JPH0734803A - Axial flow turbine nozzle - Google Patents

Abstract

PURPOSE:To provide an axial flow turbine nozzle capable of preventing the separation of the flow. CONSTITUTION:In an axial flow turbine nozzle where a plurality of nozzle blades 3 arranged in the circumferential direction and inner and outer circumferential walls 6, 7 consisting of a flow passage to be expanded toward the downstream in the axial direction are provided, and the inner and outer circumferential walls 6, 7 are integrated with the nozzle blades 3 to form the annular flow passage, the following edge 8 of the nozzle blades 3 is formed inclined in the axial and circumferential direction according to the expansion angle in the radial direction of the flow passage and the flow angle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an axial flow turbine nozzle, and more particularly to an axial flow turbine nozzle having an enlarged flow path toward the downstream side in the axial direction of the turbine and reducing separation of the flow of the axial flow turbine.

[0002]

2. Description of the Related Art In recent years, it has been an important subject to improve turbine performance in order to improve the operating economy of a power plant and improve the power generation efficiency. Among them, particularly in the low pressure section of the turbine, the output per section is large, and the improvement in performance in this low pressure section plays a major role in improving the performance of the entire turbine.

FIG. 9 is a sectional view showing a low pressure part of a conventional axial flow turbine. In FIG. 9, Xa indicates the axial direction of the turbine. As shown in FIG. 9, a low pressure portion of an axial flow turbine is generally composed of a nozzle blade 3 fixed by a nozzle outer ring 1 and a nozzle inner ring 2 and a moving blade 5 fixed to a rotating shaft 4. It is constructed by combining one or more paragraphs in the flow direction.

The inner peripheral wall 6 of the nozzle is parallel to the axial direction Xa, while the outer peripheral wall 7 of the nozzle is enlarged toward the downstream side in the axial direction. This is to realize smooth expansion in response to a sudden increase in the specific volume of the fluid in the low pressure portion of the axial flow turbine.

FIG. 10 is a sectional view taken along the line C--C in FIG. 9. As shown in FIG. 10, the nozzle blade 3 is mounted so that its trailing edge 8 is along the radial line Xr.

[0006]

In order to improve the performance of the turbine, in the turbine stage constructed as described above, the flow passage smoothly passes through without separation of the flow causing loss. It is important to.

However, in the conventional nozzle of the low pressure part of the axial flow turbine constructed as described above, it has been impossible to prevent the separation of the flow, which causes a loss, particularly in the vicinity of the leading end of the paragraph. The reason will be described in detail below.

That is, the separation of the flow is a major factor in that the nozzle outer peripheral wall 7 expands toward the downstream side in the axial direction as described above. Therefore, a description will be given in comparison with the case where the nozzle outer peripheral wall 7 does not expand toward the downstream side in the axial direction.

First, the case where the nozzle outer peripheral wall 7 is not enlarged will be described. FIG. 11 shows a high pressure section or an intermediate pressure section of the axial flow turbine. Since the increase in the specific volume of the fluid is relatively small in the high pressure section or the intermediate pressure section, the nozzle outer peripheral wall 7 is directed toward the downstream side in the axial direction. Not expanded according to.

FIG. 12 is a sectional view taken along the line D--D in FIG. 11. Even in the high / medium pressure stage, the nozzle blade 3 is attached so that its trailing edge 8 is along the radial line Xr. 13 is a cross-sectional view taken along the line EE of FIG. 11. In FIG. 13, Xa indicates the axial direction and Xc indicates the circumferential direction, and the throat 9 as the minimum passage is provided in the passage through which the fluid passes. The fluid flows out in a direction orthogonal to the throat 9.

Further, since the throat 9 is inclined by the angle α with respect to the circumferential direction Xc, the fluid flows out in the direction inclined by the angle α from the axial direction Xa. As shown in FIG. 13, when viewed two-dimensionally, the throat 9 is a line, but the blade cross section is a plane because the nozzle blades 3 are stacked in the radial direction.

