JP2023001450A - multistage centrifugal fluid machine - Google Patents

Abstract

To make it possible not only to prevent rotating stall but also to achieve downsizing while maintaining conventional performance and reliability.SOLUTION: In order to solve the above problem, a multistage centrifugal fluid machine of the invention includes: a rotary shaft; a bearing which rotatably supports the rotary shaft; multiple impellers installed at the rotary shaft; first diffusers each of which is attached to at least the impeller at a first stage and installed at the radial outer side of the impeller; a return bend which guides a working fluid to the next stage; and a return vane which is connected to the downstream side of the return bend and guides the working fluid in a radial inward direction. At the downstream side of the first diffuser, a second diffuser, in which a passage width gradually narrows from an inlet to an outlet and two facing wall surfaces which convert a flow to a flow in an axial direction are formed, is provided. At the downstream of the second diffuser, the return bend comprising a straight part and a curved part is disposed.SELECTED DRAWING: Figure 4

Description

The present invention relates to a multistage centrifugal fluid machine, and more particularly to a multistage centrifugal fluid machine suitable for use as a centrifugal compressor, a centrifugal blower, or the like, which handles a relatively small amount of gas and is equipped with a diffuser.

In general, in high-pressure multistage centrifugal fluid machines that handle high-pressure gas, noise, damage to the impeller, vibration of the shaft system, and other phenomena that hinder stable operation of the centrifugal compressor are more likely to occur than in ordinary multistage centrifugal fluid machines. . One of these phenomena is rotating stall.

Rotating stall in a high-pressure multistage centrifugal fluid machine mainly occurs in impeller stages with low specific speeds. It is believed that the mechanism of its occurrence is due to the backflow of the flow that occurs within the diffuser. The flow in the diffuser is a decelerating flow, and separation from the flow wall is likely to occur due to the reverse pressure gradient.

This phenomenon is more likely to occur downstream as the ratio of the flow path width of the diffuser to the impeller outlet radius increases. It is thought that this flow separation gradually increases and develops into a rotating stall.

In a multi-stage centrifugal fluid machine where there is concern about the occurrence of rotating stall, there are techniques using two types of diffusers as described in Patent Document 1 and Patent Document 2.

The techniques described in these Patent Documents 1 and 2 are, as the first diffuser, a vaned diffuser with a small chord ratio having a constant flow path height or a first vaneless diffuser downstream of the impeller. A diffuser is provided, and a vaneless diffuser whose flow path width decreases in the flow direction is provided as a second diffuser downstream of the diffuser. This structure improves compressor efficiency while preventing rotating stall.

WO 97/33092 Japanese Patent No. 5233436

By the way, in the multi-stage centrifugal fluid machine having the diffuser described above, it is desired to reduce the manufacturing cost. The diffuser diameter ratio of 2 must be small.

However, the first diffuser may employ a diffuser with blades having a small chord ratio, and the blades must be shortened in order to reduce the diameter of the diffuser, which may impair its function. On the other hand, if the diameter of the second diffuser is reduced, the width of the flow path is reduced in a short section, resulting in increased pressure loss and reduced efficiency.

In addition, a distance must be provided between the impeller and the return vane in order to provide an inter-stage seal that prevents the working fluid from short-circuiting and flowing from the impeller of the previous stage to the impeller of the next stage. There is a problem in that if it is composed only of circular arcs, it becomes large in the radial direction, and the multistage centrifugal fluid machine becomes large.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and its object is to prevent turning stall and to reduce the size of the multi-stage centrifugal fluid machine while maintaining the conventional performance and reliability. is to provide

In order to achieve the above object, the multistage centrifugal fluid machine of the present invention comprises a rotating shaft, a bearing that rotatably supports the rotating shaft, a plurality of impellers installed on the rotating shaft, and at least the impellers. , a first diffuser installed radially outward of the impeller, a return bend that guides the working fluid to the next stage, and a return bend connected downstream of the return bend, radially inwardly A multi-stage centrifugal fluid machine comprising return vanes for guiding the working fluid, wherein the flow path width gradually narrows from the inlet to the outlet downstream of the first diffuser, and the flow is turned in the axial direction. A second diffuser having two opposing wall surfaces is provided, and the return bend composed of a straight portion and a curved portion is arranged downstream of the second diffuser.

