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 steam turbines. [Background technology]

[0002] A steam turbine comprises a rotor (turbine rotor) arranged within a casing, a row of rotor blades arranged radially outside the rotor, a diaphragm arranged radially inside the casing, and a row of stator blades supported radially inside the diaphragm (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-101565 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, in the steam turbine as described above, there is a structure in which an impulse stage having parallel blades is formed in the upstream rotor blade row, and a reaction stage having three-dimensional blades is formed in the downstream rotor blade row, thereby improving efficiency. In general, a reaction blade can improve efficiency, but it is necessary to design it taking into account the large axial thrust load and the large leakage of the rotor blades, and a complex structure is required. On the other hand, it is difficult to achieve the same high efficiency as a reaction blade with an impulse blade, but it is possible to have a simple structure. Therefore, in such a steam turbine, in order to facilitate design and improve efficiency, there is always a demand for further improvement in efficiency by mixing parallel blades (impulse blades) and three-dimensional blades (reaction blades).

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a steam turbine that can improve efficiency while mixing parallel blades and three-dimensional blades. [Means for solving the problem]

[0006] In order to solve the above problems, a steam turbine according to the present disclosure includes a rotor shaft rotatable about an axis, a plurality of moving blade rows fixed to the outside of the rotor shaft in a radial direction based on the axis and arranged at intervals in the axial direction along which the axis extends, a casing covering the rotor shaft and the plurality of moving blade rows from the outside in the radial direction and having a main flow passage 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 a first side in the axial direction with respect to each of the plurality of moving blade rows, and a plurality of downstream flow wing rows arranged in a downstream region located on the second side in the axial direction relative to the upstream region, wherein the upstream flow wing row has a plurality of parallel blades arranged at intervals in the circumferential direction around the axis, the downstream flow wing row has a plurality of three-dimensional blades arranged at intervals in the circumferential direction, and the stator blade row has a plurality of stator blades arranged at intervals in the circumferential direction, and the outer peripheral surface of the rotor shaft facing radially outward is formed in a region in the downstream region where the three-dimensional blades are arranged, so that in a cross section parallel to the axis, the outer peripheral surface gradually expands in diameter parallel to the axis or radially outward toward the second side in the axial direction relative to the axis. Effect of the Invention

[0007] According to the steam turbine of the present disclosure, it is possible to improve efficiency while mixing parallel blades (impulse blades) and three-dimensional blades (reaction blades). [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing an overall configuration of a steam turbine according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing a row of rotor blades and a row of stator blades of the steam turbine. [Diagram 3] FIG. 4 is a diagram showing a change in throat width in a stator blade row located on the second most side in the axial direction of the steam turbine. [Figure 4]2 is a cross-sectional view showing a configuration around a diffuser provided in the steam turbine. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of a steam turbine according to the present disclosure will be described with reference to the accompanying drawings. However, the present disclosure is not limited to the embodiment.

[0010] (Steam turbine configuration) As shown in FIG. 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 convenience of the following description, the direction in which the axis Ar extends is referred to as the axial direction Da. The first side of the axial direction Da is referred to as the upstream side (one side) Dau, and the second side of the axial direction Da is referred to as the downstream side (the other side) Dad. The radial direction of the rotor 20 based on the axis Ar is simply referred to as the radial direction Dr. The side of the radial direction Dr that approaches the axis Ar is referred to as the inner side Dri of the radial direction Dr, and the side of the radial direction Dr opposite to the inner side Dri of the radial direction Dr is referred to as the outer side Dro of the radial direction Dr. The circumferential direction of the rotor 20 centered on the axis Ar is simply referred to as the circumferential direction Dc.

[0012] As shown in FIGS. 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 the 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 centered on the axis Ar and extends in the axial direction Da. The disk portions 23 extend from the core portion 22 to the outside Dro in the radial direction Dr. The disk portions 23 are arranged at intervals 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 row 31 is fixed to the outside of the rotor shaft 21 in the radial direction Dr. Specifically, as shown in FIG. 2, the rotor blade row 31 is fixed to the outside Dro of the disk portion 23, which is the outer circumferential portion of the rotor shaft 21 in the radial direction Dr. A plurality of rotor blade rows 31 are arranged at intervals in the axial direction Da of the rotor shaft 21. In the case of this embodiment, for example, a total of seven rotor blade rows 31 are arranged from the rotor blade row 31A located on the most upstream side Dau in the axial direction Da to the rotor blade row 31G located on the most downstream side Dad in the axial direction Da. Each rotor blade row 31 has a plurality of rotor blades 32 arranged in the circumferential direction Dc. The plurality of rotor blades 32 are respectively attached to the disk portion 23. Each rotor blade 32 has a platform 32a, a blade body 32b, and a shroud 32c.

