axial turbine

Abstract

The axial turbine of the present application includes a rotating shaft, a plurality of rotating blades having a rotating blade main body (42) and a shroud (43) and arranged at intervals in the circumferential direction, a casing (5) formed with a recess (8) that accommodates the shroud (43), a fin (7) that forms a gap (C) between its outer peripheral surface (43A) and the shroud (43), a stationary blade support portion (90) disposed on the downstream side of the recess (8), a plurality of stationary blades arranged at intervals in the circumferential direction, and an annular partition plate (70) that extends from the recess downstream surface (8D) to the upstream side, with a bypass flow path (P) formed in the casing that connects a region radially further outward than the partition plate (70) and regions between the stationary blades.

Description

[0001] This application is a divisional application of the invention patent application filed on July 30, 2020, with application number 202080051648.5 and invention title "Axial Flow Turbine". Technical Field

[0002] This invention relates to an axial flow turbine. This application claims priority based on Japanese Patent Application No. 2019-141489, filed on July 31, 2019, the contents of which are incorporated herein by reference. Background Technology

[0003] A steam turbine, or an axial-flow turbine including a gas turbine, is configured such that the rotor is supported by bearings within a casing and rotates freely. Multiple rotating blades are fixed to the rotor, while multiple fixed blades are fixed to the casing between the rotating blades. When steam is supplied from the casing's supply port, the steam passes through the rotating and fixed blades, driving the rotor to rotate via the rotating blades, thereby discharging the steam to the outside through the outlet.

[0004] In steam turbines, a gap is provided between the leading end of the rotating blades (shroud) and the inner circumferential surface of the casing to ensure smooth rotor rotation. Steam passing through this gap flows downstream as a leakage stream, without imparting rotational energy to the rotor. Here, the loss caused by the energy held by the leakage stream not being effectively used as the turbine's rotational power is generally called bypass loss; the loss caused by the leakage stream flowing into the main flow path after passing through the gap is called mixing loss; and the loss caused by the leakage stream flowing into the main flow path interfering with the downstream blade row is called interference loss. To reduce this mixing loss, a method exists where, as in Patent Document 1, a component restricting the direction of the leakage stream is provided at the downstream end of the rotating blade shroud, thereby adjusting the direction of the leakage stream to the direction of the main flow path.

[0005] Previous technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2019-35347 Summary of the Invention

[0008] The technical problem to be solved by the invention

[0009] The technology in Patent Document 1 is effective in reducing mixing losses. However, it is difficult to ensure that the flow from the outer periphery of the rotating blade array toward the stationary component (i.e., the fixed blade array) located downstream is always aligned with the direction of the circumferentially uneven main flow passing through the rotating blade arrays arranged at intervals in the circumferential direction, and interference losses are also generated at the fixed blade array on the downstream side.

[0010] The present invention was made to solve the above-mentioned problems, and its purpose is to provide an axial flow turbine that improves efficiency by reducing mixing losses while also reducing the impact of interference losses.

[0011] means for solving technical problems

[0012] An axial turbine according to one aspect of the present invention comprises: a rotating shaft extending along an axis; a plurality of rotating blades having a rotating blade body extending radially outward from the rotating shaft and a shroud disposed at the radially outward end of the rotating blade body, and arranged at intervals in the circumferential direction; a housing surrounding the rotating blades from the radially outward direction, and having a recess formed on the inner circumferential surface to accommodate the shroud; fins protruding radially inward from the opposing surface of the recess opposite to the shroud, thereby forming a gap between them and the outer circumferential surface of the shroud; a fixed blade support disposed downstream of the recess on the inner circumferential surface of the housing; a plurality of fixed blades extending radially inward from the fixed blade support and arranged at intervals in the circumferential direction; and an annular baffle extending upstream from the downstream side of the recess, i.e., the downstream surface of the recess, and having a bypass flow path formed on the housing about the axis, connecting the region on the downstream surface of the recess that is radially outward from the baffle and the region on the inner circumferential surface of the housing between the fixed blades.

[0013] Inside the axial turbine, a main flow (the flow path) is formed between adjacent rotating blade bodies, and a leakage flow (the flow branching off from the main flow) flows into the recess. After passing through a gap, the leakage flow forms a vortex that rotates in a direction from the downstream face of the recess toward the opposing face. A component of the vortex forms another vortex by interfering with the leakage flow flowing in from the gap. Because this small vortex merges with the main flow, mixing loss sometimes occurs. However, in the above structure, a component of the leakage flow is directly guided to the area between the stationary blades through a bypass flow path. Therefore, the generation of small vortices caused by the interference between the leakage flow and the vortex, as described above, can be suppressed. Furthermore, the main flow containing the small vortex is not uniform in the circumferential direction and has a rotational component about the axis of rotation, so the direction of the flow flowing into the stationary blade row will pulsate. However, the relative position between the bypass flow path outlet and the stationary blades is constant, so the leakage flow can be supplied to the stationary blades from a consistently constant relative position as a flow with a constant direction.

