JP5916586B2 - Steam turbine - Google Patents

Description

  The present invention relates to a steam turbine.

  A steam turbine is a prime mover that converts the thermal energy of steam into kinetic energy and converts it into mechanical work. When high-pressure steam is introduced at a location lower than the steam, the steam expands due to a decrease in pressure. At that time, the heat energy of the steam is converted into kinetic energy, and a high temperature steam flow is obtained. Then, steam flowing at a high speed is supplied to the moving blade, and the rotating shaft supporting the moving blade is rotated together with the moving blade. By transmitting the rotational force to a generator or the like, the kinetic energy of the steam is converted into mechanical work.

  Steam expands and works in the steam turbine with changes in state such as pressure and temperature drops. For example, superheated steam is ejected from a boiler to a steam turbine, and the degree of superheat decreases as the pressure expands, resulting in a dry saturated state. Such dry and saturated steam is further expanded to become wet steam containing moisture.

  In the region of wet steam, moisture tends to aggregate on the surface of the stationary blade, and the moisture aggregated on the surface of the stationary blade becomes a water vein and circulates downstream by being blown by the steam flow. When the water vein reaches the trailing edge of the stationary blade, it scatters and becomes water droplets. Thus, the water droplets scattered from the stationary blade collide with the moving blade installed on the downstream side of the stationary blade by the steam flow, and may cause erosion (erosion phenomenon) of the moving blade.

  As described above, when water droplets scattered from the stationary blade collide with the moving blade on the downstream side, a force opposite to the rotating direction of the rotating shaft acts on the moving blade, and a braking action that suppresses the rotation occurs. . Generally, it is said that when the moisture in the steam increases by 1%, the internal efficiency of the steam turbine decreases by 1 to 1.2%.

  For example, those disclosed in Patent Documents 1 to 5 are known as techniques for suppressing problems caused by water veins on the blade surface caused by moisture condensing in wet steam.

In the techniques disclosed in Patent Documents 1 to 3, a plurality of injection holes are provided in the whole or a part of the suction surface on the back side and the pressure surface on the abdomen side of the blade, and introduced into the blade inner space from the discharge hole. The water vein is scattered by ejecting steam.
In the technique disclosed in Patent Document 4, steam is introduced into the blade inner space to heat the blade, and steam is ejected from the ejection holes to reduce the wetness around the blade.
Further, in the technique disclosed in Patent Document 5, the trailing edge of the wing is formed into a substantially serrated shape, so that water droplets that are scattered are made finer, a part of the water vein is sucked from the slit on the wing surface, and discharged outside. It is said.

Japanese Patent Laid-Open No. 7-034804 Japanese Utility Model Publication No. 61-151004 Japanese Patent No. 4101358 JP 2001-501700 A JP-A 63-195302

However, in the techniques disclosed in Patent Documents 1 to 3, moisture in the vapor does not adhere to the entire blade surface, and the blade surface is divided into a portion to which water droplets adhere and a portion to which water droplets do not adhere. Therefore, there is a possibility that a slit is not provided in a portion where moisture removal is necessary or a slit is provided in an unnecessary portion.
Moreover, the technique disclosed in Patent Document 4 is difficult to employ steam having a high calorific value that can sufficiently remove moisture, and steam with low calorific value cannot completely remove moisture.
Furthermore, the technique disclosed in Patent Document 5 has a fear of steam turbulence and strength reduction due to the substantially sawtooth shape. Moreover, there exists a possibility of leading to the internal efficiency fall of a steam turbine accompanying discharging | emitting steam outside with a water vein.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a steam turbine that can more effectively suppress erosion of a moving blade and a decrease in efficiency due to water droplets.

In order to achieve the above object, the present invention provides the following means.
The steam turbine according to the present invention includes a moving blade that rotates a rotating shaft by a fluid pressure of steam, and a plurality of blades that are disposed radially outward of the rotating shaft and spaced apart from each other in a circumferential direction of the rotating shaft. A plurality of protrusions in a range from a front edge of the stationary blade on the back side of the stationary blade to 50% to 70% of the blade width of the stationary blade. The protrusion has a slope that increases as the amount of protrusion from the surface of the stationary blade increases toward the downstream side of the steam, and a cliff that forms an acute angle with the slope, and the width of the slope Is formed so as to become narrower toward the downstream side.