[0015] The platform 32a is disposed on the outer side Dro in the radial direction Dr with respect to the disk portion 23. The 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 collectively form a cylindrical shape centered on the axis line Ar.

[0016] The blade body 32b extends from the platform 32a to the outside Dro in the radial direction Dr. The blade body 32b is integrally formed with the platform 32a and the shroud 32c. The blade body 32b is disposed in a main flow passage 15, which will be described later. The blade body 32b has an airfoil cross section when viewed from the outside in the radial direction Dr.

[0017] The shroud 32c is connected to an end of the blade body 32b on the outer side Dro in the radial direction Dr. In other words, in the radial direction Dr, the shroud 32c is disposed on the opposite side of the platform 32a across the blade body 32b. The shroud 32c extends in the circumferential direction Dc. The shrouds 32c of the multiple rotor blades 32 are aligned in the circumferential direction Dc to form a cylindrical shape as a whole.

[0018] The casing 10 is formed so as to cover the rotor shaft 21 and the multiple rotor blade rows 31 from the outside Dro in the radial direction Dr. Inside the casing 10, there are formed a nozzle chamber 11 into which the steam S flows from the outside, a flow passage chamber 12 through which the steam S from the nozzle chamber 11 flows, and an exhaust chamber 13 through which the steam S flowing from the flow passage chamber 12 is exhausted. Between the nozzle chamber 11 and the flow passage chamber 12, the rotor blade row 31A and the stator blade row 41A of the first stage 50A on the most upstream side Dau among the multiple rotor blade rows 31 and the stator blade row 41 are arranged. In other words, the inside of the casing 10 is divided into the nozzle chamber 11 and the flow passage chamber 12 by the rotor blade row 31A and the stator blade row 41A on the most upstream side Dau. The nozzle chamber 11, the flow passage chamber 12, and the exhaust chamber 13 form a main flow passage 15 through which high-pressure steam S flows.

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

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

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

[0022] A single stage 50 is formed by a pair of a rotor blade row 31 and a stator blade row 41 arranged on the upstream side Dau of the rotor blade row 31. In the steam turbine 1 of this embodiment, a stator blade row 41 is arranged for each of the seven rotor blade rows 31 in Fig. 2. Therefore, the steam turbine 1 of this embodiment has seven stages 50. In other words, the steam turbine 1 of this embodiment has, in order from the upstream side Dau to the downstream side Dad, the rotor blade rows 31 and the stator blade rows 41 of a first stage 50A, a second stage 50B, a third stage 50C, a fourth stage 50D, a fifth stage 50E, a sixth stage 50F, and a seventh stage 50G.

[0023] In the steam turbine 1 of the present embodiment, the first stage 50A to the fourth stage 50D arranged on the upstream side Dau in the axial direction Da among the multiple stages 50 constitute a high-pressure stage 50x. In addition, the fifth stage 50E to the seventh stage 50G (the 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 among the multiple stages 50 constitute a low-pressure stage 50y.

[0024] Here, a region in the main flow passage 15 where the high-pressure stage 50x is arranged is referred to as an upstream region P1. Also, a region in the main flow passage 15 located downstream 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 a downstream region P2.

[0025] The multiple moving blade rows 31 include multiple upper flow blade rows 31U arranged in the upstream region P1 and multiple lower flow blade rows 31L arranged in the downstream region P2. In this embodiment, the multiple upper flow blade rows 31U are impulse stages and constitute a part of the high pressure stage 50x. The multiple upper flow blade rows 31U include the moving blade row 31A of the first stage 50A to the moving blade row 31D of the fourth stage 50D. That is, the moving blade row 31A of the first stage 50A is the upper flow blade row 31U located at the most upstream side Dau in the axial direction Da among the multiple upper flow blade rows 31U. Also, the moving blade row 31D of the fourth stage 50D is the upper flow blade row 31U located at the most downstream side Dad in the axial direction Da.

[0026] The multiple downstream blade rows 31L are reaction stages and constitute a part of the low pressure stage 50y. In this embodiment, the multiple downstream blade rows 31L include the rotor blade row 31E of the fifth stage 50E to the rotor blade row 31G of the seventh stage 50G. That is, the rotor blade row 31E of the fifth stage 50E is the downstream blade row 31L located at the most upstream side Dau in the axial direction Da among the multiple downstream blade rows 31L. The rotor blade row 31G of the seventh stage 50G is the downstream blade row 31L located at the most downstream side Dad in the axial direction Da.

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

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

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

[0030] When the degree of reaction R is 0, there is no pressure change at the moving blades 32. On the other hand, when the degree of reaction R is not 0, there is a pressure drop at the moving blades 32, while there is an increase in the flow velocity of the steam S at the moving blades 32. For this reason, when the degree of reaction R is not 0, the steam S expands as it passes through the moving blades 32. The reaction force generated by this expansion acts on the moving blades 32. When the degree of reaction R is 0, only the impulse action of the steam S becomes the work of the steam S on the moving blades 32, but when the degree of reaction R is not 0, in addition to the impulse action of the steam S, the reaction action becomes the work of the steam S on the moving blades 32.

