JPH0475361B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a blade arrangement structure for rotating machines such as steam turbines and compressors, and in particular to a blade arrangement for a steam turbine that improves the vibration characteristics of turbine blades near the rated speed. Regarding structure.

[Technical background of the invention and its problems]

Generally, as shown in FIG. 1, the rotating body part of a steam turbine is formed by integrally or integrally molding a rotor wheel 2 with a turbine rotor 1, and turbine blades 3 are arranged at equal pitches around the entire circumference of the rotor wheel 2. It is constructed by planting. and,
By applying high-temperature, high-pressure steam to the turbine blades 3, the turbine rotor 1 is rotated, and a generator (not shown) directly connected to the rotor 1 is rotated. Therefore, stably rotating the turbine rotor 1 without causing damage or destruction to the turbine blades 3 improves the reliability of the steam turbine and contributes to a stable supply of electric power. . Therefore, improving the reliability of the turbine blades 3 is an important issue.

Regarding the reliability improvement of the turbine blade 3, when the turbine blade is handled as a single blade A, when handled as a group of blades continuous around the entire circumference of B, and when the turbine blade C
It is conceivable that the blades are embedded in the rotor wheel and treated as their coupled vibration, but when the rotor wheel 2 is soft, the turbine blades are short, and the turbine blades have a single group structure all around, , B, and C, and generally treat the entire circumference as coupled vibration of the rotor wheel, or treat it as a disk consisting of a group of blades all around the circumference.

FIG. 2 shows one of the experimental data of the vibration characteristics of the blade group under the above conditions, and FIGS. 3 to 6 show the vibration mode of a disk consisting of one group all around the circumference. FIG. 2 is generally called a Campbell diagram, and the horizontal and vertical axes indicate the rotational speed of the turbine and the natural frequency of the turbine blade system, respectively. The diagonal straight lines extending radially from the origin 0 indicate the order line A that plots the natural frequency points, and in this order line A, the numbers 1, 2...7 are 1 times the turbine rotation speed. , 2 times...7 times, respectively.
Experiment B is actually measured vibration frequency data, and shows, for example, a vibration characteristic line in the axial direction of a turbine rotor. Experiment B thus shows the variation of the natural frequency of a turbine blade or rotor wheel with respect to rotational speed. Vibration characteristic line B is each order curve A
The turbine blade or rotor wheel resonates at the point where it intersects, creating resonant stress. The relative magnitude of this resonant stress is shown in Figure 2 by the diameter of the stress circle, and as can be seen from this figure, the turbine blades or rotor wheel rotate at around the rated speed. A large resonant stress (stress circle C) is experienced at the node that intersects the double order straight line A. If the turbine blades etc. are subjected to large resonant stress in the rated speed range and continue to operate in this resonant stress state,
There are problems such as the turbine blades being damaged or destroyed due to fatigue failure, and the reliability of the turbine blades being significantly impaired.

Figures 3 to 6 show the axial vibration modes when the turbine blade and rotor wheel are circular disks, respectively: 0-node diameter mode, 1-node diameter mode, 2-node diameter mode, and 3-node diameter mode. It is called the diameter mode, and the + and - signs represent the phase of the amplitude. The phase of this amplitude changes depending on the rotational position of the turbine blades and rotor wheel. For example, at a certain moment, as shown in the 1-node diameter mode in Figure 4, if the part that swings toward the other side of the paper with the nodal radius as a border is +, and the part that swings toward the front is -, then after half a cycle, this becomes the opposite. . The number of nodal radii varies depending on the frequency of the turbine blades and rotor wheel.

Now, if the Campbell diagram shown in Fig. 2 is obtained through experiment and calculation, the rotational speed multiple line A and the frequency line B intersect near the rated rotational speed of the turbine, and at this intersection The vibration stress is large at the nodes. For this reason, it is necessary to tune (select) the turbine blades by some means to provide sufficient detuning so that the nodes do not pass near the rated rotational speed to reduce vibration stress. In this regard, conventionally, the shape of the turbine blade is modified at the design stage, or after the manufacturing stage, the turbine blade is tuned by means such as cutting the turbine blade to achieve detuning.

However, in the case of short blades where coupled vibration with the rotor wheel is a problem in the vibration characteristics of turbine blades, it is difficult to achieve sufficient detuning by just slightly modifying the turbine blades. In the case of blades, it is possible to detune them by slightly modifying the shape of the turbine blades, but each turbine blade must be tuned individually, which takes a long time and is difficult for quality control. Variations in natural frequencies were a problem.

[Purpose of the invention]

In consideration of the above-mentioned points, the present invention reduces the vibration stress near the rated rotation speed, effectively prevents damage or destruction of blades such as turbine blades, and improves the reliability of the blades. The purpose is to provide a mechanical wing arrangement structure.

