CENTRIFUGAL TURBOMACHINE

Abstract

A plurality of vaned diffusers is disposed on a concentric plate at intervals in a circumferential direction thereof, and each of the diffusers is a curvilinear element three-dimensional diffuser having blades which are extended from a hub side of a impeller to a shroud side thereof. The blades are formed in a form in which a blade serving as a reference is stacked in a direction of the height of the blade, which is a direction of a gap between the hub and the shroud. A dihedral distribution in which moving in a direction perpendicular to a chord direction linking a leading edge of the blade as the reference with a tailing edge thereof, is set as a positive movement is non-uniform from an end portion on the hub side to an intermediate portion of the height of the blade.

Description

TECHNICAL FIELD

The present invention relates to a centrifugal turbomachine including a centrifugal impeller, such as a centrifugal compressor, centrifugal blower, centrifugal fan or centrifugal pump.

BACKGROUND ART

The multistage centrifugal compressor, a kind of centrifugal turbomachine, has a number of impellers mounted on the same shaft. A diffuser and a return guide vane are installed side by side downstream of each of the impellers. The impeller, the diffuser, and the return guide vane constitute a stage. Here, a vaneless diffuser, a vaned diffuser, a low solidity diffuser that is a kind of the vaned diffuser, or the like, is used as the diffuser, depending on the purpose and intended use.

Among these diffusers, the low solidity diffuser has the property of being able to increase the choke margin that is the operating range on a high flow side, because it does not have a geometrical throat. Also, the low solidity diffuser has the advantage of being able to sufficiently ensure the surge margin that is the operating range on a low flow side, because separation on the blade surface in a low flow area is suppressed by the effect of a secondary flow which sweeps the boundary layer on the blade surface. For this reason, the low solidity diffuser is frequently used.

A 2D blade with the same blade profiles stacked in a blade height direction is commonly used for a vaned diffuser for centrifugal turbomachines as typified by the low solidity diffuser. However, in response to the demands for a further performance improvement, attempts are also being made to use a 3D blade. For example, in a centrifugal compressor disclosed in Patent Literature 1, the stagger angle of a diffuser blade section is gradually varied in the blade height direction of the diffuser to form the 3D blade, thereby realizing a collisionless flow for an unevenly distributed inflow and achieving both of an improvement in efficiency and an increase in operating range.

Furthermore, in a centrifugal compressor disclosed in Patent Literature 2, a diffuser inlet diameter is changed by bending downstream a heightwise central portion of a blade at a leading edge portion of a diffuser. Thus, a collision-free flow for the unevenly distributed inflow is realized and both of an improvement in efficiency and an increase in operating range are achieved.

CITATION LIST

Patent Literature

• Patent Literature 1: JP-A No, 2009-504974
• Patent Literature 2: JP-A No. 2004-92482

SUMMARY OF INVENTION

Technical Problem

In the airfoil diffuser for the centrifugal compressor disclosed in the above-described Patent Literature 1, a 3D diffuser blade is formed by stacking divided diffuser blades virtually in an axial direction (direction from a hub plane to a shroud plane). At this time, there is also suggested a bow diffuser blade in which a lean angle is varied along a diffuser blade span, the lean angle meaning the angle which the stacking direction of the blades makes with the direction perpendicular to the hub or shroud plane.

However, the authors consider that the curvilinear element blade does not necessarily lead to sufficient improvements because many options are available. That is, if lean distribution is applied to the blade, the secondary flow might be increased by its application, resulting in performance deterioration. Therefore, there is a need for clarification of the stacking pattern of divided blades which leads to performance improvement.

Furthermore, in the centrifugal compressor disclosed in the Patent Literature 2, lean is applied to a local portion, namely, the diffuser leading edge to achieve inflow angle matching. However, any construction of the curvilinear element diffuser is not adopted, and no consideration is given to control of the secondary flow in a flow path between diffuser blades which becomes more conspicuous when the curvilinear element diffuser is employed.