According to the present invention, it is possible to obtain a multistage centrifugal fluid machine that can be reduced in size while maintaining the conventional performance and reliability as well as preventing turning stall.

1 is a cross-sectional view showing the overall configuration of a first embodiment of a multistage centrifugal fluid machine of the present invention; FIG. 2 is a cross-sectional view showing one stage of the multistage centrifugal fluid machine shown in FIG. 1; FIG. FIG. 11 is a characteristic diagram showing the relationship between the height ratio of the flow path at which a rotating stall occurs and the radius ratio at the position at which a reverse flow occurs. 1 is a cross-sectional view showing the vicinity of a first diffuser, a second diffuser, and a return bend portion in Embodiment 1 of the multistage centrifugal fluid machine of the present invention; FIG. FIG. 2 is a cross-sectional view showing part of a conventional multistage centrifugal fluid machine;

The multistage centrifugal fluid machine of the present invention will be described below based on the illustrated embodiments. In addition, in each figure, the same code|symbol is used for the same component.

FIG. 1 shows the overall configuration of Embodiment 1 of a multistage centrifugal fluid machine 100 of the present invention.

As shown in FIG. 1, the multistage centrifugal fluid machine 100 of this embodiment includes a plurality of impellers 1a, 1b, 1c, 1d, and 1e, first diffusers 2a, 2b, 2c, 2d, and 2e with vanes, and A plurality of second diffusers 3a, 3b, 3c, 3d, and 3e without blades and a plurality of compressor stages formed in multiple stages are stacked in the axial direction.

That is, a plurality of impellers 1a, 1b, 1c, 1d, and 1e are stacked on the rotating shaft 8 in the axial direction, and both ends of the rotating shaft 8 are rotatably supported by bearings 10a and 10b. . On the radially outer side downstream of each impeller 1a, 1b, 1c, 1d, 1e is a first diffuser 2a, 2b, 2c, 2d, 2e with vanes and further radially on the outer side without vanes. second diffusers 3a, 3b, 3c, 3d, 3e are provided. The vaneless second diffusers 3a, 3b, 3c, 3d of each stage except the final stage are connected to a return bend 4 that guides the working fluid 11 to the next stage. Return vanes 5 are formed for guiding the working fluid 11 inwardly. A discharge flow path 6 is formed downstream of the final-stage bladeless second diffuser 3e for collecting the working fluid 11 flowing out from the final-stage impeller 1e and discharging it from a discharge pipe (not shown). It is

The vaned first diffusers 2a, 2b, 2c, 2d, 2e, the vaned second diffusers 3a, 3b, 3c, 3d, 3e, the return bends 4, the return vanes 5 and the discharge channels 6 are stationary members. It is attached to or integrally formed with the compressor casing 7 .

Between the stages of the multistage centrifugal fluid machine 100, an interstage seal portion is provided to prevent the working fluid 11 from short-circuiting and flowing from the impeller (for example, 1a) of the previous stage to the impeller (for example, 1b) of the next stage. 12 are installed.

Next, the operation of the multistage centrifugal fluid machine 100 configured in this manner will be described.

In the multistage centrifugal fluid machine 100 shown in FIG. 1, the working fluid 11 sucked from the suction port 9 is pressurized by the impeller 1a of the first stage, the first diffuser 2a with blades, and the second diffuser without blades. After the working fluid 11 is further pressurized through 3a, the flow direction of the working fluid 11 is changed from the radially outer side to the radially inner side by the return bend 4, and is led through the return vane 5 to the second-stage impeller 1b.

Thereafter, by repeating such a flow of the working fluid 11 in each stage, the working fluid 11 is pressurized in order, passes through the vaneless second diffuser 3e in the last stage, and is led through the discharge passage 6 to the discharge pipe.

