Seal structure and rotating machine

Abstract

A seal structure includes a plurality of step portions that protrude such that a base surface facing a radial direction and a stepped surface facing an upstream side are formed, and a seal fin that forms a minute clearance with the base surface. The step portion includes an inclined surface that connects the base surface and the stepped surface to each other. The seal fin includes a seal opposing surface. A cavity connected to the minute clearance is formed on the upstream side with respect to the seal opposing surface. The step portion is formed such that, in a case where a first length is defined as L and a second length is defined as W, L satisfies a condition of 0.3W or more and 0.9W or less, and in a case where a third length is defined as C, 4 L satisfies a condition of 4C or more.

Description

SEAL STRUCTURE AND ROTATING MACHINE

[0001] The present disclosure relates to a seal structure and a rotating machine. 　　　　Priority is claimed on Japanese Patent Application No. 2024-192879, filed on November 1, 2024, the content of which is incorporated herein by reference.

[0002] A rotating machine such as a compressor or a steam turbine includes a casing and a rotor rotatably disposed inside the casing. The rotor includes, for example, a rotor shaft and an impeller fixed to the rotor shaft. In such a rotating machine, a clearance is formed between the rotor and the casing, which is a stator. However, a fluid that passes to leak through such a clearance does not impart a rotational force to the rotor including the impeller. Therefore, for improving performance of the rotating machine, it is important to reduce a flow rate of the fluid that leaks to pass through the clearance.

[0003] To address this, for example, PTL 1 describes a seal structure provided in a steam turbine, which is one of rotating machines. The seal structure described in PTL 1 includes a step portion including a stepped surface and a seal fin that forms a minute clearance with respect to the step portion. In addition, in this seal structure, a space referred to as a cavity is formed on an upstream side with respect to the seal fin. By defining a relationship between a size of the cavity, a size of the step portion, and the minute clearance, the leakage flow rate is further reduced, and sealing performance is improved.

[0004] [PTL 1] Japanese Unexamined Patent Application, First Publication No. 2011-80452

[0005] Meanwhile, in a case where a seal structure including a step portion and a seal fin is actually formed in a rotating machine, chamfering is applied to a corner formed in the step portion to form an inclined surface such as a C surface (chamfered surface) or an R surface (rounded surface). However, in a case of a small rotating machine, the step portion is also small, so that a region in which the inclined surface is formed with respect to the step portion becomes large. As a result, an influence of the region in which the inclined surface is formed becomes large, thereby leading to an increase in the leakage flow rate in the seal structure. Therefore, a structure capable of ensuring sealing performance even when the inclined surface is formed is desired.

[0006] The present disclosure provides a seal structure and a rotating machine capable of ensuring sealing performance even when an inclined surface is formed.

[0007] According to the present disclosure, there is provided a seal structure that seals a clearance through which a fluid flows from an upstream side toward a downstream side in an axial direction in which an axis extends, the clearance being formed between an outer peripheral surface of a rotor configured to rotate around the axis and an inner peripheral surface of a stator disposed to surround the rotor from an outside in a radial direction, the seal structure including: a plurality of step portions formed on one of the outer peripheral surface of the rotor and the inner peripheral surface of the stator and disposed side by side in the axial direction, each of the plurality of step portions protruding in the radial direction toward the other one of the outer peripheral surface of the rotor and the inner peripheral surface of the stator such that a base surface facing the radial direction and a stepped surface facing the upstream side are formed; and a seal fin formed on the other one, protruding in the radial direction toward each of the plurality of step portions, and forming a minute clearance with the base surface of each corresponding one of the plurality of step portions, in which each of the plurality of step portions includes an inclined surface connecting the base surface and the stepped surface to each other, the seal fin includes a seal opposing surface spreading in the radial direction and facing the upstream side in the axial direction, a cavity connected to the minute clearance is formed on the upstream side with respect to the seal opposing surface in the axial direction, the cavity being a space between the outer peripheral surface of the rotor and the inner peripheral surface of the stator in the radial direction, and each of the plurality of step portions is formed such that: in a case where a first length, which is the length in the axial direction from the seal opposing surface to the stepped surface, is defined as L and a second length, which is the length of the cavity in the axial direction, is defined as W, L satisfies a condition that L is 0.3W or more and 0.9W or less; and in a case where a third length, which is the length of the inclined surface in the axial direction, is defined as C, L satisfies a condition that L is 4C or more.

