compressor

Abstract

With this compressor, gas compressed by a first impeller is further compressed by a second impeller. The compressor includes an interstage flow path through which the gas from the first impeller is introduced into the second impeller, and a bypass flow path through which the gas is recirculated to the interstage flow path from downstream of the second impeller. The downstream end of the bypass flow path is open to the interstage flow path so as to face the direction toward which the gas in the interstage flow path swirls in the flow path cross section of the interstage flow path.

Description

Technical Field

[0001] This disclosure relates to a compressor.

Background Art

[0002] Patent Document 1 discloses a centrifugal compressor provided with a bypass flow path that returns a part of the high-pressure air in the scroll flow path to the inlet side of the impeller in consideration of surging.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the centrifugal compressor of the above prior art, the impeller is configured as a single stage. In a multi-stage compressor with two or more stages, the gas compressed by the first impeller on the upstream side is further compressed by the second impeller on the downstream side. In such a configuration, the swirling flow generated in the gas during the compression by the first impeller may affect the compression performance of the second impeller.

[0005] This disclosure describes a compressor capable of suppressing the influence of the swirling flow generated in the gas during the compression by the first impeller on the second impeller.

Means for Solving the Problems

[0006] One aspect of this disclosure is a compressor that further compresses the gas compressed by the first impeller with the second impeller, comprising an inter-stage flow path that introduces the gas from the first impeller to the second impeller, and a bypass flow path that refluxes the gas from the downstream of the second impeller to the inter-stage flow path. The downstream end of the bypass flow path opens to the inter-stage flow path so as to face the direction in which the gas in the inter-stage flow path swirls within the flow path cross-section of the inter-stage flow path.

Effects of the Invention

[0007] According to some aspects of this disclosure, the influence of the swirling flow generated in the gas during compression by the first impeller on the second impeller can be suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a cross-sectional view showing a schematic configuration of a compressor according to one embodiment. [Figure 2] Figure 2 is an enlarged cross-sectional view of the compression unit of the compressor shown in Figure 1. [Figure 3] Figure 3 illustrates the swirling flow at the intake port in front of the second impeller. [Figure 4] Figure 4 is an enlarged cross-sectional view of the compression unit of a modified compressor. [Modes for carrying out the invention]

[0009] One aspect of the present disclosure is a compressor that further compresses a gas compressed by a first impeller with a second impeller, comprising: an interstage passage for introducing gas from the first impeller to the second impeller; and a bypass passage for returning gas from downstream of the second impeller to the interstage passage, wherein the downstream end of the bypass passage opens into the interstage passage such that it faces the direction in which the gas in the interstage passage swirls within the cross-sectional area of ​​the interstage passage.

[0010] According to one aspect of the present disclosure, the gas compressed by the second impeller is returned to the interstage flow channel via a bypass channel downstream of the second impeller and flows out into the interstage flow channel from the downstream end of the bypass channel. The downstream end of the bypass channel faces the direction in which the gas in the interstage flow channel swirls within the cross-sectional area of ​​the interstage flow channel. As a result, the swirling flow generated in the gas during compression by the first impeller is weakened by the gas flowing out into the interstage flow channel from the downstream end of the bypass channel. Therefore, according to one aspect of the present disclosure, the influence of the swirling flow generated in the gas during compression by the first impeller on the second impeller can be suppressed.

[0011] In some embodiments, the interstage flow path has a bent portion at the inlet of the second impeller, and the downstream end of the bypass flow path may open downstream of the bent portion. With this configuration, the swirling flow is weakened at the inlet of the second impeller, thereby effectively suppressing the effect of the swirling flow on the second impeller.

[0012] In some embodiments, the opening direction of the downstream end may be aligned with the tangential direction of a virtual concentric circle concentric with the shaft of the second impeller. With this configuration, since the recirculated gas flows out along the tangential to the concentric circle of the second impeller shaft, the effects of swirling flow having a velocity component along the circumferential direction of the concentric circle can be suppressed more effectively.

[0013] In some embodiments, the downstream end opening is located on a virtual line extending radially in a virtual concentric circle concentric with the shaft of the second impeller, and the virtual line and the direction of the downstream end opening may be perpendicular. With this configuration, the recirculated gas flows out facing the swirling flow on the tangent to the concentric circle of the second impeller shaft, thus more effectively suppressing the influence of the swirling flow having a velocity component in the concentric circle.

