JP2023058646A - multistage centrifugal fluid machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multistage centrifugal fluid machine which can suppress an increase of a pressure loss by suppressing the occurrence of an exfoliation of fluid at a return vane even if a length of the return vane cannot be sufficiently secured, and can sufficiently remove a swirl component of the fluid.

SOLUTION: A multistage centrifugal fluid machine comprises: a plurality of impellers; a rotating shaft to which the plurality of impellers are attached; a diffuser arranged outside the impellers in a radial direction; a return flow passage for introducing fluid to a rear-stage impeller from the diffuser; and a plurality of pieces of return vanes which are arranged with intervals along a peripheral direction. The return flow passage has a return bend for guiding the fluid which is sent from the impellers to the outside of the radial direction to the inside of the radial direction, the return bend is constituted of a return bend first bent part and a return bend second bent part which is located at a downstream side, and a flow passage cross section area or a flow passage width of an intermediate part of the return bend is set to a value equal to or smaller than flow passage cross section areas or flow passage widths of an inlet and an outlet of the return bend.

SELECTED DRAWING: Figure 3

COPYRIGHT: (C)2023,JPO&INPIT

Description

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

In a multi-stage centrifugal fluid machine in which a plurality of centrifugal impellers are mounted on one rotating shaft, the fluid pressurized by each stage impeller is swirled and discharged radially outward. In addition, in order to guide the fluid to the inlet of the next-stage impeller radially inward, a curved flow path (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 that flows into the inlet of the next-stage impeller, a Circular cascade elements (return vanes) are installed. It is generally known that if the pre-swirl cannot be sufficiently removed by the return vanes, the efficiency and pressure rise of the next-stage impeller will decrease.

On the other hand, at the return bend, the flow is turned from radially outward to inward with as little pressure loss as possible, and the working fluid enters the return vane so that the return vane can sufficiently remove the pre-swirl. is required to be properly controlled. Hereinafter, the return bend and the return channel are collectively referred to as a return channel.

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 (the second curved portion of the return bend) is set larger than the radius of curvature of the wall surface on the upstream side (the first curved portion of the return bend) in the flow channel wall surface on the radially inner side of the return bend. In addition, the leading edge of the return vane is configured to be positioned at the return bend second curved portion.

Also, at this time, the cross-sectional area of the flow path at the end of the return bend outlet (the end of the return vane inlet) is the same as the cross-sectional area of the flow path at the end of the return bend inlet (the end of the diffuser outlet). Configured to grow.

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 is increased. decreases. At the same time, by locating the front edge of the return vane closer to the outer diameter side than in the conventional art, the area of the return vane inlet is increased and the dynamic pressure at the return vane inlet is reduced.

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

As described above, the uniformity of the flow velocity of the fluid is improved, the separation of the fluid in the return flow path is suppressed, and the pressure loss of the centrifugal fluid machine is reduced.

Japanese Patent No. 6140736

By the way, in order to reduce the manufacturing cost of the multistage centrifugal fluid machine, if the diameter of the return passage is to be reduced, the diameter of the inlet of the return vane must be reduced and the length of the return vane must be shortened.

The return bend and return vane structure 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 return vane leading edge 12 shown in FIG. show trends.

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

Therefore, when the diameter of the return channel is reduced, if the return channel shape as described in Patent Document 1 is adopted, a very large deflection of the fluid from the direction of the inlet angle βb ₅ of the return vane 8 toward the center direction will occur. In order to achieve this, the return vane must have a short blade length and a large blade angle difference between the inlet and outlet of the blade.

However, if an attempt is made to divert the fluid significantly in a short section, the fluid cannot flow along the return vane suction surface 8S as shown in the streamline shown in FIG. There is a problem that the loss increases and the return vane 8 cannot sufficiently remove the swirl component of the fluid.

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

In order to achieve the above object, a multistage centrifugal fluid machine according to the present invention includes a plurality of impellers, a rotating shaft to which the plurality of impellers are attached, and radially outside the impellers. a diffuser, a return channel provided downstream of the diffuser for guiding the fluid from the diffuser to the impeller in the subsequent stage, and a plurality of discs provided in the return channel and spaced apart along the circumferential direction. wherein the return passage has a return bend that guides radially inward the fluid that has been sent out radially outward from the impeller, and the return bend is the return bend A return bend first curved portion located upstream and a return bend second curved portion located downstream of the return bend first curved portion, and the front edge of the return vane is positioned at the outlet of the return bend. and a cross-sectional area or flow path at an intermediate portion of the return bend located between the first return bend curve and the second return bend curve at the return bend of the return flow path The width is set to be equal to or less 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 a sufficient length of the return vanes cannot be secured, the occurrence of separation of the fluid in the return vanes is suppressed to suppress an increase in pressure loss, and the swirling component of the fluid is sufficiently removed. It becomes possible to

