JP2017061898A - Steam turbine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steam turbine capable of controlling a flow of a tip leak flow and improving a diffuser performance while maintaining a structure of a shroud suited for a rotor blade.SOLUTION: A steam turbine 10 in an embodiment is configured such that in a last turbine stage, a diaphragm outer ring 26a includes an extension part 81 extending in a turbine rotor axial direction and surrounding a rotor blade 24a immediately downstream of a stator vane 28a supported by the diaphragm outer ring 26a radially outward. Furthermore, in the last turbine stage, a seal fin 111 has an upstream side surface 111a inclined radially outward, an angle θ1 of the side surface 111a with respect to the turbine rotor axial direction is set in a range of ±10 degrees of an enlargement inclination angle θ2 of an inner surface 41 of a steam guide 40 with respect to the turbine rotor axial direction at an inlet of an annular diffuser 60.SELECTED DRAWING: Figure 2

Description

  Embodiments described herein relate generally to a steam turbine including an exhaust chamber.

Improving the thermal efficiency of steam turbines used in thermal power plants and the like is an important issue that leads to effective use of energy resources and reduction of carbon dioxide (CO ₂ ) emissions. An improvement in the thermal efficiency of a steam turbine can be achieved by effectively converting the given energy into mechanical work. For that purpose, it is necessary to reduce various internal losses.

  The internal loss of a steam turbine is typified by the turbine blade row loss based on the profile loss due to the blade shape, steam secondary flow loss, steam leakage loss, steam wetting loss, etc., steam valves and crossover pipes. There are passage portion loss in passages other than the blade row, turbine exhaust loss due to the turbine exhaust chamber, and the like.

  Among these losses, the turbine exhaust loss is a large loss that accounts for 10 to 20% of the total internal loss. The turbine exhaust loss is a loss that occurs between the outlet of the turbine stage of the final stage and the condenser inlet. Turbine exhaust loss is further classified into leaving loss, hood loss, annular area limit loss, turn-up loss, and the like. Of these, the hood loss is the pressure loss from the exhaust chamber to the condenser. This hood loss depends on the type, shape and size of the exhaust chamber including the diffuser.

  In general, the pressure loss increases in proportion to the square of the steam flow velocity. Therefore, it is effective to reduce the steam flow rate by increasing the size of the exhaust chamber within an allowable range. However, when the size of the exhaust chamber is increased, there are restrictions from the manufacturing cost and the layout space of the building. Such restrictions are also imposed when the size of the exhaust chamber is increased in order to reduce the hood loss.

  The hood loss depends on the axial flow speed that is the speed in the turbine rotor axial direction, in other words, the volume flow rate passing through the exhaust chamber. Also, the hood loss depends on the design of the exhaust chamber including the diffuser. The exhaust chamber of the low-pressure turbine occupies a large capacity in the entire steam turbine. Therefore, enlarging the size of the exhaust chamber in order to reduce the hood loss greatly affects the size and manufacturing cost of the entire steam turbine. Therefore, it is important to have a shape with a small pressure loss with a limited exhaust chamber size.

  For example, in a conventional double flow type (double flow type) low pressure turbine having a lower exhaust type exhaust chamber, in order to reduce the loss (static pressure loss) in the exhaust chamber, it is composed of a steam guide and a bearing cone. It is most important to slow down the flow in the annular diffuser and restore sufficient static pressure. In conventional low-pressure turbines, it has been studied to increase the length of the bearing cone in the turbine axial direction to increase the length of the diffuser in the turbine axial direction to sufficiently recover the static pressure.

  However, in recent years, from the viewpoint of making the steam turbine more compact, it has been studied to sufficiently recover the static pressure while reducing the length of the bearing cone in the turbine axial direction.

  Here, FIGS. 6 and 7 show the turbine blades 310 in the final stage of a double-flow exhaust type (double flow type) low-pressure turbine 300 having a conventional lower exhaust type exhaust chamber and the vertical direction of the rotor blades 310 in the vicinity thereof. It is the figure which showed a part of meridian cross section.

  In the conventional low-pressure turbine 300 shown in FIG. 6, the shroud 311 that is the tip of the moving blade 310 is configured horizontally. The inner surface 360a of the diaphragm outer ring 360 surrounding the rotor blade 310 from the outer periphery is also configured horizontally. A predetermined gap 365 is formed between the shroud 311 and the inner surface 360a. For example, a seal fin 370 is provided on the outer surface 311 a of the shroud 311 to seal the gap 365.

  As shown in FIG. 6, a steam guide 320 and a bearing cone 330 are provided on the downstream side of the moving blade 310 in the final turbine stage. An annular diffuser 340 is formed between the steam guide 320 and the bearing cone 330. The annular diffuser 340 constitutes an enlarged flow path through which the steam that has passed through the moving blade 310 of the turbine stage at the final stage is guided. Further, the annular diffuser 340 constitutes a part of the exhaust chamber. The steam guided to the annular diffuser 340 flows out radially outward.

  Here, in order to improve the performance in a compact exhaust chamber, for example, the flow 350 spreads at an optimal spread angle at the inlet of the annular diffuser 340, that is, the outlet of the moving blade 310 of the turbine stage in the final stage, and the steam guide It is important to be able to flow along the inner surface 320a of 320 and exhibit the diffuser effect. In addition, it is important that the flow 350 flowing into the annular diffuser 340 does not peel on the inner surface 320 a of the steam guide 320. For this purpose, it is a condition that the spread angle of the flow 350 outward in the radial direction with respect to the turbine rotor axial direction is a spread angle α in a predetermined range.

