CENTRIFUGAL COMPRESSOR IMPELLER

Abstract

Provided is a centrifugal compressor impeller capable of improving machine operation efficiency, by making the total pressure distribution of a fluid that flowed into a vaneless diffuser constant. To this end, the provided centrifugal compressor impeller has a plurality of vanes radially provided around a rotating shaft, uses centrifugal force produced by rotating along with the rotating shaft, pumps a fluid (G) taken in from the leading edge side of the vanes to the outside in the radial direction of the rotating shaft from the trailing edge side of the vanes, and thereafter, discharges the fluid (G) into a vaneless diffuser. Furthermore, the edge front end and the edge rear end of the trailing edge are positioned to the outside in the radial direction of the rotating shaft relative to the edge center section of the trailing edge.

Description

TECHNICAL FIELD

The present invention relates to a shape of a trailing edge of a blade in an impeller used in a centrifugal compressor.

BACKGROUND ART

Generally, a centrifugal compressor utilizes centrifugal force of an impeller rotating together with a rotating shaft to pump a fluid, taken in from the leading edge side of the impeller, outward in a rotating shaft radial direction from the trailing edge side of the impeller and discharge the fluid into a diffuser. Specifically, the fluid taken into the centrifugal compressor is increased in pressure while passing through a flow passage of the rotating impeller and then the speed of the fluid is decreased by flowing through a diffuser. For example, Patent Document 1 discloses such a conventional centrifugal compressor.

PRIOR ART DOCUMENT

Patent Document

Patent Document 1: Japanese Patent No. 3383023

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

When the fluid passes through the flow passage of the impeller, friction is generated between the fluid and a flow passage wall surface. Accordingly, the total pressure of the fluid flowing on the flow passage wall surface side decreases at the trailing edge of the impeller which forms an exit of the flow passage, and this leads to pressure loss. Particularly, when the centrifugal compressor is operated at a low flow rate, separation of the fluid becomes significant on a flow passage wall surface of the diffuser, and this leads to further pressure loss.

Moreover, diffusers of centrifugal compressors include a vaned diffuser and a vaneless diffuser. Generally, the pressure loss can be suppressed by providing diffuser vanes in the diffuser.

The centrifugal compressor disclosed in Patent Document 1 listed above includes a vaned diffuser, and the shape of a trailing edge of an impeller is specified in order to reduce noise and pressure pulsation generated when a fluid flowing into the diffuser comes into contact with diffuser vanes. In other words, the shape of the trailing edge of the impeller disclosed in Patent Document 1 is not for dealing with pressure loss occurring in a vaneless diffuser.

The present invention solves the problem described above and an object thereof is to provide a centrifugal compressor impeller capable of improving machine operation efficiency by causing a fluid flowing into a vaneless diffuser to have even total pressure distribution.

Means for Solving the Problem

A centrifugal compressor impeller in a first aspect of the present invention for solving the aforementioned problem is a centrifugal compressor impeller which comprises a plurality of blades provided radially about a rotating shaft and which utilizes centrifugal force generated by rotating together with the rotating shaft to pump a fluid, taken in from a leading edge side of each of the blades, outward in a rotating shaft radial direction from a trailing edge side of the blade and then discharge the fluid into a vaneless diffuser, the impeller characterized in that

an edge front end and an edge rear end of the trailing edge are disposed outside an edge center portion of the trailing edge in the rotating shaft radial direction.

A centrifugal compressor impeller in a second aspect of the present invention for solving the aforementioned problem is characterized in that the edge front end and the edge rear end are disposed to be shifted from each other in the rotating shaft radial direction.

A centrifugal compressor impeller in a third aspect of the present invention for solving the aforementioned problem is characterized in that thicknesses of the edge front end and the edge rear end are smaller than a thickness of the edge center portion.

