Impeller and centrifugal compressor

Abstract

The impeller has a hub in a disc shape centered on an axis, and a plurality of blades projecting from a surface of the hub on a side in the direction of the axis and arranged in the circumferential direction. When a cross section including a blade height direction, which is a direction away from the hub toward a blade tip side, of the blade is observed, the blade is formed with a concave surface curved in a manner of projecting toward a rear side in a rotation direction. In a case where a distance in a direction orthogonal to an imaginary line connecting an end edge of the blade tip side and an end edge of the hub side, which are observed from the cross section, and a middle span of the blade is defined as a recess amount, the blade has a portion in which the recess amount increases from a leading edge side to a trailing edge side.

Description

TECHNICAL FIELD

[0001] The present specification relates to an impeller and a centrifugal compressor.

[0002] This application claims priority based on Japanese Patent Application No. 2020-076704 filed on April 23, 2020 with the Japan Patent Office, and the content thereof is incorporated herein. BACKGROUND

[0003] An impeller for a centrifugal compressor has a hub in a disc shape and a plurality of blades provided to a face of the hub on one side.

[0004] In the above-described impeller, in the case where a high pressure ratio is sought, there has conventionally been a method of increasing a circumferential component of an absolute flow velocity at an outlet by reducing a back rake angle of the blade. The back rake angle refers to an angle formed by a tangent line at a trailing edge of the blade with respect to a radial direction of the rotation axis. As a specific example of an impeller having such a shape, there is known the structure described in Patent Literature 1.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: Japanese Patent Application Publication No. 2014-109193

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] However, in the above-described impeller having such a shape, the blade load from the hub to the tip of the blade becomes large uniformly, and thus losses due to a two-dimensional flow caused by a pressure gradient inside the impeller, a flow structure due to a leakage vortex at the end of the blade, and the like become large. Therefore, it is possible to incur a decrease in efficiency and a reduction in a stable operating region. SUMMARY

[0010] The present application has been achieved in order to solve the above-described technical problem, and has an object to provide an impeller and a centrifugal compressor that are high in pressure ratio and high in efficiency.

[0011] TECHNICAL MEANS FOR SOLVING THE PROBLEMS

[0012] In order to solve the above-described technical problem, the impeller according to the present application has a hub in a disc shape centered on an axis, and a plurality of blades that project from a face of the hub on one side toward the axis direction and are arranged in a circumferential direction, and when viewed from a cross section including a blade height direction that is a direction away from the hub toward a tip side of the blade, a concave surface that is curved in a manner of projecting toward a rear side in a rotation direction is formed in the blade, and the blade has a portion in which a curvature of the concave surface increases from a leading edge side to a trailing edge side.

[0013] Effects of the Invention

[0014] According to the present application, a high pressure ratio and high efficiency impeller and centrifugal compressor can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a sectional view showing the configuration of a centrifugal compressor to which the embodiment of the present application relates.

[0016] Figure 2 is a perspective view showing the configuration of an impeller to which the embodiment of the present application relates.

[0017] Figure 3 is a meridian view showing the configuration of an impeller to which the embodiment of the present application relates.

[0018] Figure 4 is a graph showing the blade angle distribution of an impeller to which the embodiment of the present application relates.

[0019] Figure 5A is a graph showing the shape in the blade height direction of a full blade to which the embodiment of the present application relates.

[0020] Figure 5B is a graph showing the shape in the blade height direction of a full blade to which the embodiment of the present application relates.

[0021] Figure 6 is a graph for defining the blade angle of a blade to which the embodiment of the present application relates.

[0022] Figure 7 is an explanatory view showing the relationship between the blade angle of a full blade and the camber line to which the embodiment of the present application relates.

[0023] Figure 8 is an explanatory view showing the state of the two-dimensional flow of an impeller to which the embodiment of the present application relates.

