Patent Publication Number: US-9429022-B2

Title: Steam turbine

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a turbine used in, for example, a power generation plant, a chemical plant, a gas plant, steelworks, a ship, or the like. 
     Priority is claimed on Japanese Patent Application No. 2010-217218, filed on Sep. 28, 2010, the content of which is incorporated herein by reference. 
     2. Background Art 
     In the related art, as one kind of a steam turbine, a steam turbine including a casing, a shaft body (rotor) rotatably installed in the casing, turbine vanes fixedly disposed at an inner circumferential section of the casing, and turbine blades radially installed at the shaft body in a downstream side of the turbine vanes, which are provided in a plurality of stages, is well-known. The steam turbine is generally classified as an impulse turbine or a reaction turbine according to a difference in operation type. In the impulse turbine, the turbine blades are rotated only by an impulsive force received from steam. 
     In the impulse turbine, the turbine vanes have a nozzle shape, steam passing through the turbine vanes is injected to the turbine blades, and the turbine blades are rotated only by an impulsive force received from the steam. Meanwhile, in the reaction turbine, the turbine vanes have the same shapes as the turbine blades, and the turbine blades are rotated by an impulsive force received from the steam passing through the turbine vanes and a reactive force with respect to expansion of the steam generated when passing through the turbine blades. 
     Here, in such a steam turbine, a clearance having a predetermined width in a radial direction is formed between tip sections of the turbine blades and the casing, and a clearance having a predetermined width in the radial direction is also formed between tip sections of the turbine vanes and the shaft body. Then, some of the steam flowing in an axial direction of the shaft body is leaked to a downstream side through the clearances with the tip sections of these turbine blades or the turbine vanes. Here, since the steam leaked downstream from the clearance between turbine blades and the casing applies neither the impulsive force nor the reactive force with respect to the turbine blades, the steam hardly contributes to a driving force to rotate the turbine blades regardless of the impulse turbine or the reaction turbine. In addition, since the steam leaked from the clearance between the turbine vanes and the shaft body to the downstream side is neither varied in velocity nor expanded even when passing over the turbine vanes, the steam hardly contributes to a driving force to rotate the turbine blades of the downstream side regardless of the impulse turbine or the reaction turbine. Accordingly, in order to improve performance of the steam turbine, it is important to reduce a leakage amount of the steam in the clearance with the tip sections of the turbine blade or the turbine vane. 
     Here, a seal fin is conventionally used as a means for preventing a leakage of the steam from the clearance with the tip sections of the turbine blades or the turbine vanes. For example, when the seal fin is used at the tip section of the turbine blade, the seal fin is installed to protrude from any one of the turbine blade and the casing and form a small clearance with the other. 
     In addition, in the steam turbine in the related art, it is known that a casing corner is formed in a curved shape in a cross-section in the axial direction such that a stress concentration is not generated due to thermal expansion or the like of the casing at a corner formed at a wall surface of the casing (for example, see FIG. 2 of Patent Document 1). Here, in general, the curved shape of the casing corner is formed in an arc shape having a radius of about 1 mm. 
     PRIOR ART DOCUMENTS 
     Patent Document 
     [Patent Document 1] Japanese Patent Application, First Publication No. 2000-073702 
     PROBLEMS TO BE SOLVED BY THE INVENTION 
     However, improvement in performance of the steam turbine is strongly needed, and a leakage amount of steam from a clearance between a blade body such as a turbine blade or the like and a structure such as a casing or the like should be further reduced. 
     SUMMARY OF THE INVENTION 
     In consideration of the above-mentioned circumstances, it is an object of the present invention to provide a high performance turbine capable of reducing a leakage amount of steam in a clearance with a tip section of a turbine blade or a turbine vane. 
     MEANS FOR SOLVING THE PROBLEMS 
     A turbine according to the present invention includes a blade disposed at a flow path through which a fluid flows, a structure installed at a tip side of the blade via a clearance and relatively rotated with respect to the blade, and a seal fin formed to protrude from any one of the blade and the structure and configured to form a small clearance with the other, wherein a dead water region-filling section is formed in a space formed by the blade, the structure and the seal fin and in which a vortex flow of the fluid is generated, such that a dead water region that the vortex flow cannot reach is filled. 
     According to the above-mentioned configuration, since the dead water region of the space is filled with the dead water region-filling section, energy loss due to introduction of the vortex flow generated in the space into the dead water region can be reduced. Accordingly, the vortex flow can be strengthened in comparison with the case in which the dead water region-filling section is not provided, a contraction flow effect is increased when the vortex flow has the contraction flow effect, and a leakage amount of the fluid in the clearance between a blade tip section and the structure can be reduced. 
     In addition, in the turbine according to the present invention, the dead water region-filling section has an inclined surface along the vortex flow of the fluid. 
     According to the above-mentioned configuration, since the vortex flow flows along the inclined surface of the dead water region-filling section configured to fill the dead water region of the space, the energy loss of the vortex flow in the dead water region can be securely reduced. Accordingly, the vortex flow can be further strengthened, the contraction flow effect is increased when the vortex flow has the contraction flow effect, and the leakage amount of the fluid can be further reduced. 
     In addition, in the turbine according to the present invention, the inclined surface is formed in a concave-shaped curve in a cross-section in an axial direction thereof. 
     According to the above-mentioned configuration, since the inclined surface of the dead water region-filling section can more accurately follow the vortex flow moving along a curved orbit, the energy loss of the vortex flow in the dead water region can be more securely reduced. Accordingly, the vortex flow can be further strengthened, the contraction flow effect is increased when the vortex flow has the contraction flow effect, and the leakage amount of the fluid can be further reduced. 
     In addition, in the turbine according to the present invention, the inclined surface is formed in a substantially linear shape in a cross-section in the axial direction thereof. 
     According to the above-mentioned configuration, the dead water region-filling section can be formed at the blade or the structure by simple processing or a simple mold shape. 
     In addition, in the turbine according to the present invention, the dead water region-filling section is formed at a corner of the space formed by an axial direction wall surface in an axial direction and a radial direction wall surface in a radial direction. 
     According to the above-mentioned configuration, since the dead water region-filling section is formed at the corner formed by the axial direction wall surface and the radial direction wall surface, generation of stress concentration in the corner of the blade or the structure due to thermal expansion or expansion due to a centrifugal force can be attenuated. Accordingly, damage to the blade or the structure due to the stress concentration can be prevented in advance. 
     In addition, in the turbine according to the present invention, a first seal fin formed at a furthest upstream side in the axial direction of the seal fin forms substantially the same surface as an axial direction end surface of the blade disposed at a furthest upstream section in the axial direction. 
     According to the above-mentioned configuration, since partial separation of the vortex flow is not generated at an angled section of the blade, the leakage amount of the fluid can be further reduced by the high contraction flow effect of the vortex flow itself, rather than the contraction flow effect of the separation vortex generated due to the separation. 
     In addition, in the turbine according to the present invention, the seal fin is formed to protrude from the blade, and the axial direction wall surface in the axial direction of the structure is formed to step down in the radial direction from the first seal fin at an upstream side portion rather than a downstream side portions thereof. 
     According to the above-mentioned configuration, since the seal fin protrudes from the blade side, the small clearance through which the fluid leaks is formed at a position near the structure. Then, since the axial direction wall surface of the structure is stepped down in the radial direction at the upstream side of the first seal fin, a pivot center of the vortex flow approaches closer to the small clearance in comparison with the case in which there is no step-down. Accordingly, since a radial direction velocity of the vortex flow near the small clearance is higher when the step-down is present than when there is no step-down, and the contraction flow effect of the vortex flow can be increased, the leakage amount of the fluid in the small clearance can be further reduced. 
     In addition, in the turbine according to the present invention, the axial direction wall surface in the axial direction of the structure has a level difference in the radial direction between a portion opposite to one of a pair of seal fins adjacent to each other in the axial direction and a portion opposite to the other. 
     According to the above-mentioned configuration, in the space formed between a pair of seal fins adjacent to each other, as the vortex flow is separated at a stepped angled section, the separation vortex is generated at a downstream side of the vortex flow with respect to the angled section as a boundary. Then, the leakage amount of the fluid in the clearance between the seal fin and the structure at the downstream side can be reduced by the contraction flow effect of the separation vortex. 