[0014] In the aforementioned axial turbine, in a cross-sectional view including the axis, the bypass flow path can extend radially outward and inward as it moves from the upstream side toward the downstream side.

[0015] According to the above structure, the bypass flow path can guide a portion of the leakage flow passing through the recess to the area between the fixed blades with a shorter distance. On the other hand, for example, if the bypass flow path bends along its course, the flow will be obstructed at the bend, thus preventing the leakage flow from being effectively bypassed. The above structure reduces this possibility.

[0016] In the aforementioned axial turbine, when viewed from the radially outer side, the bypass flow path can extend to the rearward side in the rotational direction of the rotating shaft as it moves from the upstream side toward the downstream side.

[0017] According to the above structure, the bypass flow path extends rearward in the direction of rotation of the rotating shaft, moving from the upstream side to the downstream side. This reduces the inflow angle (incident angle) of the flow relative to the fixed blades on the downstream side. As a result, the flow of fluid within the axial turbine becomes smoother.

[0018] In the aforementioned axial flow turbine, when the dimension of the fixed blade support in the axial direction is set as L, and the dimension from the upstream end of the fixed blade support to the downstream end of the bypass flow path is set as A, the value of A / L can satisfy 0 < A / L < 0.15.

[0019] According to the above structure, with the value of A / L satisfying 0 < A / L < 0.15, the downstream end of the bypass flow path is formed at a position offset upstream from each other between the fixed blades. Therefore, the angle of incidence of the flow exiting the bypass flow path relative to the fixed blades can be reduced.

[0020] In the aforementioned axial flow turbine, when the dimension of the fixed blade support in the axial direction is set as L, and the dimension from the upstream end of the fixed blade support to the downstream end of the bypass flow path is set as A, the value of A / L can satisfy 0.2 < A / L < 0.4.

[0021] According to the above structure, with the A / L value satisfying 0.2 < A / L < 0.4, the downstream end of the bypass flow path is formed at a position offset downstream from each other between the fixed blades. Therefore, the secondary flow generated on the downstream side of the fixed blades can be dispersed by the flow exiting the bypass flow path. As a result, the efficiency reduction of the axial turbine caused by the influence of the secondary flow can be suppressed.

[0022] In the aforementioned axial turbine, the downstream surface of the recess can be located further downstream than the end of the upstream side of the fixed blade in the axial direction.

[0023] According to the above structure, the downstream surface of the recess is located further downstream in the axial direction than the upstream end of the fixed blade. This reduces the axial distance between the rotating blade and the fixed blade. Consequently, losses can be further reduced compared to cases where the axial distance is larger.

[0024] In the aforementioned axial turbine, the cross-sectional area of ​​the bypass flow path can gradually decrease from the upstream side to the downstream side.

[0025] According to the above structure, the cross-sectional area of ​​the bypass flow path gradually decreases from the upstream side to the downstream side. This allows for an increase in the flow velocity of the fluid ejected from the bypass flow path. Consequently, the incident angle relative to the fixed blades can be further optimized, and the influence of secondary flows generated around the fixed blades can be further reduced.

[0026] In the aforementioned axial turbine, the bypass flow path can have a circular cross-sectional shape.

[0027] Based on the above structure, since the cross-sectional shape of the bypass flow path is circular, it is easier to manufacture compared to cases with, for example, a rectangular cross-sectional shape. This reduces manufacturing and maintenance costs.

[0028] The aforementioned axial turbine may also include multiple anti-rotation plates, which extend from the outer periphery of the partition plate to the inner periphery of the recess and are arranged at intervals in the circumferential direction.

[0029] Based on the above structure, the circumferential rotation component of the flow within the recess can be reduced by using a rotation prevention plate.

[0030] Invention Effects

[0031] According to the present invention, an axial turbine can be provided that improves efficiency by reducing mixing losses while also reducing the impact of interference losses. Attached Figure Description

[0032] Figure 1 This is a cross-sectional view showing the structure of the steam turbine (axial flow turbine) according to the first embodiment of the present invention.

[0033] Figure 2 This is an enlarged cross-sectional view of the main part of the steam turbine according to the first embodiment of the present invention.

[0034] Figure 3 This is a view of the downstream surface of the concave portion of the steam turbine according to the first embodiment of the present invention, viewed from the upstream side.

