JP2006291967A - Axial flow turbine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a leakage preventing device installed in a moving blade tip part of high sealing effect to reduce an amount of leakage fluid passing through a clearance between the moving blade tip part and a stationary part of an axial flow turbine. <P>SOLUTION: This axial flow turbine comprises: a nozzle diaphragm constituting the stationary part together with a casing; a plurality of moving blades 71 disposed around a turnable rotor arranged almost concentrically with a nozzle diaphragm inside the casing, and receiving an operating fluid flowing out of the nozzle diaphragm, to turn integrally with the rotor; an integral cover 72 provided at the tip part of each moving blade 71 so that its outer peripheral surface faces the stationary part; a plurality of flat parts 73a, 73b, 73c, etc. different in outer diameter dimension and provided in the outer peripheral surface of the integral cover 72; and a plurality of seal fins 78 provided in the surfaces of the stationary part, facing the flat parts 73a, 73b, 73c, etc. and projecting toward the flat parts, respectively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an axial flow turbine that prevents fluid leakage from a gap between a rotating portion at the tip of a moving blade and a stationary portion such as a casing in an axial flow turbine or the like.

In general, an axial flow turbine such as a steam or gas turbine is composed of a stationary nozzle and rotating blades. The nozzle expands a working fluid such as steam from an upstream with a high pressure to a downstream with a low pressure, and converts thermal energy into velocity energy. The rotor blades are rotated by this velocity energy to become rotational energy, and the generator is rotated by the rotational energy and taken out as power.

By the way, as described above, in the axial flow turbine, the rotating blade tip and the stationary portion including the nozzle are close to each other with an appropriate gap. Therefore, a part of the working fluid such as steam flowing from the nozzle to the moving blade flows in this gap. Since this flow does not contribute to the energy for rotating the turbine, the efficiency is reduced. Therefore, in order to reduce this flow as much as possible,
Fins are provided on the moving blade or stationary part. As an example, FIG. 10 shows a leakage preventing device for a moving blade tip part conventionally used in a steam turbine.

The turbine stage portion 1 includes a nozzle diaphragm 4 fixed by a casing 2, a plurality of nozzles 5 arranged in a circumferential direction to form a flow path portion, and a rotor 3 that is rotatable at the center of the casing 2. A plurality of blades 7 are provided in a circumferential direction on a wheel 6 provided concentrically with the rotor 3 to form a passage portion, and the rotor 3, the wheel 6, and the blade 7 are provided in the field of the nozzle diaphragm 4. The working fluid that has flowed out of the nozzle 5 is received and rotated integrally. A shroud 9 is fixed to the tip of the moving blade 7 with a tenon 8, and a seal fin 10 is attached to the nozzle diaphragm 4. In such a turbine stage 1, the leaked fluid 14 that passes through the blade tip 11 flows through the gap 13 between the shroud 9 and the seal fin 10. This leakage amount is about 1 to 3% of the total flow rate in the paragraph, and energy conversion cannot be performed effectively.
Turbine efficiency is decreasing and has a significant impact on performance.

In order to reduce the amount of leakage, there is a method of reducing the gap 13 between the shroud 9 and the seal fin 10. However, if the gap 13 is made too small, mechanical contact is likely to occur between the shroud 9 and the seal fin 10. There is a limit to the value.

For this reason, conventionally, the structure shown in FIGS. 11 to 14 has been proposed in order to prevent leakage. In the example of FIG. 11, the number of teeth of the seal fins 10 is increased and continuously arranged in the flow direction to enhance the sealing effect.