The present invention has been made in view of problems of the related art described above, and an object of the present invention is to provide effectively suppress a secondary flow between blades and improve performance when a curvilinear element diffuser is used to increase efficiency in a vaned diffuser for use in a centrifugal turbomachine. Another object of the present invention is to obtain a stacking pattern of divided blades which leads to performance improvement, in the curvilinear element diffuser for use in a centrifugal turbomachine.

Solution to Problem

Firstly, referring to FIGS. 1 and 2, some terms used in this specification will be defined as follows. FIG. 1 is a plan view of one diffuser blade for explaining the movement of a blade profile. FIG. 2 is a perspective view of one blade taken from a vaned diffuser, showing the state in which basic blade profiles are stacked in a Z direction. A coordinate system is a cylindrical coordinate system (R, θ, Z), in which the radial direction of an impeller is denoted by R, the direction of rotation of the impeller is denoted by θ, and the axial direction of a rotating shaft is denoted by Z. The Z direction from a shroud 102 to a hub 101 is set as positive.

Chord (C): line that connects a leading edge 208 and a trailing edge 209 of a blade profile 104 serving as a basis of a diffuser blade 103.

Lean: degree of tilt of the diffuser blade 103 relative to the surface of the hub 101, and it can be regarded as a combination of sweep and dihedral to be described below.

Stagger Angle (θ_SG): angle (tan θ_SG=dC/dR) which the chord C forms with the radial direction (R direction).

Sweep (Δσ): as indicated by alternate long and short dashed lines in FIG. 1, to move the blade profile 104 of the diffuser blade 103 parallel to the direction of the chord C. The movement in a downstream direction is set as positive.

Dihedral (Δδ): as indicated by dashed lines in FIG. 1, to move the blade profile 104 of the diffuser blade 103 in the direction perpendicular to the chord C. The movement in the opposite direction of rotation of the impeller is set as positive.

Blade Height (h): height of the diffuser blade, the height being measured from the hub surface. If the hub and shroud surfaces are parallel walls normal to the axis, the blade height is the height in the negative Z direction. If at least one of the hub and shroud surfaces includes a tilted surface, the blade height is the height measured from a line that connects the leading edge and the trailing edge on the hub side of the diffuser blade. The height of an intermediate point in a flow direction between the leading edge and the trailing edge is determined with reference to a line that connects the leading edges on the hub and shroud sides of the diffuser blade and a line that connects the trailing edges on the hub and shroud sides of the diffuser blade. The total height of the blades is represented by H.

Using these definitions, in order to address the above-described problems, the present invention provides a centrifugal turbomachine including: at least one or more impellers attached to an identical rotating shaft and composed of a hub, a shroud, and a plurality of circumferentially spaced apart blades between the hub and the shroud; and a vaned diffuser disposed downstream of at least one of the impellers, wherein: the vaned diffuser includes a plurality of circumferentially spaced apart blades in a flow passage that is formed downstream of the impeller, each of the blades being formed with basic blade profiles stacked in a blade height direction that corresponds to an axial direction of the rotating shaft; and dihedral distribution in which movement in a direction perpendicular to a chord direction connecting leading and trailing edges of each of the basic blade profiles and in an opposite direction of rotation of the impeller is set as positive is made uneven from a hub-side end to an intermediate portion in the blade height direction on a hub wall surface side.

Also in this feature, preferably, the dihedral distribution of each of the diffuser blades is increased from the hub-side end to the intermediate portion in the blade height direction, and, in each of the diffuser blades, an angle between a plane virtually formed at a leading edge portion on the hub-side end and a suction surface of the diffuser blade is an obtuse angle.

Furthermore, preferably, the dihedral distribution increases from a shroud-side end to the intermediate portion in the blade height direction, and, in each of the diffuser blades, an angle between a plane virtually formed at the leading edge portion on the shroud-side end and the suction surface of the diffuser blade is an obtuse angle.

In the above-described feature, the arrangement may be such that the dihedral distribution of each of the diffuser blades decreases from the hub-side end to the intermediate portion in the blade height direction, and sweep distribution in which movement in a direction parallel to the chord direction of the basic blade profiles and in a downstream direction is set as positive is decreased from the hub-side end to the intermediate portion in the blade height direction.