  The steam guide 320 is inclined outwardly in the radial direction from the downstream end of the diaphragm outer ring 360 toward the downstream side in the turbine rotor axial direction with a predetermined enlarged inclination angle with respect to the turbine rotor axial direction.

  In the conventional low-pressure turbine 300 having such a configuration, a tip leak flow 351 that is a leak flow flowing downstream through the gap 365 is generated. The tip leak flow 351 flows from the gap 365 toward the annular diffuser 340 in the turbine rotor axial direction at a high speed.

  The tip leak flow 351 prevents the steam flowing on the outer periphery near the inlet of the annular diffuser 340 from spreading outward in the radial direction, and flows at an angle smaller than the spread angle α. That is, of the steam that has passed through the moving blade 310, the steam that flows on the outer peripheral side cannot flow along the inner surface 320 a of the steam guide 320. As a result, flow separation occurs on the inner surface 320 a of the steam guide 320.

  In order to prevent the seal fin 370 rotating at high speed from coming into contact with the inner surface 360a of the diaphragm outer ring 360, it is necessary to provide a predetermined gap between the tip of the seal fin 370 and the inner surface 360a. Therefore, the chip leak flow 351 cannot be eliminated.

  Therefore, as shown in FIG. 7, a technique of providing a guide 312 at the rear edge of the shroud 311 and guiding the tip leak flow 351 in a direction along the inner surface 320 a of the steam guide 320 has been studied.

  Here, in recent years, the rotor blade 310 in the final stage has been made longer from the viewpoint of improving turbine efficiency. Further, such a moving blade 310 is composed of a blade that is twisted three-dimensionally from the root of the blade toward the tip in order to optimize the flow in the blade height direction. In the case of this twisted blade, at the tip, for example, the chord direction is the circumferential direction, and the length of the shroud 311 in the turbine rotor axial direction is shortened.

  Therefore, for example, when the above-described guide 312 for guiding the flow is provided on the twisted blade, it is necessary to extend the shroud 311 in the turbine rotor axial direction. This increases the shroud 311 and results in a reduction in the strength of the wing.

JP 2012-82826 A

  As described above, in the conventional steam turbine, the tip leak flow 351 cannot be guided in the direction along the inner surface 320 a of the steam guide 320 while maintaining the structure of the shroud 311 suitable for the moving blade 310.

  The problem to be solved by the present invention is to provide a steam turbine capable of controlling the flow of the tip leak flow and improving the diffuser performance while maintaining a shroud structure suitable for a moving blade.

  The steam turbine according to the embodiment includes a casing, a moving blade implanted in a circumferential direction of a turbine rotor penetrating the casing, a shroud provided in a circumferential direction at a tip of the moving blade, and a shroud of the shroud. A seal fin provided in the circumferential direction on the outer periphery, a diaphragm outer ring provided inside the casing, a diaphragm inner ring provided inside the diaphragm outer ring, and a circumferential direction between the diaphragm outer ring and the diaphragm inner ring And the stationary blades alternately arranged in the axial direction of the rotor blade and the rotor blade, and an annular diffuser into which steam that has passed through the final stage of the turbine stage including the stationary blade and the rotor blade flows.

  In the last turbine stage of the steam turbine, the diaphragm outer ring extends in the turbine rotor axial direction and surrounds the moving blade immediately downstream of the stationary blade supported by the diaphragm outer ring from the outside in the radial direction. An extending part is provided. Further, in the turbine stage at the final stage, the seal fin has an upstream inclined surface that is inclined outward in the radial direction, and an angle θ1 of the upstream inclined surface with respect to the turbine rotor axial direction is defined by the annular diffuser. The angle is set in a range of ± 10 degrees of the angle θ2 with respect to the turbine rotor axial direction of the outer wall constituting the annular diffuser at the inlet.

It is a figure which shows the meridional section of the perpendicular direction of the steam turbine of 1st Embodiment. It is the figure which expanded the meridional section of the perpendicular direction of the turbine stage of the last stage in the steam turbine of a 1st embodiment, and a part of annular diffuser. It is the figure which expanded the meridional section of the vertical direction of the turbine stage of the last stage in a steam turbine of a 2nd embodiment, and a part of annular diffuser. It is the figure which expanded the meridional section of the vertical direction of a turbine stage of the last stage in a steam turbine of a 3rd embodiment, and a part of annular diffuser. It is the figure which expanded the meridional section of the perpendicular direction of the turbine stage of the last stage in the steam turbine of a 4th embodiment, and a part of annular diffuser. It is the figure which showed a part of vertical meridional section of the moving blade of the turbine stage of the last stage of the low pressure turbine of the double flow exhaust type (double flow type) low pressure turbine provided with the conventional lower exhaust type exhaust chamber, and its vicinity. It is the figure which showed a part of vertical meridional section of the moving blade of the turbine stage of the last stage of the low pressure turbine of the double flow exhaust type (double flow type) low pressure turbine provided with the conventional lower exhaust type exhaust chamber, and its vicinity.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram showing a meridional section in the vertical direction of the steam turbine 10 of the first embodiment. Here, the steam turbine 10 will be described by exemplifying a double-flow exhaust type low-pressure turbine having a lower exhaust type exhaust chamber.

  As shown in FIG. 1, in the steam turbine 10, an inner casing 21 is provided in the outer casing 20. A turbine rotor 22 is provided in the inner casing 21. The turbine rotor 22 is formed with a rotor disk 23 that protrudes radially outward in the circumferential direction. The rotor disk 23 is formed in a plurality of stages in the turbine rotor axial direction.

