steam turbine

Abstract

To improve efficiently while mixing parallel blades and three-dimensional blades.SOLUTION: A steam turbine is equipped with a rotor shaft, a plurality of rotor vane rows, a casing, and a plurality of stator vane rows. The plurality of rotor vane rows is equipped with a plurality of upstream rotor vane rows disposed in an upstream area in a main channel, and a plurality of downstream rotor vane rows disposed in a downstream area with respect to the upstream area in the main channel. The upstream rotor vane row has a plurality of parallel blades, and the downstream vane row has a plurality of stator vanes disposed at intervals in a circumferential direction. An outer peripheral surface of the rotor shaft is formed so as to gradually increase a diameter in parallel with an axis or outward in a diametrical direction toward a second side in an axial direction with respect to the axis, on a cross section parallel with the axis in an area where the three-dimensional blades are disposed in the downstream area.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a steam turbine.

Background Art

[0002] A steam turbine includes a rotor (turbine rotor) disposed in a casing, a moving blade row provided on the outer side in the radial direction of the rotor, a diaphragm provided on the inner side in the radial direction of the casing, and a stationary blade row supported on the inner side in the radial direction of the diaphragm (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the steam turbine as described above, there is a structure in which an impulse stage having parallel blades is formed in the upstream moving blade row and a reaction stage having three-dimensional blades is formed in the downstream moving blade row to improve efficiency. Generally, although the reaction blades can improve efficiency, a design considering a large axial thrust load and a large leak of the moving blades is required, and a complex structure is required. On the other hand, the impulse blades are difficult to achieve higher efficiency than the reaction blades, but can have a simple structure. Therefore, in such a steam turbine, in order to improve the ease of design and efficiency, there is always a demand for further improvement in efficiency in a state where parallel blades (impulse blades) and three-dimensional blades (reaction blades) are mixed.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to provide a steam turbine capable of improving efficiency while mixing parallel blades and three-dimensional blades.

Means for Solving the Problems

[0006] To solve the above problems, the steam turbine according to the present disclosure comprises a rotor shaft that can rotate about an axis, a plurality of rotor blade rows fixed to the outside of the rotor shaft in the radial direction with respect to the axis and spaced apart in the axial direction extending from the axis, a casing that covers the rotor shaft and the plurality of rotor blade rows from the outside in the radial direction and has a main flow path formed inside through which steam can flow, and a plurality of stator blade rows fixed to the inside of the casing in the radial direction and arranged on the first side in the axial direction with respect to each of the plurality of rotor blade rows, wherein the plurality of rotor blade rows include a plurality of upflow blade rows arranged in the upstream region of the main flow path and The rotor comprises a plurality of downward-flowing blade rows located in a downstream region situated on a second side in the axial direction relative to the upstream region, the upper-flowing blade row having a plurality of parallel blades spaced apart in the circumferential direction around the axis, the lower-flowing blade row having a plurality of three-dimensional blades spaced apart in the circumferential direction, the stator blade row having a plurality of stator blades spaced apart in the circumferential direction, and the outer peripheral surface facing radially outward on the rotor axis is formed in the region where the three-dimensional blades are arranged in the downstream region, in a cross section parallel to the axis, so as to be parallel to the axis or gradually widening radially outward toward a second side in the axial direction relative to the axis. In the downstream region, the positions of the radially outer three-dimensional wingtips of the multiple three-dimensional wings are formed to expand radially outward from the downward-flowing wing row located on the first axial side toward the downward-flowing wing row located on the second axial side, and the amount of radial outward change in the position of the three-dimensional wingtips in the two closest pairs of downward-flowing wing rows, including the downward-flowing wing row located furthest to the first axial side, is greater than the amount of radial outward change in the position of the three-dimensional wingtips in the closest pair of downward-flowing wing rows, including the downward-flowing wing row located furthest to the second axial side. . [Effects of the Invention]

[0007] The steam turbine of this disclosure makes it possible to improve efficiency while using a mixture of parallel blades (impulse blades) and three-dimensional blades (reaction blades). [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram showing the overall configuration of the steam turbine according to this embodiment. [Figure 2] This is a cross-sectional view showing the rotor blade row and stator blade row of the steam turbine described above. [Figure 3] This figure shows the change in throat width in the second-to-last row of stator blades in the axial direction of the steam turbine described above. [Figure 4]This is a cross-sectional view showing the configuration around the diffuser installed in the above-mentioned steam turbine. [Modes for carrying out the invention]

[0009] The following describes embodiments for implementing the steam turbine according to this disclosure with reference to the attached drawings. However, this disclosure is not limited to these embodiments.

[0010] (Steam turbine configuration) As shown in Figure 1, the steam turbine 1 of this embodiment has a rotor 20 that rotates about an axis Ar, a casing 10 that rotatably covers the rotor 20, and a plurality of stator blade rows 41.

[0011] For the purposes of the following explanation, the direction in which the axis Ar extends will be referred to as the axial direction Da. The first side of the axial direction Da will be the upstream side (one side) Dau, and the second side of the axial direction Da will be the downstream side (the other side) Dad. Furthermore, the radial direction of the rotor 20 with respect to the axis Ar will simply be referred to as the radial direction Dr. The side of this radial direction Dr that approaches the axis Ar will be referred to as the inner side Dri of the radial direction Dr, and the side of this radial direction Dr opposite to the inner side Dri will be referred to as the outer side Dro of the radial direction Dr. Furthermore, the circumferential direction of the rotor 20 centered on the axis Ar will simply be referred to as the circumferential direction Dc.

[0012] As shown in Figures 1 and 2, the rotor 20 has a rotor shaft 21 and a plurality of rotor blade rows 31.

[0013] The rotor shaft 21 rotates about axis Ar relative to the casing 10. The rotor shaft 21 has a core portion 22 and a plurality of disk portions 23. The core portion 22 is formed in a cylindrical shape about axis Ar and extends in the axial direction Da. The disk portions 23 extend outward from the core portion 22 in the radial direction Dr. The disk portions 23 are spaced apart from each other in the axial direction Da. The disk portions 23 are arranged for each of the plurality of rotor blade rows 31.

