JP2006207554A - Turbine nozzle and axial-flow turbine using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a turbine nozzle capable of positively reducing a secondary flow loss and a boundary layer development from the initial stage to the final stage of a multi-stage turbine while securing improvement in performance by reducing the number of nozzles. <P>SOLUTION: A maximum value δmax of a circumferential protrusion amount of a curved nozzle is determined so as to satisfy the relation δmax/T=C1 (constant) according to a nozzle circular pitch T. At the same time, the value of δmax is determined to satisfy the relation of δmax/H=C2 (constant) according to a blade length H. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a turbine nozzle of an axial flow turbine, and more particularly to a technique for actively reducing secondary flow loss and boundary layer development.

  FIG. 3 is a view showing a cross-sectional shape of a nozzle constituting a general axial turbine, and a plurality of nozzle blades 1 are arranged in the circumferential direction at intervals of an annular pitch T.

Referring to the factors that decrease the internal efficiency of such an axial turbine, the first is that the trailing edge of the nozzle blade cross section has a finite thickness TE.
Generally, the ratio of the shortest distance (throat) S between adjacent blades arranged in the circumferential direction of the turbine nozzle to the trailing edge thickness (TE) of the blade cross section, that is, the smaller the TE / S value, the more the rear of the turbine blade. The loss due to the edge thickness is small.
The relationship between the loss due to the trailing edge thickness and the value of TE / S is shown in FIG. Accordingly, in order to prevent a decrease in internal efficiency due to the thickness of the trailing edge of the nozzle blade, the throat length is increased from S to S ′ by reducing the number of nozzle blades 1 as shown in FIG. The performance can be improved by reducing the value of S.

On the other hand, there is a secondary flow loss as a second factor that lowers the turbine internal efficiency.
As shown in FIG. 6, this secondary flow loss is caused by fluid flowing from the ventral side where the pressure on the blade surface is high toward the back side where the pressure is low near the base of the nozzle blade 1 and the wall surfaces 2 and 3 on the tip side. This is caused by the secondary flow vortex 5 generated by the force 4 to flow.
As shown in FIG. 7, the secondary flow loss increases as the pressure difference between the wings of the blade surface increases and the blade annular pitch T increases.
That is, if the number of nozzle blades 1 is reduced in order to reduce the loss caused by the thickness TE of the trailing edge of the nozzle, the load per blade increases (that is, the pressure difference between the backs of the blade surfaces increases). At the same time, the annular pitch T increases.
Since this is a direction in which the secondary flow loss increases as described above, it is difficult to reduce the optimum number of nozzle blades determined based on many experiments and analyses.

Therefore, in order to reduce the secondary flow loss, a nozzle blade having a shape curved toward the fluid outflow side in the circumferential direction (hereinafter referred to as a curved nozzle) is used (for example, see Patent Document 1 below). ).
FIG. 8 shows an example of the shape of the trailing edge of the curved nozzle as viewed from the fluid outflow side. As a parameter indicating the characteristics of the curved nozzle, there is a maximum protrusion amount δmax in the circumferential direction.
The value of δmax has usually been constant regardless of the annular pitch T of the nozzle blades.

However, according to the result of the viscosity analysis, FIG. 9 shows a comparison of nozzle energy loss distribution in the blade height direction when the value of δmax is constant despite the increase in the annular pitch T due to the reduction in the number of nozzle blades 1. As described above, the secondary flow loss at the center in the longitudinal direction of the blade is reduced by the effect of the reduction in the number of sheets, but the secondary flow loss near the wall surface is increased.
That is, the increase in the secondary flow loss due to the increase in the annular pitch T cannot be suppressed by the curved nozzle.

On the other hand, the third factor that reduces the internal efficiency of the turbine is the development of the boundary layer due to friction with the wall surfaces 2 and 3 on the base side and the tip side of the nozzle blade 1.
This is due to the boundary layer that develops due to the deceleration caused by friction with the wall surface, and the boundary layer development is promoted as the Reynolds number of the fluid decreases, and the vicinity of the wall surface including the boundary layer loss is included in the secondary flow loss. Increase the absolute amount of loss.