  According to the above configuration, when water droplets scattered from the moving blade adhere to the back side of the stationary blade, while flowing on the slope of the projection toward the downstream side of the steam, at the end of the slope formed by the slope and the cliff face Spatters into the steam. In other words, the projections formed on the stationary blades allow water droplets that can collide with the moving blades located on the downstream side of the stationary blades to be scattered without being coarsened. Thereby, it becomes possible to more effectively suppress the erosion of the moving blades and the decrease in efficiency due to the water droplets.

  In the steam turbine, it is preferable that the protrusion is formed in a range from 50% to 70% of the height of the stationary blade from the outer peripheral side of the stationary blade.

  According to the said structure, the water droplet which can collide with a moving blade can be scattered, suppressing the fall of the aerodynamic characteristic by protrusion.

  In the steam turbine, it is preferable that the plurality of protrusions are formed so as to be adjacent to each other in one direction toward the downstream side and to be adjacent to each other in a direction orthogonal to the one direction.

  According to the said structure, aggregation of the water droplet adhering to the surface of a stationary blade can be suppressed because a protrusion is formed without the clearance gap.

  In the steam turbine, it is preferable that the plurality of protrusions are formed so as to be shifted in a direction perpendicular to the one direction with respect to the protrusions adjacent in the one direction.

  According to the above configuration, the water droplets scattered from the slopes of the protrusions are scattered in the steam in a well-balanced manner, so that aggregation of the water droplets in the steam can be suppressed.

  According to the present invention, when water droplets scattered from the moving blade adhere to the back side of the stationary blade, while flowing on the slope of the projection toward the downstream side of the steam, at the end of the slope formed by the slope and the cliff face Spatters into the steam. In other words, the projections formed on the stationary blades allow water droplets that can collide with the moving blades located on the downstream side of the stationary blades to be scattered without being coarsened. Thereby, it becomes possible to more effectively suppress the erosion of the moving blades and the decrease in efficiency due to the water droplets.

It is a longitudinal section showing a schematic structure of a steam turbine concerning an embodiment of the present invention. It is a longitudinal section showing the important section of the steam turbine concerning an embodiment of the present invention. It is a side view showing a stationary blade concerning an embodiment of the present invention. It is a top view which shows the protrusion concerning embodiment of this invention. It is a side view which shows the protrusion concerning embodiment of this invention. It is explanatory drawing which shows the flow with respect to the downstream stationary blade of the steam and water droplet in a steam turbine. It is explanatory drawing which shows the track analysis result of the particle | grains of 50 micrometers in diameter adhering to a stationary blade. It is explanatory drawing which shows the track analysis result of the particle | grains with a diameter of 100 micrometers adhering to a stationary blade.

Hereinafter, embodiments of a steam turbine of the present invention will be described in detail with reference to the drawings.
As shown in FIG. 1, the steam turbine 1 according to the present embodiment is rotatably provided inside a casing 10, a regulating valve 20 that adjusts the amount and pressure of steam S flowing into the casing 10, and the casing 10. A rotating shaft 30 that transmits power to a machine (not shown) such as a generator, a bearing portion 40 that supports the rotating shaft 30, an outer shroud 50 fixed to the inner surface of the casing 10, and the outer shroud 50. A stationary blade 60 held by the stationary blade 60, an inner shroud 70 fixed to the stationary blade 60, and a moving blade 80 provided on the rotary shaft 30 on the downstream side of the stationary blade 60.

The casing 10 is configured to form a space inside thereof, and hermetically seals the inside space.
A plurality of regulating valves 20 are attached to the inside of the casing 10, and each includes a regulating valve chamber 21 into which steam S flows from a boiler (not shown), a valve body 22, a valve seat 23, and a steam chamber 24. Yes. In this regulating valve 20, the steam passage is opened by separating the valve body 22 from the valve seat 23, and the steam S flows into the internal space of the casing 10 through the steam chamber 24.

The rotating shaft 30 includes a shaft main body 31 and a plurality of disks 32 provided so as to project annularly from the outer periphery of the shaft main body 31 outward in the radial direction. The rotating shaft 30 transmits rotational energy to a machine such as a generator (not shown).
The bearing portion 40 includes a journal bearing device 41 and a thrust bearing device 42, and supports the rotary shaft 30 inserted into the casing 10 so as to be rotatable outside the casing 10.