Effect of the Invention

In the centrifugal compressor impeller of the present invention, the edge front end and the edge rear end in the trailing edge of the blade are disposed outside the edge center portion in the trailing edge of the blade in the rotating shaft radial direction. The centrifugal force acting on the fluid passing the edge front end and the edge rear end can be thereby made greater than the centrifugal force acting on the fluid passing the edge center portion. Accordingly, the total pressure distribution of the fluid passing the trailing edge can be set such that the pressure gradually increases from the edge center portion toward the edge front end and the edge rear end. Hence, even when pressure loss occurs due to friction generated between the fluid discharged from the impeller into the vaneless diffuser and a wall surface of the diffuser, the fluid flowing through the diffuser can have an even (uniform) total pressure distribution. As a result, operation efficiency of the centrifugal compressor can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view illustrating a schematic configuration of a centrifugal compressor to which an impeller in one embodiment of the present invention is applied.

FIG. 2 is an enlarged view of a main portion of FIG. 1 and is a view illustrating an example of a trailing edge shape in a blade.

FIGS. 3A to 3D are views illustrating other examples of the trailing edge shape in the blade.

FIG. 4 is a graph illustrating a relationship between a trailing edge height of the blade and a trailing edge thickness of the blade.

MODE FOR CARRYING OUT THE INVENTION

A centrifugal compressor in the present invention is described below in detail by using the drawings.

Embodiment

As illustrated in FIG. 1, the centrifugal compressor 1 includes a casing 10, a rotating shaft 20, an impeller 30, and the like. Specifically, the casing 10 has a hollow shape and the rotating shaft 20 is rotatably supported in the hollow portion via a bearing. The impeller 30 is fitted on the rotating shaft 20.

The impeller 30 includes a hub 31, a front shroud 32, and multiple blades 33. The hub 31 is formed in an annular shape whose outer diameter gradually increases from front to rear in a rotating shaft direction, and the rotating shaft 20 is fitted in a center hole of the hub 31. Moreover, the front shroud 32 is disposed outside the hub 31 in a radial direction, and is formed in an annular shape whose inner diameter gradually increases from front to rear in the rotating shaft direction.

Furthermore, the blades 33 are provided radially about the rotating shaft 20, between an outer peripheral surface of the hub 31 and an inner peripheral surface of the front shroud 32, and are formed to gradually curve toward the outside in the rotating shaft radial direction while extending from front to rear in the rotating shaft direction.

Specifically, multiple spaces which are each surrounded by the outer peripheral surface of the hub 31, the inner peripheral surface of the front shroud 32, and two blades 33 adjacent to each other in a rotating shaft circumferential direction are formed in the impeller 30 radially about the rotating shaft 20, and each serve as a flow passage 34 through which a fluid G passes. A front wall surface 34a and a rear wall surface 34b of the flow passage 34 are formed by the inner peripheral surface of the front shroud 32 and the outer peripheral surface of the hub 31, and the flow passage 34 as a whole is formed to gradually curve toward the outside in the rotating shaft radial direction while extending from front to rear in the rotating shaft direction.

The impeller 30 can thus utilize centrifugal force generated by rotating together with the rotating shaft 20 to take in the fluid G from the leading edge 33a side of the blade 33 forming an entrance of the flow passage 34, and then discharge the fluid G outward in the rotating shaft radial direction from the trailing edge 33b side of the blade 33 forming an exit of the flow passage 34. In this case, the fluid G taken into the impeller 30 is increased in pressure while passing through the flow passage 34.

Meanwhile, an intake passage 11 and a diffuser 12 serving as a discharge passage are formed in the casing 10.

The intake passage 11 is disposed in front of the impeller 30 in the rotating shaft direction (upstream of the impeller 30 in a fluid flow direction), and is an annular passage which guides the fluid G taken in from the outside of the casing 10 toward the leading edge 33a of the blade 33 in the impeller 30 in the rotating shaft direction.