[0014] The following describes exemplary embodiments with reference to the drawings. In each drawing, the same or corresponding elements are denoted by the same reference numerals, and redundant explanations are omitted.

[0015] The compressor 1 shown in Figure 1 is, for example, a series-type two-stage compressor. The compressor 1 comprises a shaft 20, a compression unit 30, and a motor unit 50. The compression unit 30 has a first impeller 31, a second impeller 32, and an impeller housing 33. The first impeller 31 and the second impeller 32 are attached to one end of the shaft 20. The first impeller 31 and the second impeller 32 are arranged, for example, so that their backs face each other with a gap between them. The first impeller 31 is arranged coaxially with the second impeller 32. The first impeller 31 is located between the second impeller 32 and the motor unit 50.

[0016] The impeller housing 33 has a first housing 41 that houses the first impeller 31 and a second housing 42 that houses the second impeller 32. The second housing 42 is connected in series with the first housing 41 in the axial direction D1 to which the shaft 20 extends. The first impeller 31 and the first housing 41 constitute a low-pressure compression stage that draws in and compresses the gas R1. The second impeller 32 and the second housing 42 constitute a high-pressure compression stage that further compresses the gas R1 compressed by the low-pressure compression stage. In other words, compressor 1 is a compressor that further compresses the gas R1 compressed by the first impeller 31 with the second impeller. That is, the first impeller 31 is the impeller corresponding to the first stage of the compressor. The second impeller 32 is the impeller corresponding to the second stage of the compressor.

[0017] The compression unit 30 further comprises an interstage plate 43 and an interstage housing 44. The interstage plate 43 and the interstage housing 44 are interstage components connected to the impeller housing 33. Together with the impeller housing 33, the interstage plate 43 and the interstage housing 44 form an interstage passage 60 that introduces gas R1 from the first impeller 31 of the low-pressure compression stage to the second impeller 32 of the high-pressure compression stage. In other words, the interstage passage 60 is a passage that connects the first-stage compressor and the second-stage compressor. The interstage plate 43 is a plate-shaped component sandwiched between the first housing 41 and the second housing 42. The interstage housing 44 is a housing component connected to the second housing 42 in the axial direction D1 from the opposite side from the first housing 41. The interstage housing 44 is connected in series to the first housing 41 in the axial direction D1 via the second housing 42 and the interstage plate 43. The interstage plate 43, the first housing 41, and the second housing 42 may be separate components. The compression unit 30 is formed by integrating these components. As means for integrating the interstage plate 43, the first housing 41, and the second housing 42, known fastening means such as screws or bolts and nuts, or known joining means such as welding or fusion joining can be used.

[0018] The motor unit 50 comprises a motor 51 and a motor housing 52. The motor 51 is the power source for driving the compression unit 30. The motor 51 is mounted on the other end of the shaft 20. Inside the motor housing 52, the shaft 20 is rotatably supported by bearings. The motor housing 52 houses the motor 51. The motor housing 52 is connected in series with the first housing 41 in the axial direction D1. The motor housing 52, the first housing 41, the interstage plate 43, the second housing 42, and the interstage housing 44 are each separate and independent components. The combination of these constitutes the housing of the compressor 1.

[0019] Figure 2 is an enlarged cross-sectional view of the compression unit of the compressor shown in Figure 1. As shown in Figure 2, the first housing 41 includes an inlet 41a, a diffuser passage 41b, and a scroll passage 41c. The inlet 41a is an opening coaxial with the shaft 20 and communicates with the interior of the motor housing 52 (see Figure 1). Gas R1 drawn in from the inlet of the motor housing 52 flows into the inlet 41a. The first impeller 31 is located behind the inlet 41a. The rotation of the first impeller 31 imparts kinetic energy to the gas R1. The scroll passage 41c is formed to surround the first impeller 31. The diffuser passage 41b is formed between the first impeller 31 and the scroll passage 41c. The diffuser passage 41b converts the kinetic energy imparted to the gas R1 into compression energy, thereby compressing the gas R1. The scroll channel 41c discharges the gas R1 compressed by the diffuser channel 41b.