At this time, since the actual axial flow turbine is composed of a large number of stages, the temperature and pressure of the fluid decrease and the viscosity increases as it goes to the subsequent stage, and the Reynolds number also decreases.
FIG. 10 shows the boundary layer thickness estimated as the representative Reynolds number of each stage of the high-pressure steam turbine.
As is clear from FIG. 10, the boundary layer increases as it goes to the subsequent stage, and the development of secondary flow vortices is promoted to further increase the absolute amount of energy loss.

Further, the blade height of the axial flow turbine constituted by a large number of paragraphs becomes higher as it goes to the subsequent stage in accordance with the expansion of the fluid.
However, the maximum circumferential protrusion amount δmax of the trailing edge of the conventional curved nozzle is constant regardless of the blade length H.

FIG. 11 shows a comparison of the blade height direction velocity distribution at the nozzle outlet when the value of δmax is the same for two cases with different blade heights.
The minus side velocity indicates the direction in which the fluid is pressed against the blade root wall surface, and the plus side indicates the blade tip wall surface direction.
According to the result of the viscosity analysis, it can be seen that the flow velocity at which the fluid is pressed against the nozzle root and the tip side wall generated at the curved nozzle outlet is constant regardless of the blade length.

Thus, the effect of suppressing the boundary layer and the secondary flow vortex by pressing them against the wall surface is considered to be constant regardless of the blade length.
That is, the boundary layer that develops as it goes to the subsequent stage of the axial flow turbine and the secondary flow loss promoted by the boundary layer cannot be suppressed by the curved nozzle in which δmax is constant regardless of the blade length.
However, since the blade length increases as going to the rear stage, the influence of the nozzle root and the wall surface on the tip side becomes relatively small, and the loss ratio in the vicinity of the wall surface including the loss due to the boundary layer and the secondary flow loss is shown in FIG. It becomes smaller as shown in.
As a result, no means for actively reducing the loss due to the wall surface has been adopted on the turbine rear stage side.

JP-A-6-81603

  As described above, the main factors for reducing the turbine internal efficiency are the loss caused by the thickness of the trailing edge of the turbine nozzle cross section and the loss caused by the secondary flow vortices generated near the nozzle base side and tip side wall surfaces. Attention can be paid to three of the losses caused by the boundary layer developed by friction with these wall surfaces.

If the number of nozzle blades is reduced in order to reduce the trailing edge loss of the nozzle cross section, there is a problem that the secondary flow loss increases.
Further, the curved nozzle, which is an effective means for reducing the secondary flow loss, has a problem that the secondary flow loss cannot be suppressed in a design in which the maximum value δmax of the circumferential protrusion amount is constant regardless of the nozzle annular pitch T. Yes, the number of nozzle blades could not be reduced.

In a multi-stage turbine, the Reynolds number decreases as it goes to the subsequent stage, so that the loss due to the boundary layer that promotes secondary flow loss also increases.
At this time, in the conventional nozzle blade 1, since the maximum value δmax of the circumferential protrusion amount of the curved nozzle is constant regardless of the blade length H, the loss is caused by pressing the fluid against the wall surfaces on the root side and the tip side of the nozzle. The effect of suppressing the flow rate is also constant, and the development of the boundary layer is effectively suppressed in the paragraph where the blade length is high at the subsequent stage, thereby preventing the secondary flow loss.

  Therefore, an object of the present invention is to eliminate the problems in the prior art described above, and to positively develop secondary flow loss and boundary layer development from the first stage to the last stage of a multi-stage turbine while ensuring a performance improvement amount by reducing the number of nozzles. It is to provide a turbine nozzle that can be reduced.

The turbine nozzle of the present invention that solves the above-described problems is obtained by setting the circumferential protrusion maximum value δmax of the curved nozzle, which is effective for suppressing the secondary flow loss and the boundary layer development, in accordance with the nozzle annular pitch T.
δmax / T = C1 (constant)
Decide to keep the relationship.
Thereby, the secondary flow loss which increases when the number of nozzle blades is reduced in order to reduce the loss due to the thickness of the trailing edge of the nozzle blades can be suppressed.

