JP2022130751A - Impeller and centrifugal compressor using the same - Google Patents

Abstract

To achieve efficient compression by reducing stagnation in the flow of working fluid.SOLUTION: An impeller (2) includes a hub (20) having a hub surface (25), and blades (21, 22) fixed on the hub surface (25) of the hub (20). The hub surface (25) includes a concave surface (25p) positioned in an inner side of a radial direction, and a plane (25q) positioned in an outer side of the radial direction. A centrifugal compressor (100) includes the impeller (2), and a shroud wall (3) surrounding the impeller (2).SELECTED DRAWING: Figure 3

Description

The present disclosure relates to impellers and centrifugal compressors using the same.

In a centrifugal compressor, the working fluid is accelerated by an impeller. By converting velocity to pressure, the working fluid is decelerated and compressed. In order to decelerate the working fluid, it is necessary to increase the cross-sectional area of the flow path. That is, the working fluid pressure is primarily increased by the diffuser. However, since the velocity of the working fluid accelerated by the impeller is close to the speed of sound, large losses tend to occur in the process of moving from the flow path of the impeller to the diffuser. Therefore, a general impeller is designed so that the cross-sectional area of the flow passage is enlarged at its outer peripheral portion.

JP 2015-212551 A

As is known to those skilled in the art, the flow of working fluid stagnates near the outlet of the impeller flow path. This tendency is conspicuous in small-sized, high-compression-ratio centrifugal compressors. More efficient compression is possible if stagnation in the working fluid flow can be reduced.

The present disclosure provides techniques for reducing stagnation in working fluid flow to achieve efficient compression.

This disclosure is
a hub having a hub surface;
a plurality of wings secured to the hub surface of the hub;
with
The hub surface has a curved portion located radially inward and a planar portion located radially outward.
Provide impeller.

According to the technique of the present disclosure, stagnation in the flow of working fluid can be reduced to achieve efficient compression.

1 is a cross-sectional view of a centrifugal compressor according to a first embodiment of the present disclosure; FIG. 2 is a meridional projection of the impeller of the centrifugal compressor shown in FIG. 1. FIG. 3 is a partially enlarged view of FIG. 2. FIG. 4A is a partially enlarged view of FIG. 2. FIG. FIG. 4B is an enlarged cross-sectional view of another example of the annular recess. FIG. 5 is a diagram showing another positional relationship between the curved surface portion and the flat surface portion. FIG. 6 is a plan view of the impeller showing the position of the boundary between the curved surface portion and the flat surface portion. FIG. 7 is another plan view of the impeller showing the position of the boundary between the curved surface portion and the flat surface portion. FIG. 8 is a configuration diagram of a fluid machine according to the second embodiment of the present disclosure. FIG. 9 is a graph showing the results of calculating the cross-sectional area of the flow path from the upstream end to the downstream end for the impellers of Examples and Comparative Examples. FIG. 10 is a graph showing the results of computer simulation of the meridional surface flow velocity of the working fluid from the upstream end to the downstream end for the impellers of Examples and Comparative Examples. FIG. 5 is a graph showing the results of computing the static pressure from the upstream end to the downstream end of the impellers of Examples and Comparative Examples by computer simulation. FIG. FIG. 12 is a contour diagram showing the results of calculation of the flow velocity of the working fluid by computer simulation for the impellers of Example and Comparative Example. FIG. 13 is a partially enlarged view of a meridional projection of a conventional centrifugal compressor.

(Findings on which this disclosure is based)
The inventors of the present invention have extensively studied the causes that hinder efficient compression. As a result, the inventors have noticed the following two main causes, and have arrived at the present disclosure.

FIG. 13 shows an enlarged part of a meridional projection of a conventional centrifugal compressor. A thick arrow line represents the main flow of the working fluid. There is a gap sh between the impeller 120 and the shroud wall 103 in the centrifugal compressor. This gap sh causes the working fluid to leak from the flow path between the blades, as indicated by the thin arrow line. Working fluid leakage contributes to Eckert vortices. As indicated by the circular arrow line, the Eckert vortex grows as the flow velocity of the working fluid decreases at the outer circumference of the impeller 120 . In particular, the Eckert vortices hinder smooth flow on the shroud wall 103 side, which greatly contributes to the flow rate. If the loss due to the Eckhart vortex can be suppressed, it is considered that efficient compression can be achieved, that is, a high compression ratio can be achieved.

