阅读说明：本技术 离心旋转机械的制造方法、及离心旋转机械 (Method for manufacturing centrifugal rotary machine, and centrifugal rotary machine ) 是由 枡谷穰 山下修一 于 2020-02-03 设计创作，主要内容包括：一种离心旋转机械的制造方法、及离心旋转机械,该离心旋转机械的制造方法包括：固定工序(S1),将具有假想翼形的返回叶片原体固定在引导流路上,该假想翼形随着朝向径向内侧而向旋转轴的旋转方向前方侧弯曲且由朝向旋转方向前方侧凹陷的压力面及朝向旋转方向前方侧凸出的负压面形成；及切削工序(S2),通过将返回叶片原体的包含径向内侧的端部的部分从压力面切除至负压面而形成切断面。(A method of manufacturing a centrifugal rotary machine, and a centrifugal rotary machine, the method of manufacturing the centrifugal rotary machine including: a fixing step (S1) for fixing a return blade original having a virtual wing shape, which is curved toward the front side in the rotation direction of the rotation shaft as it goes toward the radial inner side and is formed by a pressure surface that is concave toward the front side in the rotation direction and a negative pressure surface that is convex toward the front side in the rotation direction, to the guide flow path; and a cutting step (S2) for cutting out a portion including the radially inner end of the return blade from the pressure surface to the suction surface to form a cut surface.)

1. A method of manufacturing a centrifugal rotary machine, the centrifugal rotary machine comprising:

a rotating shaft rotatable about an axis;

a plurality of impellers fixed to the rotating shaft;

a casing that covers the impeller from the outside and that is formed with a diffuser flow path extending from the outer peripheral side of the impeller to the radially outer side, a bent back portion that turns from the radially outer end of the diffuser flow path to the radially inner side, and a guide flow path extending from the bent back portion to the radially inner side; and

a plurality of return blades provided on the guide flow path at intervals in a rotation direction of the rotary shaft,

wherein the content of the first and second substances,

the method for manufacturing a centrifugal rotary machine includes:

a fixing step of fixing a return blade original having a virtual wing shape, which is curved toward the front side in the rotation direction as it goes toward the inside in the radial direction and is formed of a positive pressure surface that is concave toward the front side in the rotation direction and a negative pressure surface that is convex toward the front side in the rotation direction, to the guide flow path; and

and a cutting step of cutting a portion including a radially inner end of the return blade from the positive pressure surface to the negative pressure surface to form a cut surface.

2. The method of manufacturing a centrifugal rotary machine according to claim 1,

in the cutting step, the cut surface is formed so as to be linear when viewed from the axial direction.

3. The method of manufacturing a centrifugal rotary machine according to claim 1,

in the cutting step, the cut surface is formed in an arc shape that is recessed toward the front side in the rotation direction when viewed from the axial direction.

4. The method of manufacturing a centrifugal rotary machine according to claim 1,

in the cutting step, the cut surface is formed so as to form an angle of 10 ° or more with respect to a radial direction.

5. The method of manufacturing a centrifugal rotary machine according to claim 1,

in the cutting step, the cut surface is formed such that a separation distance between a pair of the return blades adjacent to each other in the rotational direction is minimized between the suction surface of one of the return blades and a radially outer end of the cut surface of the other of the return blades.

6. The method of manufacturing a centrifugal rotary machine according to any one of claims 1 to 5,

the method further includes a curved connecting surface forming step of forming a curved connecting surface portion connecting the positive pressure surface and the cut surface in a curved shape after the cutting step.

7. A centrifugal rotary machine is provided with:

a rotating shaft rotatable about an axis;

a plurality of impellers fixed to the rotating shaft;

a casing that covers the impeller from the outside and that is formed with a diffuser flow path extending from the outer peripheral side of the impeller to the radially outer side, a bent back portion that turns from the radially outer end of the diffuser flow path to the radially inner side, and a guide flow path extending from the bent back portion to the radially inner side; and

a plurality of return blades provided on the guide flow path at intervals in a rotation direction of the rotary shaft,

the return blade has a cut surface formed by cutting out a portion including a radially inner end portion of a virtual airfoil shape from the positive pressure surface to the negative pressure surface, the virtual airfoil shape being curved toward the front side in the rotation direction as it goes toward the radially inner side and being formed of a positive pressure surface recessed toward the front side in the rotation direction and a negative pressure surface protruding toward the front side in the rotation direction.

