JP6242775B2 - Centrifugal compressor - Google Patents

Description

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

  In general, industrial centrifugal compressors are used in petrochemical plants and natural gas plants. In this type of centrifugal compressor, a configuration using a vaneless diffuser in which no vane is provided in the diffuser portion on the outlet side of the impeller is widely adopted. The configuration using the vaneless diffuser has an advantage that the structure is simple, and if the flow angle is appropriate, the loss is small, the operating range is wide, and no fluid excitation force is generated on the impeller. 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 turning stall occurs particularly when the centrifugal compressor is operated in a small flow rate region.

  For this reason, in order to suppress the occurrence of turning stall, conventionally, a fluid circulation channel in which an inlet is opened on the outlet side of the vaneless diffuser and an outlet is opened on the wall surface of the casing facing the rear surface of the hub disk of the impeller. And a centrifugal compressor in which a part of the high-pressure fluid is recirculated through a fluid circulation channel has been proposed (for example, see Patent Document 1).

JP 2008-38894 A

  By providing the above-described fluid circulation flow path, a reduction in the turning stall starting flow rate when the turning stall is first generated in the vaneless diffuser is achieved while suppressing a decrease in efficiency of the centrifugal compressor. On the other hand, a configuration for further reducing the turning stall start flow rate is being sought.

  This invention is made in view of such a situation, Comprising: It aims at providing the centrifugal compressor which aimed at the small flow volume of a turning stall start flow rate in the structure which provided the fluid circulation flow path. .

  In order to solve the above-described problems and achieve the object, a centrifugal compressor according to the present invention includes a vaneless diffuser provided on an outlet side of an impeller, and a fluid in a first wall portion of a hub casing that forms the vaneless diffuser. A fluid circulation passage having an inlet opened and a fluid outlet opened in a second wall portion of the hub casing facing the rear surface of the hub disk of the impeller. The vaneless diffuser includes at least the first wall portion of the hub casing. The vaneless diffuser has a channel width smaller than the outlet width of the impeller by projecting toward the wall portion side of the shroud casing facing the first wall portion, and the hub casing is connected to the outlet of the impeller. An inclined wall portion that connects the second wall portion and the first wall portion, starting from the entrance of the vane-less diffuser, is provided.

  According to this configuration, the fluid inlet is opened in the first wall portion of the hub casing forming the vaneless diffuser, and the fluid outlet is opened in the second wall portion of the hub casing facing the back surface of the hub disk of the impeller. Since the flow path is provided, a part of the high-pressure fluid can be circulated to the inlet side of the vaneless diffuser by the fluid circulation flow path, and the flow rate of the fluid flowing through the vaneless diffuser can be increased. For this reason, the turning stall occurrence point can be shifted to the small flow rate side by the increased flow rate ratio, and the occurrence of turning stall can be suppressed. The vaneless diffuser projects at least the first wall portion of the hub casing toward the wall portion of the shroud casing facing the first wall portion, thereby reducing the flow path width of the vaneless diffuser to the outlet width of the impeller. And the hub casing has an inclined wall portion that starts between the outlet of the impeller and the inlet of the vaneless diffuser and connects the second wall portion and the first wall portion. By flowing the circulation flow blown out from the outlet of the circulation flow path along the inclined wall portion, the fluid main flow blown out from the impeller outlet can be smoothly merged, and the fluid flow in the vaneless diffuser is disturbed. It will not be done. In addition, since the flow path width of the vaneless diffuser is narrowed by the inclined wall, the flow in the vaneless diffuser is smooth even at a small flow rate with a small fluid flow rate, and the turning stall point is further reduced to the smaller flow rate side. Can be shifted to.

  In this configuration, it is preferable that the inclined wall portion has a terminal end connected to the first wall portion positioned on the radially outer side of the radially inner end portion of the impeller in the wall portion of the shroud casing. According to this configuration, the inclination angle of the inclined wall portion on the hub casing side can be formed more gently than on the shroud casing side, so that the main flow circulates in the main fluid flow without disturbing the flow of the main fluid blown from the impeller outlet. The flow can be smoothly merged.