"Eckhart vortices" are vortices that occur at the outer periphery of the impeller, resulting in flow velocity reduction and pressure loss. "Impeller periphery" means the downstream portion of the flow path between the blades of the impeller.

Another factor that hinders efficient compression is believed to be the flow velocity distribution of the working fluid in the spanwise direction. That is, the flow velocity of the working fluid is relatively high near the shroud walls and relatively low near the hub. For efficient pressure rise in the diffuser, it is desirable that the flow velocity distribution in the spanwise direction be as small as possible.

In addition, in Patent Document 1, it is assumed that the impeller and the shroud wall are integrated. Since the shroud wall rotates together with the impeller, it is difficult to apply the technique of Patent Document 1 to a centrifugal compressor that should be operated at a high rotational speed (for example, an outer circumferential speed of 500 m/s or more).

(Overview of one aspect of the present disclosure)
The impeller according to the first aspect of the present disclosure includes:
a hub having a hub surface;
wings secured to the hub surface of the hub;
with
The hub surface has a curved portion located radially inward and a flat portion located radially outward.

According to the first aspect, the growth of the Eckert vortex is suppressed, and the working fluid flows smoothly in the outer peripheral portion of the impeller. As a result, efficient compression can be achieved.

In the second aspect of the present disclosure, for example, in the impeller according to the first aspect, the planar portion may be parallel to the radial direction. With such a configuration, the cross-sectional area of the flow path can be appropriately reduced, so that the above effects can be obtained while avoiding a large decrease in the flow rate of the working fluid.

In the third aspect of the present disclosure, for example, in the impeller according to the first or second aspect, in a meridional plane projection view obtained by rotationally projecting the blade on a meridional plane containing the rotation axis of the impeller, the blade A profile may include a curved portion facing the planar portion of the hub surface. With such a configuration, a sufficient flow rate of the working fluid can be ensured.

In the fourth aspect of the present disclosure, for example, in the impeller according to any one of the first to third aspects, the hub includes an upper surface located on one end side in a direction parallel to the rotation axis, and an upper surface parallel to the rotation axis. and a lower surface located on the other end side in the direction of the hub, and the lower surface of the hub may be provided with an annular recess recessed from the lower surface toward the upper surface, and the hub When viewed in plan from the axial direction, the annular recess may be housed inside the flat portion of the hub surface. According to such a configuration, stress concentration on the inner peripheral portion of the hub can be alleviated, and displacement of the outer peripheral portion of the hub in the axial direction can be suppressed.

In the fifth aspect of the present disclosure, for example, in the impeller according to the fourth aspect, the annular recess may have an outer peripheral portion on the outer peripheral side in the radial direction, and in a plane including the rotation axis, the The outer peripheral portion of the annular recess may be linear. According to such a configuration, it is possible to reduce the stress generated in the inner peripheral portion of the lower surface of the hub while preventing the inner peripheral portion of the lower surface of the hub from protruding in the axial direction.

In the sixth aspect of the present disclosure, for example, in the impeller according to the fifth aspect, the outer peripheral portion and the lower surface of the hub may be in contact with each other at a point of contact P1 in a plane including the rotating shaft, and the rotating shaft When a straight line parallel to and passing through the contact point P1 and the hub surface intersect with the contact point P2, the inclination of the outer peripheral portion of the annular recess at the contact point P1 with respect to the plane perpendicular to the rotation axis is the contact point P2. The inclination of the hub surface at P2 with respect to a plane orthogonal to the rotation axis may be smaller. According to such a configuration, it is possible to more effectively relieve the stress generated in the inner peripheral side portion of the lower surface of the hub while suppressing a decrease in rigidity at the outer peripheral end of the impeller.

A centrifugal compressor according to a seventh aspect of the present disclosure includes
an impeller of any one of the first to sixth aspects;
a shroud wall surrounding the impeller;
It has

According to the fifth aspect, a high compression ratio can be achieved.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

(First embodiment)
FIG. 1 shows a cross section of a centrifugal compressor 100 according to the first embodiment of the present disclosure. A centrifugal compressor 100 of this embodiment includes a shaft 11 , an impeller 2 , a back plate 13 and a housing 15 . Impeller 2 is fixed to shaft 11 . The back plate 13 is arranged at a position facing the lower surface of the impeller 2 . Impeller 2 is housed in housing 15 . The centrifugal compressor 100 is driven by the rotation of the shaft 11 and compresses the working fluid. In this specification, the direction parallel to the rotation axis O of the impeller 2 is called "axial direction". The direction perpendicular to the axis of rotation O is called the "radial direction".

