JP2011122516A - Centrifugal compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a centrifugal compressor capable of expanding a rotating stall starting margin, preventing a rotating stall, and suppressing a decrease in efficiency. <P>SOLUTION: In a centrifugal compressor 1, a vaneless diffuser 7A is disposed on an outlet side of an impeller 5A. A fluid inlet 12A is opened on a wall surface of a hub side casing 2B of the vaneless diffuser 7A. A slit-like fluid circulation passage 12 is disposed whose fluid outlet 12B is opened on a wall surface of the hub side casing 2B facing a back surface of a hub disk 5C of the impeller 5A. A liquid inlet 12A of the slit-like fluid circulation passage 12 has the center of the opening at a position of 1.1R2 or 1.4R2, given that an outlet diameter of the impeller 5A is R2. The opening is opened at a position radially more outward than a rotating stall starting diameter position at the vaneless diffuser 7A. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a centrifugal compressor in which a vaneless diffuser is provided on the outlet side of an impeller.

  Centrifugal compressors have a simple structure, have a small loss if the flow angle is appropriate, have a wide operating range, and do not generate fluid excitation force on the impeller. Not vaneless diffusers are widely adopted. However, vaneless diffusers, when the flow angle increases, cause loss, and also cause rotational stall that causes uneven flow in the circumferential direction, which may be caused by pressure fluctuations, shaft vibration, discharge pipe vibration, etc. Will occur. It is known that this rotating stall occurs particularly when the centrifugal compressor is operated in a low flow rate region. FIG. 10B shows the relationship between the flow rate Q, the outlet pressure (head pressure) H of the compressor, and the efficiency η. The flow rate Q1 is the turning stall occurrence point, and the flow rate range in the lower flow rate region is lower than that. It shows that it becomes the turning stall occurrence region W1.

  When the rotation stall occurs, the pressure fluctuation, the shaft vibration, the discharge pipe vibration and the like are caused as described above, and it becomes difficult to continuously operate the centrifugal compressor stably. Therefore, for the purpose of preventing the occurrence of turning stall, as shown in FIG. 9, an inlet 012A is opened on the outlet side of the vaneless diffuser 07, and the casing 02 facing the rear surface of the hub disk 05C of the impeller 05 is formed. Patent Document 1 proposes a centrifugal compressor 01 in which a part of a high-pressure fluid is recirculated through a fluid circulation path 012 by providing a fluid circulation path 012 having an outlet 012B opened on a wall surface. Yes.

JP 2008-38894 A

  What is shown in Patent Document 1 aims to reduce the turning stall starting flow rate when the turning stall first occurs in the vaneless diffuser 07, as shown in FIG. 10 (A). By recirculating 10% of the flow rate of the main fluid in the fluid circulation path 012, the turning stall start margin can be increased by 10% (refer to the flow rate Q 2 and the turning stall generation region W 2). However, as a result, the efficiency was reduced by about 1% as compared with the case where the recirculation was not performed. Similarly, 20% recirculation flow rate increases 20% turning stall start margin, 2% efficiency drop, 30% recirculation flow rate increases 30% turning stall start margin, 3% efficiency drop As described above, the reduction in efficiency increases as the turning stall start margin increases.

  Further, since the inlet 012A of the fluid circulation path 012 is opened at the outlet side of the vaneless diffuser 07 and the outlet 012B is opened at a position equal to or less than half of the radius of the impeller outlet, the fluid circulation path 012 becomes longer, and the wall friction loss is mainly caused. The pressure loss becomes larger. In order to recirculate a required flow rate against such a loss, it is necessary to supply energy from the mainstream as well, resulting in a problem that efficiency is lowered.

  The present invention has been made in view of such circumstances, and provides a centrifugal compressor capable of suppressing a decrease in efficiency while expanding a turning stall start margin and preventing a turning stall. Objective.

