Turbine nozzle and axial-flow turbine including same

Abstract

A turbine nozzle includes a plurality of blades arranged so as to form a tapered flow passage between each two adjacent blades. A suction surface of each blade includes a curved surface, and a throat 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 throat position. An upstream end of the curved surface is positioned upstream of the throat position, and a downstream end of the curved surface is positioned downstream of the throat position.

Claims

1. A turbine nozzle comprising a plurality of blades arranged so as to form a tapered flow passage between each two adjacent blades, wherein a suction surface of each blade includes a curved surface, and a throat 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 throat position: wherein an upstream end of the curved surface is positioned upstream of the throat position, and a downstream end of the curved surface is positioned downstream of the throat position, wherein the suction surface of each blade includes a flat surface extending flat from the downstream end of the curved surface to a trailing edge of the blade, and wherein when L is a dimensionless axial chord length which 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 expression is satisfied: $.Math.\frac{\mathrm{AR}\left(1.0\right)-\mathrm{AR}\left(0.98\right)}{1.0-0.98}.Math.\geqq 0.5.$

2. The turbine nozzle according to claim 1, wherein a suction-side deflection angle between the flat surface and a tangent plane to the curved surface at the throat position is equal to or less than 10°.

3. The turbine nozzle according to claim 1, wherein a trailing-edge included angle between two tangent planes at contact points of a trailing edge incircle with a pressure surface and the suction surface of the blade is equal to or greater than 3°, the trailing edge incircle being an incircle of minimum area touching the pressure surface and the suction surface.

4. The turbine nozzle according to claim 1, wherein the suction surface of each blade includes a second concave surface concavely curved between a leading edge and the throat position.

5. The turbine nozzle according to claim 4, wherein each blade includes a hub-side edge and a tip-side edge on both edges in a blade height direction, and wherein the second concave surface has a depth decreasing from the hub-side edge toward a first boundary position away from the hub-side edge at a distance of 20% of a blade height in a direction from the hub-side edge toward the tip-side edge, between the first boundary position and the hub-side edge.

6. The turbine nozzle according to claim 4, wherein each blade includes a hub-side edge and a tip-side edge on both edges in a blade height direction, and wherein the second concave surface has a depth increasing 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 toward the tip-side edge, toward the tip-side edge, between the second boundary position and the tip-side edge.

7. An axial-flow turbine comprising the turbine nozzle according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic configuration diagram of a turbine nozzle according to a first embodiment of the present invention.

(2) FIG. 2 is an enlarged view of a suction surface of a blade of a turbine nozzle according to the first embodiment of the present invention.

(3) FIG. 3 is a graph showing a relationship between dimensionless axial chord length and ratio of flow passage area on a suction surface of a blade of a turbine nozzle according to the first embodiment of the present invention.

(4) FIG. 4 is a schematic diagram for describing difference in operation and effect between blades having different flow-passage-area-ratio change rates.

(5) FIG. 5 is a diagram for describing the shape of a suction surface of a blade of a turbine nozzle according to the first embodiment of the present invention.

(6) FIG. 6 is a diagram for describing the shape of a suction surface of a blade of a turbine nozzle according to the first embodiment of the present invention.

(7) FIG. 7 is a diagram for describing the shape of a suction surface of a blade of a turbine nozzle according to a second embodiment of the present invention.

(8) FIG. 8 is a diagram for describing the shape of a suction surface of a blade of a turbine nozzle according to a third embodiment of the present invention.

(9) FIG. 9 is a diagram for describing the shape of a suction surface of a blade of a turbine nozzle according to a fourth embodiment of the present invention.

(10) FIG. 10 is a cross-sectional view taken along line X-X in FIG. 9.

(11) FIG. 11 is a diagram for describing the shape of a suction surface of a blade of a turbine nozzle according to a fifth embodiment of the present invention.

(12) FIG. 12 is a diagram for describing the shape of a suction surface of a blade of a turbine nozzle according to a sixth embodiment of the present invention.

(13) FIG. 13 is a cross-sectional view taken along line XIII-XIII in FIG. 12.

(14) FIG. 14 is a diagram for describing the shape of a suction surface of a blade of a turbine nozzle according to a seventh embodiment of the present invention.

(15) FIG. 15 is a schematic configuration diagram of a conventional turbine nozzle.

DETAILED DESCRIPTION

(16) Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. However, the scope of the present invention is not limited to the following embodiments. It is intended that dimensions, materials, shapes, relative positions and the like of components described in the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention.

