JP7429810B2 - Multi-stage centrifugal fluid machine - Google Patents

Description

The present invention relates to a multi-stage centrifugal fluid machine, and in particular, a curved flow path (return bend) for turning fluid from radially outward to inward, and a swirling component (return bend) of the fluid in the same direction as the rotational direction of an impeller. The present invention relates to a multi-stage centrifugal fluid machine suitable for a machine having circular blade row elements (return vanes) arranged axially symmetrically in the circumferential direction in order to eliminate pre-swirling.

In a multi-stage centrifugal fluid machine with multiple centrifugal impellers mounted on one rotating shaft, the fluid pressurized by each stage impeller is discharged radially outward while swirling, so that on the downstream side in the direction of the rotating shaft, In addition, in order to guide the fluid to the inlet of the next-stage impeller located on the radially inner side, a return bend is provided for turning the fluid from radially outward to inward.

In addition, on the downstream side of the return bend, in order to remove the swirl component (pre-swirl) in the same direction as the rotation direction of the impeller of the fluid flowing into the inlet of the next stage impeller, a A circular cascade element (return vane) is installed. It is generally known that if the pre-swirling cannot be sufficiently removed by the return vanes, the efficiency and pressure rise of the next-stage impeller will decrease.

On the other hand, in the return bend, the flow is turned from radially outward to inward with as little pressure loss as possible, and the flow of working fluid into the return vane is controlled so that the return vane can sufficiently remove pre-swirl. Appropriate control is required. Hereinafter, the return bend and the return channel will be collectively referred to as a return flow path.

A conventional example of reducing pressure loss in a return flow path of a multistage centrifugal fluid machine is described in Patent Document 1.

In Patent Document 1, the radius of curvature of the wall surface on the downstream side (second curved portion of the return bend) is made larger than the radius of curvature of the wall surface on the upstream side (first curved portion of the return bend) in the flow path wall surface on the radially inner side of the return bend. At the same time, the leading edge of the return vane is configured to be located at the second curved portion of the return bend.

In addition, in this case, the flow path cross-sectional area at the end of the return bend outlet (end of the return vane inlet) is equal to or greater than the flow path cross-sectional area at the end of the return bend inlet (end of the diffuser outlet). It is configured to be large.

With this configuration, the centrifugal force acting on the fluid on the inner wall side of the second curved portion of the return bend is reduced and at the same time the static pressure increases, so that the flow velocity of the working fluid is increased on the radially inner side of the second curved portion of the return bend. decreases. At the same time, by locating the leading edge of the return vane closer to the outer diameter than in the past, the area of the return vane inlet increases, and the dynamic pressure at the return vane inlet is reduced.

Furthermore, since the cross-sectional area of the flow path at the end of the return bend outlet is made equal to or larger than the cross-sectional area of the flow path at the end of the return bend inlet, the dynamic pressure at the return vane inlet is further reduced.

As a result, the uniformity of the fluid flow rate is improved, separation of the fluid in the return flow path is suppressed, and pressure loss of the centrifugal fluid machine is reduced.

Patent No. 6140736

By the way, if an attempt is made to reduce the diameter of the return flow path in order to reduce the manufacturing cost of a multistage centrifugal fluid machine, it is necessary to reduce the diameter of the return vane inlet and shorten the length of the return vane.

The structure of the return bend and return vane described in Patent Document 1 aims to set the area of the return vane inlet as large as possible to reduce the meridional flow velocity Cm of the fluid at the return vane inlet.

Therefore, the inflow angle β of the fluid into the return vane 8 tends to be smaller than the velocity triangle at the leading edge 12 of the return vane shown in FIG. Show trends.

In order to suppress flow separation in the return vane 8, the inlet angle _βb5 of the return vane 8 is often designed to match the inflow angle β of the fluid into the return vane 8. In this case, the return vane 8 The entrance angle βb ₅ becomes smaller. On the other hand, the return vane outlet 10 is generally designed so that the return vane trailing edge 8TE faces the direction of the rotation axis in order to eliminate swirling of the fluid.

