one side in the direction of the axis O will be referred to as the "hub side flat surface 36." Further, the straight portion 31 is provided with a plurality of return vanes 4a.

[0028] (return vane) The plurality of return vanes 4a are arranged radially around the axis O. The plurality of return vanes 4a are arranged around the axis O at intervals in the circumferential direction.

[0029] (curved part) The curved portion 32 extends radially inward from the downstream end of the straight portion 31. The curved portion 32 curves toward the impeller 2 as it extends radially inward. The curved portion 32 is connected at its downstream end to the compression flow path 26 inside the impeller 2. A pair of wall surfaces that constitute the curved portion 32 and face each other in the direction of the axis O each form an arc shape extending from the radially inner end of the wall surface of the straight portion 31 toward the impeller 2 in a cross section including the axis O. Hereinafter, of the pair of wall surfaces that constitute the curved portion 32, the wall surface on the other side in the direction of the axis O will be referred to as the "tip side curved surface 37," and the wall surface on one side in the direction of the axis O will be referred to as the "hub side curved surface 38." The tip-side curved surface 37 is smoothly connected to the radially inner end of the tip-side flat surface 35. The hub-side curved surface 38 is smoothly connected to the radially inner end of the hub-side flat surface 36.

[0030] (Baseline and Limit Points) The reference point 33 is the boundary between the tip-side flat surface 35 and the tip-side curved surface 37 . The limit point 34 is a position downstream of the reference point 33. More specifically, the limit point 34 is a position where the central angle θ of the arc of the tip-side flat surface 35 when viewed downstream from the reference point 33 is 30°.

[0031] (Exhaust flow path) The discharge flow path 40 is a flow path 11 through which the fluid G pumped from the impeller 2 flows. The discharge flow path 40 constitutes a part of the flow path 11 inside the casing 3. The discharge flow path 40 is provided downstream of each impeller 2. The upstream end of the discharge passage 40 is connected to the compression passage 26 inside the impeller 2. In a cross-sectional view including the axis O, the discharge passage 40 extends linearly radially outward from the compression passage 26.

[0032] (return flow path) The return flow passage 41 is a flow passage 11 that returns the fluid G pressure-fed from the impeller 2 in the preceding stage to the impeller 2 in the succeeding stage. The return flow passage 41 constitutes a part of the flow passage 11 in the casing 3. In a cross-sectional view including the axis O, the return flow passage 41 is formed in a U-shape that opens radially inward. The return flow passage 41 connects the discharge flow passage 40 on the preceding stage side and the introduction flow passage 30 on the succeeding stage side. More specifically, the upstream end of the return flow passage 41 is directly connected to the downstream end of the discharge flow passage 40. Furthermore, the downstream end of the return flow passage 41 is directly connected to the upstream end of the introduction flow passage 30.

[0033] (Impeller housing) The impeller accommodating section 42 is an internal space provided within the casing 3. The impeller 2 is accommodated in the impeller accommodating section 42. One impeller accommodating section 42 is formed for each impeller 2. The impeller accommodating section 42 connects the inlet flow passage 30 and the outlet flow passage 40 on both sides of the impeller 2 in the direction of the axis O. The impeller accommodating section 42 has an opposing surface 43 that covers the cover 22 of the impeller 2 from the radial outside. The opposing surface 43 faces the cover 22 in the radial direction. The opposing surface 43, together with the cover 22, forms an outer passage 60 that connects the inlet flow passage 30 and the outlet flow passage 40.

[0034] (Outside passage) One end of the outer passage 60 in the direction of the axis O is connected to the downstream end of the introduction flow path 30. The other end of the outer passage 60 in the direction of the axis O is connected to the upstream end of the discharge flow path 40. The outer passage 60 is formed around the axis O over the entire circumferential direction. The outer passage 60 has an outer peripheral passage 61 , a first connecting passage 62 , and a second connecting passage 63 .

[0035] The outer peripheral passage 61 extends in the direction of the axis O along the outer peripheral surface of the cover 22 in a cross-sectional view including the axis O. The outer peripheral passage 61 has a straight passage 64 and a curved passage 65. The straight passage 64 is a passage formed by the outer peripheral surface of the cylindrical portion 23 of the cover 22. The straight passage 64 extends linearly in the direction of the axis O in a cross-sectional view including the axis O. The curved passage 65 is a passage formed by the outer peripheral surface of the tapered portion 24 of the cover 22. The curved passage 65 gradually curves from the end of the straight passage 64 on the other side in the direction of the axis O to be positioned radially outward as it moves from one side to the other side in the direction of the axis O.