[0035] Figure 4 This is an enlarged cross-sectional view of the main part of the steam turbine according to the second embodiment of the present invention.

[0036] Figure 5 This is a view of the casing of the steam turbine according to the second embodiment of the present invention, viewed from the radial inside.

[0037] Figure 6 This is a view of the casing of a modified example of the second embodiment of the present invention, viewed from the radial inside.

[0038] Figure 7 This is an enlarged cross-sectional view of the main part of the steam turbine according to the third embodiment of the present invention.

[0039] Figure 8 This is a view of the casing of the steam turbine according to the third embodiment of the present invention, viewed from the radial inside.

[0040] Figure 9 This is a view of the casing of a modified example of the third embodiment of the present invention, viewed from the radial inside.

[0041] Figure 10 This is an enlarged cross-sectional view of the main part of the steam turbine according to the fourth embodiment of the present invention.

[0042] Figure 11 This is an enlarged cross-sectional view of the main part of the steam turbine according to the fifth embodiment of the present invention.

[0043] Figure 12 This is a diagram illustrating a general variation of various embodiments of the present invention, and is a view of the downstream surface of the recess from the upstream side.

[0044] Symbol Explanation

[0045] 1-Steam turbine, 2-Rotating shaft, 3-Bearing assembly, 4-Rotating blade row, 5-Shell, 5A-Inner circumferential surface of the shell, 6-Fixed blade row, 7-Fin, 8-Recess, 31-Journal bearing, 32-Thrust bearing, 40-Rotating blade, 41-Rotating blade platform, 42-Rotating blade body, 43-Rotating blade shroud, 43A-Outer circumferential surface of the shroud, 51-Inlet, 52-Exhaust port, 60-Fixed blade, 61-Fixed blade body, 62-Inner ring of fixed blade, 71-Shell Body-side fins, 71D-downstream-side fins, 71S-downstream surface of fins, 72-rotating blade-side fins, 81-first region, 82-second region, 8A-upstream surface of the recess, 8B-opposing surface, 8C-downstream-side opposing surface, 8D-downstream surface of the recess, C-gap, Fb-bypass flow, Fm-mainstream flow, Fr-backflow, Fs-leakage flow, Ft-through flow, 0-axis, P, Pb, Pc, Pd-bypass flow paths, t-downstream-side end, t'-upstream-side end, V1-vortex. Detailed Implementation

[0046] [First Implementation Method]

[0047] refer to Figures 1 to 3 The first embodiment of the present invention will be described. In this embodiment, a steam turbine 1 will be used as an example of an axial flow turbine. However, in addition to the steam turbine 1, a gas turbine can also be used as an axial flow turbine. Figure 1 As shown, the steam turbine 1 includes a rotating shaft 2, a bearing assembly 3, multiple rows of rotating blades 4, a casing 5, multiple rows of fixed blades 6, and fins 7 (see reference). Figure 2 The rotating shaft 2 is cylindrical, extending along axis O. A bearing assembly 3 supports the shaft end of the rotating shaft 2. The bearing assembly 3 has a pair of journal bearings 31 and only one thrust bearing 32. The pair of journal bearings 31 are respectively disposed at the ends of the rotating shaft 2 on both sides in the direction of axis O. Each journal bearing 31 supports a radial load relative to axis O. The thrust bearing 32 is disposed only on one side in the direction of axis O. The thrust bearing 32 supports a load in the direction of axis O. Multiple rows of rotating blades 4 are provided on the outer circumferential surface of the rotating shaft 2, spaced apart in the direction of axis O. Each row of rotating blades 4 has multiple rotating blades 40 arranged at intervals in the circumferential direction relative to axis O. Each rotating blade 40 has a rotating blade platform 41, a rotating blade body 42, and a rotating blade cover 43 (cover). The rotating blade platform 41 protrudes radially outward from the outer circumferential surface of the rotating shaft 2. The rotating blade body 42 is mounted on the outer circumferential surface of the rotating blade platform 41. The rotating blade body 42 extends radially and has a blade-like cross-sectional shape when viewed radially. A rotating blade guard 43 is installed at the radially outer end of the rotating blade body 42.

