Multistage centrifugal turbomachine

Abstract

To improve a pressure ratio of each stage of a multistage centrifugal turbomachine.SOLUTION: A centrifugal turbomachine comprises: a rotary shaft; and a plurality of stages each consisting of a unit of an impeller rotating integrally with the rotary shaft, and a stationary flow passage sending a fluid discharged from an exit of the impeller to an entrance of an impeller of the next stage, the stages being arrayed in an axial direction of the rotary shaft. The stationary flow passage has: a diffuser having a plurality of diffuser vanes arranged radially outside the exit of the impeller; a restriction flow passage arranged between the exit of the impeller and an entrance of the diffuser; a return bend connected to the exit of the diffuser; a return guide connected to an exit of the return bend; and an L-shaped bend connected to the exit of the return guide, wherein an outer diameter of the stationary flow passage is 1.8 times or more as large as an outer diameter of the impeller, and the return bend has a long path which has a larger radius of curvature as compared with when a flow is turned in the shortest path.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to the configuration of multi-stage centrifugal turbomachines. [Background technology]

[0002] Conventionally, centrifugal turbomachines have been known that convert energy between a machine and a fluid by rotating an impeller with the fluid. Examples of centrifugal turbomachines include compressors, blowers, and pumps. Multi-stage centrifugal turbomachines include multiple stages, with each stage consisting of an impeller and a stationary flow path that sends the fluid discharged from the impeller to the impeller of the next stage. For example, Patent Document 1 discloses this type of multi-stage centrifugal turbomachine.

[0003] The multi-stage centrifugal fluid machine disclosed in Patent Document 1 includes a rotating shaft, multiple impellers mounted on the rotating shaft, and a stationary flow path that sends fluid discharged from the impeller to the next impeller. The stationary flow path includes a diffuser disposed radially outside the impeller, a return bend connected downstream of the diffuser to convert the fluid flow from a radially outward direction to a radially inward direction, and a return vane connected downstream of the return bend to guide the radially inward flowing fluid to the inlet of the next impeller. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-1450 Summary of the Invention [Problem to be solved by the invention]

[0005] There is a demand for compressors that can compress low-molecular-weight gases such as hydrogen and helium at a high pressure ratio. Considered compressors include turbo compressors and positive displacement compressors (e.g., reciprocating compressors), which generate pressure by compressing the volume of a sealed gas. Generally, turbo compressors can handle larger flow rates than positive displacement compressors, but it is difficult to provide a high pressure ratio. To achieve the same pressure ratio as a positive displacement compressor, a turbo compressor must have a higher pressure ratio per stage.

[0006] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a configuration that can improve the pressure ratio per stage in a multi-stage centrifugal turbomachine. [Means for solving the problem]

[0007] In order to solve the above problems, a centrifugal turbomachine according to one aspect of the present disclosure includes: A rotation axis; a plurality of stages arranged in the axial direction of the rotary shaft, each stage including an impeller that rotates integrally with the rotary shaft and a stationary flow path that sends fluid discharged from an outlet of the impeller to an inlet of an impeller of a next stage; the stationary flow path includes a diffuser having a plurality of diffuser vanes arranged circumferentially around the rotation axis and radially outward of an outlet of the impeller; a throttle flow path arranged between the outlet of the impeller and an inlet of the diffuser; a return bend connected to the outlet of the diffuser and turning the fluid flow from the radially outward direction to the radially inward direction; a return guide connected to the outlet of the return bend and having a plurality of return guide vanes arranged circumferentially around the rotation axis; and an L-shaped bend connected to the outlet of the return guide and turning the fluid flow from the radially inward direction to the axial direction, The outer diameter of the stationary flow path is 1.8 times or more the outer diameter of the impeller, The return bend has a larger radius of curvature and a longer path than when the flow is turned along the shortest path. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a configuration that can improve the pressure ratio per stage in a multi-stage centrifugal turbomachine. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a meridian plane view showing the overall configuration of a multi-stage centrifugal turbo compressor according to one embodiment of the present disclosure. [Figure 2] FIG. 2 is an enlarged meridian view of a multi-stage centrifugal turbocompressor showing the impellers and stationary flow paths. [Figure 3] FIG. 3 is a graph showing the relationship between the ratio of the outer diameter D1 of the stationary flow passage to the outer diameter D2 of the impeller and the polytropic efficiency. DETAILED DESCRIPTION OF THE INVENTION

[0010] Next, an embodiment of the present disclosure will be described with reference to the drawings. Here, a multi-stage centrifugal turbo-compressor will be used as an example of a multi-stage centrifugal turbo-machine. However, the configuration of the multi-stage centrifugal turbo-machine according to the present disclosure is not limited to compressors, and may also be applied to pumps, blowers, and the like.