In FIG. 12, stepped portions 15 are provided on the inflow side and the outflow side of the shroud 9, and the stepped portion 15 attenuates the velocity energy of the leaked steam 14 flowing into the seal chamber 20 so that the leaked steam 14 is sealed.
It is a structure that prevents the inside of the chamber 20 from being blown through. Further, as shown in FIG. 13, as a method having a high sealing effect, the conventional tenon 8 is abolished and the shroud 9 is integrated with the moving blade 7 to form an integral cover 17, and a concave groove 18 is formed in the center of the cover 17. As described above with reference to FIG.
Some have improved the sealing effect by providing a plurality of step portions 15 in FIG.
(For example, see Patent Document 1)

Also, as shown in FIG. 14, the turbine is usually used when the fluid expands from high pressure to low pressure.
Specific volume increases. For this reason, in order to increase the height of the nozzle and blade in the paragraph passage from the high pressure portion toward the low pressure portion, inclined portions 5a and 17a are formed in the tip flow path portion of the nozzle 5 and blade 7. The structure is adopted. In this case, since the conventional seal fins 16 shown in FIGS. 11 to 13 cannot be structurally installed, a flat surface 19 is provided on the outflow side of the shroud 9, and the seal fins 16 are partially disposed. It is installed.

JP 57-52603 A (FIG. 3)

By the way, in the conventional leakage prevention means, for example, in the case of FIG. 11, if the number of the seal fins 10 is increased excessively or the gap 13 is enlarged, the velocity energy from the upstream is sufficiently attenuated in the narrowed portion of the tip of the seal fin 10. However, the residual energy causes a phenomenon that the gap 13 between the seal fin 10 and the shroud 9 is blown out, and the sealing effect is lowered.

On the other hand, in the case of FIG. 12, the above-described drawbacks can be eliminated by installing the stepped portion 15.
When the number of the seal fins 16 is large, the volume of the seal chamber 20 is reduced. Therefore, the attenuation of velocity energy is reduced and the effect is lowered.

Further, in the case of FIG. 13, when the axial extension due to thermal expansion of the turbine (rotor 3) is large, contact between the concave groove 18 and the seal fin 16 can be considered, and in the worst case, the seal fin 16 is installed. There are things that cannot be done. Further, in the case of FIG. 14, since the nozzle 5 and the moving blade 7 have the inclined portions 5 a and 17 a, the number of the seal fins 16 is reduced and the sealing effect is low.

As described above, the conventional leakage prevention device has various disadvantages and contributes to a decrease in efficiency of the turbine.

The present invention has been made in view of the circumstances as described above, and prevents an increase in the amount of fluid leakage due to a blow-through phenomenon of the seal fin portion, and also has a large difference in elongation between the turbine and the casing, and the blade tip is inclined. It is an object of the present invention to provide a leakage prevention device that can also be applied in the paragraph, and to provide an axial turbine that improves the paragraph efficiency of the turbine.

In order to solve the above-described problem, an axial flow turbine according to claim 1 of the present invention includes a casing and a plurality of nozzle blades arranged in a circumferential direction, and is fixed to the casing to form a stationary portion together with the casing. A nozzle diaphragm that is disposed in the casing and is substantially concentric with the nozzle diaphragm and is rotatable, and is disposed adjacent to the nozzle diaphragm and disposed in a circumferential direction with respect to the rotor, and receives a working fluid that has flowed out of the nozzle diaphragm. A plurality of moving blades that rotate integrally with the rotor, a shroud that is provided at a tip portion of the moving blade, an outer peripheral surface thereof facing a stationary portion including the casing and the nozzle diaphragm, and an outer peripheral surface of the shroud Provided on each of a plurality of flat portions each having a different outer diameter size, and a stationary portion surface facing each of the flat portions, Characterized in that it comprises a seal fins plurality protrudes toward the flat portion

In order to solve the above-mentioned problem, an axial flow turbine according to a second aspect of the present invention is the axial flow turbine according to the first aspect, wherein the outer diameters of the plurality of flat portions are respectively inflow of working fluid. It is characterized by being formed large from the side to the outflow side.

Furthermore, in order to solve the above-mentioned subject, the axial flow turbine which concerns on Claim 3 of this invention is further formed in the axial flow turbine of any one of Claim 1 or 2 between several flat parts. The stepped portion is further provided with an axial fin projecting upstream of the working fluid.