It is a meridional cross-sectional view showing a part of a conventional multistage centrifugal fluid machine. FIG. 2 is a meridional cross-sectional view showing the overall configuration of a conventional multistage centrifugal fluid machine including the portion shown in FIG. 1; 1 is a meridional sectional view near a return bend showing Embodiment 1 of the multistage centrifugal fluid machine of the present invention; FIG. FIG. 4 is a diagram for explaining inflow flow vectors to return vanes and streamlines between the return vanes in Embodiment 1 of the multistage centrifugal fluid machine of the present invention; FIG. 4 is a diagram for explaining changes in flow passage cross-sectional area at the position of the return bend in Example 1 of the multistage centrifugal fluid machine of the present invention; FIG. 5 is a diagram for explaining an inflow flow vector to a return vane and a streamline between the return vanes in an arbitrary stage of return vanes 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 is a meridional cross-sectional view of a portion of a conventional multistage centrifugal fluid machine 20, and FIG. 2 is a meridional cross-sectional view of the entire conventional multistage centrifugal fluid machine 20 including the portion shown in FIG. , is an example of a single-shaft multistage centrifugal compressor.

First, a conventional multistage centrifugal fluid machine 20 will be described with reference to FIG.

As shown in FIG. 1, a multistage centrifugal fluid machine 20 includes a centrifugal impeller 1 that imparts rotational energy to a fluid, a rotating shaft 4 to which this centrifugal impeller 1 is attached, and radially outside of the centrifugal impeller 1. and a diffuser 5 for converting the dynamic pressure of the fluid discharged from the centrifugal impeller 1 into static pressure. Further, downstream of the diffuser 5, a return flow passage 6 is provided for guiding the fluid to the centrifugal impeller 1 in the latter stage.

The centrifugal impeller 1 includes a disk (hub) 2 fastened to a rotating shaft 4, a side plate (shroud) 3 arranged opposite the hub 2, and positioned between the hub 2 and the shroud 3 in the circumferential direction (see FIG. 1). and a plurality of blades 1A arranged at intervals in the direction perpendicular to the plane of the paper.

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

As the diffuser 5, either a diffuser with vanes having a plurality of blades arranged at substantially equal pitches in the circumferential direction or a vaneless diffuser having no blades (not shown in FIG. 1) is used. .

The return channel 6 is composed of return bends 7 and turn vanes 8 . The return bend 7 turns the fluid that has passed through the diffuser 5 from radially outward to the radially inward direction, and the return vane 8 removes the swirling component of the fluid, rectifying the fluid to the next-stage centrifugal impeller 1. and play a role in influx.

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

FIG. 2 shows a multistage centrifugal fluid machine 20 in which a plurality of 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 on both end sides 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.

In addition, a multi-stage compression-stage centrifugal impeller (five centrifugal impellers in FIG. 2) 1 is fixedly attached to the rotating shaft 4, and downstream of each centrifugal impeller 1, shown in FIG. A diffuser 5 and a return channel 6 are provided as well.

The centrifugal impeller 1 , the diffuser 5 and the return flow path 6 are housed inside a casing 19 . A suction flow path 15 is provided on the suction side of the casing 19 , and a discharge flow path 16 is provided on the discharge side of the casing 19 .

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

Next, features of the multistage centrifugal fluid machine 20 in this embodiment will be described with reference to FIGS. 3, 4 and 5. FIG.

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

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

Then, the return vane front edge 12 mounted downstream of the return bend 7 shown in FIG. The curvature radius ρ2 at the flow channel wall surface 14A radially inner of the return bend 7 of the return bend second curved portion 14 is defined as the curvature radius ρ1 at the flow channel wall surface 13A radially inner of the return bend 7 of the return bend first curved portion 13. Further, the flow channel cross-sectional area at the return bend outlet 10 is set to be equal to or less than the flow channel cross-sectional area at the return bend inlet 9 .

The effects of the structure of the return bend 7 in this embodiment described above will be described 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, the cross-sectional area of the flow path is set small at the return bend outlet 10 located immediately upstream of the return vane leading edge 12, so as shown in FIG. The meridional flow velocity Cm increases, and the inflow angle β of the fluid into the return vanes 8 becomes larger than the inflow angle β of the fluid into the return vanes 8 in the conventional multistage centrifugal fluid machine 20 shown in FIG.