Therefore, when reducing the diameter of the return flow path, if the return flow path shape as described in Patent Document 1 is adopted, a very large amount of fluid will be diverted from the direction of the inlet angle βb ₅ of the return vane 8 toward the center. In order to achieve this, it is necessary to use a return vane with a short blade length and a large difference in blade angle between the entrance and exit of the blade.

However, when attempting to divert the fluid greatly in a short section, the fluid cannot flow along the return vane negative pressure surface 8S and separation occurs, as shown by the streamlines shown in FIG. There are problems in that loss increases and the return vane 8 cannot sufficiently remove swirling components of the fluid.

The present invention has been made in view of the above-mentioned points, and its purpose is to suppress the occurrence of fluid separation in the return vanes and increase pressure loss even when the length of the return vanes cannot be ensured sufficiently. An object of the present invention is to provide a multi-stage centrifugal fluid machine capable of suppressing this and sufficiently removing swirling components of fluid.

In order to achieve the above object, the multi-stage centrifugal fluid machine of the present invention includes a plurality of impellers, a rotating shaft to which each of the plurality of impellers is attached, and a rotating shaft provided outside the impeller in the radial direction. a diffuser, a return flow path provided downstream of the diffuser and guiding fluid from the diffuser to the impeller at a later stage; and a plurality of sheets provided in the return flow path and arranged at intervals along the circumferential direction. and a return vane, the return flow path having a return bend that guides the fluid sent radially outward from the impeller radially inward, and the return bend It is composed of a first curved portion of the return bend located on the upstream side and a second curved portion of the return bend located on the downstream side of the first curved portion of the return bend, and the front edge of the return vane is located at the exit of the return bend. A flow path cross-sectional area or a flow path at an intermediate portion of the return bend, which is installed immediately downstream of the return flow path, and is located between the return bend first curved portion and the return bend second curved portion in the return bend of the return flow path. The width is characterized in that it is set smaller than the channel cross-sectional area or channel width at the inlet and outlet of the return bend.

According to the present invention, even when the length of the return vane cannot be ensured sufficiently, the occurrence of fluid separation in the return vane is suppressed, an increase in pressure loss is suppressed, and the swirling component of the fluid is sufficiently removed. It becomes possible to do so.

FIG. 2 is a meridional cross-sectional view showing a part of a conventional multi-stage centrifugal fluid machine. FIG. 2 is a meridional cross-sectional view showing the overall configuration of a conventional multi-stage centrifugal fluid machine including the parts shown in FIG. 1; 1 is a meridional cross-sectional view of the vicinity of a return bend showing Example 1 of the multistage centrifugal fluid machine of the present invention. It is a figure explaining the inflow flow vector to the return vane and the streamline between return vanes in Example 1 of the multistage centrifugal fluid machine of this invention. FIG. 3 is a diagram illustrating a change in flow path cross-sectional area at the position of a return bend in Example 1 of the multistage centrifugal fluid machine of the present invention. FIG. 2 is a diagram illustrating inflow flow vectors to return vanes and streamlines between return vanes in return vanes of arbitrary stages of a conventional multistage centrifugal fluid machine.

Hereinafter, a multi-stage centrifugal fluid machine of the present invention will be explained based on the illustrated embodiment. In each figure, the same reference numerals are used for the same components.

FIG. 1 is a meridional cross-sectional view of a part of a conventional multi-stage centrifugal fluid machine 20, and FIG. 2 is a meridional cross-sectional view of the entire conventional multi-stage centrifugal fluid machine 20 including the portion shown in FIG. , is an example of a single-shaft multi-stage centrifugal compressor.

First, a conventional multi-stage centrifugal fluid machine 20 will be explained using FIG.

As shown in FIG. 1, the multistage centrifugal fluid machine 20 includes a centrifugal impeller 1 that imparts rotational energy to fluid, a rotating shaft 4 to which the centrifugal impeller 1 is attached, and a rotary shaft 4 located outside the centrifugal impeller 1 in the radial direction. The diffuser 5 generally includes a diffuser 5 that converts the dynamic pressure of the fluid discharged from the centrifugal impeller 1 into static pressure. Further, downstream of the diffuser 5, a return passage 6 is provided for guiding fluid to the subsequent centrifugal impeller 1.