[0008] Additionally, according to the present disclosure, there is provided a rotating machine including the seal structure.

[0009] With the seal structure and the rotating machine of the present disclosure, sealing performance can be ensured even when an inclined surface is formed.

[0010] FIG. 1 is a schematic configuration diagram of a centrifugal chiller according to the present embodiment.FIG. 2 is a schematic cross-sectional view of a turbo compressor according to the present embodiment.FIG. 3 is a detailed view of a seal structure according to the present embodiment and is an enlarged view of a principal part showing a principal part I in FIG. 2.FIG. 4 is a detailed view of a seal fin according to the present embodiment and is an enlarged view of a principal part showing a principal part II in FIG. 3.

[0011] An embodiment for implementing a rotating machine and a seal structure according to the present disclosure will be described below with reference to the attached drawings. However, the present disclosure is not limited to the embodiment alone.

[0012] (Centrifugal Chiller) 　　　　A centrifugal chiller 100 according to the embodiment of the present invention will be described with reference to FIG. 1. As shown in FIG. 1, the centrifugal chiller 100 includes a turbo compressor 1 that compresses a refrigerant W as a fluid, a condenser 2 that condenses the refrigerant W compressed by the turbo compressor 1 using cooling water, a first expansion valve 3 that is an expansion unit which depressurizes the refrigerant W from the condenser 2, and an economizer 4 that separates the refrigerant W from the first expansion valve 3 into a gas-liquid two-phase.

[0013] In addition, the centrifugal chiller 100 includes an inflow passage that guides the gas phase of the refrigerant W from the economizer 4 to the turbo compressor 1, a second expansion valve 6 that serves as an expansion unit which depressurizes the liquid phase from the economizer 4 again, and an evaporator 7 that evaporates the refrigerant W from the second expansion valve 6.

[0014] The centrifugal chiller 100 has a refrigeration cycle in which the turbo compressor 1, the condenser 2, the first expansion valve 3, the second expansion valve 6, and the evaporator 7 are sequentially connected by piping.

[0015] The condenser 2 cools the refrigerant W compressed by the turbo compressor 1 by causing heat exchange with cooling water or the like, thereby bringing the refrigerant into a liquid state. For example, the condenser 2 is a shell-and-tube type heat exchanger. The condenser 2 is connected to a discharge port of the turbo compressor 1 by piping. A gas phase portion of the condenser 2 and a gas phase portion of the evaporator 7 are connected to each other by piping.

[0016] The first expansion valve 3 adiabatically expands the liquid refrigerant W from the condenser 2 to depressurize the refrigerant W and to evaporate a part of the liquid, thereby bringing the refrigerant W into a gas-liquid two-phase state. The first expansion valve 3 is connected to the condenser 2 by piping. The first expansion valve 3 is disposed between the condenser 2 and the economizer 4.

[0017] The economizer 4 separates the refrigerant W, which has been brought into a gas-liquid two-phase state by the first expansion valve 3, into a gas phase and a liquid phase. The economizer 4 is connected to the first expansion valve 3 by piping. The gas phase separated from the refrigerant W of the gas-liquid two-phase by the economizer 4 flows into the turbo compressor 1 through piping. The liquid phase separated from the refrigerant W of the gas-liquid two-phase by the economizer 4 flows into the second expansion valve 6 through piping.

[0018] The second expansion valve 6 adiabatically expands the refrigerant W, from which the gas phase has been separated by the economizer 4 so that only the liquid phase remains, to depressurize the refrigerant W. In the centrifugal chiller 100 of the present embodiment, a configuration has been employed in which the refrigerant W is depressurized by using expansion valves such as the first expansion valve 3 and the second expansion valve 6; however, the configuration is not limited to this, and the refrigerant W may be depressurized by using another expansion unit. The second expansion valve 6 is connected to the evaporator 7 by piping.

[0019] The evaporator 7 evaporates the refrigerant W from the second expansion valve 6 by causing heat exchange with water or the like, thereby bringing the refrigerant W into a saturated vapor state. The refrigerant W that has been brought into a saturated vapor state in the evaporator 7 flows into the turbo compressor 1 through piping.

[0020] (Turbo Compressor) 　　　　Next, the turbo compressor 1, which is the rotating machine of the present embodiment, will be described in detail with reference to FIG. 2. The turbo compressor 1 includes a rotor 10, a stator 20, a bearing portion 40, and a seal structure 50.