[0020] The second housing 42 includes a suction port 42a, a diffuser flow path 42b, a scroll flow path 42c, and a scroll flow path outlet 42d. The suction port 42a is an opening coaxial with the suction port 41a of the first housing 41. The suction port 42a faces the opposite side of the suction port 41a. The suction port 42a is connected to the scroll flow path 41c of the first housing 41 via an inter-stage flow path 60. Therefore, the gas R1 from the scroll flow path 41c flows into the suction port 42a via the inter-stage flow path 60. A second impeller 32 is disposed on the back side of the suction port 42a. By the rotation of the second impeller 32, velocity energy is imparted to the gas R1. The scroll flow path 42c is formed so as to surround the second impeller 32. The diffuser flow path 42b is formed between the second impeller 32 and the scroll flow path 42c. The diffuser flow path 42b converts the velocity energy imparted to the gas R1 into compression energy to further compress the gas R1. The scroll flow path 42c discharges the compressed gas R1 to the outside from the scroll flow path outlet 42d.

[0021] The configuration of the inter-stage flow path 60 will be described. In the following description, "upward" means the upper side in the vertical direction D2 when the compressor 1 is installed at the place of use, for example. "Downward" means the lower side in the vertical direction D2 when the compressor 1 is installed at the place of use, for example. In the present embodiment, for example, a state is assumed in which the shaft 20 extends in the horizontal direction when the compressor 1 is installed at the place of use, and the description will be made. The axial direction D1 is orthogonal to the vertical direction D2.

[0022] The inter-stage flow path 60 includes, for example, a curved flow path 61, a straight flow path 62, a curved flow path 63, a straight flow path 64, and a curved flow path 65. These flow paths are formed on the same plane. The same plane may be, for example, a plane along the axial direction D1 and the vertical direction D2. FIG. 2 shows a cross section of the compression unit 30 when cut along the center line of the inter-stage flow path 60 in a plane along the axial direction D1 and the vertical direction D2, for example. The curved flow path 61, the straight flow path 62, the curved flow path 63, the straight flow path 64, and the curved flow path 65 are arranged in this order from the upstream to the downstream in the flow direction of the gas R1.

[0023] The straight flow path 62 extends axially in the downward direction D1 below the second impeller 32. For example, the straight flow path 62 extends parallel to the shaft 20. The curved flow path 61 is located below the first impeller 31. The curved flow path 61 extends in an arc-like shape between the outlet 41e of the scroll flow path 41c and the straight flow path 62. The curved flow path 63, the straight flow path 64, and the curved flow path 65 are located on the side opposite to the first impeller 31 with respect to the second impeller 32 in the axial direction D1.

[0024] The straight flow path 64 extends linearly along the vertical direction D2 at a position above the straight flow path 62 and below the shaft 20. The curved flow path 63 is arranged on the side opposite to the curved flow path 61 with the straight flow path 62 interposed therebetween in the axial direction D1. The curved flow path 63 extends in an arc-like shape between the straight flow path 62 and the straight flow path 64. The curved flow path 65 is arranged on the side opposite to the curved flow path 63 with the straight flow path 64 interposed therebetween in the vertical direction D2. The curved flow path 65 extends in an arc-like shape between the straight flow path 64 and the suction port 42a. That is, the inter-stage flow path 60 has a curved flow path (bending portion) 65 at the suction port 42a which is the inlet portion of the second impeller 32.

[0025] The cross-sectional area of each flow path of the inter-stage flow path 60 is, for example, constant. An annular seal member such as an O-ring for suppressing the occurrence of leakage of the gas R1 may be provided at the connection portion between each component of the inter-stage flow path 60.

[0026] The compressor 1 includes a bypass flow path 10 for refluxing the gas R2 from the downstream of the second impeller 32 to the inter-stage flow path 60. The bypass flow path 10 is provided for the first purpose of suppressing surge in the second impeller 32 of the compressor 1.

[0027] The bypass channel 10 has an upstream end 11, a downstream end 12, and a connecting section 13. The upstream end 11 communicates with the downstream channel of the second impeller 32. The downstream end 12 communicates with the upstream channel of the second impeller 32. The connecting section 13 connects the upstream end 11 and the downstream end 12. In the bypass channel 10, the pressure difference of gas R1 between the upstream end 11 and the downstream end 12 allows gas R2 to flow from the upstream end 11 to the downstream end 12 via the connecting section 13.