The centrifugal impeller 1 includes a disk (hub) 2 fastened to a rotating shaft 4, a side plate (shroud) 3 disposed facing the hub 2, and a side plate (shroud) 3 located between the hub 2 and the shroud 3 in the circumferential direction (in FIG. It has a plurality of blades 1A arranged at intervals in a direction perpendicular to the paper surface.

Although FIG. 1 shows the case of a closed type impeller having a shroud 3, an open type impeller without a shroud 3 may be used.

As the diffuser 5, either a vaned diffuser having a plurality of blades arranged at approximately equal pitches in the circumferential direction, or a vaneless diffuser having no blades, although not shown in FIG. 1, is used. .

The return passage 6 is composed of a return bend 7 and a turn vane 8. The return bend 7 turns the fluid that has passed through the diffuser 5 from outward to inward in the radial direction, and the return vane 8 removes the swirling component of the fluid, rectifying the fluid and directing it to the next centrifugal impeller 1. It is responsible for the influx of people.

The return bend 7 is formed as a U-shaped curved flow path surrounded by surrounding structures in the meridian plane, and the return bend inlet 9 is defined as a substantially cylindrical surface corresponding to the outlet of the diffuser 5, The return bend outlet 10 is defined as the section from the return bend inlet 9 to the return bend outlet 10 defined by a substantially cylindrical surface corresponding to the end of the meridional curved flow path located immediately upstream of the leading edge 12 of the return vane. The return vane 8 is composed of a plurality of blades arranged around the rotating shaft 4 at substantially equal pitches in the circumferential direction.

FIG. 2 shows a multi-stage centrifugal fluid machine 20 in which the compression stages shown in FIG. 1 are stacked in the axial direction.

As shown in FIG. 2, radial bearings 17 that rotatably support the rotating shaft 4 are arranged at both ends of the rotating shaft 4, and one end of the rotating shaft 4 supports the rotating shaft 4 in the axial direction. A thrust bearing 18 is arranged.

Further, a multi-stage compression stage centrifugal impeller 1 (five centrifugal impellers in FIG. 2) is fixedly attached to the rotating shaft 4, and the downstream side of each centrifugal impeller 1 is provided as shown in FIG. Similarly, a diffuser 5 and a return flow path 6 are provided.

These centrifugal impeller 1, diffuser 5, and return flow path 6 are housed in a casing 19. Further, a suction passage 15 is provided on the suction side of the casing 19, and a discharge passage 16 is provided on the discharge side of the casing 19.

In the multi-stage centrifugal fluid machine 20 configured as described above, the fluid sucked from the suction channel 15 is pressurized every time it passes through the centrifugal impeller 1 and diffuser 5 of each stage and the return channel 6, and the final The pressure reaches a predetermined pressure and is discharged from the discharge passage 16.

Next, features of the multistage centrifugal fluid machine 20 in this embodiment will be explained using FIGS. 3, 4, and 5.

FIG. 3 is a meridional cross-sectional view of the vicinity of the return bend 7 in the multistage centrifugal fluid machine 20 in this embodiment.

In this embodiment, the return flow path 6 has the return bend 7 that guides the fluid sent radially outward from the centrifugal impeller 1 radially inward, as described above, and this return bend 7 It is composed of a first return bend curved section 13 located upstream of the bend 7 and a second return bend curved section 14 located downstream of the first return bend curved section 13 .

The leading edge 12 of the return vane, which is mounted downstream of the return bend 7 shown in FIG. The radius of curvature ρ2 at the channel wall surface 14A on the radially inner side of the return bend 7 of the second return bend curved section 14 is the radius of curvature ρ1 on the channel wall surface 13A on the radially inner side of the return bend 7 of the first return bend curved section 13. Furthermore, the cross-sectional area of the flow path at the return bend outlet 10 is set to be smaller than the cross-sectional area of the flow path at the return bend inlet 9.

The effects of the structure of the return bend 7 in this embodiment described above will be explained below.

FIG. 4 shows the inlet velocity triangle of the return vane 8 and the streamline of the return vane 8 when this embodiment is applied.