The outer shroud 50 is fixed to the inner wall surface of the casing 10 and has a ring shape centered on the axis of the rotating shaft 30 (hereinafter simply referred to as the axis) as shown in FIGS. 1 and 2. A plurality (six in this embodiment) of outer shrouds 50 are provided at intervals in the axial direction.
In the present embodiment, the radially inner surface 51 of the outer shroud 50 is inclined toward the radially outer side toward the downstream side, and a moving blade, which will be described later, is disposed on an extension line on the downstream side of the inclination. The tip of 80 (end part on the outside in the radial direction) is located.

  As shown in FIG. 1 and FIG. 2, the stationary blade 60 has a proximal end that is a radially outer end attached to the outer shroud 50, and extends radially inward from the outer shroud 50. The wing shape is made. The stationary blade 60 is formed so that the dimension in the axial direction becomes smaller toward the inner side in the radial direction. Note that the surface of the stationary blade 60 facing the one side in the circumferential direction (front side in FIG. 2) is a dorsal side 61 (negative pressure surface) having a convex curved surface, and the other side in the circumferential direction (in FIG. 2). The surface facing the back side of the paper surface is a ventral side 62 (positive pressure surface) having a concave curved surface.

  A plurality of stationary blades 60 are provided at intervals in the circumferential direction of the rotating shaft 30 and the outer shroud 50, that is, a plurality of stationary blades 60 are arranged radially. Thereby, the base ends of the stationary blades 60 arranged in the circumferential direction are connected to each other by the outer shroud 50.

  A plurality of stationary blades 60 arranged in the circumferential direction in this manner constitute a group of annular stationary blades that radiate so as to surround the rotating shaft 30 from the outer circumferential side. The annular stationary blade group is fixed to each of the plurality of outer shrouds 50, and is provided in the same number (six in this embodiment) as the outer shrouds 50 apart from each other in the axial direction.

  The inner shroud 70 is an annular member centering on the axis similar to the outer shroud 50, and the distal end of the stationary blade 60 extending from the outer shroud 50, that is, the radially inner end of the stationary blade 60. It is fixed to the part. That is, the inner shroud 70 connects the tips, which are the radially inner ends of the stationary blades 60 arranged in the circumferential direction, in the circumferential direction.

  The rotating shaft 30 is inserted inside the inner shroud 70, and a gap is formed between the inner shroud 70 and the rotating shaft 30. As a result, the rotating shaft 30 rotates about the axis without being interfered by the inner shroud 70.

  The base end portion of the moving blade 80 is attached to the outer peripheral portion of the disk 32 of the rotating shaft 30 and extends radially outward from the disk 32. The rotor blade 80 is formed so that the dimension in the axial direction of the rotary shaft 30 becomes smaller toward the outside in the radial direction. Further, a plurality of moving blades 80 are attached to the outer peripheral portion of the disk 32 at intervals in the circumferential direction of the rotating shaft 30, that is, a plurality of moving blades 80 are arranged radially. Thus, the moving blade 80 constitutes an annular moving blade group so as to surround the rotating shaft 30.

  This annular blade group is provided downstream of each annular stator group so as to form a pair with the annular stator group, that is, the same number (six in this embodiment) as the annular stator groups are arranged. Has been. That is, the steam turbine 1 of the present embodiment is a six-stage steam turbine 1 in which six stages including an annular stationary blade group and an annular moving blade group are arranged.

Here, as shown in FIG. 3, a plurality of protrusions 90 are formed on the back side 61, which is the back side of the stationary blade 60, and the plurality of protrusions 90 are regularly arranged without gaps. It is scaly.
As shown in FIGS. 4 and 5, the protrusion 90 includes a slope 91 in which the amount of protrusion from the surface of the stationary blade 60 increases toward the downstream side of the steam, and a cliff 92 that forms an acute angle with the slope 91. Have. The slope 91 is a gentle slope that intersects the surface of the stationary blade 60 at an angle of about 20 °. The angle of the inclined surface 91 with respect to the surface of the stationary blade 60 is not limited to this, and can be appropriately changed according to the specifications of the steam turbine 1.
The cliff 92 is a steep slope that rises substantially perpendicular to the surface of the stationary blade 60, and is formed to make an acute angle with the slope 91.