[Summary of the invention]

In order to achieve the above-mentioned object, the blade array structure of a rotating machine according to the present invention includes a blade array arranged around the entire circumference of a rotary body such as a steam turbine, in which a blade is arranged around a rotary body such as a steam turbine, and in which the blades are arranged around the natural frequency of another blade or blade group. On the other hand, the arrangement angle θ of the blade or blade group whose natural frequency is selected is:
They are arranged at intervals in the circumferential direction so that the relationship expressed by θ=π/N (where N=2 to 4) holds, where N is the number of node diameter modes.

[Embodiments of the invention]

Preferred embodiments of the invention will be described with reference to the accompanying drawings.

FIG. 7 shows an example in which the rotary machine blade array structure according to the present invention is applied to a steam turbine, in which a large number of turbine blades are installed at equal pitches around the outer periphery of the rotor wheel 2, forming a blade group 10. Among this wing group 10, the wing or wing group 11 is different from the other wing or wing group 1.
It is made of a metal material such as titanium, which is different from those of Nos. 2, 13, and 14. Other wings or groups of wings 12, 13, 1
4 is generally made of 12-chromium steel or the like. The blades or blade groups 11 are installed equiangularly on the rotor wheel 2 at intervals of an array angle θ, for example, 60 degrees, and their natural frequency is different from that of the other blades or blade groups 12, 1.
For quality control purposes, the natural frequencies of 3 and 14 are selected within a predetermined range of, for example, about 10% above and below. The wing or wing group 11 is connected to other wings or wing groups 12, 13, 14
They have the same shape but different vibration characteristics.

By the way, in order to damp the vibration of a certain nodal diameter mode near the rated rotation speed, if the number of other nodal diameter modes that relatively amplify the vibration, unlike this nodal diameter mode, is N, then the arrangement angle θ is: θ =π/N...(1) It is expressed as follows.

In the embodiment shown in FIG. 7, in the first equation,
This is when N=3. In other words, the blades or blade groups 11 made of different materials whose natural frequencies have been selected are divided into six equal parts on the entire circumference of the rotor wheel 2, and the center angle
They are arranged at equal pitches of 60 degrees.

Next, the operation will be explained by taking as an example the case where the blade arrangement structure shown in FIG. 7 is applied to a blade group having the characteristics shown in FIG. 2.

The vibration characteristics shown in the Campbell diagram in Figure 2 are such that the vibration caused by the interaction between the turbine blades and the rotor wheel resonates with excitation forces of 2, 4, and 5 times the turbine rotation speed, resulting in large vibrations. A vibration stress is generated, and conversely, the vibration stress is small for an excitation force of 3, 6, or 7 times, which is a characteristic of coupled vibration.
In other words, it can be seen that the blade or blade group of a rotating machine having the vibration characteristics shown in Fig. 2 resonates in response to an excitation force twice the rotation speed near the rated rotation speed. Due to this resonance, there is a problem in that long-term operation near the rated rotational speed may lead to fatigue failure, and the problem is how to suppress the resonance phenomenon in the rated rotational speed range.

However, with the blade group of turbine blades having the vibration characteristics shown in Fig. 2, resonance with twice the rotational speed becomes a problem near the rated rotational speed under normal operating conditions. We will focus on the vibration for an excitation force three times that of the previous one. At this time, the blade or blade group is vibrating in the vibration mode shown in FIGS. 5 and 6, and the stress circle C in FIG.
From the size of , it is inferred that the two-node diameter mode has higher sensitivity than the three-node diameter mode.

By the way, the two-node diameter mode, which is a problem with the blade or blade group shown in Figure 2, occurs when the waves transmitted through the blade or blade group and the rotor wheel are transmitted in two directions in the circumferential direction.
It is a vibration mode that is transmitted in cycles. On the other hand, in FIG. 7, the blades or blade groups 11 made of different materials are divided into six equal parts in the blade group 10 around the entire circumference and arranged at pitch intervals of 60 degrees, so that the structure forms three periods in the circumferential direction. It is becoming. This means that the mode caused by the transmitted wave that travels around the entire circumference in three cycles, that is, the three
This shows that the sensitivity of the nodal diameter mode is increased, and the vibration of the three nodal diameter mode at the rated rotation speed becomes larger than before the application of the present invention. That is, it can be seen that resonance occurs at three times the rotation speed that is far from the rated rotation speed range, and a large resonance stress is generated.

By the way, during rated rotation operation, assuming that the operating conditions do not change before and after applying the present invention, the external force is the same and the energy due to vibration is also constant, so if the vibration in the 3-node diameter mode increases, the 2-node diameter mode vibration increases. The vibration components of the diameter mode and other modes are relatively reduced, as shown in FIG. This FIG. 8 shows that the resonance stress becomes small at the node where the multiple line A and the frequency line B intersect in the vicinity of the rated rotation speed. On the other hand, the number of rotations is 3.
Resonant stress increases at the node where the multiple line A and the frequency line B intersect.