Embodiment 1

(17) FIG. 1 shows a turbine nozzle 1 provided to an axial-flow turbine such as a steam turbine. The turbine nozzle 1 includes a plurality of blades 2. The plurality of blades 2 is arranged so as to form a flow passage 3 between adjacent blades 2′. The flow passage 3 has a tapered shape with a flow passage area gradually decreasing downstream, and a throat 4 having the minimum flow passage area is formed at a downstream end of the flow passage 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 at which the throat 4 is formed is referred to as a throat position 5.

(18) As shown in FIG. 2, the suction surface 2c of the blade 2 includes a curved surface 11 convexly curved toward the blade 2′ adjacent to the blade 2 and a flat surface 12 extending flat 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 throat position 5.

(19) When a fluid flows through the flow passage 3, a boundary layer is formed on the suction surface 2c. In the first embodiment, however, since the curved surface 11 is provided at the throat position 5 at which the throat 4 of the flow passage 3 is formed, even if a boundary layer is formed on the suction surface 2c, the flow passage area of the flow passage 3 is minimized at the throat position 5. Accordingly, the throat 4 is prevented from shifting toward a leading edge 2a, and thus it is possible to suppress the reduction in performance of the turbine nozzle 1 (see FIG. 1) due to the influence of a boundary layer developed on the suction surface 2c.

(20) Further, since the blade 2 has the flat surface 12 extending flat from the downstream end 11b of the curved surface 11 to the trailing edge 2b, the occurrence of expansion wave due to curvature of the suction surface 2c is suppressed, and thus the reduction in blade element performance in a transonic range is suppressed. As a result, it is possible to suppress the reduction in turbine nozzle performance due to the influence of a boundary layer developed on the suction surface 2c of the blade 2.

(21) The blade 2 preferably has any of features described below to reliably achieve the configuration in which the suction surface 2c has the curved surface 11 and the flat surface 12.

(22) 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 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 blade 2 has the following conditions of 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.

(23) $\begin{array}{cc}.Math.\frac{\mathrm{AR}\left(1.0\right)-\mathrm{AR}\left(0.98\right)}{1.0-0.98}.Math.\geqq 0.5& \left(\mathrm{Expression}2\right)\end{array}$

(24) FIG. 3 is a graph of the change in the flow passage area ratio AR(L) in the vicinity of the trailing edge 2b of the blade 2 in the first embodiment. As a control, the change in the flow passage area ratio AR(L) of a turbine nozzle provided with blades having a lower change rate of AR(L) than the blade 2 is also shown. The difference in shape between these blades is that the flow passage area of the blade 2 in the vicinity of the throat position more greatly changes than that of the control.

(25) As shown in FIG. 4, in the control blade having a flow-passage-area-ratio change rate of less than 0.5, the flow passage cross-sectional area less changes along the axial direction in the vicinity of the throat position. Thus, the control blade has a shape such that a portion of minimum flow passage area is easily shifted toward the leading edge, i.e., the throat is easily 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 passage cross-sectional area greatly changes along the axial direction in the vicinity of the throat position 5. Thus, the blade 2 has a shape such that a portion of minimum flow passage area is kept at the throat position 5, i.e., the throat is not easily shifted toward the leading edge, even when a boundary layer is formed on the suction surface. The blade 2 having this feature prevents the throat from shifting toward the leading edge 2a even when a boundary layer is formed on the suction surface 2c.

(26) Further, as shown in FIG. 5, on the suction surface 2c of the blade 2, a suction-side deflection angle θ.sub.1 between the flat surface 12 and a tangent plane S.sub.1 to the curved surface 11 at the throat position 5 satisfies 5°θ.sub.1≤10°. In the conventional blade (see FIG. 15) having a flat surface from the throat position 5 to the trailing edge 2b, the suction-side deflection angle θ.sub.1 is 0°. When the suction-side deflection angle is equal to or less than 10°, the configuration of FIG. 2 is achieved, so that the throat 4 is prevented from shifting toward the leading edge 2a.

(27) Further, as shown in FIG. 6, in the blade 2, a trailing-edge included angle θ.sub.2 between two tangent planes S.sub.2 and S.sub.3 at contact points 13 and 14 of a trailing edge incircle C1, which is an incircle of minimum area touching the suction surface 2c and the pressure surface 2d of the blade 2, with the suction surface 2c and the pressure surface 2d is equal to or greater than 3°. When the trailing-edge included angle 2z is equal to or greater than 3°, since the suction surface 2c is shaped so as to protrude relative to the pressure surface 2d, the flat surface 12 can be easily formed, and the curved surface 11 with a high curvature relative to the flat surface 12 can be easily formed. As a result, the configuration of FIG. 2 is achieved, and the throat 4 is prevented from shifting toward the leading edge 2a. In addition, the occurrence of expansion wave due to curvature of the suction surface 2c is suppressed, and thus the reduction in blade element performance in a transonic range is suppressed.