[0021] The rotor 10 is rotatable with respect to the stator 20 about an axis O. The rotor 10 extends in an axial direction Da in which the axis O extends. The rotor 10 of the present embodiment includes a rotor body 11, a first impeller 12, a second impeller 13, and a rotor core 14.

[0022] The rotor body 11 has a rod shape extending along the axis O. The rotor body 11 extends straight in the axial direction Da about the axis O. An axial rotor disc 11a that projects toward an outer peripheral side in a flange shape from an outer peripheral surface of the rotor body 11 is formed on a part of the outer peripheral surface of the rotor body 11 in the axial direction Da.

[0023] The first impeller 12 is integrally fixed to an end portion of the rotor body 11 on one side (a left side in FIG. 2) in a direction of the axis O. The first impeller 12 rotates together with the rotor body 11 about the axis O, thereby pumping the refrigerant W, which flows in from the one side in the axial direction Da, toward an outside Dro in a radial direction Dr.

[0024] The second impeller 13 is integrally fixed to an end portion of the rotor body 11 on the other side (a right side in FIG. 2) in the axial direction Da. That is, the second impeller 13 is disposed on an opposite side of the rotor body 11 from the first impeller 12 in the axial direction Da. The second impeller 13 rotates together with the rotor body 11 about the axis O, thereby pumping the refrigerant W, which flows in from the other side in the axial direction Da, toward the outside Dro in the radial direction Dr. In this way, the turbo compressor 1 including the first impeller 12 and the second impeller 13 is configured as a two-stage compression structure in which the refrigerant W compressed by the first impeller 12 is further compressed by the second impeller 13. Additionally, in addition to the refrigerant W compressed by the first impeller 12, a gas phase of the refrigerant W introduced from the economizer 4 is introduced into the second impeller 13.

[0025] The rotor core 14 is integrally fixed to the outer peripheral surface of the rotor body 11. The rotor core 14 has a laminated steel plate structure externally fitted on the outer peripheral surface of the rotor body 11. In the laminated steel plate structure, a plurality of permanent magnets are disposed at intervals in a circumferential direction of the rotor 10 about the axis O.

[0026] The stator 20 is disposed to surround the rotor 10 from the outside Dro in the radial direction Dr. The stator 20 of the present embodiment includes a housing 21 and a stator core 22.

[0027] The housing 21 is disposed to surround the rotor body 11 from the outside Dro in the radial direction Dr. From openings at both ends of the housing 21, both ends of the rotor body 11 in the axial direction Da are exposed.

[0028] The stator core 22 is disposed to surround the rotor core 14 from the outside Dro in the radial direction Dr. The stator core 22 is disposed with a spacing in the radial direction Dr with respect to the rotor core 14. The stator core 22 is fixed to the housing 21. The stator core 22 constitutes a motor 30 together with the rotor core 14. In such a motor 30, a current is supplied to the stator core 22 from outside, and the rotor core 14 and the rotor body 11 integrally fixed to the rotor core 14 rotate about the axis O with respect to the stator core 22 as each permanent magnet follows a rotating magnetic field generated by the supply of the current.

[0029] The bearing portion 40 is fixed to the housing 21. The bearing portion 40 rotatably supports the rotor body 11. The bearing portion 40 includes a pair of radial bearings 41 and an axial bearing 42.

[0030] The pair of radial bearings 41 are disposed with the motor 30 interposed therebetween in the axial direction Da. The pair of radial bearings 41 are disposed inside the housing 21 with a spacing in the axial direction Da such that the rotor core 14 is interposed therebetween. Movement of the rotor body 11 in the radial direction Dr is restricted by the radial bearing 41.

[0031] The axial bearing 42 is disposed to sandwich the axial rotor disc 11a of the rotor body 11 in the axial direction Da. The axial bearing 42 is disposed between the pair of radial bearings 41 in the axial direction Da. The axial bearing 42 is disposed between the radial bearing 41 disposed at a position closer to the second impeller 13 and the rotor core 14 in the axial direction Da. The axial bearing 42 supports the rotor body 11 in the axial direction Da in a non-contact manner such that the rotor body 11 is positioned at a predetermined position in the axial direction Da. Movement of the rotor body 11 in the axial direction Da is restricted by the axial bearing 42.