FIG. 14 is a view seen from the center of the nozzle flow path shown in FIG. 13 in the FF direction. In FIG. 14, 1
0 indicates the leading edge of the nozzle. As described above, the nozzle blade 3 is attached so that the trailing edge 8 is along the radial line Xr, and the nozzle outer peripheral wall 7 and the nozzle inner peripheral wall 6 formed from the nozzle outer ring 1 and the nozzle inner ring 2 are axially arranged. Since they are parallel to each other, the throat 9 is perpendicular to the outer peripheral wall 7 of the nozzle and the inner peripheral wall 6 of the nozzle, and the flow at the nozzle outlet is along a parallel flow path from the root to the tip.

In order to prevent flow separation near the wall surface, it is necessary that the flow direction is not in the direction away from the wall surface, that is, the flow is parallel to or toward the wall surface. Hereinafter, the flow direction in which the flow separation does not occur is referred to as a proper fluid outflow direction.

In this case, since the flow of the fluid is parallel to the nozzle outer peripheral wall 7 and the nozzle inner peripheral wall 6, the flow never separates from the nozzle outer peripheral wall 7 and the nozzle inner peripheral wall 6. No flow separation occurs. This will be described in detail below.

FIG. 15 is a three-dimensional view showing the relationship between the throat 9 of the nozzle and the direction of fluid flow in the vicinity of the outer peripheral wall of the nozzle. In FIG. 15, Xa represents the axial direction and X
c indicates the circumferential direction, and Xr indicates the radial line.

In this case, since the flow path does not expand toward the downstream side in the axial direction Xa, the proper outflow direction of the fluid is a direction two-dimensionally inclined from the axial direction Xa by an angle α, and at least the axial direction Xa. It is on the plane formed by the circumferential direction Xc or is the direction of the radial line Xr from that plane.

That is, the proper outflow direction of the fluid needs to be higher than the direction represented by the vector OA in the figure. This vector OA is called the lower limit of the proper outflow direction of the fluid. When the component of the vector OA is expressed in the form of (Xa axis direction, Xc axis direction, Xr axis direction), it is expressed by the following equation from the geometrical relation.

[0018]

[Formula 3] OA = (cos α, sin α, 0) (1)

Assuming that the vector representing the proper outflow direction of the fluid is OA ', the component of this vector OA' is expressed by the following equation from the geometrical relation.

[0020]

[Expression 4] OA '= (Xoa, Yoa, Zoa) (2)

[Equation 5] Xoa = cos α (3)

[Equation 6] Yoa = sin α (4)

[Equation 7] Zoa ≧ 0 (5)

On the other hand, the throat 9 of the nozzle blade 3 is orthogonal to the plane represented by the axial direction Xa and the circumferential direction Xc because the trailing edge 8 of the nozzle blade 3 is along the radial line Xr.

The throat 9 and the axis in the circumferential direction Xc intersect at an angle α. As described above, since the actual outflow angle of the fluid is perpendicular to the throat 9, the actual outflow direction of the fluid is represented by the vector OB.

[0023]

OB = (cos α, sin α, 0) (6) That is, since the vector OA ′ and the vector OB are in the same direction, the lower limit of the actual outflow direction of the fluid and the lower limit of the proper outflow direction of the fluid are set. Match and there is no possibility of flow separation.

Next, a case where the outer peripheral wall 7 of the nozzle is enlarged in the axially downstream direction will be described. FIG. 16 is a cross-sectional view showing the nozzle of the axial flow turbine when the outer peripheral wall 7 of the nozzle is enlarged toward the downstream side in the axial direction Xa.

As shown in FIG. 16, the nozzle blade 3 is attached so that its trailing edge 8 is along the radial line Xr. The nozzle outer peripheral wall 7 has an angle θ with respect to the axial direction Xa.
It is inclined by _t . Since the flow passage is enlarged, it is clear that the flow along the enlargement angle θ of the flow passage at that position at the arbitrary blade height position of the outlet of the nozzle blade 3 becomes the optimum flow.