[0036] The first connection passage 62 is provided at one end of the outer peripheral passage 61 in the direction of the axis O. In a cross-sectional view including the axis O, the first connection passage 62 extends linearly radially inward from the one end of the outer peripheral passage 61 in the direction of the axis O. The first connection passage 62 is connected to the introduction flow path 30.

[0037] The second connection passage 63 is provided at the end of the outer peripheral passage 61 on the other side in the direction of the axis O. In a cross-sectional view including the axis O, the second connection passage 63 extends linearly from the end of the outer peripheral passage 61 on the other side in the direction of the axis O to the other side in the direction of the axis O. The second connection passage 63 is connected to the discharge flow path 40.

[0038] The outer passage 60 is provided with a pair of seal portions 5 spaced apart in the direction of the axis O. More specifically, the pair of seal portions 5 are provided in the outer peripheral passage 61 of the outer passage 60.

[0039] (Sealing part) The seal portion 5 prevents the fluid G from leaking out through the outer passage 60. Hereinafter, of the pair of seal portions 5, the seal portion 5 on one side in the direction of the axis O will be referred to as the "first seal portion 51," and the seal portion 5 on the other side in the direction of the axis O will be referred to as the "second seal portion 52."

[0040] The first seal portion 51 is disposed in the linear passage 64. The first seal portion 51 is a normal labyrinth seal that extends linearly in the direction of the axis O. The first seal portion 51 has a plurality of first fins 51a arranged in the direction of the axis O. Each of the first fins 51a is formed in an annular shape extending in the circumferential direction. The first fins 51a are formed on the casing 3 side. More specifically, the first fins 51a are formed on the opposing surface 43 of the impeller accommodating portion 42. The radially inner ends of the first fins 51a face the outer peripheral surface of the cover 22 of the impeller 2 with a small clearance therebetween.

[0041] The second seal portion 52 is disposed at the end of the curved passage 65 on the introduction flow path 30 side. The second seal portion 52 is a labyrinth seal formed in a stepped shape that is positioned radially outward as it moves toward the other side in the direction of the axis O.

[0042] The second seal portion 52 has a step portion 53 and a second fin 52a. The step portion 53 is provided around the entire circumferential direction so as to surround the impeller from the outer periphery side. The step portion 53 has an inner periphery side step portion 53a and an outer periphery side step portion 53b. The inner peripheral step portion 53a is formed integrally with the impeller 2 on the impeller 2 side. More specifically, the inner peripheral step portion 53a is formed on the outer peripheral surface of the cover 22. The inner peripheral step portion 53a is formed in a stepped shape so as to be positioned radially outward as it moves toward the other side in the direction of the axis O.

[0043] The outer peripheral step portion 53b is formed integrally with the casing 3 on the casing 3 side. More specifically, the outer peripheral step portion 53b is formed on the opposing surface 43 of the impeller accommodating portion 42. The outer peripheral step portion 53b is formed in a stepped shape so as to be positioned radially outward as it moves toward the other side in the direction of the axis O, while maintaining a radial separation distance from the inner peripheral step portion 53a of at least a certain value.

[0044] A plurality of second fins 52a are arranged in the direction of the axis O. Each second fin 52a is formed in an annular shape extending in the circumferential direction. The second fins 52a are formed on the casing 3 side. More specifically, the second fins 52a are formed on the inner peripheral surface of the outer peripheral step portion 53b. The radially inner end of the second fin 52a faces the outer peripheral surface of the inner peripheral step portion 53a with a small clearance therebetween.

[0045] The area between the pair of seal portions 5 in the outer passage 60 is connected to the area between the disk 20 and the cover 22 (compression flow path 26) by a communication portion 25 formed in the cover 22 of the impeller 2. Furthermore, a circulation flow path 70 is formed radially outside the outer passage 60 inside the casing 3 .