[0024] SYMBOL EXPLANATION

[0025] 100 centrifugal compressor

[0026] 1 impeller

[0027] 2 hub

[0028] 3 inlet portion

[0029] 4 outlet portion

[0030] 5 full blade

[0031] 5a leading edge

[0032] 5b trailing edge

[0033] 5c hub side edge

[0034] 5d leaf tip lateral margin

[0035] 5m mid-span

[0036] 6 flow path

[0037] 7 splitter blades

[0038] 10 Rotation axis

[0039] 30. Housing

[0040] 40 Diffusion Blades

[0041] Ac axis

[0042] F outlet flow path

[0043] F1 Diffusion Flow Path

[0044] F2 Exit Vortex

[0045] P compression flow path

[0046] R is a concave surface. Detailed Implementation

[0047] (Composition of a centrifugal compressor)

[0048] The following is for reference Figures 1 to 8 The centrifugal compressor 100 according to an embodiment of the present invention will be described. For example... Figure 1 As shown, the centrifugal compressor 100 includes a rotating shaft 10, an impeller 1, a housing 30, and a diffuser blade 40. Furthermore, in this invention, the diffuser blade 40 is not a necessary structure; this invention can also be applied to centrifugal compressors that do not have a diffuser blade.

[0049] The rotating shaft 10 extends along axis Ac and is rotatable about axis Ac. An impeller 1 is fixed to the outer circumferential surface of the rotating shaft 10. The impeller 1 has a hub 2 and multiple blades 5 and 7 (full blades 5 and splitting blades 7).

[0050] The hub 2 is a disc shaped centering on the axis Ac. The outer circumferential surface of the hub 2 is a curved surface that curves radially from the inside to the outside as it moves from one side toward the other along the axis Ac.

[0051] like Figure 2 As shown, the full blade 5 is a long blade that extends from the fluid inlet 3 to the outlet 4 on the circumferential surface of the hub 2. The diverting blade 7 is a short blade that extends from the downstream side of the leading edge 5a of the full blade 5 to the outlet 4 in each flow path 6 between adjacent full blades 5 on the circumferential surface of the hub 2. Furthermore, Figure 2 The arrow (symbol N) in the diagram indicates the direction of rotation of impeller 1.

[0052] like Figure 3 As shown, the full blade 5 has a leading edge 5a as the edge on the side of the inlet portion 3, a trailing edge 5b as the edge on the side of the outlet portion 4, a hub side edge 5c as the edge on the side connected to the hub 2, and a blade tip edge 5d as the edge opposite to the hub side edge 5c. The splitter blade 7 has a leading edge 7a as the edge on the side of the inlet portion 3, a trailing edge 7b as the edge on the side of the outlet portion 4, a hub side edge 7c as the edge on the side connected to the hub 2, and a blade tip edge 7d as the edge opposite to the hub side edge 7c. The blade tip edges 5d and 7d face the inner wall surface of the housing (not shown) and form a gap (hereinafter referred to as "gap") between them and the inner wall surface of the housing. The detailed configuration of the full blade 5 will be described later.

[0053] The housing 30 surrounds the rotating shafts 10 and the impeller 1 from the outer periphery. Inside the housing 30, a compression flow path P and an outlet flow path F are formed. The compression flow path P houses the impeller 1 and compresses the fluid introduced from the outside. The outlet flow path F is connected to the radially outer side of the compression flow path P.

[0054] The compression flow path P and the impeller 1 have correspondingly increased diameters as they move from one side of the axis Ac towards the other. The outlet of the compression flow path P on its radially outer side is connected to the outlet flow path F.

[0055] The outlet flow path F has a diffusion flow path F1 and an outlet vortex F2. The diffusion flow path F1 is configured to restore the static pressure of the fluid introduced from the compression flow path P. The diffusion flow path F1 is annular, extending radially outward from the outlet of the compression flow path P. When viewed from a cross-section including the axis Ac, the width of the diffusion flow path F1 is constant throughout the entire extension direction. Multiple diffusion blades 40 may also be provided in the diffusion flow path F1.