[0014] The rotor blade rows 31 are fixed to the outside of the rotor shaft 21 in the radial direction Dr. Specifically, as shown in Figure 2, the rotor blade rows 31 are fixed to the outside Dro of the disk portion 23, which is the outer circumference of the rotor shaft 21, in the radial direction Dr. Multiple rotor blade rows 31 are arranged at intervals in the axial direction Da of the rotor shaft 21. In this embodiment, for example, there are a total of seven rotor blade rows 31, from the rotor blade row 31A located at the upstreammost Dau in the axial direction Da to the rotor blade row 31G located at the downstreammost Dad in the axial direction Da. Each rotor blade row 31 has multiple rotor blades 32 arranged in the circumferential direction Dc. Each of the multiple rotor blades 32 is attached to the disk portion 23. Each rotor blade 32 has a platform 32a, a blade body 32b, and a shroud 32c.

[0015] Platform 32a is positioned radially outward (Dr) relative to the disk portion 23. Platform 32a extends in the circumferential direction (Dc). The platforms 32a of the multiple rotor blades 32 are aligned in the circumferential direction (Dc) to form a cylindrical shape centered on the axis (Ar).

[0016] The wing body 32b extends radially outward from the platform 32a. The wing body 32b is integrally formed with the platform 32a and the shroud 32c. The wing body 32b is located within the main flow path 15, which will be described later. When viewed from the outside radially outward, the wing body 32b has an airfoil cross-section.

[0017] The shroud 32c is connected to the outer end of the wing body 32b in the radial direction Dr. That is, in the radial direction Dr, the shroud 32c is positioned on the opposite side of the platform 32a from the wing body 32b. The shroud 32c extends in the circumferential direction Dc. The shrouds 32c of multiple control surfaces 32 are aligned in the circumferential direction Dc to form a cylindrical shape as a whole.

[0018] The casing 10 is formed to cover the rotor shaft 21 and the plurality of moving blade rows 31 from the outside Dro in the radial direction Dr. Inside the casing 10, a nozzle chamber 11 into which steam S flows from the outside, a flow path chamber 12 through which the steam S from the nozzle chamber 11 flows, and an exhaust chamber 13 that discharges the steam S flowing from the flow path chamber 12 are formed. Between the nozzle chamber 11 and the flow path chamber 12, the moving blade row 31A and the stationary blade row 41A of the first stage 50A, which are the most upstream Dau among the plurality of moving blade rows 31 and stationary blade rows 41, are arranged. In other words, the inside of the casing 10 is partitioned into the nozzle chamber 11 and the flow path chamber 12 by the moving blade row 31A and the stationary blade row 41A that are the most upstream Dau. The nozzle chamber 11, the flow path chamber 12, and the exhaust chamber 13 constitute a main flow path 15 through which high-pressure steam S flows.

[0019] In the main flow path 15, the high-pressure steam S flows while gradually decreasing in pressure from the upstream side Dau toward the downstream side Dad. The main flow path 15 is annular around the rotor shaft 21. The main flow path 15 extends in the axial direction Da across the plurality of moving blade rows 31 and stationary blade rows 41. The main flow path 15 is partially formed by an annular space in which stationary blades 42, which will be described later, are arranged.

[0020] The stationary blade row 41 is fixed to the inner side Dri of the casing 10 in the radial direction Dr. It includes a plurality of stationary blade rows 41. The stationary blade rows 41 are arranged at intervals in the axial direction Da. In this embodiment, a total of seven stationary blade rows 41 are arranged, for example, from the stationary blade row 41A located most upstream Dau in the axial direction Da to the stationary blade row 41G located most downstream Dad in the axial direction Da. Each stationary blade row 41 is arranged side by side upstream Dau with respect to one corresponding moving blade row 31.

[0021] The stationary blade row 41 has stationary blades 42, an outer ring 43, and an inner ring 46. A plurality of stationary blades 42 are arranged at intervals in the circumferential direction Dc. The outer ring 43 is arranged on the outer side Dro in the radial direction Dr with respect to the plurality of stationary blades 42. The outer ring 43 is formed in an annular shape centered on the axis Ar. The inner ring 46 is arranged on the inner side Dri in the radial direction Dr with respect to the plurality of stationary blades 42. The inner ring 46 is formed in an annular shape centered on the axis Ar. That is, the plurality of stationary blades 42 are arranged between the outer ring 43 and the inner ring 46. The stationary blades 42 are fixed to the outer ring 43 and the inner ring 46.

[0022] One stage 50 is formed by each set of a moving blade row 31 and one stationary blade row 41 arranged upstream Dau of this moving blade row 31. In the steam turbine 1 of the present embodiment, a stationary blade row 41 is arranged for each of the seven moving blade rows 31 in FIG. 2. Therefore, it includes seven stages 50. That is, the steam turbine 1 of the present embodiment includes moving blade rows 31 and stationary blade rows 41 of the first stage 50A, the second stage 50B, the third stage 50C, the fourth stage 50D, the fifth stage 50E, the sixth stage 50F, and the seventh stage 50G in order from the upstream side Dau to the downstream side Dad.

[0023] Further, in the steam turbine 1 of the present embodiment, among the plurality of stages 50, the first stage 50A to the fourth stage 50D arranged on the upstream side Dau in the axial direction Da form a high-pressure stage 50x. Also, among the plurality of stages 50, the fifth stage 50E to the seventh stage 50G (three stages from the most downstream stage) arranged on the downstream side Dad in the axial direction Da with respect to the high-pressure stage 50x form a low-pressure stage 50y.

[0024] Here, the region where the high-pressure stage 50x is arranged in the main flow path 15 is referred to as the upstream region P1. Also, in the main flow path 15, the region located on the downstream side Dad in the axial direction Da with respect to the upstream region P1 and where the low-pressure stage 50y is arranged is referred to as the downstream region P2.

[0025] The multiple rotor blade rows 31 comprise multiple upper-flow blade rows 31U located in the upstream region P1 and multiple lower-flow blade rows 31L located in the downstream region P2. In this embodiment, the multiple upper-flow blade rows 31U constitute an impulse stage and form part of the high-pressure stage 50x. The multiple upper-flow blade rows 31U are provided from the rotor blade row 31A of the first stage 50A to the rotor blade row 31D of the fourth stage 50D. That is, the rotor blade row 31A of the first stage 50A is the upper-flow blade row 31U located furthest upstream Dau in the axial direction Da among the multiple upper-flow blade rows 31U. Also, the rotor blade row 31D of the fourth stage 50D is the upper-flow blade row 31U located furthest downstream Dad in the axial direction Da.

[0026] Furthermore, the multiple downward-flowing blade rows 31L are reaction stages and constitute part of the low-pressure stage 50y. In this embodiment, the multiple downward-flowing blade rows 31L are provided from the blade row 31E of the fifth stage 50E to the blade row 31G of the seventh stage 50G. That is, the blade row 31E of the fifth stage 50E is the downward-flowing blade row 31L located furthest upstream Dau in the axial direction Da among the multiple downward-flowing blade rows 31L. Also, the blade row 31G of the seventh stage 50G is the downward-flowing blade row 31L located furthest downstream Dad in the axial direction Da.

