Axial Turbine

Abstract

An axial turbine has a turbine stage including stator blades fixedly provided on a stationary section and moving blades fixedly provided on a rotating section and has a structure in which a flow blowing out from a space formed between the stator blades and the moving blades exists. In order to prevent a decrease in stage output power due to such blowout flow thereby to improve the turbine stage efficiency, the axial turbine comprises a member coupling an inner circumferential side of the stator blades, and a structure provided on a surface of the member opposed to the moving blades for bending a flow blowing out from the side of the rotating section into a space between the stator blades and the moving blades in a rotational direction of the rotating section.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to axial turbines and more particularly to a drum-type rotor turbine.

[0003] 2. Description of the Related Art

[0004] The axial turbine such as a steam turbine or gas turbine comprise a turbine stage including stator blades formed to transform the pressure of a fluid into kinetic energy and moving blades for transforming the pressure or kinetic energy of the fluid into the rotational energy of a rotating section. The stator blades are fixedly provided between an outer circumferential diaphragm and inner circumferential diaphragm forming a stationary section. The moving blades are provided on a rotor that forms the rotating section. A clearance is provided between the inner circumferential diaphragm and the rotor, and the clearance has a seal. This seal reduces a leakage flow that passes through the clearance. This leakage flow passing through the clearance, however, cannot be completely zeroed since the clearance must be maintained within a definite dimensional range to obtain stable rotation of the rotor.

[0005] In addition, JP-A-59-122707 proposes a turbine structure that cools a rotor by introducing steam through a clearance first and then through a balance hole formed in extend-through form in a rotor disc. In JP-A-1984-122707, the remainder of the steam which has been passed through the clearance is further diffused outward to cool the outer surface of the rotor disc and then join the main flow of steam.

[0006] In case where the balance hole is formed, since steam leakage will flow into the balance hole, the leakage flow blowing out between stator blades and moving blades will not be significant.

SUMMARY OF THE INVENTION

[0007] The method of providing a plurality of balance holes in a circumferential direction cannot be used for an axial turbine not having such a space as a drum-type rotor in which to provide the balance holes. In addition, a stage with significant differences in pressure between the front and rear of the moving blades increases the flow rate of the steam flowing through the balance holes, and takes in this flow between the stator blades and the moving blades. Accordingly, the amount of steam flowing into the moving blades will be reduced and this, in turn, could reduce stage output power.

[0008] In case where the balance holes are not present, the leakage flow that has passed through the clearance will blow out from a space formed between the stator blades and the moving blades. However, this blowout flow will, as detailed later herein, interfere with the flow that has run in from an upstream direction as the main flow of steam between stators, and the interference will disturb the main flow of steam, thus reducing the output power of the stage.

[0009] An object of the present invention is to provide an axial turbine having a structure in which a flow blowing out from a space formed between stator blades and moving blades exists and in which a decrease in stage output power due to such blowout flow is prevented to occur thereby to enable the turbine stage efficiency to be improved.

[0010] According to one aspect of the present invention, there is provided an axial turbine having a turbine stage including stator blades fixedly provided on a stationary section and moving blades fixedly provided on a rotating section of a rotor, wherein said axial turbine comprises a member coupling an inner circumferential side of said stator blades, and a structure provided on a surface of said member opposed to said moving blades for bending a flow blowing out from the side of said rotor into a space between said stator blades and said moving blades in a rotational direction of the rotating section.

[0011] According to another aspect of the present invention, there is provided an axial turbine having a turbine stage including stator blades fixedly provided on a stationary section and moving blades fixedly provided on a rotating section of a rotor, wherein said axial turbine comprises a diaphragm disposed at the inner circumferential side of said stator blades, and a structure provided on a surface of said diaphragm opposed to said moving blades for bending a flow blowing out from the side of said rotor into a space between said stator blades and said moving blades in a rotational direction of the rotating section.

