Turbine nozzle and axial turbine with the same

Abstract

Turbine nozzle (1) having a plurality of blades (2) arranged to form a conical flow passage (3) between each two adjacent blades (2, 2'), wherein a suction surface (2c) of each blade (2) has a curved surface (11), and a constriction (4) of the flow passage (3) is formed between the curved surface (11) of one blade (2) and a trailing edge (2b) of the other blade (2') of the two adjacent blades (2, 2') at a constriction position (5), wherein an upstream end (11a) of the curved surface (11) is arranged upstream of the constriction position (5), and a downstream end (11b) of the curved surface (11) is arranged downstream of the constriction position (5), wherein the suction surface (2c) of each blade (2) has a flat surface (12) extending flatly from the downstream end (11b) of the curved surface (11) to a trailing edge (2b) of the blade (2), and where, if L is a dimensionless axial chord length which is a ratio of a length from a leading edge (2a) of the blade (2) in an axial direction to a length from the leading edge (2a) to the trailing edge (2b) of the blade (2) in the axial direction, and AR(L) is a ratio of a flow passage area of the flow passage (3) at a dimensionless axial chord length of L to a flow passage area of the flow passage (3) at a dimensionless axial chord length of 1.0, the following equation is satisfied: | AR ( 1.0 ) − AR ( 0.98 ) 1.0 − 0.98 | ≥ _ 0.5

Description

BACKGROUND OF THE INVENTIONTechnical field

[0001] The present disclosure relates to a turbine nozzle and an axial turbine having the same. Description of the state of the art

[0002] A conventional transonic turbine nozzle 100 has a plurality of blades 102 arranged to define a conical flow passage 101 between each two adjacent blades, as shown in Fig. 15. A constriction 105 of the flow passage 101 is formed between a suction surface 103 of one blade 102 and a trailing edge 104' of the other blade 102' adjacent to the blade 102. The suction surface 103 of each blade 102 has a flat surface 107 that extends flat from a constriction position 106, where the constriction 105 is formed, to the trailing edge 104. As shown in JP S61 232301 A and JP 2016 / 166614 A, the performance of the blade element is typically influenced by the curvature of the suction surface and the constriction position.

[0003] Further examples of previously known turbine nozzles can be found in US 2013 / 0 224 034 A1, DE 601 12 986 T2 and DE 10 2010 038 074 A1. PRESENTATION OF THE INVENTION Problems to be solved

[0004] Although there are concerns that a boundary layer developed on the intake surface causes a shift of the throat towards the leading edge and thus reduces the performance of the blade element, neither JP S61 232301 A nor JP 2016 / 166614 A discloses a blade whose profile is designed taking into account the influence of the boundary layer.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure is directed to providing a turbine nozzle and an axial turbine having the same, whereby it is possible to suppress the power reduction due to the influence of the boundary layer developed on the suction surface of the blade. Solving the problems

[0006] The above objects are achieved by a turbine nozzle having the features of independent claim 1 or the features of independent claim 5 or the features of independent claim 8 or the features of independent claim 9 and / or by an axial turbine having the features of claim 10. Further embodiments emerge from the dependent claims.

[0007] (1) A turbine nozzle according to at least one embodiment of the present disclosure includes a plurality of blades arranged to form a conical flow passage between each two adjacent blades. A suction surface of each blade has a curved surface, and a constriction of the flow passage is formed between the curved surface of one blade and a trailing edge of the other blade of the two adjacent blades at a constriction position. An upstream end of the curved surface is located upstream of the constriction position, and a downstream end of the curved surface is located downstream of the constriction position.

[0008] The intake surface of each blade has a flat surface extending flat from the downstream end of the curved surface to a trailing edge of the blade.

[0009] If L is a dimensionless axial chord length that is a ratio of a length from a leading edge of the blade in an axial direction to a length from the leading edge to the trailing edge of the blade in the axial direction, and AR(L) is a ratio of a flow passage area of the flow passage at a dimensionless axial chord length of L to a flow passage area of the flow passage at a dimensionless axial chord length of 1.0, the following equation is satisfied: |AR(1.0)−AR(0.98)1.0−0.98|≥_0.5

[0010] In the above configuration (1), since the suction surface of each blade of the turbine nozzle has a curved surface at the throat position where the throat of the conical flow passage is formed between adjacent blades, even if a boundary layer is formed on the suction surface, the flow passage area of the conical flow passage at the throat position is minimized, so that the throat is prevented from shifting toward the leading edge. This makes it possible to suppress the power reduction of the turbine nozzle due to the influence of a boundary layer formed on the suction surface of the blade.

[0011] Since the above configuration (1) provides a flat surface extending flatly from the downstream end of the curved surface to the trailing edge of the blade, the above configuration (1) suppresses the occurrence of an expansion wave due to the curvature of the intake surface, thus suppressing the reduction in blade element performance in a transonic region. This makes it possible to suppress the reduction in the performance of the turbine nozzle caused by the influence of a boundary layer developed on the intake surface of the blade.