8. The centrifugal rotary machine of claim 7,

the cut surface is linear when viewed from the axial direction.

9. The centrifugal rotary machine of claim 7,

the cut surface is in an arc shape recessed toward the front side in the rotation direction when viewed from the axis direction.

10. The centrifugal rotary machine of claim 7,

the cut surface is at an angle of 10 DEG or more with respect to the radial direction.

11. The centrifugal rotary machine of claim 7,

the distance between the pair of return blades adjacent to each other in the rotation direction is smallest between the suction surface of one of the return blades and a radially outer end of the cut surface of the other of the return blades.

12. The centrifugal rotary machine according to any one of claims 7 to 11,

the centrifugal rotary machine further includes a curved connecting surface portion connecting the positive pressure surface and the cut surface in a curved shape.

Technical Field

The present invention relates to a method for manufacturing a centrifugal rotary machine, and a centrifugal rotary machine.

The present application claims priority to japanese patent application No. 2019-018760 filed on 5.2.2019, the contents of which are incorporated herein by reference.

Background

The centrifugal compressor includes a rotating shaft extending along an axis, a plurality of impellers attached to the rotating shaft, and a casing covering the rotating shaft and the impellers from an outer peripheral side. A flow path is formed in the housing, the diameter of which is repeatedly reduced and expanded from one side to the other side in the axial direction. The flow path includes a diffuser flow path extending radially outward from an outlet of the impeller, a return portion extending radially inward by turning 180 DEG from a radially outer end of the diffuser flow path, and a guide flow path extending radially inward from the return portion. A plurality of return vanes are provided in the guide flow path for the purpose of rectifying the flow of the fluid. As a specific example of such a return blade, the one described in japanese utility model registration No. 3187468 is known.

The return vane described in japanese utility model registration No. 3187468 is curved so as to be oriented radially from the circumferential direction as it is oriented toward the front side in the rotation direction of the impeller (rotating shaft). The outlet angle of the return vane (the angle formed by the radially inner end surface with respect to the radial direction) is set to 0 °. This rectifies the flow of the fluid coming into contact with the return vane from the radially outer side, and removes the swirling flow component contained in the flow. As a result, the head of the compressor is improved.

[ problem to be solved by the invention ]

It is known that when the outlet angle of the return vane is set to 0 ° as in japanese utility model registration No. 3187468, the operating range of the compressor decreases although the head pressure rises. Further, there is a demand for expanding the operating range of the centrifugal compressor after the actual use thereof. Therefore, a technique for easily and subsequently expanding the operating range of the centrifugal compressor is desired.

Disclosure of Invention

The present invention has been made to solve the above-described problems, and an object thereof is to provide a method of manufacturing a centrifugal rotary machine capable of easily and subsequently expanding an operation range, and a centrifugal rotary machine having an expanded operation range.

[ MEANS FOR solving PROBLEMS ] A method for solving the problems

In a method for manufacturing a centrifugal rotary machine according to an aspect of the present invention, the centrifugal rotary machine includes: a rotating shaft rotatable about an axis; a plurality of impellers fixed to the rotating shaft; a casing that covers the impeller from the outside and that is formed with a diffuser flow path extending from the outer peripheral side of the impeller to the radially outer side, a bent back portion that turns from the radially outer end of the diffuser flow path to the radially inner side, and a guide flow path extending from the bent back portion to the radially inner side; and a plurality of return blades provided on the guide flow path at intervals in a rotation direction of the rotary shaft, wherein the method of manufacturing the centrifugal rotary machine includes: a fixing step of fixing a return blade original having a virtual wing shape, which is curved toward the front side in the rotation direction as it goes toward the inside in the radial direction and is formed of a positive pressure surface that is concave toward the front side in the rotation direction and a negative pressure surface that is convex toward the front side in the rotation direction, to the guide flow path; and a cutting step of cutting a portion including a radially inner end of the return blade original from the positive pressure surface to the negative pressure surface to form a cut surface.