The impeller 2 has a hub 20, a plurality of main blades 21 (full blades) and a plurality of secondary blades 22 (splitter blades). Hub 20 has a top surface 23 , a bottom surface 24 and a hub surface 25 . The upper surface 23 is a surface located on one end side in the axial direction. The lower surface 24 is a surface located on the other end side in the axial direction. Upper surface 23 has a relatively small diameter and lower surface 24 has a relatively large diameter. The upper surface 23 and the lower surface 24 are each flat surfaces. Hub surface 25 is the surface located between upper surface 23 and lower surface 24 . The hub 20 smoothly expands in diameter along the rotation axis O from the upper surface 23 toward the lower surface 24 . The main wing 21 and the secondary wing 22 are fixed to the hub 20 and radially mounted on the hub surface 25 . The main blades 21 and the sub blades 22 are alternately arranged in the circumferential direction of the impeller 2 . The secondary wing 22 is a wing shorter than the main wing 21 . A flow path of the impeller 2 is formed between these blades.

The secondary wings 22 are not essential and may be omitted.

Housing 15 has shroud wall 3 , peripheral member 17 and front member 18 . The shroud wall 3 has a shape along the impeller 2 and surrounds the impeller 2 . The shroud wall 3 extends axially beyond the impeller 2 to form an inlet 12 . A diffuser 26 is formed between the shroud wall 3 and the back plate 13 radially outside the outer peripheral edge of the impeller 2 . Diffuser 26 may be a vaneless diffuser or a vaned diffuser. A peripheral member 17 forms a spiral chamber 16 around the impeller 2 . The swirl chamber 16 communicates with the diffuser 26 .

FIG. 2 is a meridional plane projection (rotational projection) obtained by rotationally projecting the main wing 21 and the secondary wing 22 onto the meridional plane including the rotation axis O of the impeller 2 . 3 is a partially enlarged view of FIG. 2. FIG. The meridional plane projection view is a view obtained by adding the trajectories of the main blades 21 and the secondary blades 22 obtained when the impeller 2 is rotated around the rotation axis O to a longitudinal section including the rotation axis O of the impeller 2. be.

In this embodiment, hub surface 25 has a curved portion 25p and a planar portion 25q. The curved surface portion 25p is a portion located radially inward. The curved portion 25p has a concave shape. Specifically, the curved portion 25p is convex from the upper surface 23 toward the lower surface 24 in the axial direction. The flat portion 25q is a portion located radially outward. In the meridional projection view, the curved portion 25p shows a curved contour, and the planar portion 25q shows a straight contour.

As shown in FIG. 13, in the conventional impeller 120, the hub surface 125 is composed only of curved surfaces.

In contrast, in this embodiment, the hub surface 25 has a planar portion 25q at its outer periphery. The plane portion 25q reduces the height of the flow path between the blades, so that the cross-sectional area of the flow path is reduced when the conventional impeller 120 is used as a standard. In the section of the flat portion 25q, the cross-sectional area of the channel is substantially constant. Suppressing the expansion of the cross-sectional area of the flow path increases the flow velocity of the working fluid. As a result, the growth of the Eckert vortex is suppressed, and the working fluid flows smoothly around the outer peripheral portion of the impeller 2 . As a result, efficient compression can be achieved.

The flow cross-sectional area is increased or decreased by changing the shape of the hub 20 and/or the shape of the shroud wall 3 . The flow velocity of the working fluid is high near the shroud wall 3 and low near the hub 20 . Therefore, when the flow passage cross-sectional area is reduced by changing the shape of the shroud wall 3, in other words, when the flow passage cross-sectional area is reduced by reducing the wingspan of the main wing 21 and the sub-wing 22, the flow rate is greatly affected. It can become too much. In this embodiment, the flow passage cross-sectional area is reduced by changing the shape of the hub 20 . According to such a configuration, a desired effect can be obtained while ensuring a sufficient flow rate.