[0032] (Configuration of Seal Structure) 　　　　The seal structure 50 is formed between an outer peripheral surface of the rotor 10 and an inner peripheral surface of the stator 20. The seal structure 50 of the present embodiment seals a clearance between the rotor body 11 and the casing over an entire circumference. The seal structure 50 seals a clearance through which the refrigerant W (fluid) flows from an upstream side toward a downstream side in the axial direction Da. Here, the upstream side is an inflow side in the axial direction Da in a flow direction of the refrigerant flowing through the clearance between the rotor body 11 and the casing, which is sealed by the seal structure 50. In addition, the upstream side of the seal structure 50 is a position at which pressure is high in the axial direction Da with respect to the seal structure 50. Therefore, the upstream side of the seal structure 50 in the present embodiment is a side closer to the impeller with respect to the seal structure 50. Additionally, the downstream side is an outflow side in the axial direction Da in the flow direction of the refrigerant flowing through the clearance between the rotor body 11 and the casing, which is sealed by the seal structure 50. Further, the downstream side of the seal structure 50 is a position at which pressure is low in the axial direction Da with respect to the seal structure 50. Therefore, the downstream side of the seal structure 50 in the present embodiment is a side closer to the motor 30 with respect to the seal structure 50.

[0033] The seal structure 50 is disposed in a pair. The pair of seal structures 50 suppress leakage of the refrigerant W compressed by the first impeller 12 and the second impeller 13 to a position in the casing where the motor 30 and the bearing portion 40 are disposed. The pair of seal structures 50 are disposed between the first impeller 12 and the radial bearing 41 and between the second impeller 13 and the radial bearing 41 in the axial direction Da. The pair of seal structures 50 are disposed alongside the first impeller 12 and the second impeller 13 in the axial direction Da.

[0034] Here, as one example, the seal structure 50 disposed at a position closer to the second impeller 13 will be described. Note that the seal structure 50 disposed at a position closer to the first impeller 12 also has the same structure as the seal structure 50 disposed at a position closer to the second impeller 13, except that an orientation in the axial direction Da is different. As shown in FIGS. 3 and 4, the seal structure 50 of the present embodiment includes a plurality of step portions 51 and a plurality of seal fins 52.

[0035] The step portion 51 is formed on one of the outer peripheral surface of the rotor 10 and the inner peripheral surface of the stator 20. The step portion 51 of the present embodiment is formed on the outer peripheral surface of the rotor body 11, which is the rotor 10. The step portion 51 protrudes in the radial direction Dr toward the other one of the outer peripheral surface of the rotor 10 and the inner peripheral surface of the stator 20. Therefore, the step portion 51 of the present embodiment protrudes from the outer peripheral surface of the rotor body 11 toward the inner peripheral surface of the casing, which is the stator 20. The step portions 51 are disposed side by side in the axial direction Da. The plurality of step portions 51 are formed in a stepped shape such that an amount of protrusion from the outer peripheral surface of the rotor body 11 toward the outside Dro in the radial direction Dr gradually increases to approach the inner peripheral surface of the casing from the upstream side toward the downstream side in the axial direction Da. In the present embodiment, the seal structure 50 includes step portions 51 such that, for example, three stages are formed. The step portion 51 includes a base surface 511, a stepped surface 512, and at least one inclined surface 513.

[0036] The base surface 511 is a surface facing the radial direction Dr. The base surface 511 of the present embodiment is a smooth surface facing the outside Dro in the radial direction Dr. The base surface 511 is formed in parallel with the outer peripheral surface of the rotor body 11.

[0037] The stepped surface 512 is a surface facing the upstream side in the axial direction Da. The stepped surface 512 extends in the radial direction Dr to be orthogonal to the base surface 511. That is, the step portion 51 protrudes from the outer peripheral surface of the rotor body 11 such that the base surface 511 and the stepped surface 512 are formed. The stepped surfaces 512 of the step portions 51 extend in the radial direction Dr to be parallel to each other. A plurality of stepped surfaces 512 are formed to have the same height.

[0038] The inclined surface 513 connects the base surface 511 and the stepped surface 512. The inclined surface 513 is a flat surface facing the upstream side in the axial direction Da and the outside Dro in the radial direction Dr. The inclined surface 513 is formed as a C surface by chamfering to cut off a corner portion where the base surface 511 and the stepped surface 512 intersect. That is, the inclined surface of the present embodiment is inclined at 45° with respect to the base surface 511 and the stepped surface 512. Therefore, by forming the inclined surface 513, no acute corner portion connected to the base surface 511 and the stepped surface 512 is formed in the step portion 51.