In this embodiment, since the flow passage cross-sectional area is set small at the return bend outlet 10 located immediately upstream of the return vane leading edge 12, as shown in FIG. The meridional flow velocity Cm increases, and the fluid inflow angle β into the return vane 8 becomes larger than the fluid inflow angle β into the return vane 8 in the conventional multistage centrifugal fluid machine 20 shown in FIG.

Therefore, the entrance angle _βb5 of the return vane 8, which is set to match the inflow angle β of the fluid into the return vane 8, can be increased. In addition, when the return vane trailing edge 8TE is set to face the direction of the rotation axis 4 with the aim of eliminating fluid swirl, from the above-mentioned content, it can be seen that from the return vane leading edge 12 to the return vane trailing edge 8TE, Fluid deflection can be reduced.

As a result, as shown in FIG. 4, the separation of the flow near the negative pressure surface 8S of the return vane, which was likely to occur in the conventional return flow path in which the inlet area of the return vane 8 shown in FIG. , is suppressed in this example.

Furthermore, by setting the flow passage cross-sectional area of the return bend outlet 10 small, the flow velocity of the fluid in the return bend second curved portion 14 increases, but the flow passage wall surface 14A on the radially inner side of the return bend 7 in this region increases. By setting the radius of curvature ρ2 large, flow separation is suppressed, so uniformity of the inflow flow to the return vane leading edge 12 is ensured, pressure loss is reduced, and the return vane 8 is The swirling components of the fluid are sufficiently removed.

In order to reduce the diameter of the return flow path 6 in order to reduce the manufacturing cost of the multi-stage centrifugal fluid machine 20, it is necessary to reduce the diameter of the return vane leading edge 12 and shorten the length of the return vane 8.

At this time, in the conventional return flow path, the length of the return vane 8 is short and the difference in blade angle between the return vane leading edge 12 and the return vane trailing edge 8TE is large. This forces the fluid to be largely diverted, making flow separation at the return vane negative pressure surface 8S even more likely to occur.

On the other hand, in the structure of this embodiment, in order to reduce the diameter of the return flow path 6, even when the length of the return vane 8 is shortened, the diversion of the fluid from the return vane leading edge 12 to the return vane trailing edge 8TE is reduced. In addition, the radius of curvature ρ2 is made large so that the flow velocity of the channel wall surface 14A on the radially inner side of the return bend 7 in the second return bend curved portion 14 is reduced, and separation in the return vane 8 can be prevented.

Therefore, the structure of this embodiment is particularly effective when used in combination when reducing the diameter of the return flow path 6.

Here, the flow path cross-sectional area in the return bend intermediate section 11 located between the return bend first curved section 13 and the return bend second curved section 14 shown in FIG. 3 is the position of the return bend 7 shown in FIG. As shown in the flow path cross-sectional area change diagram at each position of the return bend inlet 9, return bend intermediate portion 11, and return bend outlet 10, the flow path cross-sectional area is less than or equal to the return bend inlet 9, and the flow at the return bend outlet 10 is It may be set to be larger than the channel cross-sectional area (solid line in FIG. 5), or it may be set to be smaller than any of the flow channel cross-sectional areas at the return bend inlet 9 and the return bend outlet 10 (dotted line in FIG. 5).

However, when the cross-sectional area of the flow path in the return bend 7 is set as indicated by the dotted line in FIG. 5, the outermost radius Rtop of the return bend 7 shown in FIG. The flow path width bm will be reduced.

At this time, if the radius of curvature ρ1 of the radially inner channel wall surface 13A in the return bend first curved portion 13 is also maintained at the same value, the diameter of the return bend inlet 9, that is, the outlet of the diffuser 5 can be set larger. .

Therefore, the radial length of the diffuser 5 can be increased while keeping the outermost radius Rtop of the return bend 7 the same.

In addition, when the diffuser 5 is equipped with a diffuser with vanes, the length of the return vane 8 can be increased by increasing the outlet diameter of the diffuser 5, increasing the amount of static pressure recovery within the diffuser 5, and returning The flow velocity at the bend inlet 9 can be reduced.