[0011] Fig. 1 is a meridian plane view showing the overall configuration of a multi-stage centrifugal turbo compressor 1 according to one embodiment of the present disclosure. The multi-stage centrifugal turbo compressor 1 shown in Fig. 1 includes a casing 2, a rotating shaft 3 rotatably supported by the casing 2, and multiple impellers 4 disposed inside the casing 2 and fixed to the rotating shaft 3. The multiple impellers 4 are aligned in an axial direction X of the rotating shaft 3. Here, the direction in which a central axis A of the rotating shaft 3 extends is referred to as the "axial direction X," the radial direction relative to the central axis A is referred to as the "radial direction," the direction approaching the central axis A in this radial direction is referred to as the "radially inward direction," the direction moving away from the central axis A in the radial direction is referred to as the "radially outward direction," and the circumferential direction centered on the central axis A is referred to as the "circumferential direction."

[0012] The casing 2 is provided with a suction passage 22 that draws in fluid and sends it to the first-stage impeller 4, and a discharge passage 23 that discharges the fluid from the final-stage impeller 4 to the outside. The casing 2 also is provided with a stationary passage 5 that sends the fluid discharged from the impeller 4 to the impeller 4 of the next stage. A combination of the impeller 4 and the stationary passage 5 constitutes a stage, which serves as a unit of pressure increase in the multi-stage centrifugal turbo compressor 1. The fluid drawn into the suction passage 22 is pressurized each time it passes through a stage consisting of an impeller 4 and a stationary passage 5, and is discharged to the outside from the discharge passage 23. However, the passage shape and the number of pressure increase stages of the multi-stage centrifugal turbo compressor 1 are merely examples.

[0013] FIG. 2 is an enlarged meridian view of the multi-stage centrifugal turbo compressor 1, showing the impeller 4 and the stationary flow path 5. As shown in FIG. 2, each impeller 4 of the multi-stage centrifugal turbo compressor 1 has a known structure, for example, including an impeller hub through which the rotating shaft 3 is inserted, a disk centered on the impeller hub, multiple blades arranged on the disk in the circumferential direction around the rotating shaft 3, and a shroud covering the blades. While the impeller 4 is a closed type, it may also be an open type in which the shroud is omitted. In the impeller 4, the disk, the blades, and the shroud form an impeller flow path 40 through which the fluid to be compressed passes. The inlet of the impeller flow path 40 (hereinafter referred to as the impeller inlet 41) faces the axial direction X, and the outlet of the impeller flow path 40 (hereinafter referred to as the impeller outlet 42) faces radially outward on the outer periphery of the impeller 4. The fluid is compressed by centrifugal force generated when passing through the impeller flow passage 40 of the rotating impeller 4, and the compressed fluid is discharged radially outward in the radial direction from the impeller outlet 42.

[0014] The stationary flow path 5 includes a diffuser 51 disposed on the outer periphery of the impeller 4 and a return flow path 52 connected downstream of the diffuser 51 .

[0015] The diffuser 51 reduces the velocity of the fluid pressurized by the impeller 4 and discharged from the impeller outlet 42, thereby increasing the static pressure. The diffuser 51 is a flow passage whose cross-sectional area increases radially outward. The diffuser 51 has a plurality of diffuser vanes 56 arranged circumferentially around the rotary shaft 3. The fluid passes through spaces between adjacent diffuser vanes 56. The diffuser 51 has the diffuser vanes 56, which allows for earlier recovery of static pressure and rectifies the flow, thereby suppressing unstable flow phenomena (i.e., local stalls) compared to a diffuser without the diffuser vanes 56.

[0016] A throttle passage 60 is provided between the impeller outlet 42 and the inlet of the diffuser 51 (hereinafter referred to as the diffuser inlet 58). The flow path cross-sectional area of ​​the diffuser inlet 58 is smaller than the flow path cross-sectional area of ​​the impeller outlet 42. In detail, the flow path cross-sectional area of ​​the annular flow path of the diffuser inlet 58, centered on the rotation axis 3, is smaller than the flow path cross-sectional area of ​​the annular flow path of the impeller outlet 42, centered on the rotation axis 3. The throttle passage 60 abruptly reduces the flow path area of ​​the fluid in the short distance from the impeller outlet 42 to the diffuser inlet 58.

[0017] The return flow passage 52 includes a return bend 53 connected to the outlet of the diffuser 51, a return guide 54 downstream of the return bend 53, and an L-shaped bend 55 downstream of the return guide 54. The outlet of the L-shaped bend 55 is connected to the inlet 41 of the impeller of the next stage.