[0012] In the above configuration (1), since the absolute value of the flow passage area ratio change rate is equal to or greater than 0.5 in a dimensionless axial chord length range of 0.98 to 1.0, even when a boundary layer forms on the intake surface, a minimum flow passage area of the conical flow passage is located at the throat position. This prevents the throat from shifting toward the leading edge. This makes it possible to suppress the power reduction of the turbine nozzle due to the influence of a boundary layer formed on the intake surface of the blade.

[0013] (2) In some embodiments, in the above configuration (1), a suction-side deflection angle between the flat surface and a tangential plane to the curved surface in the constriction position is equal to or less than 10°.

[0014] With the above configuration (2), since the intake-side deflection angle is equal to or less than 10°, the configuration (1) is achieved, preventing the throat from shifting toward the leading edge. This makes it possible to suppress the power degradation of the turbine nozzle caused by the influence of a boundary layer formed on the intake surface of the blade.

[0015] (3) In some embodiments, in one of the above configurations (1) or (2), a trailing edge included angle between two tangential planes at contact points of a trailing edge inscribed circle with a pressure surface and the suction surface of the blade is equal to or greater than 3°, wherein the trailing edge inlet circle is an inlet circle of minimum surface area contacting the pressure surface and the suction surface.

[0016] In the above configuration (3), since the included trailing edge angle is equal to or greater than 3°, the suction surface is shaped to protrude relative to the pressure surface, so that the flat surface can be easily formed and the curved surface with a high curvature relative to the flat surface can be easily formed. This achieves the configuration (1) and prevents the throat from shifting toward the leading edge. In addition, the occurrence of expansion waves due to the curvature of the suction surface is suppressed, thus suppressing the reduction in blade element performance in the transonic region. This can suppress the performance reduction of the turbine nozzle due to the influence of a boundary layer formed on the suction surface of the blade.

[0017] (4) In some embodiments, in any of the above embodiments (1) to (3), the suction surface of each blade has a second concave surface that is concavely curved between a leading edge and the throat position.

[0018] In the above configuration (4), since the second concave surface between the leading edge and the throat position is concavely curved, when a liquid film forms on the intake surface, the liquid film is deposited on the second concave surface. Thus, the throat is prevented from shifting toward the leading edge by the liquid film deposited on the second concave surface. This makes it possible to suppress the power reduction of the turbine nozzle caused by the influence of a liquid film formed on the intake surface of the blade.

[0019] (5) A turbine nozzle according to at least one embodiment of the present disclosure includes a plurality of blades arranged to form a conical flow passage between each two adjacent blades. A suction surface of each blade has a curved surface, and a constriction of the flow passage is formed between the curved surface of one blade and a trailing edge of the other blade of the two adjacent blades at a constriction position. An upstream end of the curved surface is located upstream of the constriction position, and a downstream end of the curved surface is located downstream of the constriction position.

[0020] The suction surface of each blade has a first concave surface which extends in a concave curve from the downstream end of the curved surface to a trailing edge of the blade.

[0021] Each blade has a hub-side edge and a tip-side edge at both edges in a blade height direction, and the first concave surface has a depth that increases from a second limit position away from the hub-side edge at a distance of 50% of a blade height in a direction from the hub-side edge to the tip-side edge between the second limit position and the tip-side edge.

[0022] In a case where the turbine nozzle is used in a humid area such as a steam turbine, a liquid film may form on the suction surface of the blade. If the liquid film is formed on a flat surface, the surface may become uneven from the downstream end of the curved surface to the trailing edge, which may reduce the performance of the blade element in a transonic region. In the above configuration (5), since the first concave surface extending from the downstream end of the curved surface to the trailing edge of the blade is concavely curved, the liquid film is deposited on the first concave surface, and the surface of the liquid film forms a flat surface. Accordingly, the occurrence of the expansion wave due to the curvature of the suction surface is suppressed, thus suppressing the reduction of the blade element performance in the transonic region.This makes it possible to suppress the power reduction of the turbine nozzle caused by the influence of a liquid film formed on the intake surface of the blade.

[0023] In the above configuration (5), since the depth of the first concave surface increases from the second boundary position toward the tip-side edge, when a liquid film formed on the suction surface flows toward the first concave surface, the liquid film easily flows toward the tip-side edge and moves away from the blade as droplets. Since the droplets can be easily trapped by a drain catcher attached to the casing wall surface, it is possible to reduce the erosion of the drain caused by the droplets.

[0024] In some embodiments, in the above configuration (4), each blade has a hub-side edge and a tip-side edge at both edges in a blade height direction, and the first concave surface has a depth that decreases from the hub-side edge to a first limit position away from the hub-side edge at a distance of 20% of a blade height in a direction from the hub-side edge to the tip-side edge between the first limit position and the hub-side edge.