When reducing the diameter of the return flow path 6, the radial length of the diffuser 5 must also be shortened, and the flow velocity at the return bend inlet 9 tends to increase. By making the cross-sectional area smaller, the flow velocity at the return bend inlet 9 can be reduced while keeping the outermost radius Rtop of the return bend 7 the same when the diameter is reduced.

Therefore, when the diameter of the return flow path 6 is reduced, it is more desirable to set the flow path cross-sectional area as indicated by the dotted line in FIG.

At this time, the flow velocity at the return bend intermediate portion 11 tends to increase, but as described above, in this embodiment, the radius of curvature ρ2 is increased, so that the return bend 7 at the return bend second curved portion 14 increases. The occurrence of peeling near the radially inner channel wall surface 14A is suppressed.

According to the configuration of this embodiment, since the flow passage cross-sectional area is set small at the return bend outlet 10 upstream of the return vane leading edge 12, the meridional flow velocity Cm at the return vane leading edge 12 increases. However, the inflow angle β of the fluid into the return vane 8 increases. Therefore, the inlet angle βb ₅ of the return vane 8 can be set large, and the diversion of the fluid from the return vane inlet 9 to the return vane outlet 10 can be reduced.

Furthermore, even when the length of the return vane 8 cannot be ensured sufficiently, the length of the return vane 8 can be increased by extending the return vane leading edge 12 into the return bend 7 and making the return vane 8 into a three-dimensional complex shape. It becomes possible to suppress the occurrence of separation of the fluid in the return bay 8 and to sufficiently remove the swirling component of the fluid without having to ensure the above-mentioned conditions.

At this time, by setting the flow passage cross-sectional area of the return bend outlet 10 small, the flow velocity of the fluid in the return bend second curved part 14 increases. By setting the radius of curvature of the flow path wall surface 14A to be large, separation of the fluid flow is suppressed, uniformity of the inflow flow to the return vane leading edge 12 is ensured, pressure loss is reduced, and It becomes possible to sufficiently remove swirling components of the fluid by the return vanes 8.

In Example 1 described above, the explanation was given based on the flow path cross-sectional area of the return bend 7, but the flow path cross-sectional area is applied by replacing the flow path cross-sectional area with the flow path width in the meridional cross-sectional view of the return bend 7 shown in FIG. It's okay.

That is, if the flow path width at the return bend inlet 9 is bs and the flow path width at the return bend outlet 10 is be, then the leading edge 12 of the return vane mounted downstream of the return bend 7 is placed directly downstream of the return bend outlet 10. At the same time, the radius of curvature ρ2 is made larger than the radius of curvature ρ1 on the flow path wall surfaces 13A and 14A on the radially inner side of the return bend 7, and the flow path width be at the return bend outlet 10 is set to be larger than the radius of curvature ρ1 at the return bend inlet 9. The channel width may be set to be less than or equal to the channel width bs in .

Further, at this time, the channel width bm in the return bend intermediate portion 11 may be set to be less than or equal to the channel width bs at the return bend inlet 9 and greater than or equal to the channel width be at the return bend outlet 10, or It may be set to be less than any of the flow path widths bs and be at the bend inlet 9 and the return bend outlet 10.

Even with this configuration of this embodiment, the same effects as in the first embodiment can be obtained.

Furthermore, in each of the above-described embodiments, a multi-stage centrifugal compressor with a single-shaft swirl removal element was used as an example of a multi-stage centrifugal fluid machine. It can also be applied to centrifugal fluid machines.

Note that the present invention is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above are described in detail to explain the present invention in an easy-to-understand manner, and the present invention is not necessarily limited to having all the configurations described. Furthermore, it is possible to replace a 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. Furthermore, it is possible to add, delete, or replace a part of the configuration of each embodiment with other configurations.