     EFFECT OF THE INVENTION 
     According to the turbine of the present invention, a leakage amount of a fluid in a clearance between the blade tip section and the structure can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view showing a steam turbine according to a first embodiment of the present invention. 
         FIG. 2  is a partially enlarged cross-sectional view showing surroundings of a tip section of a turbine blade of  FIG. 1 . 
         FIG. 3  is a view describing a contraction flow effect of a separation vortex, a partially enlarged cross-sectional view showing surroundings of a tip section of a first seal fin in  FIG. 2 . 
         FIG. 4  is a schematic cross-sectional view showing surroundings of a tip section of a turbine blade of a second embodiment. 
         FIG. 5  is a schematic cross-sectional view showing surroundings of a tip section of a turbine blade of a third embodiment. 
         FIG. 6  is a schematic cross-sectional view showing surroundings of a tip section of a turbine blade of a fourth embodiment. 
         FIG. 7  is a schematic cross-sectional view showing surroundings of a tip section of a turbine blade of a fifth embodiment. 
         FIG. 8  is a partially enlarged cross-sectional view showing surroundings of a tip section of a turbine vane of a sixth embodiment. 
         FIG. 9  is a partially enlarged cross-sectional view of surroundings of a tip section of a turbine vane of a seventh embodiment. 
         FIG. 10  is a partially enlarged cross-sectional view of surroundings of a tip section of a turbine vane of an eighth embodiment. 
         FIG. 11  is a partially enlarged cross-sectional view showing a variant of the eighth embodiment. 
         FIG. 12  is a schematic cross-sectional view showing surroundings of a tip section of a turbine blade of a ninth embodiment, particularly, enlarging a tip section of a first seal fin. 
         FIG. 13  is a schematic cross-sectional view showing surroundings of a tip section of a turbine blade of a tenth embodiment. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     First Embodiment 
     Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. First, a configuration of a steam turbine according to a first embodiment of the present invention will be described.  FIG. 1  is a schematic cross-sectional view showing a steam turbine  1  according to the first embodiment. 
     The steam turbine  1  includes a hollow casing  10 , a regulating valve  20  configured to adjust an amount and a pressure of steam S (fluid) flowing into the casing  10 , a shaft body  30  rotatably installed in the casing  10  and configured to transmit power to a machine such as a power generator or the like (not shown), an annular turbine vane group  40  held in the casing  10 , an annular turbine blade group  50  (a blade) installed at the shaft body  30 , and a bearing  60  configured to rotatably support the shaft body  30  about an axis thereof. 
     The casing  10  has an inner space, which is hermetically sealed, and functions as a flow path of the steam S. A ring-shaped diaphragm outer ring  11  (a structure) into which the shaft body  30  is inserted is securely fixed to an inner wall surface of the casing  10 . 
     The plurality of regulating valves  20  are disposed in the casing  10 , each of the regulating valves  20  includes a regulating valve chamber  21  into which steam S flows from a boiler (not shown), a valve body  22 , and a valve seat  23 , a steam flow path is opened when the valve body  22  is separated from the valve seat  23 , and the steam S flows into the inner space of the casing  10  via a steam chamber  24 . 
     The shaft body  30  includes a shaft body  31  and a plurality of discs  32  extending in a radial direction from an outer circumference of the shaft body  31 . The shaft body  30  is configured to transmit rotational energy to a machine such as a power generator or the like (not shown). 
     The annular turbine vane group  40  includes a plurality of turbine vanes  41  installed to surround the shaft body  30  at predetermined intervals in a circumferential direction and having base end sections held by the diaphragm outer rings  11 , and a ring-shaped hub shroud  42  configured to connect radial direction tip sections of the turbine vanes  41  to each other in the circumferential direction. Then, the shaft body  30  is inserted into the hub shroud  42  to form a clearance having a predetermined width in the radial direction. 
     Then, six annular turbine vane groups  40  having the above-mentioned configuration are installed at predetermined intervals in the axial direction of the shaft body  30 , and pressure energy of the steam S is converted into velocity energy to be guided toward a turbine blade  51  adjacent to a downstream side thereof. 
     The bearing  60  has a journal bearing apparatus  61  and a thrust bearing apparatus  62 , and rotatably supports the shaft body  30 . 
     The annular turbine blade group  50  has a plurality of turbine blades  51  installed to surround the shaft body  30  at predetermined intervals in the circumferential direction and having base end sections thereof fixed to the disc  32 , and a ring-shaped tip shroud (not shown in  FIG. 1 ) configured to connect the radial direction tip sections of the turbine blades  51  to each other in the circumferential direction. 
     Then, six annular turbine blade groups  50  having the above-mentioned configuration are installed to be adjacent to downstream sides of the six annular turbine vane groups  40 . Accordingly, the annular turbine vane groups  40  and the annular turbine blade groups  50 , in which one set constitutes one stage, are provided to a total of six stages in the axial direction. 
     Here,  FIG. 2  is a partially enlarged cross-sectional view showing surroundings of a tip section of the turbine blade  51  in  FIG. 1 . A ring-shaped tip shroud  52  is disposed at the tip section of the turbine blade  51  as described above. The tip shroud  52  has a stepped cross-sectional shape, and includes three axial direction wall surfaces  521   a ,  521   b  and  521   c  in the axial direction and three radial direction wall surfaces  522   a ,  522   b  and  522   c  in the radial direction. In addition, a cross-sectional shape of the tip shroud  52  is not limited to the embodiment but a design thereof may be appropriately changed. 
     Meanwhile, an annular groove  111  having a concave cross-sectional shape is formed at an inner circumferential surface of the diaphragm outer ring  11  shown in  FIG. 2 . Then, three seal fins  12  are formed at a bottom surface  111   a  of the annular groove to protrude in the radial direction. 
     Here, among the three seal fins  12 , a first seal fin  12 A disposed at the furthest upstream side in a flow direction of the steam, i.e., the axial direction, is formed at a slight downstream side of a radial direction wall surface  522   a  of the tip shroud  52 , and a small clearance  13 A is formed in the radial direction between a tip thereof and an axial direction wall surface  521   a  of the tip shroud  52 . In addition, among the three seal fins  12 , a second seal fin  12 B disposed at a second upstream side is formed at a slight downstream side of a radial direction wall surface  522   b  of the tip shroud  52 , and a small clearance  13 B is also formed in the radial direction between a tip thereof and an axial direction wall surface  521   b  of the tip shroud  52 . Further, among the three seal fins  12 , a third seal fin  12 C disposed at the furthest downstream side is formed at a slight downstream side of a radial direction wall surface  522   c  of the tip shroud  52 , and a small clearance  13 C is also formed in the radial direction between a tip thereof and an axial direction wall surface  521   c  of the tip shroud  52 . The seal fins  12  having the above-mentioned configuration have lengths reduced in a sequence of the first seal fin  12 A, the second seal fin  12 B, and the third seal fin  12 C. 
     In addition, a length, a shape, an installation position or the number of the seal fins  12  is not limited to the embodiment but may be appropriately design-changed according to a cross-sectional shape of the tip shroud  52  and/or the diaphragm outer ring  11 . Further, a dimension of the small clearance  13  is appropriately set to a minimum value within a safe range in which the seal fin  12  is not in contact with the tip shroud  52  in consideration of a thermal expansion amount of the casing  10  or the turbine blade  51 , a centrifugal expansion amount of the turbine blade, or the like. In the embodiment, while all of the three small clearances  13  are set to have the same dimensions, according to necessity, the small clearances  13  may be set to have different dimensions according to the seal fins  12 . 
     In addition, in the embodiment, while the seal fin  12  is installed to protrude from the diaphragm outer ring  11  and the small clearance  13  is formed between the seal fin  12  and the tip shroud  52 , the seal fin  12  may also be formed to protrude from the tip shroud  52  and the small clearance  13  may be formed between the seal fin  12  and the diaphragm outer ring  11 . 
     Then, according to a configuration of surroundings of a tip section of the turbine blade  51 , as shown in  FIG. 2 , three cavities C (spaces) are formed by the diaphragm outer ring  11 , the seal fin  12  and the tip shroud  52 . 
     Here, among the three cavities C, a first cavity C 1  disposed at the furthest upstream side in the axial direction is formed by, as shown in  FIG. 2 , the bottom surface  111   a  and a side surface  111   b  of the annular groove  111 , the first seal fin  12 A, and the radial direction wall surface  522   a  and the axial direction wall surface  521   a  of the tip shroud  52 . The first cavity C 1  as configured above has a substantially rectangular cross-section in the axial direction. However, a widened section  14  slightly widened in the axial direction is formed at a downstream section in an axial direction of the first cavity C 1  to an extent to which the first seal fin  12 A as configured above is formed at a slight downstream side of the radial direction wall surface  522   a.    