[0031] The outer peripheral surface 21f facing the outer side Dro in the radial direction Dr of the rotor shaft 21 is formed in a region where the rotor blades 32 (parallel blades 35) are arranged in the upstream region P1 so as to be parallel to the axis Ar in a cross section parallel to the axis Ar, or to gradually expand in diameter toward the outer side Dro in the radial direction Dr toward the downstream side Dad in the axial direction Da relative to the axis Ar. Note that this embodiment illustrates a case where the outer peripheral surface 21f is formed parallel to the axis Ar in a cross section parallel to the axis Ar in a region where the parallel blades 35 are arranged in the upstream region P1.

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

[0033] As a result, in the upstream region P1, the parallel blade base end 35b is disposed at the same position in the radial direction Dr in the rotor blade row 31A of the first stage 50A to the rotor blade row 31D of the fourth stage 50D (multiple upper flow blade rows 31U). Here, the parallel blade base end 35b is a region including an end of the inner side Dri of the parallel blade 35 in the radial direction Dr, and is a region close to the outer circumferential surface 21f of the rotor shaft 21. More specifically, the parallel blade base end 35b is a region of about 30% from the outer circumferential surface of the platform 32a with respect to the blade length Hb (the total length of the blade height from the inner circumferential surface of the platform 32a to the tip of the shroud 32c).

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

[0035] As a result, in the multiple upper flow blade cascades 31U, the parallel blade tip portions 35s are arranged so that their positions in the radial direction Dr gradually expand to the outer side Dro from the rotor blade cascade 31A of the first stage 50A toward the rotor blade cascade 31D of the fourth stage 50D. Here, the parallel blade tip portion 35s is a region of the parallel blade 35 that includes the end of the outer side Dro of the parallel blade 35 in the radial direction Dr, and is a region close to the inner circumferential surface of the casing 10. More specifically, the parallel blade tip portion 35s is a region of about 30% from the inner circumferential surface of the shroud 32c with respect to the blade length Hb.

[0036] On the other hand, the downstream cascade 31L has a three-dimensional blade 37 as the blade main body 32b, unlike the upstream cascade 31U. The three-dimensional blade 37 is formed so that the length in the radial direction Dr is longer than that of the parallel blade 35. The three-dimensional blade 37 is curved three-dimensionally so that the blade surface (pressure surface) facing one side of the circumferential direction Dc and the blade surface (suction surface) facing the other side of the circumferential direction Dc are twisted as they proceed in the blade height direction (radial direction Dr). In other words, the blade cross section of the three-dimensional blade 37 is not constant in the blade height direction, and the shape and cross-sectional area change. The three-dimensional blade 37 of the downstream cascade 31L is a reaction blade with a reaction degree R of, for example, 45% to 60%.

[0037] Among the multiple downstream blade cascades 31L, at least the three-dimensional blade 37 of the rotor blade cascade 31G of the final stage (seventh stage 50G) has a transonic blade type. The transonic blade type is a blade type that has a high critical speed at which a supersonic flow that deteriorates performance due to shock waves or separation occurs on the blade surface, and is unlikely to cause a sudden increase in resistance due to the generation of shock waves. Specifically, the transonic blade type is a blade type with a Mach number (a dimensionless quantity obtained by the ratio of the flow speed of steam S flowing out from the blade body to the speed of sound) of about 0.8 to 1.5. In this embodiment, the three-dimensional blade 37 of all the downstream blade cascades 31L has a transonic blade type.

[0038] The outer peripheral surface 21f of the rotor shaft 21 is formed in the area where the rotor blades 32 (three-dimensional blades 37) are arranged in the downstream region P2 so that in a cross section parallel to the axis Ar, the diameter gradually increases toward the outer side Dro in the radial direction Dr toward the downstream side Dad in the axial direction Da relative to the axis Ar.

[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 arranged at the same position in the radial direction Dr in the blade row 31E of the fifth stage 50E to the blade row 31G of the seventh stage 50G (plurality of downward flow blade rows 31L). Here, the three-dimensional blade base end 37b is a region including the end of the inner side Dri in the radial direction Dr of the three-dimensional blade 37 in the three-dimensional blade 37, and is a region close to the outer circumferential surface 21f of the rotor shaft 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 rows 31 are arranged in the main flow passage 15 including the upstream region P1 and the downstream region P2, the outer circumferential surface 21f is not formed so as to not shrink toward the inner side Dri in the radial direction Dr toward the downstream side Dad in the axial direction Da (so as not to 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 at the innermost side Dri in the radial direction Dr among the three-dimensional blade base ends 37b of the multiple downstream flow blade rows 31L.