[0025] In a steam turbine, the liquid phase can be drawn up by secondary flow to the intake surface of the blade, causing additional moisture loss. Since the depth of the first concave surface decreases from the hub-side edge to the first boundary position in the above design, it is possible to prevent the liquid film from being drawn onto the intake surface from the first concave surface to the tip-side edge and reduce secondary flow vortex. This makes it possible to reduce moisture loss.

[0026] (6) In some embodiments, in the above configuration (4), each blade has a hub-side edge and a tip-side edge at both edges in a blade height direction, and the second concave surface has a depth that decreases from the hub-side edge to a first limit position away from the hub-side edge at a distance of 20% of a blade height in a direction from the hub-side edge to the tip-side edge between the first limit position and the hub-side edge.

[0027] In the above configuration (6), since the depth of the second concave surface decreases from the hub-side edge to the first boundary position, it is possible to prevent the liquid film from being sucked onto the suction surface from the second concave surface toward the tip-side edge and reduce secondary flow vortex. This makes it possible to reduce moisture loss.

[0028] (7) In some embodiments, in the above configuration (4), each blade has a hub-side edge and a tip-side edge at both edges in a blade height direction, and the second concave surface has a depth that increases from a second limit position away from the hub-side edge at a distance of 50% of a blade height in a direction from the hub-side edge to the tip-side edge between the second limit position and the tip-side edge.

[0029] In the above configuration (7), since the depth of the second concave surface increases from the second boundary position toward the tip-side edge, the liquid film formed on the suction surface easily flows toward the tip-side edge and moves away from the blade as droplets. Since the droplets can be easily trapped by a drain catcher attached to the casing wall surface, it is possible to reduce the erosion of the drain caused by the droplets.

[0030] (8) A turbine nozzle according to at least one embodiment of the present disclosure includes a plurality of blades arranged to form a conical flow passage between every two adjacent blades. Each blade has a hub-side edge and a tip-side edge at both edges in a blade height direction, a suction surface of each blade has a concave curved surface, and the concave curved surface has a depth between a first boundary position and the hub-side edge, which increases from the first boundary position to the hub-side edge, the first boundary position being positioned away from the hub-side edge at a distance of 20% of a blade height in a direction from the hub-side edge to the tip-side edge.

[0031] In the above configuration (8), since the depth of the concave surface decreases from the hub-side edge to the first boundary position, the liquid film on the suction surface can be prevented from being drawn by the concave curved surface toward the tip-side edge and secondary flow vortex can be reduced. This makes it possible to reduce moisture loss.

[0032] (9) A turbine nozzle according to at least one embodiment of the present disclosure includes a plurality of blades arranged to form a conical flow passage between every two adjacent blades. Each blade has a hub-side edge and a tip-side edge at both edges in a blade height direction, a suction surface of each blade has a concave curved surface, and the concave curved surface has a depth that increases from a second boundary position away from the hub-side edge at a distance of 50% of a blade height in a direction from the hub-side edge to the tip-side edge between the second boundary position and the tip-side edge.

[0033] In the above configuration (9), since the depth of the concave surface increases from the second boundary position toward the tip-side edge, the liquid film formed on the suction surface easily flows toward the tip-side edge and moves away from the blade as droplets. Since the droplets can be easily trapped by a drain catcher attached to the casing wall surface, it is possible to reduce the erosion of the drain caused by the droplets.

[0034] (10) An axial flow turbine according to at least one embodiment of the present disclosure comprises: the turbine blade described in any one of the above (1) to (9).

[0035] With the above configuration (10), it is possible to suppress the power reduction due to the influence of a boundary layer developed on the intake surface of the blade, since a shift of the constriction towards the leading edge is prevented. Beneficial effects