  Further, the first wall portion of the hub casing protrudes toward the wall portion side of the shroud casing from the hub side extension line extending radially outward from the outlet of the impeller, and the hub side protruding length from the hub side extension line to the first wall portion. Is preferably 50% or less of the exit width of the impeller. According to this configuration, it is possible to suppress a decrease in the efficiency of the centrifugal compressor while shifting the turning stall occurrence point to the small flow rate side.

  Further, the wall portion of the shroud casing protrudes toward the first wall portion side of the hub casing from the shroud side extension line extending radially outward from the outlet of the impeller, and the shroud side protrusion length from the shroud side extension line to the wall portion is: It is preferably 20% or less of the outlet width of the impeller. Within this range, the effect of shifting the turning stall occurrence point to the small flow rate side is exhibited.

  According to the centrifugal compressor according to the present invention, the vaneless diffuser projects at least the first wall portion of the hub casing toward the wall portion side of the shroud casing facing the first wall portion, thereby the vaneless diffuser. The hub casing is formed to be smaller than the outlet width of the impeller, and the hub casing is connected between the second wall portion and the first wall portion, starting from the impeller outlet and the vaneless diffuser inlet. Therefore, by flowing the circulating flow blown out from the outlet of the fluid circulation channel along the inclined wall portion, it can smoothly merge with the fluid main flow blown out from the impeller outlet. The flow of fluid in the less diffuser is not disturbed. In addition, since the flow path width of the vaneless diffuser is narrowed by the inclined wall, the flow in the vaneless diffuser is smooth even at a small flow rate with a small fluid flow rate, and the turning stall point is further reduced to the smaller flow rate side. Can be shifted to.

FIG. 1 is a longitudinal sectional view of a centrifugal compressor according to this embodiment. FIG. 2 is a cross-sectional view of a main part showing a configuration in the vicinity of the vaneless diffuser. FIG. 3 is a graph showing the relationship between the flow coefficient, the pressure coefficient, and the efficiency in Comparative Examples 1 to 8 and Examples. FIG. 4 is a graph showing the relationship between the flow coefficient at the turning stall start point and the efficiency of the design point. FIG. 5 is a cross-sectional view of a main part showing a configuration in the vicinity of a vaneless diffuser according to another embodiment.

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, this invention is not limited by the following embodiment. In addition, constituent elements in the following embodiments include those that can be easily replaced by those skilled in the art or those that are substantially the same.

  FIG. 1 is a longitudinal sectional view of a centrifugal compressor according to this embodiment. The centrifugal compressor 1 includes a casing 2 configured by combining a plurality of parts, and a rotating shaft 5 that is rotatably supported around the axis L in the casing 2 via a bearing (not shown). And closed type impellers 6 and 6 provided so as to rotate integrally with the rotary shaft 5. That is, the centrifugal compressor 1 of the present embodiment is a two-stage centrifugal compressor.

  The centrifugal compressor 1 is driven by a driving device (not shown), and the impellers 6 and 6 are rotated to rotate the impellers 6 and 6 through a suction port 10 provided in the casing 2. Etc. are sucked. A suction passage 11 is connected to the suction port 10 via a suction space 10A formed in the casing 2, and the suction passage 11 bends along the axis L direction (axial direction) of the rotary shaft 5. The first stage impeller 6 is opened facing the suction port 6A.

  Centrifugal force is applied to the fluid sucked from the suction port 10 by the rotation of the first stage impeller 6, and the kinetic energy is pressured by the first stage vaneless diffuser 12 provided at the outlet 6 </ b> B of the impeller 6. Converted into energy. Further, this fluid is guided through the return bend 14 and the return vane 15 to the suction port 6A of the second stage impeller 6 which is the next stage compression stage.

  The compressed fluid is similarly given a centrifugal force by the second stage impeller 6, and the kinetic energy is converted into pressure energy by the second stage vaneless diffuser 12, and further becomes a high pressure compressed fluid to the scroll 16. Discharged. The scroll 16 is then sent to a discharge pipe (not shown) via a discharge port 17 provided in the casing 2. In addition, the code | symbol 18 in FIG. 1 is a balance piston provided in order to adjust the thrust of the impeller 6. FIG.