[0046] (Circulation flow path) The circulation flow path 70 connects the region between the pair of seal portions 5 in the outer passage 60 with the introduction flow path 30. The circulation flow path 70 is formed around the axis O over the entire circumferential direction. Hereinafter, of the two openings of the circulation flow path 70, the opening on the outer passage 60 side will be referred to as the "inlet side opening 71", and the opening on the introduction flow path 30 side will be referred to as the "outlet side opening 72". The inlet side opening 71 and the communication portion 25 formed in the cover 22 of the impeller 2 are opposed to each other with the outer passage 60 interposed therebetween.

[0047] The outlet-side opening 72 is located upstream of the limit point 34 in a cross-sectional view including the axis O. In this embodiment, the radially inner end of the outlet-side opening 72 is located at the reference point 33 in a cross-sectional view including the axis O. More specifically, the downstream end of the outlet-side opening 72 is provided at a position that overlaps with the reference point 33 in a cross-sectional view including the axis O. Furthermore, the outlet-side opening 72 opens downstream of the downstream trailing edge 15a of the return vane 4a. In addition, the outlet-side opening 72 is located downstream of the outermost diameter position 39 in the introduction passage 30 that corresponds to the outermost diameter end 27 of the impeller 2.

[0048] The circulation flow path 70 also has an inlet region 73 , an intermediate region 74 , and an outlet region 75 . The inlet side region 73 is a region of the circulation flow path 70 that has the inlet side opening 71. The inlet side region 73 is formed in a curved shape as it approaches the outer passage 60 in a cross section including the axis O.

[0049] The intermediate region 74 extends from the inlet-side region 73 toward the introduction channel 30. The intermediate region 74 of this embodiment has a first straight region 76, a curved region 77, and a second straight region 78. The first linear region 76 extends radially outward from the inlet region 73 in a cross-sectional view including the axis O, and is formed linearly so as to incline toward one side in the direction of the axis O as it extends radially outward.

[0050] The curved region 77 is provided at the end of the first straight region 76 opposite to the inlet-side region 73. The curved region 77 extends to one side in the direction of the axis O, and curves radially inward as it extends to that side in the direction of the axis O. The second straight region 78 extends linearly from the end of the curved region 77 opposite to the first straight region 76 to one side in the direction of the axis O.

[0051] The outlet-side region 75 is provided at the end of the intermediate region 74 opposite to the inlet-side region 73. The outlet-side region 75 is a portion on the outlet-side opening 72 side of the circulation flow path 70. In a cross-sectional view including the axis O, the outlet-side region 75 extends so as to curve radially inward as it approaches the outlet-side opening 72. Furthermore, in the circulation flow path 70, a second straight region 78 of the intermediate region 74 is provided with fin blades 6.

[0052] (fin wing) The fin vanes 6 function as supports that support the circulation flow path 70 from the inside. The fin vanes 6 also support the island portion 44 of the casing 3 that is surrounded from the radial outside by the circulation flow path 70. A plurality of fin vanes 6 are arranged in the circumferential direction within the circulation flow path 70.

[0053] (Operation of centrifugal compressor) Next, the operation of the centrifugal compressor 100 according to this embodiment will be described. Fluid G is taken into the flow passage 11 from the intake port 9 as the rotating shaft 1 and impeller 2 rotate, and then flows through the first-stage introduction flow passage 30 into the compression flow passage 26 in the impeller 2. Because the impeller 2 rotates around the axis O as the rotating shaft 1 rotates, a centrifugal force acting radially outward from the axis O is applied to the fluid G in the compression flow passage 26. In addition, because the cross-sectional area of ​​the compression flow passage 26 gradually increases from the radially outer side to the radially inner side, the fluid G is gradually decelerated and compressed. As a result, the high-pressure fluid G is sent out from the compression flow passage 26 to the subsequent discharge flow passage 40.

[0054] The high-pressure fluid G pumped from the compression flow path 26 then passes through the discharge flow path 40, the return flow path 41, and the introduction flow path 30 in that order. Similar compression is also applied to the second and subsequent impellers 2 and flow paths 11. Finally, the fluid G reaches a desired pressure state and is supplied to an external device (not shown) from the exhaust port 10.

[0055] (Action and effect) In the centrifugal compressor 100 having the above configuration, a pair of seal portions 5 are provided in the outer passage 60. The pair of seal portions 5 are arranged spaced apart in the direction of the axis O. This makes it possible to suppress leakage of the fluid G into the gap between the outer peripheral surface of the cover 22 of the impeller 2 and the inner peripheral surface of the impeller accommodating portion 42.