[0027] Each upper flow blade row 31U has a parallel blade 35 as the blade body 32b. The parallel blade 35 has a cross-section such that the distance between the blade surface facing one side of the circumferential direction Dc (pressure surface) and the blade surface facing the other side of the circumferential direction Dc (negative pressure surface) is constant in the blade height direction (radial direction Dr). In other words, the cross-section of the parallel blade 35 is constant in the blade height direction. The parallel blade 35 is a so-called two-dimensional blade. The parallel blade 35 of the upper flow blade row 31U is an impulse blade with a reaction degree R of, for example, 25% or more and less than 40%. In each upper flow blade row 31U, multiple parallel blades 35 are arranged at intervals in the circumferential direction Dc.

[0028] Here, we will explain the reaction degree R. The reaction degree R is the ratio of the heat drop at the rotor blade 32 in stage 50 to the heat drop at stage 50. In other words, the reaction degree R is the proportion of the change in static enthalpy at the rotor blade 32 to the total change in enthalpy per stage 50.

[0029] Therefore, the reaction degree R in the second stage 50B is expressed by the following formula, where H1 is the enthalpy of the steam S upstream of the second stage stator blade row 41B, H2 is the enthalpy of the steam S downstream of the second stage stator blade row 41B and upstream of the second stage rotor blade row 31B, and H3 is the enthalpy downstream of the second stage rotor blade row 31B. R = (H2 - H3) / (H1 - H3)

[0030] When the reaction force R is 0, there is no pressure change at the rotor blade 32. On the other hand, when the reaction force R is not 0, there is a pressure drop at the rotor blade 32, while the flow velocity of the steam S at the rotor blade 32 increases. Therefore, when the reaction force R is not 0, the steam S expands as it passes through the rotor blade 32. The reaction force generated by this expansion acts on the rotor blade 32. When the reaction force R is 0, only the impulse action of the steam S is the work done by the steam S on the rotor blade 32, but when the reaction force R is not 0, in addition to the impulse action of the steam S, the reaction force is also the work done by the steam S on the rotor blade 32.

[0031] The outer circumferential surface 21f of the rotor shaft 21, facing outward in the radial direction Dr, is formed in the region where the rotor blades 32 (parallel blades 35) are arranged in the upstream region P1, in a cross section parallel to the axis Ar, so as to be parallel to the axis Ar, or to gradually widen in the radial direction Dr outward towards Dad, downstream in the axial direction Da relative to the axis Ar. In this embodiment, the case in which the outer circumferential surface 21f is formed parallel to the axis Ar in a cross section parallel to the axis Ar in the region where the parallel blades 35 are arranged in the upstream region P1 is illustrated.

[0032] Here, the outer circumferential surface 21f of the rotor shaft 21 is the surface to which the rotor blades 32 and stator blades 42 are connected. In other words, the outer circumferential surface 21f of the rotor shaft 21 is the outer circumferential surface of the disk portion 23 that contacts the inner circumferential surface of the platform 32a, and the outer circumferential surface of the inner ring 46.

[0033] As a result, in the upstream region P1, the parallel wing bases 35b are positioned at the same location in the radial direction Dr in the rotor blade rows 31A of the first stage 50A to the fourth stage 50D (multiple upward-flowing blade rows 31U). Here, the parallel wing base 35b is the region of the parallel wing 35 that includes the inner Dri end of the parallel wing 35 in the radial direction Dr, and is close to the outer circumferential surface 21f of the rotor shaft 21. More specifically, the parallel wing base 35b is the region approximately 30% of the wing length Hb (the total wing height from the inner circumferential surface of the platform 32a to the tip of the shroud 32c) from the outer circumferential surface of the platform 32a.

[0034] Furthermore, in the rotor blade rows 31A of the first stage 50A to the rotor blade rows 31D of the fourth stage 50D (multiple upward-flowing rotor blade rows 31U), the length of the rotor blades 32 in the radial direction Dr gradually increases from the parallel blades 35 of the rotor blade row 31A on the upstream side Dau in the axial direction Da to the parallel blades 35 of the rotor blade row 31C on the downstream side Da in the axial direction Da.

[0035] As a result, in multiple upward-flowing blade rows 31U, the parallel blade tips 35s are positioned such that their radial position Dr gradually expands outward towards Dro from the first stage blade row 31A to the fourth stage blade row 31D. Here, the parallel blade tip 35s is the region of the parallel blade 35 that includes the outer end of the parallel blade 35 in the radial direction Dr, and is a region close to the inner surface of the casing 10. More specifically, the parallel blade tip 35s is a region of about 30% of the blade length Hb from the inner surface of the shroud 32c.

[0036] On the other hand, unlike the upper flow blade row 31U, the lower flow blade row 31L has a three-dimensional blade 37 as the blade body 32b. The three-dimensional blade 37 is formed with a radial length Dr longer than that of the parallel blade 35. The three-dimensional blade 37 is curved in three dimensions such that the blade surface facing one side of the circumferential direction Dc (pressure surface) and the blade surface facing the other side of the circumferential direction Dc (negative pressure surface) twist as they advance in the blade height direction (radial direction Dr). In other words, the cross-section of the three-dimensional blade 37 is not constant in the blade height direction, and its shape and cross-sectional area change. The three-dimensional blade 37 of the lower flow blade row 31L is a reaction blade with a reaction degree R of, for example, 45% to 60%.

[0037] Furthermore, of the multiple downflow blade rows 31L, at least the three-dimensional blades 37 of the final stage (seventh stage 50G) blade row 31G have transonic airfoils. Transonic airfoils have a high limiting speed at which supersonic flow that degrades performance due to shock waves and separation occurs on the blade surface, and are less prone to a sudden increase in drag due to the generation of shock waves. Specifically, transonic airfoils are airfoils with a Mach number (a dimensionless quantity determined by the ratio of the flow velocity of the vapor S flowing out of the blade to the speed of sound) of approximately 0.8 to 1.5. In this embodiment, all three-dimensional blades 37 of the downflow blade rows 31L have transonic airfoils.

[0038] The outer circumferential surface 21f of the rotor shaft 21 is formed in the region where the rotor blades 32 (three-dimensional blades 37) are arranged in the downstream region P2, with a cross section parallel to the axis Ar, so as to be parallel to the axis Ar, or to gradually widen radially outward in the direction of Dr towards Da, downstream of the axis Ar in the direction of Da.