  By the way, the vaneless diffuser 12 is provided in communication with the exit side of the space where the impeller 6 rotates, and a flow path for converting the kinetic energy of the fluid to which the centrifugal force is given by the impeller 6 into pressure energy and sending it out. Configure. In the vane-less diffuser 12, when the centrifugal compressor 1 is operated in a small flow rate region, a rotating stall may occur in which the circumferential flow becomes non-uniform. 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 a configuration in the vicinity of the vaneless diffuser. The vaneless diffuser 12 is formed by a shroud casing 2A and a hub casing 2B that constitute the casing 2. The hub casing 2B is provided with a fluid circulation passage (bypass passage, also simply referred to as bypass) 21 for circulating the fluid in the vaneless diffuser 12 back to the vicinity of the blower outlet (impeller outlet) 6B of the impeller 6. It has been. Specifically, as shown in FIG. 2, the fluid circulation channel 21 includes an inlet 21 </ b> A and an outlet 21 </ b> B, and the inlet 21 </ b> A opens to the first wall portion 22 of the hub casing 2 </ b> B that forms the vaneless diffuser 12. The outlet 21B opens to the second wall portion 23 of the hub casing 2B facing the back surface of the hub disk 6C constituting the impeller 6.

  The fluid circulation passage 21 takes in a part of the high-pressure compressed fluid that has passed through the vaneless diffuser 12 from the inlet 21A and blows it out from the outlet 21B to blow out the vaneless diffuser 12 and the impeller 6 outlet 6B. And a part of the compressed fluid is circulated. A plurality of fluid circulation channels 21 may be provided, and the outlet 21B of the fluid circulation channel 21 is formed to face the back surface of the hub disk 6C of the impeller 6. Thereby, the fluid blown out from the outlet 21 </ b> B is given a circumferential flow velocity by the back surface of the hub disk 6 </ b> C of the impeller 6 as the impeller 6 rotates. Thereby, the circumferential flow velocity when the fluid blown out from the outlet 21B merges with the fluid main flow blown out from the impeller 6 can be set to a circumferential flow velocity substantially equal to the fluid main flow.

  Further, the first wall portion 22 of the hub casing 2B is formed so as to protrude from the second wall portion 23 toward the wall portion 31 side of the shroud casing 2A facing the first wall portion 22. Specifically, the first wall portion 22 of the hub casing 2B is a hub side that extends radially outward (in the direction of arrow A in FIG. 2) of the impeller 6 from the end of the air outlet 6B of the impeller 6 on the hub casing 2B side. It protrudes toward the wall 31 side of the shroud casing 2A from the extension line HA. The first wall portion 22 and the second wall portion 23 are connected by an inclined wall portion 24.

  On the other hand, in the present embodiment, the wall portion 31 of the shroud casing 2A is also the hub casing 2B than the shroud side extension line SA extending from the end on the shroud casing 2A side of the air outlet 6B of the impeller 6 to the radially outer side of the impeller 6. It protrudes toward the first wall portion 22 side. The shroud casing 2 </ b> A includes a horizontal wall 30 that faces the air outlet 6 </ b> B of the impeller 6 and extends in the direction of the axis L of the rotating shaft 5, and the horizontal wall 30 and the wall portion 31 are connected via a connecting wall 32. The connecting wall 32 can adopt various shapes, and may be an R wall or an inclined wall formed with a predetermined radius of curvature. When such a connection wall 32 is provided, the end 31 </ b> A on the radially inner side of the impeller 6 in the wall portion 31 described above serves as a connection portion with the connection wall 32.

  In the present embodiment, the wall portion 31 of the shroud casing 2A and the first wall portion 22 of the hub casing 2B both extend within the projection plane of the air outlet 6B of the impeller 6, and the wall portion 31 and the first wall portion 22. The flow path width D of the vaneless diffuser 12 is formed smaller than the width (outlet width) W of the outlet 6B of the impeller 6. Thus, the flow path width D of the vaneless diffuser 12 is formed so as to narrow the width W of the air outlet 6B of the impeller 6.