It should be noted that, in any of the above-described features, preferably, at least one of the dihedral distribution and the sweep distribution is applied to at least a first half portion in a flow direction of the diffuser blades.

Advantageous Effects of Invention

According to the present invention, in the vaned diffuser for use in the centrifugal turbomachine, the 3D curvilinear-element blade is applied to the diffuser blade, and the sweep and dihedral distributions are given, thereby reducing the loss due to the collision of the flow with the diffuser blade. Furthermore, because the flow at the intermediate portion of the blade can be controlled, the secondary flow between the blades is effectively suppressed and the diffuser performance and the compressor performance can be improved. Moreover, in the present invention, in this curvilinear-element diffuser for use in the centrifugal compressor, a stacking pattern of divided blades which leads to performance improvement can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating tilting in a vaned diffuser.

FIG. 2 is a view illustrating a 3D blade included in the vaned diffuser.

FIG. 3 is a longitudinal sectional view of one embodiment of a centrifugal turbomachine according to the present invention.

FIG. 4 is a view illustrating the classification of vaned diffusers.

FIG. 5 is a graph illustrating dihedral distribution, according to one embodiment, of the diffuser included in a compressor shown in FIG. 3.

FIG. 6 is a perspective view of the diffuser having the dihedral distribution shown in FIG. 5, and a partially-enlarged view thereof.

FIG. 7 is a graph illustrating dihedral distribution, according to another embodiment, of the diffuser included in the compressor shown in FIG. 3.

FIG. 8 is a perspective view of the diffuser having the dihedral distribution shown in FIG. 7, and a partially-enlarged view thereof.

FIG. 9 is a graph illustrating dihedral and sweep distributions, according to still another embodiment, of the diffuser included in the compressor shown in FIG. 3.

FIG. 10 is a perspective view of the diffuser having the dihedral and sweep distributions shown in FIG. 9, and a partially-enlarged view thereof.

FIG. 11 is an exemplary performance diagram of the centrifugal compressor including the diffuser according to the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, several embodiments of the present invention will be described by using the accompanying drawings. Firstly, a multistage centrifugal compressor 300 serving as an example of a centrifugal turbomachine will be described by using a longitudinal sectional view of FIG. 3. The multistage centrifugal compressor 300 is a two-stage centrifugal compressor. It should be noted that the subject of the present invention is not particularly limited to the two-stage centrifugal compressor, but also can include single-stage or multistage centrifugal turbomachines.

The multistage centrifugal compressor 300 shown in FIG. 3 is the two-stage centrifugal compressor that is composed of a first stage 301 and a second stage 302. A first-stage impeller 308 and a second stage impeller 311 are attached to an identical rotating shaft 303 to constitute a rotating body. The rotating shaft 303 is rotatably supported by a journal bearing 304 and a thrust bearing 305 that are attached to a compressor casing 306 for storing the rotating shaft 303 and the impellers 308 and 311.

Downstream of the first-stage impeller 308, there are disposed a diffuser 309 that recovers the pressure of working gas compressed by the impeller 308 and forms a radially outwardly directed flow, and a return guide vane 310 that directs radially inwardly the radially outward flow of working gas caused by the diffuser 309 and guides it to the second-stage impeller 311. Downstream of the second-stage impeller 311, a diffuser 312 is similarly disposed, and recovery means 313, called a collector or scroll, for gathering and sending out the working gas subjected to pressure rise by the second-stage diffuser 312 is disposed.

The first- and second-stage impellers 308 and 311 have hub-side plates 308a and 311a, shroud-side plates 308b and 311b, and a plurality of blades 308c and 311c arranged circumferentially with almost equal spacing between the core plate 308a and the side plate 308b and between the core plate 311a and the side plate 311b, respectively. Labyrinth seals 315 are disposed at outer peripheral portions of the shroud-side plates 308b and 311b on the entrance sides of the impellers 308 and 311. Also, shaft seals 316 and 317 are disposed at the rear of the hub-side plates 308a and 311a. Working gas flowing from a suction nozzle 307 passes in order through the first-stage impeller 308, the vaned diffuser 309, the return guide vane 310, the second-stage impeller 311, and the vaned diffuser 312, and is guided without leakage to the recovery means 313 such as the collector or scroll.

