JPH0478803B2 - - Google Patents

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a turbine nozzle for an axial flow turbine, and in particular to suppressing the development of a boundary layer that occurs on the peripheral wall surface of an annular flow path of the turbine nozzle. The present invention relates to a turbine nozzle that can improve turbine performance by preventing the generation of secondary flows and reducing loss due to secondary vortices generated by agitation of the secondary flows.

(Prior Art) In recent years, it has become an important issue to improve turbine performance in order to improve the operating economy of power plants and improve power generation efficiency.

To improve turbine performance, it is necessary to reduce losses in each turbine stage. Internal losses in turbine stages include airfoil loss, leakage loss, outflow loss, etc., but especially in turbine stages with small aspect ratios and low nozzle blade heights, the ratio of secondary losses due to secondary flow is dominant. Therefore, reducing secondary losses is a major issue in improving turbine performance.

FIG. 7 shows the nozzle configuration of a typical axial flow turbine. A plurality of nozzle blades 1 are fixedly installed in an annular flow path 4 formed between a diaphragm outer ring 2 and a diaphragm inner ring 3. In addition, as shown in FIG.
will be placed. The rotor blades 5 are installed in rows at predetermined intervals in the circumferential direction of the outer periphery of the rotor disk 6. A shroud 7 is fixed to the outer peripheral end of the rotor blade 5 in order to fix the rotor blade tip and to prevent leakage of working fluid.

Next, the inventive mechanism of the secondary flow in the nozzle blade 1 in the above paragraph configuration will be explained with reference to FIG. 7. FIG. 7 is an oblique view of the turbine nozzle shown in FIG. 4, viewed from the nozzle outlet side.

Each nozzle blade 1 is shown as an example in which it is not inclined with respect to a reference line E passing through the center of rotation of the rotor disk 6, but is disposed perpendicularly to the outer peripheral surface of the diaphragm inner ring 3.

When the working fluid such as high-pressure steam flows through the inter-blade flow path between adjacent nozzle blades 1, 1, it is bent into an arc shape in the flow path. At this time, centrifugal force is generated from the back surface B of the nozzle blade 1 in the direction of the ventral surface F, and since this centrifugal force and static pressure are in balance, the static pressure on the ventral surface F becomes high, while the flow rate of the working fluid on the back surface B is large, so the static pressure is low. Therefore, a pressure gradient is generated in the flow path from the ventral surface F side to the back surface B side. This pressure gradient is the same in the slow flow layer, that is, the boundary layer, formed on the peripheral wall surfaces of the diaphragm outer ring 2 and the diaphragm inner ring 3.

However, near the boundary layer, the flow velocity is low and the centrifugal force acting is small, so the flow from the ventral surface F side to the back surface B side, that is, the secondary flow 8, cannot resist the pressure gradient from the ventral surface F side to the back surface B side. arise.

Then, the secondary flow 8 collides with the back surface B side of the nozzle blade 1 and rolls up, and at both the joint ends of the inner ring side and the outer ring side of the nozzle blade 1, a secondary vortex 9 is created.
Generate a, 9b. The energy possessed by the working fluid is thus partially dissipated to form the secondary vortex 9.

The secondary vortex 9 generated in the nozzle flow path in this way
a and 9b cause non-uniform flow of the working fluid, which not only significantly reduces nozzle performance but also causes energy loss of the working fluid flowing into the rotor blade 5 on the downstream side, reducing the performance of each turbine stage. .

Secondary vortices 9a, 9 generated within the nozzle flow path described above
Various turbine nozzle structures have been investigated to reduce the secondary losses caused by b.

For example, a turbine nozzle structure that reduces the heat of the boundary layer that develops on the peripheral wall surface of an annular flow path was disclosed in Japanese Patent Application Laid-Open No. 53-
It is disclosed in Publication No. 90502. FIG. 8a is a cross-sectional view of a conventional turbine nozzle, in which a boundary layer control rod 10 is arranged in a boundary layer generation region upstream of a nozzle blade 1. This boundary layer control rod 10 is designed to reduce the thickness of the boundary layer that develops on the peripheral wall surface and reduce losses due to secondary flow.

FIG. 9 is a sectional view showing a conventional example of a turbine nozzle disclosed in Japanese Patent Application Laid-Open No. 52-54809, in which a suction hole 11 is provided at the joint end on the ventral surface F side of the nozzle blade 1.
On the other hand, a blow-off hole 12 is provided at the joint end on the back side B side, and a communication hole 13 passing from the suction hole 11 to the blow-off hole 12 is formed.

