JPH04232305A - Rotary blade for steam turbine and forming method therefor - Google Patents

Abstract

PURPOSE: To provide a steam turbine moving-blade and a forming method therefor making it possible for the end portion of the blade to partition a steam flow control passage of similar degree as the base end of the blade and to form the steam flow control passage of a shape narrowed in the middle. CONSTITUTION: A steam turbine blade 22 is formed in an aerofoil shape giving optimum blade width distribution from the base end to the end 20 so as to correspond to a selected optimum steam passing efficiency. Starting from the end 20 of the blade, a hollow part 28 is formed inside the blade and the hollow part 28 extends towards the base end. The hollow part 28 is centered with respect to the axis of the blade and includes a cross-section area of such that maintains blade wall thickness within a structural design limit as making it possible to remove sufficient material from the blade in order to maintain centrifugal stress load within the design limit.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION The present invention relates to steam turbine blade rows and, more particularly, to a method and apparatus for controlling resonant frequency and weight distribution in a steam turbine rotating blade or rotor blade.

[0002] The rotor blades of highly loaded steam turbines and the long low pressure blades of steam turbines having small tip/boss ratios are generally twisted and tapered. Twisting is required to accommodate the pressure gradients that occur in the front region of the rotating vane and the variations in vane speed that occur in the same region. As a result, the vane entrance angle changes dramatically between the proximal and distal ends of the vane.

Tapered blade structures have been used to control centrifugal stress. Such stress control requires a significantly smaller cross-sectional area at the blade tip than at the blade root. In order to maintain a finite thickness at the vane tip, the width of the vane must be reduced.

The twisted and tapered structure of steam turbine blades reduces the steam flow control area near the blade tips. Moreover, as a result, the steam inlet angle becomes larger, and the magnitude of the rotation of the steam flow at the tip of the blade decreases. As a result, blade efficiency is also reduced. Furthermore, in highly loaded vanes, especially in the last row of low pressure vanes, the steam velocity can be quite high and supersonic. In such blades, it is desirable to use medium-narrow steam channels to improve efficiency. However, such vapor flow path shapes are difficult to achieve where the width-to-pitch ratio is large, such as at the tips of long low-pressure vanes.

[0005]

SUMMARY OF THE INVENTION One object of the present invention is to provide a method and apparatus that overcomes the drawbacks of conventional steam turbine blades as described above.

Another object of the present invention is to enable the tip end of the blade to have a vapor flow control passage area comparable to that of the base end of the blade, and to form a medium-thin vapor flow control passage. An object of the present invention is to provide a method and apparatus for forming a steam turbine blade.

According to one aspect of the invention, a steam turbine is provided, wherein the blades have a proximal end and a distal end, the proximal end being secured to a rotor of the steam turbine within a blade row that includes a plurality of blades. A method is provided for forming a long low pressure rotary vane for use. Each adjacent pair of vanes defines a steam flow path from the proximal end of the vane to the distal end of the vane. Further, according to this method, a blade is formed having a blade shape having an optimal blade width distribution from the base end to the tip so as to correspond to the selected optimal steam flow control passage. A hollow section is machined into the blade that begins at the tip of the blade and extends toward the proximal end of the blade. The hollow section is centered with respect to the blade axis and allows sufficient material to be removed from the blade to maintain centrifugal stress loads within design limits and to keep the blade wall thickness within structural design limits. It has a cross-sectional area that can be maintained at The hollow portion is configured to tune or tune each individual blade in a manner that avoids the blade having a natural resonant frequency that matches the excitation frequency expected to be experienced within the steam turbine. and sufficient material is removed. In one form, material is removed from the vane using electrical discharge machining or electrolytic machining.

For a clearer understanding of the invention, reference may be made to the following detailed description taken in conjunction with the accompanying drawings.