Further, by narrowing the flow path by providing the flat portion 25q on the hub 20, the flow velocity of the working fluid in the vicinity of the hub 20 increases. Along with this, in the vicinity of the shroud wall 3, the flow velocity of the working fluid is suppressed from decreasing, or the flow velocity increases. The flow near the hub 20 is more affected than the flow near the shroud wall 3 by increasing the thickness of the outer peripheral portion of the hub 20 to narrow the flow path. Therefore, the difference between the flow velocity near the hub 20 and the flow velocity near the shroud wall 3 is reduced at the outer peripheral end of the impeller 2, which is the outlet of the flow path between the blades. That is, the high-speed flow of the working fluid is adjusted, and the flow velocity distribution in the spanwise direction is reduced. As a result, the efficiency of pressure conversion in diffuser 26 is increased.

For example, if the diffuser 26 is a vaned diffuser, the following effects are expected. That is, when the flow velocity distribution of the working fluid is small, the working fluid collides with the vane at a uniform speed and angle, so that the flow of the working fluid is less disturbed. As a result, a higher compression ratio can be achieved.

Further, since the planar portion 25q is present on the outer peripheral portion of the hub 20, the thickness of the outer peripheral portion of the hub 20 is increased by the planar portion 25q. As a result, the outer peripheral portion of hub 20 is accurately supported by the inner peripheral portion of hub 20 .

In this embodiment, the planar portions 25q are radially parallel. With such a configuration, the cross-sectional area of the flow path can be appropriately reduced, so that the above effects can be obtained while avoiding a large decrease in the flow rate of the working fluid. However, the plane portion 25q may be inclined with respect to the radial direction.

In the meridional plane projection view shown in FIG. 2, the outline of the tip of the main wing 21, the outline of the tip of the sub wing 22, and the outline of the shroud wall 3 are all curved lines. In other words, the contours of the main wing 21 and the secondary wing 22 include curvilinear portions facing the planar portion 25q of the hub surface 25. As shown in FIG. Curves forming the contours of the main wing 21 and the sub-wing 22 are convex from the upper surface 23 to the lower surface 24 in the axial direction. In this embodiment, each contour consists only of curved lines. With such a configuration, a sufficient flow rate of the working fluid can be ensured. The “tip of the main wing 21 ” means the end of the main wing 21 facing the shroud wall 3 . “Tips of the sub-wings 22 ” means the ends of the sub-wings 22 facing the shroud wall 3 .

As shown in FIG. 3, in this embodiment, the curved portion 25p and the planar portion 25q are adjacent to each other. In this case, the impeller 2 is easy to manufacture.

In the meridional projection view, the total length of the boundary line between the main wing 21 and the hub surface 25 is defined as the wing surface length of the main wing 21 . The position of the upstream end of the main wing 21 is defined as the 0% position, and the position of the downstream end of the main wing 21 is defined as the 100% position. At this time, the boundary B between the curved surface portion 25p and the flat surface portion 25q can exist in the range from 75% to 90% of the length of the blade surface. That is, the length of the plane portion 25q in the radial direction can be 10% or more and 25% or less of the blade surface length. By appropriately adjusting the length of the planar portion 25q, the above effects can be sufficiently obtained.

As shown in FIGS. 2 and 3, the lower surface 24 of the impeller 2 is a flat surface. A lower surface 24 of the impeller 2 is not provided with a portion projecting from the upper surface 23 toward the lower surface 24 . Such a configuration is advantageous for downsizing the centrifugal compressor 100 .

An annular recess 27 is provided in the lower surface 24 of the hub 20 . The annular recess 27 is a portion that is recessed from the lower surface 24 toward the upper surface 23. When the hub 20 is viewed from above in the axial direction, the annular recess 27 is accommodated inside the flat portion 25q of the hub surface 25. . In this embodiment, since the lower surface 24 is also a flat surface, the thickness of the portion of the hub 20 that constitutes the planar portion 25q is constant. Based on the conventional impeller 120 (see FIG. 13), the thickness of the hub 20 at the portion forming the plane portion 25q is increased. In other words, the rigidity of the outer peripheral portion of the hub 20 is increased.

Since the hub 20 supports the centrifugal force applied to the hub 20 , the main wing 21 and the sub wing 22 , stress concentrates on the inner peripheral portion of the hub 20 . The annular recess 27 serves to relieve stress concentration on the inner periphery of the hub. Furthermore, if the annular recess 27 is provided inside the planar portion 25q, the thickness of the planar portion 25q is not consumed by the annular recess 27. FIG. At the outer peripheral portion where the hub 20 is thinnest, the thickness of the hub 20 can be sufficiently secured in combination with the increase in thickness due to the flat portion 25q. As a result, axial displacement of the outer peripheral portion of the hub 20 can be suppressed.