  A plurality of rotor blades 24 are implanted in the circumferential direction on the rotor disk 23 of the turbine rotor 22 to constitute a rotor blade cascade 170. The rotor blade cascade 170 is provided in a plurality of stages in the turbine rotor axial direction. The turbine rotor 22 is rotatably supported by a rotor bearing 25.

  A diaphragm outer ring 26 and a diaphragm inner ring 27 are provided inside the inner casing 21. Between the diaphragm outer ring 26 and the diaphragm inner ring 27, a plurality of stationary blades 28 are disposed in the circumferential direction to form a stationary blade cascade 180. The stationary blade cascade 180 is arranged so as to alternate with the moving blade cascade 170 in the turbine rotor axial direction. The stationary blade cascade 180 and the moving blade cascade 170 immediately downstream of the stationary blade cascade 180 constitute one turbine stage. Further, the diaphragm outer ring 26 extends downstream and surrounds the moving blade 24 immediately downstream of the stationary blade 28.

  In the center of the steam turbine 10, an intake chamber 30 into which steam from the crossover pipe 29 is introduced is provided. Steam is distributed and introduced from the intake chamber 30 to the left and right turbine stages.

  An annular diffuser 60 is formed on the downstream side of the final stage turbine stage by an outer peripheral steam guide 40 and an inner peripheral bearing cone 50. The annular diffuser 60 discharges steam, for example, radially outward. For example, a rotor bearing 25 is provided on the inner diameter side of the bearing cone 50.

  For example, a condenser (not shown) is provided below the lower exhaust type exhaust chamber provided with the annular diffuser 60.

  Note that the outer casing 20, the inner casing 21, the steam guide 40, the bearing cone 50, and the like described above have a vertically split structure. For example, a cylindrical steam guide 40 is constituted by the steam guides 40 on the upper half side and the lower half side. A cylindrical bearing cone 50 is constituted by the bearing cones 50 on the upper half side and the lower half side. And the annular diffuser 60 is comprised by the cylindrical steam guide 40 and the cylindrical bearing cone 50 provided in the inner side. The configurations of the upper half side and the lower half side of the steam guide 40 and the bearing cone 50 are the same.

  Next, the configuration of the last turbine stage will be described in detail.

  FIG. 2 is an enlarged view of a vertical meridional section of a turbine stage and a part of the annular diffuser 60 in the final stage in the steam turbine 10 of the first embodiment. In FIG. 2, for convenience of explanation, “a” is added to the constituent parts of the turbine stage in the final stage with the reference numerals of the constituent parts shown in FIG. 1 (the same applies to the following embodiments). . The configuration shown in FIG. 2 is not limited to the vertical cross section along the turbine rotor axial direction, but is the same in the vertical cross section along the turbine rotor axial direction.

  As shown in FIG. 2, the diaphragm outer ring 26 a in the last turbine stage includes an expanded portion 80 and an extending portion 81.

  The expanding portion 80 has an inner diameter that expands radially outward as it goes downstream in the turbine rotor axial direction. The inner surface 82 of the expanding portion 80 expands, for example, linearly outward in the radial direction as it goes downstream in the turbine rotor axial direction. The inner surface 82 is inclined at an enlarged inclination angle β (degrees) with respect to the turbine rotor axial direction.

  For example, on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60, the expansion inclination angle β is a predetermined expansion angle α (degrees) when the steam flow 185 extends radially outward with respect to the turbine rotor axial direction. Is set to be Here, the predetermined spread angle is, for example, an angle in a range where flow separation does not occur on the inner surface 41 of the steam guide 40.

  As shown in FIG. 2, the stationary blade 28a of the turbine stage at the final stage is attached between the expanded portion 80 of the diaphragm outer ring 26a and the diaphragm inner ring 27a.

  The extending portion 81 extends in the turbine rotor axial direction (horizontal direction) from the downstream end portion of the expanding portion 80, and faces the tip of the rotor blade 24a from the outside in the radial direction. That is, the extending portion 81 surrounds the rotor blade 24a from the outer periphery.

  A predetermined gap is formed between the horizontal inner surface 83 of the extending portion 81 extending in the turbine rotor axial direction and the seal fin 111 provided at the tip of the rotor blade 24a. For example, as shown in FIG. 2, the seal fin 111 is provided in the circumferential direction on the outer periphery of the shroud 130 provided in the circumferential direction on the tip of the moving blade 24 a. Therefore, the seal fin 111 is formed in an annular shape.

  FIG. 2 shows an example in which the seal fin 111 is provided once in the circumferential direction. In other words, an example in which the seal fins 111 are provided in one stage in the turbine rotor axial direction is shown. When the one-stage seal fin 111 is provided, the seal fin 111 is preferably provided at the center of the shroud 130 in the turbine rotor axial direction, for example, in consideration of the weight balance during rotation. The seal fins 111 may be provided in a plurality of stages in the turbine rotor axial direction.

  As shown in FIG. 2, the seal fin 111 has, for example, a triangular shape in a cross section perpendicular to the circumferential direction. The upstream side surface 111a of the seal fin 111 is inclined outward in the radial direction. That is, the side surface 111a protrudes radially outward as it goes downstream. And the inner peripheral end of the side surface 111a is in contact with the outer peripheral surface of the shroud 130, for example.