[0056] Furthermore, the cover 22 has a communication portion 25 that radially penetrates the cover 22 between the pair of seal portions 5 in the outer passage 60. The communication portion 25 connects the area between the disk 20 and the cover 22 with the outer passage 60. In addition, the introduction passage 30 has a limit point 34, which is a position where the central angle θ of the arc of the tip-side flat surface 35 toward the downstream side from the reference point 33 is 30°. The casing 3 also has a circulation passage 70 that connects the area between the pair of seal portions 5 in the outer passage 60 with the introduction passage 30. An outlet-side opening 72 of the circulation passage 70 is located upstream of the limit point 34.

[0057] As a result, near the surge point flow rate, the wall pressure difference between the outlet side opening 72 and the inlet side opening 71 causes the fluid G to flow into the circulation flow path 70, and the fluid G can be extracted from the inside of the impeller 2 (compression flow path 26) to the introduction flow path 30. Furthermore, even near the choke point flow rate, the wall pressure difference between the outlet side opening 72 and the inlet side opening 71 causes the fluid G to flow into the circulation flow path 70. As a result, in a choke state, contrary to the surge state, the fluid G can be extracted from the middle of the introduction flow path 30 to the inside of the impeller 2 (compression flow path 26).

[0058] Therefore, during surging, the unstable flow rate range decreases as fluid G is bled from the middle of the flow inside impeller 2 to inlet passage 30, and during choking, the maximum flow rate increases as fluid G is bled from the middle of inlet passage 30 to the middle of the flow inside impeller 2. Therefore, as shown in Figure 4, the flow rate range in which surging occurs can be shifted to the small flow rate side, and the flow rate range in which choking occurs, particularly at high rotation speeds, can be shifted to the large flow rate side, thereby expanding the operating range.

[0059] Here, the flow velocity along the tip-side curved surface 37 is maximum and the wall pressure is lowest near the middle of the tip-side curved surface 37 in the axial direction O. According to the above configuration, the limit point 34 is located upstream of the portion of the tip-side curved surface 37 where the wall pressure is lowest. Furthermore, the outlet-side opening 72 of the circulation channel 70 is located upstream of the limit point 34. This prevents a significant decrease in wall pressure at the outlet-side opening 72. This prevents an unintended decrease in wall pressure at the outlet-side opening 72 near the design flow rate, which in turn prevents an increase in the wall pressure difference between the outlet-side opening 72 and the inlet-side opening 71. Therefore, near the design flow rate, the flow in the circulation channel 70 due to the wall pressure difference is suppressed, and power loss caused by the fluid G flowing through the circulation channel 70 is suppressed. Therefore, a decrease in operating efficiency due to power loss near the design flow rate is suppressed. As described above, according to the centrifugal compressor 100 of this embodiment, it is possible to reduce the surge point flow rate and increase the choke point flow rate, while suppressing a decrease in efficiency due to power loss.

[0060] In this embodiment, the outlet opening 72 of the circulation flow path 70 on the introduction flow path 30 side is located at the reference point 33 in a cross section including the axis O.

[0061] At the tip-side flat surface 35, the flow velocity does not change significantly, and therefore the wall pressure is also approximately constant. According to the above configuration, the outlet-side opening 72 of the circulation channel 70 is located in a region where the wall pressure is approximately constant. This makes it possible to further suppress a decrease in wall pressure at the outlet-side opening 72. Therefore, the flow within the circulation channel 70 due to the wall pressure difference is further suppressed, and therefore, a decrease in efficiency due to power loss can be further suppressed.

[0062] In this embodiment, an outlet opening 72 of the circulation flow path 70 on the introduction flow path 30 side is located downstream of the outermost diameter position 39 in the introduction flow path 30 corresponding to the outermost diameter end 27 of the impeller 2 .

[0063] This makes it possible to prevent the outlet opening 72 from being excessively separated from the impeller 2. As a result, it is possible to shorten the distance that the fluid G flows through the flow path 11, for example, near a surge point flow rate or a choke point flow rate. This reduces the pressure loss that occurs as the fluid G flows through the circulation flow path 70, making it possible to further prevent a decrease in efficiency.