In order to solve the above-described problems, the centrifugal compressor of the present invention employs the following means.
That is, the centrifugal compressor according to the present invention is the centrifugal compressor in which the vaneless diffuser is provided on the outlet side of the impeller, the fluid inlet is opened on the hub-side casing wall surface of the vaneless diffuser, and the hub disk of the impeller A slit-like fluid circulation path in which a fluid outlet is opened is provided in the hub-side casing wall surface facing the back surface, and the center of the opening of the slit-like fluid circulation path is the outlet of the impeller When the radius is R2, it is located at a position of 1.1R2 to 1.4R2, and is open to a radially outer position from a turning stall starting radial position in the vaneless diffuser.

As a result of analysis of the flow in the vaneless diffuser, the turning stall in the vaneless diffuser is defined as a diffuser width ratio b / R2 (b; diffuser width) where the radial position where the turning stall first occurs is the turning stall start radius Rrev. , R2: Impeller exit radius) is smaller, the turning stall start radius Rrev is smaller and the radius ratio (Rrev / R2) is closer to 1.0. This means that as the diffuser with a smaller diffuser width ratio b / R2, a turning stall occurs on the inner diameter side, that is, near the diffuser inlet. Further, even when the diffuser width ratio b / R2 was set to the maximum value, the radius ratio (Rrev / R2) of the turning stall start radius Rrev was about 1.3. From the above, it is confirmed that the turning stall start radius Rrev is in the range of 1.0R2 to 1.3R2.
In the present invention, in consideration of the above points, a slit-like fluid in which a fluid inlet is opened in the hub-side casing wall surface of the vaneless diffuser and a fluid outlet is opened in the hub-side casing wall surface facing the rear surface of the hub disk of the impeller. A circulation path is provided, and the fluid inlet of this slit-like fluid circulation path is located at a position of 1.1R2 to 1.4R2, where the center of the opening is the exit radius of the impeller, and is swung by the vaneless diffuser. Since it is configured to be opened radially outward from the stall starting radial position, a part of the high-pressure fluid flowing through the vaneless diffuser is circulated to the inlet side of the vaneless diffuser through the slit-like fluid circulation path. The flow rate of the fluid flowing through the vaneless diffuser is not 1.0R2 where the above-described turning stall start radius Rrev exists It can be locally increased in the range of 1.3R2. Therefore, the turning stall occurrence point can be shifted to the low flow rate side by the increased flow rate ratio, and the occurrence of turning stall can be suppressed. The fluid circulation path is slit-shaped, and the fluid inlet is opened at a position of 1.1R2 to 1.4R2 radially outside the range of 1.0R2 to 1.3R2 where the turning stall start radius Rrev exists. Therefore, compared with the conventional one, the length of the fluid circulation path is relatively short and can be formed widely in the circumferential direction, and the high-pressure fluid flowing through the vaneless diffuser can be smoothly circulated through the slit-like fluid. It can be introduced into the road and flow out to the back side of the impeller while maintaining the swirling flow. Therefore, pressure loss, mainly wall friction loss in the recirculation system of high-pressure fluid, can be reduced to increase the flow rate in the region where the rotating stall occurs, and the decrease in efficiency can be suppressed while preventing the rotating stall. Can do. Further, since the swirl component can be held in the recirculation flow, the mixing loss when rejoining the main flow can be reduced.

  Furthermore, the centrifugal compressor of the present invention is the above centrifugal compressor, wherein the fluid outlet of the slit-like fluid circulation path has a center of the opening at a position of 0.90R2 to 0.97R2, and the impeller It is characterized by being opened at a radially inner position than the outer peripheral end.

  According to the present invention, the fluid outlet of the slit-like fluid circulation path is 0.90R2 to 0.97R2 when the center of the opening is R2 and the outlet radius of the impeller, and is more than the outer peripheral end of the impeller. Since it is configured to open to the radially inner position, the recirculation flow that flows out through the slit-like fluid circulation path can be reliably jetted to the back surface of the impeller hub, and the recirculation flow causes the main fluid flow that flows through the impeller to flow. There is no disturbance, and an increase in pressure loss due to shearing of the flow at the time of merging with the main flow can also be suppressed. In addition, since the fluid outlet can be opened to the radially outer position as much as possible without leaving the outer periphery of the impeller, the length of the slit fluid circulation path is made as short as possible. Pressure loss, mainly wall friction loss, can be further reduced. Therefore, the reduction in efficiency can be further suppressed.

