Closed impeller

Abstract

A closed impeller according to one embodiment is used in a centrifugal compressor, said closed impeller comprising a hub (2) having a concave curved surface (20) for guiding an axial flow to a radial flow, a shroud (4) including a convex curved surface (40) facing the concave curved surface (20), and a plurality of blades (3) that are arranged in the circumferential direction between the hub (2) and the shroud (4) and that connect the hub (2) and the shroud (4). The plate thickness of each blade (3) increases from a leading edge (31) to a predetermined position P, and decreases from the predetermined position P to a trailing end (32). In a meridian plane diagram, when the length of the blade (3) from the leading edge (31) to the trailing edge (32) is expressed as a percentage, the predetermined position P is within a range of 30 to 60% inclusive.

Description

Closed impeller

[0001] The present disclosure relates to a closed impeller for use in a centrifugal compressor.

[0002] In centrifugal compressors, a closed impeller in which the gas flow path is closed is sometimes used to ensure efficiency. In a closed impeller, a hub and a shroud are connected by a number of blades arranged in the circumferential direction. The hub has a concave curved surface that guides the axial flow into a radial flow, and the shroud has a convex curved surface that faces the concave curved surface.

[0003] Japanese Patent Application Laid-Open No. 2016-98757

[0004] In centrifugal compressors, there is a demand for rotating the closed impeller at high speeds. In particular, in centrifugal compressors for hydrogen, the maximum peripheral speed of the closed impeller can be 500 m / s or more.

[0005] When a closed impeller rotates at high speed, a large centrifugal force acts on the closed impeller, and therefore it is desirable to reduce the stress on the closed impeller. In this regard, Patent Document 1 describes tapering the blades radially outward to improve strength, but Patent Document 1 relates to an open impeller with a separate shroud, and not to a closed impeller.

[0006] Therefore, an object of the present disclosure is to provide a closed impeller that can reduce stress.

[0007] The present disclosure provides a closed impeller for use in a centrifugal compressor, comprising: a hub including a concave curved surface that guides an axial flow into a radial flow; a shroud including a convex curved surface that faces the concave curved surface; and a plurality of blades that are arranged circumferentially between the hub and the shroud and connect the hub and the shroud, wherein the plate thickness of each of the plurality of blades increases from a leading edge to a predetermined position and decreases from the predetermined position to a rear end, and when the length of the blade from the leading edge to the trailing edge is expressed as a percentage in a meridian plane, the predetermined position is within a range of 30% to 60%.

[0008] According to the present disclosure, a closed impeller is provided that allows for reduced stress.

[0009] 1 is a plan view of a closed impeller according to an embodiment; FIG. 2 is a meridian plane view taken along line II-II of FIG. 1; FIG. 3 is a graph showing the change in thickness of a blade from the leading edge to the trailing edge; FIG. 4 is a meridian plane view showing the ratio of the blade from the leading edge to the trailing edge; and FIG. 5 is an enlarged view of a portion of FIG. 1.

[0010] 1 shows a closed impeller 1 according to one embodiment. The closed impeller 1 is used in a centrifugal compressor.

[0011] The closed impeller 1 has a generally disk-like shape with a through hole 11 in the center. A rotary shaft is fitted into the through hole 11.

[0012] Inside the closed impeller 1, a plurality of flow paths 5 are formed that open in the axial direction of the closed impeller 1, i.e., in the direction of extension of the center line 10, around the through hole 11, and that open on the end face facing radially outward of the closed impeller 1.

[0013] 2 , the closed impeller 1 includes a hub 2 having a concave curved surface 20 that guides axial flow into radial flow, an annular shroud 4 having a convex curved surface 40 that faces the concave curved surface 20, and a plurality of blades 3 that are arranged in the circumferential direction between the hub 2 and the shroud 4. The hub 2 and the shroud 4 are connected by the blades 3.

[0014] The hub 2 includes a cylindrical portion 21 that forms the through hole 11, and a disk portion 22 that extends radially along the concave curved surface 20. In other words, the hub 2 forms the through hole 11, the central portion of the front surface of the closed impeller 1, and the back surface of the closed impeller 1. In this embodiment, the disk portion 22 extends radially outward from the center of the cylindrical portion 21. However, the length of the cylindrical portion 21 may be shortened, and the disk portion 22 may extend radially outward from the end of the cylindrical portion 21.

[0015] In this embodiment, the back surface 23 of the disk portion 22 opposite the concave curved surface 20 has a recess 24 that recesses radially inward to approach the concave curved surface 20. However, the back surface 23 may not have the recess 24 and may be entirely flat.

[0016] The shroud 4 covers the hub 2 from one side in the axial direction of the closed impeller 1, and constitutes the outer peripheral portion of the front surface of the closed impeller 1. The shroud 4 is in the shape of a plate that is curved 90 degrees along the concave curved surface 20 of the hub 2, and in addition to the above-mentioned convex curved surface 40, has a front surface 41 on the opposite side to the convex curved surface 40, an axial end surface facing the axial direction of the closed impeller 1, and a radial end surface facing radially outward.

[0017] In this embodiment, the radially inner portion of the front surface 41 has a straight cylindrical shape, but the entire front surface 41 may be curved. Also, in this embodiment, the axial end face of the shroud 4 is located at the same height as the front end face of the cylindrical portion 21 of the hub 2, but the axial end face may be located behind the front end face of the cylindrical portion 21.

[0018] The blades 3 divide the annular space curved at 90 degrees between the concave curved surface 20 of the hub 2 and the convex curved surface 40 of the shroud 4 into the above-mentioned plurality of flow passages 5. Each blade 3 is perpendicular to the concave curved surface 20 and the convex curved surface 40. Each blade 3 is also curved in one circumferential direction toward the radially outer side of the closed impeller 1.

