JP2004332562A - Stationary blade cascade of axial compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To considerably reduce a vibrational stress due to resonance in all vibration mode in an operation region of an axial compressor, and prevent performance reduction of an entire stationary blade cascade. <P>SOLUTION: In the stationary blade cascade of this axial compressor in which a plurality of stationary blades 2 are arranged over an entire periphery in a peripheral direction, each pitch between the stationary blades constituting the stationary blade cascade periodically varies in the peripheral direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a stator blade row of an axial compressor, and more particularly, to a circumferential arrangement of stator blades.
[0002]
[Prior art]
In an axial flow compressor that constitutes an aero engine, an industrial gas turbine, or the like, a periodic excitation force acts on the moving blade row by a stationary blade row located upstream of the moving blade. Therefore, the excitation frequency of the stationary blade and the natural frequency of the moving blade have a relationship as shown in FIG. 6, and at a resonance point where the two intersect, the moving blade resonates in its natural vibration mode. In some cases, this can lead to damage.
[0003]
As an anti-vibration design means for suppressing the above-mentioned rotor blade resonance, reduction of the amplitude at the resonance point and avoidance of the resonance point are known. Among these, as means for reducing the amplitude at the resonance point, for example, there is a design change of the rotor blade shape such as increasing the blade thickness, but this involves a sacrifice in aerodynamic performance, for example, a problem that the stage efficiency is greatly reduced. There is.
[0004]
On the other hand, Patent Document 1 has been proposed as a means for avoiding the resonance point.
[0005]
[Patent Document 1]
JP-A-11-200808
As shown in FIG. 7, the "compressor stator vane" of Patent Document 1 is arranged such that the circumferential arrangement of the stator vanes is different in pitch angles θ ₁ , θ ₂ between the upper half and the lower half of the air flow path. This prevents the blades passing through the non-uniform flow field from receiving the excitation force of a constant frequency.
[0007]
[Problems to be solved by the invention]
Since the blade shape in recent years is very complicated, vibration modes of the first to fourth order generally exist, and it is very difficult to remove the resonance point from the operating range of the axial flow compressor in all the vibration modes.
[0008]
For example, in the apparatus disclosed in Patent Document 1 described above, half of a row of 40 stationary blades is divided into a sparse array, and half of the row is divided into a dense array. Resonance is avoided by eliminating a periodic component of (number of sheets) × N (rotor blade rotation speed). However, in this case, two new resonance points are generated before and after the original resonance point frequency (40 × N), and the amplitude level is large. In addition, since the arrangement in which the blades are sparsely arranged is arranged over half the circumference, aerodynamic performance is reduced over half the circumference, and as a result, there is a problem that the performance of the entire stationary blade row cannot be reduced.
[0009]
The present invention has been made to solve such a problem. That is, an object of the present invention is to provide a vane of an axial compressor in which the vibration stress due to resonance in all vibration modes can be significantly reduced in the operating range of the axial compressor and the performance of the entire vane row can be prevented from deteriorating. Is to provide columns.
[0010]
[Means for Solving the Problems]
According to the present invention, in the stator blade row of the axial flow compressor in which a plurality of stator blades are arranged in the circumferential direction over the entire circumference, the pitch between the stator blades constituting the stator blade row changes periodically in the circumferential direction. A stationary blade row of an axial compressor is provided.
[0011]
According to the configuration of the present invention, since the pitch between the stationary blades constituting the stationary blade row changes periodically in the circumferential direction, the stationary blade rows having the same pitch are hardly continuous. Therefore, the frequency component (number of stator blades) × (rotor blade rotation speed) included in the excitation force generated by the wake of the stator blade can be effectively reduced, and the vibration of the rotor blade generated by resonance with the frequency component Stress can be greatly reduced. Further, since the stationary blade rows of the same pitch are hardly continuous and only change periodically in the circumferential direction, the stall performance is not impaired, and the performance deterioration of the entire stationary blade row can be avoided.
These effects were obtained by performing an FFT analysis on the circumferential waveform of the wake of the stationary blade row, examining the increase and decrease of the frequency component, calculating the aerodynamic force acting on the moving blade by an unsteady stage CFD (computational fluid dynamics), and calculating the structural response. It was confirmed analytically by performing calculations.
[0012]
According to a preferred embodiment of the present invention, the stationary blade row includes a plurality of divided sectors divided in a circumferential direction, and each divided sector includes a plurality of stationary blades whose pitch gradually changes in a circumferential direction.