[0056] The radially outer outlet of the diffusion path F1 is connected to the outlet vortex F2. The outlet vortex F2 is a vortex extending circumferentially along the axis Ac. The outlet vortex F2 has a circular flow path cross-section. A vent hole (not shown) for guiding the high-pressure fluid to the outside is provided in a portion of the outlet vortex F2.

[0057] (Composition of the entire leaf)

[0058] Figure 4 This represents the distribution of the hub side edge 5c and the tip side edge 5d of the entire blade 5 from the leading edge 5a to the trailing edge 5b at the blade angle. Figure 4The axis of the ratio m of the length in the meridional length direction of the full blade 5 from the leading edge 5a of the full blade 5 to the length in the meridional length direction of the full blade 5. According to the definition of m, the position of the leading edge 5a is m = 0, and the position of the trailing edge 5b, 7b is m = 1. In addition, the same value of m means the same position when the impeller 1 is viewed in the meridional direction. Figure 4 The solid line in FIG. 6 indicates the blade angle distribution of the tip side edge 5d, the broken line indicates the blade angle distribution of the hub side edge 5c, and the one-dot chain line indicates the blade angle distribution of the midspan 5m between these tip side edge 5d and hub side edge 5c. Here, in a case where the position of the hub side edge 5c in the blade height direction of the blade is set as the 0% span position, and the position of the tip side edge 5d is set as the 100% span position, Figure 4 The position of the midspan 5m in FIG. 6 is the 50% span position (the intermediate position of the tip side edge 5d and the hub side edge 5c). However, the position of the midspan 5m in the present application is not limited to the 50% span position. The position of the midspan 5m can be set as an arbitrary span position within the range of 30 to 70% span position, thereby defining the position of the concave surface R described later.

[0059] Figure 6 FIG. 7 is a planar developed view of the blade 5 at an arbitrary span position from the inlet portion 3 to the outlet portion 4 in the meridional length direction. In the developed view, the vertical axis indicates the rotational direction of the blade 5, and the horizontal axis indicates the meridional length direction. In this plane, the angle β of the blade (full blade 5 or splitter blade 7) with respect to the meridional length direction is defined as the blade angle. That is, the blade angle β at the position of the trailing edge of the blade (the back rake angle) refers to the angle of the tangent line of the blade surface at the trailing edge position of the blade with respect to the meridional length direction. In addition, with reference to FIG. 8, the blade angle β at the position of the leading edge of the blade (the front rake angle) refers to the angle of the tangent line of the blade surface at the leading edge position of the blade with respect to the meridional length direction. Figure 7 In a coordinate system represented by the axial direction z, the radial direction R, and the rotational angle θ around the axis, the blade angle β of a small interval between the coordinate point 1 and the coordinate point 2 is defined by the following formula (1).

[0060] tan β = R2 · dθ / dm... (1)

[0061] Here, dθ = θ2 - θ1, S is the pitch line.

[0062] In Figure 4In the illustrated embodiment, in the full blade 5, on the side of the leading edge 5a, the blade angle βt of the tip side edge 5d is the largest, and the blade angle βm of the midspan 5m is next larger. Also, on the side of the leading edge 5a, the blade angle βh of the hub side edge 5c is the smallest (βt > βm > βh). On the other hand, as the side of the leading edge 5a is approached toward the side of the trailing edge 5b, the blade angle distribution changes. Specifically, on the side of the trailing edge 5b, the blade angle βh of the hub side edge 5c is the largest, and the blade angle βt of the tip side edge 5d is next larger. Also, on the side of the trailing edge 5b, the blade angle βm of the midspan 5m is the smallest (βh > βt > βm).