[0064] In this embodiment, an outlet opening 72 of the circulation flow passage 70 on the introduction flow passage 30 side opens downstream of the trailing edge 15a of the return vane 4a.

[0065] As a result, for example, near the surge point flow rate, the fluid G supplied from the circulation flow path 70 through the outlet opening 72 into the introduction flow path 30 does not collide with the return vane 4a. This allows the main flow of the introduction flow path 30 and the flow from the circulation flow path 70 to merge smoothly. This makes it possible to suppress an increase in the mixing loss of the fluid G at the outlet opening 72. This makes it possible to further suppress a decrease in efficiency.

[0066] In this embodiment, the communication portion 25 and the inlet side opening 71 of the circulation flow path 70 face each other with the outer passage 60 interposed therebetween.

[0067] This allows the fluid G to flow smoothly between the communication part 25 and the circulation flow path 70, for example, near a surge point flow rate or a choke point flow rate. This reduces the pressure loss that occurs when the fluid G flows between the communication part 25 and the circulation flow path 70, further suppressing a decrease in efficiency.

[0068] In this embodiment, an outlet-side region 75 , which is a portion of the circulation flow path 70 on the outlet-side opening 72 side, extends so as to curve radially inward as it approaches the outlet-side opening 72 .

[0069] This allows the fluid G to flow from the outlet opening 72 toward the introduction flow path 30 along the flow in the introduction flow path 30, for example, near the surge point flow rate. This allows the main flow of the introduction flow path 30 and the flow from the circulation flow path 70 to merge more smoothly. This further reduces the increase in mixing loss of the fluid G at the outlet opening 72. This further reduces the decrease in efficiency.

[0070] In this embodiment, the centrifugal compressor 100 further includes fin blades 6 in the circulation flow path 70.

[0071] As a result, the fin vanes 6 support the wall surface of the circulation flow path 70, improving the strength of the circulation flow path 70. Furthermore, the fin vanes 6 can remove the swirling flow generated in the circulation flow path 70. Therefore, it is possible to suppress a head drop of the impeller 2 caused by the inlet swirling flow.

[0072] In this embodiment, the communication portion 25 extends along the cross section of the compression flow passage 26 in the impeller 2 . As a result, the communicating section 25 can suppress the flow of fluid G from the compression flow path 26 to the circulation flow path 70 near the design point flow rate, while smoothly guiding fluid G from the compression flow path 26 to the circulation flow path 70 near the surge point flow rate.

[0073] Furthermore, the radially inner end 25a of the communication portion 25 is formed in a tapered shape that gradually increases in diameter in the direction of the axis O as it goes radially inward in a cross-sectional view including the axis O. This makes it easier for the fluid to flow into the circulation flow path 70. Furthermore, the inner circumferential surface of the communication portion 25 on the end portion 25a side is formed in a curved shape and smoothly connected to the inner circumferential surface of the cover 22. This allows the fluid G to be smoothly guided into the communication portion 25. In addition, vortices are less likely to be formed in the main flow flowing through the compression flow passage 26 in the impeller 2, which further reduces pressure loss.

[0074] (Other embodiments) The above describes in detail the embodiments of the present disclosure with reference to the drawings, but the specific configuration is not limited to this embodiment, and design changes and the like are also included within the scope that does not deviate from the gist of the present disclosure.

[0075] In the above embodiment, the outlet-side opening 72 of the circulation flow path 70 is located upstream of the limit point 34 of the introduction flow path 30 in a cross-sectional view including the axis O, and further the downstream end of the outlet-side opening 72 is located at the reference point 33. However, this is not limited to this. For example, the outlet-side opening 72 may be located at the limit point 34 of the introduction flow path 30. When the outlet-side opening 72 is located at the limit point 34, more specifically, the center of the outlet-side opening 72 overlaps with the limit point 34.

[0076] Furthermore, the outlet-side opening 72 may be located upstream of the reference point 33 of the introduction passage 30. In this case, the downstream end of the outlet-side opening 72 is located upstream of the reference point 33. However, from the viewpoint of suppressing a decrease in efficiency due to power loss, it is preferable that the entire outlet-side opening 72 is located on the tip-side flat surface 35, which is the straight portion 31 of the introduction passage 30. Furthermore, it is most preferable that the upstream end of the outlet-side opening 72 is located downstream of the trailing edge 15a of the return vane 4a and downstream of the outermost diameter position 39 in the introduction passage 30 that corresponds to the outermost diameter end 27 of the impeller 2.