1... Centrifugal impeller, 1A... Centrifugal impeller blade, 2... Hub, 3... Shroud, 4... Rotating shaft, 5... Diffuser, 6... Return channel, 7... Return bend, 8... Return vane, 8S... Return Vane negative pressure surface, 8TE...Return vane trailing edge, 9...Return bend inlet, 10...Return bend outlet, 11...Return bend middle part, 12...Return vane leading edge, 13...Return bend first curved part, 13A...Return bend Radially inner channel wall surface in the first curved section, 14... Return bend second curved section, 14A... radially inner channel wall surface in the return bend second curved section, 15... Suction channel, 16... Discharge channel , 17...Radial bearing, 18...Thrust bearing, 19...Casing, 20...Multi-stage centrifugal fluid machine, be...Flow path width at return bend outlet, bm...Flow path width at return bend intermediate portion, bs...Flow at return bend inlet Road width, C...Absolute flow velocity, Cm...Meridional flow velocity, Cu...Circumferential component of absolute flow velocity, Rtop...Outermost radius of return bend, β...Inflow angle to return vane, βb ₅ ...Entrance angle of return vane , ρ1... The radius of curvature of the radially inner channel wall surface at the first curved portion of the return bend, ρ2... The radius of curvature of the radially inner channel wall surface at the second curved portion of the return bend.

Claims (8)

a plurality of impellers, a rotating shaft to which each of the plurality of impellers is attached, a diffuser provided on the radially outer side of the impeller, and a diffuser provided downstream of the diffuser, and a rotation shaft to which the plurality of impellers are respectively attached; comprising a return flow path that guides fluid to the impeller, and a plurality of return vanes provided in the return flow path and arranged at intervals along the circumferential direction,
The return flow path has a return bend that guides the fluid sent radially outward from the impeller radially inward, and the return bend is a return bend located upstream of the return bend. It is composed of a first curved section and a second return bend curved section located downstream of the first return bend curved section, and the leading edge of the return vane is installed immediately downstream of the exit of the return bend,
The flow passage cross-sectional area or flow passage width at the intermediate part of the return bend located between the return bend first curved part and the return bend second curved part in the return bend of the return flow passage is A multi-stage centrifugal fluid machine, characterized in that the cross-sectional area or width of a flow path at an inlet and an outlet is set smaller than that of the flow path. The multi-stage centrifugal fluid machine according to claim 1,
A multi-stage centrifugal fluid machine characterized in that the radius of curvature of the radially inner wall surface of the second return bend curved section is larger than the radius of curvature of the radially inner wall surface of the first return bend curved section. . The multi-stage centrifugal fluid machine according to claim 2,
A multi-stage centrifugal fluid machine characterized in that a flow passage cross-sectional area or flow passage width at an outlet of the return bend is set smaller than a flow passage cross-sectional area or a flow passage width at an entrance of the return bend. The multi-stage centrifugal fluid machine according to claim 3,
The return flow path is composed of the return bend and the return vane, the return bend turns the fluid that has passed through the diffuser from radially outward to inward, and the return vane turns the fluid into a swirling component. A multi-stage centrifugal fluid machine, characterized in that the fluid is rectified and flows into the impeller of the next stage. The multi-stage centrifugal fluid machine according to claim 4,
The return bend is formed in a meridian plane as a U-shaped curved flow path surrounded by surrounding structures, and the inlet of the return bend is defined by a substantially cylindrical surface corresponding to the outlet of the diffuser, The exit of the return bend is defined as the section from the entrance to the exit of the return bend defined by a substantially cylindrical surface corresponding to the end of the meridional curved flow path located immediately upstream of the leading edge of the return vane. A multi-stage centrifugal fluid machine with special features. The multi-stage centrifugal fluid machine according to claim 5,
A multi-stage centrifugal fluid machine, wherein the return vane is composed of a plurality of blades arranged at substantially equal pitches in a circumferential direction around the rotation axis. A multistage centrifugal fluid machine according to any one of claims 1 to 6,
A multi-stage centrifugal fluid machine characterized in that the diffuser is either a vaned diffuser having a plurality of blades arranged at approximately equal pitches in the circumferential direction or a vaneless diffuser having no blades. . A multistage centrifugal fluid machine according to any one of claims 1 to 7,
The multistage centrifugal fluid machine is characterized in that the multistage centrifugal fluid machine is a single-shaft multistage centrifugal compressor or a multistage centrifugal pump.

Images