[0039] The inclined surface 513 is not limited to the flat surface. The inclined surface 513 may be a curved surface formed by R-chamfering. In addition, the inclined surface 513 is not limited to a structure in which, even when the inclined surface 513 is a flat surface, the flat surface is inclined at 45° with respect to the base surface 511 and the stepped surface 512. The inclined surface 513 may be inclined at different angles with respect to the base surface 511 and the stepped surface 512.

[0040] Additionally, in the casing, an annular groove 57 is formed in the axial direction Da to face the step portion 51. The annular groove 57 is formed to extend in the circumferential direction. The annular groove 57 is recessed from the inner peripheral surface of the casing toward the outside Dro in the radial direction Dr. In the annular groove 57, a plurality of annular recessed portions 571 are formed side by side in the axial direction Da to face the plurality of step portions 51. The plurality of annular recessed portions 571 are formed in a stepped shape to gradually spread toward the outside Dro in the radial direction Dr from the upstream side toward the downstream side in the axial direction Da. In the present embodiment, the annular groove 57 includes annular recessed portions 571 such that, for example, three stages are formed to have the same number as the step portions 51.

[0041] The seal fin 52 is formed on the other one of the outer peripheral surface of the rotor 10 and the inner peripheral surface of the stator 20. That is, the seal fin 52 is formed on whichever of the outer peripheral surface of the rotor 10 and the inner peripheral surface of the stator 20 where no step is formed. The seal fin 52 of the present embodiment is formed on the inner peripheral surface of the casing. Specifically, the seal fin 52 is formed on an inner peripheral surface of the annular recessed portion 571 that faces an inside Dri in the radial direction Dr. The seal fin 52 protrudes in the radial direction Dr toward each of the step portions 51. That is, one seal fin 52 is formed for one annular recessed portion 571, whereby one seal fin 52 is disposed for one step portion 51. Therefore, a plurality of seal fins 52 are disposed apart from each other in the axial direction Da. The seal fin 52 forms a minute clearance 70 with the base surface 511 of the corresponding step portion 51. Each dimension of the minute clearance 70 is set to be minimal within a safe range in which the casing and a shaft of the rotor 10 do not come into contact with each other, in consideration of a thermal expansion amount of the casing and the shaft of the rotor 10, and the like. That is, the seal fin 52 and the base surface 511 are formed not to come into contact with each other during the operation of the turbo compressor 1. In addition, the seal fin 52 is formed in a shape such that the length in the axial direction Da is smaller than that of the base surface 511. That is, the seal fin 52 is formed such that the length in the radial direction Dr is greater than the length in the axial direction Da. The seal fin 52 includes a seal opposing surface 521.

[0042] The seal opposing surface 521 is a flat surface spreading in the radial direction Dr. The seal opposing surface 521 faces the upstream side in the axial direction Da.

[0043] Additionally, the plurality of seal fins 52 are formed, whereby a plurality of cavities 60 are formed in a space between the outer peripheral surface of the rotor 10 and the inner peripheral surface of the stator 20. The cavities 60 are formed in the same number as the number of the seal fins 52 and the steps. The cavity 60 is formed between the seal fin 52 corresponding to each of the step portions 51 and a wall portion (or another seal fin 52) of the casing that faces the seal fin 52 on the upstream side in the axial direction Da. The cavity 60 is a space communicating with the minute clearance 70.

[0044] In addition, a first length, which is the length in the axial direction Da from the seal opposing surface 521 to the stepped surface 512, is defined as L. Further, a second length, which is the length of the cavity 60 in the axial direction Da, is defined as W. Furthermore, a third length, which is the length of the inclined surface 513 in the axial direction Da, is defined as C. Additionally, a fourth length, which is the length of the minute clearance 70 in the radial direction Dr, is defined as H. Further, a fifth length, which is a protrusion length of the seal fin 52 in the radial direction Dr (the length of the seal opposing surface 521 in the radial direction Dr), is defined as h1. Furthermore, a sixth length, which is a protrusion length of the step portion 51 in the radial direction Dr, is defined as h2.

[0045] In such a case, the step portion 51 is formed so that L satisfies the condition that L is 0.3W or more and 0.9W or less. In addition, the step portion 51 is formed so that L satisfies the condition that L is 4C or more. Further, the step portion 51 is formed so that L satisfies the condition that L is 3H or more.