[0077] In the above embodiment, the communication part 25 and the inlet opening 71 of the circulation flow path 70 are opposed to each other across the outer passage 60, but this is not limited to this. For example, the communication part 25 and the inlet opening 71 of the circulation flow path 70 may be disposed at positions offset from each other in the direction of the axis O and may not be opposed to each other.

[0078] In the above embodiment, the communication portion 25 is a slit provided around the entire circumferential direction of the cover 22, but this is not limited to this. For example, the communication portion 25 may be a group of multiple through holes provided spaced apart in the circumferential direction.

[0079] In the above embodiment, the first fin 51a of the first seal portion 51 and the second fin 52a of the second seal portion 52 are formed on the casing 3 side, but this is not limiting. For example, the first fin 51a and the second fin 52a may be formed on the impeller 2 side.

[0080] In the above embodiment, the inlet-side region 73 is formed in a curved shape toward the outer passage 60 in a cross-sectional view including the axis O, but this is not limited to this. The inlet-side region 73 may be formed in a linear shape with a uniform width in a cross-sectional view including the axis O.

[0081] In the above embodiment, the outlet-side region 75 having the outlet-side opening 72 extends so as to curve radially inward toward the outlet-side opening 72 in a cross-sectional view including the axis O, but this is not limited to this. The outlet-side region 75 may be formed in a linear shape with a uniform width in a cross-sectional view including the axis O.

[0082] In the above embodiment, a stage having a return vane 4a on the upstream side is described as an example, but the configuration of the present disclosure described above can also be applied to a first stage having an inlet guide vane 4b on the upstream side. In this stage, as shown in FIG. 1, for example, the outlet opening 72 of the circulation channel 70 on the introduction channel 30 side opens downstream of the trailing edge 15b of the inlet guide vane 4b. This prevents the fluid G supplied from the circulation channel 70 through the outlet opening 72 into the introduction channel 30 from colliding with the inlet guide vane 4b, for example, near the surge point flow rate, and suppresses an increase in the mixing loss of the fluid G at the outlet opening 72.

[0083] <Additional Notes> The centrifugal compressor 100 described in each embodiment can be understood, for example, as follows.

[0084] (1) A centrifugal compressor 100 according to a first aspect includes a rotating shaft 1 rotatable around an axis O, and an impeller 2 arranged in the direction of the axis O of the rotating shaft 1 to compress and send out a fluid G flowing in from one side in the direction of the axis O radially outward, the impeller 2 including a disk 20 fixed to the rotating shaft 1, a plurality of blades 21 provided on the disk 20, and a cover 22 covering the plurality of blades 21 and extending radially outward toward the other side in the direction of the axis O; The casing 3 surrounds the impeller 2, and has an impeller accommodating section 42 having an inlet flow path 30 through which a fluid G flowing into the impeller 2 flows, a discharge flow path 40 through which a fluid G pressure-fed from the impeller 2 flows, and an impeller accommodating section 42 having opposing surfaces 43 that accommodate the impeller 2 and form, together with the cover 22, an outer passage 60 that connects the inlet flow path 30 and the discharge flow path 40, and a pair of seal sections 5 that are provided in the outer passage 60 and are arranged spaced apart in the direction of the axis O, and the cover The guide passage 30 has a communicating portion 25 that penetrates the cover 22 in the radial direction between the pair of seal portions 5 in the outer passage 60 and communicates the area between the disk 20 and the cover 22 with the outer passage 60, and the guide passage 30 has a straight portion 31 that has a tip-side flat surface 35 that extends linearly in the radial direction in a cross section including the axis O, a curved portion 32 that has a tip-side curved surface 37 that forms an arc from the radially inner end of the tip-side flat surface 35 toward the impeller 2, and a guide passage 35 that extends linearly in the radial direction from the tip-side curved surface 37 toward the impeller 2. The casing 3 has a reference point 33 which is the boundary between the side flat surface 35 and the tip side curved surface 37, and a limit point 34 which is the position from the reference point 33 downstream where the central angle θ of the arc of the tip side flat surface 35 is 30°, and the casing 3 has a circulation flow path 70 which connects the area between the pair of seal portions 5 in the outer passage 60 with the introduction flow path 30, and whose outlet side opening 72 on the introduction flow path 30 side is located at the limit point 34 or upstream of the limit point 34 in the cross-sectional view.