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

[0042] As a result, in the multiple downstream blade cascades 31L, the three-dimensional blade tip 37s is arranged such that the position in the radial direction Dr gradually expands to the outside Dro from the blade cascade 31E of the fifth stage 50E to the blade cascade 31G of the seventh stage 50G. Here, the three-dimensional blade tip 37s is a region of the three-dimensional blade 37 that includes the end of the outside Dro in the radial direction Dr of the three-dimensional blade 37 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% from the tip of the three-dimensional blade 37 including the shroud 32c with respect to the blade length Hb.

[0043] Furthermore, the amount of change in 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 to the outside Dro in the radial direction Dr is defined as ΔS1. Also, the amount of change in 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 to the outside Dro in the radial direction Dr is defined as ΔS2. In this case, in this embodiment, it is preferable that the amount of change ΔS1 is larger than the amount of 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 the two most adjacent pairs of the downstream blade rows 31L including the downstream blade row 31L (the rotor blade row 31E of the fifth stage 50E) located on the most upstream side Dau in the axial direction Da among the multiple downstream 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 the most adjacent pairs of the downstream blade rows 31L including the downstream blade row 31L (the rotor blade row 31G of the seventh stage 50G) located on the most downstream side Dad in the axial direction Da among the multiple downstream blade rows 31L.

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

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

[0047] In addition, in the 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] In addition, in the stator vane row 41G of the seventh stage 50G, which is the stator vane row 41 located at the most downstream side Dad in the axial direction Da, as shown in Figure 3, the throat width at the stator vane middle portion (middle portion) 42c is formed to be larger than the throat width at the stator vane tip portion 42s and the throat width at the stator vane base end portion 42b.

[0049] 2, the stator blade tip portion 42s is a region of the stator blade 42 that includes an end portion of the outer side Dro in the radial direction Dr of the stator blade 42 and is a region close to the inner circumferential surface of the outer ring 43. More specifically, the stator blade tip portion 42s is a region that is about 30% from the inner circumferential surface of the outer ring 43 with respect to the total length of the blade height of the stator blade 42 (the length in the radial direction Dr from the outer circumferential surface of the inner ring 46 to the inner circumferential surface of the outer ring 43).

[0050] Moreover, the stator blade base end 42b is a region of the stator blade 42 that includes an end of the inner side Dri in the radial direction Dr of the stator blade 42 and is a region close to the outer circumferential surface of the inner ring 46. More specifically, the stator blade base end 42b is a region that is about 30% of the entire blade height of the stator blade 42 from the outer circumferential surface of the inner ring 46.

[0051] Moreover, the stator blade intermediate portion 42c is a region sandwiched between the stator blade tip portion 42s and the stator blade base portion 42b in the radial direction Dr in the stator blade 42. More specifically, the stator blade intermediate portion 42c is a region that is about 40% of the total length of the blade height of the stator blade 42, including the central portion.

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

[0053] Furthermore, as shown in FIG. 4, the casing 10 of this embodiment further includes 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 exhausts the steam S that has flowed through the main flow path 15 to the outside of the casing 10. The exhaust casing 51 is disposed on the second-most side Dad in the axial direction Da in the casing 10. An exhaust chamber 13 that opens downward is formed in the lower part of the exhaust casing 51. The exhaust casing 51 exhausts to the outside the steam S whose static pressure has been restored by a diffuser 70 described later.

[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 disposed 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 of the present embodiment has an outer guide (guide member) 71 and an inner guide 72.

[0056] The outer guide 71 is disposed on the downstream side Dad in the axial direction Da with respect to the rotor blade row 31G of the seventh stage 50G. The outer guide 71 is formed so as to gradually expand from the upstream side Dau in the axial direction Da to the downstream side Dad to the outer side Dro in the radial direction Dr. The length L in the axial direction Da of 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 in the axial direction Da of 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 disposed at a distance from the outer guide 71 on the inner side Dri in the radial direction Dr. As a result, an annular flow passage 100, which is a flow passage through which steam S can flow, is defined between the outer guide 71 and the inner guide 72. The annular flow passage 100 is defined between the outer guide 71 and the inner guide 72 so as to have a circular ring shape when viewed from the axial direction Da. The annular flow passage 100 is connected to the main flow passage 15 on the downstream side Dad in the axial direction Da. The inner guide 72 extends from the upstream side Dau in the axial direction Da toward the downstream side Dad, inclining straight toward the outer side Dro in the radial direction Dr.