[0046] Moreover, it is preferable that the first length L is formed large within a range in which the second length W can be secured (within a range in which the cavity 60 can be formed). That is, it is preferable that the first length L is smaller than the second length W. Additionally, the third length C is smaller than the sixth length h2. The third length C is preferably, for example, 0.1 mm or greater and 5.0 mm or less. It is preferable that the fourth length H is smaller than the fifth length h1 and the sixth length h2. It is preferable that the fifth length h1 is greater than the first length L and the sixth length h2.

[0047] (Operation and Effect) 　　　　In the seal structure 50 of the present embodiment as mentioned above, a part of the refrigerant W (for example, several %) compressed by the first impeller 12 and the second impeller 13 flows out from the first impeller 12 and the second impeller 13, then passes around back surfaces of the first impeller 12 and the second impeller 13, and flows into the annular groove 57. The refrigerant W that has flowed into the annular groove 57 reaches the step portion 51. Then, the refrigerant W leaking from a position on the upstream side, such as the first impeller 12 or the second impeller 13, moves onto the step portion 51 via the stepped surface 512. At that time, flow separation occurs, and a contracted flow like a vortex is generated in a space on the upstream side in the axial direction Da with respect to the minute clearance 70 and on the outside Dro in the radial direction Dr with respect to the base surface 511. In the seal structure 50, this contracted flow generates a downflow immediately before the minute clearance 70, thereby suppressing the flow rate of the refrigerant W passing through the minute clearance 70. However, the step portion 51 of the present embodiment includes the inclined surface 513 that connects the base surface 511 and the stepped surface 512 to each other. In the seal structure 50 of the present embodiment, by forming the inclined surface 513, the first length L, which is the length of the base surface 511, becomes shorter. In addition, when the refrigerant W moves onto the step portion 51, the flow of the refrigerant W flows along the inclined surface 513 and the base surface 511, so that flow separation does not occur and the contracted flow becomes small. As a result, the sealing performance of the seal structure 50 may not be sufficiently ensured. To address this, the seal structure 50 of the present embodiment is formed so as to satisfy both the condition that L is 0.3 W or more and 0.9 W or less, and the condition that L is 4 C or more. Therefore, even when the inclined surface 513 is formed, it is possible to form the step portion 51 including the base surface 511 having a sufficient length secured in the axial direction Da. As a result, it is possible to cause flow separation in the flow of the refrigerant W that has moved onto the step portion 51 and to generate a contracted flow with high accuracy. Therefore, it is possible to stably reduce the leakage flow rate at the minute clearance 70. Accordingly, even when the inclined surface 513 is formed, sealing performance can be stably ensured.

[0048] Additionally, the step portion 51 is formed so that L satisfies the condition of 3H or more. Therefore, even when the inclined surface 513 is formed, it is possible to more reliably form the step portion 51 including the base surface 511 having a sufficient length secured in the axial direction Da. As a result, it is possible to cause flow separation in the flow of the refrigerant W that has moved onto the step portion 51 and to generate a contracted flow with higher accuracy. Therefore, it is possible to more stably reduce the leakage flow rate at the minute clearance 70. Accordingly, even when the inclined surface 513 is formed, sealing performance can be more stably ensured.

[0049] In addition, the inclined surface 513 is formed as a flat surface. Therefore, the inclined surface 513 can be formed in the step portion 51 by simple machining such as C-chamfering.

[0050] Further, by providing the rotating machine with the seal structure 50 as mentioned above, sealing performance can be enhanced. In particular, in a case where the rotating machine is the turbo compressor 1 of the centrifugal chiller 100 as in the present embodiment, the rotating machine is a very small device. As a result, the seal structure 50 disposed in the small rotating machine is also very small. Therefore, in a case where the inclined surface 513 is formed in the step portion 51, the formation is greatly affected by the shape of the step portion 51 such as the length of the base surface 511. However, by applying the seal structure 50 of the present embodiment, even when the inclined surface 513 is formed, sealing performance can be stably ensured.

[0051] (Other Embodiments) 　　　　As described above, the embodiment of the present disclosure has been described in detail with reference to the drawings; however, the specific configuration is not limited to the embodiment, and design modifications and the like within a scope not departing from the concept of the present disclosure are also included.