[0063] In addition, in an embodiment not shown, on the side of the trailing edge 5b, the blade angle βt of the tip side edge 5d can also be the largest. In addition, the blade angle βt of the tip side edge 5d and the blade angle βh of the hub side edge 5c can also be the same size. In this case, on the side of the trailing edge 5b, the blade angle βm of the midspan 5m is also the smallest (βt > βh > βm).

[0064] Figure 5A 、 Figure 5B is a graph showing the shape of the blade in the blade height direction of the blade involved in the embodiment of the present application. Here, Figure 5A 、 Figure 5B shows the shape of the full blade (blade thick center line) at the portion of 40 to 100% from the leading edge (m = 0.4 to 1.0), Figure 5A is located on the side of the leading edge 5a compared to Figure 5B .

[0065] That is, as shown in Figure 2 and Figure 5A 、 Figure 5B , Figure 4 the blade angle distribution means that, in the full blade 5 involved in the present embodiment, when viewed from a cross section including the blade height direction that is a direction away from the hub 2 toward the tip side, a concave surface R is formed that curves in a manner that protrudes toward the rear side in the rotation direction N.

[0066] In addition, in a case where the distance in the direction orthogonal to the above-mentioned imaginary line IL that links the tip side edge 5d and the hub side end edge 5c of the full blade 5 when viewed from the above-mentioned cross section and the above-mentioned midspan is defined as the amount of recess d, the full blade 5 has a portion where the amount of recess d increases from the leading edge 5a side to the trailing edge 5b side (d2 > dl). Figure 5B The amount of recess d2 at the midspan 5m in Figure 5A is larger than the amount of recess dl at the midspan 5m in .

[0067] In addition, it is understood from Figure 4 that the full blade 5 has a portion where the curvature of the concave surface R increases from the leading edge 5a side to the trailing edge 5b side. Figure 5BThe curvature of the concave surface R at the mid-span 5m is greater than Figure 5A The curvature of the concave surface R at the mid-span of 5m. Here, the curvature of the concave surface R is defined as the reciprocal of the radius of curvature of the smallest imaginary circle that intersects the concave surface R at at least two points.

[0068] The concave surface R is preferably formed in at least a portion of the entire blade 5, specifically in the 40-100% portion (m = 0.4-1.0) from the leading edge 5a side. Furthermore, the concave surface R is preferably formed in at least 60% of the portion (m = 0.6) from the leading edge 5a where the two-dimensional flow over the blade surface is particularly strong. Additionally, the portion of the concave surface R with the greatest curvature is preferably formed in the 60-70% portion (m = 0.6-0.7) from the leading edge 5a side of the entire blade 5.

[0069] In the full blade 5 of this embodiment, as described above, at the trailing edge 5b of the full blade 5, the blade angle βm of the middle span 5m is smaller than the blade angle βh on the hub side and the blade angle βt on the tip side.

[0070] In addition, such as Figure 4 As shown, in the full blade 5 of this embodiment, when the smaller of the blade angle βh on the hub side and the blade angle βt on the tip side at the trailing edge 5b of the full blade 5 (min(βh, βt)) is defined as dβ, and the blade angle βm at the mid-span 5m is defined as Δβ, the absolute value of the difference between the blade angle βh on the hub side and the blade angle βt on the tip side (|βh-βt|) is defined as Δβ, dβ > Δβ. Preferably, the relationship dβ > Δβ + 2° is satisfied. More preferably, the relationship dβ > Δβ + 5° is satisfied.

[0071] (Effects)

[0072] According to the above configuration, a concave surface R is formed on the entire blade 5, curving in a manner that protrudes towards the rearward side in the direction of rotation. Furthermore, the amount of concavity d of this concave surface R on the entire blade 5 increases from the leading edge 5a side to the trailing edge 5b side (d2 > d1). Figure 8 As shown, when the fluid flows along the entire blade 5, the flow is actively introduced towards the concave surface R. Thus, the two-dimensional flow is captured by the concave surface R and guided towards the trailing edge 5b rather than the tip edge 5d. Figure 8 (Solid line in the diagram). On the other hand, without the aforementioned concave surface R, as shown by the dashed arrow, the two-dimensional flow moves from the leading edge 5a towards the tip edge 5d due to centrifugal force. This results in increased losses. On the other hand, according to this embodiment, the losses caused by such a two-dimensional flow can be reduced. Therefore, according to the above configuration, the compression ratio of the impeller 1 can be increased accordingly to the amount by which dβ is greater than Δβ.