     Then, as shown in  FIG. 2 , dead water region-filling sections  15  are formed at two corners of the first cavity C 1 , more specifically, a corner formed by the bottom surface  111   a  and the side surface  111   b  of the annular groove  111 , and a corner formed by the bottom surface  111   a  of the annular groove  111  and the first seal fin  12 A. The two dead water region-filling sections  15  are provided to bury and remove dead water regions formed at the corners of the first cavity C 1 , and have an inclined surface K formed in a concave-shaped curve in a cross-section in the axial direction. As described above, the concave-shaped curve has a shape along a vortex flow of the steam S generated in the first cavity C 1 , and has an arc shape having a radius of 5 mm or more in the embodiment. Accordingly, a size of the dead water region-filling section  15  becomes larger by about 25 times in a cross-sectional area ratio in comparison with an arc-shaped portion having a radius of about 1 mm and formed at the corner of the casing to prevent stress concentration as described above. 
     However, in the embodiment, while the dead water region-filling section  15  is constituted by a separate member from the diaphragm outer ring  11 , the dead water region-filling section  15  may be integrally formed with the diaphragm outer ring  11 . In addition, an installation position of the dead water region-filling section  15  is not limited to the corner of the first cavity C 1  but may be an arbitrary position at which the dead water region is generated in the first cavity C 1 . Further, a shape of the inclined surface K may have an arbitrary shape according to a shape of the vortex flow of the steam S as well as the arc shape of the embodiment. 
     In addition, among the three cavities C, a second cavity C 2  disposed at a second upstream side in the axial direction is formed by, as shown in  FIG. 2 , the bottom surface  111   a  of the annular groove  111 , the first seal fin  12 A, the axial direction wall surfaces  521   a  and  521   b  and the radial direction wall surface  522   b  of the tip shroud  52 , and the second seal fin  12 B. Then, a widened section  16  slightly widened in the axial direction is also formed at the downstream section in the axial direction of the second cavity C 2 , similar to the first cavity C 1 . Further, dead water region-filling sections  17  are also formed at two corners of the second cavity C 2 , more specifically, a corner formed by the bottom surface  111   a  of the annular groove  111  and the first seal fin  12 A and a corner formed by the bottom surface  111   a  of the annular groove  111  and the second seal fin  12 B. Functions and shapes of the two dead water region-filling sections  17  are the same as those of the dead water region-filling section  15  of the first cavity C 1 . 
     In addition, among the three cavities C, a third cavity C 3  disposed at the furthest downstream side in the axial direction is formed by, as shown in  FIG. 2 , the bottom surface  111   a  of the annular groove  111 , the second seal fin  12 B, the axial direction wall surfaces  521   b  and  521   c  and the radial direction wall surface  522   c  of the tip shroud  52 , and the third seal fin  12 C. Then, a widened section  18  slightly widened in the axial direction is also formed at the axial direction downstream section of the third cavity C 3 , similar to the first cavity C 1 . Further, dead water region-filling sections  19  are also formed at two corners of the third cavity C 3 , more specifically, a corner formed by the bottom surface  111   a  of the annular groove  111  and the second seal fin  12 B and a corner formed by the bottom surface  111   a  of the annular groove  111  and the third seal fin  12 C. Functions and shapes of the two dead water region-filling sections  19  are the same as those of the dead water region-filling section  15  of the first cavity C 1 . 
     Next, effects of the steam turbine  1  according to the first embodiment will be described using  FIGS. 1 and 2 . When the regulating valve  20  shown in  FIG. 1  is in an open state, the steam S flows into the casing  10  from the boiler (not shown). The steam S is guided to the annular turbine blade group  50  by the annular turbine vane group  40  of each stage, and the annular turbine blade group  50  starts to rotate. Accordingly, energy of the steam S is converted into rotational energy by the annular turbine blade group  50 , and the rotational energy is transmitted to a power generator or the like (not shown) from the shaft body  30  integrally rotated with the annular turbine blade group  50 . 
     Here, as shown in  FIG. 2 , some of the steam S passing through the annular turbine vane group  40  passes through the small clearance  13  between the seal fin  12  and the annular turbine blade group  50  to be leaked to the downstream side without contributing to rotation driving of the annular turbine blade group  50 . 
     Leakage of the steam S will be described in more detail. As shown in  FIG. 2 , some of the steam S passing through the annular turbine vane group  40  and flowing in the axial direction flows into the first cavity C 1  without colliding with the turbine blade  51 . The steam S flowing into the first cavity C 1  collides with the radial direction wall surface  522   a  of the tip shroud  52  to form, for example, a main counterclockwise vortex SU 1  (a vortex flow) in  FIG. 2 . Accordingly, as some of the main vortex SU 1  is separated therefrom at an angled section  52 A of the tip shroud  52 , a separation vortex HU 1  (a vortex flow) in a reverse direction of the main vortex SU 1 , i.e., a clockwise direction of  FIG. 2 , is generated in the widened section  14  of the first cavity C 1 . The separation vortex HU 1  shows a so-called contraction flow effect of reducing a leakage amount of the steam S in the small clearance  13 A between the first seal fin  12 A and the tip shroud  52 . 
     Here,  FIG. 3  is a view for describing the contraction flow effect of the separation vortex HU 1 , showing a partially enlarged cross-sectional view of surroundings of a tip section of the first seal fin  12 A of  FIG. 2 . The separation vortex HU 1  in a clockwise direction has an inertial force inward in the radial direction just before the small clearance  13 A between the first seal fin  12 A and the tip shroud  52 . Accordingly, as the steam S leaked to the downstream side through the small clearance  13 A is pushed thereinto by an inertial force of the separation vortex HU 1 , a width in the radial direction is reduced as shown by a dashed line of  FIG. 3 . As described above, the separation vortex HU 1  has an effect of reducing a leakage amount by pushing and reducing the steam S inward in the radial direction, i.e., the contraction flow effect. In addition, the contraction flow effect is increased as the inertial force of the separation vortex HU 1  is increased, i.e., a flow velocity of the separation vortex HU 1  is increased. 
     Further, as shown in  FIG. 2 , the dead water region-filling sections  15  having substantial arc shapes are formed along a flow of the main vortex SU 1  at two corners of the first cavity C 1 . Accordingly, the dead water region, i.e., a region that the main vortex SU 1  does not reach, is not formed at the corner of the first cavity C 1 . Accordingly, as the steam S forming the main vortex SU 1  flows into the dead water region, energy loss of the steam S can be prevented. As a result, since the main vortex SU 1  can be strengthened, the separation vortex HU 1  separated from the main vortex SU 1  can also be strengthened. Accordingly, as the contraction flow effect of the separation vortex HU 1  is increased in comparison with the case in which the dead water region-filling section  15  is not provided, the leakage amount of the steam S in the small clearance  13 A between the first seal fin  12 A and the tip shroud  52  can be reduced. 
     In addition, as shown in  FIG. 2 , the steam S leaked from the small clearance  13 A flows into the second cavity C 2 . The steam S collides with the radial direction wall surface  522   b  of the tip shroud  52  to form a main vortex SU 2  in a counterclockwise direction. Then, some of the main vortex SU 2  is separated therefrom, and a separation vortex HU 2  in a clockwise direction is generated in the widened section  16  of the second cavity C 2 . Similar to the separation vortex HU 1 , the separation vortex HU 2  also shows the contraction flow effect of reducing the leakage amount of the steam S in the small clearance  13 B between the second seal fin  12 B and the tip shroud  52 . 
     Further, as shown in  FIG. 2 , even in the second cavity C 2 , the dead water region-filling sections  17  having substantial arc shapes are formed at the two corners. Accordingly, similar to the dead water region-filling section  15  of the first cavity C 1 , the main vortex SU 2  can be strengthened, and as a result, the separation vortex HU 2  can also be strengthened. Accordingly, in comparison with the case in which the dead water region-filling section  17  is not provided, the contraction flow effect of the separation vortex HU 2  can be increased, and the leakage amount of the steam S in the small clearance  13 B can be reduced. 