FIG. 17 is a cross-sectional view taken along the line GG in FIG. 16. As described above, the flow passage of the fluid has the throat 9 and the fluid is in a direction perpendicular to the throat 9, that is, the drawing. It flows out in the direction indicated by the medium vector OB. Since the throat 9 is inclined by the angle α with respect to the circumferential direction Xc, the fluid flows out from the axial direction Xa in the direction of the angle α.

FIG. 18 is a view of the nozzle channel seen from the center of the nozzle channel shown in FIG. FIG.
In the figure, 10 indicates the nozzle leading edge. As described above, since the trailing edge 8 of the nozzle blade 3 is attached along the radial line Xr, the throat 9 is perpendicular to the inner peripheral wall 6 of the nozzle, but the outer peripheral wall 7 of the nozzle extends in the axial direction Xa. The throat 9 is not orthogonal to the outer peripheral wall 7 of the nozzle because it is enlarged toward the downstream side. The outflow direction of the fluid is throat 9
Since it is perpendicular to, the outflow direction of the fluid is along the flow path in the vicinity of the nozzle inner peripheral wall 6, but as it approaches the nozzle outer peripheral wall 7,
It gradually stops following the enlarged flow path. This will be described below.

FIG. 19 is a three-dimensional view showing the relationship between the throat 9 of the nozzle and the flow direction of the fluid. In this case, the lower limit of the proper outflow direction of the fluid is the direction indicated by the vector OC in consideration of the two-dimensional outflow angle α and the flow channel expansion angle θ. When this vector OC is displayed as a component, the following expression is obtained.

[0029]

[Equation 9]

If the vector representing the proper outflow direction of the fluid is OC ', the vector OC' is expressed by the following equation.

[0031]

## EQU10 ## OC '= (Xoc, Yoc, Zoc) (8)

[Equation 11] Xoc = cos α (9)

(12) Yoc = sin α (10)

[Equation 13] Zoc ≧ cos α × tan θ (11)

Since the throat 9 is parallel to the radial line Xr and is inclined by the angle α with respect to the axis in the circumferential direction Xc,
The actual outflow direction of the fluid is the direction perpendicular to the throat 9, that is, the direction represented by the vector OB shown in the equation (6). The fact that the vector OB representing the actual outflow direction of the fluid and the vector OC ′ representing the proper outflow direction of the fluid are not the same direction means

It is geometrically clear that OB · OC ′ ≠ | OB | × | OC ′ | (12). Formula (12)
In, · represents the inner product of the vector, and || represents the magnitude of the vector. Therefore, the result is that the outflow direction of the fluid is different from the proper outflow direction. If the flow stagger angle between the actual fluid outflow direction and the proper fluid outflow direction is δ,
This δ is expressed by the following equation from the geometrical relation.

[0033]

Tan δ ≧ tan θ × cos α (13) As can be seen from the equation (13), the flow stagger angle δ increases as the flow channel expansion angle θ increases.

FIG. 20 shows the relationship between the dimensionless nozzle height position H and the flow channel expansion angle θ. As shown in FIG. 20, the enlargement angle θ of the flow path increases toward the nozzle tip portion and reaches the maximum at the nozzle tip portion, so the flow stagger angle δ also reaches the nozzle tip portion. That is, there is a problem that the turbine performance is deteriorated because the flow is most easily separated at the tip of the nozzle.

As a means for solving this problem,
For example, as disclosed in Japanese Utility Model Publication No. 63-26001, the nozzle trailing edge is inclined only in the axial direction, or as disclosed in Japanese Examined Patent Publication No. 4-124406, the nozzle trailing edge is arranged in the circumferential direction. There are things that are only tilted.