The diffusers 309 and 312 for use in the centrifugal compressor 300 as constructed in this manner will be described in detail below. It should be noted that the diffuser 309 is attached to a diaphragm constituting a portion of the compressor casing 306 and has a hub 309a with a passage plane located at almost the same axial position as that of the impeller 308 and a plurality of circumferentially-spaced-apart blades 309c provided in a standing manner on the surface of the hub 309a. Furthermore, the wall surface of an inner casing constituting a portion of the compressor casing 306 forms a flow passage as a shroud surface. Although not descried here, the diffuser 312 has the same construction. It should be noted that, although the above construction is described in this embodiment, the construction of the diffuser is not limited thereto. The present invention, of course, also includes the construction being such that the diffuser is separate from the diaphragm.

In FIG. 4, vaned diffusers 400 to be used in the following description are classified and shown. FIG. 4(a) is a cross-sectional view of the diffuser 400. A plurality of diffuser blades 420a arranged circumferentially with almost equal spacing are provided in a standing manner on a hub plate 410a. The flow from the impeller, which is not shown, is guided so as to flow along the diffuser blades 420a from the inner periphery as indicated by arrow FL in the drawing. At this time, the impeller, not shown, rotates in the direction of arrow R_N.

The shapes of the diffuser are classified into: a 2D diffuser which has conventionally been employed (FIG. 4(b)); a 3D straight-line element diffuser having a lean (FIG. 4 (c)); and a 3D curvilinear-element diffuser also having a lean and represented by a set of curvilinear elements (FIG. 4(d)). Here, diffuser blades 420b to 420d are represented as a shape with linear elements 423b to 423d connecting the contours of hub-plate-side sections 421b to 421d and shroud-side sections 422b to 422d. The same flow is discharged from the impeller to the diffuser blades 420b to 420d to form a diffuser entry flow 402.

The 2D straight-line element diffuser blade 420b shown in FIG. 4 (b) is a 2D diffuser that is formed of the straight-line element 423b, not tilted, with the same blade profiles stacked straight in a height direction of the blade 420b. That is, the straight-line element 423b is perpendicular to the hub plate 410a. In the diffuser having this blade 420b, it is impossible to prevent the flow from colliding with the blade 420b in all positions in the height direction (h direction) of a leading edge of the blade 420b when the inlet flow 402 is distributed, and there is a limit to the improvement in performance.

In the 3D straight-line element diffuser shown FIG. 4 (c), a twist is added to the diffuser blade 420c by varying the stagger angle (θ_SG). This allows the flow from the impeller to flow into the diffuser blade 420c without colliding with the diffuser blade 420c. That is, even if an uneven flow is discharged from the impeller, the shape at a leading edge portion of the diffuser blade 420c can be changed according to the inlet flow 402.

In this 3D straight-line element diffuser blade 420c, the linear element 423c connecting the contours of the hub-plate-side section 421c and the shroud-side section 422c is a straight line, and the lean distribution in the height direction (h direction) of the blade 420c also has a linear design. However, the linear element 423c is not necessarily perpendicular to the hub plate 410a. After entry of the flow between the blades 420c and 420c, the lean angle cannot be changed to a value corresponding to a flow angle because the blade 420c is formed, for example, in a basic NACA airfoil shape. Therefore, although a greater improvement in efficiency than the 2D diffuser can be expected, sufficient flow control is difficult.

In the 3D curvilinear-element diffuser shown FIG. 4 (d), the blade profiles are stacked along the optional curvilinear element 423d. In other words, the curvilinear element 423d connecting the contours of the hub-plate-side section 421d and the shroud-side section 422d is a curve line. In this diffuser, the lean angle is varied, rather than being constant, in the height direction (h direction) of the blade 420d. Thus, with the 3D curvilinear-element diffuser, it is possible to not merely realize a collision-free inflow at a leading edge portion of the blade 420d but also change the direction of action of blade force by bending a passage plane of the blade 420d.