     In addition, as shown in  FIG. 2 , the steam S leaked from the small clearance  13 B flows into the third cavity C 3 . The steam S collides with the radial direction wall surface  522   c  of the tip shroud  52  to form a main vortex SU 3  in a counterclockwise direction. Then, as some of the main vortex SU 3  is separated therefrom, in the widened section  18  of the third cavity C 3 , a separation vortex HU 3  in a clockwise direction is generated. Similar to the separation vortex HU 1 , the separation vortex HU 3  also shows the contraction flow effect of reducing the leakage amount of the steam S in the small clearance  13 C between the third seal fin  12 C and the tip shroud  52 . 
     Further, as shown in  FIG. 2 , in the third cavity C 3 , the dead water region-filling sections  19  having substantial arc shapes are formed at the two corners. Accordingly, similar to the dead water region-filling section  15  of the first cavity C 1 , the main vortex SU 3  can be strengthened, and as a result, the separation vortex HU 3  can also be strengthened. Accordingly, in comparison with the case in which the dead water region-filling section  19  is not provided, the contraction flow effect of the separation vortex HU 3  can be increased, and the leakage amount of the steam S in the small clearance  13 C can be reduced. 
     As described above, as the leakage amount of the steam S can be reduced by the contraction flow effect of the separation vortexes HU 1 , HU 2  and HU 3  in the three cavities C 1 , C 2  and C 3 , respectively, the leakage amount of the steam S can be suppressed to be minimal. In addition, the number of cavities C in the axial direction is not limited to three cavities but an arbitrary number of cavities may be formed. Further, in the embodiment, while the dead water region-filling section  15  is installed in the first cavity C, the dead water region-filling section  17  is installed in the second cavity C 2  and the dead water region-filling section  19  is installed in the third cavity C 3 , installation of the dead water region-filling sections in all of the cavities C is not needed, and installation of the dead water region-filling sections in at least one cavity C is sufficient. 
     Second Embodiment 
     Next, a configuration of a steam turbine according to a second embodiment of the present invention will be described. The steam turbine according to the embodiment is distinguished from the steam turbine  1  of the first embodiment in that the dead water region-filling section is formed at a different position in the cavity C formed at surroundings of a tip section of the moving blade  51 . Since the other constitutions are the same as those of the first embodiment, the same reference numerals are designated and description thereof will be omitted. 
       FIG. 4  is a schematic cross-sectional view showing surroundings of a tip section of the turbine blade  51  of the second embodiment. Similar to the first embodiment, the three cavities C are formed between the annular turbine blade group  50  and the diaphragm outer ring  11 . Then, among the three cavities C, dead water region-filling section is not formed in the first cavity C 1  disposed at the furthest upstream side in the axial direction. In addition, in  FIG. 4 , same constitutions in the first embodiment are designated by same reference numerals of  FIG. 2 . 
     Further, as shown in  FIG. 4 , among the three cavities C, a dead water region-filling section  70  is formed at one corner of the second cavity C 2  disposed at a second upstream side in the axial direction. The dead water region-filling section  70  has the inclined surface K having a substantial arc shape in a cross-section in the axial direction, and is formed at a corner formed by the axial direction wall surface  521   a  and the radial direction wall surface  522   b  of the tip shroud  52 . 
     In addition, as shown in  FIG. 4 , among the three cavities C, a dead water region-filling section  71  is formed at one corner of the third cavity C 3  disposed at the furthest downstream side in the axial direction. The dead water region-filling section  71  also has an inclined surface K having a substantial arc shape, and is formed at a corner formed by the axial direction wall surface  521   b  and the radial direction wall surface  522   c  of the tip shroud  52 . 
     Next, effects of the steam turbine  1  according to the second embodiment will be described focusing on differences from the first embodiment. According to the configuration shown in  FIG. 4 , the steam S leaked to the downstream side through the small clearance  13 A between the first seal fin  12 A and the tip shroud  52  forms the main vortex SU 2  and the separation vortex HU 2  when flowing into the second cavity C 2 , similar to the first embodiment. Then, the separation vortex HU 2  shows a contraction flow effect of reducing a leakage amount of the steam S in the small clearance  13 B. 
     Further, as shown in  FIG. 4 , the dead water region-filling section  70  having the substantially arc-shaped inclined surface K is formed at one corner of the second cavity C 2 . Accordingly, since the main vortex SU 2  can be strengthened by preventing energy loss of the steam S in the dead water region, the separation vortex HU 2  can also be resultantly strengthened. Accordingly, in comparison with the case in which the dead water region-filling section  70  is not provided, the contraction flow effect of the separation vortex HU 2  can be increased, and the leakage amount of the steam S in the small clearance  13 B can be reduced. 
     In addition, in the embodiment, the dead water region-filling section  70  is formed at a corner formed by the axial direction wall surface  521   a  and the radial direction wall surface  522   b  of the tip shroud  52 . Accordingly, in angled sections  52 B and  52 C of the tip shroud  52  formed by the axial direction wall surface  521   a  and the radial direction wall surface  522   b  and having an acute shape, generation of stress concentration due to thermal expansion or expansion due to a centrifugal force can be attenuated. 
     Further, as shown in  FIG. 4 , in one corner of the third cavity C 3 , the dead water region-filling section  71  having the substantially arc-shaped inclined surface K is formed. Accordingly, since the separation vortex HU 3  can be strengthened by strengthening the main vortex SU 3 , in comparison with the case in which the dead water region-filling section  71  is not provided, the leakage amount of the steam S in the small clearance  13 C can be reduced. In addition, the dead water region-filling section  71  can be formed at a corner formed by the axial direction wall surface  521   b  and the radial direction wall surface  522   c  of the tip shroud  52 . Accordingly, in the angled sections  52 B and  52 C of the tip shroud  52  having an acute shape, generation of stress concentration due to thermal expansion or expansion due to a centrifugal force can be attenuated. 
     Third Embodiment 
     Next, a configuration of a steam turbine according to a third embodiment of the present invention will be described. In comparison with the steam turbine  1  of the first embodiment, in the steam turbine according to the embodiment, in the cavity C formed at surroundings of a tip section of the turbine blade  51 , a position at which the dead water region-filling section is installed is different. Since the other configurations are the same as those of the first embodiment, the same reference numerals are used and description thereof will be omitted. 
       FIG. 5  is a schematic cross-sectional view showing surroundings of a tip section of the turbine blade  51  of the third embodiment. Similar to the first embodiment, the three cavities C are formed between the annular turbine blade group  50  and the diaphragm outer ring  11 . Then, among the three cavities C, the dead water region-filling sections  15  are formed at the same two corners as in the first embodiment shown in  FIG. 2 , respectively, in the first cavity C 1  disposed at the furthest upstream side in the axial direction. In addition, in  FIG. 5 , the same configurations as those of the first embodiment are designated by the same reference numerals of  FIG. 2 . 
     Further, as shown in  FIG. 5 , among the three cavities C, in the second cavity C 2  disposed at a second upstream side in the axial direction, the dead water region-filling sections  17  are formed at the same two corners as in the first embodiment shown in  FIG. 2 , respectively, and the dead water region-filling section  70  is also formed at the same one corner as in the second embodiment shown in  FIG. 4 . 
     In addition, as shown in  FIG. 5 , among the three cavities, in the third cavity C 3  disposed at the furthest downstream side in the axial direction, the dead water region-filling sections  19  are formed at the same two corners as in the first embodiment shown in  FIG. 2 , respectively, and the dead water region-filling section  71  is also formed at the same one corner as in the second embodiment of  FIG. 4 . 
     Next, effects of the steam turbine  1  according to the third embodiment will be described focusing on differences from the first embodiment. According to the configuration shown in  FIG. 5 , since the dead water region-filling section  70  is further formed in the second cavity C 2  in addition to the two dead water region-filling sections  17 , in comparison with the first embodiment, energy loss of the steam S in the dead water region can be further prevented. Accordingly, the separation vortex HU 2  can also be further strengthened because the main vortex SU 2  can be further strengthened, and the leakage amount of the steam S in the small clearance  13 B can be further reduced compared with the first embodiment. In addition, in the third cavity C 3 , for the same reason as in the second cavity C 2 , the leakage amount of the steam S in the small clearance  13 C can be even further reduced compared with the first embodiment. 