[0073] Here, the above-described two-dimensional flow is known to easily occur in a portion of 40 to 100% from the leading edge side of the blade, particularly, a portion of about 60% from the leading edge side. According to the above-described configuration, by forming the concave surface in the portion where the two-dimensional flow easily occurs, the two-dimensional flow can be more actively reduced.

[0074] According to the above-described configuration, at the position of the trailing edge 5b of the entire blade 5, the blade angle βm of the midspan 5m at the midspan 5m is smaller than the blade angle βh of the hub side and the blade angle βt of the tip side. In addition, as described above, the relation of dβ > Δβ is satisfied. It is preferable that the relation of dβ > Δβ + 2° is satisfied. It is more preferable that the relation of dβ > Δβ + 5° is satisfied.

[0075] Therefore, the compression ratio of the impeller 1 can be increased in accordance with the amount by which dβ is larger than Δβ.

[0076] (Other Embodiments)

[0077] The embodiments of the present application are described in detail above with reference to the drawings, but the specific configuration is not limited to the embodiments, and variations involving changes within a range not departing from the gist of the present application are also included. For example, in the above-described embodiments, the case where the above-described concave surface R is formed in the entire blade 5 is exemplified, but such a concave surface R can also be formed in the splitter blade 7.

[0078] <Notes>

[0079] The impeller 1 and the centrifugal compressor 100 described in each of the embodiments can be grasped as described below, for example.

[0080] (1) The impeller 1 according to a first aspect includes: a hub 2 that is disc-shaped and that is centered on an axis Ac; and a plurality of blades 5 that project from a surface of the hub 2 on a side facing the axis Ac direction and that are arranged in a circumferential direction, in which, when viewed in a cross section of the blade 5 including a blade height direction that is a direction away from the hub 2 toward a tip side, a concave surface R that curves in a manner projecting toward a rear side in a rotation direction is formed in the blade 5, and in a case where a distance in a direction orthogonal to an imaginary line IL connecting an end edge 5d of the tip side and an end edge 5c of the hub side of the blade 5 with the blade 5 at the midspan 5m is defined as a recess amount d, the blade 5 has a portion in which the recess amount d increases from a leading edge side to a trailing edge side.

[0081] According to the above configuration, the concave surface R is formed in the blade 5 so as to be curved in a manner of protruding toward the rear side in the rotation direction. Further, the portion in which the recessed amount d increases from the leading edge 5a side to the trailing edge 5b side is formed in the blade 5. In the case where the fluid flows along the entire blade 5, the flow is actively introduced toward the concave surface R. Thus, the secondary flow is captured by the concave surface R and is guided toward the trailing edge 5b side rather than the tip side edge 5d. Therefore, it is possible to reduce the loss due to the secondary flow, and thus, it is possible to increase the compression ratio of the impeller 1.

[0082] (2) In the impeller 1 according to the second aspect, the portion in which the recessed amount d increases is configured so that the curvature of the concave surface R increases from the leading edge side to the trailing edge side.

[0083] According to the above configuration, in the portion in which the recessed amount d increases, the curvature of the concave surface R is configured to increase from the leading edge side to the trailing edge side. Thus, it is possible to more effectively reduce the loss due to the secondary flow, and it is possible to increase the compression ratio of the impeller 1.