[0018] The return bend 53 has a flow path whose meridional shape is U-shaped. The inlet and outlet of the return bend 53 are oriented in the radial direction. The point in the return bend 53 where the flow direction starts to change significantly (hereinafter referred to as the "bending point P") is preferably located away from the end of the diffuser vane 56 within the range allowed by the outer diameter D1 of the stationary flow path 5. Here, the outer diameter D1 of the stationary flow path 5 is the distance from the central axis A to the outermost part of the return bend 53.

[0019] The flow path cross section of the return bend 53 gradually expands from the inlet to the outlet. The return bend 53 is a "circumferential path" with a larger radius of curvature and a longer flow path than when the flow is turned along the shortest path. A case where the flow is turned along the shortest path is, for example, when the return bend has a shape that abruptly changes the flow angle by 180 degrees, like a hairpin curve. The return bend 53 with a large circuit allows for a larger expansion rate of the flow path cross section from the inlet to the outlet of the return bend 53 compared to when the flow is turned along the shortest path, which is expected to increase the static pressure recovery rate. Furthermore, the return bend 53 with a large circuit can suppress flow separation and reduce pressure loss compared to when the flow is turned along the shortest path.

[0020] The fluid that flows radially outward into the return bend 53 changes direction while passing through the return bend 53, flows out radially inward from the return bend 53, and flows into the return guide 54. The return guide 54 has a plurality of return guide vanes 57 arranged circumferentially around the rotation axis 3. The fluid passes between adjacent return guide vanes 57. The distance in the axial direction X between the inlet of the return bend 53 and the inlet of the return guide 54 is smaller than the distance in the axial direction X between the inlet of the return bend 53 and the inlet of the return guide 54. In other words, in the meridian shape, the extension direction of the return guide 54 is inclined from the radial direction.

[0021] The L-shaped bend 55 has a flow path whose meridian cross section is L-shaped. The inlet of the L-shaped bend 55 faces the radial direction, and the outlet of the L-shaped bend 55 faces the axial direction X. The fluid that flows radially inward into the L-shaped bend 55 changes direction while passing through the L-shaped bend 55, and flows out of the L-shaped bend 55 in the axial direction X.

[0022] The outer diameter D1 of the stationary flow passage 5 is at least 1.8 times the outer diameter D2 of the impeller 4. Here, the outer diameter D2 of the impeller 4 is the distance from the central axis A to the outermost part of the impeller 4. By making the outer diameter D1 of the stationary flow passage 5 at least 1.8 times the outer diameter D2 of the impeller 4, it becomes possible to provide the multi-stage centrifugal turbo compressor 1 with a pressure ratio equivalent to that of a positive displacement compressor. There is no particular upper limit set for the outer diameter D1 of the stationary flow passage 5, but if the outer diameter D1 of the stationary flow passage 5 is too large, the entire multi-stage centrifugal turbo compressor 1 will become large and the load on the bearings of the rotating shaft 3 will increase. Therefore, the outer diameter D1 of the stationary flow passage 5 is preferably no more than 2.2 times the outer diameter D2 of the impeller 4.

[0023] In the stationary flow passage 5 configured as described above, the fluid discharged radially outward from the impeller outlet 42 passes through the throttle flow passage 60 and then flows into the diffuser 51. While passing through the diffuser 51, the fluid is decelerated by the action of the diffuser vanes 56, and flows into the return flow passage 52 with increased static pressure. In the return flow passage 52, the fluid first passes through the return bend 53, thereby redirecting its flow from radially outward to radially inward. Next, while passing through the return guide 54, the return guide vanes 57 remove the swirling velocity component of the fluid, thereby rectifying the flow. Next, the fluid passes through the L-shaped bend 55, thereby redirecting its flow from radially inward to the axial direction X. In this manner, the fluid that has passed through the stationary flow passage 5 flows into the impeller inlet 41 of the impeller 4 of the next stage.

[0024] Downstream of the diffuser 51, a wake is generated by the diffuser vane 56. The flow velocity of the wake of the diffuser vane 56 is slower than that of the surrounding area, resulting in a flow velocity distribution (i.e., non-uniformity) at the outlet of the diffuser 51. The diffuser 51 is connected to a return bend 53 of the return flow passage 52. If the degree of non-uniformity in the flow velocity distribution at the bending point P of the return bend 53 is large, the pressure loss of the fluid passing through the return bend 53 increases, resulting in a deterioration in the performance of the multi-stage centrifugal turbo compressor 1. Therefore, in the multi-stage centrifugal turbo compressor 1 according to the present disclosure, the degree of non-uniformity in the flow velocity distribution in the stationary flow passage 5 is suppressed by the following (i) to (iii), thereby making the stationary flow passage 5 a more uniform flow field.

