JP2002048095A - Blade for axial flow compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a blade 6 for an axial flow compressor prevented from damage due to resonance with a fluid vibrating force by selectively increasing a stripe natural frequency 19 of the blade 6 for the axial flow compressor. SOLUTION: In this blade 6 for the axial flow compressor, when a cross section having a maximum thickness 10 smaller than that of a blade tip part 11 cross section is decided to the thickness 10 of the intermediate part 13 in the blade height 12 direction, the stripe natural frequency 19 is increased higher than that of a conventional blade, and consequently, resonance with a fluid vibrating force can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blade of an axial compressor.

[0002]

2. Description of the Related Art As shown in FIG. 4 of Japanese Patent Application Laid-Open No. H11-343998, for example, an axial flow compressor includes a rotating rotor having a plurality of rows of moving blades 6 attached thereto, as shown in FIG. And a casing to which a plurality of rows of stationary blades are attached, and an annular flow path is formed by the rotor, the casing, and the six rows of blades. The inflow airflow is compressed by the six rows of blades while passing through the annular flow path, and becomes a high-temperature, high-pressure outflow airflow.

[0003] In the six-row design of the axial flow compressor, the blade root portion 9 is formed by centrifugal force due to rotation and fluid force received from airflow.
In order to reduce the stress acting on the blade below a permissible value, a sufficient blade root 9 thickness 10 is provided. On the other hand, the blade thickness 10 is reduced at the blade tip 11 in order to prevent flow choke.

[0004]

Various fluid exciting forces act on the blades 6 of the axial compressor due to the wake of the front blades 6 and potential interference with the rear blades 6. Wings 6 by vibration
In order not to break the resonance frequency, it is necessary to implement a resonance avoidance design so that the natural frequency of the blade 6 does not coincide with the excitation frequency 21 near the rated rotation speed 22.

In the resonance avoidance design, the natural frequency of the blade 6 is often changed by changing the blade thickness 10. When the thickness 10 of the entire blade 6 is increased, the natural frequency increases. For example, the bending natural frequency is proportional to the blade thickness 10 as shown in Expression 1.

[0006]

(Equation 1)

Here, fb is the natural frequency of bending, and T is the blade thickness 10.

Among the higher-order natural vibration modes of the blade 6 of the axial flow compressor, there is a stripe natural vibration mode in which the blade height direction node 16 exists only at the blade root 9. FIG.
3 shows an example of the stripe natural vibration mode when there are three lines.

In general, even if the natural frequency and the excitation frequency 21 match, if the excitation force pattern 18 and the natural vibration mode do not match, no large vibration is generated, so that many complicated deformation patterns are formed. There is no need to implement resonance avoidance design for higher-order natural vibration modes.

However, the stripe natural vibration mode is in phase in the blade height 12 direction, and the fluid excitation force pattern 18 is also in phase in the blade height 12 direction. Vibration can occur. Therefore, in order to avoid the problem caused by the resonance of the stripe natural vibration mode, together with the resonance avoidance design of the low-order natural vibration mode implemented in the normal design,
It is necessary to implement a design for avoiding resonance of the stripe natural vibration mode.

The natural vibration mode of the stripe is the blade tip 11
, The natural frequency is substantially proportional to the thickness 10 of the blade tip 11 as shown in Expression 2, and the influence of the blade root thickness on the natural frequency is small.

[0012]

(Equation 2)

Where fs is the natural frequency of the stripe, T
t is the thickness 10 of the blade tip 11.

FIG. 3 is a schematic diagram showing the relationship between the natural frequency of the blade 6 of the axial flow compressor and the shaft rotation speed. The horizontal axis in the figure represents the shaft rotation speed, and the vertical axis represents the vibration frequency. The bold line in the figure represents the natural frequency, and the thin line passing through the origin represents the excitation frequency 21. To avoid resonance, the line between the natural frequency and the excitation frequency 21
It is necessary to avoid crossing near.

For example, as shown by a broken line in FIG. 3, it is assumed that the low-order natural frequency 20 is sufficiently lower than the excitation frequency 21 and the stripe natural frequency 19 matches the excitation frequency 21 at the rated rotation speed 22. . As shown by a symbol b in FIG. 3, by increasing the blade thickness 10 while keeping the ratio of the thickness 10 of the conventional blade root portion 9 to the thickness 10 of the blade tip portion 11, the stripe natural frequency 19 is increased. To avoid resonance by increasing
Since the low-order natural frequency 20 also increases and matches the excitation frequency, it has been difficult to avoid resonance at both natural frequencies.

It is an object of the present invention to selectively increase the stripe natural frequency 19 of the blade 6 of the axial flow compressor,
An object of the present invention is to provide a blade 6 of an axial compressor which does not break due to resonance with a fluid exciting force.

[0017]

According to the first aspect of the present invention, there is provided a blade of an axial flow compressor according to the present invention, wherein a maximum thickness of the blade in the axial flow compressor is fixed at a root portion. The cross section smaller than the cross section of the section 11 is provided in the intermediate section 13 in the blade height 12 direction.