[0028] The upstream end 11 introduces the gas R1 compressed by the second impeller 32 as the recirculating gas R2. Gas R2 is a high-pressure gas that has been compressed by the second impeller 32 and is therefore at a higher pressure than the upstream side of the second impeller 32. Here, the upstream end 11 is connected, for example, to the portion of the second housing 42 that constitutes the scroll flow outlet 42d, so as to communicate with the scroll flow outlet 42d.

[0029] The downstream end 12 causes the gas R2 introduced from the upstream end 11 to flow out to the upstream side of the second impeller 32. Here, the downstream end 12 is connected to the interstage housing 44 so as to communicate with the inside of the interstage passage 60. In the bypass passage 10, the pressure difference of gas R1 between the scroll passage outlet 42d and the interstage passage 60 causes gas R2 to flow from the scroll passage outlet 42d to the interstage passage 60.

[0030] The bypass channel 10 is made of a pipe member such as stainless steel. Part of the bypass channel 10 may be formed by casting as part of the second housing 42. Part of the bypass channel 10 may be formed by casting as part of the interstage housing 44.

[0031] The bypass channel 10 is provided for a second purpose: to mitigate the swirling flow of gas R1 flowing into the second impeller 32. Swirling flow of gas R1 refers to the flow of gas R1 flowing into the second impeller 32 while swirling. Swirling flow of gas R1 occurs, for example, in the scroll channel 41c when gas R1 is compressed by the first impeller 31. The scroll channel 41c has an inner wall surface 41d that has a partially arc-shaped channel cross-section. In the scroll channel 41c, gas R1 flows in along the diffuser channel 41b. In the scroll channel 41c, gas R1 flows in a swirling manner along the inner wall surface 41d. In this state, gas R1 travels through the scroll channel 41c along the circumferential direction of the first impeller 31. This forms a flow of gas R1 accompanied by a swirling flow. The swirling flow of gas R1 reaches the intake port 42a and the second impeller 32 via the interstage flow path 60. At the intake port 42a, the swirling flow of gas R1 may swirl around the axial direction D1 in the same direction as or opposite to the rotation direction of the second impeller 32, depending on, for example, the rotation direction of the first impeller 31 and the winding direction of the scroll flow path 41c.

[0032] Figure 3 illustrates the swirling flow at the intake before the second impeller. In Figure 3, the second impeller 32 is shown as a solid line in a plan view from the interstage flow path 60 side in the axial direction D1 in Figure 2. In Figure 3, the straight flow path 64 and curved flow path 65 are shown as dashed lines in a plan view from the interstage flow path 60 side in the axial direction D1 in Figure 2. In the example in Figure 3, the gas R1 flows through the straight flow path 64 located in the upper right of the page toward the center of the page. The gas R1 flows through the curved flow path 65 located in the center of the page, bending toward the back of the page, toward the intake 42a at the back of the page. As an example, the direction of the swirling flow of gas R1 at the intake 42a is clockwise, as indicated by the thick solid arc arrow. The intake 42a is located downstream of the curved flow path 65. The direction of the swirling flow of gas R1 can be determined, for example, based on the stream vector obtained from a simulation of the gas R1 flow in the compressor 1. The swirling flow of gas R1 at the intake port 42a swirls in accordance with the direction in which gas R1 in the interstage flow path 60 swirls within the flow path cross-section of the interstage flow path 60.

[0033] In the example shown in Figure 3, when the second impeller 32 rotates, multiple large and small blades 32a centrifugally compress the gas R1. In the example shown in Figure 3, the rotation direction of the second impeller 32 is counterclockwise. Therefore, the swirling flow of gas R1, which swirls in a clockwise direction, swirls in the opposite direction to the rotation direction of the second impeller 32 (counter-swirl). When such a swirling flow of gas R1 enters the second impeller 32, surges tend to occur easily. In contrast to the example shown in Figure 3, when a counterclockwise swirling flow (pre-swirl) in the same direction enters the second impeller 32, which rotates counterclockwise, a decrease in the pressure ratio before and after the second impeller 32 tends to occur easily.

[0034] To mitigate the swirling flow of gas R1, which swirls in a clockwise direction, the downstream end 12 opens into the interstage flow channel 60 so as to be opposite to the direction of the swirling flow of gas R1, as shown by the partially rectangular dashed line in Figure 3.