The working fluid flowing near the circumferential wall of the annular flow path is allowed to escape via the communication hole 13 to reduce as much as possible the secondary flow flowing from the ventral surface F side to the back surface B side between adjacent nozzle blades 1, 1. This is how it was done.

Furthermore, FIG. 10 shows a turbine nozzle disclosed in Japanese Utility Model Application No. 52-148802, in which a baffle plate 14 is arranged between adjacent nozzle blades 1 on the peripheral wall surface of the diaphragm outer ring 2 or the diaphragm inner ring 3. This is a conventional example.

The secondary flow 8 is suppressed by the baffle plate 14 having a height exceeding the thickness of the wall boundary layer of the working fluid that is expected to occur.

(Problems to be Solved by the Invention) However, in the conventional turbine nozzle shown in FIG. The subsequent flow can be suppressed to some extent. However, as shown in FIG. 8b, the velocity distribution G of the turbine working fluid is disturbed, causing a large velocity deficit in the main flow of the working fluid on the secondary side of the boundary layer control rod 10, which drastically improves the turbine performance. It cannot be used as a means.

Furthermore, as shown in FIG. 9, in a conventional turbine nozzle in which a communication hole 13 is provided at the base of the nozzle blade 1, in the flow path between the adjacent nozzle blades 1, from the ventral surface F side of one nozzle blade 1. , the secondary flow generated on the back surface B side of the other nozzle blade 1 can be significantly reduced. However, since the flow sucked in from the ventral surface F side is blown out to the rear surface B, there is a risk that the flow line of the main flow of the working fluid will be greatly disturbed, and the loss may conversely increase.

Further, according to this conventional example, the structure of the communicating hole 13 is complicated, and the machining accuracy must be set to be high, so there is a problem that the machining and manufacturing cost increases.

Furthermore, as shown in FIG. 10, in a conventional turbine nozzle in which a baffle plate 14 is provided between the nozzle blades 1, 1, the baffle plate 14 is provided on the peripheral wall surface of the annular flow path 4, so that the peripheral wall surface Although the flow that crosses between the nozzle blades in the vicinity is reduced to some extent, the secondary flow 8 from the ventral surface F side of the nozzle blade 1 to the baffle plate 14 or the back side B side of the nozzle blade 1 adjacently installed from the baffle plate 14 Since the secondary flow 8 leading to the above remains unresolved, there is a problem that it does not directly lead to a significant reduction in secondary loss.

The present invention has been made to solve the above problems, has a simple structure, suppresses the development of a boundary layer that occurs on the peripheral wall surface of the annular flow path of a turbine nozzle, and suppresses the development of a boundary layer caused by secondary flow. It is an object of the present invention to provide a turbine nozzle that can reduce loss due to the generation of secondary vortices and improve turbine performance.

[Composition of occurrence]

(Means for Solving the Problems) In order to achieve the above object, the present invention arranges a plurality of nozzle blades in a row in the circumferential direction of an annular flow path formed between a diaphragm inner ring and a diaphragm outer ring. , in a turbine nozzle in which each nozzle blade is fixed at a joint end on the inner ring side of the diaphragm and a joint end on the outer ring side of the diaphragm, the trailing edge line at both joint ends of the nozzle blade is formed into a straight line, and the trailing edge The joint end is joined so that the line is inclined toward the ventral surface of the nozzle blade with respect to a reference line passing through the center of rotation of the turbine, and the trailing edge line at the middle part of the nozzle blade is formed to be curved toward the ventral surface. The height of the nozzle blade is h, and the inclination angles of the linear and inclined trailing edge line at both joint ends of the nozzle blade with respect to a reference line passing through the rotation center of the turbine are θ _r and θ _t , Further, when the heights of the straight and inclined trailing edge lines at both joint ends of the nozzle blade are l _r and l _t , 2.5°≦θ _r and θ _t ≦25° 0.05≦l _r / h and l _t /h≦0.35.

(Function) According to the turbine nozzle having the above configuration, the trailing edge line at both joint ends of the nozzle blade is formed into a straight line,
In addition, since the trailing edge line is inclined toward the ventral surface of the nozzle blade with respect to the reference line passing through the rotation center of the turbine, the working fluid flowing into the vicinity of the peripheral wall surface of the diaphragm inner ring is pressed against the peripheral wall surface on the diaphragm inner ring side. On the other hand, the working fluid that has flowed into the vicinity of the peripheral wall surface of the diaphragm outer ring is pressed against the peripheral wall surface on the diaphragm outer ring side. Therefore, the development of a boundary layer on both peripheral wall surfaces is effectively suppressed, and furthermore, the growth of secondary vortices generated on the back side of each nozzle blade by the secondary flow is suppressed.