At the same time, the value of δmax depends on the blade length H,
δmax / H = C2 (constant)
Decide to keep the relationship.
Thereby, it is possible to suppress the development of the boundary layer on the wall surfaces on the root side and the tip side of the nozzle, which increases as the Reynolds number decreases and goes to the subsequent stage of the multi-stage axial flow turbine.

  In the turbine nozzle of the present invention, the ratio S / T of the shortest distance S between the trailing edge of the nozzle blade and the back surface of the nozzle blade adjacent to the nozzle blade and the annular pitch T of the nozzle blade is It can be formed so as to be maximum at the center of the height.

  Further, the turbine nozzle of the present invention can be formed such that the chord length of the nozzle blade cross section is maximum at the blade tip position and minimum at the blade root position.

  Further, the turbine nozzle of the present invention can tilt the trailing edge position of the nozzle blade in the axial direction in the range from the blade root to the blade tip.

  Moreover, the turbine nozzle of the present invention can curve the position of the trailing edge of the nozzle blade in the axial direction.

  Furthermore, an axial flow turbine can be comprised by using the turbine nozzle of this invention mentioned above, respectively.

  According to the present invention, it is possible to provide a turbine nozzle capable of actively reducing secondary flow loss and boundary layer development from the first stage to the last stage of a multistage turbine while ensuring a performance improvement amount by reducing the number of nozzles. .

  Hereinafter, an embodiment of a turbine nozzle according to the present invention will be described in detail with reference to FIGS. 1 and 2.

  FIG. 1A shows a blade height H, an annular pitch T in the center of the blade height, which is disposed in an annular flow path 13 between the diaphragm outer ring 11 and the diaphragm inner ring 12, and a blade cross-section trailing edge. A nozzle blade 14 whose maximum protrusion amount on the circumferential fluid outflow side at the end position is δmax is shown.

In the nozzle blade 15 of the present embodiment shown in FIG. 1B, as a result of reducing the number of nozzles compared to the nozzle blade 14 shown in FIG. 1A, the annular pitch T spreads to T1, The wing length H remains the same.
The value of δmax1 in the nozzle blade 15 depends on the expansion of the annular pitch.
δmax / T = δmax1 / T1
It is determined to satisfy the relationship.

The nozzle blade 16 of the present embodiment shown in FIG. 1C is obtained by increasing the blade length from H to H1 with respect to the nozzle blade 15 shown in FIG. 1B.
The value of δmax2 in this nozzle blade 15 depends on the increase in blade length.
δmax1 / H = δmax2 / H1
It is determined to satisfy the relationship.

That is, in the turbine nozzle of the present embodiment, a paragraph in which the nozzle annular pitch T is expanded by reducing the number of nozzle blades in order to reduce the loss due to the nozzle trailing edge thickness TE, and other blade length paragraphs. In this case, the effect of the curved nozzle capable of suppressing the secondary flow loss and the boundary layer development can be obtained.
As a result, the secondary flow loss that increases due to the expansion of the annular pitch T and the blade length increases in the latter stage while ensuring the performance improvement amount by reducing the number of nozzles throughout the entire stage of the axial turbine constituted by multiple stages. It is possible to positively suppress the development of the wall boundary layer that increases due to the decrease in the number and the secondary flow loss promoted thereby.

FIG. 2 shows a turbine nozzle of the present embodiment in which δmax is increased in accordance with the increase in the annular pitch T and the change in the blade length H by reducing the number of nozzles, and a conventional turbine in which δmax is constant regardless of the annular pitch and the blade length. The comparison of energy loss distribution with a nozzle is shown.
As is clear from FIG. 2, according to the analysis result, the loss at the center of the blade height is good in both turbine nozzles, but the turbine nozzle of the present embodiment exceeds the performance in the vicinity of the wall surface. ing.