  Furthermore, the centrifugal compressor according to the present invention is characterized in that, in any of the above centrifugal compressors, the width of the slit-like fluid circulation path is at least 20% or more of the flow path width of the vaneless diffuser. And

  According to the present invention, since the width of the slit-shaped fluid circulation path is at least 20% or more of the flow path width of the vane-less diffuser, the fluid inlet and the fluid outlet of the slit-shaped fluid circulation path are provided at the above positions. The pressure difference between them is reduced, and it is difficult for the fluid to flow into the slit-like fluid circulation path, whereas the width of the slit-like fluid circulation path is at least 20% or more of the channel width of the vaneless diffuser portion, The required recirculation flow rate is ensured by expanding the channel width and reducing the pressure loss. Accordingly, it is possible to reliably increase the flow rate of the fluid flowing in the turning stall generation region of the vaneless diffuser and suppress the turning stall.

  Furthermore, in the centrifugal compressor according to any one of the above-described centrifugal compressors, connecting members are provided in a plurality of locations in the circumferential direction in the slit fluid circulation path, and the slits are interposed via the connecting members. The two hub-side casing members that form a fluid circulation path are integrally joined together.

  According to the present invention, connecting members are provided at a plurality of locations in the circumferential direction in the slit-shaped fluid circulation path, and the two hub-side casing members that form the slit-shaped fluid circulation path are integrally coupled via the connecting member. Therefore, a hub-side casing member divided into two parts is connected by a connecting member, and a slit is provided between them, so that a fluid circulation path having a slit shape is formed in the hub-side casing over the entire circumference. Can be formed. Therefore, a slit-like fluid circulation path that can reduce pressure loss in the hub-side casing can be easily configured, and this can also suppress a decrease in efficiency.

  Furthermore, the centrifugal compressor of the present invention is characterized in that, in the above centrifugal compressor, the connecting member is a columnar member having a circular cross section.

  According to the present invention, since the connecting member is a columnar member having a circular cross section, the flow resistance by the connecting member is made as small as possible, and the recirculation flow that flows through the slit-like fluid circulation path is kept swirling. It can be circulated smoothly to the fluid outlet. Therefore, the pressure loss due to the connecting member can be minimized and a decrease in efficiency can be suppressed.

  Furthermore, the centrifugal compressor according to the present invention is the centrifugal compressor according to any one of the above-described centrifugal compressors, wherein the connecting member includes a fin-like columnar member having a fin extending from the columnar member having a circular cross section toward the direction of fluid swirling. It is characterized by being.

  According to the present invention, since the connecting member is a fin-like columnar member having a fin extending in the direction of swirling of the fluid from the columnar member having a circular cross section, separation of the flow generated downstream of the connecting member. And vortices can be suppressed by fins. Therefore, pressure loss due to flow separation or vortex generated by the connecting member can be suppressed, and a decrease in efficiency can be suppressed. Moreover, since the cross-sectional area of the columnar member can be increased by providing fins, it is possible to sufficiently secure the strength of the connecting member and the hub-side casing member that is integrally coupled by the connecting member.

  Furthermore, the centrifugal compressor of the present invention is characterized in that, in the above centrifugal compressor, the connecting member is a columnar member having an airfoil cross section.

  According to the present invention, since the connecting member is a columnar member having an airfoil cross section, the flow resistance by the connecting member is made as small as possible, and the high-pressure fluid flowing through the slit-like fluid circulation path is made into an airfoil. It is possible to smoothly circulate to the fluid outlet while maintaining the swirl flow along the line. Therefore, the pressure loss due to the connecting member can be minimized and a decrease in efficiency can be suppressed.