[0035] Specifically, the downstream end 12 opens to the downstream side of the curved passage 65. The downstream side of the curved passage 65 is downstream in the flow direction of gas R1 from the midpoint 66 of the section in which the curved passage 65 bends, as shown in Figure 2. The downstream side of the curved passage 65 may also be downstream in the flow direction of gas R1 from the end point 67 of the section in which the curved passage 65 bends. Here, the downstream end 12 is connected to the interstage housing 44 so as to open between the end point 67 of the section in which the curved passage 65 bends and the inlet 42a of the second housing 42. The downstream end 12 may also be connected to the second housing 42 so as to open to the downstream side of the curved passage 65.

[0036] As shown in Figure 3, the opening direction 12x of the downstream end 12 is, for example, along the tangential direction of a virtual concentric circle 21 concentric with the shaft 20 at the intake port 42a in the cross-section of Figure 3. The opening position 12y of the downstream end 12 may lie on a virtual line 22 extending radially along the virtual concentric circle 21 concentric with the shaft 20. The virtual line 22 and the opening direction 12x of the downstream end 12 are perpendicular. Since the recirculated gas R2 flows out along the opening direction 12x, it flows out along the tangential to the concentric circle 21 of the shaft 20 of the second impeller 32. The swirling flow of gas R1 has a clockwise velocity component along the circumferential direction of the concentric circle 21. Therefore, gas R2 flows out with a velocity component in the opposite direction to the swirling flow of gas R1. Gas R2 flows out so as to be opposite to the swirling flow of gas R1 on the tangential to the concentric circle 21. The opening direction 12x and opening position 12y of the downstream end 12 are not limited to this example, and may be adjusted according to the strength (swirl velocity within the cross-section), direction, and distribution of the swirling flow of the gas R1, for example, by referring to the stream vector obtained by simulation. The inner diameter of the bypass flow path 10 may be constant, or it may taper towards the downstream end 12.

[0037] The direction and strength of the swirling flow of gas R1 within the flow path cross-section from the first impeller 31 to the second impeller 32 are determined before passing through the curved flow path 65, and do not increase further downstream of the curved flow path 65. In this way, by opening the downstream end 12 so as to be opposite to the direction of the swirling flow of gas R1 downstream of the curved flow path 65, it becomes less likely for the swirling flow of gas R1 to occur again after the swirling flow of gas R1 has subsided.

[0038] Incidentally, the bypass passage 10 may be provided with a control valve to adjust the flow rate of gas R2. The control valve is adjusted to suppress surges at the second impeller 32 of the compressor 1 while mitigating the swirling flow of gas R1 flowing into the second impeller 32. The control valve may be adjusted based on, for example, the rotational speed of the shaft 20, the flow rate and pressure of gas R1, etc. The rotational speed of the shaft 20 can be the motor drive rotation or the measured turbine rotation, etc. The flow rate and pressure of gas R1 may be measured values ​​(for example, the downstream pressure or interstage pressure of the second impeller 32). The flow rate and pressure of gas R1 may be substituted with the output of the motor unit 50.

[0039] In the compressor 1 described above, the gas R1 compressed by the second impeller 32 is returned as gas R2 to the interstage flow path 60 via the bypass flow path 10 from downstream of the second impeller 32, and flows out into the interstage flow path 60 from the downstream end 12 of the bypass flow path 10. The downstream end 12 of the bypass flow path 10 is opposite to the direction in which the gas R1 in the interstage flow path 60 swirls within the flow path cross-section of the interstage flow path 60. The gas R2 flows out into the interstage flow path 60 from the downstream end 12 of the bypass flow path 10. As a result, the swirling flow generated in the gas R1 when it is compressed by the first impeller 31 is weakened by the gas R2. Therefore, the compressor 1 can suppress the effect of the swirling flow generated in the gas R1 when it is compressed by the first impeller 31 on the second impeller 32.

[0040] Surges are suppressed by the circulating flow that bypasses from the scroll flow path outlet 42d of the high-pressure stage to the intake port 42a of the high-pressure stage. By returning the circulating flow upstream of the second impeller 32 of the high-pressure stage in a direction that counteracts the swirling of gas R1, the performance degradation of the compressor 1 can be suppressed.