Therefore, the inlet angle _βb5 of the return vane 8, which is set to match the inflow angle β of the fluid to the return vane 8, can be increased. Further, when the return vane trailing edge 8TE is set to face the direction of the rotation axis 4 with the aim of eliminating the swirl of the fluid, from the above-mentioned content, the distance 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, separation of the flow occurs near the suction surface 8S of the return vane, which is likely to occur in the conventional return flow path in which the inlet area of the return vane 8 is set as large as possible shown in FIG. , is suppressed in this embodiment.

In addition, by setting the flow passage cross-sectional area of the return bend outlet 10 to be small, the flow velocity of the fluid in the return bend second curved portion 14 increases. By setting the radius of curvature ρ2 large, separation of the flow is suppressed, so the uniformity of the flow entering the return vane leading edge 12 is ensured, the pressure loss is reduced, and the return vane 8 The swirl component of the fluid is sufficiently removed by

To reduce the diameter of the return flow passage 6 in order to reduce the manufacturing cost of the multistage centrifugal fluid machine 20, it is necessary to reduce the diameter of the return vane front edge 12 and shorten the length of the return vane 8. FIG.

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. Inevitably, the fluid has to be diverted greatly at , and separation of the flow at the return vane suction surface 8S is more likely to occur.

On the other hand, in the structure of the present embodiment, even if the length of the return vane 8 is shortened in order to reduce the diameter of the return passage 6, the deflection of the fluid from the return vane leading edge 12 to the return vane trailing edge 8TE is small. In addition, the radius of curvature ρ2 is increased so as to reduce the flow velocity of the flow path wall surface 14A on the radially inner side of the return bend 7 in the return bend second curved portion 14, so that separation of the return vane 8 can be prevented.

Therefore, it is effective to use the structure of this embodiment in combination, particularly when the diameter of the return flow path 6 is reduced.

Here, the cross-sectional area of the flow path in the intermediate return bend portion 11 positioned between the return bend first curved portion 13 and the return bend second curved portion 14 shown in FIG. Return bend inlet 9, return bend intermediate portion 11, return bend outlet 10). It may be set to be larger than the cross-sectional area of the passage (solid line in FIG. 5), or may be set to be smaller than the cross-sectional area of the return bend inlet 9 or 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 in FIG. The flow channel width bm is reduced.

At this time, if the radius of curvature ρ1 of the radially inner channel wall surface 13A of the return bend first curved portion 13 is also held 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 the outermost radius Rtop of the return bend 7 remains the same.

Further, when a diffuser with vanes is mounted on the diffuser 5, the length of the return vanes 8 can be increased by increasing the exit diameter of the diffuser 5, increasing the amount of static pressure recovery in the diffuser 5 and increasing the return The flow velocity at the bend inlet 9 can be reduced.

When the diameter of the return channel 6 is reduced, the radial length of the diffuser 5 must be shortened, and the flow velocity at the return bend inlet 9 tends to increase. By using the cross-sectional area, 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 channel 6 is reduced, it is more desirable to set the cross-sectional area of the channel as indicated by the dotted line in FIG.

At this time, the flow velocity at the return bend intermediate portion 11 tends to increase. The occurrence of separation near the flow path wall surface 14A on the radially inner side of 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 on the upstream side of the return vane leading edge 12, the flow velocity Cm in the meridional plane direction at the return vane leading edge 12 increases. As a result, the inflow angle β of the fluid to the return vanes 8 increases. Therefore, the inlet angle _βb5 of the return vane 8 can be set large, and the deflection of the fluid from the return vane inlet 9 to the return vane outlet 10 can be reduced.

In addition, even when the length of the return vane 8 cannot be secured sufficiently, the return vane leading edge 12 is extended into the return bend 7, and the return vane 8 is formed into a three-dimensional complex shape so that the length of the return vane 8 can be increased. It is possible to suppress the occurrence of separation of the fluid in the return bay 8 and sufficiently remove the swirling component of the fluid.

At this time, by setting the flow passage cross-sectional area of the return bend outlet 10 to be small, the flow velocity of the fluid in the return bend second curved portion 14 increases. By setting the radius of curvature of the channel wall surface 14A to be large, the separation of the fluid flow is suppressed, the uniformity of the flow entering the return vane front edge 12 is ensured, and the pressure loss is reduced. The return vane 8 can sufficiently remove the swirling component of the fluid.

In the first embodiment described above, the description was made based on the cross-sectional area of the flow path of the return bend 7, but the cross-sectional area of the flow path is replaced with the width of the flow path in the meridional cross-sectional view of the return bend 7 shown in FIG. can be

That is, if the width of the flow path at the return bend inlet 9 is bs, and the width of the flow path 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 positioned immediately downstream of the return bend outlet 10. , the radius of curvature ρ2 of the channel wall surfaces 13A and 14A on the radially inner side of the return bend 7 is made larger than the radius of curvature ρ1, and the channel width be at the return bend outlet 10 is set at the return bend inlet 9 may be set to be equal to or less than the channel width bs in .