[0036] According to at least one embodiment of the present disclosure, since the suction surface of each blade of the turbine nozzle has a curved surface at the throat position where the throat of the conical flow passage is formed between adjacent blades, even if a boundary layer is formed on the suction surface, the flow passage area of the conical flow passage at the throat position is minimized, preventing the throat from shifting toward the leading edge. This makes it possible to suppress the power reduction of the turbine nozzle due to the influence of a boundary layer formed on the suction surface of the blade. SHORT DESCRIPTION OF THE CHARACTERS Fig. 1 is a schematic diagram of the configuration of a turbine nozzle according to a first embodiment of the present invention. Fig. 2 is an enlarged view of the suction surface of the blade of a turbine nozzle according to the first embodiment of the present invention. Fig. 3 is a diagram showing the relationship between the dimensionless axial chord length and the ratio of the flow passage area at the suction surface of the blade of a turbine nozzle according to the first embodiment of the present invention. Fig. Figure 4 is a schematic diagram describing the differences in use and effect between blades with different flow passage area ratios. Fig. 5 is a diagram for describing the shape of the suction surface of the blade of a turbine nozzle according to the first embodiment of the present invention. Fig. 6 is a diagram for describing the shape of the suction surface of the blade of a turbine nozzle according to the first embodiment of the present invention. Fig. 7 is a diagram for describing the shape of the suction surface of the blade of a turbine nozzle according to a second embodiment of the present invention. Fig. 8 is a diagram for describing the shape of the suction surface of the blade of a turbine nozzle according to a third embodiment of the present invention. Fig. 9 is a diagram for describing the shape of the suction surface of the blade of a turbine nozzle according to a fourth embodiment of the present invention. Fig. 10 is a cross-sectional view taken along the line XX in Fig. 9. Fig. 11 is a diagram for describing the shape of the suction surface of the blade of a turbine nozzle according to a fifth embodiment of the present invention. Fig. 12 is a diagram for describing the shape of the suction surface of a blade of a turbine nozzle according to a sixth embodiment of the present invention. Fig. 13 is a cross-sectional view taken along the line XIII-XIII in Fig. 12. Fig. 14 is a diagram for describing the shape of the suction surface of a blade of a turbine nozzle according to a seventh embodiment of the present invention. Fig. Figure 15 is a schematic representation of the design of a conventional turbine nozzle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0037] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. (Embodiment 1)

[0038] Fig. 1 shows a turbine nozzle 1 provided for an axial-flow turbine, e.g., a steam turbine. The turbine nozzle 1 has a plurality of blades 2. The plurality of blades 2 are arranged to form a flow passage 3 between adjacent blades 2'. The flow channel 3 has a conical shape with a flow passage area that gradually decreases downstream, and a throat 4 with the minimum flow passage area is formed at a downstream end of the flow channel 3 by a suction surface 2c of one blade 2 and a trailing edge 2b' of the other blade 2' of two adjacent blades 2, 2'. A position where the throat 4 is formed is referred to as a throat position 5.

[0039] As in Fig. 2, the suction surface 2c of the blade 2 has a curved surface 11 that is convexly curved toward the blade 2' adjacent to the blade 2, and a flat surface 12 that extends flatly from a downstream end 11b of the curved surface 11 to a trailing edge 2b of the blade 2. The curved surface 11 forms the throat 4 at the throat position 5, with the trailing edge 2b' of the blade 2' adjacent to the blade 2. An upstream end 11a of the curved surface 11 is positioned downstream of the throat position 5, and the downstream end 11b of the curved surface 11 is positioned downstream of the throat position 5. That is, the curved surface 11 extends both upstream and downstream of the constriction position 5.

[0040] When flowing through the flow passage 3, a boundary layer forms on the intake surface 2c. However, since in the first embodiment, the curved surface 11 is provided at the constriction position 5 where the constriction 4 of the flow channel 3 is formed, the flow passage area of the flow passage 3 at the constriction position 5 is minimized even if a boundary layer forms on the intake surface 2c. Accordingly, the constriction 4 is prevented from shifting toward a leading edge 2a, and thus the power reduction of the turbine nozzle 1 (see Fig. 1) are suppressed by the influence of a boundary layer forming at the intake surface 2c.

[0041] Furthermore, since the flat surface 12 of the blade 2 is flat from the downstream end 11b of the curved surface 11 to the trailing edge 2b, the occurrence of expansion waves caused by the curvature of the intake surface 2c is suppressed, thus suppressing the reduction in blade element power in a transonic region. This can suppress the power reduction of the turbine nozzle caused by the influence of a boundary layer developed on the intake surface 2c of the blade 2.

[0042] The blade 2 preferably has one of the features described below in order to reliably achieve the configuration in which the suction surface 2c has the curved surface 11 and the flat surface 12. As shown in Fig. 1, L (0≤L≤1.0) is a dimensionless axial chord length, which is a ratio of a certain length from the leading edge 2a in the axial direction to a length from the leading edge 2a to the trailing edge 2b of the blade 2 in the axial direction. Further, AR(L) is a ratio of the flow passage area of the flow passage 3 at a dimensionless axial chord length of L to a flow passage area of the flow passage 3 at a dimensionless axial chord length of 1.0. The blade 2 has the following conditions for the flow passage area ratio change rate, which is a change rate of the flow passage area ratio in a certain range of the dimensionless axial chord length. |AR(1.0)−AR(0.98)1.0−0.98|≥_0.5

[0043] Fig. Figure 3 is a graph showing the change in the flow passage area ratio AR(L) near the trailing edge 2b of the blade 2 in the first embodiment. For reference, the change in the flow passage area ratio AR(L) of a turbine nozzle equipped with blades with a lower rate of change of AR(L) than the blade 2 is also shown. The shape difference between these blades is that the flow passage area of the blade 2 changes more significantly near the throat than that of the control version.