  Here, the shape of the seal fin 111 is not limited to a triangular shape. The seal fin 111 only needs to have a side surface 111a on the upstream side. Therefore, in the cross section shown in FIG. 2, for example, a trapezoid having an upstream side surface 111a may be used. The side surface 111a functions as an upstream inclined surface.

  In the cross section shown in FIG. 2, the angle of the side surface 111a with respect to the turbine rotor axial direction (horizontal direction) is θ1 (degrees). That is, the angle formed between the side surface 111a and the turbine rotor axial direction is θ1.

  The steam guide 40 is adjacent to the downstream end surface 84 of the extending portion 81. The steam guide 40 constitutes an outer wall of the annular diffuser 60. For example, as shown in FIG. 2, the upstream end surface 42 of the steam guide 40 is in contact with the radially inner portion of the downstream end surface 84 of the extending portion 81. Specifically, in the cross section shown in FIG. 2, for example, the radially inner end of the upstream end surface 42 of the steam guide 40 and the radially inner end of the downstream end surface 84 of the extending portion 81 are in contact with each other. Yes.

  The steam guide 40 is configured in an enlarged cylindrical shape that expands radially outward as it goes downstream in the turbine rotor axial direction. For example, as shown in FIG. 2, the upstream portion of the steam guide 40 linearly expands outward in the radial direction as it goes downstream in the turbine rotor axial direction. For example, as shown in FIG. 1, the downstream portion of the steam guide 40 expands while curving radially outward as it goes downstream in the turbine rotor axial direction.

  The shape of the steam guide 40 is not limited to this. For example, the steam guide 40 may be configured in a trumpet shape that expands while curving outward in the radial direction from the upstream end to the downstream end as it goes downstream in the turbine rotor axial direction.

  As shown in FIG. 2, the inner surface 41 at the inlet of the steam guide 40 is inclined radially outward with an enlarged inclination angle θ <b> 2 with respect to the turbine rotor axial direction as it goes downstream in the turbine rotor axial direction. .

  When the steam guide 40 expands from the upstream end to the downstream end while curving outward in the radial direction as it goes downstream in the turbine rotor axial direction, the expansion inclination angle θ2 (degrees) is shown in FIG. In the cross section shown, it is defined by the angle formed between the tangent line at the upstream end of the inner surface 41 of the steam guide 40 and the turbine rotor axial direction.

Here, the enlarged inclination angle θ <b> 2 is set to such an angle that the steam that has passed through the last turbine stage does not peel on the inner surface 41 of the steam guide 40. Further, the enlarged inclination angle θ2 and the angle θ1 described above satisfy the relationship of the following equation (1).
Angle θ1 = Enlarged inclination angle θ2 ± 10 degrees Equation (1)

  That is, the angle θ1 is set within a range of ± 10 degrees of the enlarged inclination angle θ2.

  By satisfying the relationship of the expression (1), the chip leak flow 115 that has passed between the seal fin 111 and the inner surface 83 of the extending portion 81 flows along the inner surface 41 of the steam guide 40. Therefore, on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60, the spread angle of the steam flow 185 radially outward with respect to the turbine rotor axial direction is the spread angle α. Thereby, separation of the flow on the inner surface 41 of the steam guide 40 can be prevented.

  The bearing cone 50 is configured in an enlarged cylindrical shape that expands radially outward while curving as it goes downstream in the axial direction of the turbine rotor. As shown in FIG. 2, the upstream end of the bearing cone 50 is adjacent to the radially outer portion of the downstream end surface of the rotor disk 23a to the extent that it does not contact the rotating rotor disk 23a. As shown in FIG. 1, the downstream end of the bearing cone 50 is in contact with the inner wall surface 141 of the side wall 140 on the downstream side in the turbine rotor axial direction of the outer casing 20.

  Here, the configuration in the present embodiment is, for example, a steam turbine that reduces the length of the bearing cone 50 in the turbine axial direction to achieve a compact size and sufficiently recovers the static pressure in the annular diffuser 60. It is suitable for.

  Specifically, the steam turbine in which the ratio (L / D) of the length L in the turbine rotor axial direction of the bearing cone 50 to the outer diameter D of the rotor blade 24a in the last turbine stage is 2/5 or less, for example. In addition, the configuration in this embodiment is preferable (see FIG. 1).

  Here, as shown in FIG. 1, the length L is the distance from the end of the bearing cone 50 on the moving blade 24 a side to the inner wall 141 of the side wall 140 where the downstream end of the bearing cone 50 contacts. The outer diameter D is equal to the diameter of a circle drawn by the tip of the rotor blade 24a when the rotor blade 24a rotates. Since the moving blade 24 a includes the shroud 130, the outer diameter D is an outer diameter including the shroud 130.

  In a steam turbine having an L / D of 2/5 or less, the exhaust chamber is sufficiently miniaturized, and costs for manufacturing and installation are reduced. Note that L / D can be set to about 1/5 in consideration of bending loss in the annular diffuser 60 and the like.

  Next, the operation of the steam turbine 10 will be described with reference to FIGS. 1 and 2.

  As shown in FIG. 1, the steam that flows into the intake chamber 30 in the steam turbine 10 through the crossover pipe 29 branches and flows to the left and right turbine stages. Then, the steam passes through the steam flow path including the stationary blade 28 and the moving blade 24 of each turbine stage, and rotates the turbine rotor 22.