  According to the present invention, a part of the high-pressure fluid flowing through the vaneless diffuser is circulated to the inlet side of the vaneless diffuser via the slit-like fluid circulation path, and the flow rate of the fluid flowing through the vaneless diffuser is changed to the above-described turning stall start radius. Since it can be increased locally in the range of 1.0R2 to 1.3R2 where Rrev exists, the turning stall point is shifted to the low flow rate side by the increased flow rate ratio, and the occurrence of turning stall is suppressed. can do. The fluid circulation path is slit-shaped, and the fluid inlet is opened at a position 1.1R2 to 1.4R2 radially outside the range of 1.0R2 to 1.3R2 where the turning stall start radius Rrev exists. Therefore, compared with the conventional one, the length of the fluid circulation path is relatively short and can be widely formed in the circumferential direction, and the high-pressure fluid flowing through the vaneless diffuser is smoothly slit-like fluid circulation path It can be made to flow into the back side of the impeller while maintaining the swirling flow. Therefore, pressure loss, mainly wall friction loss in the recirculation system of high-pressure fluid, can be reduced to increase the flow rate in the region where the rotating stall occurs, and the decrease in efficiency can be suppressed while preventing the rotating stall. Can do. In addition, since the swirl component can be retained in the recirculation flow, the mixing loss when recombining with the main flow can be reduced.

1 is a longitudinal sectional view of a two-stage centrifugal compressor according to a first embodiment of the present invention. It is principal part sectional drawing of the two-stage centrifugal compressor shown in FIG. It is aa expanded sectional view in FIG. It is a performance curve figure which shows the turning stall generation | occurrence | production point and efficiency of the two-stage centrifugal compressor shown in FIG. It is an aa expanded sectional equivalent figure (A) and (B) in Drawing 2 of a two-stage centrifugal compressor concerning a 2nd embodiment of the present invention. It is an aa expanded sectional equivalent view in Drawing 2 of a two-stage centrifugal compressor concerning a 3rd embodiment of the present invention. FIG. 7 is an enlarged cross-sectional view corresponding to aa in FIG. 2 illustrating a first modification of the two-stage centrifugal compressor illustrated in FIG. 6. FIG. 7 is an enlarged cross-sectional view corresponding to aa in FIG. 2 illustrating a second modification of the two-stage centrifugal compressor illustrated in FIG. 6. It is principal part sectional drawing of the two-stage centrifugal compressor of a prior art example. It is a performance curve figure (A) and (B) which shows the turning stall generating point and efficiency of the two-stage centrifugal compressor of a conventional example.

Embodiments according to the present invention will be described below with reference to the drawings.
[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 to 3.
FIG. 1 is a longitudinal sectional view of a centrifugal compressor 1 according to the first embodiment of the present invention.
The centrifugal compressor 1 includes a casing 2 configured by combining a plurality of parts, a rotating shaft 4 that is rotatably supported around the axis L in the casing 2 via a bearing (not shown), Closed type or open type two impellers 5A and 5B (closed impellers are shown in this embodiment) provided so as to rotate integrally with the shaft 4.

  The centrifugal compressor 1 is driven by a driving device (not shown), and the impellers 5A and 5B are rotated to rotate the gas or air to be compressed through the fluid suction port 6 provided in the casing 2. Etc. are sucked. First, centrifugal force is applied to the fluid by the rotation of the first stage impeller 5A, and the kinetic energy is converted into pressure energy by the first stage vaneless diffuser 7A provided at the outlet of the impeller 5A. The bend 8 and the return vane 9 are led to the inlet of the second stage impeller 5B, which is the next stage compression stage.

  This compressed fluid is similarly given a centrifugal force by the second stage impeller 5B, and the kinetic energy is converted into pressure energy by the second stage vaneless diffuser 7B, and further becomes a high-pressure compressed fluid to the scroll 10. Discharged. The scroll 10 is sent to a discharge pipe (not shown) through a fluid discharge port 11 provided in the casing 2. Thus, in this embodiment, the two-stage centrifugal compressor 1 is illustrated.