Even with these means, the actual outflow direction of the fluid cannot be matched with the optimum outflow direction. This will be described below. FIG. 21 is a view of Shoko 63-2006.
It is sectional drawing of the axial-flow turbine nozzle disclosed by the 01 publication. 22 is a cross-sectional view taken along the line I-I in FIG.

As shown in FIGS. 21 and 22, the trailing edge 8 of the nozzle blade 3 is inclined only in the axially upstream side from the root to the tip of the nozzle blade 3, and is inclined in the circumferential direction. Absent. Here, the inclination angle of the trailing edge 8 in the axial direction at an arbitrary nozzle height position is ε.

The relationship between the throat surface and the outflow direction of the fluid in this case will be described three-dimensionally as shown in FIG. 19, as shown in FIG. That is, the trailing edge 8 of the nozzle blade 3
Is inclined in the axial direction Xa by an angle ε, the throat 9
Also inclines in the axial direction Xa, and the actual outflow angle of the fluid also inclines in the axial direction Xa.

Vector OD representing the actual outflow angle of fluid
Is expressed by the following equation by inclining the vector OB shown in FIG. 19 by an angle ε on a plane formed by the radial line Xr and the axial direction Xa.

[0040]

[Equation 16]

On the other hand, the proper outflow direction of the flow is the direction of the vector OC 'represented by the above equations (8) to (11), and represents the vector OD representing the actual outflow angle of the fluid and the appropriate outflow angle. The vector OC ′ is the trailing edge 8 of the nozzle blade 3.
No matter how the angle ε for inclining to the upstream side in the axial direction is determined, the relations of the following equation are geometrically established, and therefore the directions are not the same.

[0042]

OD · OC ′ ≠ | OD | × | OC ′ | (15) That is, even if the trailing edge 8 of the nozzle blade 3 is inclined only to the upstream side in the axial direction, the actual flow matches the proper outflow direction. It is impossible to make them.

FIG. 24 is a sectional view of an axial turbine nozzle disclosed in Japanese Patent Publication No. 4-124406. Figure 25
FIG. 25 is a sectional view taken along line JJ in FIG. 24. Figure 24
Further, as shown in FIG. 25, the trailing edge 8 of the nozzle blade 3 is inclined only in the circumferential direction, and is not inclined in the axial direction.

Here, the nozzle blade 3 at an arbitrary nozzle height
Let ζ be the inclination angle of the trailing edge 8 in the circumferential direction. The relationship between the throat surface and the fluid in this case will be described three-dimensionally as shown in FIG. 19, as shown in FIG. That is,
Since the trailing edge 8 of the nozzle blade 3 is inclined in the circumferential direction Xc by the angle ζ, the throat 9 is also inclined in the circumferential direction Xc,
The actual outflow angle of the fluid also inclines in the circumferential direction Xc.

Vector OE representing the actual outflow angle of fluid
Is expressed by the following equation by inclining the vector OB shown in FIG. 19 by an angle ζ on a plane formed by the radial line Xr and the axial direction Xc.

[0046]

[Equation 18]

On the other hand, the proper outflow direction of the flow is the direction of the vector OC 'represented by the above equations (8) to (11), and represents the vector OE representing the actual outflow angle of the fluid and the appropriate outflow angle. The vector OC ′ is the trailing edge 8 of the nozzle blade 3.
No matter how the inclination angle ζ in the circumferential direction of is determined, the geometrical relations of the following expressions are established, and therefore the directions are not the same.

[0048]

OE · OC ′ ≠ | OE | × | OC ′ | (17) That is, even if the trailing edge 8 of the nozzle blade 3 is inclined only in the circumferential direction, the actual flow is different from the proper outflow direction. It will be.

As described above, according to the conventional technique, it is impossible to match the actual flow with the proper outflow direction, and it is impossible to prevent separation of the flow.

The present invention has been made in consideration of the above circumstances, and an object thereof is to provide an axial flow turbine nozzle capable of preventing flow separation.