[0012] According to still another aspect of the present invention, there is provided an axial turbine having a turbine stage including stator blades fixedly provided on a stationary section and moving blades fixedly provided on a rotating section of a rotor, wherein said axial turbine comprises a cover formed integrally with the inner circumferential side of said stator blades, and a structure provided on a surface of said cover opposed to said moving blades for bending a flow blowing out from the side of said rotor into a space between said stator blades and said moving blades in a rotational direction of the rotating section.

[0013] According to the present invention, since the flow blowing out from the space between the stator blades and the moving blades is bent in the rotational direction of the rotor, it is possible to suppress interference of the blowout flow with a main flow of steam that has run in from an upstream direction between stator blades, and consequently to prevent a decrease in stage output power to occur, thereby improving turbine stage efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a view showing a turbine structure of an embodiment of the present invention;

[0015] FIG. 2 is a view that shows the interference between the leakage flow in the conventional turbine structure and a flow that has run in from an upstream direction between stator blades;

[0016] FIG. 3 is a view that shows from a downstream side of the stator blades the interference between the leakage flow in the conventional turbine structure and the flow that has run in from the upstream direction between stator blades;

[0017] FIG. 4 is a diagram illustrating the way the interference between the leakage flow in the conventional turbine structure and the flow that has run in from the upstream direction between stator blades affects the moving blades;

[0018] FIG. 5 is a view showing a turbine stage of the present invention from a downstream side of stator blades;

[0019] FIG. 6 is a view showing the turbine stage of the present invention from a downstream side of stator blades;

[0020] FIG. 7 is a view showing a turbine structure of another embodiment of the present invention; and

[0021] FIG. 8 is a view showing a turbine structure of yet another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereunder, an axial turbine having a turbine stage according to a first embodiment of the present invention will be described by using the accompanying drawings.

[0023] A sectional view of the turbine stage of the present invention is shown in FIG. 1. As shown therein, the turbine stage is provided between a high-pressure side P0 and a low-pressure side P1, and includes stator blades 1 fixed to an outer circumferential diaphragm 6 and an inner circumferential diaphragm 7, and moving blades 10 provided on a rotor 15 that rotates. In case of a turbine having a plurality of turbine stages, moving blades 10a of another stage exist at an upstream side of the stator blades 1.

[0024] A main flow of steam 20 is induced by a differential pressure P0-P1, and the flow 20 is speeded up by the stator blades 1 and deflected in a circumferential direction thereof. The flow to which the circumferential velocity component has been assigned by the stator blades 1 gives kinetic energy to the moving blades 10 and rotates the rotor 15 provided with the moving blades 10.

[0025] The turbine stage has a clearance 2 between the inner circumferential diaphragm 7 and the rotor 15, and is constructed so that the rotor can rotate at high speed and stably. However, a flow running from the high-pressure side to the low-pressure side occurs in the clearance 2. This flow is called the leakage flow. Since the leakage flow keeps away from the stator blades 1, the leakage flow is not deflected in the circumferential direction of the stator blades and cannot assign usable rotational energy to the moving blades 10. If the leakage flow is significant, therefore, this reduces the rotational energy or output power obtained by the turbine stage. In order to reduce the leakage flow, a seal exists in the clearance 2. The seal is formed by, for example, a combination of multiple fins 4 and multiple protrusions 5. The fins 4 themselves have a flow contraction effect, and the combination between the fins 4 and the protrusions 5 yields a thermal dissipation effect to dissipate kinetic energy by creating a complex flow path. These effects reduce the leakage flow. This leakage flow passing through the clearance 2, however, cannot be completely zeroed since the clearance between the fins 4 and the rotor 15 must be maintained within a definite dimensional range to obtain stable rotation of the rotor 15.

[0026] The leakage flow blows out into a space formed between the stator blades and the moving blades. In the present invention, in order to suppress a disturbance in the main steam flow due to the blowout flow, the inner circumferential diaphragm 7 has a structure 40 that bends the leakage flow in a rotational direction of the rotor when the flow blows out into the space between the stator blades and the moving blades. The structure 40 is based on the analyses described in detail below.