[0009]

[Detailed description of the preferred embodiment]

FIG. 1 is an elevational view of a conventional steam turbine blade viewed perpendicular to the blade's normal plane of rotation. In this plane, the vane 10 is essentially a tapered vane with a pair of connection points 12 and 14 for attaching the vane to an adjacent vane. These vanes are preferably grouped and tuned in groups to avoid resonance in tangential, axial and torsional modes at multiple harmonics. Tuning designs are also used to avoid excitation frequencies at multiple turbine speeds. Connection points 12 and 14 are referred to as inner and outer presser feet, respectively. To simplify the manufacturing process, the proximal end of the vane is formed with a zero taper angle, giving the airfoil a taper and twist, e.g.
approximately 1.22i from the proximal end 16 of the in (10.8cm)
The blade can be formed to vary in the axial width of the blade tip 18 of n (approximately 3.1 cm). The vanes are attached at the proximal end 16 to a steam turbine rotor (not shown) and are joined together by clasps 12 and 14 in selected groups. The vane row consists of a plurality of vanes 10 attached to the rotor in a common circumferential row. One typical blade row consists of the blades shown in Figure 1.
It can contain 20 sheets. 2 and 3, presser foot 1
A cross-sectional view of the blade at 2 and 14 is shown, illustrating the reduction in blade width and the change in blade curvature at two different radial distances from the rotor. Figures 4 and 5
is a radial view of a pair of adjacent vanes illustrating the difference in steam flow control area adjacent the proximal end of the vane compared to the area adjacent the tip of the pair of vanes. be. In FIG. 4, the steam flow control region 15 extends over the concave surface of one vane and the convex surface of the adjacent vane, whereas in FIG. It occupies only a small portion of the blade surface. For the type of blade shown in Figure 1, the width-to-pitch ratio at the blade tip is about 1 of the width-to-pitch ratio at the blade base when compared with the measured dimensions shown in Figures 4 and 5.
It is 0 times.

FIG. 6 shows a steam turbine blade similar to the blade shown in FIG. 1, but in which the teachings of the present invention allow the blade tips 20 to have a greater width. It is an elevational view. Blade (rotating blade) 2
2 includes a proximal end 24 that can have substantially the same width as the distal end 20. The proximal end 24 can be attached to the dome-shaped root portion 26 in the same manner as is done in the conventional example of FIG. FIG. 7 is a partial cross-sectional view of the tip of the vane of FIG. 6 illustrating the formation of a cutout or hollow 28 within the tip of the vane 22. FIG. The contour of the hollow is shown by dashed line 30 and extends downwardly toward the proximal end of the vane for a predetermined radial distance that may vary as a function of the design conditions for the vane. The design conditions are determined by the centrifugal stress applied to the blades, and
This can be set by the need to machine or remove sufficient material from the vane to avoid the natural resonant frequency. FIG. 8 is a radial view of the tips 20 of a pair of vanes 22 showing the long steam flow control passage or region (steam flow path) 19 at the tips of the vanes. It should be noted that by clipping off the tips of the vanes 22, the external dimensions of the vanes can be formed into any desired shape. For example, in FIG. 8, it can be seen that the outer shape of the vane forms a medium-thin steam flow control passage. Such a shape of the steam flow control passage has been very difficult to achieve with conventional tapered blades.

[0011] In order to make the blade have the required airfoil cross-sectional area,
Electrical discharge milling (EDM) or electrolytic milling (ECM) can be used to form the hollow portion within the tip of the vane. The hollow portion can extend to any desired depth with any predetermined taper angle. The precise nature of ECM and EDM processing allows manufacturers to maintain the walls of the vanes at any predetermined thickness. The details of ECM and EDM processing are well known in the art and are not considered to constitute the present invention, and therefore will not be described. By allowing the blades to be cut with hollow tips, the blades themselves can be designed with any blade width distribution required to ensure optimal steam flow path efficiency.

By employing the method of the present invention to form a steam flow path within the tip of a long low pressure steam vane,
The vanes now have virtually unlimited resonant frequency control capability and airfoil area control capability. Furthermore, the steam flow path can be controlled and designed to provide a highly efficient steam flow path near the tips of the vanes. In addition,
The tips of the blades can be designed to sandwich a medium-thin steam flow path, which was impossible in the past. Furthermore, great flexibility is provided in the external shape of the vanes. This is because centrifugal stress and frequency adjustment can be achieved by cutting out the vanes to any desired cross-sectional area or to any desired depth. Also, the presser foot previously required to join adjacent vanes can be eliminated to prevent undesirable vibrations. The reason is,
This is because each blade can be individually tuned to avoid vibration at the resonant frequency. Removal of the presser foot also improves steam flow efficiency. Furthermore, since the width of the blades at the blade tips can be increased, it is possible to reduce the number of blades per blade row, thereby achieving cost savings. In particular, performance gains are expected to result from a 0.4% improvement in heat dissipation rate by employing steam flow control in the blade tip region, and by as much as 0.3% by removing the presser feet. In a typical thermal turbine power generation unit, this heat rate improvement is 52BT
It will be about U/KW time.