[0084] (3) In the impeller 1 according to the third aspect, at the position of the trailing edge 5b of the blade 5, the blade angle βm at the midspan 5m between the hub side end edge 5c and the tip side end edge 5d of the blade 5 is smaller than the blade angle βh at the hub side and the blade angle βt at the tip side.

[0085] According to the above configuration, by making the dihedral angle (blade angle at the trailing edge) at the midspan 5m smaller than the hub 2, the shroud, and the like, it is possible to increase the pressure ratio while changing the load around the wall surface of the hub 2, the shroud, and the like, which are deeply associated with the secondary flow and the leakage flow, as little as possible (while suppressing the pressure loss due to the flow structure as much as possible).

[0086] (4) In the impeller 1 according to the fourth aspect, the concave surface R is formed in a portion of the blade 5 from the leading edge side by 40 to 100%.

[0087] Here, it is known that the above-described secondary flow is particularly likely to occur in a portion of the blade 5 from the leading edge 5b side by 40 to 100%. According to the above configuration, by forming the concave surface R in the portion in which the secondary flow is likely to occur, it is possible to more actively reduce the secondary flow.

[0088] (5) In the impeller 1 according to the fifth aspect, in the third aspect described above, in a case where a difference between the smaller one of the blade angle βh at the hub side and the blade angle βt at the tip side at the position of the trailing edge 5a of the blade 5 and the blade angle βm at the midspan is defined as dβ, and an absolute value of the difference between the blade angle βh at the hub side and the blade angle βt at the tip side is defined as Δβ, the relationship of dβ > Δβ is satisfied.

[0089] According to the above configuration, it is possible to increase the effect described in the third aspect described above.

[0090] (6) In the impeller 1 according to the sixth aspect, in the fifth aspect described above, the relationship dβ > Δβ + 2° is satisfied.

[0091] According to the above configuration, the effect described in the third aspect above can be further improved.

[0092] (7) The centrifugal compressor 100 according to the seventh aspect includes the impeller 1 and the casing 30 covering the impeller. According to the above configuration, a centrifugal compressor with a high pressure ratio and improved efficiency can be provided.

Claims

1. An impeller, characterized by, Possessing: a hub in a disc shape, the hub being centered on an axis; and a plurality of blades, the plurality of blades projecting from a face of the hub on a side toward the axis direction, and being arranged in a circumferential direction, when viewed from a cross section of the blade in a blade height direction that is a direction away from the hub toward a blade tip side, a concave surface curved in a manner that protrudes toward a rear side in a rotation direction is formed in the blade, in a case where a distance in a direction orthogonal to an imaginary line connecting an end edge of the blade tip side and an end edge of the hub side when viewed from the cross section and a midspan of the blade is defined as a recess amount, the blade has a portion where the recess amount increases from a leading edge side to a trailing edge side, at a position of the trailing edge of the blade, a blade angle at the midspan is smaller than a blade angle at the hub side and a blade angle at the blade tip side.

2. The impeller according to claim 1, wherein the portion where the recess amount increases is configured so that a curvature of the concave surface increases from the leading edge side to the trailing edge side.

3. The impeller according to claim 1 or 2, wherein a portion where the curvature of the concave surface is the largest is formed in a portion of the blade that is 60 to 70% from the leading edge side.

4. The impeller according to claim 1 or 2, wherein the concave surface is formed in at least a portion of a portion of the blade that is 40 to 100% from the leading edge side.

5. The impeller according to claim 3, wherein in a case where a difference between the smaller one of the blade angle at the hub side and the blade angle at the blade tip side at a position of the trailing edge of the blade and the blade angle at the midspan is defined as dβ, and an absolute value of a difference between the blade angle at the hub side and the blade angle at the blade tip side is defined as Δβ, a relationship of dβ > Δβ is satisfied.

6. The impeller according to claim 5, wherein a relationship of dβ > Δβ + 2° is satisfied. Possessing:

7. A centrifugal compressor characterized by, the impeller according to claim 1 or 2; and a housing that covers the impeller. ​

Images