[0085] As a result, near the surge point flow rate, the wall pressure difference between the outlet opening 72 and the inlet opening 71 causes the fluid G to flow within the circulation flow path 70, and the fluid G can be extracted from inside the impeller 2 to the introduction flow path 30. Here, the flow velocity along the tip-side curved surface 37 is maximum near the middle of the tip-side curved surface 37 in the direction of the axis O, and the wall pressure is lowest. According to this embodiment, the limit point 34 is located upstream of the portion of the tip-side curved surface 37 where the wall pressure is lowest. Furthermore, the outlet-side opening 72 of the circulation flow path 70 is located at or upstream of the limit point 34. This makes it possible to prevent a significant decrease in wall pressure at the outlet-side opening 72. This makes it possible to prevent an unintended decrease in the wall pressure at the outlet-side opening 72 near the design flow rate, which would increase the wall pressure difference between the outlet-side opening 72 and the inlet-side opening 71.

[0086] (2) The centrifugal compressor 100 of the second aspect may be the centrifugal compressor 100 of the aspect (1), wherein the outlet opening 72 of the circulation flow path 70 on the side of the introduction flow path 30 is located at the reference point 33 or upstream of the reference point 33 in the cross-sectional view.

[0087] At the tip-side flat surface 35, the flow velocity does not change significantly, and therefore the wall pressure is also approximately constant. According to this embodiment, the outlet-side opening 72 of the circulation channel 70 is located in a region where the wall pressure is approximately constant. Therefore, the decrease in the wall pressure at the outlet-side opening 72 can be further suppressed.

[0088] (3) The centrifugal compressor 100 of a third aspect is the centrifugal compressor 100 of the aspect (1) or (2), and the outlet side opening 72 of the circulation flow path 70 on the introduction flow path 30 side may be located downstream of the outermost diameter position 39 in the introduction flow path 30 corresponding to the outermost diameter end 27 of the impeller 2.

[0089] This makes it possible to prevent the outlet opening 72 from being excessively separated from the impeller 2. As a result, the distance that the fluid G flows through the flow path 11 can be shortened.

[0090] (4) The centrifugal compressor 100 of a fourth aspect is the centrifugal compressor 100 of any one of the aspects (1) to (3), and further includes a return vane 4a or an inlet guide vane 4b provided in the straight section 31, and the outlet side opening 72 of the circulation flow path 70 on the introduction flow path 30 side may open downstream of the trailing edges 15a, 15b of the return vane 4a or the inlet guide vane 4b.

[0091] This prevents the fluid G supplied from the circulation flow path 70 into the introduction flow path 30 through the outlet opening 72 from colliding with the return vane 4a. This allows the main flow of the introduction flow path 30 and the flow from the circulation flow path 70 to merge smoothly. This makes it possible to suppress an increase in the mixing loss of the fluid G at the outlet opening 72.

[0092] (5) The centrifugal compressor 100 of a fifth aspect is the centrifugal compressor 100 of any one of aspects (1) to (4), and the communication part 25 and the inlet side opening 71 in the circulation flow path 70 may be opposed to each other across the outer passage 60.

[0093] This allows the fluid G to flow smoothly between the communication portion 25 and the circulation flow path 70.

[0094] (6) The centrifugal compressor 100 of the sixth aspect is the centrifugal compressor 100 of any one of the aspects (1) to (5), and the outlet side region 75, which is the part of the circulation flow path 70 on the outlet side opening 72 side, may extend so as to curve radially inward as it approaches the outlet side opening 72.

[0095] This allows the fluid G to flow from the outlet opening 72 toward the introduction flow path 30 along the flow in the introduction flow path 30. This allows the main flow of the introduction flow path 30 and the flow from the circulation flow path 70 to merge more smoothly. This further prevents an increase in the mixing loss of the fluid G at the outlet opening 72.

[0096] (7) The centrifugal compressor 100 of the seventh aspect is the centrifugal compressor 100 of any one of the aspects (1) to (6), and may be provided in the circulation flow path 70 and further include fin blades 6 in the circulation flow path 70.