  The vane-less diffusers 7A and 7B are provided in communication with the exit side of the space in which the impellers 5A and 5B rotate, respectively, and convert the kinetic energy of the fluid given centrifugal force by the impellers 5A and 5B into pressure energy. The flow path to be sent out is configured. In the vane-less diffusers 7A and 7B, as described above, it is known that when the centrifugal compressor 1 is operated in a low flow rate region, a rotating stall that causes uneven flow in the circumferential direction occurs. In order to suppress the occurrence of the turning stall, the present embodiment employs the following configuration.

FIG. 2 is a cross-sectional view of a main part showing the configuration of the vaneless diffuser 7A, and FIG. 3 is an enlarged aa cross-sectional view thereof.
The vane-less diffuser 7A is formed by a shroud side casing 2A and a hub side casing 2B constituting the housing 2. In the hub side casing 2B, the fluid inlet 12A is opened at a predetermined position on the wall surface of the hub side casing 2B constituting the vaneless diffuser 7A, and the fluid outlet 12B is opposed to the rear surface of the hub disk 5C constituting the impeller 5A. A slit-like fluid circulation path 12 opened in the wall surface of the hub-side casing 2B is provided.

  The slit-like fluid circulation path 12 takes in a part of the compressed fluid flowing through the vaneless diffuser 7A from the fluid inlet 12A and passes it from the fluid outlet 12B opened to the back surface of the hub disk 5C of the impeller 5A to the main flow path side. This is for ejecting and recirculating a part of the compressed fluid between before and after the inlet portion of the vaneless diffuser 7A. The slit-shaped fluid circulation path 12 is formed by providing a slit having a predetermined width between two divided hub side casing members 13A and 13B. The two hub side casing members 13A and 13B are circumferentially arranged. Are joined together by a connecting member 14 made of a columnar member 14A having a circular cross section provided at equal intervals. In addition, the circumferential direction arrangement | positioning of the connection member 14 does not necessarily need to be equal intervals, and what is necessary is just to set an interval suitably.

The fluid inlet 12A of the slit-like fluid circulation path 12 is located at a position of 1.1R2 to 1.4R2 when the center of the opening is R2 and the outlet radius of the impeller 5A, and the rotation stall start at the vaneless diffuser 7A is started. The opening is made radially outward from the radial position.
This is because the turning stall in the vaneless diffuser 7A is the result of analysis of the flow in the vaneless diffuser 7A (CFD, model verification test, etc.). Assuming that the radius is Rrev, the smaller the diffuser width ratio b / R2 (b; diffuser width, R2; impeller exit radius), the smaller the turning stall start radius Rrev, and the radius ratio (Rrev / R2) approaches 1.0. It becomes like this. This means that as the diffuser with a smaller diffuser width ratio b / R2, a turning stall occurs on the inner diameter side, that is, near the diffuser inlet. Further, even when the diffuser width ratio b / R2 was set to the maximum value, the radius ratio (Rrev / R2) of the turning stall start radius Rrev was about 1.3. From the above, it is based on the fact that the turning stall start radius Rrev is confirmed to be in the range of 1.0R2 to 1.3R2.

  In this way, the fluid inlet 12A is located slightly outside the range in which the radius ratio (Rrev / R2), which is the range of the turning stall start radius Rrev in the vaneless diffuser 7A, is 1.0R2 to 1.3R2. The opening is made so that the center of the opening is located at 1.1R2 to 1.4R2.

  The fluid outlet 12B of the slit-like fluid circulation path 12 is located at a position of 0.90R2 to 0.97R2 when the center of the opening is R2 and the outlet radius of the impeller 5A, and from the outer peripheral end 5D of the impeller 5A. Is also opened at a radially inner position. This is a position where the fluid ejected from the fluid outlet 12B surely hits the back surface of the hub disk 5C of the impeller 5A, and a position that is as radially outer as possible as long as it does not come out from the outer peripheral end 5D of the impeller 5A. This is for opening the fluid outlet 12B.