[0044] As in Fig. 4, in the control blade with a flow area ratio change of less than 0.5, the flow cross-sectional area in the axial direction near the throat changes less. Thus, the control blade has a shape in which a part of the minimum flow passage area is slightly shifted toward the leading edge, that is, the throat is slightly shifted toward the leading edge when a boundary layer is formed on the suction surface of the blade. In contrast, in the blade 2, the flow cross-sectional area changes greatly along the axial direction near the throat position 5. The blade 2 is therefore shaped to retain a part of the minimum flow cross-sectional area at the throat position 5, that is, the throat is not slightly shifted toward the leading edge even when a boundary layer is formed on the suction surface.The blade 2 with this property prevents the constriction from being shifted towards the leading edge 2a even when a boundary layer forms on the intake surface 2c.

[0045] Furthermore, as in Fig. 5, at the suction surface 2c of the blade 2, a suction-side deflection angle θ1 between the flat surface 12 and a tangential plane S1 to the curved surface 11 at the constriction position 5 is 5°≤θ1≤10°. In the conventional blade (see Fig. 15) with a flat surface from the constriction position 5 to the trailing edge 2b, the suction-side deflection angle θ1 is 0°. If the suction-side deflection angle is equal to or less than 10°, the design of Fig. 2 is reached, so that a displacement of the constriction 4 towards the front edge 2a is prevented.

[0046] Furthermore, as in Fig. 6, in the blade 2, an included trailing edge angle θ2 between two tangential planes S2 and S3 at the contact points 13 and 14 of a trailing edge inscribed circle C1, which is an inscribed circle of minimal surface area, touching the suction surface 2c and the pressure surface 2d of the blade 2, wherein the suction surface 2c and the pressure surface 2d is equal to or greater than 3°. When the included trailing edge angle θ2 is equal to or greater than 3°, since the suction surface 2c is shaped to protrude from the pressure surface 2d, the flat surface 12 can be easily formed, and the curved surface 11 with a strong curvature relative to the flat surface 12 can be easily formed. This facilitates the design of Fig. 2, and the constriction 4 is prevented from shifting toward the leading edge 2a. Furthermore, the occurrence of expansion waves is suppressed by the curvature of the intake surface 2c, thus suppressing the reduction in blade element performance in the transonic range.

[0047] Since the intake surface 2c of each blade 2 of the turbine nozzle 1 has the curved surface 11 at the constriction position 5, which forms the constriction 4 of the conical flow channel 3 between the blade 2 and its adjacent blade 2', even if a boundary layer forms on the intake surface 2c, the flow channel area of the conical flow channel 3 is minimized at the constriction position 5, which prevents the constriction 4 from shifting toward the leading edge 2a. This makes it possible to suppress the power reduction of the turbine nozzle 1 due to the influence of a boundary layer forming on the intake surface 2c of the blade 2. (Second embodiment)

[0048] Next, a turbine nozzle according to the second embodiment will be described. The turbine nozzle according to the second embodiment differs from the first embodiment in that the flat surface 12 is modified into a first concave surface that is concavely curved. In the second embodiment, the same components as in the first embodiment are designated by the same reference numerals and will not be described in detail again.

[0049] As in Fig. As shown in Fig. 7, the suction surface 2c of the blade 2 has a concave surface 20 (first concave surface) that is concavely curved from the downstream end 11b of the curved surface 11 to the trailing edge 2b of the blade 2. The configuration is otherwise the same as in the first embodiment.

[0050] If the turbine nozzle 1 (see Fig. 1) When used in a humid environment such as a steam turbine, a liquid film may form on the suction surface 2c of the blade 2. In the second embodiment, since the concave surface 20 is concavely curved from the downstream end 11b of the curved surface 11 to the trailing edge 2b of the blade 2, a liquid film 21 is deposited on the concave surface 20 in the second embodiment. As a result, a surface 22 of the liquid film 21 forms a flat surface on the concave surface. When the surface 22 of the liquid film 21 forms the flat surface, the occurrence of the expansion wave due to the curvature of the suction surface 2c is suppressed, and thus the reduction of the blade element power in the transonic region is suppressed. As a result, the power reduction of the turbine nozzle 1 due to the influence of a liquid film formed on the suction surface 2c of the blade 2 can be suppressed. (Third embodiment)

[0051] Next, a turbine nozzle according to the third embodiment will be described. The turbine nozzle according to the third embodiment differs from the first and second embodiments in that a second concave curved surface is formed between the upstream end 11a of the curved surface 11 and the leading edge 2a. The following description will be given based on an embodiment in which the second concave surface is formed starting from the first embodiment. However, embodiments are also possible in which the second concave surface is formed starting from the second embodiment, that is, both the first concave surface and the second concave surface are formed. In the third embodiment, the same components as in the first embodiment are provided with the same reference numerals and will not be described in detail again.