  When the length in the axis L direction from the hub side extension line HA to the first wall portion 22 is the hub side projection length HD, the hub side projection length HD is 50 of the width W of the outlet 6B of the impeller 6. % Or less is preferable. Further, as in the present embodiment, in the configuration in which both the first wall portion 22 of the hub casing 2B and the wall portion 31 of the shroud casing 2A protrude so as to extend within the projection surface of the air outlet 6B of the impeller 6, When the length in the axis L direction from the shroud side extension line SA to the wall portion 31 is the shroud side projection length SD, the sum of the hub side projection length HD and the shroud side projection length SD is the width W of the outlet 6B of the impeller 6. It is preferable to make it 50% or less. The shroud side protrusion length SD is preferably 20% or less of the width W of the air outlet 6B of the impeller 6.

  Next, the restriction of the first wall portion 22 of the hub casing 2B will be described. As described above, the first wall portion 22 protrudes so as to gradually extend into the projection plane of the air outlet 6B of the impeller 6 by the inclined wall portion 24. Experiments and the like have revealed that the shape of the inclined wall portion (protrusion) 24 is important. In the present embodiment, the inclined wall portion 24 is connected to the second wall portion 23 between the air outlet 6B of the impeller 6 and the inlet (position of the horizontal wall 30) of the vaneless diffuser 12 in the radial direction of the impeller 6. 24A is provided. Further, the end 24B of the inclined wall portion 24 is provided at a position radially outside the end portion 31A on the radially inner side of the impeller 6 in the wall portion 31 of the shroud casing 2A. According to this configuration, the inclined wall portion 24 can be formed to have a gentle throttle, and the circulating flow can be smoothly flowed into the main fluid flow without disturbing the flow of the main fluid flow blown from the outlet 6B of the impeller 6. Can be joined. Note that the inclined wall portion 24 includes not only a flat wall formed at a predetermined angle but also a curved wall having a curved surface, for example. Next, examples and comparative examples will be described.

[Comparative Example 1]
In Comparative Example 1, the wall portion 31 of the shroud casing 2A protrudes from the shroud side extension line SA, and the first wall portion 22 of the hub casing 2B is formed on the hub side extension line HA. The shroud casing 2A and the hub casing 2B each have an inclined wall portion (not shown), and the end of the inclined wall portion on the shroud casing 2A side is formed radially outward from the end of the inclined wall portion of the hub casing 2B. (SH side loose protrusion). The shroud side protrusion length SD of the wall portion 31 of the shroud casing 2A is 40% of the width W of the blower outlet 6B of the impeller 6, and the flow path width D of the vaneless diffuser 12 and the width W of the blower outlet 6B are The ratio D / W is 0.6. In Comparative Example 1, the fluid circulation channel 21 is not provided.

[Comparative Example 2]
In Comparative Example 2, the shroud side protrusion length SD of the wall portion 31 of the shroud casing 2A is changed, and only the corner R portion having a small curvature radius R exists between the wall portion 31 of the shroud casing 2A and the horizontal wall 30. (SH side sudden protrusion). The shroud side protrusion length SD is 17% of the width W of the air outlet 6B of the impeller 6, and the ratio D / W of the flow path width D of the vaneless diffuser 12 and the width W of the air outlet 6B is 0.83. It has become. Other configurations are the same as those of the first comparative example.

[Comparative Example 3]
In Comparative Example 3, there is only a corner R portion having a small radius of curvature R between the wall portion 31 of the shroud casing 2A and the horizontal wall 30 (SH side sudden protrusion). Other configurations are the same as those of the first comparative example.

[Comparative Example 4]
In Comparative Example 4, the shroud side protrusion length SD of the wall portion 31 of the shroud casing 2A is changed. The shroud side protrusion length SD is 60% of the width W of the air outlet 6B of the impeller 6, and the ratio D / W between the flow path width D of the vaneless diffuser 12 and the width W of the air outlet 6B is 0.4. It has become. Other configurations are the same as those of the first comparative example.

[Comparative Example 5]
In Comparative Example 5, there is only a corner R portion having a small radius of curvature R between the wall portion 31 and the horizontal wall 30 of the shroud casing 2A (SH side sudden protrusion). Other configurations are the same as those in Comparative Example 4.

[Comparative Example 6]
In Comparative Example 6, the fluid circulation channel 21 is provided in the first wall portion 22 and the second wall portion 23 of the hub casing 2B. The fluid circulation channel 21 has a position where the radius R2 of the opening center of the inlet 21A of the fluid circulation channel 21 satisfies 1.1R1 ≦ R2 ≦ 1.4R1 when the radius of the outlet 6B of the impeller 6 is R1. Is open. Other configurations are the same as those of the first comparative example.