  As shown in FIG. 2, in the final stage turbine stage, the steam that has passed through the stationary blade 28a flows into the moving blade 24a while spreading outward in the radial direction. The steam that has flowed into the rotor blade 24a performs expansion work and passes through the rotor blade 24a. In addition, the flow of the vapor | steam which passed the moving blade 24a has the spreading angle (alpha).

  On the other hand, part of the steam that has passed through the stationary blade 28 a flows as a tip leak flow 115 between the shroud 130 and the inner surface 83 of the extending portion 81. The chip leak flow 115 flows along the side surface 111 a of the seal fin 111.

  The tip leak flow 115 that has passed between the seal fin 111 and the inner surface 83 has a velocity component of an angle θ1 and flows downstream along the inner surface 83. In addition, by providing the seal fin 111, the flow rate of the chip leak flow 115 is suppressed.

  At the inlet of the annular diffuser 60, the tip leak flow 115 has a velocity component of the angle θ1, and therefore flows along the inner surface 41 of the steam guide 40. Therefore, the steam flow on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60 spreads radially outward at the spread angle α without being blocked by the tip leak flow 115. The steam flow on the inner surface 41 side of the steam guide 40 flows downstream without peeling on the inner surface 41 of the steam guide 40.

  The steam that has flowed into the annular diffuser 60 flows between the steam guide 40 and the bearing cone. Then, the flow is decelerated by the annular diffuser 60 to sufficiently recover the static pressure.

  At the outlet of the annular diffuser 60, the steam flows radially outward as shown in FIG. The steam that has flowed radially outward is diverted downward. Then, the redirected steam is guided to, for example, a condenser (not shown) installed below the turbine rotor 22.

  As described above, according to the steam turbine 10 of the first embodiment, the chip leak flow 115 can flow along the inner surface 41 of the steam guide 40 by providing the above-described seal fins 111. Thus, the steam flow on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60 can be spread radially outward at the spread angle α without being obstructed by the tip leak flow 115.

  Therefore, separation of the steam flow along the inner surface 41 of the steam guide 40 is suppressed, and the pressure loss in the annular diffuser 60 can be reduced. And turbine efficiency improves by improving diffuser performance.

  Further, according to the steam turbine 10, the flow of the tip leak flow 115 can be controlled and the diffuser performance can be improved without changing the shape of the shroud 130 at the tip of the rotor blade 24a. That is, the diffuser performance can be improved while maintaining the structure of the shroud 130 suitable for the moving blade 24a.

(Second Embodiment)
FIG. 3 is an enlarged view of a vertical meridional section of a turbine stage and a part of the annular diffuser 60 in the final stage in the steam turbine 11 of the second embodiment. In FIG. 3, the same components as those of the steam turbine 10 of the first embodiment are denoted by the same reference numerals, and redundant description is omitted or simplified (the same applies to the following embodiments).

  In the second embodiment, the structure of the inner surface 83 of the extending portion 81 in the diaphragm outer ring 26a is different from the structure of the inner surface 83 of the extending portion 81 in the first embodiment. Here, this different configuration will be mainly described.

  As shown in FIG. 3, a step 90 that is recessed radially outward from the inner surface 83 on the downstream side of the extending portion 81 of the diaphragm outer ring 26 a to the inner surface 41 of the steam guide 40 on the inlet side of the annular diffuser 60. Prepare. The step 90 is formed in an annular shape over the circumferential direction.

  As shown in FIG. 3, the stepped portion 90 includes, for example, an upstream end surface 90 a and a bottom surface 90 b constituting the bottom portion. The end surface 90a is, for example, an annular surface perpendicular to the turbine rotor axial direction. The bottom surface 90b is, for example, an annular surface parallel to the turbine rotor axial direction. The downstream end of the stepped portion 90 is opened. For example, the stepped portion 90 has a depth enough to form a vortex in the stepped portion 90.

  For example, in the cross section shown in FIG. 3, the stepped portion 90 is formed downstream from the point P where the extension line X along the side surface 111 a of the seal fin 111 intersects the inner surface 83 of the extending portion 81. That is, the starting point on the upstream side of the stepped portion 90 is the point P.

  By forming the step 90 on the downstream side from the point P, the step 90 can be formed without impairing the sealing effect of the seal fin 111. The configuration of the seal fin 111 is the same as that of the first embodiment.

  In the steam turbine 11 including the inner surface 83 of the extending portion 81, the tip leak flow 115 that flows between the shroud 130 and the inner surface 83 of the extending portion 81 flows along the side surface 111 a of the seal fin 111.

  The tip leak flow 115 that has passed between the seal fin 111 and the inner surface 83 has a velocity component of an angle θ1 and flows downstream along the inner surface 83. Then, a part of the flow along the inner surface 83 is separated at the step portion 90, and a vortex 91 is formed in the step portion 90 as shown in FIG.

  The vortex 91 draws the flow along the inner surface 83 toward the inner surface 41 side. That is, the tip leak flow 115 has a velocity component of an angle θ1 and is attracted to the inner surface 41 side by the vortex 91. Therefore, the tip leak flow 115 flows along the inner surface 41 of the steam guide 40 at the inlet of the annular diffuser 60.

  The steam flow on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60 spreads radially outward at the spread angle α without being blocked by the tip leak flow 115. That is, the flow of steam on the inner surface 41 side of the steam guide 40 flows downstream without being separated on the inner surface 41 of the steam guide 40. The subsequent steam flow is the same as the steam flow in the first embodiment.

  As described above, according to the steam turbine 11 of the second embodiment, the chip fin flow 115 can be reliably flowed along the inner surface 41 of the steam guide 40 by including the seal fin 111 and the stepped portion 90. it can. Thus, the steam flow on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60 can be spread radially outward at the spread angle α without being obstructed by the tip leak flow 115.