[0039] In this embodiment, the outer circumferential surface 21f is formed parallel to the axis Ar in a cross-section parallel to the axis Ar in the region where the three-dimensional blade 37 is arranged in the downstream region P2. As a result, in the downstream region P2, the three-dimensional blade base end 37b is located at the same position in the radial direction Dr from the rotor blade row 31E of the fifth stage 50E to the rotor blade row 31G of the seventh stage 50G (multiple downward flow blade rows 31L). Here, the three-dimensional blade base end 37b is the region of the three-dimensional blade 37 that includes the inner Dri end in the radial direction Dr of the three-dimensional blade 37, and is a region close to the outer circumferential surface 21f of the rotor axis 21. More specifically, the three-dimensional blade base end 37b is a region of about 30% from the outer circumferential surface of the platform 32a with respect to the blade length Hb.

[0040] Therefore, in this embodiment, in the entire region where the rotor blade row 31 is arranged in the main flow path 15 including the upstream region P1 and the downstream region P2, the outer peripheral surface 21f is not formed in such a way that it does not contract toward the inner Dri in the radial direction Dr toward the downstream Da in the axial direction Da (i.e., it does not approach the axis Ar). In other words, the three-dimensional blade base end 37b of the rotor blade row 31E of the fifth stage 50E is located furthest in the inner Dri in the radial direction Dr among the three-dimensional blade base end 37b of the multiple downward flow blade rows 31L.

[0041] Furthermore, in the rotor blade rows 31E of the fifth stage 50E to the rotor blade rows 31G of the seventh stage 50G (multiple downward-flowing rotor blade rows 31L), the length of the rotor blades 32 in the radial direction Dr gradually increases from the three-dimensional blades 37 of the rotor blade row 31F upstream of the axial direction Da Dau to the three-dimensional blades 37 of the rotor blade row 31G downstream of the axial direction Da Da.

[0042] As a result, in multiple downward-flowing blade rows 31L, the three-dimensional blade tip 37s is positioned such that its position in the radial direction Dr gradually expands outward towards Dro, from the fifth stage blade row 31E to the seventh stage blade row 31G. Here, the three-dimensional blade tip 37s is the region of the three-dimensional blade 37 that includes the outer end of the three-dimensional blade 37 in the radial direction Dr, and is a region close to the inner circumferential surface of the casing 10. More specifically, the three-dimensional blade tip 37s is a region of about 30% of the blade length Hb from the tip of the three-dimensional blade 37 including the shroud 32c.

[0043] Furthermore, let ΔS1 be the change in the radial Dr outward Dro of the position of the three-dimensional wingtip 37s in the rotor blade row 31E of the fifth stage 50E and the rotor blade row 31F of the sixth stage 50F. Also, let ΔS2 be the change in the radial Dr outward Dro of the position of the three-dimensional wingtip 37s in the radial Dr outward Dro of the position of the rotor blade row 31F of the sixth stage 50F and the rotor blade row 31G of the seventh stage 50G. In this embodiment, it is preferable that the change ΔS1 is greater than the change ΔS2 (ΔS1 > ΔS2).

[0044] Here, the rotor blade row 31E of the fifth stage 50E and the rotor blade row 31F of the sixth stage 50F are two of the closest pairs of downward-flowing rotor blade rows 31L, including the downward-flowing rotor blade row 31L located furthest upstream in axial Da (the rotor blade row 31E of the fifth stage 50E) among a plurality of downward-flowing rotor blade rows 31L. Also, the rotor blade row 31F of the sixth stage 50F and the rotor blade row 31G of the seventh stage 50G are two of the closest pairs of downward-flowing rotor blade rows 31L, including the downward-flowing rotor blade row 31L located furthest downstream in axial Da (the rotor blade row 31G of the seventh stage 50G) among a plurality of downward-flowing rotor blade rows 31L.

[0045] Furthermore, in the seventh stage 50G, which is the rotor blade row 31 located furthest downstream in the axial direction Da, the throat width at the three-dimensional wingtip 37s is formed to be smaller than the throat width at the three-dimensional wing base 37b and the throat width at the three-dimensional wing intermediate 37c in the radial direction Dr of the three-dimensional wing 37. Here, the three-dimensional wing intermediate 37c is the region of the three-dimensional wing 37 sandwiched between the three-dimensional wingtip 37s and the three-dimensional wing base 37b in the radial direction Dr. More specifically, the three-dimensional wing intermediate 37c is a region of about 40% of the wing length Hb, including the central portion. The throat width is the width of the flow path at the position where the flow path cross-sectional area is smallest in the flow path formed between a pair of wing bodies (wing body 32b and stator blade 42) in the circumferential direction Dc.

[0046] Furthermore, in this embodiment, the throat width of the three-dimensional wing intermediate portion 37c in the radial direction Dr of the three-dimensional wing 37 is formed to be larger than the throat width at the three-dimensional wing base portion 37b. In other words, in the rotor blade row 31G of the seventh stage 50G, the throat width of the three-dimensional wing 37 widens from the smallest three-dimensional wing tip portion 37s toward the widest radial direction Dr three-dimensional wing intermediate portion 37c, and then narrows again at the three-dimensional wing base portion 37b.

[0047] Furthermore, in the rotor blade row 31G of the seventh stage 50G, the clearance C in the radial direction Dr between the three-dimensional blade tip 37s and the casing 10 is formed to be 1.5 to 2.5% of the blade length Hb in the radial direction Dr of the three-dimensional blade 37.

[0048] Furthermore, in the seventh stage 50G stator vane row 41G, which is the stator vane row 41 located furthest downstream Da in the axial direction Da, as shown in Figure 3, the throat width at the intermediate portion (intermediate portion) 42c of the stator vane is larger than the throat width at the tip portion 42s and the throat width at the base portion 42b of the stator vane.

[0049] Here, as shown in Figure 2, the stator vane tip 42s is the region of the stator vane 42 that includes the outer end of the radial Dr of the stator vane 42 and is close to the inner surface of the outer ring 43. More specifically, the stator vane tip 42s is the region from the inner surface of the outer ring 43 to about 30% of the total length of the stator vane height of the stator vane 42 (the length of the radial Dr from the outer surface of the inner ring 46 to the inner surface of the outer ring 43).

[0050] Furthermore, the base portion 42b of the stator vane is a region of the stator vane 42 that includes the end of the inner Dri in the radial direction Dr of the stator vane 42, and is close to the outer circumferential surface of the inner ring 46. More specifically, the base portion 42b of the stator vane is a region of approximately 30% of the total wing height of the stator vane 42 from the outer circumferential surface of the inner ring 46.