In order to solve the above-described problem, an axial flow turbine according to a fourth aspect of the present invention is the axial flow turbine according to the first aspect, wherein each of the outer diameter dimensions of the plurality of flat portions is a working fluid. It is characterized by being formed small from the inflow side to the outflow side.

ADVANTAGE OF THE INVENTION According to this invention, the increase in the amount of fluid leaks by the blow-off phenomenon of a seal fin part can be prevented, and the axial flow turbine which improved the stage efficiency of the turbine by this can be provided.

Hereinafter, an axial turbine according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of a moving blade tip portion of a stage passage portion of an axial flow turbine according to a first reference example of the present invention. An integral cover 52 formed integrally with the blade 51 is provided at the tip of the blade 51 as a shroud. On the outer peripheral surface, flat portions 53a and 53b are formed at the inflow side end portion and the outflow side end portion of the working fluid, and a plurality of protruding fins 54 are formed at an intermediate portion thereof.

Here, the outer diameter of each of the flat portion 53a, the protruding fin 54, and the flat portion 53b is defined as D1, D2.
, D3, and C1 is the radial gap distance between the flat portion 53a and the tip of the seal fin 58 at a position facing the flat portion 53a, and the tip of the seal fin 58 at the position facing the protrusion fin 54 and the protrusion fin 54 If the gap distance in the radial direction is C2, the structure satisfying the following formula is obtained.

D1 <D3 <D2
C2 = (0.5 to 1.0) × C1
In this reference example, the flat portion 53a on the outer peripheral surface of the integral cover 52 at the tip of the blade and the outer diameter size of the projection fin 54 are different, so that after the fluid 57 flows out from the nozzle 55, the tip of the rotor blade 51 is removed. The leaking fluid 56 passing therethrough flows through the flat portion 53a on the inflow side, and collides with the side surface of the downstream projection fin 54 (arrow a in the figure). Similarly, the leaked fluid that has reached the outflow side also collides with the seal fin 58 (arrow b in the figure). As a result, the phenomenon that the leaked fluid blows out from the inflow side flat portion 53a through the protruding fin 54 to the outflow side flat portion 53b is eliminated, and the flow resistance is increased, so that the sealing effect can be further improved.

Further, since the seal fin 58 at the center is arranged to face the protruding fin 54 protruding from the integral cover 52, the sealing effect is higher than that of the conventional continuous fin. Further, even if the seal fin 58 and the projecting fin 54 come into contact with each other due to some abnormal phenomenon during the rotation of the turbine, the contact portion becomes a point contact, so that the damage is less than the conventional seal fin and the radial gap is further reduced. It is possible to further reduce the amount of leakage.

On the other hand, by improving the leakage preventing means at the central portion of the integral cover 52 composed of the projecting fins 54 and the seal fins 58, the length W1 of the central portion can be made shorter than before, and the flat portion is correspondingly reduced. The length W2 of 53a and the length W3 of the flat portion 53b can be extended. Therefore, the difference in expansion and contraction due to the thermal expansion of the turbine shaft and the casing 2 is represented by this length W.
Since it can be absorbed by 2 and W3, contact between the seal fin 58 and the side surface of the protruding fin 54 is avoided. That is, the present invention can be applied to a paragraph portion in which the difference between the axial expansion / contraction amount due to the thermal expansion of the turbine and the expansion / contraction amount of the casing 2 is large.

Since it is comprised in this way, the leak amount from a moving blade front-end | tip part can be reduced significantly and the big improvement effect can be acquired in the paragraph efficiency of a turbine.
Next, an axial turbine according to the second embodiment will be described with reference to FIG.