FIG. 4A shows a partially enlarged view of FIG. 4A is also a longitudinal section of hub 20 including axis of rotation O. FIG. Part or all of the contour of the annular recess 27 has an arc shape. According to such a configuration, it is possible to reduce the stress generated in the inner peripheral portion of the lower surface 24 of the hub 20 while preventing the inner peripheral portion of the lower surface 24 of the hub 20 from protruding in the axial direction. .

In the longitudinal section of FIG. 4A, the angle θ1 formed by the tangent line L1 of the annular recess 27 and the lower surface 24 of the hub 20 is, for example, 45 degrees or less. The angle θ1 may be in the range of 30 degrees or more and 40 degrees or less. A tangent line L1 is a tangent line to the contour of the annular recess 27 and is a tangent line that passes through the point of contact P1 between the annular recess 27 and the outer peripheral portion 24b of the lower surface 24 of the hub 20 . The point of contact P1 is a point on the boundary between the annular recess 27 and the bottom surface 24 of the hub 20 . With such a configuration, the stress applied to the surface of the annular recess 27 can be reduced, and the stress generated in the inner peripheral side portion 24a of the lower surface 24 of the hub 20 can be more effectively relieved.

FIG. 4B is an enlarged cross-sectional view of an annular recess 270 according to a modification. The annular recess 270 includes an inner peripheral portion 27a and an outer peripheral portion 27b (outer peripheral portion). The inner peripheral portion 27 a has an arc-shaped profile and is connected to the inner peripheral portion 24 a of the lower surface 24 of the hub 20 . The outer peripheral portion 27 b has a linear contour and is connected to the outer peripheral portion 24 b of the lower surface 24 of the hub 20 . The inner peripheral side portion 27a and the outer peripheral side portion 27b are connected on the outer peripheral side of the center of the annular recess 270 in the radial direction. According to such a configuration, the stress generated in the inner peripheral portion 24a of the lower surface 24 of the hub 20 can be reduced while suppressing the axial protrusion of the inner peripheral portion 24a of the lower surface 24 of the hub 20. can be done.

Stress tends to concentrate near the center of the annular recess 270 . Since the outer peripheral portion 27b of the annular recess 270 has a planar shape, the distribution of stress in the vicinity of the center of the annular recess 270 can be shifted toward the inner side of the hub 20, that is, toward the upper surface 23. As shown in FIG. Thereby, the stress on the surface near the center of the annular recess 270 and the stress generated in the inner peripheral side portion 24a (the portion indirectly connected to the shaft 11) of the lower surface 24 of the hub 20 can be relaxed.

In the cross section of FIG. 4B, the angle θ2 between the outer peripheral portion 27b of the annular recess 270 and the reference plane R1 is, for example, 45 degrees or less. The angle θ2 may be in the range of 30 degrees or more and 40 degrees or less. With such a configuration, the stress applied to the surface of the annular recess 270 can be reduced, and the stress generated in the inner peripheral side portion 24a of the lower surface 24 of the hub 20 can be more effectively relieved. The reference plane R1 is a plane that includes the lower surface 24 of the hub 20 and is parallel to the radial direction of the hub 20 . In the cross section of FIG. 4B, the reference plane R1 is represented by a straight line.

The angle θ2 may be less than or equal to the angle φ between the tangent line L2 of the hub surface 25 and the reference plane R2. According to such a configuration, it is possible to more effectively relieve the stress generated in the inner peripheral side portion 24a of the lower surface 24 of the hub 20 while suppressing a decrease in rigidity at the outer peripheral end of the impeller 2 . A tangent line L2 is a tangent line passing through the contact point P2. The reference plane R2 is a plane that passes through the point of contact P2 and is parallel to the radial direction of the hub 20 . The tangent point P2 is the intersection of the reference plane R3 and the hub surface 25. As shown in FIG. The reference plane R3 is a plane that passes through the point of contact P1 between the annular recess 270 and the lower surface 24 of the hub 20, is parallel to the axial direction, and is perpendicular to the radial direction. In the section of FIG. 4B, the reference planes R2 and R3 are represented by straight lines.