[Comparative Example 7]
In Comparative Example 7, there is only a corner R portion with a small radius of curvature R between the wall portion 31 of the shroud casing 2A and the horizontal wall 30 (SH side sudden protrusion). Other configurations are the same as those in Comparative Example 6.

[Comparative Example 8]
In Comparative Example 8, the shroud side protrusion length SD of the wall portion 31 of the shroud casing 2A is changed, and only the corner R portion having a small curvature radius R exists between the wall portion 31 of the shroud casing 2A and the horizontal wall 30. (SH side sudden protrusion). The shroud side protrusion length SD is 17% of the width W of the air outlet 6B of the impeller 6, and the ratio D / W of the flow path width D of the vaneless diffuser 12 and the width W of the air outlet 6B is 0.83. It has become. Other configurations are the same as those of Comparative Example 6.

[Example]
In the embodiment, the wall portion 31 of the shroud casing 2A protrudes from the shroud side extension line SA, and the first wall portion 22 of the hub casing 2B also protrudes from the hub side extension line HA. The shroud side protrusion length SD is 17% of the width W of the air outlet 6B of the impeller 6, and the hub side protrusion length HD is 23% of the width W of the air outlet 6B of the impeller 6. For this reason, the ratio D / W of the flow path width D of the vaneless diffuser 12 and the width W of the outlet 6B is 0.6. Further, there is only a corner R portion having a small radius of curvature R between the wall portion 31 of the shroud casing 2A and the horizontal wall 30 (SH side sudden protrusion). In addition, the inclined wall portion 24 of the hub casing 2B has a terminal end 24B provided in the vicinity of the inlet 21A of the fluid circulation channel 21, and narrows the channel width D of the vaneless diffuser 12 with a gentle inclination (the hub side is loose). Protruding). Other configurations are the same as those of Comparative Example 6.

  FIG. 3 is a graph showing the relationship between the flow coefficient, the pressure coefficient, and the efficiency in Comparative Examples 1 to 8 and Examples, and FIG. 4 shows the flow coefficient and design point of the turning stall start point (of FIG. 3). It is a graph which shows the relationship with the efficiency of a vertical broken line position. In FIG. 4, the ratio is expressed as a ratio based on Comparative Example 1.

  As shown in the region surrounded by the broken ellipse in FIG. 4, in the configuration in which the fluid circulation channel is not provided (Comparative Examples 1 to 5), the efficiency decreases when the shroud side protrusion length SD is roughly increased. Although there is a tendency, the turning stall start point can be shifted to the small flow rate side.

  On the other hand, in the configuration provided with the fluid circulation channel 21 (Comparative Example 6 to Comparative Example 8: with bypass), it is not necessary to increase the shroud side protrusion length SD. Specifically, as shown in Comparative Examples 7 and 8, when the shroud side protrusion length SD is changed from 17% (Comparative Example 8) to 40% (Comparative Example 7) of the width W of the air outlet 6B of the impeller 6, the turning As the flow rate coefficient at the stall start point increased, the efficiency decreased. If the wall (31 of shroud casing 2A) on the opposite side to the wall from which the circulating flow of the fluid circulation flow path 21 blows largely protrudes, the wall 31 and the circulating flow collide with each other, and the wall 31 instead. It seems to promote the exfoliation flow part on the wall surface. For this reason, when projecting the wall portion 31 of the shroud casing 2A, the shroud side protrusion length SD is preferably 20% or less of the width W of the air outlet 6B of the impeller 6.