     Further, in the embodiment, as the dead water region-filling sections  70  and  71  are formed at the acute angled sections  52 B and  52 C of the tip shroud  52 , respectively, similar to the second embodiment, generation of stress concentration at the section due to thermal expansion or expansion due to a centrifugal force can be attenuated. 
     Fourth Embodiment 
     Next, a configuration of the steam turbine according to a fourth embodiment of the present invention will be described. In comparison with the steam turbine  1  of the first embodiment, the steam turbine according to the embodiment has a different installation position and shape of the dead water region-filling section from the steam turbine  1  in the cavity C formed at surroundings of a tip section of the moving blade  51 . Since the other configurations are the same as those of the first embodiment, the same reference numerals are used and description thereof will be omitted. 
       FIG. 6  is a schematic cross-sectional view showing surroundings of a tip section of the turbine blade  51  of the fourth embodiment. Similar to the first embodiment, the three cavities C are formed between the annular turbine blade group  50  and the diaphragm outer ring  11 . Then, while the dead water region-filling sections are formed at the same corners as in the third embodiment shown in  FIG. 5  in the three cavities C, shapes of the inclined surfaces K included in the dead water region-filling sections are different from those of the third embodiment. In addition, in  FIG. 6 , the same configurations as those of the first embodiment are designated by the same reference numerals as in  FIG. 2 . 
     More specifically, as shown in  FIG. 6 , among the three cavities C, in the first cavity C 1  disposed at the furthest upstream side in the axial direction, dead water region-filling sections  72  having substantially oval arc-shaped inclined surfaces K are formed at the same two corners as in the first embodiment shown in  FIG. 2 . 
     In addition, in the second cavity C 2  disposed at a second upstream side in the axial direction, dead water region-filling sections  73  having substantially oval arc-shaped inclined surfaces K are formed at the same two corners as in the first embodiment, and a dead water region-filling section  74  having a substantially oval arc-shaped inclined surface K is formed at the same one corner as in the second embodiment. 
     Further, in the third cavity C 3  disposed at the furthest downstream side in the axial direction, dead water region-filling sections  75  having substantially oval arc-shaped inclined surfaces K are formed at the same two corners as in the first embodiment, and a dead water region-filling section  76  having a substantially oval arc-shaped inclined surface K is formed at the same one corner as in the second embodiment. 
     Next, effects of the steam turbine  1  according to the fourth embodiment will be described focusing on differences from the third embodiment. According to the configuration shown in  FIG. 6 , since all of the dead water region-filling sections  72  to  76  formed in the three cavities C have substantially oval arc-shaped inclined surfaces K, in addition to the effect performed by the steam turbine  1  of the third embodiment, according to the shape of the three cavities C, the leakage amount of the steam S in the small clearances  13 A,  13 B and  13 C can be further reduced more than in the third embodiment. 
     This is because, since a cross-sectional shape in the axial direction of the main vortexes SU 1 , SU 2  and SU 3  generated in the three cavities C generally has an oval shape rather than a perfect circle, shapes of the inclined surfaces K of the dead water region-filling sections  72  to  76  also have substantially oval arc shapes to more accurately conform to the shapes of the main vortexes SU 1 , SU 2  and SU 3  so that the energy loss of the steam S due to a flow in the dead water region can be more securely prevented than in the third embodiment. 
     In addition, as shown in  FIG. 6 , in the embodiment, while the inclined surface K of the dead water region-filling sections  72 ,  73  and  75  formed at the diaphragm outer ring  11  side has a substantially oval arc shape elongated in the radial direction, the inclined surface K of the dead water region-filling sections  74  and  76  formed at the tip shroud  52  side has a substantially oval arc shape elongated in the axial direction. According to the above-mentioned configuration, since the main vortexes SU 1 , SU 2  and SU 3  can be accurately guided to collide with the angled section of the tip shroud  52 , separation directions of the separation vortexes HU 1 , HU 2  and HU 3  can coincide in the radial direction. Accordingly, since the separation vortexes HU 1 , HU 2  and HU 3  just before the small clearances  13 A,  13 B and  13 C have inertial forces in the radial direction, the contraction flow effect of the separation vortexes HU 1 , HU 2  and HU 3  can be increased. In addition, design of the formation of the inclined surface K of the dead water region-filling sections  72  to  76  having the substantially oval arc shapes in any one of the axial direction and the radial direction can be appropriately changed. 
     Fifth Embodiment 
     Next, a configuration of a steam turbine according to a fifth embodiment of the present invention will be described. In comparison with the steam turbine  1  of the first embodiment, the steam turbine according to the embodiment has different positions and shapes of dead water region-filling sections in the cavity C formed at surroundings of a tip section of the moving blade  51 . Since the other configurations are the same as those of the first embodiment, the same reference numerals are used and description thereof will be omitted. 
       FIG. 7  is a schematic cross-sectional view showing surroundings of a tip section of the turbine blade  51  of the fifth embodiment. Similar to the first embodiment, the three cavities C are formed between the annular turbine blade group  50  and the diaphragm outer ring  11 . Then, in the three cavities C, while dead water region-filling sections are formed at the same corners as in the third embodiment shown in  FIG. 5 , a shape of the inclined surface K included in each of the dead water region-filling section is different from that of the third embodiment. In addition, in  FIG. 7 , the same configurations as those of the first embodiment are designated by the same reference numerals as in  FIG. 2 . 
     More specifically, as shown in  FIG. 7 , among the three cavities C, in the first cavity C 1  disposed at the furthest upstream side in the axial direction, dead water region-filling sections  77  having substantially linear shaped inclined surfaces K are formed at the same two corners as in the first embodiment shown in  FIG. 2 . 
     In addition, in the second cavity C 2  disposed at a second upstream side in the axial direction, dead water region-filling sections  78  having substantially linear shaped inclined surfaces K are formed at the same two corners as in the first embodiment, and a dead water region-filling section  79  having a substantially linear shaped inclined surface K is formed at the same one corner as in the second embodiment. 
     Further, in the third cavity C 3  disposed at the furthest downstream side in the axial direction, dead water region-filling sections  80  having substantially linear shaped inclined surfaces K are formed at the same two corners as in the first embodiment, and a dead water region-filling section  81  having a substantially linear shaped inclined surface K is formed at the same one corner as in the second embodiment. 
     Next, effects of the steam turbine  1  according to the fifth embodiment will be described focusing on differences from the third embodiment. According to the configuration shown in  FIG. 7 , since all of the dead water region-filling sections  77  to  81  installed at the three cavities C have the substantially linear shaped inclined surfaces K, in addition to an effect performed by the steam turbine  1  of the third embodiment, manufacture of the dead water region-filling sections  77  to  81  can be simplified more than in the third embodiment. Specifically, when the dead water region-filling sections  77  to  81  are constituted by separate members from the diaphragm outer ring  11  or the tip shroud  52 , a processing operation of the dead water region-filling sections  77  to  81  can be easily performed. Meanwhile, when the dead water region-filling sections  77  to  81  are integrally configured with the diaphragm outer ring  11  or the tip shroud  52 , a shape of a mold for forming the diaphragm outer ring  11  or the tip shroud  52  can be simplified. 
     In addition, in the embodiment, while the case in which the dead water region-filling sections  77  to  81  have one inclined surface K having a substantially linear shape has been described, the dead water region-filling sections  77  to  81  may have a plurality of inclined surfaces K having substantially linear shapes. That is, the cross-sectional shape of the dead water region-filling sections  77  to  81  is not limited to a triangular shape of the embodiment but may be a polygonal shape. 
     Sixth Embodiment 
     Next, a configuration of a steam turbine according to a sixth embodiment of the present invention will be described. In comparison with the steam turbine  1  of the first embodiment, the steam turbine according to the embodiment, an installation position of the dead water region-filling section is at surroundings of a tip section of the turbine vane  41  rather than surroundings of a tip section of the turbine blade  51 . Since the other components are the same as those of the first embodiment, the same reference numerals are used and description thereof will be omitted. In addition, in the embodiment, the annular turbine vane group  40  corresponds to the blade according to the present invention, and the shaft body  30  corresponds to the structure according to the present invention. 
       FIG. 8  is a partially enlarged cross-sectional view showing surroundings of a tip section of the turbine vane  41  of the sixth embodiment. The above-mentioned ring-shaped hub shroud  42  is disposed at a tip section of the turbine vane  41 . Then, three seal fins  84  are installed to protrude from an outer circumferential surface  42   a  of the hub shroud  42  in the radial direction. Then, among the three seal fins  84 , a first seal fin  84 A formed at the furthest upstream side in the axial direction is configured to form substantially the same surface as an axial direction end surface  42   b  of the hub shroud  42  disposed at a furthest upstream section in the axial direction. 