[0013]
With this configuration, it is possible to gradually change the velocity distribution of the stator blade wake acting on each rotor blade while maintaining the same pitch as in the conventional example in which the pitch is equally spaced, and the entire stator blade row due to a sudden change in the velocity can be changed. Performance can be avoided.
[0014]
It is preferable that the pitch between the blades of the divided sector is wider at the center or at the end than at the pitch at the equal interval, and conversely at the end or at the center, it is narrower and the same in the entire divided sector.
[0015]
With this configuration, it is possible to periodically change the pitch between the stator blades constituting the stator blade row in the circumferential direction by simply manufacturing a plurality of the same divided sectors and combining them in the circumferential direction, thereby improving productivity. Thus, cost can be reduced.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In each of the drawings, common portions are denoted by the same reference numerals, and redundant description is omitted.
[0017]
1A and 1B are blade arrangement diagrams showing a stationary blade row of the present invention, wherein FIG. 1A shows a conventional example and FIG. 1B shows the present invention. In this figure, reference numeral 2 denotes a stationary blade, 4 denotes a moving blade, and 6 denotes a distribution line of entropy generated between the blades.
[0018]
The stationary blade row of the present invention is a stationary blade row of an axial flow compressor in which a plurality of stationary blades 2 are arranged along the entire circumference in the circumferential direction. Further, as shown in FIG. 1B, in the present invention, the pitch P between the stationary blades 2 constituting the stationary blade row is configured to periodically change in the circumferential direction. In the example of the figure, the pitch P of the eight stator blades is −10%, −5%, + 5%, + 10%, + 10%, + 5%, −5% in the example of FIG. , -10%.
[0019]
That is, the stator blade row of the present invention is composed of a plurality of (for example, four) divided sectors 8 divided in the circumferential direction, and each of the divided sectors 8 has a pitch P gradually changing in the circumferential direction (this example). In this case, eight vanes 2 are provided.
[0020]
In this example, the pitch P between the wings of the divided sector 8 is 10% wider at the center and 10% narrower at the end with respect to the pitch at the equal interval (A). The entire divided sector has the same configuration.
[0021]
1A and 1B are obtained by numerical analysis based on computational fluid dynamics. From this comparison, it can be seen that the equal distribution line 6 of the entropy is hardly different between the conventional example and the present invention.
[0022]
This was also confirmed from the results of numerical analysis of the stage efficiency. That is, it was found that there was only a difference of less than about 0.1% in the step efficiency between the conventional example and the present invention, and substantially the same step efficiency could be maintained.
[0023]
FIG. 2 is a diagram illustrating a vibration mode in the stationary blade. In this figure, (A) shows a third-order stripe mode (1-3S mode), and (B) shows a fourth-order stripe mode (1-4S mode). The stripe mode means a vibration mode perpendicular to the wing cord.
[0024]
FIG. 3 is a diagram showing a vibration stress reducing effect according to the present invention. In this figure, the horizontal axis indicates the two stripe modes shown in FIG. 2, and the vertical axis indicates the ratio of the vibration stress of the present invention to the vibration stress at equal intervals.
[0025]
From this figure, it was found that the vibration stress was reduced by about 30% in the 1-3S mode and about 27% in the 1-4S mode. In addition, the circumferential waveform of the wake of the stationary blade group arranged at unequal intervals according to the present invention is subjected to FFT analysis to check the increase and decrease of the frequency component, and the aerodynamic force acting on the rotor blade by the unsteady stage CFD (computational fluid dynamics) is determined. By performing the calculation and the structural response calculation, it was confirmed that the vibration stress can be reduced by about 30% in all the vibration modes other than those described above.
[0026]
FIG. 4 is an explanatory diagram of the distortion caused by the stationary blades, and shows a case in which one circumference is divided at 180 deg and the intervals are irregular.
In general, when the blade interval of the vanes spreads by 10% pitch, the flow of about 1 deg does not bend at the outlet between the vanes (in the case of a typical compressor rear stage vane), and the static pressure is reduced by several minutes. %descend. This is because pressure recovery by deceleration is not performed.
[0027]
Further, it is known that when the blade interval of the stationary blades is reduced by 10% pitch, the solidity (blade cord / pitch ratio) increases and energy loss increases. Also in the above-described configuration of the present invention, the loss factor increases by about 5 to 10% in the CFD result.