[0051] Furthermore, the intermediate portion 42c of the stator vane is the region of the stator vane 42 sandwiched radially in the direction Dr between the tip portion 42s and the base portion 42b. More specifically, the intermediate portion 42c of the stator vane is a region of approximately 40% of the total wing height of the stator vane 42, including the central portion.

[0052] Furthermore, in this embodiment, the throat width at the tip portion 42s of the stator vane and the throat width at the base portion 42b of the stator vane are formed to be substantially the same. In other words, in the stator vane row 41G of the seventh stage 50G, the throat width of the stator vane 42 gradually widens from the tip portion 42s toward the middle portion 42c of the stator vane with the widest radial direction Dr, and then narrows again at the base portion 42b of the stator vane, which is about the same as the tip portion 42s.

[0053] Furthermore, as shown in Figure 4, the casing 10 of this embodiment further comprises an exhaust casing 51 and a diffuser 70.

[0054] The exhaust casing 51 is connected to the outside of the casing 10. The exhaust casing 51 discharges the steam S that has flowed through the main passage 15 to the outside of the casing 10. The exhaust casing 51 is located in the casing 10 at the second-to-last Da in the axial direction Da. An exhaust chamber 13 opening downwards is formed at the bottom of the exhaust casing 51. The exhaust casing 51 exhausts the steam S, whose static pressure has been restored by the diffuser 70 (described later), to the outside.

[0055] The diffuser 70 guides the steam S flowing out from the rotor blade row 31G of the seventh stage 50G to the outside of the casing 10 via the exhaust chamber 13. The diffuser 70 is positioned between the rotor blade row 31G of the seventh stage 50G and the exhaust casing 51 that forms the exhaust chamber 13 in the casing 10. The diffuser 70 in this embodiment has an outer guide (guide member) 71 and an inner guide 72.

[0056] The outer guide 71 is positioned downstream of the rotor blade row 31G of the seventh stage 50G in the axial direction Da. The outer guide 71 is formed to gradually expand radially outward from the upstream side Dau in the axial direction Da to the downstream side Da. The length L of the axial direction Da in the outer guide 71 of the diffuser 70 is formed to be 85% to 120% of the blade length of the three-dimensional blade 37 of the rotor blade row 31G of the seventh stage 50G. In particular, it is preferable that the length L of the axial direction Da in the outer guide 71 is 100% or more of the blade length of the three-dimensional blade 37 of the rotor blade row 31G of the seventh stage 50G.

[0057] The inner guide 72 is positioned with a gap between it and the outer guide 71 in the radial direction Dr, in the inner Dri. This defines an annular flow path 100, which is a flow path through which steam S can flow, between the outer guide 71 and the inner guide 72. The annular flow path 100 is defined between the outer guide 71 and the inner guide 72 in an annular shape when viewed from the axial direction Da. The annular flow path 100 is connected to the main flow path 15 at the downstream side Da in the axial direction Da. The inner guide 72 extends straight inclined outward in the radial direction Dr, in the outer Dro, from the upstream side Dau in the axial direction Da to the downstream side Da.

[0058] (Effects and Benefits) The steam turbine 1 with the above configuration includes an upper flow blade row 31U having a plurality of parallel blades 35, and a lower flow blade row 31L having a plurality of three-dimensional blades 37. Furthermore, in this embodiment, the outer circumferential surface 21f of the rotor shaft 21 is formed parallel to the axis Ar in a cross section parallel to the axis Ar. In other words, the outer circumferential surface 21f of the rotor shaft 21 is formed so as not to shrink inward in the radial direction Dr from the upstream side Dau to the downstream side Da in the region where the three-dimensional blades 37 are arranged in the downstream region P2. Therefore, in order to suppress the length of the radial direction Dr in the rotor blade row 31G of the final stage, the seventh stage 50G, it is not necessary to position the position of the three-dimensional blade base end 37b of the rotor blade row 31E of the fifth stage 50E to be outside the radial direction Dr relative to the position of the three-dimensional blade base end 37b of the rotor blade row 31G of the seventh stage 50G. Therefore, the position of the radial Dr of the three-dimensional blade base end 37b of the rotor blade row 31E of the fifth stage 50E can be kept within the inner Dri of the radial Dr. In other words, the increase in the diameter of the rotor shaft 21 at the position where the rotor blade row 31E of the fifth stage 50E is positioned is suppressed.

[0059] Here, in an upper flow blade row 31U having parallel blades 35, in order to improve efficiency, it is necessary to increase the number of stages in the upper flow blade row 31U. As the number of stages in the upper flow blade row 31U increases, the step pressure in each upper flow blade row 31U decreases. And as the step pressure decreases, the velocity of the steam S also decreases. Even in this state where the step pressure is small, it is necessary to maintain an appropriate velocity ratio with respect to the parallel blades 35 (the ratio of the peripheral velocity of the parallel blades 35 to the velocity of the steam S). In order to maintain the velocity ratio, it is necessary to suppress the peripheral velocity of the parallel blades 35. And in order to suppress the peripheral velocity of the parallel blades 35, it is necessary to bring the position of the parallel blade base end 35b, which is the root of the parallel blades 35, closer to the inner Dri in the radial direction Dr. In other words, it is necessary to bring the position of the outer circumferential surface 21f of the rotor shaft 21 connected to the parallel blades 35 closer to the inner Dri in the radial direction Dr.

[0060] On the other hand, in an upper flow blade row 31U having parallel blades 35, if the position of the outer surface 21f of the rotor shaft 21 is brought closer to the inner Dri in the radial direction Dr, a large step difference occurs in the region where the upper flow blade row 31U with parallel blades 35 transitions to a lower flow blade row 31L having three-dimensional blades 37, due to the difference in diameter of the rotor shaft 21. To prevent such a structure, it is necessary to align the position of the radial direction Dr of the outer surface 21f of the rotor shaft 21 between the upper flow blade row 31U, which is located at the downstream Da in the axial direction Da, and the lower flow blade row 31L, which is located at the upstream Dau in the axial direction Da.