In addition, since the trailing edge line at the middle part of each nozzle blade is curved toward the ventral surface, the working fluid streamlines distributed parallel to the middle part in the span direction from both joint ends are smooth. change and large agitation does not occur. Therefore, even when the working fluid flows into the rotor blades, there is little loss between the rotor blades.

As described above, according to the present invention, the secondary loss at both joint ends of each nozzle blade is reduced, and the loss between the rotor blades is also small, so that turbine efficiency can be significantly improved.

(Example) Next, regarding an example of the present invention, attached drawing No. 1
This will be explained with reference to FIGS. FIG. 1 is an oblique view showing the structure of a turbine nozzle according to the present invention, and shows an example observed from the nozzle outlet side. FIG. 2 shows the shape of the nozzle blade 1 as seen from the nozzle outlet side, and the same elements as those in the conventional example shown in FIG. 7 are given the same reference numerals and their explanation will be omitted.

The turbine nozzle according to this embodiment has a plurality of nozzle blades 1a arranged in a row at predetermined intervals in the circumferential direction in an annular flow path 4 formed between a diaphragm outer ring 2 and a diaphragm inner ring 3. Configure. The tip-side and root-side joint ends of each nozzle blade 1a are joined to a diaphragm outer ring 2 and a diaphragm inner ring 3, respectively.

As shown in FIG. 2, each nozzle blade 1a has trailing edge lines α ₁ and α ₂ formed in straight lines at both joint ends thereof, and the trailing edge lines α ₁ and α ₂ point at the center of rotation of the turbine. The joint ends are joined so as to be inclined toward the ventral surface of the nozzle blade 1a by angles θ _r and θ _t , respectively, with respect to the reference line E passing therethrough. Further, the trailing edge line α ₃ at the intermediate portion of the nozzle blade 1a is formed so as to smoothly connect to both trailing edge lines α ₁ and α ₂ of the inclined portion and curved toward the ventral surface.

Also, the height of the inclined joint end of the nozzle blade 1a
l _r and l _t are 0.05 to 0.05 to the total height h of the nozzle blade 1a.
Set to a range of 0.35h.

Further, the inclination angles θ _r and θ _t of the joint ends are set to 2.5 to 25 degrees with respect to the reference line E.

In the turbine nozzle according to this embodiment, the working fluid that has flowed into the inclined portion on the side of the diaphragm outer ring 2 flows along the inclined abdominal surface F of the nozzle blade 1a and is pressed against the peripheral wall surface of the diaphragm outer ring 2.
Therefore, the development of a boundary layer on the peripheral wall surface is suppressed, and the generation of secondary vortices is prevented.

On the other hand, since the working fluid that has flowed into the inclined part on the side of the diaphragm inner ring 3 is similarly pressed against the peripheral wall surface of the diaphragm inner ring 3, the development of a boundary layer on the peripheral wall surface is suppressed and loss due to secondary vortices in this part is reduced. Ru.

In addition, in the middle part of the nozzle blade 1a, the trailing edge line α ₃ is formed so as to have a smooth curved shape in the direction of the ventral surface, so that the mainstream flow line of the working fluid is not stirred to a large extent, and the working fluid moving blade 5
Mixing loss between the two is also suppressed.

As a result, loss in the entire nozzle blade 1a is reduced, and turbine efficiency can be significantly improved.

Furthermore, with reference to FIG. 3, the loss reduction effect will be explained. FIG. 3 is a graph showing the distribution of total pressure loss at the outlet of the turbine nozzle shown in FIG. 1 in comparison with the conventional example. Compared to the total pressure loss of the conventional turbine nozzle shown in FIG. 7, according to this embodiment, the pressure loss distribution in the middle region of the nozzle blade 1a is almost similar. On the other hand, the pressure loss at both the joint ends on the root side and the tip side of the nozzle blade 1a is significantly reduced compared to the conventional example.

Further, with reference to FIG. 4, changes in streamlines of the working fluid flowing through the turbine nozzle of this embodiment will be explained. Fourth
The figure is a streamline diagram of the turbine stage observed from the meridional plane. The streamlines in the conventional turbine nozzle shown by broken lines are formed approximately parallel, and no deviation in the radial direction is observed.

On the other hand, the streamline K in the turbine nozzle of this embodiment shown by a solid line is slightly deviated in the radial direction near the diaphragm outer ring 2 and the diaphragm inner ring 3. This deviation is caused by the fact that both joint ends of the nozzle blade 1a are configured to be inclined, so that the working fluid is pressed against the respective peripheral wall surfaces. This pressing force suppresses the development of a boundary layer on the peripheral wall surface,
Generation of secondary vortices is prevented.