[0019] Each blade 3 has a leading edge 31 that defines an axial opening of the flow passage 5, and a trailing edge 32 that defines a radial opening of the flow passage 5. In this embodiment, the leading edge 31 is parallel to the radial direction of the closed impeller 1 and is located on the rear side of the front end face of the cylindrical portion 21 of the hub 2. However, the leading edge 31 may be located at the same height as the front end face of the cylindrical portion 21 of the hub 2. Furthermore, the leading edge 31 of each blade 3 may be inclined radially inward so as to move away from the front end face of the cylindrical portion 21.

[0020] The trailing edge 32 constitutes the end face of the closed impeller 1 together with the outer end face of the disk portion 22 of the hub 2 and the radial end face of the shroud 4 .

[0021] Furthermore, in this embodiment, as shown in Fig. 3, the plate thickness of each blade 3 increases from the leading edge 31 to a predetermined position P, and decreases from the predetermined position P to the trailing edge 32. As shown in Fig. 4, the predetermined position P is in the range of 30% to 60% when the length of the blade 3 from the leading edge 31 to the trailing edge 32 is expressed as a percentage in a meridian plane. Here, the meridian plane is a view obtained by rotating the shape of the blade 3 around the center line 10 onto a cross section passing through the center line 10 of the closed impeller 1.

[0022] 5, each blade 3 has a pair of side surfaces 33, 34 facing opposite each other. In this embodiment, the pair of side surfaces 33, 34 connect to the concave curved surface 20 while moving away from each other, and also connect to the convex curved surface 40 while moving away from each other. In other words, corner portions between each of the side surfaces 33, 34 and the concave curved surface 20 are padded, and corner portions between each of the side surfaces 33, 34 and the convex curved surface 40 are padded.

[0023] In FIG. 5, the corner portions between each of the side surfaces 33, 34 and the concave curved surface 20 and the corner portions between each of the side surfaces 33, 34 and the convex curved surface 40 are curved, but the corner portions may be inclined.

[0024] As described above, in the closed impeller 1 of this embodiment, the thickness of the blade 3 at the portion most susceptible to deformation due to centrifugal force is greatest, so stress can be reduced.

[0025] In addition, in this embodiment, the back surface 23 of the disk portion 22 of the hub 2 has the recess 24, which suppresses deformation such as rearward tilting of the outer peripheral portion of the closed impeller 1. As a result, stress can be further reduced.

[0026] <Modifications> The present disclosure is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present disclosure.

[0027] For example, the side surfaces 33, 34 of each blade 3 do not necessarily need to be connected to the concave curved surface 20 and the convex curved surface 40 while moving away from each other, and the side surfaces 33, 34 may be connected perpendicularly to the concave curved surface 20 and the convex curved surface 40. However, as in the above embodiment, if the side surfaces 33, 34 of each blade 3 are connected to the concave curved surface 20 and the convex curved surface 40 while moving away from each other, stress concentration at the corners between the side surfaces 33, 34 of the blade 3 and the concave curved surface 20 and the convex curved surface 40 can be reduced.

[0028] <Summary> In a first aspect, the present disclosure provides a closed impeller for use in a centrifugal compressor, the closed impeller comprising: a hub including a concave curved surface that guides an axial flow into a radial flow; a shroud including a convex curved surface that faces the concave curved surface; and a plurality of blades that are aligned in the circumferential direction between the hub and the shroud and connect the hub and the shroud, wherein the plate thickness of each of the plurality of blades increases from a leading edge to a predetermined position and decreases from the predetermined position to a rear end, and when the length of the blade from the leading edge to the trailing edge is expressed as a percentage in a meridian plane, the predetermined position is within a range of 30% to 60%.

[0029] According to the above configuration, the thickness of the blade is greatest at the portion that is most susceptible to deformation due to centrifugal force, thereby reducing stress.

[0030] In a second aspect, in the first aspect, the hub may include a disk portion that extends radially along the concave curved surface, and a back surface of the disk portion opposite the concave curved surface may have a recess that recesses radially inward to approach the concave curved surface. With this configuration, deformation such that the outer peripheral portion of the closed impeller falls backward is suppressed, thereby further reducing stress.

[0031] As a third aspect, in the first or second aspect, each of the plurality of blades may have a pair of side surfaces facing opposite each other, the pair of side surfaces moving away from each other to connect to the concave curved surface and also moving away from each other to connect to the convex curved surface. With this configuration, stress concentration at corners between the side surfaces of the blades and the concave and convex curved surfaces can be reduced.

Claims

1. A closed impeller used in a centrifugal compressor, comprising: a hub including a concave curved surface that guides axial flow into radial flow; a shroud including a convex curved surface that faces the concave curved surface; and a plurality of blades that are arranged circumferentially between the hub and the shroud and connect the hub and the shroud, wherein the plate thickness of each of the plurality of blades increases from the leading edge to a predetermined position and decreases from the predetermined position to the rear end, and when the length of the blade from the leading edge to the trailing edge is expressed as a percentage in a meridian plane, the predetermined position is within a range of 30% to 60%.

2. A closed impeller as set forth in claim 1, wherein the hub includes a disk portion that extends radially along the concave curved surface, and the back surface of the disk portion opposite the concave curved surface has a recess that recesses radially inward and approaches the concave curved surface.

3. A closed impeller as set forth in claim 1 or 2, wherein each of said plurality of blades has a pair of side surfaces facing opposite each other, said pair of side surfaces diverging from each other to connect to said concave curved surface, and also diverging from each other to connect to said convex curved surface.

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