JPH04292502A - Stationary blade of axial flow turbine - Google Patents

Abstract

PURPOSE:To increase the quantity of steam flowing from the inlet of a stationary blade toward its tip and to improve the efficiency of a turbine by increasing the throttle rate of a flow passage at the inlet of a cascade of blades, which is dependent on blade thickness at the front edge of the stationary blade, in the side toward the inner wall from a spot at a fixed height of the blade, and moreover the above- mentioned blade thickness in the side toward the inner wall from a spot at a fixed height. CONSTITUTION:Only the thickness the front edge 6 of the elementary blade form 10 of a stationary blade cascade on the low pressure stage of a steam turbine is made somewhat larger from a position having a blade height h2 on a inlet side from an outer ring wall toward an inner ring wall, and only the front edge 6 is formed into the same shape in teh inside of a spot having blade height h1 on the inlet side. The blade at the front edge 6 is thickened to narrow the width of a dimensionless flow passage at an inlet part continuously and sharply from a position away as much as a distance h2 from a blade root and to narrow it continuously and slowly from a position way as much as a distance h1 from the blade root. Thus the quantity of steam flowing toward the tip of the stationary blade can be increased, and the radial outward flow of a steam flow between the stationary blades can be lessened.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of stator blades for axial flow turbines.

0002

BACKGROUND OF THE INVENTION Improving the efficiency of large-capacity steam turbines and the like is an important research topic, and in particular, as the capacity increases, improving the efficiency of low-pressure stage sections has become important. However, the steam flow in the low-pressure stage of a steam turbine has not yet been sufficiently elucidated or improved based on it.

FIG. 7 shows a meridional cross section of the final stage of a low pressure turbine with a flare angle (the angle at which the stator vane diaphragm outer ring widens downstream to increase the flow area). static wing 1
and rotor blades 2 are provided in the flow path of the working fluid, and the stator blade 1 is connected to a diaphragm outer ring 3 and a diaphragm inner ring 4 that constitute the flow path.
is held in The moving blades 2 are attached to a rotating rotor 5.

When the flare angle of the stationary blade 1 is large, the steam flowing out almost uniformly from the front rotor blade 7 needs to be largely deflected in the direction of the diaphragm outer ring 3, but at the tip, the flow path area sharply increases due to the flare angle. However, since the steam is not sufficiently replenished, the flow becomes difficult at the tips of the stator blades, the flow rate decreases, and the outflow angle in the radial direction increases. As a result, the pressure at the tip of the stationary blade outlet becomes lower than the planned value, and the radial velocity component, which directly becomes a loss, increases. Furthermore, when the pressure at the tip of the stator blade outlet becomes lower than the planned value, the outflow speed from the stator blade becomes faster, resulting in a state of belly-strike inflow with respect to the rotor blade inlet angle, and the angle of attack loss increases. Furthermore, if the pressure at the tip of the stator blade outlet becomes lower than the planned value, the relative outflow speed from the moving blade becomes slow, so the absolute outflow speed increases and the leaving loss increases.

As a conventional countermeasure, when the flare angle of a low-pressure turbine is large, as described in Japanese Patent Application No. 2-67045, the minimum flow passage width of the blade row is suddenly increased from the middle of the blade span toward the tip. The method used was to twist the wings in the direction of making them wider. Although this method is improved to increase the flow rate at the tip of the stator blade, it is still not sufficient. In other words, the amount of flow that moves toward the tip within the stator vane row increases, and the radial velocity increases, so the flow does not increase sufficiently.

[0006]

SUMMARY OF THE INVENTION The above-mentioned prior art attempts to adjust the outflow angle of the flow behind a stator blade, the radial distribution of steam amount, etc. by the geometric outflow angle of the stator blade. FIG. 8 is a cross-sectional view showing the configuration of the blade row in one radial cross-section of the stationary blade group. The amount of steam passing through the stationary blades is determined by the radial distribution of the narrowest parts O and O of the blade row flow path. As the blade length becomes longer, such as in the downstream stage of a low-pressure turbine, the blade cross-sectional shape shown in Figure 8 is formed to gradually increase from the root side to the tip side, and in general, the blade chord length C and the blade row pitch The structure is such that the ratio of p is approximately constant. Therefore, at the inlet portion of the blade row, the throttling ratio of the blade row flow path due to the blade thickness is substantially uniform from the root to the tip. For this reason, although steam is replenished at the tip by the flow rectification effect by the throttle at the inlet of the blade row channel, it is still not sufficient.