[0052] The shape of the seal structure 50 is not limited to the shape as in the present embodiment. For example, the numbers of the step portions 51, the seal fins 52, and the annular recessed portions 571 are not limited to three as in the present embodiment. The numbers of the step portions 51, the seal fins 52, and the annular recessed portions 571 need only be determined in accordance with sealing performance required in the rotating machine in which the seal structure 50 is installed. Accordingly, the numbers of the step portions 51, the seal fins 52, and the annular recessed portions 571 may be four or more, or may be two or less.

[0053] Additionally, the rotating machine is not limited to the turbo compressor 1. The rotating machine need only allow a fluid to flow inside and include the rotor 10 and the stator 20. Accordingly, the rotating machine may be a multi-shaft centrifugal compressor, an axial compressor, a steam turbine, a gas turbine, or a pump.

[0054] In addition, the step portion 51 is not limited to being formed on the rotor 10 as in the rotor body 11 of the present embodiment. That is, conversely to the present embodiment, the seal fins 52 may be disposed on the rotor 10, and the step portions 51 may be formed on the stator 20.

[0055] <Supplementary Notes> 　　　　The seal structure 50 and the rotating machine described in each embodiment are understood, for example, as follows.

[0056] (1) According to a first aspect, there is provided a seal structure 50 that seals a clearance through which a fluid flows from an upstream side toward a downstream side in an axial direction Da in which an axis O extends, the clearance being formed between an outer peripheral surface of a rotor 10 configured to rotate around the axis O and an inner peripheral surface of a stator 20 disposed to surround the rotor 10 from an outside Dro in a radial direction Dr, the seal structure 50 including: a plurality of step portions 51 formed on one of the outer peripheral surface of the rotor 10 and the inner peripheral surface of the stator 20 and disposed side by side in the axial direction Da, each of the plurality of step portions 51 protruding in the radial direction Dr toward the other one of the outer peripheral surface of the rotor 10 and the inner peripheral surface of the stator 20 such that a base surface 511 facing the radial direction Dr and a stepped surface 512 facing the upstream side are formed; and a seal fin 52 formed on the other one, protruding in the radial direction Dr toward each of the plurality of step portions 51, and forming a minute clearance 70 with the base surface 511 of each corresponding one of the plurality of step portions 51, in which each of the plurality of step portions 51 includes an inclined surface 513 connecting the base surface 511 and the stepped surface 512 to each other, the seal fin 52 includes a seal opposing surface 521 spreading in the radial direction Dr and facing the upstream side in the axial direction Da, a cavity 60 connected to the minute clearance 70 is formed on the upstream side with respect to the seal opposing surface 521 in the axial direction Da, the cavity 60 being a space between the outer peripheral surface of the rotor 10 and the inner peripheral surface of the stator 20 in the radial direction Dr, and each of the plurality of step portions 51 is formed such that: in a case where a first length, which is the length in the axial direction Da from the seal opposing surface 521 to the stepped surface 512, is defined as L and a second length, which is the length of the cavity 60 in the axial direction Da, is defined as W, L satisfies a condition that L is 0.3W or more and 0.9W or less; and in a case where a third length, which is the length of the inclined surface 513 in the axial direction Da, is defined as C, L satisfies a condition that L is 4C or more.

[0057] With such a configuration, the seal structure 50 is formed so as to satisfy both the condition that L is 0.3 W or more and 0.9 W or less, and the condition that L is 4 C or more. Therefore, even when the inclined surface 513 is formed, it is possible to form the step portion 51 including the base surface 511 having a sufficient length secured in the axial direction Da. As a result, it is possible to cause flow separation in the flow of the refrigerant W that has moved onto the step portion 51 and to generate a contracted flow with high accuracy. Therefore, it is possible to stably reduce the leakage flow rate at the minute clearance 70. Accordingly, even when the inclined surface 513 is formed, sealing performance can be stably ensured.

[0058] (2) The seal structure 50 according to a second aspect is the seal structure 50 of (1), in which each of the plurality of step portions 51 is formed such that, in a case where a fourth length, which is the length of the minute clearance 70 in the radial direction Dr, is defined as H, L satisfies a condition that L is 3H or more.