  Thus, by determining the opening position of the fluid inlet 12A and the opening position of the fluid outlet 12B, the length from the fluid inlet 12A to the fluid outlet 12B of the slit-like fluid circulation path 12 can be shortened as much as possible. It is possible to reduce as much as possible the pressure loss, mainly the wall friction loss of the recirculation fluid generated in the slit fluid circulation path 12.

  Further, by providing the fluid inlet 12A at the position of 1.1R2 to 1.4R2 as described above, the pressure difference between the fluid inlet 12A and the fluid outlet 12B becomes relatively small compared to the conventional one. Since the compressed fluid does not easily flow to the slit-like fluid circulation path 12 side, the slit width b1 (see FIG. 3) of the slit-like fluid circulation path 12 is at least 20% or more, preferably 30% or more of the diffuser width b. The compressed fluid is easily recirculated.

With the configuration described above, according to the present embodiment, the following operational effects can be obtained.
Even when the centrifugal compressor 1 is operated in a low flow rate region, since the slit-like fluid circulation path 12 is provided as described above, the fluid inlet 12A and the fluid outlet 12B of the slit-like fluid circulation path 12 are provided. Due to the pressure difference therebetween, a part of the compressed fluid flowing through the vaneless diffuser 7A is circulated through the slit-like fluid circulation path 12 to the back surface position of the hub disk 5C of the impeller 5A. Then, after being ejected toward the rear surface of the hub disk 5C, the fluid main flow flowing through the impeller 5A and the outlet thereof, that is, the inlet portion of the vaneless diffuser 7A are joined together with the circumferential flow velocity applied by the hub disk 5C. Then, it flows again into the vaneless diffuser 7A.

  In this way, a part of the compressed fluid is recirculated through the slit-like fluid circulation path 12 between before and after the inlet portion of the vaneless diffuser 7A, so that the vicinity of the inlet portion of the vaneless diffuser 7A, that is, The flow rate of the fluid flowing in the turning stall start radius Rrev region can be locally increased. For this reason, as shown in FIG. 4, the turning stall occurrence point Q3 can be moved toward the low flow rate region by the increased flow rate ratio, thereby suppressing the occurrence of turning stall. In addition, pressure fluctuations, shaft vibrations, discharge pipe vibrations, and the like caused by turning stall can be suppressed, so that the range in which the centrifugal compressor 1 can be stably operated can be expanded.

  In FIG. 4, the flow rate Q3 is the turning stall occurrence point, the lower flow rate side is the turning stall occurrence region W3, and it does not have the fluid circulation path shown in FIG. 10 (B). In comparison, it can be seen that the turning stall occurrence point Q3 is shifted to the low flow rate region side, and the turning stall occurrence region W3 is remarkably narrow. Therefore, the range in which the centrifugal compressor 1 can be stably operated is expanded accordingly.

  On the other hand, the fluid inlet 12A of the slit-shaped fluid circulation path 12 has a radial ratio (Rrev / R2) that is a range of the turning stall start radius Rrev in the vaneless diffuser 7A in a radial direction than the range of 1.0 to 1.3. The fluid outlet 12B is opened so as to be located outside (the center of the opening is located at 1.1R2 to 1.4R2), and the fluid outlet 12B has a center at which the outlet radius of the impeller 5A is R2. , 0.90R2 to 0.97R2, the distance from the fluid inlet 12A to the fluid outlet 12B of the slit-like fluid circulation path 12 can be shortened compared to the conventional one. In addition, since the slit-like fluid circulation path 12 is constituted by one slit over the entire circumference, the flow path can be wide in the circumferential direction.

  Thus, by making the length of the slit-like fluid circulation path 12 short and wide in the circumferential direction, the compressed fluid flowing through the vaneless diffuser 7A is smoothly introduced to the slit-like fluid circulation path 12 side, The compressed fluid can be discharged to the back side of the impeller 5A while maintaining the swirling flow. As a result, pressure loss, mainly wall friction loss in the recirculation system of the compressed fluid, can be reduced, and as shown in FIG. Can be suppressed.