     Meanwhile, an annular groove  301  having a concave cross-sectional shape is formed at the outer circumferential surface of the shaft body  30 , and a portion reduced in diameter by forming the annular groove  301  is inserted into the hub shroud  42 . Accordingly, small clearances  85  are formed between a bottom surface  301   a  of the annular groove  301  and the seal fins  84  in the radial direction, respectively. 
     In addition, a length, a shape, an installation position, the number, or the like, of the seal fins  84  is not limited to the embodiment but design thereof may be appropriately changed according to a cross-sectional shape or the like of the hub shroud  42  and/or the shaft body  30 . Further, a dimension of the small clearance  85  may be appropriately set to a minimum value within a safe range in which the seal fin  84  is not in contact with the shaft body  30 . Furthermore, in the embodiment, while the seal fin  84  is formed to protrude from the hub shroud  42  and the small clearance  85  is formed between the seal fin  84  and the shaft body  30 , the seal fin  84  may also be formed to protrude from the shaft body  30  and the small clearance  85  may be formed between the seal fin  84  and the hub shroud  42 . 
     Then, according to the configuration of the surroundings of the tip section of the above-mentioned turbine vane  41 , as shown in  FIG. 8 , the three cavities C are formed by the shaft body  30 , the seal fin  84  and the hub shroud  42 . Here, among the three cavities C, as shown in  FIG. 8 , a fourth cavity C 4  disposed at the furthest upstream side in the axial direction is formed by the bottom surface  301   a  and a side surface  301   b  of the annular groove  301 , the first seal fin  84 A, and the axial direction end surface  42   b  of the hub shroud  42 . The fourth cavity C 4  formed as described above has a substantially rectangular cross-sectional shape in the axial direction. 
     Then, as shown in  FIG. 8 , a dead water region-filling section  86  is formed at one corner of the fourth cavity C 4 , more specifically, a corner formed by the bottom surface  301   a  and the side surface  301   b  of the annular groove  301 . The one dead water region-filling section  86  has a substantially oval arc-shaped inclined surface K in a cross-section in the axial direction. 
     In addition, the dead water region-filling section  86  has the same function as that of the first embodiment. Further, a shape of the inclined surface K of the dead water region-filling section  86  may be a substantial arc shape or a substantially linear shape as well as the substantially oval arc shape of the embodiment. Furthermore, in the embodiment, while the dead water region-filling section  86  is formed in only the fourth cavity among the three cavities C, a dead water region-filling section may also be formed in a fifth cavity C 5  disposed at a second upstream side or a sixth cavity C 6  disposed at the furthest downstream side. That is, the dead water region-filling section may be formed at a corner formed by the outer circumferential surface  42   a  of the hub shroud  42  and a second seal fin  84 B or a corner formed by the outer circumferential surface  42   a  of the hub shroud  42  and a third seal fin  84 C. 
     Next, effects of the steam turbine  1  according to the sixth embodiment will be described. While the steam S flowing into the casing  10  shown in  FIG. 1  normally passes between the plurality of turbine vanes  41  constituting the annular turbine vane group  40  to be guided to the annular turbine blade group  50 , some of the steam S passes through the small clearance  85  ( 85 A,  85 B and  85 C) between the annular turbine vane group  40  and the shaft body  30  to be leaked to the downstream side. 
     The leakage of the steam S will be more specifically described. As shown in  FIG. 8 , the steam S flowing in the axial direction flows into the fourth cavity C 4 , while some of the steam S is not guided to the downstream side by the turbine vane  41 . The steam S flowing into the fourth cavity C 4  collides with the axial direction end surface  42   b  of the hub shroud  42  to form, for example, a main vortex SU 4  in a clockwise direction of  FIG. 8 . Here, since the first seal fin  84 A is formed to have substantially the same surface as the axial direction end surface  42   b  of the hub shroud  42 , the main vortex SU 4  does not generate a separation vortex at an angled section  42 A of the hub shroud  42 . However, in the embodiment, since the main vortex SU 4  is rotated clockwise, the main vortex SU 4  has an inertial force outward in the radial direction just before the small clearance  85 A. Accordingly, the main vortex SU 4  shows the contraction flow effect of reducing the leakage amount thereof by pushing and reducing the steam S passing through the small clearance  85 A to be leaked to the downstream side. 
     Further, as shown in  FIG. 8 , the dead water region-filling section  86  having a substantially oval arc shape is formed at one corner of the fourth cavity C 4  along a flow of the main vortex SU 4 . Accordingly, the dead water region generated in the fourth cavity C 4  can be reduced, and energy loss of the steam S due to a flow in the dead water region can be reduced. Therefore, since the main vortex SU 4  can be strengthened in comparison with the case in which dead water region-filling section  86  is not provided, as a result, the contraction flow effect of the main vortex SU 4  can be increased, and the leakage amount of the steam S in the small clearance  85 A can be reduced. 
     Seventh Embodiment 
     Next, a configuration of a steam turbine according to a seventh embodiment of the present invention will be described. The steam turbine according to the embodiment is distinguished from the steam turbine of the sixth embodiment in that a shape of a cavity formed at the furthest upstream side in the axial direction is different therefrom. Since the other configurations are the same as those of the sixth embodiment, the same reference numerals are used and description thereof will be omitted. 
       FIG. 9  is a partially enlarged cross-sectional view showing surroundings of a tip section of the turbine vane  41  of the seventh embodiment. Similar to the sixth embodiment, the three cavities C are formed between the annular turbine vane group  40  and the shaft body  30 . However, among the three cavities C, a seventh cavity C 7  disposed at the furthest upstream side in the axial direction, i.e., a portion of an upstream side rather than a downstream side of the first seal fin  84 A is formed to be stepped downward in the radial direction, formed to be disposed inside in the radial direction in the embodiment. In addition, in the sixth embodiment, while the seal fin  84  can be formed to protrude from the shaft body  30  rather than the hub shroud  42  side, in the embodiment, the seal fin  84  should be formed at the hub shroud  42  side and cannot be formed at the shaft body  30 . Further, the seal fin  84  is formed to protrude from the tip shroud  52  constituting the turbine blade  51  without being limited to the surroundings of the tip section of the turbine vane  41 , and the portion of the upstream side rather than the area of the downstream side of the seal fin  84  may be formed to be stepped downward in the radial direction, i.e., disposed outside in the radial direction. 
     Then, as shown in  FIG. 9 , dead water region-filling sections  87  and  88  are formed at two corners of the seventh cavity C 7 . More specifically, the dead water region-filling section  87  is formed at the corner formed by the bottom surface  301   a  and the side surface  301   b  of the annular groove  301 , and the dead water region-filling section  88  is formed at the corner formed by the bottom surface  301   a  and a stepped surface  301   c . The two dead water region-filling sections  87  and  88  have the inclined surfaces K having substantially oval arc shapes in a cross-section in the axial direction, respectively. 
     Next, effects of the steam turbine  1  according to the seventh embodiment will be described focusing on differences from the sixth embodiment. In the embodiment, as shown in  FIG. 9 , as the first seal fin  84 A is formed to protrude from the hub shroud  42 , a position at which the small clearance  85 A is formed becomes a position near the shaft body  30 . Then, the seventh cavity C 7  of the upstream side of the small clearance  85 A is formed to be stepped downward from an eighth cavity C 8  and a ninth cavity C 9  of the downstream side. 
     According to the above-mentioned configuration, as shown in  FIG. 9 , a main vortex SU 5  rotated clockwise in the seventh cavity C 7  passes through the small clearance  85 A to reach a further downward side (inward in the radial direction). 
     Accordingly, in the main vortex SU 5  of the embodiment, in comparison with the case in which there is no step-down such as the sixth embodiment shown in  FIG. 8 , a pivot center of the main vortex SU 5  approaches the small clearance  85 A. Therefore, since a velocity in the radial direction of the main vortex SU 5  in the vicinity of the small clearance  85 A is higher when there is a step-down than when there is no step-down, and the contraction flow effect of the main vortex SU 5  is increased, the leakage amount of the steam S in the small clearance  85 A can be further reduced. 