[0058] (Action and effect) The steam turbine 1 having the above-mentioned 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 peripheral surface 21f of the rotor shaft 21 is formed parallel to the axis Ar in a cross section parallel to the axis Ar. That is, the outer peripheral surface 21f of the rotor shaft 21 is formed so as not to be reduced inward Dri in the radial direction Dr from the upstream side Dau to the downstream side Dad in the axial direction Da in the region where the three-dimensional blade 37 is arranged in the downstream region P2. Therefore, in order to reduce the length of the radial direction Dr in the rotor blade row 31G of the seventh stage 50G, which is the final stage, it is not necessary to arrange the position of the three-dimensional blade base end 37b of the rotor blade row 31E of the fifth stage 50E on the outer side Dro in the radial direction Dr with respect 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 in the radial direction Dr of the three-dimensional blade base end 37b of the rotor blade row 31E of the fifth stage 50E can be kept to the inner side Dri of the radial direction Dr. In other words, an 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 is suppressed.

[0059] Here, in order to improve the efficiency of the upper flow cascade 31U having the parallel blades 35, it is necessary to increase the number of stages of the upper flow cascade 31U. When the number of stages of the upper flow cascade 31U is increased, the step pressure in each upper flow cascade 31U becomes smaller. When the step pressure becomes smaller, the speed of the steam S also becomes smaller. Even in this state where the step pressure becomes smaller, it is necessary to maintain an appropriate speed ratio (ratio of the circumferential speed of the parallel blade 35 to the speed of the steam S) for the parallel blade 35. In order to maintain the speed ratio, it is necessary to suppress the circumferential speed of the parallel blade 35. And, in order to suppress the circumferential speed of the parallel blade 35, it is necessary to move the position of the parallel blade base end 35b, which is the root of the parallel blade 35, closer to the inner side Dri in the radial direction Dr. In other words, it is necessary to move the position of the outer circumferential surface 21f of the rotor shaft 21 connected to the parallel blade 35 closer to the inner side Dri in the radial direction Dr.

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

[0061] In contrast, in the present invention, the increase in the diameter of the rotor shaft 21 at the position where the moving blade row 31E of the fifth stage 50E is arranged is suppressed. Therefore, it is not necessary to increase the diameter of the rotor shaft 21 at the moving blade row 31D of the fourth stage 50D aligned with the fifth stage 50E. In other words, the position of the outer circumferential surface 21f of the rotor shaft 21 at the downstream blade row 31L located at the most upstream side Dau in the axial direction Da is suppressed to the inner side Dri in the radial direction Dr. Therefore, even if the number of stages of the upper flow blade row 31U having the parallel blades 35 is increased, it is possible to suppress the occurrence of a large step on the rotor shaft 21 in the region where the upper flow blade row 31U having the parallel blades 35 switches to the lower flow blade row 31L having the three-dimensional blades 37. As a result, it is possible to increase the number of stages of the upper flow blade row 31U while suppressing the structural influence on the rotor 20 and the casing 10. This makes it possible to improve efficiency while mixing the parallel blades 35 and the three-dimensional blades 37.

[0062] In addition, the change amount ΔS2 of the position of the three-dimensional blade tip 37s in the rotor blade row 31F of the sixth stage 50F and the rotor blade row 31G of the seventh stage 50G to the outside Dro in the radial direction Dr is larger than the change amount ΔS1 of the position of the three-dimensional blade tip 37s in the rotor blade row 31E of the fifth stage 50E and the rotor blade row 31F of the sixth stage 50F to the outside Dro in the radial direction Dr. Therefore, in the region where the upper flow blade row 31U switches to the lower flow blade row 31L, the main flow passage 15 suddenly widens to the outside Dro in the radial direction Dr. Therefore, when the steam S flows from the upstream region P1 to the downstream region P2, it is easy for the steam S to flow to the outside Dro in the radial direction Dr rather than the inside Dri. Therefore, the entire length of the three-dimensional blade 37 can be effectively utilized.

[0063] In addition, in the stator vane row 41G of the seventh stage 50G, the throat width of the stator vane 42 is larger in the stator vane intermediate portion 42c than in the stator vane tip portion 42s and the stator vane base portion 42b. In particular, in this embodiment, the throat width becomes smaller from the stator vane intermediate portion 42c toward the stator vane tip portion 42s. Therefore, the radial flow, which is a flow in which the steam S spreads to the outside Dro in the radial direction Dr, is suppressed. In addition, the throat width of the stator vane 42 becomes smaller from the stator vane intermediate portion 42c toward the stator vane base portion 42b. Therefore, the degree of reaction can be reduced, and the leakage flow of steam into the gap between the stator vane tip portion 42s and the outer circumferential surface 21f of the rotor can be suppressed.

[0064] In addition, in the rotor blade row 31G of the seventh stage 50G, the clearance 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. Therefore, the leakage flow of the steam S between the three-dimensional blade tip 37s and the casing 10 can be effectively suppressed. Furthermore, by suppressing the leakage flow in the vicinity of the three-dimensional blade tip 37s, the radial flow can be suppressed by the three-dimensional blade 37 of the rotor blade row 31G of the seventh stage 50G. This suppresses loss and allows the three-dimensional blade 37 of the seventh stage 50G to effectively perform work.