Therefore, when there are regions where the blade spacing of the vanes differs, there are regions where the static pressure decreases and regions where the energy loss increases due to the circumferential position at the vane outlet. Such non-uniform regions are referred to as distortion to the downstream blade.
[0028]
FIG. 5 is a diagram showing a decrease in outlet pressure when a surge occurs due to distortion. In this figure, the ratio occupied by the distortion region is 90 deg in total, and shows the relationship between the case of four divisions, two divisions, no division, and the outlet pressure.
Even if there is a total 90 deg distortion region in the circumferential direction, one region is narrow (for example, 22.5 deg) and dispersed in a plurality of (for example, four) regions, the reduction in pressure ratio when a surge occurs is smaller. Can be seen from this figure.
In other words, in the means for changing the blade interval over a half of 180 deg in the circumferential direction as in Patent Document 1, distortion that causes a decrease in the surge margin of the compressor occurs. On the other hand, in the present invention in which the interval is increased or decreased by about 8 pitches, for example, in the case of 40 sheets per round, the distortion is suppressed to about 8/40 × 360 deg / 2 = 36 deg, and the influence on the surge margin is reduced.
[0029]
As described above, according to the configuration of the present invention, since the pitch between the stationary blades constituting the stationary blade row changes periodically in the circumferential direction, the stationary blade rows having the same pitch are hardly continuous. Therefore, the frequency component of (number of stationary blades) × (rotating blade rotation speed) included in the excitation force caused by the wake of the stationary blade can be effectively reduced, and the vibration of the rotating blade generated by resonance with the frequency component can be effectively reduced. Stress can be greatly reduced. In addition, it was analytically confirmed that the stationary blade rows of the same pitch were hardly continuous and only changed periodically in the circumferential direction, so that the stall performance was not impaired and that the performance degradation of the entire stationary blade row could be avoided.
[0030]
Note that the present invention is not limited to the above-described embodiments and examples, and it is needless to say that various changes can be made without departing from the gist of the present invention.
[0031]
【The invention's effect】
As described above, according to the present invention, the frequency component of (number of stationary blades) × (rotor blade rotation speed) included in the excitation force generated by the wake of the stationary blade is reduced, and the blade vibration level at the time of resonance is reduced. You. Further, since the stationary blades are not sparsely arranged over a long section, the influence on the aerodynamic performance can be minimized. Further, in the embodiment of the present invention, the interval between the two vanes in the center is widened by 10%, the pitches at both ends are narrowed by 10%, and the width between the remaining vanes changes smoothly, with eight vanes of the stationary vane as one section. By setting, the vibration level at the resonance point of the lower flow blade in the higher-order panel mode can be predicted to be reduced by about 30%.
[0032]
Therefore, the stator blade row of the axial flow compressor of the present invention can significantly reduce the vibration stress due to resonance in all vibration modes in the operation range of the axial flow compressor, and can avoid the performance deterioration of the entire stator row. , Etc. have excellent effects.
[Brief description of the drawings]
FIG. 1 is a blade arrangement diagram showing a stationary blade row of the present invention.
FIG. 2 is a diagram showing a vibration mode in a stationary blade.
FIG. 3 is a diagram showing a vibration stress reducing effect according to the present invention.
FIG. 4 is an explanatory diagram of distortion by a stationary blade.
FIG. 5 is a diagram showing a decrease in outlet pressure when a surge occurs due to distortion.
FIG. 6 is a diagram illustrating a relationship between an excitation frequency of a stationary blade and a natural frequency of a moving blade.
FIG. 7 is a blade arrangement diagram of a conventional stationary blade row.
[Explanation of symbols]
2 stationary blades, 4 blades, 6 distribution lines of entropy,
8 divided sectors

Claims (3)

In a stator blade row of an axial flow compressor in which a plurality of stator blades are arranged along the entire circumference in a circumferential direction, a pitch between the stator blades constituting the stator blade row changes periodically in a circumferential direction. Stator row of axial compressor. The said stationary blade row is comprised from the several divided sector divided | segmented in the circumferential direction, and each divided sector is comprised from the several stator blade whose pitch changes gradually in a circumferential direction. Stator row of axial compressor. The pitch between the blades of the divided sector is wider at a central portion or an end portion than at a pitch at an equal interval, and conversely narrow at an end portion or a central portion, and is the same in the entire divided sector. 3. A stator blade row of the axial compressor according to 2.

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