[0061] In contrast, the present invention suppresses the increase in the diameter of the rotor shaft 21 at the position where the rotor blade row 31E of the fifth stage 50E is arranged. Therefore, there is no need to increase the diameter of the rotor shaft 21 in the rotor blade row 31D of the fourth stage 50D, which is adjacent to the fifth stage 50E. In other words, the position of the outer surface 21f of the rotor shaft 21 at the lower flow blade row 31L, which is located at the upstream Dau in the axial direction Da, is suppressed to the inner Dri in the radial direction Dr. Therefore, even if the number of stages of the upper flow blade row 31U with parallel blades 35 is increased, it is possible to suppress the occurrence of a large step in the rotor shaft 21 in the region where it switches from the upper flow blade row 31U with parallel blades 35 to the lower flow blade row 31L with three-dimensional blades 37. As a result, the number of stages of the upper flow blade row 31U can be increased while suppressing structural effects on the rotor 20 and casing 10. This makes it possible to improve efficiency while mixing parallel blades 35 and three-dimensional blades 37.

[0062] Furthermore, the change in the radial Dr to the outer Dro of the position of the three-dimensional blade tip 37s in the blade row 31F of the sixth stage 50F and the blade row 31G of the seventh stage 50G is greater than the change in the radial Dr to the outer Dro of the position of the three-dimensional blade tip 37s in the blade row 31E of the fifth stage 50E and the blade row 31F of the sixth stage 50F is greater than the change in the radial Dr to the outer Dro of the position of the three-dimensional blade tip 37s in the outer Dro of the position of the blade row 31F of the fifth stage 50E. Therefore, in the region where the flow switches from the upper flow blade row 31U to the lower flow blade row 31L, the main flow path 15 rapidly expands to the outer Dro of the radial Dr. As a result, when flowing from the upstream region P1 to the downstream region P2, the steam S is more likely to flow to the outer Dro of the radial Dr rather than the inner Dri. Thus, the entire length of the three-dimensional blade 37 can be effectively utilized.

[0063] Furthermore, in the stator vane row 41G of the seventh stage 50G, the throat width of the stator vane 42 is larger at the intermediate portion 42c of the stator vane compared to the tip portion 42s and the base portion 42b of the stator vane. In particular, in this embodiment, it decreases from the intermediate portion 42c of the stator vane towards the tip portion 42s of the stator vane. As a result, radial flow, which is the flow in which steam S spreads outward in the radial direction Dr, is suppressed. In addition, the throat width of the stator vane 42 decreases from the intermediate portion 42c of the stator vane towards the base portion 42b of the stator vane. As a result, the degree of reaction can be reduced, and leakage flow of steam into the gap between the tip portion 42s of the stator vane and the outer circumferential surface 21f of the rotor can be suppressed.

[0064] Furthermore, in the rotor blade row 31G of the seventh stage 50G, the radial clearance Dr between the three-dimensional blade tip 37s and the casing 10 is formed to be 1.5 to 2.5% of the blade length Hb in the radial Dr of the three-dimensional blade 37. Therefore, leakage flow of steam S between the three-dimensional blade tip 37s and the casing 10 can be effectively suppressed. Also, by suppressing leakage flow near the three-dimensional blade tip 37s, radial flow can be suppressed by the three-dimensional blade 37 of the rotor blade row 31G of the seventh stage 50G. As a result, losses can be reduced and work can be effectively performed on the three-dimensional blade 37 of the seventh stage 50G.

[0065] Furthermore, in the rotor blade row 31G of the seventh stage 50G, the three-dimensional blade 37 has a transonic airfoil. This allows the three-dimensional blade 37 of the rotor blade row 31G of the seventh stage 50G to be configured to correspond to the flow velocity of the accelerated steam S flowing through the main flow path 15 located at the downstream Da of the axial direction Da. In particular, in this embodiment, the three-dimensional blade 37 in all the downstream airfoil rows 31L has a transonic airfoil. Therefore, the three-dimensional blade 37 of all the downstream airfoil rows 31L, including the seventh stage 50G, can be configured to correspond to the flow velocity of the accelerated steam S. This allows the three-dimensional blade 37 to work effectively while minimizing losses.

[0066] Furthermore, in the diffuser 70, the axial length Da of the outer guide 71 is formed to be 85% to 120% of the radial length Hb of the three-dimensional blade 37 of the lower flow blade row 31L located at the downstream Da in the axial direction. Therefore, the outer guide 71 guides the steam S flowing through the annular flow channel 100 of the diffuser 70 over a long distance in the axial direction Da. As a result, separation of the steam S flow at the outer Dr in the radial direction Dr can be suppressed in the annular flow channel 100 of the diffuser 70. Thus, the diffuser 70 can reduce the flow velocity while suppressing the separation of the steam S. Therefore, even if the flow velocity (average flow velocity) of the steam S flowing out from the final stage blade row 31G is transonic, the occurrence of separation can be suppressed. Thus, it is possible to efficiently recover the static pressure of the steam S within the diffuser 70.

[0067] (Other embodiments) Although embodiments of this disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and may include design changes and the like that do not depart from the gist of this disclosure.

[0068] For example, the configuration of each part of the steam turbine 1, including the number of stages of the rotor blade rows 31 and stator blade rows 41, can be changed as appropriate. In other words, the steam turbine 1 is not limited to a structure having 7 stages (7 rotor blade rows 31 and stator blade rows 41) as in this embodiment. Therefore, the steam turbine 1 may have 6 stages or fewer, as in this embodiment, or 8 stages or more.

[0069] Furthermore, in this embodiment, the outer circumferential surface 21f of the rotor shaft 21 is formed parallel to the axis Ar in a cross section parallel to the axis Ar across the entire region of the upstream region P1 and the downstream region P2. However, the outer circumferential surface 21f of the rotor shaft 21 is not limited to this structure. For example, the outer circumferential surface 21f of the rotor shaft 21 may be formed to gradually widen radially outward in the region where the three-dimensional blades 37 are arranged in the downstream region P2, toward the downstream side Da in the axial direction Da relative to the axis Ar. Even with such a structure, efficiency can be improved while mixing parallel blades 35 and three-dimensional blades 37, similar to the case where the outer circumferential surface 21f of the rotor shaft 21 is formed parallel to the axis Ar. Moreover, the outer circumferential surface 21f of the rotor shaft 21 may be formed to gradually widen radially outward in the upstream region P1, toward the downstream side Da in the axial direction Da relative to the axis Ar.