  Further, the protrusion 90 is formed so that the width of the inclined surface 91 (the width in the vertical direction in FIG. 4) becomes narrower toward the downstream side of the steam. That is, the shape of the protrusion 90 viewed from the direction perpendicular to the surface of the stationary blade 60 is an isosceles triangle shape whose bottom is along the height direction of the stationary blade (vertical direction in FIG. 4). Hereinafter, a line corresponding to the bottom side is referred to as a bottom line 93. In addition, the equilateral sides in the isosceles triangle are curved so as to protrude outward from the triangle. Hereinafter, a line corresponding to this equal side and intersecting the slope and the cliff is called a ridgeline 94. The intersection of the ridge lines 94 is referred to as a protrusion tip 95.

  Although the specific dimension of the protrusion 90 is set according to the specification of the steam turbine 1, for example, the height of the protrusion tip from the stationary blade surface is about 12 μm.

  As described above, the plurality of protrusions 90 are regularly arranged and have a scale shape. That is, they are formed so as to be adjacent to each other at equal intervals in the width direction of the stationary blade 60 (left-right direction in FIG. 4) and the height direction of the stationary blade 60. In other words, the plurality of protrusions 90 are adjacent to each other in one direction toward the downstream side of the steam (the left-right direction in FIG. 4) and in a direction orthogonal to the one direction toward the downstream side of the steam (up and down direction in FIG. 4). It is formed as follows.

  Specifically, the bottom lines 93 adjacent to each other in the height direction of the stationary blade 60 are arranged on a straight line without any gap. Further, the protrusions 90 adjacent in the width direction of the stationary blade 60 are formed so as to be shifted in the height direction of the stationary blade 60 with respect to the adjacent protrusion 90. In other words, the plurality of protrusions 90 are formed so as to be shifted in a direction perpendicular to the one direction with respect to the protrusion 90 adjacent in one direction toward the downstream side of the steam. The shift width is the length of the bottom line 93 of the protrusion 90, that is, ½ of the width of the protrusion 90, whereby the protrusion 90 is arranged in a scale shape.

  The range in the width direction of the stationary blade 60 on which the scale-like protrusion 90 is formed is the range X from the leading edge 63 of the stationary blade 60 to 70% of the width of the stationary blade 60 on the suction surface 61 of the stationary blade 60. is there. The range in the height direction of the stationary blade 60 on which the protrusion 90 is formed is the range Y from the blade bottom 64 on the outer peripheral side of the stationary blade 60 to 70% of the height of the stationary blade.

Next, an analysis for determining the formation positions of the plurality of protrusions 90 formed on the stationary blade 60 in the present embodiment will be described.
The erosion and braking effect that occurs in the moving blade 80 is generated when water veins flowing on the surface of the stationary blade 60 adjacent to and upstream of the moving blade 80 are scattered from the trailing edge 65 of the stationary blade 60 by the steam flow. Caused by water droplets. The water vein on the surface of the stationary blade 60 adheres to the stationary blade 60 due to the water vein flowing on the surface of the moving blade 80 located adjacent to and upstream of the stationary blade 60 from the moving blade 80 by the steam flow. And then agglomerate.

  Of the water droplets scattered from the moving blades 80 in the wet steam region of the steam turbine 1, the fine water droplets having a diameter of about several μm smaller than 50 μm have a small mass and flow downstream along the steam flow. However, it does not adhere to the stationary blade 60 located on the downstream side. Medium-sized water droplets having a diameter of about 50 to 100 μm adhere to the stationary blade 60 adjacent to the moving blade 80 and located downstream, and can aggregate on the surface of the stationary blade 60 to form a water vein. Coarse water droplets having a diameter of about several hundreds of micrometers larger than the diameter of 100 μm have a large mass and are greatly affected by the centrifugal force due to the rotation of the moving blades 80, so that they flow toward the casing 10 on the outer peripheral side of the stationary blades 60 It does not adhere to the stationary blade 60 located adjacent to 80 and located downstream.

  As shown in FIG. 6, regarding the flow of steam and water droplets in the steam turbine 1 with respect to the moving blade 80, the steam flows at a high speed in the direction of the outlet of the moving blade 80 (steam vector α <b> 1), and the water droplets are slow in the same direction as the steam. Flows at a velocity (water droplet vector β1). Since the mass of the water droplet is larger than that of the steam, the speed of the water droplet is slower than that of the steam.