(28) Thus, since the suction surface 2c of each blade 2 of the turbine nozzle 1 has the curved surface 11 at the throat position 5 forming the throat 4 of the tapered flow passage 3 between the blade 2 and its adjacent blade 2′, even if a boundary layer is formed on the suction surface 2c, the flow passage area of the tapered flow passage 3 is minimized at the throat position 5, which prevents the throat 4 from shifting toward the leading edge 2a. As a result, it is possible to suppress the reduction in performance of the turbine nozzle 1 due to the influence of a boundary layer developed on the suction surface 2c of the blade 2.

Second Embodiment

(29) Next, a turbine nozzle according to the second embodiment will be described. The turbine nozzle according to the second embodiment is different from the first embodiment in that the flat surface 12 is changed to a first concave surface concavely curved. In the second embodiment, the same constituent elements as those in the first embodiment are associated with the same reference numerals and not described again in detail.

(30) As shown in FIG. 7, the suction surface 2c of the blade 2 includes a concave surface 20 (first concave surface) 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 that of the first embodiment.

(31) In a case where the turbine nozzle 1 (see FIG. 1) is used in a wetted area like a steam turbine, a liquid film may be formed on the suction surface 2c of the blade 2. In the second embodiment, since the concave surface 20 concavely curvedly extending from the downstream end 11b of the curved surface 11 to the trailing edge 2b of the blade 2 is provided, a liquid film 21 is deposited on the concave surface 20. As a result, a surface 22 of the liquid film 21 on the concave surface forms a flat surface. When the surface 22 of the liquid film 21 forms the flat surface, the occurrence of expansion wave due to curvature of the suction surface 2c is suppressed, and thus the reduction in blade element performance in a transonic range is suppressed. As a result, it is possible to suppress the reduction in performance of the turbine nozzle 1 due to the influence of a liquid film formed on the suction surface 2c of the blade 2.

Third Embodiment

(32) Next, a turbine nozzle according to the third embodiment will be described. The turbine nozzle according to the third embodiment is different from the first and second embodiments in that a second concave surface concavely curved 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, wherein, starting from the first embodiment, the second concave surface is formed. However, embodiments, wherein, starting from the second embodiment, the second concave surface is formed, i.e., both the first concave surface and the second concave surface are formed, are also possible. In the third embodiment, the same constituent elements as those in the first embodiment are associated with the same reference numerals and not described again in detail.

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

(34) 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, i.e., 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 toward the adjacent blade 2′ from the curved surface 11, so that the flow passage area of the flow passage 3 at the throat position 5 is still minimum. Thus, the throat 4 is prevented from shifting toward the leading edge 2a. As a result, it is possible to suppress the reduction in performance of the turbine nozzle 1 due to the influence of a liquid film formed on the suction surface 2c of the blade 2.

(35) In the second and third embodiments, the curved surface 11 is formed on the suction surface 2c of the blade 2 as well as the first embodiment. Therefore, the second and third embodiments likewise have the effect of preventing shifting of the throat 4 toward the leading edge 2a due to formation of a liquid film.

Fourth Embodiment

(36) Next, a turbine nozzle according to the fourth embodiment will be described. The turbine nozzle according to the fourth embodiment is different from the second embodiment in that the configuration of the first concave surface is modified. In the fourth embodiment, the same constituent elements as those in the second embodiment are associated with the same reference numerals and not described again in detail.

(37) As shown in FIG. 9, the blade 2 includes a hub-side edge 2e and a tip-side edge 2f on both edges in the blade thickness direction. 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 a direction from the hub-side edge 2e toward the tip-side edge 2f. As shown in FIG. 10, the concave surface 20 has a depth decreasing from the hub-side edge 2e toward the first boundary position 40. The configuration is otherwise the same as that of the second embodiment.

(38) In a steam turbine, as described in the second embodiment, the liquid film 21 may be formed on the suction surface 2c. The liquid film 21 may be rolled up to the suction surface 2c of the blade 2 due to secondary flow, which may cause additional moisture loss. In the fourth embodiment, since the depth of the concave surface 20 decreases from the hub-side edge 2e to the first boundary position 40, it is possible to prevent the liquid film 21 from being drawn on the suction surface 2c from the concave surface 20 toward the tip-side edge 2f (see FIG. 9) and reduce a secondary flow swirl. Thus, it is possible to reduce moisture loss.