[0052] As in Fig. As shown in Figure 8, the suction surface 2c of the blade 2 has a concave surface 30 (second concave surface) that is concavely curved between the upstream end 11a of the curved surface 11 and the leading edge 2a. The configuration is otherwise the same as in the first embodiment.

[0053] In the third embodiment, since the concave surface 30 is formed between the upstream end 11a of the curved surface 11 and the leading edge 2a on the suction surface 2c, that is, between the throat position 5 and the leading edge 2a, a liquid film 21 formed on the suction surface 2c is deposited on the concave surface 30. As long as the concave surface 30 receives the liquid film 21, the surface 22 of the liquid film 21 does not protrude from the curved surface 11 toward the adjacent blade 2', so that the flow passage surface area of the flow passage 3 at the throat position 5 is still minimal. This prevents the throat 4 from shifting toward the leading edge 2a. As a result, the power loss of the turbine nozzle 1 due to the influence of a liquid film forming on the intake surface 2c of the blade 2 can be suppressed.In the second and third embodiments, the curved surface 11 is formed on the suction surface 2c of the blade 2 as in the first embodiment. Therefore, the second and third embodiments also prevent displacement of the constriction 4 toward the leading edge 2a due to the formation of a liquid film. (Fourth embodiment)

[0054] Next, a turbine nozzle according to the fourth embodiment will be described. The turbine nozzle according to the fourth embodiment differs from the second embodiment in that the configuration of the first concave surface is modified. In the fourth embodiment, the same components as in the second embodiment are designated by the same reference numerals and will not be described in detail again.

[0055] As in Fig. As shown in Figure 9, the blade 2 has a hub-side edge 2e and a tip-side edge 2f at both edges in the direction of the blade thickness. The suction surface 2c of the blade 2 has a concave surface 20 between the hub-side edge 2e and a first boundary position 40 away from the hub-side edge 2e at a distance of 20% of the blade thickness in the direction from the hub-side edge 2e to the tip-side edge 2f. As shown in Fig. As shown in Figure 10, the concave surface 20 has a depth that decreases from the hub-side edge 2e to the first limit position 40. The configuration is otherwise the same as that of the second embodiment.

[0056] In a steam turbine, as described in the second embodiment, the liquid film 21 may form on the suction surface 2c. The liquid film 21 may be rolled up by the secondary flow to the suction surface 2c of the blade 2, which may lead to additional moisture loss. Since, in the fourth embodiment, the depth of the concave surface 20 decreases from the hub-side edge 2e to the first boundary position 40, the liquid film 21 can be prevented from being drawn from the concave surface 20 to the tip-side edge 2f on the suction surface 2c (see Fig. 9) and reduce secondary flow vortex. This makes it possible to reduce moisture loss. (Fifth embodiment)

[0057] Next, a turbine nozzle according to the fifth embodiment will be described. The turbine nozzle according to the fifth embodiment differs from the third embodiment in that the configuration of the second concave surface is modified. In the fifth embodiment, the same components as in the third embodiment are designated by the same reference numerals and will not be described in detail again.

[0058] As in Fig. As shown in Fig. 11, the blade 2 has a hub-side edge 2e and a tip-side edge 2f on both sides in the blade thickness direction. The suction surface 2c of the blade 2 has a concave surface 30 between the hub-side edge 2e and a first limit position 40 away from the hub-side edge 2e at a distance of 20% of the blade thickness in the direction from the hub-side edge 2e to the tip-side edge 2f. The concave surface 30 has a depth decreasing from the hub-side edge 2e to the first limit position 40, similar to the concave surface 20 in the fourth embodiment. The configuration is otherwise the same as in the third embodiment.

[0059] In the fifth embodiment, since the depth of the concave surface 30 decreases from the hub-side edge 2e to the first limit position 40, it is also possible to prevent the liquid film 21 (see Fig. 8) is pulled at the suction surface 2c from the concave surface 30 to the tip-side edge 2f (see Fig. 9) and to reduce secondary flow vortex. This makes it possible to reduce moisture loss. (Sixth Embodiment)

[0060] Next, a turbine nozzle according to the sixth embodiment will be described. The turbine nozzle according to the sixth embodiment differs from the second embodiment in that the configuration of the first concave surface is modified. In the sixth embodiment, the same components as in the second embodiment are designated by the same reference numerals and will not be described in detail again.

[0061] As in Fig. 12, the blade 2 has a hub-side edge 2e and a tip-side edge 2f on both sides in the direction of the blade thickness. The suction surface 2c of the blade 2 has a concave surface 20 between the tip-side edge 2f and a second limiting position 50 away from the hub-side edge 2e at a distance of 50% of the blade thickness in the direction from the hub-side edge 2e to the tip-side edge 2f. As shown in Fig. As shown in Figure 13, the concave surface 20 has a depth that increases from the second limit position 50 toward the tip-side edge 2f. The configuration is otherwise the same as that of the second embodiment.