  Therefore, separation of the steam flow along the inner surface 41 of the steam guide 40 is suppressed, and the pressure loss in the annular diffuser 60 can be reduced. And turbine efficiency improves by improving diffuser performance.

  Moreover, according to the steam turbine 11, similarly to 1st Embodiment, diffuser performance can be improved, maintaining the structure of the shroud 130 suitable for the moving blade 24a.

(Third embodiment)
FIG. 4 is an enlarged view of a vertical meridional section of a turbine stage and a part of the annular diffuser 60 in the final stage in the steam turbine 12 according to the third embodiment.

  In the third embodiment, the structure of the inner surface 41 of the steam guide 40 is different from the structure of the inner surface 41 of the steam guide 40 in the first embodiment. Here, this different configuration will be mainly described.

  In the cross section shown in FIG. 4, a stepped step portion 100 is formed on the inner surface 41 of the steam guide 40 in the turbine rotor axial direction. The step portion 100 includes a plurality of step portions 101 recessed radially outward in the turbine rotor axial direction.

  As shown in FIG. 4, the step 101 includes, for example, an upstream end surface 101 a and a bottom surface 101 b that forms the bottom. The end surface 101a is, for example, an annular surface perpendicular to the turbine rotor axial direction. The bottom surface 101b is, for example, an annular surface parallel to the turbine rotor axial direction. The downstream end of the step 101 is opened.

  Further, in the cross section shown in FIG. 4, a line connecting the inner peripheral ends of the end surfaces 101 a constituting each step 101 overlaps the inner surface 41 of the steam guide 40, for example.

  Each step 101 is formed in an annular shape in the circumferential direction. That is, the step part 100 is formed in an annular shape in the circumferential direction. The depth of the step 101 and the axial length of the bottom surface 101 b are set to such an extent that a vortex can be formed in the step 101.

  The step portion 100 is formed on the downstream side from the upstream end of the steam guide 40. The distance M in the turbine rotor axial direction from the upstream end of the steam guide 40 to the downstream end of the step 101 in the final stage is 0.05 to 0.15 times the length of the steam guide 40 in the turbine rotor axial direction. It is preferably set.

  By setting the distance M in the above range, the flow of steam on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60 is expanded radially outward while minimizing the pressure loss caused by providing the step 101. be able to.

  The configuration of the seal fin 111 is the same as that of the first embodiment.

  In the steam turbine 12 including such a stepped portion 100, the tip leak flow 115 that flows between the shroud 130 and the inner surface 83 of the extending portion 81 flows along the side surface 111 a of the seal fin 111.

  At the inlet of the annular diffuser 60, the tip leak flow 115 has a velocity component of the angle θ1, and therefore flows along the inner surface 41 of the steam guide 40. Then, a part of the flow along the inner surface 41 is separated at the step 101, and a vortex 102 is formed in the step 101 as shown in FIG.

  This vortex 102 draws the flow along the inner surface 41 toward the inner surface 41 side. The tip leak flow 115 has a velocity component of the angle θ 1 and is drawn toward the inner surface 41 side by the vortex flow 102, and therefore flows along the inner surface 41 of the steam guide 40.

  Therefore, the steam flow on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60 spreads radially outward at the spread angle α without being blocked by the tip leak flow 115. That is, the flow of steam on the inner surface 41 side of the steam guide 40 flows downstream without being separated on the inner surface 41 of the steam guide 40. The subsequent steam flow is the same as the steam flow in the first embodiment.

  As described above, according to the steam turbine 12 of the third embodiment, the chip fin flow 115 can be reliably flowed along the inner surface 41 of the steam guide 40 by including the seal fin 111 and the stepped portion 100. it can. Thus, the steam flow on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60 can be spread radially outward at the spread angle α without being obstructed by the tip leak flow 115.

  Therefore, separation of the steam flow along the inner surface 41 of the steam guide 40 is suppressed, and the pressure loss in the annular diffuser 60 can be reduced. And turbine efficiency improves by improving diffuser performance.

  Further, according to the steam turbine 12, as in the first embodiment, it is possible to improve the diffuser performance while maintaining the structure of the shroud 130 suitable for the moving blade 24a.

  Here, an example in which the stepped portion 100 is formed on the inner surface 41 of the steam guide 40 is shown, but the configuration is not limited thereto. For example, the step portion 100 may be formed from the inner surface 83 on the downstream side of the extending portion 81. In this case, the inner surface 83 of the extending portion 81 in which the step portion 100 is formed includes a plurality of steps 101 that are recessed radially outward in the turbine rotor axial direction. And the step part 100 of the extension part 81 and the step part 100 of the steam guide 40 are formed continuously.

  Here, the step portion 100 formed on the inner surface 83 is formed on the downstream side from the point where the extension line along the side surface 111a of the seal fin 111 intersects the inner surface 83 of the extending portion 81 in the cross section shown in FIG. May be.

  Thus, when forming the step part 100 from the inner surface 83 of the extension part 81, the formation start position of the step part 100 becomes an upstream rather than the formation start of the step part 100 shown in FIG. Further, the line connecting the inner peripheral ends of the end surfaces 101a constituting each step 101 formed in the steam guide 40 is inclined radially outward at the same angle as the enlarged inclination angle θ2 with respect to the turbine rotor axial direction.