[0025] (i) The stationary flow passage 5 includes a throttle passage 60 provided upstream of the diffuser 51 having the diffuser vanes 56. In the case of an impeller 4 for high-pressure ratio applications, the circumferential velocity component of the flow is larger than in the case of a low-pressure ratio application, and therefore the flow angle at the impeller outlet 42 is smaller than the inlet angle of the flow at which the application of the diffuser vanes 56 is expected to be effective. Therefore, the throttle passage 60 provided between the impeller outlet 42 and the diffuser inlet 58 increases the inlet angle of the flow to the diffuser 51 (i.e., the flow angle at the diffuser inlet 58) to a flow angle at which the application of the diffuser vanes 56 is expected to be effective. In addition, the fluid at the impeller outlet 42 has velocity distortion (i.e., non-uniformity in the flow velocity distribution), and this velocity distortion tends to increase as the pressure ratio increases. Therefore, the velocity distortion of the fluid exiting the impeller outlet 42 is reduced by passing through the throttle passage 60. Reducing the velocity distortion of the fluid flowing into the diffuser 51 suppresses fluid separation in the diffuser 51, promotes appropriate pressure recovery in the diffuser 51, and suppresses the velocity distribution caused by the wake at the outlet of the diffuser 51.

[0026] (ii) The stationary passage 5 includes a return bend 53 connected to a diffuser 51 having a diffuser vane 56, and the outer diameter D1 of the stationary passage 5 is 1.8 times or more the outer diameter D2 of the impeller 4. One index of compressor performance is the polytropic efficiency ηp, which represents the ratio of the compressor's workload to the theoretical work. The inventors investigated the relationship between the polytropic efficiency ηp and the radial dimension of the stationary passage in a compressor capable of compressing low-molecular-weight gases such as hydrogen and helium at a high pressure ratio. The polytropic efficiency ηp can be calculated using the following equation (1):

[0027]

number

[0028] In Equation 1, the ratio (D1 / D2) of the outer diameter D1 of the stationary flow passage 5 to the outer diameter D2 of the impeller 4 was used as a parameter. The polytropic efficiency ηp was calculated by varying (D1 / D2) between 1.5 and 2.2 in increments of 0.1. FIG. 3 is a graph showing the calculation results of the polytropic efficiency ηp. As shown in FIG. 3, the polytropic efficiency ηp increases with increasing (D1 / D2) up to a value of 1.8. However, when (D1 / D2) is 1.8 or greater, the polytropic efficiency ηp hardly changes even with an increase in (D1 / D2). In other words, it was found that the polytropic efficiency ηp converges to a certain value when (D1 / D2) is 1.8 or greater. Therefore, it is preferable that (D1 / D2) is 1.8 or greater. Furthermore, when (D1 / D2) is 1.8 or greater, the distance between the outlet of the diffuser 51 and the bending point P of the return bend 53 can be increased. That is, the wake of the diffuser vane 56 is diffused (mixed) before reaching the turning point P of the return bend 53, and the flow field is uniformed immediately before entering the turning point P. This reduces the degree of non-uniformity of the flow velocity distribution in the return bend 53 of the stationary flow path 5.

[0029] (iii) The return flow passage 52 of the stationary flow passage 5 includes a return bend 53 connected to a diffuser 51 having a diffuser vane 56. The return bend 53 is a long, detour-like flow passage compared to when the flow is turned along the shortest path. In this embodiment, by making the return bend 53 a detour-like flow passage, the distance in the axial direction X from the inlet of the return bend 53 to the outlet of the return bend 53 is longer than the distance in the axial direction X from the inlet of the return bend 53 to the outlet of the return guide 54. In this way, the return bend 53 has an extra flow passage length compared to when the flow is turned along the shortest path, so that the wake of the diffuser vane 56 can be diffused while the fluid passes through the return bend 53. This reduces the degree of non-uniformity in the flow velocity distribution at the inlet of the return guide 54 following the return bend 53.