As is clear from the foregoing, the vanes have a proximal end and a distal end that can be substantially the same width as the proximal end, with substantially the same pitch/width ratio between adjacent vanes. A method for forming long low-pressure rotating blades for steam turbines with The base end is connected to a rotor of a steam turbine in a blade row having a plurality of blades such that each pair of adjacent blades defines a medium-thin steam flow path capable of providing large steam flow control. It is attached. In the method disclosed herein, the blade is given a blade shape that provides an optimal blade width distribution from the base end to the tip,
This shape corresponds to the selected optimal vapor passage efficiency. A hollow portion is machined in the blade that starts at the tip of the blade and extends toward the base of the blade. This hollow section is centered with respect to the axis of the vane to allow sufficient material removal from the vane to maintain centrifugal stress loads within design limits for the vane, while maintaining the wall thickness of the vane within the design structure. have a cross-sectional area that remains within limits. In one embodiment,
Material can be removed from the blades by EDM or ECM processing. According to the methods disclosed herein, the vanes can be of any selected external shape.

Although the invention has been described in conjunction with what is presently believed to be the preferred embodiment thereof, other modifications and changes will become apparent to those skilled in the art. Therefore, the present invention is not limited to the embodiments disclosed herein, but the above-described modifications and variations are also included within the scope of the present invention.

[Brief explanation of the drawing]

FIG. 1 is an elevational view of a conventional steam turbine blade.

FIG. 2 is a cross-sectional view of the wing in FIG. 1 at a location of a presser foot 12;

FIG. 3 is a cross-sectional view of the blade of FIG. 1 at a location of the presser foot 14;

FIG. 4 is a radial cross-sectional view showing a steam flow control region between a pair of adjacent blades, such as the steam turbine blade shown in FIG. 1;

FIG. 5 is a cross-sectional view showing a small steam flow control region between the tip portions of the pair of steam turbine blades in FIG. 4;

FIG. 6 is an elevational view of a steam turbine blade formed in accordance with the teachings of the present invention.

FIG. 7 is a partial cross-sectional view of the vane of FIG. 6 illustrating a method of forming the hollow tip.

FIG. 8 is a cross-sectional view similar to FIG. 5 when using the blade of FIG. 6;

[Explanation of symbols]

19 Steam flow path (steam flow control path) 20
Blade tip 22 Rotating blade (vane) 24
Base end part 28 of the blade Hollow part

Claims (2)

[Claims] 1. A long low-pressure rotary blade having a base end and a tip end, the base end of which is attached to a rotor of a steam turbine, and arranged in a blade row including a plurality of the same rotary blades, A method of forming rotating blades for a steam turbine, such that each adjacent pair of rotating blades in the blade row defines a steam flow path therebetween, the method of forming a rotating blade for a steam turbine corresponding to a selected optimum steam passage efficiency. to form a blade having an airfoil shape that provides an optimal blade width distribution from the base end to the tip end, and a hollow space is formed in the blade, starting from the tip end of the blade and extending toward the base end of the blade. a wall of the vane while centering the hollow section with respect to the axis of the vane and removing sufficient material from the vane to maintain centrifugal stress loads within design limits. A method of forming a rotating blade for a steam turbine, wherein the hollow portion has a cross-sectional area such that the thickness is maintained within structural design limits. 2. A plurality of elongated low pressure rotating blades each having a proximal end attached to a rotor of a steam turbine and a distal end extending radially outwardly from the rotor, each of the rotating blades having an adjacent each rotary vane has an optimal blade width distribution selected from the base end to the distal end to achieve a selected optimum steam passage efficiency between the rotary vanes; from the tip over a predetermined radial distance from the proximal end so as to avoid excitation of the natural resonant frequency during operation of the steam turbine and to limit the centrifugal stress on the rotary blade to within the limits of the blade structure. A hollow rotating blade row for a steam turbine.