  Furthermore, the width b1 of the slit-shaped fluid circulation path 12 is set to at least 20% or more, preferably 30% or more, of the flow path width b of the vaneless diffuser 7A. For this reason, by providing the fluid inlet 12A and the fluid outlet 12B at the above positions, the pressure difference between the inlet and outlet is reduced, and the compressed fluid hardly flows to the slit-like fluid circulation path 12 side. The required recirculation flow rate is ensured by setting the flow path width b1 of the path 12 to at least 20% or more of the flow path width b of the vaneless diffuser 7A and relatively expanding the flow path width b1 to reduce pressure loss. I am doing so. Therefore, it is possible to reliably increase the flow rate of the fluid flowing in the turning stall generation region of the vaneless diffuser 7A and suppress the turning stall.

  Further, since the fluid outlet 12B is on the wall surface of the hub-side casing 2B facing the rear surface of the hub disk 5C and is opened at a position radially inward from the outer peripheral end 5D of the impeller 5A, the recirculation ejected therefrom The main flow of the fluid flowing through the impeller 5A is not disturbed by the flow, and the recirculation flow is given a circumferential flow velocity by the back surface of the hub disk 5C, and the main flow of the fluid at the inlet portion of the vaneless diffuser 7A. When merged, the circumferential flow velocity is approximately the same as the fluid main flow. Therefore, an increase in pressure loss due to flow shear can be suppressed, and this also can suppress a decrease in efficiency of the centrifugal compressor 1.

  In addition, in the slit-shaped fluid circulation path 12, a connecting member 14 including a columnar member 14 </ b> A having a circular cross section is provided at a plurality of locations in the circumferential direction, and the slit-shaped fluid circulation path 12 is formed via the connecting member 14. The two hub-side casing members 13A and 13B are integrally connected. For this reason, the hub side casing members 13A and 13B divided into two parts are connected by the connecting member 14, and a slit is provided between them to form one slit shape in the hub side casing 2B over the entire circumference. The fluid circulation path 12 can be easily formed.

  Therefore, the slit-like fluid circulation path 12 capable of reducing the pressure loss in the hub-side casing 2B can be simply configured, and this can also suppress the decrease in efficiency. In addition, since the connecting member 14 is a columnar member 14A having a circular cross section, the flow resistance by the connecting member 14 is made as small as possible, and the recirculation flow that flows in the slit-like fluid circulation path 12 is kept swirling. The fluid can be smoothly circulated to the fluid outlet 12B. Thereby, the pressure loss due to the connecting member 14 can be minimized, and the decrease in efficiency can be further reduced.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIGS.
This embodiment is different from the above-described first embodiment in that the connecting member 14 is finned columnar members 14B and 14B ′. Since other points are the same as those in the first embodiment, description thereof will be omitted.
In the present embodiment, the plurality of connecting members 14 integrally connecting the two hub side casing members 13A and 13B extend from the columnar member having a circular cross section toward the swirling direction of the compressed fluid flowing in the fluid circulation path 12. The streamlined fins 14b and the plate-like fins 14b 'having plate-like fins 14b' are used.

  As described above, the connecting member 14 is the columnar members 14B and 14B ′ having fins 14b and 14b ′ that extend from the columnar member having a circular cross section in the fluid swirling direction. The separation and vortex of the flow generated on the back side of the plate can be suppressed by the fins 14b and 14b ′. For this reason, pressure loss due to separation and vortexing of the circulating flow generated by the connecting member 14 can be suppressed, and a decrease in efficiency can be suppressed. Moreover, since the cross-sectional areas of the columnar members 14B and 14B ′ can be increased by providing the fins 14b and 14b ′, the connecting member 14 and the two hub-side casing members 13A and 13B integrally coupled by the connecting member 14 are provided. Sufficient strength can be secured.