[0048] The rotating shaft 2 and the rotating blade row 4 (rotating blade 40) are surrounded radially outward by the housing 5. The housing 5 is cylindrical with axis O as its center. Multiple fixed blade rows 6 are arranged at intervals along axis O on the inner circumferential surface of the housing 5. These fixed blade rows 6 alternate with the rotating blade row 4 in the direction of axis O. Each fixed blade row 6 has multiple fixed blades 60 arranged at intervals in the circumferential direction relative to axis O. Each fixed blade 60 has a fixed blade body 61, a fixed blade inner ring 62, and a fixed blade support 90. The fixed blade body 61 is mounted on the fixed blade support 90. The fixed blade support 90 is the area between the aforementioned recesses 8 on the inner circumferential surface of the housing 5. The fixed blade body 61 extends radially from the inner circumferential surface of the fixed blade support 90 and has a blade-shaped cross-section when viewed radially. The fixed blade inner ring 62 is mounted at the radially inner end of the fixed blade body 61. On the inner circumferential surface of the housing 5, a pair of adjacent fixed blades 60 have recesses 8 formed between them, extending radially outward from the inner circumferential surface of the housing 5. The aforementioned rotating blade guard 43 is accommodated in these recesses 8.

[0049] A supply port 51 is formed at one end of the housing 5 along the axial direction O to introduce high-temperature, high-pressure steam supplied from the outside. An exhaust port 52 is formed at the other end of the housing 5 along the axial direction O to discharge steam passing through the housing 5. The steam introduced from the supply port 51 collides alternately with multiple rotating blade rows 4 (rotating blades 40) and multiple fixed blade rows 6 (fixed blades 60) as it passes through the housing 5 from one side to the other along the axial direction O. This imparts rotational energy to the rotating shaft 2. The rotation of the rotating shaft 2 is taken out from the shaft end and used, for example, to drive a generator (not shown). In the following description, the steam flow flowing from one side to the other along the axial direction O within the housing 5 is called the main flow Fm. Furthermore, the side where the main flow Fm flows in (the side along the axial direction O) is called the upstream side, and the side where the main flow Fm flows out (the other side along the axial direction O) is called the downstream side.

[0050] Next, refer to Figure 2 The structure around the aforementioned recess 8 will be described. Figure 2 This is a magnified view showing the periphery of the recess 8, including the section along axis 0. (See diagram below.) Figure 2As shown, the recess 8 is recessed radially outward from the inner circumferential surface (inner circumferential surface 5A) of the housing 5, forming a square groove. The recess 8 has a first region 81 and a second region 82 located downstream of the first region 81. The first region 81 and the second region 82 are separated by the housing-side fins 71, the details of which will be described later. Among the surfaces forming the first region 81, the surface facing downstream (i.e., the surface located upstream within the first region 81) is designated as the upstream surface 8A of the recess. Among the surfaces forming the first region 81, the surface facing radially inward is designated as the opposing surface 8B. The opposing surface 8B extends along the axis O. The opposing surface 8B is radially outward opposite to the outer circumferential surface (outer circumferential surface 43A) of the aforementioned rotating blade shroud 43. In this embodiment, in the cross-sectional view, the upstream surface 8A and the opposing surface 8B of the recess are orthogonal to each other.

[0051] Multiple (two in one example) shell-side fins 71 are provided on the opposing surface 8B at intervals along the axial direction 0. Alternatively, the number of shell-side fins 71 may be three or more. Each shell-side fin 71 is plate-shaped, extending radially inward from the opposing surface 8B. A radially expanding gap (gap C) is formed between the leading end of each shell-side fin 71 and the outer peripheral surface 43A of the shield. Furthermore, rotating blade-side fins 72 are provided on the outer peripheral surface 43A of the shield, between the two shell-side fins 71. The rotating blade-side fins 72 are plate-shaped, extending radially outward from the outer peripheral surface 43A of the shield. A radially expanding gap (gap C) is formed between the leading end of the rotating blade-side fin 72 and the opposing surface 8B.

[0052] Next, the structure of the second region 82 will be described. The second region 82 is separated from the first region 81 by the shell-side fin 71 located on the most downstream side of the two shell-side fins 71 mentioned above (downstream fin 71D). The second region 82 is defined by the downstream-facing surface of the downstream fin 71D, i.e., the downstream surface 71S of the fin, the downstream surface 8D of the recess that faces the downstream surface 71S from the direction of axis O, the downstream-facing opposing surface 8C facing the radially inward side, a portion of the downstream side of the outer peripheral surface 43A of the shroud, and the partition 70 (described later).

[0053] The partition 70 extends upstream from the innermost radial end of the downstream surface 8D of the recess, and is annular about axis O. The partition 70 is located slightly radially inward than the outer peripheral surface 43A of the casing. The inner peripheral surface of the partition 70 is flush with the inner peripheral surface 5A of the aforementioned housing. The outer peripheral surface of the partition 70 faces the downstream opposing surface 8C radially. More specifically, in a cross-sectional view including axis O, the outer peripheral surface of the partition 70 extends parallel to the downstream opposing surface 8C.