Therefore, the flow in a flow passage between the blades 420d and 420d can be controlled. Therefore, in the present invention, as shown in FIG. 3, the diffusers 309 and 312 that recover the dynamic pressure at exits of the impellers 308 and 311 as static pressure are made 3D curvilinear-element diffusers.

Meanwhile, although there are various methods for making the diffuser being three dimensional, the diffuser can be systematically made three dimensional by using the above-described dihedral and sweep. Therefore, a specific example of the 3D curvilinear-element diffuser represented using the dihedral and sweep will be described by using FIGS. 5 to 11. In the following description, the first stage diffuser 309 is used as an example. However, the second and subsequent stage diffusers are also used in the same manner.

One embodiment of the 3D curvilinear-element diffuser will be described by using FIGS. 5 and 6. Only the dihedral distribution is shown. FIG. 5 is a graph illustrating dihedral distribution in a blade height direction (h direction) of a blade 620, in which the amount of dihedral (Δδ) is made dimensionless with the chord length (C) and the blade height is made dimensionless with the total height H. FIG. 6 is a perspective view of a diffuser 600 having the dihedral distribution of FIG. 5, in which FIG. 6(a) is a general perspective view; FIG. 6(b) is a detail view of portion C in FIG. 6(a); and FIG. 6(c) is a detail view of portion D in FIG. 6(a). A diffuser plate 610 is attached to the hub side of the impeller.

As shown in FIG. 5, in this embodiment, the dihedral increases in the blade height direction in the vicinity of a hub-side end face (h=0) (see a portion 501 surrounded by a circle). That is, a suction surface 601 of the diffuser blade 620 forms an obtuse angle with a hub surface 603. It should be noted that the suction surface 601 of the diffuser blade 620 corresponds to the blade surface that is located to the rear with respect to the direction of rotation of the impeller.

Studies by the inventors of the present invention showed that, in the dihedral distribution shown in FIG. 5, the influence of the dihedral or sweep distribution on performance was generally small in a portion other than the portion 501 surrounded by a circle, that is, the portion 501 in the vicinity of the hub-side end face. Therefore, the dihedral and sweep distributions can be set in the portion other than the portion 501 in the vicinity of the hub-side end face in consideration of the workability or handleability of the blades 309c.

As shown in FIG. 6(b), in the diffuser 600 of this embodiment, a blade force component 602 is generated in the blade height direction. The blade force component 602 has the effect of forcing back the secondary flow because a boundary layer on the hub surface 603 is located in the opposite direction of the secondary flow that tends to migrate toward the hub-side suction surface 601. Thus, according to this embodiment, the secondary flow is suppressed, leading uniform distribution of the flow between the blades and an improvement in diffuser performance.

Another embodiment of the present invention will be described by using FIGS. 7 and 8. These drawings are the same as those of the above-described embodiment. FIG. 7 is a graph of dihedral distribution, and FIG. 8 is a perspective view of a diffuser 800 having the dihedral distribution shown in FIG. 7. FIG. 8(a) is a general perspective view of the diffuser 800; FIG. 8(b) is a detail view of portion E in FIG. 8(a); and FIG. 8(c) is a detail view of portion F in FIG. 8(a). Also in the diffuser 800, a diffuser plate 810 is attached to the hub side of the impeller. This embodiment differs from the above-described embodiment in that the dihedral is reduced in the blade height direction in the vicinity of a shroud-side end face (a portion 702 surrounded by a circle).

Although in the above-described embodiment, the influence of the dihedral distribution is greater on the hub-surface side, it has turned out that the dihedral distribution on the shroud-surface side also exerts an influence upon the diffuser according to the flow from the impeller. It should be noted that, even in this case, the dihedral distribution on the shroud side should be the same as the above-described embodiment. A specific example thereof will be described below.