[0062] In a steam turbine, as described in the second embodiment, the liquid film 21 may form on the suction surface 2c. During operation of the steam turbine, the liquid film 21 may break up into droplets away from the blade 2. The droplets may cause drain attack erosion in the steam turbine. In the sixth embodiment, since the depth of the concave surface 20 increases from the second boundary position 50 toward the tip-side edge 2f, when the liquid film 21 forms on the suction surface 2c, the liquid film 21 easily flows toward the tip-side edge 2f and moves away from the blade 2 as droplets. By providing a drain catcher on the casing wall surface, the droplets can be caught by the drain catcher, reducing drain erosion by the droplets. (Seventh Embodiment)

[0063] Next, a turbine nozzle according to the seventh embodiment will be described. The turbine nozzle according to the seventh embodiment differs from the third embodiment in that the configuration of the second concave surface is modified. In the seventh embodiment, the same components as in the third embodiment are designated by the same reference numerals and will not be described in detail again.

[0064] As in Fig.As shown in Fig. 14, the blade 2 has a hub-side edge 2e and a tip-side edge 2f on both sides in the blade thickness direction. The suction surface 2c of the blade 2 has a concave surface 30 between the tip-side edge 2f and a second limit position 50 away from the hub-side edge 2e at a distance of 50% of the blade thickness in the direction from the hub-side edge 2e to the tip-side edge 2f. The concave surface 30 has a depth that increases from the second limit position 50 toward the tip-side edge 2f, just like the concave surface 20 in the sixth embodiment. The configuration is otherwise the same as that of the third embodiment.

[0065] Similarly, in the seventh embodiment, since the depth of the concave surface 30 increases from the second limit position 50 toward the tip-side edge 2f, the liquid film 21 formed on the suction surface 2c easily flows toward the tip-side edge 2f and moves away from the blade 2 as droplets. By providing a drain catcher on the casing wall surface, the droplets can be trapped by the drain catcher, reducing the erosion of the drain by the droplets.

[0066] Although only the concave surface 20 is formed on the suction surface 2c in the fourth and sixth embodiments, and only the concave surface 30 is formed on the suction surface 2c in the fifth and seventh embodiments, the present invention is not limited to these embodiments. Both the concave surface 20 in the fourth and sixth embodiments and the concave surface 30 in the fifth and seventh embodiments may be formed on the suction surface 2c.

[0067] Although the fourth to seventh embodiments include the configuration of the first embodiment, that is, the suction surface 2c has the curved surface 11, the present invention is not limited to these embodiments. At least one of the concave surface 20 in the fourth and sixth embodiments or the concave surface 30 in the fifth and seventh embodiments may be formed on the suction surface 2c without the curved surface 11 in the first embodiment. LIST OF REFERENCE SYMBOLS

[0068] Turbine nozzle 2 shovels 2a Front edge (of the blade) 2b Trailing edge (of the blade) 2c Suction surface (of the blade) 2d pressure surface (of the blade) 2nd hub-side edge (of the blade) 2f Tip-side edge (of the blade) 3 Flow passage 4 Constriction 5 Constriction position 11 Curved surface 11a Upstream end (of the curved surface) 11b Downstream end (of the curved surface) 12 Flat surface 13 contact point 14 contact point 20 Concave Surface (First Concave Surface) 21 Liquid film 22 Surface (of the liquid film) 30 Concave Surface (Second Concave Surface) 40 First border position 50 Second border position C1 trailing edge inscribed circle L Dimensionless axial chord length S1 Tangential plane S2 Tangential plane S3 Tangential plane θ1 Suction side deflection angle of the machine θ2 included trailing edge angle