  In the embodiment, as described above, the shroud side protrusion length SD is 17% of the width W of the air outlet 6B of the impeller 6, and the hub side protrusion length HD is 23% of the width W of the air outlet 6B of the impeller 6. The ratio D / W of the flow path width D of the vaneless diffuser 12 and the width W of the outlet 6B is set to 0.6. Further, as shown in FIG. 2, the end 24B of the inclined wall portion 24 of the hub casing 2B is located at a position radially outside the end portion 31A on the radially inner side of the impeller 6 in the wall portion 31 of the shroud casing 2A. Is provided. For this reason, the inclined wall portion 24 can be formed to have a gentle throttle, and the circulating flow can smoothly join the fluid main flow without disturbing the flow of the fluid main flow blown from the outlet 6B of the impeller 6. be able to. Therefore, as shown in FIG. 4, the turning stall starting point can be greatly shifted to the small flow rate side, and the turning stall can be prevented from occurring until the surge point. Furthermore, the efficiency can be made higher than in a configuration in which the flow passage width D of the vaneless diffuser 12 is greatly reduced to have the same rotational stall occurrence point in the state where the fluid circulation passage 21 is not provided. In the example, even if the width ratio D / W is not reduced to 0.4 of Comparative Example 5, the same turning stall occurrence point can be realized at 0.6, and the efficiency is higher than that of Comparative Example 5. Understandable.

  In the embodiment, the shroud side protrusion length SD and the hub side protrusion length HD are set to 40% of the width W of the air outlet 6B of the impeller 6. However, when these protrusion lengths are larger than 50%, turning stall In addition to the start point far overtaking the surge point, the efficiency is reduced and the significance of forming the overhang is reduced. Therefore, the hub side protrusion length HD (and the shroud side protrusion length SD) is preferably set to 50% or less of the width W of the air outlet 6B of the impeller 6.

  As described above, the centrifugal compressor 1 according to the present embodiment includes the vaneless diffuser 12 provided on the air outlet 6B side of the impeller 6 and the first wall portion 22 of the hub casing 2B that forms the vaneless diffuser 12. The vaneless diffuser 12 includes a fluid circulation channel 21 having an inlet 21A opened and an outlet 21B opened in the second wall portion 23 of the hub casing 2B facing the rear surface of the hub disk 6C of the impeller 6. By projecting the portion 22 toward the wall portion 31 side of the shroud casing 2A, the flow path width D of the vaneless diffuser 12 is formed smaller than the width W of the outlet 6B of the impeller 6, and the hub casing 2B 24 A between the blower outlet 6B of the impeller 6 and the inlet of the vaneless diffuser 12 is a starting end 24A, and the second wall portion 23 and the first wall portion 22 are connected. Comprising an inclined wall portion 24. For this reason, by flowing the circulating flow blown from the outlet 21B of the fluid circulation channel 21 along the inclined wall portion 24, the fluid main flow blown from the blower outlet 6B of the impeller 6 can be smoothly merged. The fluid flow in the vaneless diffuser 12 is not disturbed. Furthermore, since the flow path width D of the vaneless diffuser 12 is narrowed by the inclined wall portion 24, the flow in the vaneless diffuser 12 becomes smooth even at a small flow rate with a small fluid flow rate. It can be shifted to a smaller flow rate side.

  In addition, according to the present embodiment, the inclined wall portion 24 has a terminal end 24B connected to the first wall portion 22 radially outside the end portion 31A on the radially inner side of the impeller 6 in the wall portion 31 of the shroud casing 2A. Therefore, the inclination angle of the inclined wall portion 24 of the hub casing 2B can be formed more gently than the shroud casing 2A side, so that the flow of the main fluid that is blown out from the outlet 6B of the impeller 6 is not disturbed. The circulating flow can smoothly join the fluid main flow. Therefore, when the flow rate is small, the flow in the vaneless diffuser 12 can be kept smooth, and the turning stall occurrence point can be shifted to the small flow rate side.

  Further, according to the present embodiment, the first wall portion 22 of the hub casing 2B protrudes toward the wall portion 31 side of the shroud casing 2A from the hub side extension line HA extending radially outward from the air outlet 6B of the impeller 6; Since the hub-side protruding length HD from the hub-side extension line HA to the first wall portion 22 is 50% or less of the width W of the air outlet 6B of the impeller 6, the centrifugal stall generation point is shifted to the small flow rate side while centrifugal A decrease in the efficiency of the compressor 1 can be suppressed.

  Further, according to the present embodiment, the wall portion 31 of the shroud casing 2A protrudes toward the first wall portion 22 side of the hub casing 2B from the shroud side extension line SA extending radially outward from the blower outlet 6B of the impeller 6; Since the shroud side protrusion length SD from the shroud side extension line SA to the wall portion 31 is 20% or less of the outlet width W of the impeller 6, the effect of shifting the turning stall occurrence point to the small flow rate side is exhibited.