The angle θ2 is the inclination (acute angle side inclination) of the outer peripheral side portion 27b of the annular recess 24 at the point of contact P1 with respect to the reference plane R1. The angle φ is the inclination of the hub surface 25 at the point of contact P2 with respect to the reference plane R2 (inclination on the acute angle side). The reference plane R1 and the reference plane R2 are planes perpendicular to the rotation axis O. As shown in FIG. The angle θ2 may be smaller than the angle φ.

FIG. 5 shows another positional relationship between the curved portion 25p and the planar portion 25q. As shown in FIG. 5, a transition portion 25r may be provided between the curved portion 25p and the planar portion 25q. The transition portion 25r may be planar, curved, or a combination of planar and curved. With such a configuration, the flow of the working fluid is less likely to be disturbed at the transition portion 25r, so there is a possibility that a smoother flow can be achieved. The length L of the transition portion 25r is, for example, 1% or more and 10% or less of the blade surface length.

FIG. 6 is a plan view of impeller 2 showing the position of boundary B between curved surface portion 25p and flat surface portion 25q. The secondary wing 22 is omitted. In the example shown in FIG. 6, curved portion 25p is surrounded by planar portion 25q. A boundary B between the curved portion 25p and the planar portion 25q is circular, for example. That is, the planar portion 25q is annular. With such a configuration, the impeller 2 can be easily manufactured.

FIG. 7 is another plan view of the impeller 2 showing the position of the boundary B between the curved surface portion 25p and the flat surface portion 25q. The secondary wing 22 is omitted. In the example shown in FIG. 7, the boundary B between the curved portion 25p and the planar portion 25q is linear. According to such a configuration, the length of the flat portion 25q in the flow direction can be appropriately adjusted according to the position in the circumferential direction. As a result, a higher compression ratio can be achieved.

In the centrifugal compressor 100 of this embodiment, the impeller 2 rotates relative to the shroud wall 3 . Impeller 2 and shroud wall 3 are separated and only impeller 2 rotates. In this case, a gap SH exists between the main blade 21 of the impeller 2 and the shroud wall 3 . A gap SH also exists between the sub-blade 22 of the impeller 2 and the shroud wall 3 . A portion of the working fluid crosses over these gaps SH and contributes to Eckert vortices. Therefore, the technology of the present disclosure is particularly useful for this type of centrifugal compressor. However, there is a possibility that the technology of the present disclosure can be applied to a type of centrifugal compressor in which the impeller and shroud wall are integrated.

(Second embodiment)
FIG. 8 shows the configuration of a fluid machine 300 according to the second embodiment of the present disclosure. A fluid machine 300 includes a centrifugal compressor 100 , a turbine 200 and a combustor 301 . Fluid machine 300 may be used in a gas turbine system. A shaft 11 is shared by the centrifugal compressor 100 and the turbine 200 . Centrifugal compressor 100 is the compressor described with reference to FIG. The working fluid is air, for example. Air is compressed by centrifugal compressor 100 and supplied to combustor 301 . In combustor 301, a mixed gas of fuel and compressed air is combusted. Energy in the combustion gases is extracted in the form of shaft power by turbine 200 .

According to the centrifugal compressor 100, a high compression ratio can be achieved without increasing the flow rate of the working fluid. That is, the intake pressure of the turbine 200 can be increased while suppressing the torque for rotating the centrifugal compressor 100 . As a result, the efficiency of the fluid machine 300 is improved.

(verification by simulation)
FIG. 9 is a graph showing the results of calculating the flow channel cross-sectional area from the upstream end to the downstream end for the impellers of Examples and Comparative Examples. The horizontal axis indicates the value of the position of the flow path expressed as a ratio to the length of the blade surface. The position of the upstream end of the main wing 21 corresponds to 0%. The position of the downstream end of the main wing 21 corresponds to 100%. The vertical axis indicates the normalized value of the channel cross-sectional area. According to the impeller of the example, the channel cross-sectional area was constant from the position of about 70% to the position of about 100%. On the other hand, the cross-sectional area of the passage of the impeller of the comparative example decreased continuously up to the position of about 85% and started to increase from the position of about 85%.

The following simulations were performed for impellers of Examples and Comparative Examples having flow channel cross-sectional areas shown in FIG.

FIG. 10 is a graph showing the results of computer simulation of the meridional surface flow velocity of the working fluid from the upstream end to the downstream end for the impellers of Examples and Comparative Examples. The horizontal axis indicates the value of the position of the flow path expressed as a ratio to the length of the blade surface. The vertical axis indicates the meridional flow velocity. A "meridional plane flow velocity" means a flow velocity represented by a velocity component in a direction parallel to the meridional plane. Flow velocity indicates the normalized value of flow velocity in the vicinity of the hub surface. The type of working fluid was air, and the impeller speed was 107000 rpm.