In addition, the streamline K of the working fluid passing through the middle part of the nozzle blade 1a is almost similar to that of the conventional example, since the trailing edge line of the middle part of the nozzle blade 1a is smoothly curved, and no large disturbance occurs. are doing. Therefore, there is little loss due to mixing of the working fluid in the flow path between the rotor blades 5 as well.

Next, the effect on the turbine stage efficiency η when the heights l _r , l _t and the inclination angles θ _r , θ _t of the inclined portion of the nozzle blade 1a are changed will be explained. FIG. 5 shows the inclination angles θ _r and θ _t of the inclined part of the nozzle blade 1a.
7 is a graph showing the relationship between the turbine stage efficiency η and the turbine stage efficiency η, where the vertical axis shows the turbine stage efficiency η ₁ according to the present example with respect to the turbine stage efficiency η ₀ when the conventional example turbine nozzle shown in FIG. 7 is used. The ratio (η ₁ /η ₀ ) is displayed. From Figure 5, the inclination angles θ _r and θ _t
In the range of 2.5 to 25 degrees, the turbine stage efficiency ratio is
It is clear that the value exceeds 1.0 and exhibits a better effect than the conventional example. In this way, the reason why there is an optimal range for the inclination angles θ _r and θ _t in which the stage efficiency is superior to that of the conventional technology is because if the inclination angles θ _r and θ _t become too large, the loss at the nozzle exit peripheral wall surface is reduced. On the other hand, the flow rate of the working fluid near the surrounding wall increases,
One of the reasons for this is that the flow rate near the center of the blade, which originally has good performance, decreases, and the overall stage efficiency actually decreases.

In addition, FIG. 6 shows the height l _r of the inclined part of the nozzle blade 1a,
This is a graph showing the relationship between _{l t and} turbine stage efficiency η ₁ in comparison with a conventional _example . ，
The _vertical axis shows the ratio of the turbine stage efficiency η ₁ according to the present example to the turbine stage efficiency η ₀ according to the conventional example (η ₁ /η _{0 )} .
) is displayed.

From Figure 6, the heights of the slope parts l _r and l _t are determined by the nozzle blade 1.
It is demonstrated that when the total height h of a is set in the range of 0.05 to 0.35h, the turbine stage efficiency η ₁ is improved compared to the conventional example. In this way, the reason why there is an optimal range for the heights l _r and l _t of the slope part in which the stage efficiency is superior to the conventional technology is that the height l _r , l t of the slope part exists.
If l _t becomes too large, the curvature of the curved portion near the center of the blade becomes small, so it can be said that various losses due to sudden changes in the nozzle blade shape increase.

Note that, as shown in FIG. 2, the heights l _r , l _t and the inclination angles θ _r , θ _t of the inclined portion of the nozzle blade 1a do not necessarily have to be the same value at both joint ends;
2.5゜≦θ _r , θ≦25゜ and 0.05≦l _r /h, l _t /h≦0.
As long as they are within the range of 35, different values may be set taking into consideration the flow rate distribution characteristics of the working fluid.

In addition, in FIG. 2, the trailing edge lines α ₁ and α ₂ of each nozzle blade 1a are connected to the reference line E and the inner and outer rings 2 and 3 of the diaphragm.
Although the starting point is the intersection with the reference line, the starting point may be the intersection with different reference lines for the inner ring side and the outer ring side.

As explained above, according to the turbine nozzle of this embodiment, the trailing edge lines α _{1 and} α ₂ of the nozzle blade 1a at both joint ends are formed into straight lines, and the trailing edge lines α ₁ and α ₂ are formed in straight lines.
is inclined in the direction of the ventral surface F of the nozzle blade 1a with respect to the reference line, so the working fluid that has flowed into the vicinity of the circumferential wall surface of the annular flow path 4 is guided along the inclined ventral surface F and is pressed in the direction of the circumferential wall surface. Ru. Therefore, the development of the boundary layer on both peripheral wall surfaces is effectively suppressed, and furthermore, the growth of secondary vortices 9a and 9b generated on the back side of each nozzle blade 1a by the secondary flow is suppressed.
Loss of working fluid in the turbine nozzle is reduced.

In particular, the inclination angles θ _r and θ _t of the inclined part of the nozzle blade 1a
is set in the range of 2.5 to 25 degrees, and the heights of the inclined parts l _r and l _t are set in the range of 0.05 to 0.35 h relative to the total height h of the blade 1a, the degree of improvement in turbine stage efficiency is It becomes noticeable.