[0027] That is to say, as shown in FIG. 2, when the structure 40 of the present invention is absent, leakage flow 25 blows out into the space formed between the stator blades and the moving blades. The leakage flow 25 interferes with and disturbs the main steam flow 21 to which kinetic energy and a swirling or circumferential velocity component have been assigned after passing between stator blades.

[0028] FIG. 3 is a view that shows from a downstream side of the stator blades, the flow occurring at an exit of the stator blades. The leakage flow 25 forms a vortex 23 by blowing upward the flow 21 that has run in between stator blades. If the leakage flow 25 is absent, the flow between stator blades becomes a circumferentially swirling flow to produce the rotational energy 30 of the rotor. This flow is denoted by reference number 22 in FIG. 3. However, as shown in FIG. 4, the vortex 23 that has been formed by the interference between the leakage flow 25 and the stator exit flow 21 grows up into such a vortex 24 that behaves as if it twined the moving blades. Thus, the vortex 23 cannot retrieve rotational energy effectively inside the moving blades. That is to say, the leakage flow 25 yields a double effect not only in that the flow itself produces no rotational energy, but also in that the flow reduces part of the rotational energy which the flow 21 should originally produce, and consequently, the leakage flow 25 reduces stage output power.

[0029] As described in JP-A-1984-122707, when a balance hole is present, the blowout of a leakage flow into the space between the stator blades and the moving blades can be suppressed. However, if a balance hole is not present for reasons such as difficulty with formation of the balance hole, it is important that any effects of the leakage flow should be reduced to improve turbine stage efficiency.

[0030] In the first embodiment of the present invention, as shown in FIG. 1, the inner circumferential diaphragm 7 of the stator blades (i.e., a member coupling an inner circumferential side of the stator blades) has the structure 40 on a surface of the diaphragm 7 opposed to the moving blades 10. When the leakage flow from a space between the stator blades 1 and the rotor 15 blows upward into the space between the stator blades and the moving blades, the structure 40 bends the leakage flow in the rotational direction of the rotor.

[0031] Details of the structure 40 are shown in FIG. 5. FIG. 5 is a view showing the structure 40 from the downstream side of the stator blades. The structure 40 comprises a plurality of protrusions or plates provided on the surface of the diaphragm 7 opposed to the moving blades 10 and arranged to incline in the rotational direction 30 of the rotor 15 such that an outer circumferential side of the protrusions shifts relative to an inner circumferential side thereof in the rotational direction 30 of said rotor 15. When the leakage flow 25 blows upward in the flow path formed between the adjacent protrusions 40, the leakage flow 25 is guided along the flow path and deflected in the rotational direction 30 of the rotor 15. The flow 22 that runs in from an upstream direction between stator blades is also oriented in the rotational direction 30, and a difference in velocity between the leakage flow 25 and the stator blade flow 22 becomes smaller than in a turbine stage not having the structure 40 of the present invention. A loss of flow due to interference between the leakage flow 25 and the stator blade flow 22, and a vortex that causes the loss are augmented as the difference in relative velocity between the leakage flow 25 and the stator blade flow 22 increases. In the present invention, therefore, the occurrence of the vortex that causes the loss is suppressed and a decrease in stage output power can be avoided.

[0032] Another example of a structure 40 formed so that the flow blowing upward between the stator blades and the moving blades will bend in a rotational direction of the moving blades is shown in FIG. 6. In this modification, the structure 40 comprises a plurality of protrusions or plate each having a shape curved such that an inner circumferential side of the protrusion is oriented in a radial direction and an outer circumferential side thereof is oriented in a rotational direction 30 of the rotor 15, thereby enabling to form a flow path directed at an inner circumferential side thereof in a radial direction and at an outer circumferential side thereof in the rotational direction 30 of the rotor. A loss of flow due to the interference between the leakage flow 25 and the stator blade flow 22 can also be suppressed in the present modification of the structure 40.