On the hub-side end face, the amount of dihedral (Δδ) is increased in the blade height direction (h direction) in the same manner as the above-described embodiment (see a portion 701 surrounded by a circle). Also in this embodiment, the influence of the dihedral or sweep distribution on performance is small in a center region in the blade height direction other than the two regions in the vicinity of the hub-side end face and the shroud-side end face. That is, in the vicinity of the hub-side and shroud-side end faces, the angle that suction surfaces 801 and 802 of a diffuser blade 820 form with the hub and shroud end faces is an obtuse angle. Therefore, the secondary flow can be suppressed by the same working effects as the above-described embodiment.

It should be noted that the distribution shown in FIG. 7 is preferably used if the flow at the exit of the impeller is relatively uniform, while the distribution shown in FIG. 5 is preferably used if the nonuniformity is high. This is because the diffuser blade 820 is affected by the uniformity or nonuniformity of the flow at the exit of the impeller. That is, if the nonuniformity of the flow at the exit of the impeller is high, a high-energy portion of the flow is controlled by focusing on the flow control on the hub-surface side on where the mainstream exists, and consequently the overall flow can be effectively controlled.

Still another embodiment of the present invention will be described by using FIGS. 9 and 10. FIG. 9(a) is a graph of dihedral distribution, and FIG. 9(b) is a graph of sweep distribution which is made dimensionless with the chord length. FIG. 10 is a perspective view of the diffuser 309 having the distributions shown in FIG. 9, in which FIG. 10(a) is a general view of the diffuser; FIG. 10(b) is a detail view of portion G in FIG. 9(a); and FIG. 10(c) is a detail view of portion H in FIG. 9(a). In the same manner as the above-described embodiments, a diffuser plate 1010 is attached to the hub side of the impeller.

In the above-described two embodiments, the dihedral distribution on the hub side is important, and the increase in dihedral in the blade height direction is effective from the viewpoint of flow control. However, it has turned out that the combination of dihedral and sweep provides benefits even when the dihedral is reduced in the blade height direction. A specific example thereof will be described below.

As shown in FIG. 9, in this embodiment, the dihedral is reduced in the blade height direction in the vicinity of the hub-side end face (see a portion 901 surrounded by a circle), and furthermore, the sweep is reduced similarly in the vicinity of the hub-side end face (see a portion 902 surrounded by a circle). That is, the diffuser has a lean with the dihedral and sweep combined and is a diffuser 1000 in which the 3D curvilinear-element is used. Because the effects on performance are small in a region other than the vicinity of the hub-side end face, both dihedral and sweep can be arbitrarily set, as long as an extreme change is not caused.

In this embodiment, the direction of the dihedral on the hub-side end face is the reverse of those of the above-described embodiments. As a result, the angle formed by a diffuser suction surface 1001 and the surface of a hub plate 1010 is an acute angle, and a blade force opposite in direction to the blade force component 602 shown in FIG. 6 is generated. This reversed blade force appears to increase the secondary flow, but actually serves to suppress the secondary flow. The reason is as follows.

In this embodiment, a diffuser blade 1020 is composed of a combination of dihedral and sweep. Because the diffuser blade 1020 has a sweep 1002, a notch-shaped gap 1003 is formed between a leading edge 1005 of the diffuser blade 1020 and the surface of the hub plate 1010. In the notch-shaped gap 1003, a flow that tends to migrate from the pressure surface to the suction surface of the diffuser blade 1020 occurs, thereby generating a longitudinal vortex 1004. Vorticity 1006 to suppress the secondary flow is generated in a corner formed by the suction surface of the diffuser blade 1020 and the surface of the hub plate 1010. At the same time, separation on the blade surface in the diffuser blade 1020 is suppressed by the promotion of agitation with the surrounding fluid or the negative pressure effect of the vortex center. In this manner, the secondary flow is suppressed by the action of the longitudinal vortex, and the flow field is made uniform, thereby improving the performance of the 3D curvilinear-element diffuser.