According to the above method, the cutting section is formed by cutting out a portion of the return vane including the radially inner end portion from the positive pressure surface to the negative pressure surface in the cutting step. This makes it possible to make the exit angle (the angle of the radially inner end surface with respect to the radial direction) of the return vane larger than the exit angle of the virtual airfoil shape. The increase in the outlet angle causes a swirling flow component to remain in the flow of the fluid passing through the return vane. As a result, the operating range of the centrifugal rotary machine can be expanded. In the above method, the cutting step is performed after the return blade that has been attached to the casing through the fixing step. Thus, a centrifugal rotary machine having a desired operating range can be obtained without manufacturing the return blade again.

In the above method of manufacturing a centrifugal rotary machine, the cutting step may form the cut surface so that the cut surface is linear when viewed from the axial direction.

According to the above method, the outlet angle of the return vane can be changed by making the cut surface straight. That is, the operating range of the centrifugal rotary machine can be adjusted by only relatively simple machining.

In the above method of manufacturing a centrifugal rotary machine, the cutting step may form the cut surface in an arc shape that is recessed toward a front side in the rotation direction when viewed from the axial direction.

According to the above method, the cut surface is formed in an arc shape, so that the flow of the fluid flowing along the cut surface can be smoothly guided, and the possibility of occurrence of separation or vortex in the flow can be reduced.

In the above method of manufacturing a centrifugal rotary machine, the cutting step may form the cut surface so that the cut surface forms an angle of 10 ° or more with respect to a radial direction.

According to the above method, the cut surface forms an angle of 10 ° or more with respect to the radial direction. In other words, the outlet angle is an angle of 10 ° or more. This allows the swirling flow component contained in the flow of the fluid guided by the return vane to remain more positively. As a result, the operating range of the centrifugal rotary machine can be significantly expanded.

In the above-described method of manufacturing a centrifugal rotary machine, in the cutting step, the cut surface may be formed so that a separation distance between a pair of the return blades adjacent to each other in the rotation direction becomes smallest between the suction surface of one of the return blades and an end portion of the other of the return blades on a radially outer side of the cut surface.

According to the above method, the distance between the return blades is minimized between the radially outer end of the cut surface of the other return blade and the suction surface of the one return blade. This can more smoothly guide the flow of the fluid flowing between the return vanes.

In the above method of manufacturing a centrifugal rotary machine, the method may further include a curved surface forming step of forming a curved connecting surface portion connecting the normal pressure surface and the cut surface in a curved shape after the cutting step.

According to the above method, the positive pressure surface and the cut surface are connected to each other by the connecting curved surface portion in a curved surface shape, and therefore, the possibility of occurrence of separation or a vortex in the flow of the fluid flowing along the connecting curved surface portion can be reduced.

A centrifugal rotary machine according to one aspect of the present invention includes: a rotating shaft rotatable about an axis; a plurality of impellers fixed to the rotating shaft; a casing that covers the impeller from the outside and that is formed with a diffuser flow path extending from the outer peripheral side of the impeller to the radially outer side, a bent back portion that turns from the radially outer end of the diffuser flow path to the radially inner side, and a guide flow path extending from the bent back portion to the radially inner side; and a plurality of return blades provided at intervals in the rotation direction of the rotating shaft on the guide flow path, the return blades having a cut surface formed by cutting off a portion including an end portion on a radially inner side of a virtual airfoil shape from the positive pressure surface to the negative pressure surface, the virtual airfoil shape being curved toward a front side in the rotation direction as it goes toward the radially inner side and being formed of a positive pressure surface recessed toward the front side in the rotation direction and a negative pressure surface protruding toward the front side in the rotation direction.