[0033] In addition, the structure 40 for bending in the rotational direction of the moving blades the flow blowing upward between the stator blades and the moving blades does not need to have a shape that allows the formation of a flow path with protrusions. More specifically, chipping an inner circumferential diaphragm 7 of the stator blades 1, that is, adopting a shape that allows the formation of a flow path concaved in the rotational direction may allow the present modification of the structure 40 to be constructed so that the above blowout flow bends in the rotational direction of the moving blades.

[0034] According to the above-described embodiment of the present invention, since the flow blowing out from the space formed between the stator blades and the moving blades bends in the rotational direction of the rotor, it is possible to suppress interference of the above blowout flow with the main steam flow that has run in from the upstream direction along the stator blades. This makes it possible to prevent stage output power from decreasing, and thus to improve turbine stage efficiency.

[0035] In JP-A-1984-122707, a steam guide plate exists on the face of a nozzle diaphragm inner ring that is opposed to the rotor disc, and the steam guide plate gives a rotor rotational velocity component to the cooling steam that flows through the clearance formed between the nozzle diaphragm inner ring and the rotor disc. Thus, the conventional turbine structure minimizes turbine work loss by giving, by the steam guide plate, the rotor rotational velocity component to the steam that flows into a balance hole, and preventing the balance hole-through steam from being assigned some kind of work. According to JP-A-1984-122707, however, both the nozzle diaphragm inner ring and the rotor disc have a protrusion(s) to obstruct the above flow at a position even more outward than the balance hole, so the advantageous effect provided by the steam guide plate has no impacts upon the flow that blows upward between the stator blades and the moving blades. For this reason, in JP-A-1984-122707, since the balance hole is present, although the flow that blows out from the space between the stator blades and the moving blades originally has no significant effects, suppression of the interference between the blowout flow from the space between the stator blades and the moving blades and the main steam flow that has run in from an upstream direction between stator blades cannot be expected.

[0036] Next, another embodiment of the present invention is described below by using FIG. 7. The present embodiment further augments the effect of suppressing a decrease in stage output power.

[0037] While the structure for bending in the rotational direction of the moving blades the flow that blows upward between the stator blades and the moving blades is installed on a stationary section of the turbine stage, a clearance 45 must, as shown in FIG. 1, be provided between the structure 40 and a rotating section 16 of the rotor 15 in order to obtain stable rotor rotation. Depending on the structure 40, the flow that blows upward along the clearance 45 may not be bendable in the rotational direction of the rotor. Viscous force of the fluid near the rotating section 16, however, swirls the fluid synchronously with the rotating section 16 and assigns a rotational velocity component to the fluid. Accordingly, the structure 40 does not need to be in contact with the rotating section 16, and the advantageous effect of the present invention can be obtained. The advantageous effect of the present invention can be further enhanced if the structure for bending the above-described blowout flow in the rotational direction of the moving blades is installed at sections as many as possible in a direction of a rotational axis between the stator blades and the moving blades. To determine the clearance 45 formed between the structure 40 and the rotating section 16, there is a need to consider not only a steady rotational state, but also a starting/stopping non-steady operational state. During the starting/stopping non-steady operational state, that is, when a temperature of the turbine stage changes, a thermal elongation level differs according to a particular difference in thermal capacity between the rotating section and the stationary section. Therefore, the clearance 45 changes. The clearance 45 is usually set to prevent contact between the rotating section and the stationary section, even under the above temperature change, so during steady rotation, the clearance 45 becomes larger than that actually required. In the present embodiment, therefore, the structure for bending in the rotational direction of the rotor the flow that blows out from the rotor side into the space formed between the stator blades and the moving blades uses a brush seal 42 that has a brush at a side opposed to the moving blades. Since the brush becomes deformed during contact, the contact with a section opposed to the rotating section occurs for a brief time, so that stable rotation is possible. This means that when a design value is set for the clearance 45, it is necessary only to consider the fact that during steady rotation, the brush seal 42 and the rotating section 16 of the rotor do not come into contact with each other for reasons such as axial vibration. That is to say, if the brush seal 42 with a brush at the side opposed to the moving blades is used as the structure formed to bend in the rotational direction of the moving blades the flow that blows upward between the stator blades and the moving blades, it becomes possible to minimize the clearance 45. This, in turn, makes the upward blowing flow applicable to a larger number of sections between the stator blades and the moving blades, thus enhancing the advantageous effect of the present invention.