FIG. 2 shows one stage of the multistage centrifugal fluid machine 100 shown in FIG.

As shown in FIG. 2, the first stage of the multistage centrifugal fluid machine 100 of the present embodiment is positioned downstream of the first stage impeller 1a, and has a first stage first diffuser 2a having a constant flow passage width. , a bladeless first-stage second diffuser 3a that is located downstream of the first-stage first diffuser 2a and turns the flow in the axial direction while narrowing the flow path width; a return bend 4 positioned downstream of the second diffuser 3a of the first stage and for turning the flow of the working fluid 11 from the axial direction (right direction in FIG. 2) radially inward (downward direction in FIG. 2); , and a return vane 5 located downstream of the return bend 4 to remove the swirling component of the working fluid 11 and guide it to the next stage.

The axial width of the inlet channel and the outlet channel of the first diffuser 2a of the first stage is the same, and the outlet of the first diffuser 2a of the first stage is the second diffuser of the first stage without blades. is also the entrance of the diffuser 3a. The outlet channel width of the bladeless first stage second diffuser 3a is smaller than the inlet channel width, and the channel width of the bladeless first stage second diffuser 3a becomes smaller toward the downstream side. That is, the width of the flow path of the vaneless first-stage second diffuser 3a is gradually narrowed toward the downstream side.

By using such a diffuser, it is possible to prevent significant turning stall from occurring particularly in the low specific speed stage. This is for the following reasons.

FIG. 3 shows the characteristics of the critical inlet angle α _crt of the flow in the parallel-wall vaneless diffuser 2' of a portion of the conventional multi-stage centrifugal fluid machine of FIG. The inlet angle α is defined as the angle α that the flow direction makes with the tangential direction at the inlet (impeller outlet) of the diffuser 2′.

The horizontal axis of FIG. 3 indicates the ratio b/r _imp between the flow passage width b of the diffuser 2′ and the outlet radius r _imp of the impeller 1′, and the vertical axis indicates the criticality of the diffuser 2′ at the occurrence limit of the rotating stall. The inlet angle α _crt is shown.

The characteristic diagram shown in FIG. 3 shows that the critical inflow angle α _crt of the diffuser 2 ′ increases as the ratio b/r _imp between the flow channel width b of the diffuser 2 ′ and the outlet radius r _imp of the impeller 1 ′ increases. , which indicates that a rotating stall occurs when the inflow angle α becomes smaller than the critical inflow angle α _crt shown in the figure in the diffuser 2 ′ having a certain passage width ratio b/r _imp .

From the above, it can be seen that in order to prevent turning stall, the inflow angle α to the diffuser 2' should be increased. For this purpose, it is preferable to reduce the inlet channel width of the diffuser 2' and increase the vertical cross-sectional velocity of the flow.

However, in the high-pressure multi-stage centrifugal fluid machine, reducing the width of the flow passage at the inlet of the diffuser 2' immediately downstream of the outlet of the impeller 1' increases the friction loss in the diffuser 2', and the efficiency of the compressor can reduce

As a solution to this problem, a first diffuser 2 having a constant flow path width is provided downstream of the impeller 1, and a flow path width is gradually increased in the flow direction from the inlet to the outlet downstream of the first diffuser 2. It is known to provide a decreasing second diffuser 3 .

Friction loss is not increased by constructing the first diffuser 2 having a constant flow path width in the diffuser front half immediately downstream of the impeller 1 . In addition, since the flow angle can be increased by forming the second diffuser 3 in which the width of the flow path gradually decreases from the inlet to the outlet in the flow direction, the development of the wall surface boundary layer can be suppressed. As a result, the flow of the working fluid 11 is stabilized, preventing the backflow of the flow and preventing the occurrence of rotating stall.

However, the problem with this solution is that a second diffuser 3 has to be provided which narrows the channel width, which makes the multi-stage centrifugal fluid machine radially large.