[0030] [Summary] A multi-stage centrifugal turbomachine 1 according to a first aspect of the present disclosure comprises: A rotation axis 3; an impeller 4 that rotates integrally with the rotary shaft 3 and a stationary flow path 5 that sends fluid discharged from an outlet of the impeller 4 to an inlet of the impeller 4 of the next stage, the stationary flow path 5 being arranged in a stepwise manner in an axial direction X of the rotary shaft 3; The stationary flow path 5 includes a diffuser 51 having a plurality of diffuser vanes 56 arranged in a circumferential direction around the rotation axis 3 radially outward of the outlet 42 of the impeller 4, a throttle flow path 60 arranged between the outlet 42 of the impeller 4 and an inlet 58 of the diffuser 51, a return bend 53 connected to the outlet of the diffuser 51 and turning the fluid flow from a radially outward direction to a radially inward direction, a return guide 54 connected to the outlet of the return bend 53 and having a plurality of return guide vanes 57 arranged in a circumferential direction around the rotation axis 3, and an L-shaped bend 55 connected to the outlet of the return guide 54 and turning the fluid flow from a radially inward direction to an axial direction X, The outer diameter D1 of the stationary flow passage 5 is 1.8 times or more the outer diameter D2 of the impeller 4, The return bend 53 has a larger radius of curvature and a longer path than when the flow is turned along the shortest path. At least one of the multiple stages (preferably all stages) has a stationary flow path 5 that has an outer diameter 1.8 times or more the outer diameter D2 of the impeller 4, a diffuser vane 56, a throttle flow path 60, and a return bend 53 with a larger radius of curvature and a longer path.

[0031] In the multi-stage centrifugal turbomachine 1 configured as described above, the stationary flow path 5 includes the diffuser 51 having the diffuser vane 56. This allows for early recovery of static pressure, and the flow straightening effect suppresses flow instability. As a result, the pressure ratio up to the outlet of the diffuser 51 can be increased compared to a case where a vaneless diffuser is included. Furthermore, in the multi-stage centrifugal turbomachine 1, the outer diameter D1 of the stationary flow path 5 is 1.8 times or more the outer diameter D2 of the impeller 4, which is expected to increase the amount of static pressure recovery. In this way, the multi-stage centrifugal turbomachine 1 has a configuration that increases the pressure ratio. Furthermore, the degree of non-uniformity in the flow velocity distribution, which can be increased due to the diffuser vane 56, is suppressed by the action of the throttle flow path 60 provided in the stationary flow path 5 and the return bend 53, which is a large-circuit path, thereby suppressing pressure loss of the fluid flowing through the stationary flow path 5. As a result, the present disclosure can provide a configuration that can improve the pressure ratio per stage in the multi-stage centrifugal turbomachine 1. Therefore, the configuration of the multi-stage centrifugal turbomachine 1 according to the present disclosure is suitable for application to a compressor capable of compressing gases with small molecular weights, such as hydrogen and helium, at a high pressure ratio.

[0032] The foregoing discussion of the present disclosure has been presented for purposes of illustration and description and is not intended to limit the present disclosure to the form disclosed herein. For example, in the foregoing detailed description, various features of the present disclosure are grouped together in a single embodiment for the purpose of streamlining the disclosure, but some of the features may also be combined. Furthermore, the features included in the present disclosure may also be combined into alternative embodiments, configurations, or aspects other than those discussed above. [Explanation of symbols]

[0033] 1: Multi-stage centrifugal turbo compressor (an example of a multi-stage centrifugal turbomachine) 3: Rotation axis 4: Impeller 5: Stationary flow path 40: Impeller passage 41: Impeller inlet 42: Impeller outlet 51: Diffuser 52: Return flow path 53: Return Bend 54: Return guide 55: L-bend 56: Diffuser vane 57: Return guide vane 58: Diffuser inlet 60: Restricted flow channel D1: Outer diameter of stationary flow path D2: Outer diameter of impeller X: Axial direction

Claims

[Claim 1] A rotation axis; a plurality of stages arranged in the axial direction of the rotary shaft, each stage including an impeller that rotates integrally with the rotary shaft and a stationary flow path that sends fluid discharged from an outlet of the impeller to an inlet of an impeller of a next stage; the stationary flow path includes a diffuser having a plurality of diffuser vanes arranged in a circumferential direction around the rotation axis radially outward of an outlet of the impeller; a throttle flow path arranged between the outlet of the impeller and an inlet of the diffuser; a return bend connected to the outlet of the diffuser and turning the fluid flow from the radially outward direction to the radially inward direction; a return guide connected to the outlet of the return bend and having a plurality of return guide vanes arranged in the circumferential direction around the rotation axis; and an L-shaped bend connected to the outlet of the return guide and turning the fluid flow from the radially inward direction to the axial direction, The outer diameter of the stationary flow path is 1.8 times or more the outer diameter of the impeller, The return bend has a larger radius of curvature and a longer path than when the flow is turned along the shortest path. Multistage centrifugal turbomachinery.

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