[0038] Next, yet another embodiment of the present invention is described below by using FIG. 8. The present embodiment applies the invention to a turbine stage which, as shown in FIG. 8, includes: a blade section constituted by stator blades 1 formed integrally with a root 6 and a cover 9 (member for coupling an inner circumferential side of the stator blades), and by moving blades 10 likewise formed integrally with a root 18 and a cover 19; and a coupling structure.

[0039] In addition, a drum-type rotor is used as a rotor 15. As shown in FIG. 8, a structure 43 for bending in a rotational direction of the moving blades a flow that blows upward between the stator blades and the moving blades is provided on the surface of the cover 9 that is opposed to the moving blades. A more specific shape of the structure 43 is essentially the same as that of the structure 40 shown in FIG. 5 or 6. Alternatively, such brush seal 42 as shown in FIG. 7 may be used. In the present embodiment, since a leakage flow in a clearance between the cover 9 and the rotor 15 is bent in the rotational direction of the moving blades by the structure 43, loss of flow due to interference between the leakage flow and the stator blade flow can also be further suppressed.

Claims

1. An axial turbine having a turbine stage including stator blades fixedly provided on a stationary section and moving blades fixedly provided on a rotating section; wherein said axial turbine comprises a member coupling an inner circumferential side of said stator blades, and a structure provided on a surface of said member opposed to said moving blades for bending a flow blowing out from the side of said rotating section into a space between said stator blades and said moving blades in a rotational direction of the rotating section.

2. The axial turbine according to claim 1, wherein: said member coupling the inner circumferential side of said stator blades is a diaphragm disposed at the inner circumferential side of said stator blades.

3. The axial turbine according to claim 1, wherein: said member coupling the inner circumferential side of said stator blades is a cover formed integrally with said stator blades.

4. The axial turbine according to claim 1, wherein: said structure is a protrusion projecting from said member coupling the inner circumferential side of said stator blades towards said moving blades.

5. The axial turbine according to claim 1, wherein: said structure is a brush seal having a brush portion at a side opposed to said moving blades.

6. The axial turbine according to claim 1, wherein: said structure has a shape forming a flow path concaved in the rotational direction of the rotating section.

7. The axial turbine according to claim 1, wherein said rotating section is a drum-type rotor.

8. The axial turbine according to claim 1, wherein said rotating section has no holes at positions in which said moving blades are fixed.

9. An axial turbine having a turbine stage including stator blades fixedly provided on a stationary section and moving blades fixedly provided on a rotor; wherein said axial turbine comprises a stator blade coupling member provided at an inner circumferential side of said stator blades, and a protrusion provided on a surface of said stator blade coupling member opposed to said moving blades and inclined in a rotational direction of said rotor such that an outer circumferential side of said protrusion shifts relative to an inner circumferential side thereof in a rotational direction of said rotor.

10. An axial turbine having a turbine stage including stator blades fixedly provided on a stationary section and moving blades fixedly provided on a rotor; wherein said axial turbine comprises a stator blade coupling member provided at an inner circumferential side of said stator blades, and a protrusion provided on a surface of said stator blade coupling member opposed to said moving blades and having a shape curved such that an inner circumferential side thereof is oriented in a radial direction and an outer circumferential side thereof is oriented in a rotational direction of said rotor.