[0054] A rotation prevention plate 80 is provided between the outer peripheral surface of the baffle 70 and the downstream opposing surface 8C. This rotation prevention plate 80 is provided to remove rotating components from the steam flow flowing downstream through the gap C between the downstream fin 71D and the outer peripheral surface 43A of the shroud; details will be described later. (Furthermore, this rotating component refers to the velocity component remaining in the leaked steam.) Figure 3 As shown, the anti-rotation plate 80 extends radially from the outer peripheral surface of the partition plate 70 toward the downstream opposing surface 8C (the inner peripheral surface of the recess 8), and a plurality of them are arranged at intervals in the circumferential direction relative to the axis O. Furthermore, the downstream end of the anti-rotation plate 80 (i.e., the downstream surface 8D of the recess) is located upstream of the leading edge Ef of the fixed blade body 61.

[0055] like Figure 2 or Figure 3 As shown, a bypass flow path P is formed on the housing 5 (fixed blade support portion 90) connecting the downstream surface 8D of the recess and the inner circumferential surface 5A of the housing. In a cross-sectional view including axis O, the bypass flow path P extends from the upstream side toward the downstream side in a radially outward and inward manner. The upstream end of the bypass flow path P opens in the area between the aforementioned rotation prevention plates 80 and each other on the downstream surface 8D of the recess, which is radially outward of the partition plate 70. The upstream end of the bypass flow path P is located radially outward of the aforementioned outer circumferential surface 43A of the shield. The downstream end of the bypass flow path P opens in the area between the fixed blades 60 and each other on the inner circumferential surface 5A of the housing. The downstream end of the bypass flow path P is located further downstream of the leading edge of the fixed blade 60. Furthermore, in this embodiment, when viewed radially outward relative to axis O, the bypass flow path P extends parallel to axis O. And, as Figure 3 As shown, the upstream end of the bypass flow path P is formed at the center between adjacent pairs of rotation prevention plates 80.

[0056] Next, the operation of the steam turbine 1 according to this embodiment will be described. When the steam turbine 1 is running, steam is supplied from an external steam supply source (boiler, etc.) to the casing 5 through the aforementioned supply port 51. Steam forms a mainstream Fm within the casing 5, flowing from the upstream side to the downstream side. The mainstream Fm passes between multiple fixed blade rows 6 and between multiple rotating blade rows 4 as it passes through the casing 5. As it passes between the fixed blade rows 6, the steam velocity increases. The rectified steam flow collides with the rotating blade rows 4, imparting rotational energy to the rotating shaft 2.

[0057] Here, a portion of the main flow Fm flows into the aforementioned recess 8 to form a leakage flow Fs. More specifically, the leakage flow Fs flows into the first region 81 through the gap between the upstream surface 8A of the recess 8 and the rotating blade shroud 43. A portion of the leakage flow Fs is blocked by the aforementioned fins 7. On the other hand, the remaining portion of the leakage flow Fs flows into the downstream second region 82 through the gap C between the shell-side fin 71 and the outer peripheral surface 43A of the shroud, and the gap C between the rotating blade-side fin 72 and the opposing surface 8B.

[0058] A portion of the leakage flow Fs flowing into the second region 82 flows sequentially along the outer peripheral surface of the aforementioned baffle 70, the downstream surface 8D of the recess, the downstream opposing surface 8C, and the downstream surface 71S of the fin. Thus, a flow pattern is formed within the second region 82 as described above. Figure 2 The eddy V1 is shown. Additionally, accompanying the rotation of the rotating blade body 42 and the rotating blade shroud 43, the leakage flow Fs includes a rotational component that circulates in the rotational direction of these rotating blade bodies 42 and the rotating blade shroud 43. Most of this rotational component is removed by colliding with the aforementioned rotation prevention plate 80.

[0059] Of all the components of the leakage flow Fs, the remaining components that do not become the vortex V1 flow as the through flow Ft from the outer peripheral surface 43A of the shroud towards the outer peripheral surface of the baffle 70 to the downstream side. After merging with the vortex V1, a portion of the through flow Ft becomes the backflow Fr and merges again with the main flow Fm. On the other hand, the remaining components of the through flow Ft flow further downstream and flow into the bypass flow path P. The flow flowing into the bypass flow path P is gradually guided from the radially outer side to the inner side as it flows along the bypass flow path P, thus becoming the bypass flow Fb. The bypass flow Fb merges with the main flow Fm between the fixed blades 60.