In this embodiment, as shown in FIG. 4, in the second diffuser 3, the wall surface 3h on the side corresponding to the core plate side of the impeller 1 is drawn by one arc, and the outlet width b3e of the second diffuser 3 is the inlet A linear wall surface 3s2 parallel to the rotating shaft 8 is formed so as to be narrower than the width b3s, and a wall corresponding to the side wall of the impeller 1 is formed continuously with the linear wall surface 3s2 parallel to the rotating shaft 8. A curved portion wall surface 3s1 connected by a tangent circle is formed.

It is known that narrowing the flow path width increases the flow angle, suppressing the development of the boundary layer, stabilizing the flow of the working fluid 11, and suppressing the rotating stall. By turning from the radial direction to the axial direction, the multi-stage centrifugal fluid machine stage 100 can be made smaller.

In the present embodiment, the ratio b3e/b3s between the outlet width b3e of the second diffuser 3 and the inlet width b3s of the second diffuser 3, which is the throttle ratio of the passage width of the second diffuser 3, is about 0.5. and

When the throttling ratio b3e/b3s of the passage width of the second diffuser 3 is small, the average flow angle of the working fluid 11 in the second diffuser 3 increases, and the rotating stall prevention effect increases, and the rotating stall increases. improved reliability.

However, when the throttling ratio b3e/b3s of the channel width of the second diffuser 3 is decreased, the channel width downstream of the second diffuser 3 is also decreased, the wetted edge length is increased, and the friction loss is increased. For this reason, the flow passage width restriction ratio b3e/b3s of the second diffuser 3 is desirably 0.3 to 0.6, preferably about 0.5.

In this embodiment, the curvature radius ratio ρ1/b3s of the wall surface 3h on the side corresponding to the core plate side of the impeller 1 is set to about 0.85 (where ρ1 corresponds to the side wall side of the impeller 1 is the curvature wall radius of curvature of the second diffuser 3 on the side).

If the curvature radius ratio ρ1/b3s of the wall surface 3h on the side corresponding to the core plate side of the impeller 1 is reduced, the multistage centrifugal fluid machine stage 100 can be made smaller. delaminates, pressure loss occurs and efficiency decreases, so the curvature radius ratio ρ1/b3s of the wall surface 3h on the side corresponding to the core plate side of the impeller 1 is desirably 0.7 to 1.0, preferably 0.85 or more is good.

As described above, in the multistage centrifugal fluid machine 100, it is necessary to provide the seal portion 12 between the stages, so the second diffuser 3 and the return vane 5 must be spaced apart in the axial direction by a certain distance.

In this embodiment, a linear portion is provided at the connecting portion between the second diffuser 3 and the return bend 4, and the distance between the curved portion of the second diffuser 3 and the return bend 4 is increased so that the second diffuser 3 and the return vane 5 axial distance.

In this embodiment, the wall surfaces 4s1 and 4h1 forming the straight portion of the return bend 4 are parallel to the axial direction, and the cross-sectional area A (reference A4s in FIG. 4) and the cross-sectional area B (reference A4m in FIG. 4) are equal. However, the cross-sectional area B may be smaller than the cross-sectional area A. Conversely, if the cross-sectional area B is larger than the cross-sectional area A, the flow of the working fluid 11 slows down, the boundary layer develops, and separation is likely to occur, which should be avoided.

In terms of manufacturing cost, it is desirable that the wall surfaces 4s1 and 4h1 forming the straight portion of the return bend 4 are parallel to the axial direction, as in this embodiment.

Further, in the present embodiment, the curvature radius ratio ρ2/b4m of the inner wall surface 4h2 forming the curved portion of the return bend 4 is set to about 0.85 (where ρ2 is the side wall corresponding to the side wall of the impeller 1 is the radius of curvature of the curved wall surface of the return bend 4).

If the curvature radius ratio ρ2/b4m of the inner wall surface 4h2 forming the curved portion of the return bend 4 is increased, separation of the flow of the working fluid 11 can be suppressed. As the ratio of the diameter of the return vane 5 to the outlet becomes smaller, the swirling flow tends to remain at the outlet of the return vane 5, and the pressure rise in the next stage is reduced.