According to the above configuration, the portion of the return vane including the radially inner end is cut off from the positive pressure surface to the negative pressure surface, thereby forming the cut surface. This makes it possible to make the exit angle (the angle of the radially inner end surface with respect to the radial direction) of the return vane larger than the exit angle of the virtual airfoil shape. The outlet angle increases, and a swirl flow component remains in the flow of the fluid passing through the return vane. As a result, the operating range of the centrifugal rotary machine can be expanded.

In the above centrifugal rotary machine, the cut surface may be linear when viewed from the axial direction.

According to the above configuration, the outlet angle of the return vane can be changed by making the cut surface straight. That is, the operating range of the centrifugal rotary machine can be adjusted by only relatively simple machining.

In the above centrifugal rotary machine, the cut surface may have an arc shape that is recessed toward the front side in the rotation direction when viewed from the axial direction.

According to the above configuration, since the cut surface has an arc shape, the flow of the fluid flowing along the cut surface can be smoothly guided, and the possibility of occurrence of separation or a vortex in the flow can be reduced.

In the above centrifugal rotary machine, the cut surface may be at an angle of 10 ° or more with respect to a radial direction.

According to the above configuration, the cut surface forms an angle of 10 ° or more with respect to the radial direction. In other words, the outlet angle is an angle of 10 ° or more. This allows the swirling flow component contained in the flow of the fluid guided by the return vane to remain more positively. As a result, the operating range of the centrifugal rotary machine can be significantly expanded.

In the above centrifugal rotary machine, a separation distance between a pair of the return blades adjacent to each other in the rotation direction may be minimized between the suction surface of one of the return blades and a radially outer end of the cut surface of the other of the return blades.

According to the above configuration, the distance between the return blades is minimized between the radially outer end of the cut surface of the other return blade and the suction surface of the one return blade. This can more smoothly guide the flow of the fluid flowing between the return vanes.

In the above centrifugal rotary machine, the pressure-applying surface and the cut surface may be curved surfaces.

According to the above configuration, the positive pressure surface and the cut surface are connected to each other by the connecting curved surface portion in a curved surface shape, and therefore, the possibility of occurrence of separation or a vortex in the flow of the fluid flowing along the connecting curved surface portion can be reduced.

[ Effect of the invention ]

According to the present invention, it is possible to provide a method of manufacturing a centrifugal rotary machine capable of easily and subsequently expanding a working range, and a centrifugal rotary machine with an expanded working range.

Drawings

Fig. 1 is a schematic diagram showing a configuration of a centrifugal rotary machine according to an embodiment of the present invention.

Fig. 2 is a sectional view of a centrifugal rotary machine according to an embodiment of the present invention.

Fig. 3 is a diagram showing a structure of a return vane according to an embodiment of the present invention.

Fig. 4 is an enlarged view of a main portion of a return vane of the embodiment of the present invention.

Fig. 5 is a process diagram illustrating a method of manufacturing a centrifugal rotary machine according to an embodiment of the present invention.

Fig. 6 is a diagram showing a modification of the return vane according to the embodiment of the present invention.

[ Mark Specification ]

1 rotating shaft

2 flow path

3 case

4 impeller

5 journal bearing

6 thrust bearing

7 air inlet

8 exhaust port

21 suction flow path

22 compression flow path

23 diffusion flow path

24 return bend

25 guide flow path

41 disc

42 blade

43 cover

50 return blade

51 leading edge

52 trailing edge

53 negative pressure surface

54 pressure surface

55 cut surface

56 connecting the curved surface part

100 centrifugal compressor

C center line

L separation distance

O axis

R direction of rotation

V imaginary wing shape

G working fluid

Angle of alpha exit

S1 fixing step

S2 cutting process

S3 connecting curved surface forming process

Detailed Description

As shown in fig. 1, the centrifugal compressor 100 includes a rotary shaft 1 that rotates around an axis, a casing 3 that forms a flow path 2 by covering the periphery of the rotary shaft 1, a plurality of impellers 4 provided on the rotary shaft 1, and a return vane 50 provided in the casing 3.