[0059] With such a configuration, even when the inclined surface 513 is formed, it is possible to more reliably form a step portion 51 including a base surface 511 having a sufficient length secured in the axial direction Da. As a result, it is possible to cause flow separation in the flow of the refrigerant W that has moved onto the step portion 51 and to generate a contracted flow with higher accuracy. Therefore, it is possible to more stably reduce the leakage flow rate at the minute clearance 70. Accordingly, even when the inclined surface 513 is formed, sealing performance can be more stably ensured.

[0060] (3) The seal structure 50 according to a third aspect is the seal structure 50 of (1) or (2), in which the inclined surface 513 is a flat surface.

[0061] With such a configuration, the inclined surface 513 can be formed in the step portion 51 by simple machining such as C-chamfering.

[0062] (4) According to a fourth aspect, there is provided a rotating machine including the seal structure 50 of (1) to (3).

[0063] With such a configuration, sealing performance can be enhanced.

[0064] With the seal structure and the rotating machine of the present disclosure, sealing performance can be ensured even when the inclined surface is formed.

[0065] 100　　Centrifugal chiller 　　　　1　　　Turbo compressor 　　　　2　　　Condenser 　　　　3　　　First expansion valve 　　　　4　　　Economizer 　　　　6　　　Second expansion valve 　　　　7　　　Evaporator 　　　　W　　　Refrigerant 　　　　O　　　Axis 　　　　10　　Rotor 　　　　11　　Rotor body 　　　　11a　　Axial rotor disc 　　　　12　　First impeller 　　　　13　　Second impeller 　　　　14　　Rotor core 　　　　20　　Stator 　　　　21　　Housing 　　　　22　　Stator core 　　　　30　　Motor 　　　　40　　Bearing portion 　　　　41　　Radial bearing 　　　　42　　Axial bearing 　　　　50　　Seal structure 　　　　51　　Step portion 　　　　511　　Base surface 　　　　512　　Stepped surface 　　　　513　　Inclined surface 　　　　52　　Seal fin 　　　　521　　Seal opposing surface 　　　　57　　Annular groove 　　　　571　　Annular recessed portion 　　　　60　　Cavity 　　　　70　　Minute clearance 　　　　Da　　Axial direction 　　　　Dr　　Radial direction 　　　　Dro　　Outside (radial direction) 　　　　Dri　　Inside (radial direction)

Claims

1. A seal structure that seals a clearance through which a fluid flows from an upstream side toward a downstream side in an axial direction in which an axis extends, the clearance being formed between an outer peripheral surface of a rotor configured to rotate around the axis and an inner peripheral surface of a stator disposed to surround the rotor from an outside in a radial direction, the seal structure comprising: 　　　　a plurality of step portions formed on one of the outer peripheral surface of the rotor and the inner peripheral surface of the stator and disposed side by side in the axial direction, each of the plurality of step portions protruding in the radial direction toward the other one of the outer peripheral surface of the rotor and the inner peripheral surface of the stator such that a base surface facing the radial direction and a stepped surface facing the upstream side are formed; and 　　　　a seal fin formed on the other one, protruding in the radial direction toward each of the plurality of step portions, and forming a minute clearance with the base surface of each corresponding one of the plurality of step portions, 　　　　wherein each of the plurality of step portions includes at least one inclined surface connecting the base surface and the stepped surface to each other, 　　　　the seal fin includes a seal opposing surface spreading in the radial direction and facing the upstream side in the axial direction, 　　　　a cavity connected to the minute clearance is formed on the upstream side with respect to the seal opposing surface in the axial direction, the cavity being a space between the outer peripheral surface of the rotor and the inner peripheral surface of the stator in the radial direction, and 　　　　each of the plurality of step portions is formed such that: 　　　　　　　in a case where a first length, which is a length in the axial direction from the seal opposing surface to the stepped surface, is defined as L and a second length, which is a length of the cavity in the axial direction, is defined as W, L satisfies a condition that L is 0.3W or more and 0.9W or less; and 　　　　　　　in a case where a third length, which is a length of the at least one inclined surface in the axial direction, is defined as C, L satisfies a condition that L is 4C or more.

2. The seal structure according to Claim 1, 　　　　wherein each of the plurality of step portions is formed such that, in a case where a fourth length, which is a length of the minute clearance in the radial direction, is defined as H, L satisfies a condition that L is 3H or more.

3. The seal structure according to Claim 1 or 2, 　　　　wherein the at least one inclined surface is a flat surface.

4. A rotating machine comprising: 　　　　the seal structure according to any one of Claims 1 to 3.

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