Further, FIG. 9 shows a transmitted wave of vibration transmitted through the rotor wheel. The horizontal axis indicates the circumferential direction (0~
2π), and the amplitude of the vibration is plotted on the vertical axis, the three-period transmitted wave is amplified by having a three-period blade array structure over the entire circumference. That is, the transmitted wave indicated by the broken line 14 is amplified and becomes the transmitted wave indicated by the solid line 15. On the other hand, the two-period transmitted wave indicated by the broken line 16 is attenuated because it does not match the three-period period of the blade array structure, and becomes an attenuated transmitted wave indicated by the solid line 17.

Therefore, by arranging blades or blade groups 11 made of different materials whose natural frequencies are selected as shown in Fig. 7, the vibration level of the nodal diameter mode, which has high vibration stress near the rated rotation speed, can be reduced. be able to. This makes it possible to reduce the vibration of the rotating machine in the rated rotational speed range, which is the normal operating range, and effectively prevent damage to the blade group.

In one embodiment of the present invention, the case where the number N of nodal diameter modes is 3 has been described, but similar effects can be obtained with other numbers of nodal diameter modes. For example, if a certain blade or blade group has low sensitivity to vibrations related to the four-nodal diameter mode, and high sensitivity to vibrations in other nodal diameter modes, and the vibrations are around the rated rotation speed, In equation 1, N=
Blades or blade groups made of different materials whose natural frequencies are selected may be arranged at intervals of 4, that is, θ=π/4.

FIG. 10 shows a modification of the present invention.
In the embodiment shown in FIG. 7, a case has been described in which the blades or blade groups 11 made of different materials are arranged at equal intervals over the entire circumference, but as shown in FIG. Alternatively, the blade group 11 may be arranged only in several partial locations, for example, in two locations. This is a wing or wing group 1 made of different materials.
1, the period of the propagated wave is determined by the angle θ ₁ at which the blade or blade group 1 is made of different materials.
1 can amplify the transmitted waves of a specific period and relatively attenuate the transmitted waves of other periods.

Furthermore, other variants of the invention provide that, instead of having blades or blade groups of dissimilar materials, blades or blade groups of different structural damping are provided, e.g. It's okay.

〔Effect of the invention〕

As described above, in the blade arrangement structure of a rotating machine according to the present invention, among the blade groups arranged around the entire circumference, the vibration frequency is selected within a predetermined range with respect to the natural frequency of other blades or blade groups. The arrangement angle θ of the blade or blade group whose natural frequency is selected is θ=π/N (where N is the number of nodal diameter modes). Since the blades are arranged at intervals in the circumferential direction so that the relationship expressed by There is no need to select (tuning) blades individually, and it is only necessary to arrange blades or blade groups made of different materials at appropriate intervals in the circumferential direction, reducing tuning time and simplifying quality control. be able to.

In addition, it is possible to control the nodal diameter mode and vibration level near the rated rotation speed, which is the normal operating range.
Shifting the distribution of vibration stress acting on blades such as turbine blades in the rated rotation speed range reduces the large peak vibration stress of a specific nodal diameter mode, flattens the vibration stress distribution, and prevents damage to turbine blades. This brings about effects such as being able to effectively prevent fatigue damage and fatigue failure.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the turbine rotating part incorporated in a steam turbine, Figure 2 is a Campbell diagram showing the vibration characteristics of the turbine blade, and Figures 3 to 6 are a circular diagram showing a group of blades all around the circumference. FIG. 7 is a diagram showing an example of the blade arrangement structure of a rotating machine according to the present invention, and FIG. 8 is a diagram showing the nodal diameter mode when the present invention is applied. A Campbell diagram showing vibration characteristics, FIG. 9 is a graph explaining the action of the blade array structure of the present invention, and
FIG. 0 is a diagram showing a modification of the blade array structure of the rotating machine of the present invention. 1...Turbine rotor, 2...Rotor wheel, 3...Turbine blade, 10...Blade group, 11...
...wings or groups of wings made of different materials, 12, 13,
14...Other wing or wing group, A...Order line, B
...Frequency line.

Claims (1)

[Claims] 1. A blade group arranged around the entire circumference of a rotating body such as a steam turbine has a natural frequency selected within a predetermined range with respect to the natural frequency of other blades or blade groups. The arrangement angle θ of the blade or blade group whose natural frequency is selected is the nodal diameter mode number N
A blade arrangement structure for a rotating machine, characterized in that the blades are arranged at intervals in the circumferential direction so that the relationship expressed by θ=π/N (where N=2 to 4) holds. 2. The blade arrangement structure for a rotating machine according to claim 1, wherein the blade or blade group whose natural frequency is selected is made of a different material, such as titanium, that is different from other blades or blade groups. 3. The blade arrangement structure of a rotating machine according to claim 1 or 2, wherein the blades or blade groups whose natural frequencies are selected are equiangularly arranged around the entire circumference of the rotating body. . 4. The blade array structure for a rotating machine according to claim 1 or 2, wherein the blades or blade groups whose natural frequencies are selected are disposed asymmetrically around the rotating body. 5. The blade array structure for a rotating machine according to claim 1, wherein the structural damping of the blade or blade group whose natural frequency is selected is different from the structural damping of other blades or blade groups.