The housing 3 is cylindrical and extends along the axis O. The rotary shaft 1 extends through the housing 3 along the axis O. Journal bearings 5 and thrust bearings 6 are provided at both ends of the housing 3 in the axis O direction, respectively. The rotary shaft 1 is supported by the journal bearing 5 and the thrust bearing 6 to be rotatable about the axis O.

An intake port 7 for taking in air as the working fluid G from the outside is provided on one side in the axis O direction of the casing 3. Further, an exhaust port 8 for discharging the working fluid G compressed in the casing 3 is provided on the other side in the axis O direction of the casing 3.

An internal space is formed inside the casing 3, the diameter of which is repeatedly reduced and increased by communicating the intake port 7 and the exhaust port 8. The internal space accommodates a plurality of impellers 4 and forms a part of the flow path 2. In the following description, the side of the flow path 2 where the inlet 7 is located is referred to as the upstream side, and the side where the outlet 8 is located is referred to as the downstream side.

A plurality of (6) impellers 4 are provided on the outer peripheral surface of the rotary shaft 1 at intervals in the axis O direction. As shown in fig. 2, each impeller 4 has a disk 41 having a substantially circular cross section when viewed in the direction of the axis O, a plurality of blades 42 provided on the upstream surface of the disk 41, and a cover 43 covering the plurality of blades 42 from the upstream side.

The disk 41 is formed in a substantially conical shape such that the radial dimension thereof gradually increases from one side to the other side in the direction of the axis O when viewed in the direction intersecting the axis O.

The plurality of blades 42 are radially arranged outward in the radial direction around the axis O on the conical surface facing the upstream side of the two surfaces of the disk 41 in the axis O direction. More specifically, these blades are formed of thin plates that are provided upright from the upstream surface of the disk 41 toward the upstream side. The plurality of blades 42 are curved from one side to the other side in the circumferential direction when viewed from the axis O direction.

A cover 43 is provided at the upstream end edge of the vane 42. In other words, the plurality of blades 42 are sandwiched between the cover 43 and the disk 41 in the direction of the axis O. Thereby, a space is formed between the cover 43, the disk 41, and the pair of blades 42 adjacent to each other. This space becomes a part of the flow path 2 (compression flow path 22) described later.

The flow path 2 is a space that communicates the impeller 4 configured as described above with the internal space of the casing 3. In the present embodiment, a case will be described in which 1 flow path 2 is formed for every 1 impeller 4 (for every 1 compression stage). That is, in the centrifugal compressor 100, 5 flow paths 2 continuing from the upstream side to the downstream side are formed corresponding to 5 impellers 4 except for the impeller 4 of the last stage.

Each flow path 2 includes a suction flow path 21, a compression flow path 22, a diffusion flow path 23, and a guide flow path 25. Fig. 2 mainly shows the impeller 4 from the first stage to the third stage among the flow path 2 and the impeller 4.

In the impeller 4 of the first stage, the intake passage 21 is directly connected to the intake port 7. Through the suction flow path 21, the outside air is taken in as the working fluid G to each flow path on the flow path 2. More specifically, the suction flow path 21 is gradually curved from the axis O direction toward the radially outer side as going from the upstream side toward the downstream side.

The suction flow path 21 in the impeller 4 of the second stage or later communicates with the downstream end of a guide flow path 25 (described later) in the flow path 2 of the preceding stage (first stage). That is, the flow direction of the working fluid G passing through the guide flow path 25 is changed to be directed downstream along the axis O as described above.

The compression flow path 22 is a flow path surrounded by an upstream surface of the disk 41, a downstream surface of the cover 43, and a pair of circumferentially adjacent vanes 42. More specifically, the cross-sectional area of the compression flow path 22 gradually decreases from the radially inner side toward the radially outer side. As a result, the working fluid G flowing through the compression flow path 22 is gradually compressed to become a high-pressure fluid while the impeller 4 is rotating.