[0065] Also, in the rotor blade row 31G of the seventh stage 50G, the three-dimensional blade 37 has a transonic blade type. This allows the three-dimensional blade 37 of the rotor blade row 31G of the seventh stage 50G to correspond to the flow velocity of the accelerated steam S flowing through the main flow passage 15 located on the most downstream side Dad in the axial direction Da. Particularly, in this embodiment, in all the downstream blade rows 31L, the three-dimensional blade 37 has a transonic blade type. Therefore, the three-dimensional blade 37 of all the downstream blade rows 31L including the seventh stage 50G can correspond to the flow velocity of the accelerated steam S. This allows the three-dimensional blade 37 to work effectively while suppressing loss.

[0066] In the diffuser 70, the length of the outer guide 71 in the axial direction Da is 85% to 120% of the length Hb in the radial direction Dr of the three-dimensional blade 37 of the downstream blade row 31L located at the most downstream side Dad in the axial direction Da. Therefore, the outer guide 71 guides the steam S flowing through the annular passage 100 of the diffuser 70 over a long distance in the axial direction Da. As a result, in the annular passage 100 of the diffuser 70, separation of the flow of the steam S on the outer side Dro in the radial direction Dr can be suppressed. Therefore, the diffuser 70 can reduce the flow velocity while suppressing separation of the steam S. Therefore, even if the flow velocity (average flow velocity) of the steam S flowing out of the rotor blade row 31G of the final stage is transonic, separation can be suppressed. Therefore, the static pressure of the steam S in the diffuser 70 can be efficiently restored.

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

[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 the stator blade rows 41, can be changed as appropriate. That is, the steam turbine 1 is not limited to a structure having seven stages (seven rotor blade rows 31 and stator blade rows 41) as in this embodiment. Therefore, the steam turbine 1 may have six or fewer stages as in this embodiment, or eight or more stages.

[0069] In this embodiment, the outer circumferential surface 21f of the rotor shaft 21 is formed parallel to the axis Ar in the entire area of ​​the upstream region P1 and the downstream region P2 in a cross section parallel to the axis Ar. However, the outer circumferential surface 21f of the rotor shaft 21 is not limited to such a structure. For example, the outer circumferential surface 21f of the rotor shaft 21 may be formed so as to gradually expand in diameter toward the outer side Dro in the radial direction Dr toward the downstream side Dad in the axial direction Da with respect to the axis Ar in the area where the three-dimensional blades 37 are arranged in the downstream region P2. Even with such a structure, it is possible to improve efficiency while mixing the parallel blades 35 and the three-dimensional blades 37, as in the case where the outer circumferential surface 21f of the rotor shaft 21 is formed parallel to the axis Ar. Furthermore, the outer circumferential surface 21f of the rotor shaft 21 may be formed so as to gradually expand in diameter toward the outer side Dro in the radial direction Dr toward the downstream side Dad in the axial direction Da with respect to the axis Ar in the upstream region P1.

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

[0071] (1) A steam turbine 1 according to a first aspect includes a rotor shaft 21 rotatable about an axis Ar, a plurality of moving blade rows 31 fixed to an outer side Dro of the rotor shaft 21 in a radial direction Dr based on the axis Ar and arranged at intervals in an axial direction Da along which the axis Ar extends, a casing 10 covering the rotor shaft 21 and the plurality of moving blade rows 31 from the outer side Dro of the radial direction Dr and having a main flow passage 15 through which steam can flow, and a plurality of stator blade rows 41 fixed to an inner side Dri of the casing 10 in the radial direction Dr and arranged on a first side Dau in the axial direction Da with respect to each of the plurality of moving blade rows 31, and a plurality of downstream flow wing rows 31L arranged in a downstream region P2 located on the second side Dad in the axial direction Da relative to P1, wherein the upper flow wing row 31U has a plurality of parallel blades 35 arranged at intervals in the circumferential direction Dc around the axis Ar, the lower flow wing row 31L has a plurality of three-dimensional blades 37 arranged at intervals in the circumferential direction Dc, and the stator blade row 41 has a plurality of stator blades 42 arranged at intervals in the circumferential direction Dc, and the outer peripheral surface 21f of the rotor shaft 21 facing the outer side Dro in the radial direction Dr is formed so as to gradually expand in diameter parallel to the axis Ar or toward the second side Dad in the axial direction Da relative to the axis Ar in a cross section parallel to the axis Ar in the region in which the three-dimensional blades 37 are arranged in the downstream region P2.