  And the step part 100 formed in the steam guide 40 is formed in the outer peripheral surface side of the steam guide 40 rather than the step part 100 shown in FIG. As a result, the line connecting the inner peripheral ends of the end surfaces 101 a constituting each step 101 formed on the steam guide 40 is, for example, closer to the outer peripheral surface side of the steam guide 40 than the inner surface 41 of the steam guide 40.

  The distance M in the turbine rotor axial direction from the upstream end of the steam guide 40 to the downstream end of the final step 101 is the same as the above range. Further, even when the step portion 100 is formed from the inner surface 83 of the extending portion 81, the same effect as the case of providing the step portion 100 shown in FIG. 4 can be obtained.

(Fourth embodiment)
FIG. 5 is an enlarged view of a vertical meridian section of a turbine stage and a part of the annular diffuser 60 in the final stage in the steam turbine 13 according to the fourth embodiment.

  In the fourth embodiment, the structures of the inner surface 83 of the extending portion 81 and the inner surface 41 of the steam guide 40 are the same as the structures of the inner surface 83 of the extending portion 81 and the inner surface 41 of the steam guide 40 in the first embodiment. Different. Here, this different configuration will be mainly described.

  In the cross section shown in FIG. 5, a plurality of arc-shaped depressions 105 are formed in the inner surface 41 of the steam guide 40 and the inner surface 41 of the steam guide 40 in the turbine rotor axial direction. For example, the recess 105 is formed in an annular shape in the circumferential direction. In other words, the depression 105 is a groove formed in the circumferential direction and having a semicircular cross section perpendicular to the circumferential direction.

  The recess 105 is formed in a plurality of stages on the inner surface 41 and the inner surface 41 in the turbine rotor axial direction. The interval R between the recesses 105 in the turbine rotor axial direction is, for example, about the opening length W of the recess 105 in the turbine rotor axial direction.

  The configuration of the recess 105 is not limited to this. For example, the recess 105 may be a hemispherical recess. In other words, the depression 105 may be formed in a dimple shape, for example. In this case, a plurality of dimple-shaped depressions 105 are formed in the inner surface 41, the circumferential direction of the inner surface 41, and the turbine rotor axial direction. Also in this case, the interval R between the recesses 105 is, for example, about the opening length W of the recess 105 in the turbine rotor axial direction.

  When the depressions 105 have a dimple shape, the depressions 105 may be arranged in a row at a predetermined interval R in the circumferential direction and the turbine rotor axial direction. In addition, the recesses 105 may be arranged in a staggered pattern in the circumferential direction and the turbine rotor axial direction.

  Here, in the cross section shown in FIG. 5, the shape of the recess 105 may be, for example, a semicircular shape obtained by dividing a circle into two equal parts. In the cross section shown in FIG. 5, the shape of the recess 105 may be, for example, a semi-elliptical shape in which an ellipse is divided into two equal parts by a major axis or a minor axis. The depth and the opening length W of the recess 105 are set to such an extent that a vortex can be formed in the recess 105.

  For example, in the cross section shown in FIG. 5, the most upstream depression 105 is formed on the downstream side from a point P where the extension line X along the side surface 111 a of the seal fin 111 intersects the inner surface 83 of the extending portion 81. That is, the starting point of the most upstream depression 105 is the point P.

  By forming the depression 105 on the downstream side from the point P, the depression 105 can be formed without impairing the sealing effect of the seal fin 111. The configuration of the seal fin 111 is the same as that of the first embodiment.

  In the steam guide 40, the recess 105 is formed within a distance N from the upstream end of the steam guide 40 in the turbine rotor axial direction. The distance N is preferably set to 0.05 to 0.15 times the length of the steam guide 40 in the turbine rotor axial direction.

  By setting the distance N in the above-described range, the flow of steam on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60 is reduced while minimizing the pressure loss caused by providing the depression 105 in the steam guide 40. Can spread outward in the direction.

  In the steam turbine 12 having such a depression 105, the tip leak flow 115 that flows between the shroud 130 and the inner surface 83 of the extending portion 81 flows along the side surface 111 a of the seal fin 111.

  The tip leak flow 115 that has passed through the seal fin 111 has a velocity component of an angle θ1 and flows downstream along the inner surface 83 of the extending portion 81. A part of the flow along the inner surface 83 is peeled off at the recess 105, and a vortex 106a is formed in the recess 105 as shown in FIG.

  The eddy current 102 draws the flow along the inner surface 83 toward the inner surface 83 side. That is, the tip leak flow 115 has a velocity component of an angle θ1 and is drawn toward the inner surface 83 side by the vortex flow 106a.

  At the entrance of the annular diffuser 60, the tip leak flow 115 has a velocity component of an angle θ1 and is drawn toward the inner surface 83 side by the vortex flow 106a, and therefore flows along the inner surface 41 of the steam guide 40. Then, a part of the flow along the inner surface 41 is peeled off at the recess 105, and a vortex 106 b is formed in the recess 105 as shown in FIG. 5.

  The vortex 106b draws the flow along the inner surface 41 toward the inner surface 41 side. The tip leak flow 115 has a velocity component of an angle θ1 and is drawn toward the inner surface 41 by the vortex flow 106b, and therefore flows along the inner surface 41 of the steam guide 40.

  Therefore, the steam flow on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60 spreads radially outward at the spread angle α without being blocked by the tip leak flow 115. That is, the flow of steam on the inner surface 41 side of the steam guide 40 flows downstream without being separated on the inner surface 41 of the steam guide 40. The subsequent steam flow is the same as the steam flow in the first embodiment.

