JPS5925091B2 - turbine stator blade - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stator blade that constitutes an output stage of an axial flow turbine such as a steam turbine or a gas turbine.

The structure of a stator blade row used in a conventional axial flow turbine will be explained with reference to FIGS. 1 to 5.

As shown in FIGS. 1 and 2, a plurality of stationary vanes 1 are arranged between a diaphragm inner ring 2 and a diaphragm outer ring 3, which are formed in an annular shape, and form a flow path for a working fluid 7 in an annular shape. Making,
The diaphragm outer ring 3 is fixed to the inner wall of the casing 6.

The thermal energy of the working fluid 7 such as steam or combustion gas is converted into velocity energy in the stationary blades 1, and after flowing out, the velocity energy is converted into rotational motion of the rotary axle 5 by the moving blades 4.

The cross-sectional shape of the stationary blade 1 is as shown in Fig. 3, and the thickness gradually decreases toward the downstream side of the working fluid, and both the leading edge 1at and the trailing edge 1b extend in the blade length direction. It is in a straight line.

In such a row of stator blades, the working fluid 7 passing between the stator blades 1 generates a pressure difference between the convex rear surface 1c and the concave ventral surface 1d due to the action of centrifugal force, and the working fluid 7 passes between the stator vanes 1. The pressure on the back side 1c is higher than the pressure on the back side 1c.

Unfortunately, stress is generated within the stationary blade 1 due to the pressure load acting from the ventral surface 1d toward the rear surface 1c.

This stress has the highest value at the thinner trailing edge 1b.

Curve 8 in FIG. 4 shows the stress distribution in the blade span direction at the trailing edge 1b.

As shown in the figure, among the trailing edges 1b, the stress value is particularly highest near the joints (P portion) with the upper and lower diaphragm inner and outer rings.

The reason for this is that the blade thickness is increased at the joint between the stationary blade 1 and the inner and outer rings of the diaphragm for reasons of welding structure, and this highest stress part is subject to the most severe conditions in terms of strength.

Furthermore, the pressure load acting on the stationary blade 1 varies due to interference with the rotor blade located downstream, and thus acts as a repetitive load.

Under such usage conditions, the stationary blade 1 develops initial fatigue cracks at the highest stress portion, and eventually breaks.

In order to prevent this fatigue failure, conventional measures have been taken to increase the thickness of the trailing edge 1b to reduce the generated stress.

However, as shown in FIG. 5, the loss occurring within the stationary blade 1 is due to the thickness t of the blade trailing edge 1b.

increases in proportion to That is, as shown in FIG. 5, as the thickness te of the trailing edge increases, the trailing edge stress decreases as shown by the chain line 10, while the fluid loss increases as shown by the solid line 9, and the turbine It has the disadvantage of reducing efficiency.

Against this background, when the working pressure of conventional axial flow turbine stationary blades is high and the strength usage conditions are severe, it is necessary to reduce the turbine efficiency in order to ensure strength reliability. I did it out of necessity.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and provide a turbine stator blade that is excellent in strength and performance, thereby improving the strength, reliability, and performance of an axial flow turbine.

The stator vane of the present invention is characterized in that it is formed in a shape that gradually protrudes downstream from the center portion of the trailing edge of the stator blade in the blade span direction toward the upper and lower side walls consisting of the inner and outer rings of the diaphragm.

The details of the present invention will be explained below with reference to FIGS. 6 to 12.

6 and 7 show an embodiment of the stator vane according to the present invention, in which a plurality of stator vanes 11 are fixed between the diaphragm inner ring 2 and the diaphragm outer ring 3, as in the conventional example. It constitutes an annular flow path.

The trailing edge 11b of the stationary blade 11 has an arched shape that gradually protrudes downstream as it approaches the inner and outer rings of the diaphragm from the center in the blade span direction.

Further, the thickness te of the trailing edge 11b has a constant thickness at each part in the blade span direction.

With such a trailing edge shape, the stress distribution at the trailing edge becomes as shown by the solid line 12 in FIG. 8, which is similar to the stress distribution 8 in the conventional example when the trailing edge has the same thickness. Compared to a stress distribution with a peak near the sidewall, the stress distribution is more uniform and the maximum stress is lower, resulting in superior blade strength.