[0051]

In order to solve the above-mentioned problems, an axial turbine nozzle according to the present invention has a plurality of nozzle blades arranged in the circumferential direction and expands downstream in the turbine axial direction. An axial flow turbine nozzle having inner and outer peripheral walls forming a flow path, and forming an annular flow path by integrally forming the inner and outer peripheral walls and the nozzle blade, the rear edge of the nozzle blade in the radial direction of the flow path. It is characterized in that it is formed so as to be inclined in the axial direction and the circumferential direction according to the expansion angle and the flow angle.

Further, the throat surface of the flow path formed by the inner and outer peripheral walls and the nozzle vane is in the proper outflow direction of the fluid determined by the radial expansion angle of the flow path and the circumferential flow angle. It is characterized in that it is configured to be vertical with respect to.

Further, when the expansion angle of the flow path is θ, the outflow angle of the fluid is α, and the inclination angle in the axial direction of the nozzle blade trailing edge is γ,

[Equation 20] Each value is set so that tan γ ≧ tan θ × cos ² α.

When the expansion angle of the flow path is θ, the outflow angle of the fluid is α, and the inclination angle of the trailing edge of the nozzle blade in the circumferential direction is β,

It is characterized in that the respective values are set so that tan β ≧ tan θ × sin α × cos α.

[0055]

According to the present invention having the above-described structure, the trailing edge of the nozzle blade extends from the root of the turbine stage to the tip of the turbine stage in accordance with the radial expansion angle of the flow passage and the circumferential flow angle. Since it is inclined in both the axial direction and the circumferential direction, the actual outflow direction of the fluid can be matched with the proper outflow direction. Therefore, flow separation can be prevented.

[0056]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing a turbine stage in a first embodiment of an axial turbine nozzle according to the present invention,
FIG. 2 is a sectional view taken along the line AA of FIG. It should be noted that the same or corresponding portions as those of the conventional example will be described using the same reference numerals.

In FIG. 1 and FIG. 2, the axial flow turbine has a plurality of nozzle blades 3 fixed circumferentially by a nozzle outer ring 1 and a nozzle inner ring 2, and a rotor blade 5 fixed to a rotating shaft 4.
And a combination of one or more paragraphs in the axial direction.

The nozzle inner peripheral wall 6 is parallel to the axial direction Xa, but the nozzle outer peripheral wall 7 is enlarged toward the downstream side in the turbine axial direction. This is to realize smooth expansion in response to a sudden increase in the specific volume of the fluid in the low pressure portion of the axial flow turbine. The axial flow turbine has the nozzle vane 3, the nozzle inner peripheral wall 6 and the nozzle outer peripheral wall 7 integrally formed with each other to form a limited annular flow path.

The nozzle blades 3 are mounted so that their trailing edges 8 are inclined in both the axial direction Xa and the circumferential direction Xc in accordance with the radial expansion angle θ and the circumferential flow angle. When the expansion angle of the flow path at an arbitrary nozzle height position is θ and the inclination angle of the trailing edge 8 of the nozzle blade 3 in the axial direction is γ, the nozzle blade 3 is

Where tan γ ≧ tan θ × cos ² α (18) and the inclination angle β in the circumferential direction of the trailing edge 8 of the nozzle blade 3, the nozzle blade 3 is

 23] tan γ ≧ tan θ × sin α × cos α ... (19) It is attached so as to be inclined. here,
The angle α is the above-mentioned two-dimensional flow angle.

Next, the operation of this embodiment will be described.

FIG. 3 is a three-dimensional view showing the relationship between the throat 9 of the nozzle blade 3 and the fluid flow direction in this embodiment, as in FIG. In FIG. 3, the inclination angle γ of the nozzle trailing edge 8 in the axial direction satisfies the expression (18), and the inclination angle β of the trailing edge 8 of the nozzle blade 3 in the circumferential direction satisfies the expression (19).