As shown in FIG. 10, according to the impeller of the example, the flow velocity abruptly increases from the position of about 85%. Due to inertia, the rapid increase in flow velocity appeared at a position downstream of the starting position of the planar portion 25q. In contrast, according to the comparative impeller, the flow rate gradually increased to about the 90% position and gradually decreased from the about 90% position to the 100% position.

FIG. 11 is a graph showing the results of calculating the static pressure from the upstream end to the downstream end of the impellers of Examples and Comparative Examples by computer simulation. The horizontal axis indicates the value of the position of the flow path expressed as a ratio to the length of the blade surface. The vertical axis shows the normalized value of the static pressure of the working fluid in the vicinity of the hub surface.

As shown in FIG. 11, according to the impeller of Example, the static pressure dropped sharply from the position of about 85% and then recovered. In contrast, with the comparative impeller, the static pressure increased continuously up to the 100% position.

FIG. 12 is a contour diagram showing the results of calculation of the flow velocity of the working fluid by computer simulation for the impellers of Example and Comparative Example. Areas with darker colors represent areas with low Mach numbers, that is, areas with stagnant airflow. FIG. 12(a) is the simulation result of the impeller of the comparative example, and FIG. 12(b) is the simulation result of the impeller of the example. As can be seen by comparing Figures 12(a) and 12(b), the dark areas were clearly reduced when the example impeller was used.

(Verification with actual equipment)
A centrifugal compressor was manufactured using the impellers of the example and the comparative example having the flow passage cross-sectional area shown in FIG. 9, and the compression ratio at a predetermined rotation speed and a predetermined flow rate was examined. Air was used as the working fluid. By using the impeller of this example, it was confirmed that the compression ratio was improved by about 10.6% compared to the comparative example under high rotation conditions.

The technology of the present disclosure is useful for centrifugal compressors used in gas turbine systems, refrigeration cycle devices, and the like, and is particularly useful for small, high-speed centrifugal compressors.

2 Impeller 3 Shroud Wall 11 Shaft 12 Suction Port 13 Back Plate 15 Housing 16 Spiral Chamber 17 Peripheral Member 18 Front Member 20 Hub 21 Main Wing 22 Sub Wing 23 Upper Surface 24 Lower Surface 25 Hub Surface 25p Curved Surface Portion 25q Plane Portion 25r Transition Portion 26 Diffuser 27 , 270 annular recess 100 centrifugal compressor 200 turbine 300 fluid machine 301 combustor O rotating shaft SH gap B boundary

Claims (7)

a hub having a hub surface;
a plurality of wings secured to the hub surface of the hub;
with
The hub surface has a curved portion located radially inward and a planar portion located radially outward.
impeller. the planar portion is parallel to the radial direction;
Impeller according to claim 1. in a meridional projection obtained by rotationally projecting the blade onto a meridional plane containing the axis of rotation of the impeller, the profile of the blade includes a curved portion facing the planar portion of the hub surface;
The impeller according to claim 1 or 2. The hub has an upper surface located on one end side in a direction parallel to the rotation axis and a lower surface located on the other end side in a direction parallel to the rotation axis,
The lower surface of the hub is provided with an annular recess recessed from the lower surface toward the upper surface,
When the hub is viewed in plan from the axial direction, the annular recess is located inside the planar portion of the hub surface.
Impeller according to any one of claims 1 to 3. The annular recess has an outer peripheral portion on the outer peripheral side in the radial direction,
In a plane containing the rotation axis, the outer peripheral portion of the annular recess is linear.
Impeller according to claim 4. the outer peripheral portion and the lower surface of the hub are in contact with each other at a point of contact P1 in a plane containing the rotation axis;
When a straight line parallel to the rotation axis and passing through the contact point P1 and the hub surface intersect with the contact point P2,
The inclination of the outer peripheral portion of the annular recess at the contact point P1 with respect to the plane perpendicular to the rotation axis is smaller than the inclination of the hub surface at the contact point P2 with respect to the plane perpendicular to the rotation axis.
Impeller according to claim 5. an impeller according to any one of claims 1 to 6;
a shroud wall surrounding the impeller;
A centrifugal compressor with

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