[0060] As described above, inside the steam turbine 1, a main flow (Fm) is formed between adjacent rotating blade bodies 42, and a flow (Fs) branches from the main flow Fm into the recess 8. After passing through the gap C, the Fs forms a vortex V1 that rotates along the direction from the downstream face 8D of the recess towards the downstream opposing face 8C. A component of the vortex V1 forms another vortex (small vortex) by interfering with the Fs flowing in from the gap C. Because this small vortex merges with the main flow Fm, mixing loss sometimes occurs. However, in the above structure, a component of the Fs is directly guided to the area between the fixed blades 60 through the bypass flow path P. Therefore, the generation of small vortices caused by the interference between the Fs and the vortex V1, as described above, and the resulting mixing loss can be suppressed. As a result, the efficiency of the steam turbine 1 can be further improved.

[0061] Furthermore, in the above structure, in a cross-sectional view including the axis O, the bypass flow path P extends radially outward and inward from the upstream side toward the downstream side. According to this structure, a portion of the leakage flow Fs flowing through the recess 8 can be guided to the area between the fixed blades 60 via the bypass flow path P with a shorter distance. On the other hand, for example, if the bypass flow path P bends at a point along its path, the flow will be obstructed at that bend, thus preventing the leakage flow Fs from being effectively bypassed. According to the above structure, this possibility can be reduced.

[0062] Furthermore, according to the above structure, by providing the anti-rotation plate 80, the circumferential rotation component of the flow within the recess 8 can be reduced. This further improves the performance of the steam turbine 1.

[0063] The first embodiment of the present invention has been described above. Furthermore, various changes and modifications can be made to the above structure without departing from the spirit of the invention. For example, in the first embodiment described above, a structure including a rotation prevention plate 80 in addition to the bypass flow path P has been described. However, a structure without the rotation prevention plate 80 may also be used. Even in this case, the rotation component of the leakage flow Fs can be sufficiently removed through the bypass flow path P, thus reducing the aforementioned mixing losses.

[0064] [Second Implementation]

[0065] Next, refer to Figure 4 The second embodiment of the present invention will be described. Furthermore, structures identical to those in the first embodiment described above are labeled with the same reference numerals, and detailed descriptions are omitted. For example... Figure 4 As shown, in this embodiment, the position of the downstream end t of the bypass flow path Pb differs from that in the first embodiment described above. Specifically, when the dimension of the fixed blade support 90 in the axial direction O is set to L, and the dimension from the upstream end of the fixed blade support 90 to end t is set to A, the value of A / L satisfies the relationship 0 < A / L < 0.15. More preferably, the value of A / L is 0.05 < A / L < 0.10. The most preferably, the value of A / L is A / L = 0.08. That is, the downstream end t of the bypass flow path Pb is formed on the inner circumferential surface of the fixed blade support 90 at a position biased towards the upstream side.

[0066] Furthermore, such as Figure 5 As shown, in this embodiment, when viewed from the radial inside, the aforementioned end t is formed at a position offset towards one side of the adjacent rotation prevention plates 80 in the circumferential direction. More specifically, this end t is formed at a position on the front side offset towards the rotation direction R of the rotation axis 2, with reference to the bisector D between the rotation prevention plates 80.

[0067] According to the above structure, with the value of A / L satisfying 0 < A / L < 0.15, the downstream end t of the bypass flow path Pb is formed at a position offset upstream of the fixed blades 60. Therefore, the inflow angle (incident angle) of the flow exiting the bypass flow path Pb relative to the fixed blades can be reduced. As a result, the flow of the main flow Fm within the steam turbine 1 can be made smoother, thereby further improving the efficiency of the steam turbine 1.

[0068] And, as Figure 5 As shown, the circumferential position of the end t is set close to the back side (negative pressure surface side) of the fixed blade. By opening the end t at this position, peeling near the leading edge of the back side (negative pressure surface side) of the fixed blade can be suppressed.

[0069] The second embodiment of the present invention has been described above. Furthermore, various changes and modifications can be made to the above structure without departing from the spirit of the invention. For example, in the second embodiment described above, the structure of the steam turbine 1 including the anti-rotation plate 80 was described. However, as... Figure 6 As shown, a structure without the anti-rotation plate 80 can also be used.

[0070] [Third Implementation Method]

[0071] Next, refer to Figure 7 and Figure 8 The third embodiment of the present invention will be described. Furthermore, structures identical to those in the above embodiments will be labeled with the same reference numerals, and detailed descriptions will be omitted. For example... Figure 7 As shown, in this embodiment, the position of the downstream end t of the bypass flow path Pc differs from that in the embodiments described above. Specifically, when the dimension of the fixed blade support 90 in the axial direction O is set to L, and the dimension from the upstream end of the fixed blade support 90 to the end t is set to A, the value of A / L satisfies the relationship 0.2 < A / L < 0.4. A / L is more preferably 0.25 < A / L < 0.35. The most preferably is 0.3. That is, the downstream end t of the bypass flow path Pb is formed on the inner circumferential surface of the fixed blade support 90 at a position biased towards the downstream side.