Although the embodiment of the turbine nozzle according to the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made.
For example, even in a nozzle blade characterized by changing the S / T distribution in the blade height direction, or a nozzle characterized by another three-dimensional shape, the circumferential protrusion maximum value δmax of the curved nozzle is determined in the same manner. Can be expected to reduce the secondary flow loss and suppress the wall boundary layer development.
The turbine nozzle of the present invention has a ratio S / T of the shortest distance S between the trailing edge of the nozzle blade and the back surface of the nozzle blade adjacent to the nozzle blade, and the annular pitch T of the nozzle blade. It can be formed so as to be maximum at the center of the height.
Further, the turbine nozzle of the present invention can be formed such that the chord length of the nozzle blade cross section is maximum at the blade tip position and minimum at the blade root position.
Further, the turbine nozzle of the present invention can tilt the position of the trailing edge of the nozzle blade in the axial direction in the range from the blade root to the blade tip.
Moreover, the turbine nozzle of the present invention can curve the position of the trailing edge of the nozzle blade in the axial direction.
Furthermore, an axial flow turbine can be comprised by using the turbine nozzle of this invention mentioned above, respectively.

The figure explaining the nozzle curve shape in the turbine blade of the present invention. The figure which compares and shows the energy loss distribution of the curved nozzle by this invention, and the conventional nozzle. Sectional drawing which shows the structure of a turbine nozzle. The figure which showed the relationship between nozzle blade trailing edge thickness / throat ratio (TE / S) and blade loss. Sectional drawing which shows the change of a nozzle cross section when the number of nozzles is reduced. The figure which shows the mode of turbine nozzle secondary flow vortex generation | occurrence | production. The figure which shows the relationship between a nozzle blade surface back pressure difference, an annular pitch, and a secondary flow loss. The figure which shows the shape of a curved nozzle trailing edge line. The figure which compares the energy loss distribution before and behind reduction in the number of nozzles. The figure which shows the relationship between the representative Reynolds number of each high pressure turbine, and boundary layer thickness. The figure which compares the nozzle exit blade | wing height direction speed distribution before and behind a nozzle blade length change. The figure which shows the relationship between blade height and a wall surface loss ratio.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nozzle blade 2 Wall surface of nozzle blade base side 3 Wall surface of nozzle blade end side 4 Force of fluid to flow 5 Secondary flow vortex 11 Diaphragm outer ring 12 Diaphragm inner ring 13 Annular flow path 14, 15, 16 Nozzle blade

Claims (6)

In the turbine nozzle in which a plurality of nozzle blades are arranged in the circumferential direction in the internal annular flow path of the axial flow turbine, and the nozzle blades are curved toward the circumferential fluid outflow side,
When the maximum protrusion amount in the circumferential curvature of the nozzle blade trailing edge position is δmax, the annular pitch at the center of the blade height is T, and C1 is a constant,
δmax / T = C1
The value of δmax is determined according to the value of T so that the relationship of
And when the blade height is H and C2 is a constant,
δmax / H = C2
A turbine nozzle characterized in that the value of δmax is determined in accordance with the value of H so as to maintain the above relationship.   The value of the ratio S / T of the shortest distance S between the trailing edge of the nozzle blade and the back surface of the nozzle blade adjacent to the nozzle blade and the annular pitch T of the nozzle blade is maximized at the center of the blade height. The turbine nozzle according to claim 1, wherein the turbine nozzle is formed as follows.   3. The turbine nozzle according to claim 1, wherein a chord length of a cross section of the nozzle blade is formed to be maximum at a blade tip position and minimum at a blade root position.   The turbine nozzle according to any one of claims 1 to 3, wherein a rear edge end position of the nozzle blade is inclined in an axial flow direction in a range from a blade root portion to a blade tip portion.   The turbine nozzle according to any one of claims 1 to 4, wherein a position of a trailing edge of the nozzle blade is curved in an axial direction.   An axial-flow turbine comprising a plurality of turbine stages using the turbine nozzle blades according to any one of claims 1 to 5.

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