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

Even with such a configuration of the present embodiment, the same effects as those of the first embodiment can be obtained.

In each of the above-described embodiments, the multistage centrifugal fluid machine has been described as an example of a centrifugal compressor having a single-shaft multistage centrifugal compressor as the swirling removal element. It can also be applied to centrifugal fluid machines.

It should be noted that 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.

DESCRIPTION OF SYMBOLS 1... Centrifugal impeller, 1A... Blade of centrifugal impeller, 2... Hub, 3... Shroud, 4... Rotary shaft, 5... Diffuser, 6... Return channel, 7... Return bend, 8... Return vane, 8S... Return Vane suction surface 8TE Return vane trailing edge 9 Return bend inlet 10 Return bend outlet 11 Return bend intermediate portion 12 Return vane front edge 13 Return bend first curved portion 13A Return bend Radially inner channel wall surface of the first curved portion 14 Return bend second curved portion 14A Radially inner channel wall surface of the return bend second curved portion 15 Suction channel 16 Discharge channel , 17... Radial bearing, 18... Thrust bearing, 19... Casing, 20... Multi-stage centrifugal fluid machine, be... Channel width at return bend outlet, bm... Channel width at return bend intermediate part, bs... Flow at return bend inlet Road width, C... absolute flow velocity, Cm... meridional direction flow velocity, Cu... circumferential component of absolute flow velocity, Rtop... outermost radius of return bend, β... inflow angle to return vane, _βb5 ... inlet angle of return vane , ρ1 .

Claims (8)

A plurality of impellers, a rotating shaft to which the plurality of impellers are respectively attached, a diffuser provided radially outside of the impellers, and a diffuser provided downstream of the diffuser, the latter stage from the diffuser A return channel that guides fluid to the impeller, and a plurality of return vanes provided in the return channel and arranged at intervals along the circumferential direction,
The return flow path has a return bend that guides the fluid discharged radially outward from the impeller radially inward, and the return bend is positioned upstream of the return bend. comprising a first curved portion and a return bend second curved portion located downstream of the return bend first curved portion, wherein the front edge of the return vane is located immediately downstream of the outlet of the return bend ;
The flow channel cross-sectional area or flow channel width at an intermediate portion of the return bend located between the return bend first curved portion and the return bend second curved portion in the return bend of the return flow channel is A multi-stage centrifugal fluid machine, characterized in that the channel cross-sectional area or channel width at the inlet and the outlet is set to be equal to or smaller than that of the channel . The multistage centrifugal fluid machine according to claim 1,
A multistage centrifugal fluid machine, wherein a radius of curvature of a wall surface on the radially inner side of the second curved portion of the return bend is larger than a radius of curvature of a wall surface on the radially inner side of the first curved portion of the return bend. . The multistage centrifugal fluid machine according to claim 2,
A multi-stage centrifugal fluid machine, wherein a channel cross-sectional area or channel width at an outlet of the return bend is set smaller than a channel cross-sectional area or channel width at the inlet of the return bend. The multistage centrifugal fluid machine according to claim 3 ,
The return flow path is composed of the return bend and the return vane, and the return bend causes the fluid that has passed through the diffuser to turn from radially outward to the inward direction. A multi-stage centrifugal fluid machine, characterized in that the fluid is flown into the impeller of the next stage while rectifying the fluid. The multistage centrifugal fluid machine according to claim 4 ,
The return bend is formed in the meridional 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 a section from the entrance to the exit of the return bend defined by a substantially cylindrical surface corresponding to the terminal end of the meridional curved flow path located immediately upstream of the leading edge of the return vane. A multistage centrifugal fluid machine characterized by: The multistage centrifugal fluid machine according to claim 5 ,
A multistage centrifugal fluid machine, wherein the return vanes are composed of a plurality of blades arranged at substantially equal pitches in a circumferential direction around the rotating shaft. The multistage centrifugal fluid machine according to any one of claims 1 to 6 ,
The multi-stage centrifugal fluid machine, wherein the diffuser is either a vaned diffuser having a plurality of blades arranged at substantially equal pitches in the circumferential direction or a vaneless diffuser having no blades. . The multistage centrifugal fluid machine according to any one of claims 1 to 7 ,
A multistage centrifugal fluid machine, wherein the multistage centrifugal fluid machine is a single-shaft multistage centrifugal compressor or a multistage centrifugal pump.

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