[0072] Furthermore, such as Figure 8 As shown, in this embodiment, when viewed from the radially inner side, the aforementioned end t is formed at a position offset circumferentially from each other between adjacent rotation prevention plates 80. More specifically, this end t is formed at a rearward position offset in the rotation direction R of the rotation axis 2, with reference to the bisector D between the rotation prevention plates 80. Furthermore, as... Figure 8As shown, the upstream end t' of the bypass flow path Pc is positioned at the front side in the rotation direction R, with the downstream end t as a reference. That is, the bypass flow path Pc extends obliquely from the upstream side to the downstream side in a manner from the front side to the rear side in the rotation direction R.

[0073] According to the above structure, with the value of A / L satisfying 0.2 < A / L < 0.4, the downstream end t of the bypass flow path Pc is formed at a position offset downstream of the fixed blades 60. Therefore, the secondary flow generated downstream of the fixed blades 60 can be dispersed by the flow exiting the bypass flow path Pc. As a result, the efficiency reduction of the steam turbine 1 caused by the influence of the secondary flow can be suppressed.

[0074] Furthermore, according to the above structure, the bypass flow path Pc extends rearward in the rotational direction R of the rotating shaft 2 from the upstream side to the downstream side. This reduces the inflow angle (incident angle) of the flow relative to the fixed blade 60 on the downstream side. As a result, the flow of fluid (mainstream Fm) within the steam turbine 1 becomes smoother.

[0075] In addition, such as Figure 8 As shown, the circumferential position of the end t is open near the ventral side (pressure surface side) of the fixed blade. This suppresses the generation of secondary flow on the ventral side (pressure surface side) of the fixed blade.

[0076] The third embodiment of the present invention has been described above. Furthermore, various changes and modifications can be made to the above structure without departing from the spirit of the invention. For example, in the third embodiment described above, the structure of the steam turbine 1 including the anti-rotation plate 80 was described. However, as... Figure 9 As shown, a structure without the rotation prevention plate 80 can also be used. In this case, since the rotation component of the leakage flow Fs is removed only through the bypass flow path Pc, unlike the third embodiment described above, when viewed radially, the bypass flow path Pc preferably extends along the axis O.

[0077] [Fourth Implementation Method]

[0078] Next, refer to Figure 10 The fourth embodiment of the present invention will be described. Furthermore, structures identical to those in the above embodiments will be labeled with the same reference numerals, and detailed descriptions will be omitted. For example... Figure 10As shown, in this embodiment, the downstream end of the anti-rotation plate 80 (i.e., the downstream surface 8D of the recess) is located further downstream than the leading edge Ef of the fixed blade body 61. That is, in this embodiment, the distance in the axial direction O between the rotating blade 40 and the fixed blade 60 is smaller compared to the structure of the first embodiment described above. With this structure, due to space constraints, a method is used to ensure space for mounting the anti-rotation plate 80 by further excavating the downstream surface of the recess 8 (applying cutting machining). Thus, the downstream surface 8D of the recess is located further downstream than the upstream end (leading edge Ef) of the fixed blade 60 in the axial direction O.

[0079] According to the above structure, the distance in the axial direction O between the rotating blade 40 and the fixed blade 60 can be reduced. As a result, for example, compared to the case where the distance between the two in the axial direction O is large, the losses and turbulence generated in the main flow Fm can be further reduced. Furthermore, by providing a bypass flow path P together with this structure, the same effect as described in the above embodiments can be obtained. As a result, the efficiency of the steam turbine 1 can be further improved.

[0080] The fourth embodiment of the present invention has been described above. Furthermore, various changes and modifications can be made to the above structure without departing from the spirit of the present invention. For example, the structures described as second or third embodiments and their variations can be combined with the structure of this embodiment.

[0081] [Fifth Implementation]

[0082] Next, refer to Figure 11 The fifth embodiment of the present invention will now be described. Furthermore, structures identical to those in the above embodiments will be labeled with the same reference numerals, and detailed descriptions will be omitted. For example... Figure 11 As shown, in this embodiment, the structure of the bypass flow path Pd differs from the embodiments described above. Specifically, the cross-sectional area of ​​the bypass flow path Pd gradually decreases from the upstream side to the downstream side. That is, the opening area of ​​the upstream end t' of the bypass flow path Pd is larger than the opening area of ​​the downstream end t. The cross-sectional area of ​​the bypass flow path Pd decreases linearly from the upstream end t' to the downstream end t.