Fifth Embodiment

(39) Next, a turbine nozzle according to the fifth embodiment will be described. The turbine nozzle according to the fifth embodiment is different from the third embodiment in that the configuration of the second concave surface is modified. In the fifth embodiment, the same constituent elements as those in the third embodiment are associated with the same reference numerals and not described again in detail.

(40) As shown in FIG. 11, the blade 2 includes a hub-side edge 2e and a tip-side edge 2f on both side 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 boundary position 40 away from the hub-side edge 2e at a distance of 20% of the blade thickness in a direction from the hub-side edge 2e toward the tip-side edge 2f. The concave surface 30 has a depth decreasing from the hub-side edge 2e toward the first boundary position 40, as with the concave surface 20 in the fourth embodiment. The configuration is otherwise the same as that of the third embodiment.

(41) In the fifth embodiment, similarly, since the depth of the concave surface 30 decreases from the hub-side edge 2e to the first boundary position 40, it is possible to prevent the liquid film 21 (see FIG. 8) from being drawn on the suction surface 2c from the concave surface 30 toward the tip-side edge 2f (see FIG. 9) and reduce a secondary flow swirl. Thus, it is possible to reduce moisture loss.

Sixth Embodiment

(42) Next, a turbine nozzle according to the sixth embodiment will be described. The turbine nozzle according to the sixth embodiment is different from the second embodiment in that the configuration of the first concave surface is modified. In the sixth embodiment, the same constituent elements as those in the second embodiment are associated with the same reference numerals and not described again in detail.

(43) As shown in FIG. 12, the blade 2 includes a hub-side edge 2e and a tip-side edge 2f on both side in the blade thickness direction. The suction surface 2c of the blade 2 has a concave surface 20 between the tip-side edge 2f and a second boundary position 50 away from the hub-side edge 2e at a distance of 50% of the blade thickness in a direction from the hub-side edge 2e toward the tip-side edge 2f. As shown in FIG. 13, the concave surface 20 has a depth increasing from the second boundary position 50 toward the tip-side edge 2f. The configuration is otherwise the same as that of the second embodiment.

(44) In a steam turbine, as described in the second embodiment, the liquid film 21 may be formed on the suction surface 2c. During operation of the steam turbine, the liquid film 21 may break 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 formed on the suction surface 2c flows to the concave surface 20, 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 trapped by the drain catcher, which reduces drain attack erosion due to the droplets.

Seventh Embodiment

(45) Next, a turbine nozzle according to the seventh embodiment will be described. The turbine nozzle according to the seventh embodiment is different from the third embodiment in that the configuration of the second concave surface is modified. In the seventh embodiment, the same constituent elements as those in the third embodiment are associated with the same reference numerals and not described again in detail.

(46) As shown in FIG. 14, the blade 2 includes a hub-side edge 2e and a tip-side edge 2f on both side 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 boundary position 50 away from the hub-side edge 2e at a distance of 50% of the blade thickness in a direction from the hub-side edge 2e toward the tip-side edge 2f. The concave surface 30 has a depth increasing from the second boundary position 50 toward the tip-side edge 2f, as with the concave surface 20 in the sixth embodiment. The configuration is otherwise the same as that of the third embodiment.

(47) In the seventh embodiment, similarly, since the depth of the concave surface 30 increases from the second boundary position 50 toward the tip-side edge 2f, when the liquid film 21 formed on the suction surface 2c flows to the concave surface 30, 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 trapped by the drain catcher, which reduces drain attack erosion due to the droplets.

(48) Although in the fourth and sixth embodiments, only the concave surface 20 is formed on the suction surface 2c, and in the fifth and seventh embodiments, only the concave surface 30 is formed on the suction surface 2c, 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.

(49) Although in the fourth to seventh embodiments, the configuration of the first embodiment is included, i.e., 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 not having the curved surface 11 in the first embodiment.

REFERENCE SIGNS LIST

(50) 1 Turbine nozzle 2 Blade 2a Leading edge (of blade) 2b Trailing edge (of blade) 2c Suction surface (of blade) 2d Pressure surface (of blade) 2e Hub-side edge (of blade) 2f Tip-side edge (of blade) 3 Flow passage 4 Throat 5 Throat position 11 Curved surface 11a Upstream end (of curved surface) 11b Downstream end (of curved surface) 12 Flat surface 13 Contact point 14 Contact point 20 Concave surface (First concave surface) 21 Liquid film 22 Surface (of liquid film) 30 Concave surface (Second concave surface) 40 First boundary position 50 Second boundary position C.sub.1 Trailing edge incircle L Dimensionless axial chord length S.sub.1 Tangent plane S.sub.2 Tangent plane S.sub.3 Tangent plane θ.sub.1 Suction-side deflection angle θ.sub.2 Trailing-edge included angle