[0041] In compressor 1, the interstage flow path 60 has a bent flow path (bent portion) 65 at the intake port 42a, which is the inlet of the second impeller 32. The downstream end 12 of the bypass flow path 10 opens downstream of the bent flow path 65. With this configuration, the swirling flow is weakened at the inlet of the second impeller 32, so the effect of the swirling flow on the second impeller 32 can be effectively suppressed.

[0042] In compressor 1, the opening direction 12x of the downstream end 12 is aligned with the tangential direction of a virtual concentric circle 21 that is concentric with the shaft 20 of the second impeller 32. With this configuration, the recirculated gas R2 flows out along the tangential direction of the concentric circle 21 of the shaft 20 of the second impeller 32. Therefore, the effect of swirling flow having a flow velocity component along the circumferential direction of the concentric circle 21 can be suppressed more effectively.

[0043] In compressor 1, the opening position 12y of the downstream end 12 lies on a virtual line 22 extending radially from a virtual concentric circle 21 that is concentric with the shaft 20 of the second impeller 32, and on this virtual line 22 that is perpendicular to the opening direction 12x of the downstream end 12. With this configuration, the recirculated gas flows out on the tangent to the concentric circle 21 of the shaft 20 of the second impeller 32 so as to be opposite to the swirling flow. Therefore, the influence of the swirling flow having a flow velocity component of the concentric circle 21 can be suppressed more effectively.

[0044] Although embodiments of the present disclosure have been described above, the present disclosure is not limited to the embodiments and examples described above.

[0045] In the above embodiment, the downstream end 12 of the bypass channel 10 opened to the downstream side of the curved channel 65, but the invention is not limited to this example. For example, as shown in Figure 4, the downstream end 12A of the bypass channel 10A may open to the upstream side of the curved channel 65. The bypass channel 10A has an upstream end 11, a downstream end 12A, and a connecting part 13A. The upstream end 11 communicates with the flow path downstream of the second impeller 32. The downstream end 12A communicates with the flow path upstream of the curved channel 65. The connecting part 13A connects the upstream end 11 and the downstream end 12A. The downstream end 12A causes the gas R2 introduced from the upstream end 11 to flow out to the upstream side of the curved channel 65. Here, the downstream end 12A is connected to the interstage housing 44 so as to communicate with the inside of the straight channel 64. In the bypass channel 10A, gas R2 flows from the scroll channel outlet 42d to the straight channel 64 due to the pressure difference of gas R1 between the scroll channel outlet 42d and the straight channel 64. In the bypass channel 10 described above, the opening was on the downstream side of the curved channel 65 in order to direct the flow of gas R2 to the swirling flow of gas R2, which is at a point where the direction and strength of the swirling flow of gas R1 within the cross-section of the channel from the first impeller 31 to the second impeller 32 no longer change significantly. In contrast, in the modified bypass channel 10A, the downstream end 12A is opened so that the swirling flow of gas R1 settles downstream of the curved channel 65, while taking into account the changes in the swirling flow applied to gas R1 before and after the curved channel 65. The downstream end 12A is opened in a direction such that the swirling of gas R1 from the first impeller 31 side inside the straight channel 64 is canceled out in advance by the recirculated gas R2. The change in the swirling flow acting on gas R1 before and after the curved channel 65 can be referenced using the stream vectors obtained from the simulation.

[0046] In the above embodiment, the cross-sectional area of ​​each channel in the interstage channel 60 was constant, but a portion may have a different area from the other portions. For example, by taking advantage of the fact that a larger cross-sectional area of ​​the interstage channel 60 slows down the swirling flow of gas R1, and a smaller cross-sectional area of ​​the interstage channel 60 speeds up the swirling flow of gas R1, the downstream end of the bypass channel may be provided in the portion of the interstage channel 60 with a larger cross-sectional area than the other portions, so that the recirculated gas R2 is directed to the area where the flow velocity of the swirling flow of gas R1 has decreased. In this case, it becomes easier to mitigate the swirling flow of gas R1.