FIG. 2 is a cross-sectional view of the blade tip portion of the stage passage portion of the axial turbine according to the second reference example. The integral cover 6 formed integrally with the blade 61 as a shroud is attached to the tip of the blade 61.
2 is provided. On the outer peripheral surface, flat portions 63a and 63b are formed at the inflow side end portion and the outflow side end portion, respectively, and a protruding fin 64 is formed at the center portion sandwiched between the flat portions 63a and 63b. The outer diameter of each of the flat part 63a, the projecting fin 64, and the flat part 63b is D1, D2, and D3, and the radial gap between the flat part 63a and the tip of the seal fin 68 at a position facing the flat part 63a. When the distance is C1, and the radial gap distance between the projecting fin 64 and the tip of the seal fin 68 at the position facing the projecting fin 64 is C2, the structure satisfying the following formula is obtained.

D1 <D2 <D3
C2 = (0.5 to 1.0) × C1
In this reference example, since the outer diameters of the flat portions 63a and 63b on the outer peripheral surface of the integral cover 62 at the blade tip and the protruding fins 64 are different, the nozzle 5 is the same as in the first embodiment.
After the fluid 67 flows out from 5, the leaking fluid 66 that passes through the tip of the rotor blade is the flat portion 6 on the inflow side.
It flows through 3a and collides with the side surface of the protruding fin 64 located downstream thereof (arrow c in the figure). Similarly, the leaked fluid reaching the outflow side also collides with the side surface of the flat portion 63 provided at the outflow side end (arrow d in the figure).

As a result, the phenomenon that the leaked fluid is blown from the inflow side flat portion 63a through the protruding fin 64 to the outflow side flat portion 63b is eliminated and the flow resistance is increased, so that the sealing effect can be further improved. Further, the central seal fin 68 is disposed opposite to the projecting fin 64 projecting from the integral cover 62, so that even when these fins come into contact with each other, point contact occurs and the rotor blade is greatly affected. Therefore, the gap C2 can be made smaller than that of the conventional continuous fin, so that the sealing effect is improved.

Further, the difference in expansion and contraction due to the thermal expansion of the turbine shaft and the casing 2 can be absorbed by increasing the inner diameter of the casing 2 and the outer diameter of the tip of the rotor blade 61 toward the downstream side, and the seal fins 68 are projected fins. It is possible to avoid contact with the 64 side surfaces. Therefore,
This is effective when the moving blade 61 moves largely downstream due to the difference in the amount of expansion and contraction between the turbine and the casing 2 due to thermal expansion.

Next, an axial flow turbine according to the first embodiment of the present invention will be described with reference to FIG.
FIG. 3 is a cross-sectional view of the moving blade tip portion of the stage passage portion of the axial flow turbine according to the first embodiment of the present invention. An integral cover 72 formed integrally with the moving blade 71 as a shroud is provided at the tip of the moving blade 71. The outer peripheral surface is provided with a plurality of flat portions 73 and concave groove portions 75 alternately from the inflow side to the outflow side. The outer diameter of the flat portion 73 is set to D1, D2, D3, D4 in order from the flat portions 73a, 73b, 73c, 73d arranged on the inflow side.
The structure satisfying the following formula is used.

D1 <D2 <D3 <D4
And the seal fin 78 arrange | positioned in the position facing the said flat parts 73a-73d is each set so that it may have a uniform gap | interval with the flat parts 73a-73d.

In this embodiment, after the fluid 77 flows out from the nozzle 55, the leaked fluid 7 that passes through the tip of the rotor blade
6 flows through the flat portion 73a at the inflow side end, and collides with the side surface of the flat portion 73b immediately downstream (arrow f in the figure). Since each flat part 73a, 73b, 73c, 73d is stepped, the leakage fluid repeats the same movement. Since the velocity energy possessed by the leaking fluid is attenuated by the collision, the leaking fluid passing through the gap between the seal fin 78 and the flat portion 73 is reduced, and the sealing effect is improved.