[0070] <Note> The steam turbine 1 described in the embodiment can be understood, for example, as follows:

[0071] (1) The steam turbine 1 according to the first embodiment comprises a rotor shaft 21 that can rotate about an axis Ar, a plurality of rotor blade rows 31 fixed to the outer Dro of the rotor shaft 21 in the radial direction Dr with respect to the axis Ar, and spaced apart in the axial direction Da extending from the axis Ar, a casing 10 that covers the rotor shaft 21 and the plurality of rotor blade rows 31 from the outer Dro in the radial direction Dr, and has a main flow path 15 formed inside through which steam can flow, and a plurality of stator blade rows 41 fixed to the inner Dri of the casing 10 in the radial direction Dr, and arranged on the first side Dau in the axial direction Da for each of the plurality of rotor blade rows 31, wherein the plurality of rotor blade rows 31 include a plurality of upflow blade rows 31U arranged in the upstream region P1 of the main flow path 15, and the upstream region The rotor comprises a plurality of downward-flowing blade rows 31L located in a downstream region P2 situated on the second side Da in the axial direction Da relative to P1, wherein the upward-flowing blade row 31U has a plurality of parallel blades 35 spaced apart in the circumferential direction Dc around the axis Ar, the downward-flowing blade row 31L has a plurality of three-dimensional blades 37 spaced apart in the circumferential direction Dc, and the stator blade row 41 has a plurality of stator blades 42 spaced apart in the circumferential direction Dc, and the outer peripheral surface 21f of the rotor shaft 21 facing outward Dro in the radial direction Dr is formed in the region of the downstream region P2 where the three-dimensional blades 37 are arranged, in a cross section parallel to the axis Ar, parallel to the axis Ar, or gradually widening in the radial direction Dr outward Dro toward the second side Da in the axial direction Da relative to the axis Ar.

[0072] Such a steam turbine 1 comprises an upper flow blade row 31U having parallel blades 35 and a lower flow blade row 31L having three-dimensional blades 37. Furthermore, in this embodiment, the outer circumferential surface 21f of the rotor shaft 21 is formed such that, in a cross section parallel to the axis Ar, it is parallel to the axis Ar, or gradually widens radially outward in the direction of Dr towards the downstream side Da in the axial direction Da relative to the axis Ar. In other words, the outer circumferential surface 21f of the rotor shaft 21 is formed so that, in the region where the three-dimensional blades 37 are arranged in the downstream region P2, it does not narrow radially inward in the direction of Dr from the upstream side Dau in the axial direction Da to the downstream side Da. Therefore, in order to suppress the length of radial Dr in the final stage rotor blade row 31G, it is not necessary to position the position of the three-dimensional blade base end 37b of the lower flow blade row 31L, which is located at the first Dau in the axial direction Da, radially outward in the direction of Dr relative to the position of the three-dimensional blade base end 37b of the final stage rotor blade row 31G. Therefore, the position of the radial Dr of the three-dimensional blade base 37b of the downward-flowing blade row 31L, which is located in the firstmost Dau in the axial direction Da, can be kept within the inner Dri of the radial direction Dr. In other words, the increase in the diameter of the rotor shaft 21 at the position where the downward-flowing blade row 31L, located in the firstmost Dau in the axial direction Da, is positioned is suppressed. As a result, there is no need to increase the diameter of the rotor shaft 21 at the upper-flowing blade row 31U, which is located in the secondmost Da adjacent to the downward-flowing blade row 31L, located in the firstmost Dau in the axial direction Da. In other words, the position of the outer circumferential surface 21f of the rotor shaft 21 at the downward-flowing blade row 31L, located in the firstmost Dau in the axial direction Da, is kept within the inner Dri of the radial direction Dr. Therefore, even if the number of stages of the upper-flowing blade row 31U with parallel blades 35 is increased, it is possible to suppress the occurrence of a large step in the rotor shaft 21 in the region where it switches from the upper-flowing blade row 31U with parallel blades 35 to the downward-flowing blade row 31L with three-dimensional blades 37. As a result, the number of stages in the upward-flow blade row 31U can be increased while minimizing the structural impact on the rotor 20 and casing 10. This makes it possible to improve efficiency while mixing parallel blades 35 and three-dimensional blades 37.

[0073] (2) The steam turbine 1 according to the second embodiment is the steam turbine 1 of (1), wherein in the downstream region P2, the positions of the three-dimensional blade tips 37s of the plurality of three-dimensional blades 37 on the outer Dro of the radial Dr are formed to spread outwards to the outer Dro of the radial Dr from the downward flow blade row 31L located on the first side Dau of the axial direction Da to the downward flow blade row 31L located on the second side Da of the axial direction Da, and the amount of change in the position of the three-dimensional blade tips 37s on the outer Dro of the radial Dr in two of the closest pairs of downward flow blade rows 31L, including the downward flow blade row 31L located on the first side Dau of the axial direction Da, is greater than the amount of change in the position of the three-dimensional blade tips 37s on the outer Dro of the radial Dr in the closest pair of downward flow blade rows 31L, including the downward flow blade row 31L located on the second side Da of the axial direction Da.

[0074] As a result, in the region where the flow direction switches from the upper flow blade row 31U to the lower flow blade row 31L, the main flow path 15 rapidly expands to the outer Dro of the radial Dr. Therefore, when the vapor S flows from the upstream region P1 to the downstream region P2, it is more likely to flow to the outer Dro rather than the inner Dri of the radial Dr. Thus, the entire length of the three-dimensional blade 37 can be effectively utilized.

[0075] (3) The steam turbine 1 according to the third embodiment is the steam turbine 1 of (2), wherein in the lower flow blade row 31L located at the second-to-last Da in the axial direction Da, the clearance in the radial direction Dr between the three-dimensional blade tip portion 37s and the casing 10 is formed to be 1.5 to 2.5% of the blade length of the three-dimensional blade 37 in the radial direction Dr.

[0076] This effectively suppresses steam leakage flow between the three-dimensional blade tip 37s and the casing 10. Furthermore, by suppressing leakage flow near the three-dimensional blade tip 37s, radial flow can be suppressed by the three-dimensional blades 37 of the final stage rotor blade row 31G. This reduces losses and allows the final stage three-dimensional blades 37 to work effectively.

[0077] (4) The steam turbine 1 according to the fourth embodiment is any one of the steam turbine 1 from (1) to (3), wherein in the stator blade row 41 located in the secondmost Da in the axial direction Da, the throat width of the stator blade 42 in the middle of the radial direction Dr is larger than the throat width at the stator blade tip 42s in the inner Dri of the radial direction Dr of the stator blade 42 and the throat width at the stator blade base 42b in the outer Dro of the radial direction Dr of the stator blade 42.

[0078] This suppresses radial flow, which is the flow of steam S spreading outward in the radial direction Dr. In addition, the throat width of the stator vane 42 decreases from the middle section 42c towards the base end 42b of the stator vane. As a result, the degree of recoil can be reduced, and leakage flow of steam into the gap between the tip of the stator vane 42s and the outer circumferential surface 21f of the rotor can be suppressed.