[0083] According to the above structure, the cross-sectional area of ​​the bypass flow path Pd gradually decreases from the upstream side to the downstream side. This increases the flow velocity of the steam blown out from the bypass flow path Pd. Consequently, the incident angle of the flow relative to the fixed blade 60 can be further optimized, and the influence of secondary flows generated around the fixed blade 60 is further reduced. This further improves the efficiency of the steam turbine 1.

[0084] The fifth embodiment of the present invention has been described above. Furthermore, various changes and modifications can be made to the above structure without departing from the spirit of the invention. For example, in the above embodiments, examples of rectangular cross-sectional shapes for the bypass flow path P have been described. However, as a common variation in all embodiments, such as... Figure 12 As shown, the cross-sectional shape of the bypass flow path P can also be set to circular. This structure is easier to manufacture compared to a rectangular cross-sectional shape. This reduces manufacturing and maintenance costs.

Claims

1. An axial flow turbine, comprising: A rotational axis that extends along the axis; Multiple rotating blades have a rotating blade body extending radially outward from the axis of rotation and a protective cover disposed at the end of the rotating blade body radially outward, and the multiple rotating blades are arranged at intervals in the circumferential direction; The housing surrounds the rotating blade from the radially outer side and has a recess formed on the inner circumferential surface to accommodate the shield; The fins protrude radially inward from the opposing surface of the recess opposite to the shield, thereby forming a gap between them and the outer peripheral surface of the shield; The fixed blade support is disposed further downstream than the recess on the inner circumferential surface of the housing; Multiple fixed blades extend radially inward from the fixed blade support and are arranged at intervals in the circumferential direction; and An annular partition extends from the downstream side of the recess (i.e., the downstream face of the recess) to the upstream side, and is centered on the axis. A bypass flow path is formed on the housing, connecting a region on the downstream surface of the recess that is radially outward from the partition and a region on the inner circumferential surface of the housing between the fixed blades. The upstream end of the bypass flow path opens in a region radially outward on the downstream surface of the recess than the partition. The radially inner edge of the upstream end of the bypass flow path and the outer peripheral surface of the shroud of the rotating blade located on the upstream side of the bypass flow path are located at the same position radially. The radially inner end of the partition is located radially inner than the outer peripheral surface of the shield, and the downstream end of the inner peripheral surface of the shield is located radially outer than the radially inner end of the partition.

2. The axial flow turbine according to claim 1, wherein, In a cross-sectional view including the axis, the bypass flow path extends radially outward and inward as it moves from the upstream side toward the downstream side.

3. The axial flow turbine according to claim 1 or 2, wherein, When viewed from the radially outer side, the bypass flow path extends rearward in the direction of rotation of the rotation axis as it moves from the upstream side toward the downstream side.

4. An axial flow turbine, comprising: A rotational axis that extends along the axis; Multiple rotating blades have a rotating blade body extending radially outward from the axis of rotation and a protective cover disposed at the end of the rotating blade body radially outward, and the multiple rotating blades are arranged at intervals in the circumferential direction; The housing surrounds the rotating blade from the radially outer side and has a recess formed on the inner circumferential surface to accommodate the shield; The fins protrude radially inward from the opposing surface of the recess opposite to the shield, thereby forming a gap between them and the outer peripheral surface of the shield; The fixed blade support is disposed further downstream than the recess on the inner circumferential surface of the housing; Multiple fixed blades extend radially inward from the fixed blade support and are arranged at intervals in the circumferential direction; and An annular partition extends from the downstream side of the recess (i.e., the downstream face of the recess) to the upstream side, and is centered on the axis. A bypass flow path is formed on the housing, connecting a region on the downstream surface of the recess that is radially outward from the partition and a region on the inner circumferential surface of the housing between the fixed blades. When the dimension of the fixed blade support in the axial direction is set as L, and the dimension from the upstream end of the fixed blade support to the downstream end of the bypass flow path is set as A, the value of A / L satisfies 0.2 < A / L < 0.

4.

5. The axial flow turbine according to claim 1 or 4, wherein, The downstream surface of the recess is located further downstream than the upstream end of the fixed blade in the axial direction.

6. The axial flow turbine according to claim 1 or 4, wherein, The cross-sectional area of ​​the bypass flow path gradually decreases from the upstream side to the downstream side.

7. The axial flow turbine according to claim 1 or 4, wherein, The bypass flow path has a circular cross-sectional shape.

8. The axial turbine according to claim 1 or 4, further comprising a plurality of anti-rotation plates, The plurality of anti-rotation plates extend from the outer peripheral surface of the partition to the inner peripheral surface of the recess and are arranged at intervals in the circumferential direction.

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