Further, since the difference in expansion and contraction due to thermal expansion between the turbine shaft and the casing 2 can be absorbed by increasing the inner diameter of the casing 2 and the outer diameter of the tip of the rotor blade 71 toward the downstream side, This is effective when the moving blade 71 moves largely downstream due to the difference in the amount of expansion and contraction of the casing 2 in the axial direction.

In FIG. 3, the flat portion 73 has been described as having four steps, but the same effect can be obtained even when the number of steps is five or more.
Next, with reference to FIG. 4, the leakage prevention apparatus of the axial flow turbine concerning the 2nd Embodiment of this invention is demonstrated.

FIG. 4 is a cross-sectional view of the blade tip portion of the stage passage portion of the axial flow turbine according to the second embodiment of the present invention. At the tip of the moving blade 81, an integral cover 82 is provided integrally with the moving blade 81 as a shroud. The outer peripheral surface has a plurality of flat portions 83 from the inflow side to the outflow side.
Are formed, and steps are provided in steps. When the outer diameter of the flat portion 83 is set to D1, D2, and D3 in order from the flat portions 83a, 83b, and 83c arranged on the inflow side, the structure satisfying the following formula is obtained.

D1 <D2 <D3
In this embodiment, after the fluid 87 flows out from the nozzle 55, the leaked fluid 8 that passes through the tip of the rotor blade
6 flows through the flat portion 83a on the inflow side and collides with the side surface of the flat portion 83b immediately downstream (arrow g in the figure). Since each flat part 83a, 83b, 83c is stepped, the leaking fluid 86 repeats the same movement. The leakage fluid 8 that passes through the gap between the seal fin 88 and the flat portion 83 is used to attenuate the velocity energy that the leakage fluid has due to the collision.
6 is reduced and the sealing effect is improved.

Further, since the difference in expansion and contraction due to thermal expansion between the turbine shaft and the casing 2 can be absorbed by increasing the inner diameter of the casing 2 and the outer diameter of the tip of the rotor blade 81 toward the downstream side, This is effective when the moving blade 81 largely moves downstream due to the difference in the amount of axial expansion and contraction of the casing 2.

Next, with reference to FIG. 5, the leakage prevention apparatus of the axial flow turbine which concerns on the 3rd Embodiment of this invention is demonstrated.
FIG. 5 is a cross-sectional view of the blade tip portion of the stage passage portion of the axial flow turbine according to the third embodiment of the present invention. An integral cover 92 is provided at the tip of the moving blade 91 integrally with the moving blade 91 as a shroud. And on the outer peripheral surface, a plurality of flat portions 93 are provided in a stepped manner from the inflow side to the outflow side. An axial fin 94 is formed at the upper surface corner of each flat portion 93 toward the upstream side of the leaked fluid.

The seal fin 98 attached to the casing 2 and the flat portion 93 form a radial gap, and the axial fin 94 and the seal fin 98 immediately upstream thereof also form a gap in the axial direction. . Flat portions 93a, 93b having the outer diameter of the flat portion 93 arranged on the inflow side
, 93c in order from D1, D2, D3, the structure satisfying the following formula is obtained.

D1 <D2 <D3
In this embodiment, after the fluid 97 flows out from the nozzle 55, the leaked fluid 9 that passes through the tip of the rotor blade
6 flows through the flat portion 93a on the inflow side and collides with the side surface of the flat portion 93b immediately downstream thereof (arrow h in the figure). Furthermore, since the flow is once throttled by the axial gap formed by the axial fin 94 and the seal fin 98, the leakage fluid attenuates the velocity energy it has and the flow resistance increases, so the seal fin 98 and the flat portion The leakage fluid passing through the gap 93 is reduced and the sealing effect is improved.

Further, since the difference in expansion and contraction due to thermal expansion between the turbine shaft and the casing 2 can be absorbed by increasing the inner diameter of the casing 2 and the outer diameter of the tip of the rotor blade 91 toward the downstream side, This is effective when the moving blade 91 moves largely downstream due to the difference in the amount of expansion and contraction of the casing 2 in the axial direction.