An object of the present invention is to increase the amount of steam flowing from the inlet to the tip of the stator blade, to suppress the flow in the radial direction within the stator blade, and to increase the pressure at the tip of the outlet of the stator blade, thereby improving the stage performance. Our objective is to provide a turbine stationary blade that improves the

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method for increasing the thickness of the leading edge of the stator blade so as to narrow the cascade flow path width of the leading edge of the stator blade on the inner wall side from a predetermined blade height. It is characterized by thicker.

[0009]

[Operation] The present invention increases the flow resistance on the inner wall side by narrowing the width of the blade cascade flow path at the leading edge of the stator blade on the inner wall side than a predetermined blade height, and the steam on the inner wall side is directed outward in the radial direction. direction, i.e. towards the outer wall.

[0010] This makes it possible to increase the amount of steam flowing into the tip of the stator blade and to reduce the outward flow of steam in the radial direction within the stator blade.

[0011]

[Embodiment] Fig. 1 shows a stator blade row when the present invention is applied. The stator vane 1 is formed by stacking a large number of element airfoils 10, and is held by the diaphragm outer ring wall 8 and inner ring wall 9 while being inclined in the tangential direction. The element airfoil 10 of a conventional blade is generally larger on the outer ring side of the diaphragm and becomes smaller on the inner ring side, but in the stationary blade according to the present invention, only the leading edge 6 of the element airfoil 10 is lower than the inflow side blade height h2 from the outer ring wall. It becomes slightly larger toward the inner ring wall, and only the leading edge 6 has the same shape inside the inflow side blade height h1. The element airfoil shapes at blade height positions h2 and h1 are shown in FIGS. 2 and 3. Compared to the element airfoil 10a in FIG. 2, the element airfoil 10b in FIG. 3 has a thicker blade at the leading edge 6.

FIG. 4 shows the distribution in the blade span direction of the ratio of the flow passage width s of the blade cascade inlet to the blade cascade pitch p (see FIG. 8) in comparison with the distribution according to the conventional method. By increasing the thickness of the blade at the leading edge 6, the dimensionless channel width s/p of the inflow section suddenly decreases continuously from the position h2 from the root compared to the conventional blade, and from the position h1 from the root It gradually decreases in size continuously. Further, the position of h1 is assumed to be near the radial position of the tip of the front rotor blade 7 shown in FIG.

FIG. 5 shows the distribution of the flow rate Q per unit area of steam flowing out from the stator blade when the stator blade of the present invention is applied. The decrease is gone.

In the embodiment of the present invention, the blade thickness of the leading edge 6 of the element airfoil shown in FIG. 3 is approximately constant up to the root, but as shown in FIG. In some cases, the thickness of the blade at the edge 6 may be reduced again. As a result, the flow near the inner ring wall is pressed against the wall surface, and the secondary flow loss at the root of the stator blade can be reduced.

[0015]

According to the present invention, the radial velocity within the stator blade and at the stator blade outlet at the tip of the stator blade of a turbine stage where the flow passage area rapidly expands on the downstream side can be reduced. This makes it possible to increase the amount of steam at the blade tip, optimize the angle of attack of the fluid flowing into the rotor blade at the blade tip, and reduce the absolute outflow velocity of the steam flowing out from the blade tip, thereby reducing leaving loss. Since the energy of the fluid can be effectively converted into work by the rotor blades, the efficiency of the axial flow turbine can be improved.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a stator blade row according to an embodiment of the present invention.

FIG. 2 is a radial cross-sectional view of a stator blade group.

FIG. 3 is a radial cross-sectional view of the stationary blade group.

FIG. 4 is a distribution diagram of the ratio of the flow passage width to the pitch of the blade row at the inlet of the stator blade row.

FIG. 5 is a distribution diagram of the flow rate per unit area at the stationary blade outlet.

FIG. 6 is an explanatory diagram of a stator blade row according to another embodiment of the present invention.

FIG. 7 is a meridional cross-sectional view of a low-pressure turbine stage.

FIG. 8 is a radial cross-sectional view of the stationary blade group.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Stator blade, 2... Moving blade, 3... Diaphragm outer ring, 4... Diaphragm inner ring, 6... Stator blade leading edge, 10... Element airfoil shape.

Claims (2)

[Claims] Claims: 1. In a stator blade of an axial turbine stage that forms a flow path expanding in the flow direction, the throttling ratio of the inlet flow path of the blade cascade due to the blade thickness of the leading edge of the stator blade is set closer to the inner wall than a predetermined blade height. An axial flow turbine stationary blade characterized by having a larger size. 2. The axial flow turbine stator blade according to claim 1, wherein the ratio of the blade thickness of the leading edge portion of the stator blade to the blade row pitch is larger on the inner wall side than a predetermined blade height.