Meanwhile, the diffuser 12 is disposed outside the impeller 30 in the rotating shaft radial direction (downstream of the impeller 30 in the fluid flow direction), and is an annular passage extending in the rotating shaft radial direction. In other words, a front wall surface 12a and a rear wall surface 12b which have an annular shape as a whole are formed in the diffuser 12. An annular entrance 12c of the diffuser 12 is formed by an inner end of the front wall surface 12a in the radial direction (upstream end of the front wall surface 12a in the fluid flow direction) and an inner end of the rear wall surface 12b in the radial direction (upstream end of the rear wall surface 12b in the fluid flow direction), and is opposed to the exit (trailing edge 33b of the blade 33) of the flow passage 34 in the impeller 30 in the rotation shaft radial direction.

The diffuser 12 thus takes in the fluid G compressed in the flow passage 34 of the impeller 30, between the front wall surface 12a and the rear wall surface 12b and then discharges the taken-in fluid G outward in the rotating shaft radial direction while reducing the speed of the fluid G.

Note that the diffuser 12 is a so-called vaneless diffuser and do not have diffuser vanes for suppressing pressure loss inside the diffuser.

Accordingly, when the centrifugal compressor 1 is operated, the rotating shaft 20 rotates and the impeller 30 also rotates together with the rotating shaft 20. The fluid G sucked into the intake passage 11 of the casing 10 by this rotation is compressed by being taken into the flow passage 34 of the rotating impeller 30, and is then discharged from the inside of the flow passage 34. Next, the fluid G discharged from the impeller 30 is taken into the diffuser 12 such that the speed thereof is reduced and the flow thereof is regulated, and then discharged from the inside of the diffuser 12.

Here, as illustrated in FIG. 2, in the impeller 30, the trailing edge 33b of the blade 33 forming the exit of the flow passage 34 is recessed inward in the rotating shaft radial direction in an arc shape.

Specifically, the trailing edge 33b is formed to gradually curve inward in the rotating shaft radial direction from an edge front end 41 and an edge rear end 42 toward an edge center portion 43. To be more specific, the edge front end 41 and the edge rear end 42 are disposed at the same position in the rotating shaft radial direction and are disposed outside the edge center portion 43 in the rotating shaft radial direction.

Note that the edge front end 41 is a portion of the trailing edge 33b located closest to the front shroud 32 and is joined to a downstream end of the inner peripheral surface of the front shroud 32 (downstream end of the front wall surface 34a in the flow passage 34). Moreover, the edge rear end 42 is a portion of the trailing edge 33b located closest to the hub 31 and is joined to a downstream end of the outer peripheral surface of the hub 31 (downstream end of the rear wall surface 34b in the flow passage 34). Furthermore, the edge center portion 43 is located in an intermediate portion between the edge front end 41 and the edge rear end 42 and is a portion where a main flow of the fluid G flowing through the flow passage 34 passes.

The radius of a circle centered on a rotation center of the rotating shaft 20 and passing the edge front end 41 and the edge rear end 42 is thus greater than the radius of a circle centered on the rotation center of the rotating shaft 20 and passing the edge center portion 43. Centrifugal force greater than that acting on the fluid G flowing through a center portion of the flow passage 34 and passing the edge center portion 43 thereby acts on the fluid G flowing along the front wall surface 34a of the flow passage 34 and passing the edge front end 41 and the fluid G flowing along the rear wall surface 34b of the flow passage 34 and passing the edge rear end 42.

Accordingly, a total pressure distribution P of the fluid G passing the trailing edge 33b can be set such that the pressure gradually increases from the edge center portion 43 toward the edge front end 41 and the edge rear end 42. Hence, even when pressure loss occurs due to friction generated between the fluid G discharged from the impeller 30 into the diffuser 12 and each of the front wall surface 12a and the rear wall surface 12b, the fluid G flowing through the diffuser 12 can have an even (uniform) total pressure distribution. As a result, operation efficiency of the centrifugal compressor 1 can be improved.

Note that, although the recess shape of the trailing edge 33b is the arc shape in the aforementioned embodiment, the recess shape of the trailing edge 33b only needs to be such that the edge front end 41 and the edge rear end 42 are disposed outside the edge center portion 43 in the rotating shaft radial direction. For example, the recess shape of the trailing edge 33b may be the recess shapes illustrated in FIGS. 3A to 3D.