     In addition, in the embodiment, since the dead water region-filling sections  87  and  88  are formed at two corners of the seventh cavity C 7 , in comparison with the case in which the dead water region-filling section  86  is formed at only one corner of the fourth cavity C 4  of the sixth embodiment, the dead water region can be further reduced to further strengthen the main vortex SU 5 . 
     Accordingly, in the embodiment, in comparison with the sixth embodiment, the leakage amount of the steam S in the small clearance  85 A can be further reduced. 
     Eighth Embodiment 
     Next, a configuration of a steam turbine according to an eighth embodiment of the present invention will be described. The steam turbine according to the embodiment is distinguished from the steam turbine of the sixth embodiment in that shapes of the cavities are different. Since the other configurations are the same as those of the sixth embodiment, the same reference numerals are used and description thereof will be omitted. 
       FIG. 10  is a partially enlarged cross-sectional view showing surroundings of a tip section of the turbine vane  41  of the eighth embodiment. Similar to the seventh embodiment, the three cavities C are formed between the annular turbine vane group  40  and the shaft body  30 . However, among the three cavities C, while a tenth cavity C 10  disposed at the furthest upstream side has the same configuration as the seventh cavity C 7  of the seventh embodiment, configurations of an eleventh cavity C 11  and a twelfth cavity C 12  disposed at a downstream side thereof are different from the eighth cavity C 8  and the ninth cavity C 9  of the seventh embodiment. 
     More specifically, as shown in  FIG. 10 , on the bottom surface  301   a  of the annular groove  301 , a stepped section  89  is formed to step down inward in the radial direction at the downstream side rather than the upstream side in the axial direction at a position between the adjacent first seal fin  84 A and second seal fin  84 B. 
     Accordingly, a widened section  90  slightly widened in the radial direction is formed at a downstream section in an axial direction of the eleventh cavity C 11 . Then, at the downstream side of the stepped section  89 , a radial direction height position of the bottom surface  301   a  becomes substantially the same height position as the bottom surface  301   a  forming the tenth cavity C 10 . In addition, the bottom surface  301   a  at the downstream side of the stepped section  89  may be disposed at a different height position from the bottom surface  301   a  forming the tenth cavity C 10 . 
     Then, as shown in  FIG. 10 , similar to the seventh embodiment, the dead water region-filling sections  87  and  88  are formed at the two corners of the tenth cavity C 10 . In addition, dead water region-filling sections  82  and a dead water region-filling section  83  are formed at three corners of the eleventh cavity C 11 , respectively. More specifically, the dead water region-filling sections  82  are formed at a corner formed by the outer circumferential surface  42   a  of the hub shroud  42  and the first seal fin  84 A and a corner formed by the outer circumferential surface  42   a  and the second seal fin  84 B. In addition, the dead water region-filling section  83  is formed at a corner formed by the stepped section  89  and the bottom surface  301   a.    
     Next, effects of the steam turbine  1  according to the eighth embodiment will be described focusing on differences from the seventh embodiment. According to the configuration shown in  FIG. 10 , in the tenth cavity C 10 , similar to the seventh cavity C 7  of the seventh embodiment, the main vortex SU 5  in a clockwise direction is formed, and the same effect as in the seventh embodiment is performed. 
     In addition, according to the configuration shown in  FIG. 10 , the steam S flowing into the eleventh cavity C 11  from the tenth cavity C 10  via the small clearance  85 A forms a main vortex SU 6  in a counterclockwise direction in the eleventh cavity C 11 . Then, as some of the main vortex SU 6  is separated therefrom at the angled section of the stepped section  89 , a separation vortex HU 4  in a clockwise direction is generated. Here, since the separation vortex HU 4  has an inertial force inward in the radial direction just before the small clearance  85 B between the second seal fin  84 B and the shaft body  30 , a large contraction flow effect is obtained. Accordingly, in comparison with the case in which the stepped section  89  is not formed in the eleventh cavity C 11  and only the main vortex SU 6  in a counterclockwise direction is generated in the eleventh cavity C 11 , the embodiment shows an effect of further reducing the leakage amount of the steam S in the small clearance  85 B formed by the tip section of the second seal fin  84 B. 
     Further, as shown in  FIG. 10 , the dead water region-filling sections  82  are formed at two corners of the eleventh cavity C 11  along a flow of the main vortex SU 6 , and the dead water region-filling section  83  is formed at one corner along a flow of the separation vortex HU 4 . Accordingly, in both of the main vortex SU 6  and the separation vortex HU 4 , energy loss due to introduction into the dead water region can be reduced. Accordingly, in comparison with the case in which the dead water region-filling sections  82  and  83  are not provided, since both of the main vortex SU 6  and the separation vortex HU 4  can be strengthened, the leakage amount of the steam S in the small clearance  85 B can be reduced. 
     In addition, in the embodiment, while the stepped section  89  is formed to step down inward in the radial direction at the downstream side rather than the upstream side in the axial direction, as shown in  FIG. 11 , a stepped section  91  may be formed to step up outward in the radial direction at the downstream side rather than the upstream side. In this case, a widened section  92  slightly widened in the axial direction is formed at a downstream section in an axial direction of the eleventh cavity C 11 . 
     Then, similar to the configuration shown in  FIG. 10 , the dead water region-filling sections  82  are formed at a corner formed by the outer circumferential surface  42   a  of the hub shroud  42  and the first seal fin  84 A and a corner formed by the outer circumferential surface  42   a  and the second seal fin  84 B. Further, a dead water region-filling section  100  is formed at a corner formed by the stepped section  91  and the bottom surface  301   a.    
     According to the above-mentioned configuration, the steam S flowing into the eleventh cavity C 11  from the tenth cavity C 10  through the small clearance  85 A also forms a main vortex SU 7  in the eleventh cavity C 11 . Then, as some of the main vortex SU 7  is separated therefrom at the angled section of the stepped section  91 , a separation vortex HU 5  in a clockwise direction is generated. Accordingly, even when the stepped section  91  is formed, the same effect as in the case in which the stepped section  89  is formed can be obtained. 
     In addition, as shown in  FIG. 11 , since the dead water region-filling sections  82  are formed at the two corners of the eleventh cavity C 11 , energy loss of the main vortex SU 7  can be reduced similar to the configuration of  FIG. 10 , and since the dead water region-filling section  100  is formed at one corner, energy loss of the separation vortex HU 5  can also be reduced. Thus, according to the configuration shown in  FIG. 11 , in comparison with the case in which the dead water region-filling sections  82  and  100  are not provided, the leakage amount of the steam S in the small clearance  85 B can be reduced. 
     Ninth Embodiment 
     Next, a configuration of a steam turbine according to a ninth embodiment of the present invention will be described. The steam turbine according to the embodiment is distinguished from the steam turbine  1  of the first embodiment in that an installation position of a dead water region-filling section in the cavity C formed at surroundings of a tip section of the moving blade  51  is different. Here,  FIG. 12  is a schematic cross-sectional view showing surroundings of a tip section of the turbine blade  51  of the ninth embodiment, in particular, enlarging a tip section of a first seal fin  93 . In addition, since the configurations other than the first seal fin  93  are the same as those of the first embodiment, the same reference numerals are used and description thereof will be omitted. 
     In the embodiment, the first seal fin  93  has a fin body section  931  and a space limiting section  932  formed to be wider than the fin body section  931 . Accordingly, the first cavity C 1  at an upstream side of the first seal fin  93  has a widened section  94  slightly widened in axial direction at a downstream section in an axial direction thereof. Then, a dead water region-filling section  95  is formed at a corner of the widened section  94 , and more specifically, a corner formed by the fin body section  931  and the space limiting section  932 . 
     Next, effects of the steam turbine  1  according to the ninth embodiment will be described focusing on differences from the first embodiment. According to the configuration shown in  FIG. 12 , as the main vortex SU 1  in a counterclockwise direction formed in the first cavity C 1  is partially separated at an angled section of the tip shroud  52 , the separation vortex HU 1  in a clockwise direction is generated in the widened section  94 . Here, as the separation vortex HU 1  collides with the space limiting section  932  and the fin body section  931  and a flow direction thereof is guided, a vortex flow is strengthened. Further, since the dead water region-filling section  95  is formed at a corner of the widened section  94 , energy loss of the steam S due to introduction of the separation vortex HU 1  into the dead water region can be reduced. Accordingly, in comparison with the case in which the dead water region-filling section  95  is not provided, since the contraction flow effect can be increased by strengthening the separation vortex HU 1 , the leakage amount of the steam S in the small clearance  13 A can be reduced. 