At this time, if the vector representing the actual outflow direction of the fluid is OF,

[Equation 24] OF = (Xof, Yof, Zof) (20)

[Equation 25]

[Equation 26]

[Equation 27]

The actual outflow direction and the proper outflow direction are expressed by the following geometrical relations.

[Equation 28] Since OF · OC ′ ≠ | OF | × | OC ′ | (24) is satisfied, the actual outflow direction coincides with the proper outflow direction, and flow separation can be prevented.

As a typical example, the expansion angle θ of the flow path and the outflow angle α of the fluid are θ = 40 ° and α = 75 °, respectively.
Then, from equations (18) and (19), the inclination angle γ of the nozzle trailing edge 8 in the axial direction and the inclination angle β of the nozzle trailing edge 8 in the circumferential direction are γ ≧ 3.2 ° and β = 11.8 °. Becomes

FIG. 4 is a view of the nozzle channel viewed from the center of the nozzle channel as in FIGS. 14 and 18. Nozzle blade 3
Since the trailing edge 8 is inclined in both the axial direction and the circumferential direction so as to satisfy the expressions (18) and (19), the actual outflow direction of the fluid is along the expanding direction,
It is possible to prevent flow separation from the nozzle root to the nozzle tip.

FIG. 5 is a sectional view showing a turbine stage according to a second embodiment of the present invention. FIG. 6 is a sectional view taken along the line BB of FIG. The same members as those of the first embodiment will be described with the same reference numerals.

In FIGS. 5 and 6, in the axial turbine, the flow passage is enlarged at the tip and the root of the nozzle blade 3. In addition, at the tip and the root of the nozzle blade 3,
The rear edge 8 is attached so as to be inclined in both the axial direction and the circumferential direction.

Next, the operation of this embodiment will be described.

The tip of the nozzle blade 3 is the same as that of the above-mentioned embodiment, and therefore its explanation is omitted. FIG. 7 is a three-dimensional view showing the relationship between the throat 9 of the nozzle and the flow direction of the fluid at the root of the nozzle blade 3, as in FIG.

Since the flow passage expands radially inward at the root of the nozzle blade 3 as opposed to the tip, when expanding the expansion angle of the flow passage radially outward,

[Equation 29] θ> 0 (25) When expanding inward in the radial direction,

[Mathematical formula-see original document] If θ <0 (26)
It is the same as 1).

Further, if the axial inclination angle γ of the trailing edge 8 and the circumferential inclination angle β of the nozzle trailing edge 8 are respectively given positive and negative signs, the angle γ is given by the equation (18) and the angle β is given by the equation (1).
By determining so as to satisfy 9), the actual outflow direction of the flow matches the proper outflow direction. Therefore, flow separation can be prevented.

As a typical example, the flow channel expansion angle θ and the fluid outflow angle α are θ = −10 ° and α = 75, respectively.
.Degree., The tilt angle .gamma. In the axial direction of the nozzle trailing edge 8 and the tilt angle .beta. In the circumferential direction of the nozzle trailing edge 8 are .gamma..ltoreq.-0.7.degree. And .beta..ltoreq. It becomes −2.5 °.

Similar to FIGS. 14 and 18, FIG. 8 is a view of the nozzle channel viewed from the center of the nozzle channel. Since the trailing edge of the nozzle is inclined in both the axial direction and the circumferential direction so as to satisfy the expressions (18) and (19), the actual outflow direction of the fluid is along the expanding flow path, and the nozzle It is possible to prevent flow separation from the root portion to the nozzle tip portion.

[0075]

As described above, according to the axial flow turbine nozzle of the present invention, the trailing edge of the nozzle blade extends from the root of the turbine stage to the tip of the turbine stage in the radial expansion angle of the flow passage. Moreover, since it is inclined in the axial direction and the circumferential direction according to the flow angle in the circumferential direction, it is possible to match the actual outflow direction of the fluid with the proper outflow direction.

Therefore, the separation of the flow can be prevented, and the turbine performance can be greatly improved as compared with the conventional axial flow turbine nozzle.