On the other hand, if the curvature radius ratio ρ2/b4m of the inner wall surface 4h2 that constitutes the curved portion of the return bend 4 is too small, the flow of the working fluid 11 will separate, resulting in pressure loss and reduced efficiency. The curvature radius ratio ρ2/b4m of the inner wall surface 4h2 forming the curved portion of the return bend 4 is desirably 0.7 to 1.0, preferably 0.85 or more.

In this embodiment, the outlet width b4e of the return bend 4 is equal to the outlet channel width b4m of the straight portion of the return bend 4, but the outlet width b4e of the return bend 4 is equal to the outlet area A4e of the return bend 4. It should be smaller than the exit area A4m of the straight portion of the bend 4 . This is because when the exit area A4e of the return bend 4 becomes larger than the exit area A4m of the straight portion of the return bend 4, the flow of the working fluid 11b is decelerated and the boundary layer develops. This is because it is likely to occur.

As described above, according to the present embodiment, in the multistage centrifugal fluid machine 100, the second diffuser for turning the flow from the radial direction to the axial direction while narrowing the flow passage width is provided downstream of the first diffuser 2. A diffuser 3 is provided, and a return bend 4 composed of a straight portion and a curved portion is provided downstream of the second diffuser 3 to prevent rotating stall that occurs remarkably in the low specific speed impeller stage, A smaller multistage centrifugal fluid machine 100 can be obtained while maintaining conventional performance and reliability.

Therefore, according to the multistage centrifugal fluid machine 100 of the present embodiment, the second diffuser 2, which greatly contributes to the performance, is not changed, and the width of the passage is reduced to suppress the occurrence of rotating stall. 3 and a new second diffuser 3 that integrates a return bend 4 that turns the flow, and a return bend 4 that has a straight part and a curved part, the conventional efficiency and the function of suppressing the occurrence of turning stall are improved. A smaller multi-stage centrifugal fluid machine 100 can be made without loss.

In the above-described embodiment, the single-shaft multistage multistage centrifugal fluid machine 100 has been described as an example, but the multistage centrifugal fluid machine of the present invention can also be applied to other multistage centrifugal fluid machines such as multistage centrifugal pumps. is.

Moreover, the present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail to facilitate understanding of the present invention, and are not necessarily limited to those having all the described configurations. Also, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Moreover, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

1, 1', 1a, 1b, 1c, 1d, 1e... impeller, 2, 2a, 2b, 2c, 2d, 2e... first diffuser, 2'... diffuser, 3, 3a, 3b, 3c, 3d, 3e Second diffuser 4, 4' Return bend 5 Return vane 6 Discharge passage 7 Compressor casing 8 Rotary shaft 9 Suction port 10a, 10b Bearing 11 Working fluid 12 Interstage seal portion 100 Multistage centrifugal fluid machine b3s Inlet width of second diffuser b3e Outlet width of second diffuser 3h On the side corresponding to the core plate side of the impeller Wall surface of the second diffuser, 3s1: curved wall surface of the second diffuser on the side corresponding to the side wall of the impeller, 3s2: straight wall surface of the second diffuser on the side corresponding to the side wall of the impeller, ρ1 . 4h2 ... curved wall surface of the return bend on the side corresponding to the core plate side of the impeller, 4s1 ... straight wall surface of the return bend on the side corresponding to the side wall of the impeller , 4s2 . Path area, A4m... straight part outlet flow path area of return bend, A4e... curved part outlet flow path area of return bend.