[0097] This allows the fin blades 6 to support the wall surface of the circulation flow path 70. Furthermore, the fin blades 6 can remove the swirling flow generated in the circulation flow path 70. [Explanation of symbols]

[0098] 1...rotating shaft, 2...impeller, 3...casing, 4...vane, 4a...return vane, 4b...inlet guide vane, 5...seal portion, 6...fin blade, 7...journal bearing, 8...thrust bearing, 9...inlet port, 10...exhaust port, 11...flow path, 15a...trailing edge, 15b...trailing edge, 20...disk, 21...blade, 22...cover, 23...cylindrical portion, 24...tapered portion, 25...communicating portion, 25a...end, 26...compression flow path, 27...outermost diameter end, 30...inlet flow path, 31...straight portion, 32...curved portion, 33...reference point, 34...limit point, 35...tip side flat surface, 36...hub side flat surface, 37...tip side curved surface, 38...hub side curved surface, 39...outermost Radial position, 40... discharge passage, 41... return passage, 42... impeller accommodating portion, 43... opposing surface, 44... island portion, 51... first seal portion, 51a... first fin, 52... second seal portion, 52a... second fin, 53... step portion, 53a... inner peripheral step portion, 53a... outer peripheral step portion, 60... outer passage, 61... outer peripheral passage, 62... first connecting passage, 63... second connecting passage, 64... straight passage, 65... curved passage, 70... circulation passage, 71... inlet side opening, 72... outlet side opening, 73... inlet side region, 74... intermediate region, 75... outlet side region, 76... first straight region, 77... curved region, 78... second straight region, 100... centrifugal compressor, G... fluid, O... axis, θ... central angle

Claims

1. A rotation shaft that is rotatable around an axis line; an impeller arranged in the axial direction of the rotating shaft and pressure-feeding a fluid flowing in from one side in the axial direction outward in a radial direction, the impeller including a disk fixed to the rotating shaft, a plurality of blades provided on the disk, and a cover covering the plurality of blades and extending radially outward toward the other side in the axial direction; a casing surrounding the rotary shaft and the impeller, the casing including an inlet flow path through which fluid flowing into the impeller flows, a discharge flow path through which fluid pressure-fed from the impeller flows, and an impeller accommodating portion having opposing surfaces that accommodate the impeller and form, together with the cover, an outer passage that connects the inlet flow path and the discharge flow path; a pair of seal portions provided in the outer passage and spaced apart in the axial direction; Equipped with the cover has a communication portion that radially penetrates the cover between the pair of seal portions in the outer passage and communicates the area between the disk and the cover with the outer passage, The introduction flow path, in a cross-sectional view including the axis, a straight portion having a tip-side flat surface extending linearly in the radial direction; a curved portion having a tip-side curved surface that forms an arc shape from a radially inner end of the tip-side flat surface toward the impeller; a reference point that is a boundary between the tip-side flat surface and the tip-side curved surface; a limit point at which the central angle of the arc of the tip-side flat surface is 30° downstream from the reference point; and the casing has a circulation flow path that connects a region between the pair of seal portions in the outer passage with the inlet flow path, and an outlet opening on the inlet flow path side is located at the limit point or upstream of the limit point in the cross-sectional view.

2. The centrifugal compressor according to claim 1 , wherein an outlet opening of the circulation flow path on the inlet flow path side is located at the reference point or upstream of the reference point in the cross-sectional view.

3. 3. The centrifugal compressor according to claim 2, wherein an outlet opening of the circulation flow path on the inlet flow path side is located downstream of an outermost diameter position in the inlet flow path corresponding to an outermost diameter end of the impeller.

4. Further comprising a return vane or an inlet guide vane provided in the straight section, 4. The centrifugal compressor according to claim 3, wherein an outlet opening of the circulation flow path on the introduction flow path side opens downstream of a trailing edge of the return vane or the inlet guide vane.

5. 2. The centrifugal compressor according to claim 1, wherein the communication portion and the inlet opening of the circulation flow path face each other across the outer passage.

6. 2. The centrifugal compressor according to claim 1, wherein an outlet-side region, which is a portion of the circulation flow path on the outlet-side opening side, extends so as to curve radially inward toward the outlet-side opening.

7. The centrifugal compressor according to claim 1 , further comprising fin blades provided in the circulation flow path.

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