[Brief description of drawings]

FIG. 1 is a sectional view showing a turbine stage in an axial flow turbine nozzle according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is an explanatory diagram showing a fluid outflow direction in the first embodiment.

FIG. 4 is an explanatory diagram showing a flow in a nozzle channel in the first embodiment.

FIG. 5 is a sectional view showing a turbine stage in the second embodiment of the axial turbine nozzle according to the present invention.

6 is a cross-sectional view taken along the line BB of FIG.

FIG. 7 is an explanatory view showing the outflow direction of the fluid in the second embodiment.

FIG. 8 is an explanatory diagram showing a flow in a nozzle channel in the second embodiment.

FIG. 9 is a cross-sectional view showing a low pressure portion of a conventional axial flow turbine.

10 is a cross-sectional view taken along the line CC of FIG.

FIG. 11 is a cross-sectional view showing a high / medium pressure stage of a conventional axial flow turbine.

12 is a cross-sectional view taken along the line DD of FIG.

13 is a cross-sectional view taken along the line EE of FIG.

14 is a cross sectional view taken from the center of the nozzle channel shown in FIG.
The figure seen in the F direction.

FIG. 15 is an explanatory diagram showing a fluid outflow direction.

FIG. 16 is a sectional view showing a nozzle blade of a conventional axial flow turbine low pressure section.

17 is a cross-sectional view taken along the line GG of FIG.

FIG. 18 is a view of the nozzle channel seen from the line HH direction from the center of the nozzle channel shown in FIG. 17;

FIG. 19 is an explanatory diagram showing the outflow direction of fluid.

FIG. 20 is a diagram showing a relationship between a nozzle height position and a flow channel expansion angle.

FIG. 21 is a diagram showing another conventional blade of a low pressure part of an axial turbine.

22 is a cross-sectional view taken along the line II of FIG.

FIG. 23 is an explanatory diagram showing the outflow direction of fluid.

FIG. 24 is a cross-sectional view showing a nozzle blade of a low pressure portion of another conventional axial flow turbine.

25 is a cross-sectional view taken along the line JJ of FIG.

FIG. 26 is an explanatory diagram showing a fluid outflow direction.

[Explanation of symbols]

 1 Nozzle outer ring 2 Nozzle inner ring 3 Nozzle blade 4 Rotating shaft 5 Moving blade 6 Nozzle inner peripheral wall 7 Nozzle outer peripheral wall 8 Nozzle trailing edge 9 Throat 10 Nozzle front edge

Claims (4)

[Claims] 1. A plurality of nozzle blades arranged in the circumferential direction, and inner and outer peripheral walls forming a flow passage that expands downstream in the turbine axial direction. The inner and outer peripheral walls and the nozzle blade are integrated. In the axial turbine nozzle that forms an annular flow path, the trailing edge of the nozzle blade is formed to be inclined in the axial direction and the circumferential direction according to the radial expansion angle and the flow angle of the flow path. And axial flow turbine nozzle. 2. A throat surface of a flow passage formed by the inner and outer peripheral walls and the nozzle vane is in a proper fluid outflow direction determined by a radial expansion angle of the flow passage and a circumferential flow angle. The axial-flow turbine nozzle according to claim 1, wherein the axial-flow turbine nozzle is configured so as to be perpendicular to it. 3. When the expansion angle of the flow passage is θ, the outflow angle of the fluid is α, and the axial inclination angle of the nozzle blade trailing edge is γ, tan γ ≧ tan θ × cos ² The axial flow turbine nozzle according to claim 1, wherein respective values are set so as to be α. 4. When the expansion angle of the flow path is θ, the outflow angle of the fluid is α, and the inclination angle of the trailing edge of the nozzle blade in the circumferential direction is β, tan β ≧ tan θ × sin The axial flow turbine nozzle according to claim 1, wherein respective values are set so as to be α × cos α.