[0047] In the above embodiment, the interstage flow path 60 had a bent flow path (bent portion) 65 at the intake port 42a, which is the inlet of the second impeller 32, but the invention is not limited to this example. For example, a straight pipe flow path may be connected to the intake port 42a, which is the inlet of the second impeller 32. The bent flow path 65 and the intake port 42a of the second impeller 32 may be connected via a straight pipe flow path. The intake port 42a of the second impeller 32 and the intake port 41a of the first impeller 31 may be connected via a straight pipe flow path. Note that even without a bent portion like the interstage flow path 60 from the first impeller 31 in the low-pressure stage to the second impeller 32 in the high-pressure stage, a swirling flow of gas R1 will occur in the scroll flow path 41c of the first impeller 31, etc.

[0048] In the above embodiment, the upstream end 11 of the bypass channel 10 was in communication with the scroll channel outlet 42d, but the invention is not limited to this example. For example, the upstream end of the bypass channel may be in communication with the scroll channel 42c. The upstream end of the bypass channel may be in communication with the diffuser channel 42b. In short, the upstream end of the bypass channel should be in communication with the channel downstream of the second impeller and should be configured to introduce the gas compressed by the second impeller as the gas to be recirculated.

[0049] In the above embodiment, the first impeller 31 and the second impeller 32 were arranged so that their back surfaces were spaced apart and facing each other. However, the first impeller 31 and the second impeller 32 may also be arranged so that the back surface of one of them faces the front surface of the other (arranged in series).

[0050] In the above embodiment, the interstage flow path 60 was composed of four parts: a first housing 41, a second housing 42, an interstage plate 43, and an interstage housing 44. However, it is not necessarily required to be composed of four parts. For example, the interstage plate does not need to extend downward to reach the interstage flow path, and the second housing may be directly connected to the first housing. In addition, piping may be provided separately to connect the first housing and the second housing.

[0051] In the above embodiment, a two-stage compressor was used as an example, but the number of stages in the compressor is not limited to two, and may be three or more. For example, if the compressor is a three-stage series compressor, the interstage passage through which the gas is recirculated may be the passage connecting the second-stage compressor and the third-stage compressor. In this case, the first impeller may be the impeller corresponding to the second-stage compressor, the second impeller may be the impeller corresponding to the third-stage compressor, and the bypass passage may recirculate the gas from downstream of the second impeller corresponding to the third-stage compressor to the interstage passage connecting the second-stage compressor and the third-stage compressor. The same applies even if the number of stages in the compressor is four or more. In short, the bypass passage should recirculate the gas from downstream of the second impeller to the interstage passage.

[0052] In the above embodiment, the compressor 1 was exemplified as an electric centrifugal compressor, but is not limited thereto. It may be a turbocharger operated by exhaust gas from a vehicle or the like, or a mixed-flow turbo compressor. In short, this disclosure can be broadly applied to compressors in which a swirling flow is generated due to the rotational component of centrifugal compression, such as jet engines in which a fixed blade is provided in the housing to return the swirling flow back to an axial flow, and in which a gas R1 compressed by a first impeller 31 is further compressed by a second impeller. [Explanation of symbols]

[0053] 1. Compressor 10,10A Bypass channel 12,12A downstream end 12x opening direction 12y opening position 20 shafts 21 Concentric Circles 22 virtual lines 31 First Impeller 32. Second impeller 60-stage channel 65. Curved channel (bend section) R1, R2 gas

Claims

1. A compressor that compresses gas with a first impeller and then further compresses it with a second impeller, An interstage flow path for introducing the gas from the first impeller to the second impeller, The system includes a bypass channel that returns the gas from downstream of the second impeller to the interstage channel, A compressor in which the downstream end of the bypass channel opens into the interstage channel such that the direction in which the gas in the interstage channel swirls within the cross-sectional area of ​​the interstage channel is opposite to the direction in which the gas in the interstage channel swirls.

2. The interstage flow path has a bent portion at the inlet of the second impeller, The compressor according to claim 1, wherein the downstream end of the bypass channel opens to the downstream side of the bent portion.

3. The compressor according to claim 2, wherein the opening direction of the downstream end is aligned with the tangential direction of a virtual concentric circle concentric with the shaft of the second impeller.

4. The opening position at the downstream end is on a virtual line extending radially in a virtual concentric circle that is concentric with the shaft of the second impeller. The compressor according to claim 2 or 3, wherein the imaginary line and the opening direction of the downstream end are perpendicular to each other.

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