Specifically, in the recess shape illustrated in FIG. 3A, the trailing edge 33b of the blade 33 is recessed inward in the rotating shaft radial direction in an arc shape, and the edge front end 41 and the edge rear end 42 are shifted from each other in the rotation shaft radial direction. To be more specific, the edge front end 41 and the edge rear end 42 are disposed outside the edge center portion 43 in the rotating shaft radial direction and, in addition, the edge front end 41 is disposed outside the edge rear end 42 in the rotating shaft radial direction. Note that the configuration may be the opposite such that the edge rear end 42 is disposed outside the edge front end 41 in the radial direction.

Meanwhile, in the recess shape illustrated in FIG. 3B, although the trailing edge 33b of the blade 33 is recessed inward in the rotating shaft radial direction in an arc shape, only the edge center portion 43 is recessed inward in the rotating shaft radial direction. Specifically, the edge front end 41 and the edge rear end 42 are disposed at the same position in the rotating shaft radial direction and are disposed outside the edge center portion 43 in the rotating shaft radial direction.

When only the edge center portion 43 is to be recessed inward in the rotating shaft radial direction as described above, the edge center portion 43 may be notched in a rectangular shape or a wedge shape as illustrated in FIGS. 3C and 3D.

Furthermore, although the total pressure of the fluid G passing the edge front end 41 and the edge rear end 42 is made higher than the total pressure of the fluid G passing the edge center portion 43 by forming the trailing edge 33b of the blade 33 in the recess shape in the aforementioned embodiment, a further total pressure difference may be generated by additionally varying the thickness of the trailing edge 33b among the edge front end 41, the edge rear end 42, and the edge center portion 43.

Specifically, as illustrated in FIG. 4, the thickness of the trailing edge 33b is made to gradually decrease from the edge center portion 43 toward the edge front end 41 and the edge rear end 42. In the trailing edge 33b of the blade 33, the smaller the thickness is, the more the pressure loss is suppressed. Accordingly, the total pressure of the fluid G passing the edge front end 41 and the edge rear end 42 can be made higher than the total pressure of the fluid G passing the edge center portion 43.

Hence, even when large pressure loss occurs due to friction generated between the fluid G discharged into the diffuser 12 and each of the front wall surface 12a and the rear wall surface 12b, the fluid G flowing through the diffuser 12 can have an even (uniform) total pressure distribution.

INDUSTRIAL APPLICABILITY

The impeller of the centrifugal compressor in the present invention can improve the total pressure distribution of the fluid in the trailing edge. Accordingly, the impeller can be utilized to be highly beneficial in improving the operation efficiency of a machine.

EXPLANATION OF THE REFERENCE NUMERALS

• 1 centrifugal compressor
• 10 casing
• 11 intake passage
• 12 diffuser
• 20 rotating shaft
• 30 impeller
• 31 hub
• 32 front shroud
• 33 blade
• 33 a leading edge
• 33 b trailing edge
• 34 flow passage
• 41 edge front end
• 42 edge rear end
• 43 edge center portion
• G fluid
• P total pressure distribution

Claims

1. A centrifugal compressor impeller which comprises a plurality of blades provided radially about a rotating shaft and which utilizes centrifugal force generated by rotating together with the rotating shaft to pump a fluid, taken in from a leading edge side of each of the blades, outward in a rotating shaft radial direction from a trailing edge side of the blade and then discharge the fluid into a vaneless diffuser, the impeller characterized in that an edge front end and an edge rear end of the trailing edge are disposed outside an edge center portion of the trailing edge in the rotating shaft radial direction, andthicknesses of the edge front end and the edge rear end are smaller than a thickness of the edge center portion.

2. The centrifugal compressor impeller according to claim 1, characterized in that the edge front end and the edge rear end are disposed to be shifted from each other in the rotating shaft radial direction.

3. (canceled)