  With respect to the flow of steam and water droplets with respect to the stationary blade 60 located on the downstream side of the moving blade 80, inertia due to the rotation of the moving blade 80 is taken into consideration (moving blade vector γ). Since the water droplet has a mass larger than that of the vapor, the velocity is slow, and the inertia due to the rotation of the moving blade 80 greatly affects the direction in which the water droplet flows. Therefore, the steam flows toward the ventral side 62 of the stationary blade 60 positioned on the downstream side (steam vector α2), and the water droplet flows toward the back side 61 of the stationary blade 60 positioned on the downstream side (water droplet vector β2).

  In other words, medium-sized water droplets having a diameter of about 50 to 100 μm out of the water droplets scattered from the moving blades 80 are attached to the back side 61 of the stationary blade 60 adjacent to the moving blades 80 and located downstream.

  As shown in FIG. 7, the water droplet adhesion range 100 when a water droplet having a diameter of 50 μm adheres to the back side 61 of the stationary blade 60 is within 70% of the blade width W from the front edge portion 63 of the stationary blade 60 and the outer periphery. It is within 70% of the blade height H from the blade bottom 64 which is the side. The blade width W is the length in the axial direction when the stationary blade 60 is viewed from the direction orthogonal to the axis, and the blade height H is the radial length of the stationary blade 60. 7 and 8 are views of the surface of the back side 61 of the stationary blade 60 in FIG. 6 as viewed from the direction orthogonal to the axis.

  As shown in FIG. 8, the water droplet adhesion range 100 when a water droplet having a diameter of 100 μm adheres to the back side 61 of the stationary blade 60 is within 50% of the blade width W from the front edge portion 63 of the stationary blade 60 and the outer periphery. It is within 50% of the blade height H from the blade bottom 64 which is the side.

  That is, medium-sized water droplets having a diameter of about 50 to 100 μm are in the range from the leading edge 63 on the back side 61 of the stationary blade 60 to 50 to 70% of the blade width W, and from the blade bottom 64 on the outer peripheral side to the blade. It adheres within the range of 50 to 70% of the height H, that is, within the water droplet adhesion range. Therefore, the projection forming ranges X and Y are determined thereby.

  In the steam turbine 1 according to the present embodiment, water droplets having a diameter of about 50 to 100 μm are generated evenly in the stage where the stationary blade 60 is installed, and therefore the leading edge of the stationary blade 60 on the suction surface 61 of the stationary blade 60. Protrusions 90 were formed in a range X from the portion 63 to 70% of the width of the stationary blade 60 and a range Y from the blade bottom 64 on the outer peripheral side of the stationary blade 60 to 70% of the height of the stationary blade. For example, when there are not many water droplets having a diameter of about 50 μm and many water droplets having a diameter of about 100 μm are generated, the width of the stationary blade 60 from the leading edge 63 of the stationary blade 60 on the suction surface 61 of the stationary blade 60 is increased. The protrusion 90 may be formed in a range X up to 50% and a range Y from the blade bottom 64 on the outer peripheral side of the stationary blade 60 to 50% of the height of the stationary blade.

  The size of the water droplets and the water droplet adhesion range 100 that are likely to be generated vary depending on various conditions. Therefore, it is preferable to select the projection forming ranges X and Y according to the water droplet scattering state. That is, the range X in the width direction of the stationary blade 60 on which the protrusion 90 is formed is the range X from 50% to 70% of the width of the stationary blade 60 from the leading edge 63 of the stationary blade 60 on the suction surface 61. It is preferable to select the range Y in the height direction of the stationary blade 60 where the projection 90 is formed from the range Y from the blade bottom 64 to 50% to 70% of the height of the stationary blade.

Next, the operation of the steam turbine 1 of the present embodiment will be described.
The steam turbine 1 operates by introducing steam S from the boiler into the casing 10 via the regulating valve 20. That is, the steam S flowing into the casing 10 passes through the flow path between the stationary blades 60 in each stage and is supplied to the moving blades 80. When the fluid pressure of the steam S acts on the moving blade 80, the rotating shaft 30 rotates with the rotation of the moving blade 80. As a result, the machine connected to the rotating shaft 30 is driven.

  The steam sent to the steam turbine 1 of the present embodiment is superheated steam, and the degree of superheat is reduced and becomes dry saturated as it expands with a decrease in pressure, and further expands to become wet steam containing moisture.