Next, the reason why the stress distribution as shown in Fig. 8 is obtained is explained in Fig. 9.
This will be explained with reference to FIGS. 11 to 11.

As shown in FIG. 9, the stress at the point near the side wall where the stress is highest on the trailing edge 11b is expressed as follows in a simplified model: Consider the case where a load 15 due to pressure acts.

In this case, the stress at the highest stress point 14 is
The longer the length, the greater the acting moment and the greater the generated stress.

Now, FIG. 10 and FIG. 11 compare the beam element models in the conventional example and the present invention, respectively. In the present invention, as shown in FIG. The length L2 of the moment arm 13b1 with respect to the highest stress point 14 is shorter than the length Ll of the moment arm 13b in the conventional example.

Therefore, the acting bending moment is smaller than that of the conventional example for the same load, and in the case of '4' with the same trailing edge thickness as the conventional example,
It is smaller than the generated stress.

The blade thickness at the 0 point, which is the maximum moment arm, is t in Figure 7.

As shown in -C, the thickness t of the trailing edge 11b.

If the thickness is sufficiently thicker than that, the stress will be a low value.

Next, improvement in turbine efficiency will be explained in comparison with a conventional example using FIG. 12.

In the figure, a solid line 16 shows the relationship between the maximum stress at the blade trailing edge and turbine efficiency in the case of the present invention, and a broken line 17 shows that in the conventional example.

As explained with reference to FIG. 9, increasing the trailing edge thickness reduces the applied stress, but increases blade losses and reduces turbine efficiency.

However, according to the present invention, it is possible to reduce the maximum stress at the trailing edge compared to the conventional example having the same trailing edge thickness.
In the case of , the strength can be improved by reducing the blade stress by Δδmax, and conversely, in the case of the same strength, that is, the same generated stress σ1, it is possible to improve the turbine efficiency Δη by reducing the trailing edge thickness. Become.

As described above, in the present invention, the trailing edge of the stator blade is formed in a shape that gradually protrudes downstream as it approaches the inner and outer rings of the diaphragm from the central part in the blade span direction. It is possible to improve the strength of the blade and improve the turbine efficiency.

[Brief explanation of drawings]

Figure 1 is a meridional cross-sectional view of a conventional axial turbine stage section;
The figure shows the stator vane row in Figure 1 viewed from the working fluid inlet side, and Figure 3.
The figure is a sectional view taken along the line A-A in Figure 2, Figure 4 is a stress distribution diagram of a conventional stator blade, and Figure 5a is a sectional view explaining the thickness of the trailing edge of a conventional stator blade. Diagram showing the relationship between trailing edge thickness and blade loss,
FIG. 6 is a meridional sectional view of an axial flow turbine showing an embodiment of the present invention, FIG. 7 is a sectional view taken along the line B-B in FIG. 6, and FIG. FIG. 9 is a diagram used to explain the principle of the present invention, FIGS. 10 and 11 are beam element model diagrams of the conventional example and the embodiment, respectively, drawn to explain the stress reduction mechanism according to the present invention, and FIG. FIG. 3 is a diagram illustrating the relationship between maximum edge stress and turbine efficiency in comparison between a conventional example and an embodiment. 2... Diaphragm inner ring, 3... Diaphragm outer ring, 11... Stator blade, 11b... Trailing edge.

Claims (1)

[Scope of Claims] 1. In a row of stator blades of a turbine in which a plurality of stator blades are arranged between the inner and outer rings of a diaphragm to form an annular flow path, the trailing edge of the stator blade is located at the center of the blade in the blade length direction. The trailing edge of the stator blade is formed to draw a curvature along the blade length direction between the inner and outer rings of the diaphragm. The blade thickness is gradually reduced from the maximum blade thickness toward the trailing edge, and the trailing edge blade thickness is t. , the blade thickness te at the 0 point where the maximum moment arm is
A turbine stationary blade characterized by having a thick C.