[0072] Such a steam turbine 1 includes an upper flow cascade 31U having parallel blades 35 and a lower flow cascade 31L having a three-dimensional blade 37. Furthermore, in this embodiment, the outer circumferential surface 21f of the rotor shaft 21 is formed so as to gradually expand in diameter toward the outer side Dro in the radial direction Dr toward the downstream side Dad in the axial direction Da relative to the axis Ar in a cross section parallel to the axis Ar. That is, the outer circumferential surface 21f of the rotor shaft 21 is formed so as not to shrink toward the inner side Dri in the radial direction Dr from the upstream side Dau in the axial direction Da toward the downstream side Dad in the downstream region P2 in the region where the three-dimensional blade 37 is arranged. Therefore, in order to reduce the length of the radial direction Dr in the rotor blade row 31G of the final stage, it is not necessary to arrange the position of the three-dimensional blade base end 37b of the lower flow cascade 31L located on the first side Dau in the axial direction Da to the outer side Dro in the radial direction Dr with respect to the position of the three-dimensional blade base end 37b of the rotor blade row 31G of the final stage. Therefore, the position in the radial direction Dr of the three-dimensional blade base end 37b of the downstream blade row 31L located at the first side Dau in the axial direction Da can be suppressed to the inner side Dri in the radial direction Dr. In other words, an increase in the diameter of the rotor shaft 21 at the position where the downstream blade row 31L located at the first side Dau in the axial direction Da is arranged is suppressed. As a result, it is not necessary to increase the diameter of the rotor shaft 21 in the upper flow blade row 31U located at the second side Dad side by side with the downstream blade row 31L located at the first side Dau in the axial direction Da. In other words, the position of the outer circumferential surface 21f of the rotor shaft 21 in the downstream blade row 31L located at the first side Dau in the axial direction Da is suppressed to the inner side Dri in the radial direction Dr. Therefore, even if the number of stages of the upper flow blade row 31U having the 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 the upper flow blade row 31U having the parallel blades 35 switches to the downstream flow blade row 31L having the three-dimensional blades 37. As a result, the number of stages of the upper flow blade row 31U can be increased while suppressing the structural impact on the rotor 20 and the casing 10. This makes it possible to improve efficiency while mixing the parallel blades 35 and the three-dimensional blades 37.

[0073] (2) A steam turbine 1 according to a second aspect is the steam turbine 1 of (1), wherein, in the downstream region P2, the positions of the three-dimensional blade tips 37s on the outer side Dro of the radial direction Dr of the multiple three-dimensional blades 37 are formed to expand to the outer side Dro of the radial direction Dr from the downstream blade row 31L located on the first side Dau in the axial direction Da toward the downstream blade row 31L located on the second side Dad in the axial direction Da, and the amount of change in the position of the three-dimensional blade tip 37s to the outer side Dro in the radial direction Dr in the two closest pairs of downstream blade rows 31L including the downstream blade row 31L located on the furthest first side Dau in the axial direction Da is greater than the amount of change in the position of the three-dimensional blade tip 37s to the outer side Dro in the radial direction Dr in the closest pair of downstream blade rows 31L including the downstream blade row 31L located on the furthest second side Dad in the axial direction Da.

[0074] As a result, in the region where the upper flow blade row 31U switches to the lower flow blade row 31L, the main flow passage 15 suddenly widens to the outer side Dro in the radial direction Dr. Therefore, when the steam S flows from the upstream region P1 to the downstream region P2, it is easy for the steam S to flow to the outer side Dro in the radial direction Dr rather than the inner side Dri. Therefore, the entire length of the three-dimensional blade 37 can be effectively utilized.

[0075] (3) A steam turbine 1 according to a third aspect is the steam turbine 1 of (2), wherein in the downstream cascade 31L located on the second-most side Dad in the axial direction Da, the clearance 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 in the radial direction Dr of the three-dimensional blade 37.

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

[0077] (4) A steam turbine 1 according to a fourth aspect is any one of the steam turbines 1 of (1) to (3), wherein in the stator vane row 41 located on the second most side Dad in the axial direction Da, the throat width in the middle portion of the stator vane 42 in the radial direction Dr is larger than the throat width at the stator vane tip portion 42s on the inner side Dri in the radial direction Dr of the stator vane 42 and the throat width at the stator vane base end portion 42b on the outer side Dro in the radial direction Dr of the stator vane 42.

[0078] This suppresses the radial flow, which is the flow of steam S spreading outward Dro in the radial direction Dr. In addition, the throat width of the stator vane 42 becomes smaller from the intermediate portion 42c toward the stator vane base end portion 42b. This reduces the degree of reaction and suppresses the leakage of steam into the gap between the stator vane tip portion 42s and the outer circumferential surface 21f of the rotor.

[0079] (5) A steam turbine 1 according to a fifth aspect is any one of the steam turbines 1 of (1) to (4), in which in the downstream cascade 31L located on the second most side Dad in the axial direction Da, the three-dimensional blade 37 has a transonic blade type.