Claims

[1] Turbine nozzle (1) having a plurality of blades (2) arranged to form a conical flow passage (3) between each two adjacent blades (2, 2'), wherein a suction surface (2c) of each blade (2) has a curved surface (11), and a constriction (4) of the flow passage (3) is formed between the curved surface (11) of one blade (2) and a trailing edge (2b) of the other blade (2') of the two adjacent blades (2, 2') at a constriction position (5), wherein an upstream end (11a) of the curved surface (11) is arranged upstream of the constriction position (5), and a downstream end (11b) of the curved surface (11) is arranged downstream of the constriction position (5), wherein the suction surface (2c) of each blade (2) has a flat surface (12) extending flatly from the downstream end (11b) of the curved surface (11) to a trailing edge (2b) of the blade (2), and where, if L is a dimensionless axial chord length which is a ratio of a length from a leading edge (2a) of the blade (2) in an axial direction to a length from the leading edge (2a) to the trailing edge (2b) of the blade (2) in the axial direction, and AR(L) is a ratio of a flow passage area of the flow passage (3) at a dimensionless axial chord length of L to a flow passage area of the flow passage (3) at a dimensionless axial chord length of 1.0, the following equation is satisfied: |AR(1.0)−AR(0.98)1.0−0.98|≥_0.5 [2] Turbine nozzle (1) according to claim 1, wherein a suction-side deflection angle (θ1) between the flat surface (12) and a tangential plane (S1) to the curved surface (11) at the throat position (5) is equal to or less than 10°. [3] Turbine nozzle (1) according to claim 1 or 2, wherein a trailing edge inclusion angle (θ2) between two tangential planes (S2, S3) at contact points (13, 14) of a trailing edge inscribed circle (c1) with a pressure surface (2d) and the suction surface (2c) of the blade (2) is equal to or greater than 3°, wherein the trailing edge inscribed circle (c1) is an inner circle of minimal surface area touching the pressure surface (2d) and the suction surface (2c). [4] Turbine nozzle (1) according to one of the preceding claims 1 to 3, wherein the suction surface (2c) of each blade (2) has a second concave surface (30) which is concavely curved between a leading edge (2a) and the throat position (5). [5] Turbine nozzle (1) having a plurality of blades (2) arranged to form a conical flow passage (3) between each two adjacent blades (2, 2'), wherein a suction surface (2c) of each blade (2) has a curved surface (11), and a constriction (4) of the flow passage (3) is formed between the curved surface (11) of one blade (2) and a trailing edge (2b) of the other blade (2') of the two adjacent blades (2, 2') at a constriction position (5), wherein an upstream end (11a) of the curved surface (11) is arranged upstream of the constriction position (5), and a downstream end (11b) of the curved surface (11) is arranged downstream of the constriction position (5), wherein the suction surface (2c) of each blade (2) has a first concave surface (20) extending in a concave curve from the downstream end (11b) of the curved surface (11) to a trailing edge (2b) of the blade (2), each blade (2) having a hub-side edge (2e) and a tip-side edge (2f) at both edges in a blade height direction, and wherein the first concave surface (20) has a depth that increases from a second limit position (50) away from the hub-side edge (2e) at a distance of 50% of a blade height in a direction from the hub-side edge (2e) to the tip-side edge (2f) between the second limit position (50) and the tip-side edge (2f). [6] Turbine nozzle (1) according to claim 4, wherein each blade (2) has a hub-side edge (2e) and a tip-side edge (2f) at both edges in a blade height direction, and wherein the second concave surface (30) has a depth that decreases from the hub-side edge (2e) to a first limit position (40) away from the hub-side edge (2e) at a distance of 20% of a blade height in a direction from the hub-side edge (2e) to the tip-side edge (2f) between the first limit position (40) and the hub-side edge (2e). [7] Turbine nozzle (1) according to claim 4, wherein each blade (2) has a hub-side edge (2e) and a tip-side edge (2f) at both edges in a blade height direction, and wherein the second concave surface (30) has a depth that increases from a second limit position (50) away from the hub-side edge (2e) at a distance of 50% of a blade height in a direction from the hub-side edge (2e) to the tip-side edge (2f) between the second limit position (50) and the tip-side edge (2f). [8] Turbine nozzle (1) having a plurality of blades (2) arranged to form a conical flow passage (3) between each two adjacent blades (2, 2'), wherein each blade (2) has a hub-side edge (2e) and a tip-side edge (2f) on both edges in a blade height direction, wherein a suction surface (2c) of each blade (2) has at least a first concave surface (20) extending in a concave curve from a position between a trailing edge (2b) of the blade (2) and a constriction position (5) to the trailing edge (2b), or a second concave surface (30) extending in a concave curve between a leading edge (2a) and the constriction position (5), wherein a first limit position (40) is positioned away from the hub-side edge (2e) at a distance of 20% of a blade height in a direction from the hub-side edge (2e) to the tip-side edge (2f), and wherein the at least one of the first concave surface (20) or the second concave surface (30) has a depth between the first limit position (40) and the hub-side edge (2e) that increases from the limit position (40) to the hub-side edge (2e). [9] Turbine nozzle (1) having a plurality of blades (2) arranged to form a conical flow passage (3) between each two adjacent blades (2, 2'), wherein each blade (2) has a hub-side edge (2e) and a tip-side edge (2f) on both edges in a blade height direction, wherein a suction surface (2c) of each blade (2) has at least a first concave surface (20) extending in a concave curve from a position between a trailing edge (2b) of the blade (2) and a constriction position (5) to the trailing edge (2b), or a second concave surface (30) extending in a concave curve between a leading edge (2a) and the constriction position (5), and wherein the at least one of the first concave surface (20) or the second concave surface (30) has a depth that increases from a second limit position (50) away from the hub-side edge (2e) at a distance of 50% of a blade height in a direction from the hub-side edge (2e) to the tip-side edge (2f) between the second limit position (50) and the tip-side edge (2f). [10] Axial turbine comprising the turbine nozzle (1) according to one of claims 1 to 9.

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