Also, the trailing edge line α ₃ at the middle part of each nozzle blade 1a
Since it is smoothly curved in the ventral direction, the working fluid streamlines are not subject to large disturbances. Therefore, even when the working fluid flows into the rotor blade 5, there is little loss. That is, losses in the entire turbine stage are reduced, so that turbine efficiency can be significantly improved.

〔Effect of the invention〕

As explained above, according to the turbine nozzle according to the present invention, both joint ends of each nozzle blade are configured to be inclined in the direction of the ventral surface of the nozzle blade, so that the working fluid flowing into the vicinity of the peripheral wall surface is directed to the diaphragm. It is pressed in the direction of the peripheral wall surface on the inner and outer ring sides. Therefore, the development of a boundary layer on the peripheral wall surface is prevented, and the generation of secondary flows and secondary vortices is effectively suppressed.

Furthermore, since the trailing edge line at the intermediate portion of the nozzle blade is formed to be curved toward the ventral surface, the flow line of the working fluid is less likely to be disturbed, and there is less loss of the working fluid in the flow path between the rotor blades. In other words, losses throughout the turbine stage can be significantly reduced, and thus turbine efficiency can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is an inclined view showing one embodiment of the turbine nozzle according to the present invention, FIG. 2 is a view showing the shape of the nozzle blade observed from the nozzle outlet side of the turbine nozzle according to the present invention, and FIG. A graph showing the total pressure loss distribution of the example turbine nozzle in comparison with the conventional example,
FIG. 4 is a cross-sectional view showing the streamlines of the working fluid in the turbine nozzle of this embodiment in comparison with the conventional example;
The figure is a graph showing the relationship between the nozzle blade inclination angle and the turbine stage efficiency ratio, Figure 6 is a graph showing the relationship between the height of the nozzle blade slope and the turbine stage efficiency ratio, and Figure 7 is a graph showing the relationship between the nozzle blade inclination angle and the turbine stage efficiency ratio. FIG. 8a is a sectional view showing a conventional turbine nozzle equipped with a boundary layer control rod, and FIG. 8b is a perspective view showing the structure of a conventional turbine nozzle.
Figure a is a cross-sectional view showing the velocity distribution of the working fluid in the turbine nozzle, Figure 9 is a plan cross-sectional view showing a conventional turbine nozzle in which a communicating hole is provided in the nozzle blade joint, and Figure 10 is a cross-sectional view showing the flow of air between the nozzle blades. FIG. 2 is a plan cross-sectional view showing a conventional turbine nozzle provided with a plate. 1, 1a... Nozzle blade, 2... Diaphragm outer ring, 3... Diaphragm inner ring, 4... Annular flow path,
5... Moving blade, 6... Rotor disk, 7... Shroud, 8... Secondary flow, 9, 9a, 9b... Secondary vortex, 10... Boundary layer control rod, 11... Suction hole,
12...Blowout hole, 13...Communication hole, 14...Baffle plate, B...Back surface, F...Blind surface, G...Velocity distribution of working fluid, E...Reference line passing through the center of rotation of the turbine, K ...streamline, α ₁ , α ₂ , α ₃ ... trailing edge line, h ...
Nozzle blade total height, θ _r , θ _t ...Inclination angle, l _r , l _t ... Inclined part height, η, η ₀ , η ₁ ...Turbine stage efficiency.

Claims (1)

[Scope of Claims] 1. A plurality of nozzle blades are arranged in a row in the circumferential direction of an annular flow path formed between a diaphragm inner ring and a diaphragm outer ring, and each nozzle blade is connected to a joint end on the diaphragm inner ring side and a diaphragm. In a turbine nozzle configured to be fixed at the joint end on the ring side,
The trailing edge lines at both joining ends of the nozzle blade are formed into a straight line, and the joining ends are joined so that the trailing edge line is inclined toward the ventral surface of the nozzle blade with respect to a reference line passing through the rotation center of the turbine. At the same time, the trailing edge line at the middle part of the nozzle blade is formed to be curved in the ventral direction, and the height of the nozzle blade is h, and the trailing edge line at the both joint ends of the nozzle blade is straight and inclined. The inclination angle of the edge line with respect to the reference line passing through the rotation center of the turbine is θ _r , θ _t , and the height of the straight and inclined trailing edge line at both joint ends of the nozzle blade is l _r , A turbine nozzle characterized in that it is configured to satisfy the following relational expressions: 2.5°≦θ _r , θ _t ≦25°, 0.05≦l _r /h, and l _t /h≦0.35, where l _t .