The diffuser flow path 23 is a flow path extending from the radially inner side toward the radially outer side of the axis O. The radially inner end of the diffuser passage 23 communicates with the radially outer end of the compression passage 22.

The guide flow path is a flow path that turns the radially outward working fluid G radially inward and flows into the next-stage impeller 4. The guide flow path is formed by the return bend 24 and the guide flow path 25.

The bent back portion 24 reverses the flow direction of the working fluid G flowing from the radially inner side toward the radially outer side through the diffuser passage 23 toward the radially inner side. One end side (upstream side) of the bent portion 24 communicates with the diffuser channel 23, and the other end side (downstream side) communicates with the guide channel 25. In the middle of the return bend 24, the radially outermost portion serves as a top. In the vicinity of the apex, the inner wall surface of the bent back portion 24 is a three-dimensional curved surface, and does not interfere with the flow of the working fluid G.

The guide flow path 25 extends radially inward from the end on the downstream side of the return portion 24. The radially outer end of the guide passage 25 communicates with the above-described bent portion 24. The radially inner end of the guide passage 25 communicates with the intake passage 21 of the subsequent passage 2 as described above.

Next, the return vane 50 is explained. A plurality of return vanes 50 are provided in the guide flow path 25. Specifically, as shown in fig. 3, the plurality of return vanes 50 are radially arranged around the axis O in the guide flow path 25. In other words, the return blades 50 are arranged around the axis O at intervals in the circumferential direction. Both ends of the return vane 50 in the axial direction are in contact with the casing 3 forming the guide flow path 25.

The return vane 50 has an airfoil shape in which a radially outer end portion is a leading edge 51 and a radially inner end portion is a trailing edge 52 when viewed from the axis O direction. The return vane 50 is curved forward in the rotation direction R of the rotary shaft 1 from the front edge 51 toward the rear edge 52 (i.e., from the radially outer side to the radially inner side). The return vane 50 is curved so as to be convex toward the front side in the rotation direction R. The surface of the return vane 50 facing the front side in the rotation direction R is a negative pressure surface 53, and the surface facing the rear side in the rotation direction R is a pressure surface 54. A line having the same distance from the pressure surface 54 and the negative pressure surface 53 when viewed from the axis O direction is defined as a center line C.

In the present embodiment, the outlet angle α of the return vane 50 is inclined toward the front side in the rotation direction R. Here, the exit angle α is an acute angle formed by the center line C of the return vane 50 with respect to a reference line S passing through the trailing edge 52 and the axis O when viewed from the axis O direction. The outlet angles alpha are mutually the same in the return vanes 50 of the same stage. The outlet angle α is preferably 10 ° or more and 45 ° or less.

As shown in an enlarged view in fig. 4, an end surface of the return vane 50 on the pressure surface 54 side including the trailing edge 52 is a cut surface 55. The cutting surface 55 is formed by cutting a portion including the radially inner end of the virtual airfoil V shown in fig. 3 from the pressure surface 54 to the suction surface 53. The virtual airfoil V described herein is an airfoil that is assumed to extend from the pressure surface 54 and the suction surface 53 with the same curvature to a point where the radially inner ends of the pressure surface 54 and the suction surface 53 intersect with each other. The return vane 50 of the present embodiment is formed by cutting out a portion including a radially inner end of the virtual airfoil V by machining. The cut surface 55 is curved in an arc shape so as to project forward in the rotation direction R.

As shown in fig. 4, the pressure surface 54 and the cut surface 55 are connected to each other by a smooth curved surface (connecting curved surface portion 56). The pressure surface 54 and the cutting surface 55 are curved to project forward in the rotation direction R, while the connecting curved surface portion 56 is curved to project rearward in the rotation direction R. That is, the connecting curved surface portion 56 is curved in the direction opposite to the pressure surface 54 and the cutting surface 55. The connecting curved surface portion 56 is formed by chamfering a corner portion formed between the pressure surface 54 and the cut surface 55.