     Tenth Embodiment 
     Next, a configuration of a steam turbine according to a tenth embodiment of the present invention will be described. The steam turbine of the embodiment is distinguished from the steam turbine  1  of the first embodiment in that an installation position of the dead water region-filling section in the cavity C formed at surroundings of a tip section of the turbine blade  51  is different. 
     Since the other configurations are the same as those of the first embodiment, the same reference numerals are used and description thereof will be omitted. 
       FIG. 13  is a schematic cross-sectional view showing surroundings of a tip section of the turbine blade  51  of the tenth embodiment. Similar to the first embodiment, the three cavities C are formed between the annular turbine blade group  50  and the diaphragm outer ring  11 . Here, in the embodiment, clearances in the axial direction from the seal fins  12 A,  12 B and  12 C to the radial direction wall surfaces  522   a ,  522   b  and  522   c  are set to be larger than those of the first embodiment. Accordingly, the three cavities C 1 , C 2  and C 3  have widened sections  96 ,  97  and  98  formed to be wider than those of the first embodiment. 
     Then, among the three cavities C, the dead water region-filling sections  15  are formed at two corners of the first cavity C 1  disposed at the furthest upstream side in the axial direction, similar to the first embodiment. More specifically, the dead water region-filling sections  15  are formed at a corner formed by the bottom surface  111   a  and the side surface  111   b  of the annular groove  111  and a corner formed by the bottom surface  111   a  of the annular groove  111  and the first seal fin  12 A. 
     Further, in the embodiment, in the first cavity C 1 , in addition to the two corners, a dead water region-filling section  99  is formed at an intermediate position of the two corners on the bottom surface  111   a  of the annular groove  111 . The dead water region-filling section  99  has two inclined surfaces K 1  and K 2  such that one inclined surface K 1  is formed along a flow of the main vortex SU 1  generated in the first cavity C 1  and the other inclined surface K 2  is similarly formed along a flow of the separation vortex HU 1  generated in the widened section  96  of the first cavity C 1 . In addition, similar to the first cavity C 1 , the dead water region-filling sections  17  and  19  are also formed at two corners of the second cavity C 2  and the third cavity C 3 , respectively, and the dead water region-filling section  99  is formed at an intermediate position of the two corners of the bottom surface  111   a.    
     Next, effects of the steam turbine  1  according to the tenth embodiment will be described focusing on differences from the first embodiment. According to the configuration shown in  FIG. 13 , since the above-mentioned widened sections  96 ,  97  and  98  are formed to be wider than those of the first embodiment, the separation vortexes HU 1 , HU 2  and HU 3  have sufficient sizes to reach the bottom surface  111   a  of the annular groove  111 . 
     Here, in the first cavity C 1  of the embodiment, since a total of three dead water region-filling sections  15 ,  15  and  99  are formed, energy loss of the steam S due to introduction of both the main vortex SU 1  and the separation vortex HU 1  into the dead water region can be reduced. Accordingly, the separation vortex HU 1  can be indirectly strengthened by strengthening the main vortex SU 1 , and the separation vortex HU 1  can also be directly strengthened. As a result, since the contraction flow effect of the separation vortex HU 1  can be strengthened in comparison with the case in which the dead water region-filling sections  15 ,  15  and  99  are not provided, the leakage amount of the steam S in the small clearance  13 A can be reduced. 
     Similarly, since a total of three dead water region-filling sections  17 ,  17  and  99  and  19 ,  19  and  99  are formed even in each of the second cavity C 2  and the third cavity C 3  of the embodiment, and the same effect as that of the first cavity C 1  can be obtained, the leakage amount of the steam S in the small clearances  13 B and  13 C can be reduced. 
     In addition, all shapes, assemblies or operation sequences of the respective components shown in the above-mentioned embodiments are exemplarily provided, and may be variously modified based on design requirements within a range without departing from the teachings of the present invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention relates to a turbine including a blade disposed at a flow path through which a fluid flows, a structure installed at a tip side of the blade via a clearance and relatively rotated with respect to the blade, and a seal fin formed to protrude from any one of the blade and the structure and configured to form a small clearance with the other, wherein a dead water region-filling section is formed in a space formed by the blade, the structure and the seal fin and in which a vortex flow of the fluid is generated, such that a dead water region that the vortex flow cannot reach is filled. 
     According to the present invention, the vortex flow can be strengthened in comparison with the case in which the dead water region-filling section is not provided, and a contraction flow effect can be increased when the vortex flow has the contraction flow effect, and a leakage amount of the fluid in the clearance between the blade tip section and the structure can be reduced. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           1 : steam turbine 
           10 : casing 
           11 : diaphragm outer ring (structure) 
           111 : annular groove 
           111   a : bottom surface 
           111   b : side surface 
           12 : seal fin 
           12 A: first seal fin 
           12 B: second seal fin 
           12 C: third seal fin 
           13 : small clearance 
           13 A: small clearance 
           13 B: small clearance 
           13 C: small clearance 
           14 : widened section 
           15 : dead water region-filling section 
           16 : widened section 
           17 : dead water region-filling section 
           18 : widened section 
           19 : dead water region-filling section 
           20 : regulating valve 
           21 : regulating valve chamber 
           22 : valve body 
           23 : valve seat 
           24 : steam chamber 
           30 : shaft body (structure) 
           301 : annular groove 
           301   a : bottom surface 
           301   b : side surface 
           301   c : stepped surface 
           31 : shaft main body 
           32 : disc 
           40 : annular turbine vane group (blade) 
           41 : turbine vane 
           42 : hub shroud 
           42 A: angled section 
           42   a : outer circumferential surface 
           42   b : axial direction end surface 
           50 : annular turbine blade group (blade) 
           51 : turbine blade 
           52 : tip shroud 
           52 A: angled section 
           52 B: angled section 
           52 C: angled section 
           521   a : axial direction wall surface 
           521   b : axial direction wall surface 
           521   c : axial direction wall surface 
           522   a : radial direction wall surface 
           522   b : radial direction wall surface 
           522   c : radial direction wall surface 
           60 : bearing 
           61 : journal bearing apparatus 
           62 : thrust bearing apparatus 
           70 : dead water region-filling section 
           71 : dead water region-filling section 
           72 : dead water region-filling section 
           73 : dead water region-filling section 
           74 : dead water region-filling section 
           75 : dead water region-filling section 
           76 : dead water region-filling section 
           77 : dead water region-filling section 
           78 : dead water region-filling section 
           79 : dead water region-filling section 
           80 : dead water region-filling section 
           81 : dead water region-filling section 
           82 : dead water region-filling section 
           83 : dead water region-filling section 
           84 : seal fin 
           84 A: first seal fin 
           84 B: second seal fin 
           84 C: third seal fin 
           85 : small clearance 
           85 A: small clearance 
           85 B: small clearance 
           85 C: small clearance 
           86 : dead water region-filling section 
           87 : dead water region-filling section 
           88 : dead water region-filling section 
           89 : stepped section 
           90 : widened section 
           91 : stepped section 
           92 : widened section 
           93 : first seal fin 
           931 : fin body section 
           932 : space limiting section 
           94 : widened section 
           95 : dead water region-filling section 
           96 : widened section 
           97 : widened section 
           98 : widened section 
           99 : dead water region-filling section 
         C: cavity 
         C 1 : first cavity 
         C 10 : tenth cavity 
         C 11 : eleventh cavity 
         C 12 : twelfth cavity 
         C 2 : second cavity 
         C 3 : third cavity 
         C 4 : fourth cavity 
         C 5 : fifth cavity 
         C 6 : sixth cavity 
         C 7 : seventh cavity 
         C 8 : eighth cavity 
         C 9 : ninth cavity 
         HU 1 : separation vortex 
         HU 2 : separation vortex 
         HU 3 : separation vortex 
         HU 4 : separation vortex 
         HU 5 : separation vortex 
         K: inclined surface 
         K 1 : inclined surface 
         K 2 : inclined surface 
         S: steam 
         SU 1 : main vortex 
         SU 2 : main vortex 
         SU 3 : main vortex 
         SU 4 : main vortex 
         SU 5 : main vortex 
         SU 6 : main vortex 
         SU 7 : main vortex