  In the low-pressure stage that is a wet steam region in the steam turbine 1 of the present embodiment, among the water droplets in the wet steam or the water droplets scattered from the moving blades 80, the fine water droplets are flowed downstream together with the steam because they are light and coarse. Since the water droplets are heavy, they receive a large centrifugal force and scatter to the casing 10 side, and the intermediate water droplets are adjacent to the moving blades 80 due to the inertia of the steam flow and the rotation of the moving blades 80 and located on the downstream side. 60 reaches the range of 70% of the blade width from the leading edge 63 on the back side 61, and reaches the range of 70% of the blade height from the blade bottom 64 on the outer peripheral side of the stationary blade 60 by the centrifugal force acting on the outer peripheral side. .

  As shown in FIGS. 4 and 5, the water droplets that have reached the surface of the stationary blade 60 flow downstream on the slope 91 of the protrusion 90. When the water droplet reaches the ridgeline 94, the waterdrop flows downstream along the ridgeline 94. When the protrusion tip 95 is reached, the protrusion tip 95 scatters into the vapor and flows downstream as fine water droplets having a diameter smaller than 50 μm.

  According to the above embodiment, when water droplets scattered from the moving blade 80 adhere to the back side 61 of the stationary blade 60, the water droplets flow on the inclined surface 91 of the protrusion 90 toward the downstream side of the steam, and the inclined surface 91 and the cliff 92. It is scattered into the steam at the projection tip 95 which is the end of the ridgeline 94 formed by. In other words, the protrusions 90 formed on the stationary blade 60 can cause water droplets that can collide with the moving blade 80 located on the downstream side of the stationary blade 60 to be scattered without being coarsened. This leads to a reduction in the erosion phenomenon and the braking effect that occur in the moving blade 80.

  Further, since the formation range of the projection 90 is a part of the back side 61 of the stationary blade 60, water droplets that can collide with the moving blade 80 are scattered while minimizing the deterioration of the aerodynamic characteristics due to the projection 90. be able to.

  Further, since the protrusions 90 are formed without gaps, aggregation of water droplets adhering to the surface of the stationary blade 60 can be suppressed.

  Furthermore, since the protrusions 90 are regularly arranged in a scale shape, water droplets scattered from the inclined surfaces 91 of the protrusions 90 are scattered in the vapor in a well-balanced manner, so that aggregation of water droplets in the vapor can be suppressed.

The embodiment of the present invention has been described above, but the present invention is not limited to this, and can be appropriately changed without departing from the technical idea of the present invention.
For example, the protrusions 90 do not necessarily have to be arranged in a scale shape, and the density thereof is adjusted according to the state of the erosion phenomenon in the rotor blade 80.
Further, the shape of the protrusion 90 is not limited to the shape as shown in FIG. 4. For example, the shape of the ridge line 94 may be curved so as to protrude inside the triangle formed by the bottom line 93.
Further, the protrusion 90 may be formed on the surface of the shroud, for example, in addition to the back side 61 of the stationary blade 60.

DESCRIPTION OF SYMBOLS 1 Steam turbine 30 Rotating shaft 60 Stator blade 61 Back side 63 Front edge 80 Rotor blade 90 Protrusion 91 Slope 92 Cliff surface

Claims (4)

A rotor blade that rotates a rotating shaft by the fluid pressure of steam;
A plurality of blades spaced apart from each other in the circumferential direction of the rotating shaft on the radially outer side of the rotating shaft, and including a stationary blade that forms the flow of the steam to the moving blade,
A plurality of protrusions are formed in a range from the front edge of the stationary blade on the back side of the stationary blade to 50% to 70% of the blade width of the stationary blade,
The protrusion has a slope that increases as the amount of protrusion from the surface of the stationary blade increases toward the downstream side of the steam, and a cliff that forms an acute angle with the slope,
The steam turbine according to claim 1, wherein a width of the slope is formed so as to become narrower toward the downstream side.   2. The steam turbine according to claim 1, wherein the protrusion is formed in a range from 50% to 70% of a height of the stationary blade from an outer peripheral side of the stationary blade. 3.   The plurality of protrusions are formed so as to be adjacent to each other in one direction toward the downstream side and to be adjacent to each other in a direction orthogonal to the one direction. 2. The steam turbine according to 2.   The steam turbine according to claim 3, wherein the plurality of protrusions are formed so as to be shifted in a direction orthogonal to the one direction with respect to the protrusions adjacent in the one direction.

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