Next, an axial flow turbine according to a third reference example of the present invention will be described with reference to FIG.
FIG. 6 is a cross-sectional view of the blade tip portion of the stage passage portion of the axial turbine according to the third reference example of the present invention. An integral cover 102 is provided integrally with the rotor blade 101 as a shroud at the tip of the rotor blade 101, and a plurality of flat portions 103 and protruding fins 104a are provided on the outer peripheral surface from the inflow side to the outflow side. 104b are alternately formed. Inflow side flat portion 103a
In addition, the outer diameter dimensions of the inflow side projection fin 104a, the central flat portion 103b, the outflow side projection fin 104b, and the outflow side flat portion 103c are D1, D2, and D2, respectively, in order from those arranged on the inflow side.
D1, D4, and D5, C1 is the radial gap distance formed by the inflow side flat portion 103a and the tip of the seal fin 108 disposed at a position facing the inflow side flat portion 103a, and the outflow side projection fin 104b portion And a radial gap distance formed between the tip end portion of the seal fin 108 disposed at a position facing the outflow-side protruding fin and C2, the structure satisfying the following formula is obtained.

D1 <D2> D3 <D4> D5
C2 = (0.5 to 1.0) × C1
In this reference example, after the fluid 107 flows out from the nozzle 55, the leaked fluid 1 that passes through the tip of the rotor blade
06 flows through the flat surface 103a at the end of the inflow side, and the protruding fin 104a immediately downstream thereof.
(Arrow j in the figure). In addition, the leaked fluid that reaches the center is also flat portion 103b.
It collides with the side surface of the seal fin 108 provided in the vicinity of the center (arrow k in the figure).

Since the leakage fluid 106 attenuates the velocity energy possessed by this collision, the leakage fluid passing through the gap between the seal fin 108 and the flat portion 103 is reduced, and the sealing effect is enhanced.
Further, since the leakage amount in the projection fins 104a and 104b is reduced as compared with the prior art, the axial installation lengths (W4 and W5 in the figure) of the projection fins 104a and 104b can be shortened, and the flat portions 103a, 103b, and 103c are correspondingly reduced. The length (W6 to W9 in the figure) can be increased. Therefore, this is effective when the moving blade 101 is largely displaced due to the difference in the axial expansion between the turbine shaft and the casing due to thermal expansion.

Next, an axial flow turbine according to a fourth embodiment of the present invention will be described with reference to FIG.
FIG. 7 is a cross-sectional view of the blade tip portion of the stage passage portion of the axial flow turbine according to the fourth embodiment of the present invention. An integral cover 112 is provided at the tip of the moving blade 111 integrally with the moving blade 111 as a shroud. And on the outer peripheral surface, a plurality of flat portions 113 are formed by providing stepped steps from the inflow side to the outflow side. When the outer diameter of the flat portion 113 is set to D1, D2, and D3 in order from the flat portions 113a, 113b, and 113c arranged on the inflow side, respectively, a structure that satisfies the following formula is obtained.

D1>D2> D3
In this embodiment, after the fluid 117 flows out from the nozzle 55, the leaked fluid 116 that passes through the tip of the rotor blade flows through the flat portion 113a at the end of the inflow side, and on the side surface of the seal fin 118 positioned immediately downstream thereof. Collide (arrow m in the figure). Further, it collides with the side surface of the seal fin 118 located downstream (arrow n in the figure). Since the velocity energy possessed by the leaking fluid is attenuated by the collision, the leaking fluid passing through the gap between the seal fin 118 and the flat portion 113 is reduced and the sealing effect is improved.

In addition, the difference in expansion and contraction due to the thermal expansion of the turbine shaft and the casing 2 can be absorbed by reducing the inner diameter of the casing 2 and the outer diameter of the tip of the rotor blade 111 toward the downstream side. This is effective when the moving blade 111 moves largely upstream due to the difference in the amount of axial expansion and contraction of the casing 2.