[0079] (5) The steam turbine 1 according to the fifth embodiment is any one of the steam turbines 1 from (1) to (4), wherein the three-dimensional blade 37 has a transonic airfoil shape in the downward flow blade row 31L located at the second-to-last Da in the axial direction Da.

[0080] This allows the three-dimensional blades 37 of the blade row 31G located furthest to the second-to-last Da in the axial direction Da to be adjusted to the flow velocity of the accelerated steam S flowing through the main passage 15 located furthest to the second-to-last Da in the axial direction Da.

[0081] (6) The steam turbine 1 according to the sixth embodiment is any one of the steam turbines 1 of (1) to (5), wherein the casing 10 is equipped with a diffuser 70 that guides steam flowing out from the lower flow blade row 31L located at the secondmost Da in the axial direction Da to the outside of the casing 10, and the diffuser 70 has a guide member 71 that extends outward in the radial direction Dr from the first side Dau in the axial direction Da toward the second side Da, and the length of the axial direction Da in the guide member 71 is formed to be 85% to 120% of the length of the radial direction Dr in the three-dimensional blade 37 of the lower flow blade row 31L located at the secondmost Da in the axial direction Da.

[0082] As a result, The guide member 71 guides the steam S flowing through the diffuser 70 over a long distance in the axial direction Da. As a result, separation of the steam S flow in the diffuser 70 can be suppressed at the outer Dr in the radial direction Dr. Therefore, the diffuser 70 can reduce the flow velocity while suppressing the separation of the steam S. Consequently, even if the flow velocity (average flow velocity) of the steam S flowing out from the final stage rotor blade row 31G is transonic, the occurrence of separation can be suppressed. Therefore, it becomes possible to efficiently recover the static pressure of the steam S within the diffuser 70.

[0083] (7) The steam turbine 1 according to the seventh embodiment is any one of the steam turbines 1 from (1) to (6), wherein the parallel blades 35 are impulse blades and the three-dimensional blades 37 are reaction blades. [Explanation of Symbols]

[0084] 1…Steam turbine 10…Casing 51... Exhaust casing 11… Nozzle chamber 12…Flow chamber 13… Exhaust chamber 15…Main channel 20... Rotor 21…Rotor shaft 21f…Outer surface 22...Axis core part 23…Disk section 31, 31A~31G…Rotating blade row 31L…Downflow blade row 31U...Upstream flow blade row 32... Moving blade 32a…Platform 32b...Wing body 32c... Shroud 35...parallel wings 35b...Parallel wing base end 35s...parallel wing tip 37…Three-dimensional wings 37b...Three-dimensional wing base end 37c…Three-dimensional wing middle part 37s...Three-dimensional wing tip 41, 41A~41G…Stator blade row 42...Seiyoku 42b...Stator blade base end 42c…Stator blade middle part (middle part) 42s…Stator blade tip 43…Outer ring 46…Inner ring 50 steps 50A…first stage 50B…Second stage 50C…Third stage 50D…Fourth stage 50E…5th stage 50F…6th stage 50G…7th stage 50x... High-pressure stage 50y... Low-pressure stage 70... Diffuser 71…Outer guide (guide member) 72...Inner guide 100... Circular channel Ar…Axis line Da... Axis Dad…downstream side (second side) Dau… Upstream side (first side) Dc…Circumferential direction Dr…Radial direction Dri…inside Dro... outside Hb…wing length P1…Upstream region P2…downstream area S... Steam

Claims

1. A rotor shaft that can rotate around its axis, A plurality of rotor blade rows are fixed to the outside of the rotor shaft in the radial direction with respect to the aforementioned axis, and are arranged at intervals in the axial direction in which the axis extends, A casing that covers the rotor shaft and the plurality of rotor blade rows from the radial outside, and has a main passage formed inside through which steam can flow, The casing comprises a plurality of stationary vane rows fixed to the inside of the casing in the radial direction and arranged on the first side in the axial direction with respect to each of the plurality of rotor vane rows, Multiple rotor blade rows, A plurality of upward flow blade rows are arranged in the upstream region of the main flow channel, The main flow channel comprises a plurality of downward flow blade rows located in a downstream region that is positioned on the second axial side with respect to the upstream region, The aforementioned upper flow blade row has a plurality of parallel blades arranged at intervals in the circumferential direction around the axis, The aforementioned downward-flowing blade row has a plurality of three-dimensional blades arranged at intervals in the circumferential direction, The aforementioned row of stator vanes has a plurality of stator vanes arranged at intervals in the circumferential direction, In the rotor shaft, the outer circumferential surface facing radially outward is formed in the region where the three-dimensional blades are arranged in the downstream region, in a cross section parallel to the axis, so as to be parallel to the axis or gradually widening radially outward toward the second side in the axial direction relative to the axis. In the downstream region, the positions of the radially outer three-dimensional blade tips of the plurality of three-dimensional blades are formed to spread radially outward from the downward flow blade row located on the first side in the axial direction toward the downward flow blade row located on the second side in the axial direction. A steam turbine in which the radial outward change in the position of the three-dimensional blade tip in two of the closest pairs of downflow blade rows, including the downflow blade row located furthest to the first side in the axial direction, is greater than the radial outward change in the position of the three-dimensional blade tip in one of the closest pairs of downflow blade rows, including the downflow blade row located furthest to the second side in the axial direction.

2. The steam turbine according to claim 1, wherein in the lower flow blade row located furthest to the second side in the axial direction, the radial clearance between the three-dimensional blade tip and the casing is formed to be 1.5 to 2.5% of the radial blade length of the three-dimensional blade.

3. The steam turbine according to claim 1 or 2, wherein the secondmost row of stator blades in the axial direction is formed such that the throat width at the radially intermediate portion of the stator blade is larger than the throat width at the radially inner stator blade tip and the throat width at the radially outer stator blade base.

4. The steam turbine according to claim 1 or 2, wherein in the lower flow blade row located furthest to the second side in the axial direction, the three-dimensional blade has a transonic airfoil shape.

5. The casing includes a diffuser that guides the steam flowing out from the lower flow blade row, which is located on the secondmost side in the axial direction, to the outside of the casing. The diffuser has a guide member that extends radially outward from the first side in the axial direction toward the second side, The steam turbine according to claim 1 or 2, wherein the axial length of the guide member is formed to be 85% to 120% of the radial length of the three-dimensional blade of the lower flow blade row that is located on the second side in the axial direction.

6. The steam turbine according to claim 1 or 2, wherein the parallel blades are impulse blades and the three-dimensional blades are reaction blades.

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