  FIG. 5 is a cross-sectional view of a main part showing a configuration in the vicinity of a vaneless diffuser according to another embodiment. In this embodiment, the same components as those of the above-described embodiment are denoted by the same reference numerals and description thereof is omitted. In the above-described embodiment, both the wall portion 31 of the shroud casing 2A and the first wall portion 22 of the hub casing 2B are configured to extend within the projection plane of the air outlet 6B of the impeller 6, but the shroud casing 2A It is good also as a structure which arrange | positions the wall part 31 on shroud side extension line SA. That is, if at least the first wall portion 22 of the hub casing 2B is configured to protrude inward (wall portion 31 side) from the hub side extension line HA, an effect of shifting the turning stall occurrence point to the small flow rate side can be achieved. It can be demonstrated.

  As mentioned above, although embodiment of this invention was described, this invention is not limited by the above-mentioned content. For example, in the above-described embodiment, the impeller 6 and the vaneless diffuser 12 are provided in the two-stage centrifugal compressor 1, but if the compressor includes the impeller and the vaneless diffuser, a single-stage centrifugal It is applicable to a compressor and a multistage centrifugal compressor having three or more stages.

  In the embodiment described above, the wall portion 31 of the shroud casing 2A is connected to the horizontal wall 30 via the connecting wall 32 formed with a predetermined radius of curvature. An inclined wall that extends from the front end of the horizontal wall 30 toward the end portion 31 </ b> A of the wall portion 31 may be employed. When such a connection wall 32 is provided, the end portion 31 </ b> A on the inner side in the radial direction of the impeller 6 in the wall portion 31 serves as a connection portion with the connection wall 32.

DESCRIPTION OF SYMBOLS 1 Centrifugal compressor 2 Casing 2A Shroud casing 2B Hub casing 5 Rotating shaft 6 Impeller 6A Inlet 6B Outlet (outlet)
6C Hub disk 10 Suction port 10A Suction space 11 Suction channel 12 Vaneless diffuser 14 Return bend 15 Return vane 16 Scroll 17 Discharge port 18 Balance piston 21 Fluid circulation channel (bypass channel)
21A inlet (fluid inlet)
21B outlet (fluid outlet)
22 First wall portion 23 Second wall portion 24 Inclined wall portion 24A Starting end 24B Termination 30 Horizontal wall 31 Wall portion 31A End portion 32 Connecting wall D Channel width HA Hub side extension line HD Hub side extension line SA Shroud side extension line SD shroud side protrusion length W width (exit width)
L axis

Claims (4)

A vaneless diffuser provided on the exit side of the impeller,
A fluid circulation channel in which a fluid inlet is opened in a first wall portion of the hub casing forming the vaneless diffuser, and a fluid outlet is opened in a second wall portion of the hub casing facing the rear surface of the hub disk of the impeller. With
The vaneless diffuser projects at least the first wall portion of the hub casing toward the wall portion of the shroud casing facing the first wall portion, thereby reducing the flow path width of the vaneless diffuser to the outlet of the impeller. An inclined wall that is formed smaller than a width and that connects the second wall portion and the first wall portion with the hub casing as a starting point between an outlet of the impeller and an inlet of the vaneless diffuser. A centrifugal compressor comprising a section.   The end of the inclined wall portion connected to the first wall portion is located on the radially outer side of the radially inner end portion of the impeller in the wall portion of the shroud casing. The centrifugal compressor described in 1.   The first wall portion of the hub casing projects to the wall portion side of the shroud casing from the hub side extension line extending radially outward from the outlet of the impeller, and extends from the hub side extension line to the first wall portion. The centrifugal compressor according to claim 1 or 2, wherein the hub side protruding length is 50% or less of the outlet width of the impeller.   A wall portion of the shroud casing protrudes toward the first wall portion side of the hub casing from a shroud side extension line extending radially outward from the outlet of the impeller, and a shroud side protrusion from the shroud side extension line to the wall portion. The centrifugal compressor according to any one of claims 1 to 3, wherein the length is 20% or less of the outlet width of the impeller.

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