FIG. 11 shows a state in which the compressor performance is improved when the 3D curvilinear-element diffuser shown in this embodiment is used in place of the 2D straight-line element diffuser in a compressor. The horizontal axis of the graph represents flow rate Q made dimensionless with design point flow rate Qdes, and the vertical axis represents: adiabatic efficiency η of the compressor stage made dimensionless with adiabatic efficiency η_2DIM in the 2D diffuser; and pressure coefficient ψ made dimensionless with pressure coefficient ψ_2DIM in the 2D diffuser.

The adiabatic efficiency η and the pressure coefficient ψ are improved over a wide flow range, not to mention the design flow rate. Also, the vaned diffuser according to the present invention is superior in performance at an off design point (Q≠ 1.0) because the amount of performance improvement increases with distance from the design point flow rate (Q=1.0). That is, the compressor operating range is improved.

In the above-described embodiments, the diffuser blade has at least one of sweep distribution and dihedral distribution, thereby realizing the 3D curvilinear-element diffuser. Furthermore, the secondary flow in the vicinity of a hub wall surface and a shroud wall surface of the diffuser and the impinging flow near the leading edge of the diffuser blade are controlled by inclining the diffuser blades. As a result, the diffuser performance can be improved. It should be noted that the sweep and dihedral distributions shown in the above-described embodiments are just an example and, also in the region that is not limited in shape because the influence on performance is small, the sweep and dihedral distributions are illustrative only.

Furthermore, although preferably, the entire blades have the shape feature shown in the embodiments, the advantages of the present invention can be obtained even if the blades have the above-described shape especially only in a first half portion in the flow direction of the diffuser because the shapes in the first half portion (upstream) of the diffuser blades have a relatively great influence on performance. Therefore, the 2D straight-line element diffuser or the like, which has been conventionally frequently employed, may be used for a latter half portion in the flow direction.

Although in the above-described embodiments, the diffuser blades are provided on the hub plate, the diffuser blades may be of course provided on the surface thereof facing the hub plate, that is, the plate on the shroud-surface side. In any case, the diffuser blades are mounted on the hub or shroud side for ease of assembly, etc. Further, there is no need for the multistage compressor to be entirely provided with vaned diffusers. Even if a vaned diffuser is provided on at least one stage of the compressor and the present invention is applied to the diffuser, the advantages of the present invention can be obtained.

REFERENCE SINGS LIST

• 101 Hub
• 102 Shroud
• 103 Diffuser blade
• 104 Blade profile
• 105 Diffuser plate
• 208 Leading edge
• 209 Trailing edge
• 300 Centrifugal turbomachine (multistage centrifugal compressor)
• 301 First stage
• 302 Second stage
• 303 Rotating shaft
• 304 Journal bearing
• 305 Thrust bearing
• 306 Compressor casing
• 307 Suction nozzle
• 308 First-stage impeller
• 308a Hub-side plate
• 308b Shroud-side plate
• 308c Blade
• 309 Vaned diffuser
• 309a Hub
• 309c Blade
• 310 Return guide vane
• 311 Second-stage impeller
• 311a Hub-side plate
• 311b Shroud-side plate
• 311c Blade
• 312 Vaned diffuser
• 313 Recovery means (scroll or collector)
• 315 Labyrinth seal
• 316, 317 Shaft seal
• 400 Vaned diffuser
• 401 Straight-line element
• 402 Inlet flow
• 403 Hub-side blade section
• 404 Shroud-side blade section
• 405 Straight-line element
• 407 Hub-side blade section
• 408 Shroud-side blade section
• 409 Curvilinear element
• 410 Hub plate
• 411 Hub-side blade section
• 412 Shroud-side blade section
• 420a to 420d Diffuser blade
• 421b to 421d Hub surface
• 422b to 422d Shroud surface
• 423b to 423d Linear element
• 501 Dihedral distribution
• 600 Vaned diffuser
• 601 Hub-side suction surface
• 602 Blade force component
• 603 Hub surface
• 610 Hub plate
• 620 Blade
• 701 Dihedral distribution
• 702 Dihedral distribution
• 800 Vaned diffuser
• 801 Hub-side suction surface
• 802 Shroud-side suction surface
• 810 Hub surface
• 820 Blade
• 901 Dihedral distribution
• 902 Sweep distribution
• 1000 Vaned diffuser
• 1001 Hub-side suction surface
• 1002 Sweep
• 1003 Notch
• 1004 Longitudinal vortex
• 1005 Diffuser leading edge
• 1006 Vorticity
• 1010 Hub plate
• 1020 Blade
• C Chord
• FL Inlet flow
• h Height of diffuser blade
• H Total height of diffuser blades
• R_N Direction of rotation of impeller
• Δδ Amount of dihedral
• Δσ Amount of sweep
• Q Flow rate
• Qdes Design point flow rate
• η Adiabatic efficiency
• η_2DIM Efficiency of 2D blade diffuser
• ψ Pressure coefficient
• ψ_2DIM Pressure coefficient of 2D blade diffuser