[0080] This allows the three-dimensional blade 37 of the blade row 31G located on the second-most side Dad in the axial direction Da to be made to correspond to the flow velocity of the accelerated steam S flowing through the main flow passage 15 located on the second-most side Dad in the axial direction Da.

[0081] (6) A steam turbine 1 according to a sixth aspect is any one of the steam turbines 1 of (1) to (5), wherein the casing 10 is provided with a diffuser 70 that guides steam flowing out from the downstream casing 31L arranged at the second-most side Dad in the axial direction Da to the outside of the casing 10, and the diffuser 70 has a guide member 71 extending from a first side Dau in the axial direction Da toward the second side Dad to the outer side Dro in the radial direction Dr, and is formed so that the length of the guide member 71 in the axial direction Da is 85% to 120% of the length of the radial direction Dr of the three-dimensional blade 37 of the downstream casing 31L arranged at the second-most side Dad in the axial direction Da.

[0082] This means: 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, in the diffuser 70, separation of the flow of the steam S can be suppressed on the outer side Dro in the radial direction Dr. Therefore, in the diffuser 70, separation of the steam S can be suppressed while reducing the flow velocity. Therefore, even if the flow velocity (average flow velocity) of the steam S flowing out from the rotor blade row 31G of the final stage is transonic, separation can be suppressed. Therefore, the static pressure of the steam S in the diffuser 70 can be efficiently restored.

[0083] (7) A steam turbine 1 according to a seventh aspect is any one of the steam turbines 1 according to (1) to (6), in which 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 passage chamber 13...Exhaust chamber 15…Main channel 20…Rotor 21...Rotor shaft 21f…Outer surface 22...Axis core part 23...Disc 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…Stationary blade 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...Annular flow path Ar…Axis line Da…Axial direction 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 rotatable about an axis; a plurality of moving blade rows fixed to the outside of the rotor shaft in the radial direction with respect to the axis and arranged at intervals in the axial direction in which the axis extends; a casing that covers the rotor shaft and the plurality of moving blade rows from the outside in the radial direction and forms a main flow path through which steam can flow inside; a plurality of stationary 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 moving blade rows; The plurality of moving blade rows include: a plurality of upstream moving blade rows arranged in an upstream region in the main flow path; a plurality of downstream moving blade rows arranged in a downstream region in the main flow path that is located on the second side in the axial direction with respect to the upstream region; The upstream moving blade rows have a plurality of parallel blades arranged at intervals in the circumferential direction around the axis; The downstream moving blade rows have a plurality of three-dimensional blades arranged at intervals in the circumferential direction; The stationary blade rows have a plurality of stationary blades arranged at intervals in the circumferential direction; The outer peripheral surface of the rotor shaft facing the outside in the radial direction is formed such that in a cross section parallel to the axis in the region where the three-dimensional blades in the downstream region are arranged, it is parallel to the axis or gradually expands in the radial direction toward the outside in the second side in the axial direction with respect 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 so as to expand outward in the radial direction from the downstream moving blade row located on the first side in the axial direction toward the downstream moving blade row located on the second side in the axial direction; In a pair of the closest downstream moving blade rows including the downstream moving blade row located most on the first side in the axial direction, the amount of change of the position of the three-dimensional blade tip portion toward the outer side in the radial direction is larger than the amount of change of the position of the three-dimensional blade tip portion toward the outer side in the radial direction in a pair of the closest downstream moving blade rows including the downstream moving blade row located most on the second side in the axial direction. A steam turbine.

2. In the downstream moving blade row located most on the second side in the axial direction, the clearance in the radial direction between the three-dimensional blade tip portion and the casing is formed to be 1.5 to 2.5% with respect to the blade length in the radial direction of the three-dimensional blade. The steam turbine according to claim 1.

3. In the stationary blade row located most on the second side in the axial direction, the throat width at the inner stationary blade tip portion in the radial direction of the stationary blade and the throat width at the outer stationary blade base portion in the radial direction of the stationary blade are such that the throat width at the middle portion in the radial direction of the stationary blade is larger. The steam turbine according to claim 1 or 2.

4. In the downstream moving blade row located most on the second side in the axial direction, the three-dimensional blade has a transonic airfoil. The steam turbine according to claim 1 or 2.

5. The casing includes a diffuser that guides the steam flowing out from the downstream moving blade row disposed most on the second side in the axial direction to the outside of the casing. The diffuser has a guide member that extends outward in the radial direction from the first side to the second side in the axial direction. The axial length of the guide member is formed to be 85% to 120% with respect to the radial length of the three-dimensional blade in the downstream moving blade row located most on the second side in the axial direction. The steam turbine according to claim 1 or 2.

6. The parallel blade is an impulse blade, and the three-dimensional blade is a reaction blade. The steam turbine according to claim 1 or 2.

Images