As shown in fig. 3, the separation distance L between the return blades 50 is smallest between the radially outer end portions of the suction surface 53 of one return blade 50 and the cut surface 55 of the other return blade 50.

Next, a method of manufacturing the centrifugal rotary machine according to the present embodiment will be described with reference to fig. 5. As shown in the drawing, the manufacturing method includes a fixing process S1, a cutting process S2, and a connecting curved surface forming process S3.

In the fixing step S1, the pre-processed return blade 50 (return blade original) having the virtual airfoil V described above is fixed to the guide flow path 25. Although not shown in detail, the return blade is fastened and fixed to the wall surface of the guide flow path 25 by bolts.

The cutting process S2 is performed after the fixing process S1. In the cutting step S2, the aforementioned cut surface 55 is formed by machining (cutting) the return blade material in a state of being fixed to the guide flow path 25. It is preferable that the centrifugal compressor 100 is trial-operated between the fixing step S1 and the cutting step S2, and a confirmation step of confirming whether or not the operation range reaches a predetermined desired operation range is performed as necessary. If the desired working range is not satisfied (i.e., if the working range needs to be expanded), the cutting process S2 is performed. In this cutting step S2, the cutting amount is preferably adjusted so that the exit angle α of the return vane 50 after machining falls within the above-described numerical range and the working range becomes a desired value.

The connected curved surface forming process S3 is performed after the cutting process S2. In the connecting curved surface forming step S3, the connecting curved surface portion 56 is formed. More specifically, the corner portion formed between the pressure surface 54 and the cut surface 55 is chamfered to form a curved connecting curved surface portion 56. As described above, all steps of the manufacturing method of the present embodiment are completed.

According to the above method, the cutting surface 55 is formed by cutting out the portion including the radially inner end of the return blade original from the pressure surface 54 to the suction surface 53 in the cutting step S2. This makes it possible to make the exit angle α (the angle formed by the radially inner end surface with respect to the radial direction) of the return vane 50 larger than the exit angle of the virtual airfoil V. As the outlet angle α increases, the swirl flow component remains in the flow of the fluid passing through the return vane 50. As a result, the operating range of the centrifugal compressor 100 can be expanded. In the above method, the cutting step S2 is performed after the return blade original that has been attached to the casing 3 through the fixing step S1. Thus, the centrifugal compressor 100 having a desired operating range can be easily obtained without remanufacturing the return vane 50 again.

According to the above method and structure, the cut surface 55 is formed into an arc shape protruding forward in the rotation direction R, so that the flow of the fluid flowing along the cut surface 55 can be smoothly guided, and the possibility of occurrence of separation or vortex in the flow can be reduced.

According to the above method and structure, the cut surface 55 forms an angle of 10 ° or more with respect to the radial direction. In other words, the outlet angle α is an angle of 10 ° or more. This allows the swirling flow component contained in the flow of the fluid guided by the return vane 50 to remain more positively. As a result, the operating range of the centrifugal compressor 100 can be significantly expanded.

According to the above method and structure, the distance separating the return blades 50 from each other is minimized between the radially outer end of the suction surface 53 of one return blade 50 and the cut surface 55 of the other return blade 50. This can more smoothly guide the flow of the fluid flowing between the return vanes 50.

According to the above method and structure, the pressure surface 54 and the cutting surface 55 are connected in a curved shape by the connecting curved surface portion 56, and therefore, the possibility of occurrence of separation or vortex in the flow of the fluid flowing along the connecting curved surface portion 56 can be reduced.

The embodiments of the present invention have been described above. It is to be noted that various changes and modifications can be made to the above-described method and structure without departing from the spirit of the present invention. For example, in the above embodiment, an example in which the cut surface 55 has an arc shape is described. However, the shape of the cut surface 55 is not limited to this, and the cut surface 55' may be linear when viewed from the axis O direction as shown in fig. 6. Further, the connecting curved surface portion 56 may not be formed. By making the cut surface 55' straight, the operating range of the centrifugal compressor 100 can be easily adjusted by only relatively simple machining.