Claims

1. A centrifugal turbomachine comprising: at least one or more impellers attached to an identical rotating shaft and composed of a hub, a shroud, and a plurality of circumferentially spaced apart blades between the hub and the shroud; and a vaned diffuser disposed downstream of at least one of the impellers,

wherein: the vaned diffuser includes a plurality of circumferentially spaced apart blades in a flow passage that is formed downstream of the impeller, each of the blades being formed with basic blade profiles stacked in a blade height direction that corresponds to an axial direction of the rotating shaft; and

dihedral distribution in which movement in a direction perpendicular to a chord direction connecting leading and trailing edges of each of the basic blade profiles and in an opposite direction of rotation of the impeller is set as positive is made uneven from a hub-side end to an intermediate portion in the blade height direction on a hub wall surface side.

2. The centrifugal turbomachine according to claim 1, wherein the dihedral distribution of each of the diffuser blades is increased from the hub-side end to the intermediate portion in the blade height direction.

3. The centrifugal turbomachine according to claim 2, wherein, in each of the diffuser blades, an angle between a plane virtually formed at a leading edge portion on the hub-side end and a suction surface of the diffuser blade is an obtuse angle.

4. The centrifugal turbomachine according to claim 3, wherein the dihedral distribution increases from a shroud-side end to the intermediate portion in the blade height direction and from the hub-side end to the intermediate portion in the blade height direction.

5. The centrifugal turbomachine according to claim 4, wherein, in each of the diffuser blades, angles between a plane virtually formed at the leading edge portion on the shroud-side end and the suction surface of the diffuser blade and between a hub plate and the suction surface of the diffuser blade are each an obtuse angle.

6. The centrifugal turbomachine according to claim 1, wherein the dihedral distribution of each of the diffuser blades decreases from the hub-side end to the intermediate portion in the blade height direction, and sweep distribution in which movement in a direction parallel to the chord direction of the basic blade profiles and in a downstream direction is set as positive is decreased from the hub-side end to the intermediate portion in the blade height direction.

7. The centrifugal turbomachine according to claim 1, wherein at least one of the dihedral distribution and the sweep distribution is applied to at least a first half portion in a flow direction of the diffuser blades.

8. The centrifugal turbomachine according to claim 2, wherein at least one of the dihedral distribution and the sweep distribution is applied to at least a first half portion in a flow direction of the diffuser blades.

9. The centrifugal turbomachine according to claim 3, wherein at least one of the dihedral distribution and the sweep distribution is applied to at least a first half portion in a flow direction of the diffuser blades.

10. The centrifugal turbomachine according to claim 4, wherein at least one of the dihedral distribution and the sweep distribution is applied to at least a first half portion in a flow direction of the diffuser blades.

11. The centrifugal turbomachine according to claim 5, wherein at least one of the dihedral distribution and the sweep distribution is applied to at least a first half portion in a flow direction of the diffuser blades.

12. The centrifugal turbomachine according to claim 6, wherein at least one of the dihedral distribution and the sweep distribution is applied to at least a first half portion in a flow direction of the diffuser blades.