Next, an axial turbine according to a fourth reference example of the present invention will be described with reference to FIG.
FIG. 8 is a cross-sectional view of the blade tip portion of the stage passage portion of the axial flow turbine according to the fourth reference example of the present invention. The basic structure is the same as the first reference example. Working fluid inflow side flat portion 123
a, the outer diameter of each of the projecting fins 124 and the working fluid outflow side flat portion 123b is D1, D2,
When D3, the radial gap distance formed by the flat portion 123a and the tip end portion of the seal fin 128 disposed at a position facing the flat portion 123a is C1, and the protruding fin 124 portion and the protruding fin 124 are opposed to each other. When the radial gap distance formed between the tip end portions of the seal fins 128 disposed at the position where C2 is C2, the structure satisfying the following formula is obtained.

D1 = D3 <D2
C2 = (0.5 to 1.0) × C1
In this reference example, after the fluid 127 flows out from the nozzle 55, the leaked fluid 126 that passes through the tip of the rotor blade 121 flows through the flat portion 123a at the inflow side end, and on the side of the protruding fin 124 immediately downstream thereof. Collide (arrow u in the figure). Similarly, the leaked fluid 126 reaching the outflow side also collides with the seal fin 128 (arrow p in the figure). As a result, the phenomenon of leakage of leaking fluid from the inflow side flat portion 123a through the protruding fin 124 to the outflow side flat portion 123b is eliminated and the flow resistance is increased, so that the sealing effect can be further improved.

Next, an axial flow turbine according to a fifth reference example of the present invention will be described with reference to FIG.
FIG. 9 is a cross-sectional view of the rotor blade tip portion of the stage passage portion of the axial turbine according to the fifth reference example of the present invention. The basic structure is the same as the first reference example. Working fluid inflow side flat surface 133
a, D1, D2, D3, D4 are the outer diameter dimensions of the working fluid inflow side projection fin 134a, the central flat portion 133b, the working fluid outflow side projection fin 134b, and the working fluid outflow side flat portion 133c.
, D5, and C1 is a radial gap distance formed by the working fluid inflow side flat portion 133a and the tip of the seal fin 138 disposed at a position facing the working fluid inflow side flat portion 133a.
The projecting fin 134 and the seal fin 1 disposed at a position facing the projecting fin 134
If the gap distance in the radial direction formed at the tip of 38 is C2, the structure satisfies the following formula.

D1 = D5 ≦ D3 <D2 = D4
C2 = (0.5 to 1.0) × C1
In this reference example, after the fluid 137 flows out from the nozzle 55, the leaked fluid 1 that passes through the tip of the rotor blade
36 flows through the flat surface 133a at the end of the inflow side, and the protruding fin 134a immediately downstream thereof.
(Arrow q in the figure). In addition, the leaked fluid 13 that has reached the central flat portion 133b
6 also collides with the side surface of the seal fin 138 provided in the vicinity of the facing surface of the casing 2 (
Arrow r) in the figure. Since the leakage fluid attenuates the velocity energy possessed by this collision, the leakage fluid passing through the gap between the seal fin 138 and the flat portion 133 is reduced, and the sealing effect is improved.
The present invention is not limited to the above-described embodiment, and various modifications can be made.