[Third Embodiment]
Next, a third embodiment of the present invention will be described with reference to FIGS.
This embodiment is different from the first embodiment described above in that the connecting member 14 is a columnar member 14C, 14D, 14E having an airfoil cross section. Since other points are the same as those in the first embodiment, description thereof will be omitted.
In the present embodiment, the plurality of connecting members 14 integrally connecting the two hub-side casing members 13A and 13B extend along the fluid swirling direction, as shown in FIG. A straight plate-like airfoil cross-section columnar member 14C, a curved plate-like airfoil cross-section columnar member 14D as shown in FIG. 7, and an airfoil cross-section columnar member 14E as shown in FIG. Has been.

  Thus, by making the connecting member 14 columnar members 14C, 14D, and 14E having an airfoil cross section, the flow resistance by the connecting member 14 is made as small as possible, and the compression flowing in the slit fluid circulation path 12 is performed. The fluid can be smoothly circulated along the airfoil to the fluid outlet 12B while maintaining a swirling flow. Therefore, the pressure loss due to the connecting member 14 can be minimized, and the decrease in efficiency can be suppressed.

  In addition, this invention is not limited to the invention concerning the said embodiment, In the range which does not deviate from the summary, it can change suitably. For example, in the above-described embodiment, an example in which the present invention is applied to the lower stage side of the two-stage centrifugal compressor has been described, but it is needless to say that the present invention may be applied to the higher stage side. Needless to say, the present invention is not limited to the two-stage centrifugal compressor, and can be similarly applied to a single-stage or three-stage or more multi-stage centrifugal compressor.

DESCRIPTION OF SYMBOLS 1 Centrifugal compressor 2 Casing 2B Hub side casing 5A, 5B Impeller 5C Hub disk 5D Impeller outer peripheral end 7A, 7B Vaneless diffuser 12 Slit fluid circulation path 12A Fluid inlet 12B Fluid outlet 13A, 13B Two hub side casing members 14 Connecting member 14A Columnar members 14B, 14B 'with fins having circular cross-sections Columnar members 14C, 14D, 14E with fins R2 Impeller outlet radius b Vaneless diffuser channel width b1 Slit-shaped fluid circulation channel width

Claims (7)

In the centrifugal compressor provided with a vaneless diffuser on the outlet side of the impeller,
A fluid inlet is provided in the hub side casing wall surface of the vaneless diffuser, and a slit-like fluid circulation path in which a fluid outlet is opened in the hub side casing wall surface facing the rear surface of the hub disk of the impeller is provided.
The fluid inlet of the slit-like fluid circulation path is located at a position of 1.1R2 to 1.4R2, where the center of the opening is R2 when the outlet radius of the impeller is R2, and start of turning stall in the vaneless diffuser A centrifugal compressor, wherein the centrifugal compressor is opened at a radially outer position than a radial position.   The fluid outlet of the slit-like fluid circulation path is characterized in that the center of the opening is located at a position of 0.90R2 to 0.97R2 and is opened at a position radially inward from the outer peripheral end of the impeller. The centrifugal compressor according to claim 1.   The centrifugal compressor according to claim 1 or 2, wherein a width of the slit-shaped fluid circulation path is at least 20% or more of a flow path width of the vaneless diffuser.   In the slit-like fluid circulation path, connecting members are provided at a plurality of locations in the circumferential direction, and two hub side casing members that form the slit-like fluid circulation path are integrally coupled via the connecting member. The centrifugal compressor according to any one of claims 1 to 3, wherein the centrifugal compressor is provided.   The centrifugal compressor according to claim 4, wherein the connecting member is a columnar member having a circular cross section.   6. The centrifugal compressor according to claim 4, wherein the connecting member is a columnar member with a fin having a fin extending from a columnar member having a circular cross section toward a direction of swirling of the fluid. The centrifugal compressor according to claim 4, wherein the connecting member is a columnar member having an airfoil cross section.

Images