CN-116123016-B - Method and structure for adjusting natural frequency of water bucket of impulse turbine

CN116123016BCN 116123016 BCN116123016 BCN 116123016BCN-116123016-B

Abstract

The invention belongs to the technical field of water turbines, and particularly relates to a method and a structure for adjusting the natural frequency of a water bucket of an impulse water turbine. The method comprises the following steps of partitioning the back of a water bucket according to a CFD calculation result, clearly influencing a hydraulic area and a hydraulic area, establishing a three-dimensional model of the water bucket by adopting a water bucket root modeling method, adding auxiliary lines and auxiliary surfaces in the hydraulic area, constructing a frequency modulation module through stitching commands, constructing a finite element model, applying boundary conditions, solving, circularly carrying out the steps of extracting each pitch diameter mode and the corresponding natural frequency thereof under the torsional vibration mode, comparing the natural frequency with the excitation frequency of the corresponding mode, judging whether resonance occurs or not, judging and determining an adjustment direction if resonance occurs, thickening the frequency modulation module if the natural frequency needs to be improved, thinning the frequency modulation module if the natural frequency needs to be reduced, and determining the optimal thickness of the frequency modulation module. The invention provides a method and a structure for adjusting the natural frequency of a water bucket of an impulse turbine, which are simple and quick in design.

Inventors

Lv Boru
ZHOU JUNPENG
LIU LIZHENG
LIANG QUANWEI
FAN JIAYI
XIONG JIANJUN
SONG MIN
DENG JINJIE
HE QIYUAN
CHENG MENG
Zhou Hengte

Assignees

东方电气集团东方电机有限公司

Dates

Publication Date: 20260508
Application Date: 20230105

Claims (6)

1. The natural frequency adjusting method for the water bucket of the impulse turbine is characterized by comprising the following steps of: Partitioning the back of the water bucket according to the CFD calculation result, and definitely influencing the area of the water power and the area without influencing the water power; A three-dimensional model of the water bucket is built by adopting a water bucket root modeling method; adding an auxiliary line and an auxiliary surface in a hydraulic area without influencing, and constructing a frequency modulation module through a stitching command; building a finite element model, applying boundary conditions and solving; Extracting each pitch diameter mode and the corresponding natural frequency under the torsional vibration mode, comparing the extracted pitch diameter mode with the excitation frequency of the corresponding mode, judging whether resonance occurs, judging and determining the adjustment direction if resonance occurs, thickening the frequency modulation module if the natural frequency needs to be increased, and thinning the frequency modulation module if the natural frequency needs to be reduced; An optimal thickness of the tuning frequency module is determined.
2. The method for adjusting the natural frequency of a water bucket of an impulse turbine according to claim 1, wherein the frequency adjusting module is smoothly transited with the root of the water bucket in a bridging curved surface mode when the frequency adjusting module is constructed.
3. The method of adjusting the natural frequency of a water bucket of an impulse turbine as claimed in claim 1, wherein the area affecting the hydraulic power is the outside of the water bucket, and the area not affecting the hydraulic power is the back of the water bucket on the side of the hub of the rotating wheel.
4. The structure for adjusting the natural frequency of the water bucket of the impulse turbine, which is obtained by the method as claimed in claim 1, is characterized by comprising a frequency adjusting module which is arranged in the water bucket and does not influence the hydraulic area.
5. The structure of claim 4, wherein the frequency modulation module is in smooth transition with the root of the bucket.
6. The structure of claim 4, wherein the hydraulic area is a side of the back of the bucket, which is close to the hub of the runner.

Description

Method and structure for adjusting natural frequency of water bucket of impulse turbine Technical Field The invention belongs to the technical field of water turbines, and particularly relates to a method and a structure for adjusting the natural frequency of a water bucket of an impulse water turbine. Background Unlike a counterattack turbine, the water bucket rotates at a high speed in the air, and once the water bucket breaks, the life of operation and maintenance personnel of a power station is threatened, and the operation safety and stability of the impact turbine are seriously affected. Therefore, when the water bucket research and development design is carried out, besides the operation efficiency, the natural frequency of the water bucket needs to be adjusted, so that the natural frequency corresponding to each pitch diameter mode of the torsional vibration mode completely avoids the excitation frequency of the corresponding mode, thereby ensuring that resonance can not be generated forever. At present, in the structural design of the water bucket of the impulse turbine, a rapid adjustment method for the natural frequency of the water bucket is not available, but after the modeling of the root of the water bucket is completed, the natural frequency of each stage is calculated through commercial software, and compared with the excitation frequency of the water bucket, whether resonance occurs or not is judged. If resonance occurs, only the water bucket can be redesigned, so that the difficulty in research and development of the water bucket is greatly increased, and the research and development period of the water bucket is prolonged. Disclosure of Invention In order to solve the problems in the prior art, the invention aims to provide a method and a structure for adjusting the natural frequency of a water bucket of an impulse turbine, which are simple and quick in design. The technical scheme adopted by the invention is as follows: the natural frequency adjusting method for the water bucket of the impulse turbine comprises the following steps: Partitioning the back of the water bucket according to the CFD calculation result, and definitely influencing the area of the water power and the area without influencing the water power; A three-dimensional model of the water bucket is built by adopting a water bucket root modeling method; adding an auxiliary line and an auxiliary surface in a hydraulic area without influencing, and constructing a frequency modulation module through a stitching command; building a finite element model, applying boundary conditions and solving; Extracting each pitch diameter mode and the corresponding natural frequency under the torsional vibration mode, comparing the extracted pitch diameter mode with the excitation frequency of the corresponding mode, judging whether resonance occurs, judging and determining the adjustment direction if resonance occurs, thickening the frequency modulation module if the natural frequency needs to be increased, and thinning the frequency modulation module if the natural frequency needs to be reduced; An optimal thickness of the tuning frequency module is determined. The method comprises the steps of dividing the back of a water bucket according to a CFD calculation result, determining which areas influence the water power and which areas do not influence the water power, establishing a three-dimensional model of the water bucket by adopting a water bucket root modeling method, adding auxiliary lines and auxiliary surfaces in the areas which do not influence the water power, constructing a frequency modulation module by stitching commands, smoothly transiting the frequency modulation module and the root by bridging curved surfaces, adopting commercial software, constructing a finite element model, applying boundary conditions, solving, extracting each pitch diameter mode and the corresponding natural frequency thereof under the torsional vibration mode, comparing the natural frequency with the excitation frequency of the corresponding mode, judging whether resonance occurs, judging and determining the adjustment direction if resonance occurs, thickening the frequency modulation module if the natural frequency is to be improved, otherwise thinning the frequency modulation module, cycling for several times, and determining the thickness of the optimal frequency modulation module. The invention can simply and rapidly adjust the natural frequency of the water bucket, so that the natural frequency of the mode of the water bucket avoids the excitation frequency of the corresponding mode to the greatest extent in the design stage, thereby ensuring the safe and stable operation of the unit. The invention only adjusts the frequency adjusting module, reduces the difficulty of developing the water bucket and shortens the development period of the water bucket. As a preferable scheme of the invention, when the frequency modulation module is constructed, t