Sectional drawing of the paragraph part which shows the principal part of the axial flow turbine of the 1st reference example which concerns on this invention. Sectional drawing of the paragraph part which shows the principal part of the axial flow turbine of the 2nd reference example which concerns on this invention. Sectional drawing of the paragraph part which shows the principal part of the axial flow turbine of 1st Embodiment which concerns on this invention. Sectional drawing of the paragraph part which shows the principal part of the axial flow turbine of 2nd Embodiment which concerns on this invention. Sectional drawing of the paragraph part which shows the principal part of the axial flow turbine of 3rd Embodiment which concerns on this invention. Sectional drawing of the paragraph part which shows the principal part of the axial flow turbine of the 3rd reference example which concerns on this invention. Sectional drawing of the paragraph part which shows the principal part of the axial flow turbine of 4th Embodiment which concerns on this invention. Sectional drawing of the paragraph part which shows the principal part of the axial flow turbine of the 4th reference example which concerns on this invention. Sectional drawing of the paragraph part which shows the principal part of the axial flow turbine of the 5th reference example which concerns on this invention. Sectional drawing which shows the prior art example of an axial turbine stage part. Sectional drawing of the stage part of the axial flow turbine which shows another prior art example. Sectional drawing of the stage part of the axial flow turbine which shows the other conventional example using a level | step difference. Sectional drawing of the stage part of the axial flow turbine which shows the prior art example at the time of using an integral cover. Sectional drawing of the step part of an axial-flow turbine which shows the thing of the step part in which the blade | wing tip inclined.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Turbine stage part 2 ... Casing 3 ... Rotor 4 ... Nozzle diagram 5 ... Nozzle 5a ... Inclination part 6 ... Wheel 7 ... Moving blade 8 ... Tenon 9 ... Shroud 10 ... Seal fin 11 ... Blade top part 12 ... Main fluid flow 13 ... Gap 14 ... Leakage fluid 15 ... Step 16 ... Seal fin 17 ... Integral cover 17a ... Inclined part 18 ... Groove part 19 ... Flat part 20 ... Seal chamber 51, 61, 71, 81, 91, 101, 111, 121, 131 ... Rotor blades 52, 62, 72, 82, 92, 102, 112, 122, 132 ... Integral cover 75 ... Concave grooves 53a, 53b, 63a, 63b, 73, 73a, 73b, 73c, 73d, 83,
83a, 83b, 83c, 93, 93a, 93b, 93c, 103, 103a, 103b
, 103c, 113, 113a, 113b, 113c, 123, 123a, 123b, 1
33, 133a, 133b, 133c ... Flat part 54, 64, 94, 104a, 104b, 124, 134a, 134b ... Projection fin 55 ... Nozzle 56, 66, 76, 86, 96, 106, 116, 126, 136 ... Leakage Fluid 57, 67, 77, 87, 97, 107, 117, 127, 137 ... Main fluid flow 58, 68, 78, 88, 98, 108, 118, 128, 138 ... Seal fins a, b, c, d, f, g, h, j, k, m, n, p, q, r, u ... flow of leakage fluid

Claims (4)

A casing,
A plurality of nozzle blades arranged circumferentially, a nozzle diaphragm fixed to the casing and constituting a stationary portion together with the casing;
A rotatable rotor disposed substantially concentrically with the nozzle diaphragm in the casing;
A plurality of moving blades adjacent to the nozzle diaphragm and disposed in a circumferential direction with respect to the rotor, and receiving a working fluid flowing out from the nozzle diaphragm and rotating integrally with the rotor;
A shroud provided at the tip of the moving blade, the outer peripheral surface of which is opposed to the stationary part including the casing and the nozzle diaphragm;
A plurality of flat portions each having a different outer diameter provided on the outer peripheral surface of the shroud;
Seal fins provided on each of the surfaces of the stationary part facing each of the flat parts, and projecting a plurality toward the flat part,
An axial turbine comprising: The axial turbine according to claim 1, wherein the outer diameter dimensions of the plurality of flat portions are respectively
An axial turbine having a large size from the inflow side to the outflow side of the working fluid. 3. The axial turbine according to claim 1, wherein an axial fin protruding upstream of the working fluid is further provided at a step portion formed between the plurality of flat portions. A featured axial turbine. The axial turbine according to claim 1, wherein the outer diameter dimensions of the plurality of flat portions are respectively
An axial turbine having a small size from the working fluid inflow side to the outflow side.

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