  As described above, according to the steam turbine 12 of the fourth embodiment, the chip leak flow 115 can surely flow along the inner surface 41 of the steam guide 40 by providing the recess 105. Thus, the steam flow on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60 can be spread radially outward at the spread angle α without being obstructed by the tip leak flow 115.

  Therefore, separation of the steam flow along the inner surface 41 of the steam guide 40 is suppressed, and the pressure loss in the annular diffuser 60 can be reduced. And turbine efficiency improves by improving diffuser performance.

  Moreover, according to the steam turbine 13, similarly to 1st Embodiment, diffuser performance can be improved, maintaining the structure of the shroud 130 suitable for the moving blade 24a.

  According to the embodiment described above, it is possible to improve the diffuser performance by controlling the flow of the tip leak flow while maintaining the shroud structure suitable for the moving blade.

  In the above-described embodiment, the diaphragm outer ring 26a in the turbine stage at the final stage has a configuration including the expanding portion 80 and the extending portion 81. However, the configuration of the diaphragm outer ring 26 in the other turbine stages is as follows. The configuration is not limited to this.

  In the above embodiment, the double flow exhaust type low-pressure turbine provided with the lower exhaust type exhaust chamber has been described as an example. However, the configuration of the present embodiment includes, for example, an axial flow exhaust provided with an annular exhaust chamber. It can also be applied to low pressure turbines of the type.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10, 11, 12, 13 ... Steam turbine, 20 ... Outer casing, 22 ... Turbine rotor, 23, 23a ... Rotor disc, 24, 24a ... Rotor blade, 25 ... Rotor bearing, 26, 26a ... Diaphragm outer ring, 27, 27a ... inner ring of diaphragm, 28, 28a ... stationary blade, 29 ... crossover pipe, 30 ... intake chamber, 40 ... steam guide, 41, 82, 83 ... inner face, 42 ... upstream end face, 50 ... bearing cone, 60 ... annular diffuser, 80 ... Expanded part, 81 ... Extended part, 84 ... Downstream end face, 90,100 ... Step part, 90a, 101a ... End face, 90b, 101b ... Bottom face, 91,102,106a, 106b ... Vortex, 101 ... Step 111: Seal fin, 111a: Side surface, 115: Tip leak flow, 130: Shroud, 140: Side wall, 141: Inner wall surface, 170 Moving blade cascade, 180 ... stationary blade row.

Claims (9)

A casing,
A moving blade planted in the circumferential direction of a turbine rotor penetrating in the casing;
A shroud provided circumferentially at the tip of the blade,
Seal fins provided circumferentially on the outer periphery of the shroud;
A diaphragm outer ring provided inside the casing;
A diaphragm inner ring provided inside the diaphragm outer ring;
A stationary blade provided in a circumferential direction between the outer ring of the diaphragm and the inner ring of the diaphragm, and alternately disposed in the axial direction of the moving blade and the turbine rotor;
An annular diffuser into which steam that has passed through the final stage of a turbine stage including the stationary blade and the moving blade flows,
In the turbine stage of the final stage,
The diaphragm outer ring is
An extending portion that extends in the axial direction of the turbine rotor and surrounds the moving blade immediately downstream of the stationary blade supported by the diaphragm outer ring from the outside in the radial direction;
The seal fin is
An upstream inclined surface that is inclined outward in the radial direction;
The angle θ1 of the upstream inclined surface with respect to the turbine rotor axial direction is set within a range of ± 10 degrees of the angle θ2 of the outer wall constituting the annular diffuser with respect to the turbine rotor axial direction at the inlet of the annular diffuser. Features a steam turbine. In a vertical section along the axial direction of the turbine rotor, a step that is recessed radially outward from the inner surface on the downstream side of the extending portion to the inner surface of the outer wall of the annular diffuser on the inlet side of the annular diffuser. Prepared,
The steam turbine according to claim 1, wherein the stepped portion is formed in an annular shape in the circumferential direction.   3. The steam turbine according to claim 2, wherein, in the vertical cross section, an upstream start point of the stepped portion is a point where an extension line along the upstream inclined surface intersects an inner surface of the extended portion. In a vertical cross section along the turbine rotor axial direction, the inner surface of the outer wall of the annular diffuser includes a stepped step portion having a plurality of steps recessed radially outward in the turbine rotor axial direction,
The steam turbine according to claim 1, wherein each of the steps is formed in an annular shape in the circumferential direction. In the vertical cross section, the inner surface on the downstream side of the extending portion includes a stepped stepped portion having a plurality of steps recessed radially outward in the turbine rotor axial direction,
The step portion of the extending portion is formed continuously with the step portion of the outer wall,
5. The start point on the upstream side of the stepped portion of the extending portion in the vertical cross section is a point where an extension line along the upstream inclined surface intersects the inner surface of the extending portion. Steam turbine.   A vertical cross section along the turbine rotor axial direction is provided with a plurality of arc-shaped depressions on the inner surface on the downstream side of the extending portion and on the inner surface of the outer wall of the annular diffuser on the inlet side of the annular diffuser. The steam turbine according to claim 1.   The steam turbine according to claim 6, wherein each of the recesses is formed in an annular shape in the circumferential direction.   The steam turbine according to claim 6, wherein each of the recesses is a hemispherical recess.   9. The start point of the depression on the most upstream side in the vertical cross section is a point where an extension line along the upstream inclined surface intersects with an inner surface of the extension portion. The steam turbine according to item.

Images