Claims (9)

A rotating shaft, a bearing that rotatably supports the rotating shaft, a plurality of impellers installed on the rotating shaft, and at least one stage of the impeller installed outside the impeller in the radial direction. A multi-stage centrifugal fluid machine, comprising: a first diffuser, a return bend that guides the working fluid to the next stage, and a return vane that is connected downstream of the return bend and guides the working fluid radially inward. hand,
A second diffuser is provided on the downstream side of the first diffuser, and has a flow passage width that gradually narrows from the inlet to the outlet. 2. A multistage centrifugal fluid machine, wherein the return bend composed of a straight portion and a curved portion is arranged downstream of the diffuser of . The multistage centrifugal fluid machine according to claim 1,
The first diffuser is provided on the radially outer side, which is the downstream side of the plurality of impellers, and the second diffuser is provided on the radially outer side of the first diffuser, each stage except the final stage The second diffuser of is connected to the return bend, the return vane is formed downstream of the return bend, and the final stage vane is formed downstream of the second diffuser of the final stage A multi-stage centrifugal fluid machine comprising a discharge passage for collecting and discharging the working fluid flowing out from a vehicle. The multistage centrifugal fluid machine according to claim 1,
The first stage of the multistage centrifugal fluid machine includes the first diffuser of the first stage located downstream of the impeller of the first stage and having a constant flow passage width, and the first diffuser of the first stage. The second diffuser in the first stage that is located downstream of the second diffuser that redirects the flow in the axial direction while narrowing the flow path width, and the second diffuser that is located downstream of the second diffuser in the first stage, and the operation The return bend for turning the flow of fluid radially inward from the axial direction, and the return vane located downstream of the return bend for removing the swirling component of the working fluid and guiding it to the next stage. configured,
The axial width of the inlet channel and the outlet channel of the first diffuser in the first stage is the same, and the outlet channel width of the second diffuser in the first stage is smaller than the inlet channel width, The multi-stage centrifugal fluid machine is characterized in that the passage width of the second diffuser in the first stage is gradually narrowed toward the downstream side. The multistage centrifugal fluid machine according to claim 2,
The second diffuser draws a wall surface on the side corresponding to the core plate side of the impeller with one circular arc, and a straight line parallel to the rotation axis so that the outlet width of the second diffuser is narrower than the inlet width. A curved wall surface is formed by connecting a wall on the side corresponding to the side wall side of the impeller with a tangent circle, which is continuous with the linear wall surface parallel to the rotation axis. Multi-stage centrifugal fluid machine. The multistage centrifugal fluid machine according to claim 1 or 2,
The return bend installed on the downstream side of the second diffuser is composed of a straight portion and a curved portion, and the outlet cross-sectional area of the straight portion of the return bend is made equal to or smaller than the inlet cross-sectional area of the straight portion of the return bend. A multistage centrifugal fluid machine characterized by: The multistage centrifugal fluid machine according to claim 1 or 2,
The return bend installed on the downstream side of the second diffuser is composed of a straight portion and a curved portion, and the exit cross-sectional area of the curved portion of the return bend is made equal to or smaller than the exit cross-sectional area of the straight portion of the return bend. A multistage centrifugal fluid machine characterized by: The multistage centrifugal fluid machine according to any one of claims 1 to 6,
The ratio b3e/b3s between the outlet width (b3e) of the second diffuser and the inlet width (b3s) of the second diffuser, which is the throttle ratio of the flow path width of the second diffuser, is set to 0.3 to 0.3. 6, a multistage centrifugal fluid machine. The multistage centrifugal fluid machine according to claim 7,
A multistage centrifugal fluid machine, wherein the curvature radius ratio ρ1/b3s of the wall surface of the impeller on the side corresponding to the core plate side is set to 0.7 to 1.0.
(where ρ1 is the radius of curvature of the curved wall surface of the second diffuser on the side corresponding to the side wall of the impeller, and b3s is the inlet width of the second diffuser) The multistage centrifugal fluid machine according to any one of claims 5 to 8,
A multistage centrifugal fluid machine, wherein the curvature radius ratio ρ2/b4m of the inner wall surface forming the curved portion of the return bend is 0.7 to 1.0.
(where ρ2 is the radius of curvature of the wall surface of the curved portion of the return bend on the side corresponding to the side wall of the impeller, and b4m is the outlet width of the straight portion of the return bend)

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