As a result, as compared with a conventional wing in which the thickness 10 of the blade root portion 9 is large and the thickness 10 of the blade tip portion 11 is small.
The thickness 10 of the wing tip 11 becomes relatively large. Since the influence of the thickness 10 of the blade tip 11 on the stripe natural frequency 19 is greater than the low-order natural frequency 20, the blade root is adjusted so that the low-order natural frequency 20 matches the conventional blade according to the relationship of Expression 1. If the thickness 10 of the portion 9 and the wing intermediate portion 13 is determined, the stripe natural frequency 1
9 is higher than the conventional wing. That is, it is possible to selectively increase only the stripe natural frequency 19 without changing the low-order natural frequency 20, and to avoid resonance with the fluid excitation force.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows the blade 6 of the axial compressor of the present invention.
An example of the distribution of thickness 10 in the blade height 12 direction is shown. The vertical axis in the figure is the maximum thickness 10 of each section, the horizontal axis is the position in the blade height 12 direction, and the left end of the figure is the blade root 9 and the right end is the blade tip 11. FIG. 4 shows a schematic view of the blade 6 of the axial compressor. As shown in FIG. 4, the root portion 9, the intermediate portion 13, the tip portion 11, the blade height 12, and the blade width 14 of the blade are defined. FIG. 5 is a schematic view of an embodiment of the blade 6 of the axial compressor according to the present invention. FIG. 6 (a),
(B) and (c) are cross-sectional views of one embodiment of the blade 6 of the axial compressor of the present invention, and FIGS. 7 (a), (b) and (c) are blades of the axial compressor of the present invention. 6 shows a sectional view of another embodiment 6; The positions of the cross sections in FIGS. 6 and 7 are shown in FIG.

As shown in FIG. 4 of Japanese Patent Application Laid-Open No. 11-343998, for example, a multi-stage compressor includes a rotating rotor provided with a plurality of six rows of moving blades, and a plurality of rotating blades. It is composed of a casing to which six rows of stationary vanes are attached,
An annular flow path is formed by the rotor, the casing, and the six rows of blades. The inflow airflow is compressed by the six rows of blades while passing through the annular flow path, and becomes a high-temperature, high-pressure outflow airflow.

The wing 6 of this embodiment shown in FIG.
By increasing the thickness 10 of the blade 1, the blade middle portion 13 has a cross section having a maximum thickness 10 smaller than the cross section of the blade tip 11. As a result, the thickness 10 of the blade tip 11 is relatively larger than that of a conventional blade in which the thickness 10 of the blade root 9 is large and the thickness 10 of the blade tip 11 is small. Since the influence of the thickness 10 of the blade tip 11 on the stripe natural frequency 19 is greater than the low-order natural frequency 20, the blade root is adjusted so that the low-order natural frequency 20 matches the conventional blade according to the relationship of Expression 1. If the thickness 10 of the portion 9 and the wing intermediate portion 13 is determined, the stripe natural frequency 19 will be higher than that of the conventional wing according to the relationship of Expression 2. That is, only the stripe natural frequency 19 can be selectively increased without changing the low-order natural frequency 20, and resonance with the fluid excitation force can be avoided.

The distribution of the thickness 10 in the direction of the blade height 12 may change continuously as shown in Examples 1 and 2 of FIG. 1 or may change stepwise as shown in Examples 3 and 4. May be. Also,
FIGS. 6A, 6B, and 6C show cross-sectional shapes of the wing tip 11.
7 (a) and FIG. 7 (a).
It is not necessary to have a wing shape as shown in (b) and (c).

When the stress distribution of the natural vibration mode of the stripe is calculated, the generated stress is from the blade tip 11 to the blade height 12
%, It is desirable that the range of the blade tip 11 where the blade thickness 10 is increased is about 10% of the blade height 12, but other than that, the effect is also obtained.

The present invention is applicable not only to an axial compressor but also to a fluid machine such as an axial fan.

[0025]

As described above, according to the first aspect of the present invention, the blade 6 of the axial flow compressor with the root 9 fixed.
In the above, the thickness 10 of the blade root portion 9 is large and the thickness 10 of the blade tip portion 11 is small by having a cross section in which the maximum thickness 10 is smaller than the cross section of the blade tip portion 11 in the intermediate portion 13 in the blade height 12 direction. Compared to the conventional blade, the thickness of the blade tip 11
0 becomes relatively large. Since the influence of the thickness 10 of the blade tip 11 on the stripe natural frequency 19 is larger than the low-order natural frequency 20, the blade root portion is adjusted so that the low-order natural frequency 20 matches the conventional blade in accordance with the relationship of Expression 1. When the thickness 9 and the thickness 10 of the blade intermediate portion 13 are determined, the stripe natural frequency 19 becomes higher than that of the conventional blade according to the relationship of Expression 2. That is, only the stripe natural frequency 19 can be selectively increased without changing the low-order natural frequency 20, and resonance with the fluid excitation force can be avoided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a blade thickness distribution of an axial flow compressor according to an embodiment of the present invention.

FIG. 2 is a schematic view of a stripe natural vibration mode of a blade of an axial compressor.

FIG. 3 is a schematic diagram showing the relationship between the natural frequency and the rotation speed of the blade of the axial compressor.

FIG. 4 is a schematic view showing a blade of the axial compressor.

FIG. 5 is a schematic view showing an embodiment of the blade of the axial compressor of the present invention.

FIG. 6 is a sectional view showing an embodiment of the blade of the axial flow compressor of the present invention.

FIG. 7 is a sectional view showing an embodiment of the blade of the axial flow compressor of the present invention.

[Explanation of symbols]

6 wing, 9 wing root, 10 wing thickness, 11 wing tip, 12 wing height, 13 wing middle, 14 wing width, 16
... nodes in the blade height direction, 17 ... nodes in the blade width direction, 18 ... excitation force pattern, 19 ... stripe natural frequency, 20 ... lower order natural frequency, 21 ... excitation frequency, 22 ... rated rotation speed.

Claims (1)

[Claims] 1. A blade of an axial flow compressor having a fixed root portion, wherein the blade has a cross section having a maximum thickness smaller than a cross section of a blade tip portion in an intermediate portion in a blade height direction. Bucket.