CN111175018B - Method for judging insufficient rigidity of downstream side of elbow of high specific speed hydraulic mechanical model - Google Patents
Method for judging insufficient rigidity of downstream side of elbow of high specific speed hydraulic mechanical model Download PDFInfo
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- CN111175018B CN111175018B CN202010020768.0A CN202010020768A CN111175018B CN 111175018 B CN111175018 B CN 111175018B CN 202010020768 A CN202010020768 A CN 202010020768A CN 111175018 B CN111175018 B CN 111175018B
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- 238000003379 elimination reaction Methods 0.000 claims description 6
- 230000002238 attenuated effect Effects 0.000 claims description 3
- 238000005259 measurement Methods 0.000 abstract description 8
- 230000002787 reinforcement Effects 0.000 abstract description 2
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- 238000009792 diffusion process Methods 0.000 description 1
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Abstract
The invention discloses a method for judging the insufficient rigidity of the downstream side of an elbow of a high specific speed hydraulic mechanical model, which utilizes the characteristic phenomenon that high harmonics of a vortex frequency can appear when the local rigidity of the downstream side of the elbow wall of the high specific speed hydraulic mechanical model is insufficient, and can accurately judge the insufficient rigidity of the local area of the downstream side of the elbow wall by analyzing the frequency spectrum of a pressure fluctuation measuring point signal at a pressure fluctuation measuring point at the downstream side of the elbow of the high specific speed hydraulic mechanical model, thereby adopting the measures of local reinforcement to improve the local rigidity of the downstream side of the elbow wall of the high specific speed hydraulic mechanical model and further improving the accuracy of pressure fluctuation measurement at the pressure fluctuation measuring point at the downstream side of the elbow of the high specific speed hydraulic mechanical model.
Description
The technical field is as follows:
the invention relates to a method for judging insufficient rigidity of the downstream side of an elbow of a high specific speed hydraulic mechanical model.
Background art:
because a relatively complete similarity conversion system is established based on the fluid mechanics principle, the hydraulic machine can predict the performance of the prototype machine through the model test result and serve as the basis for checking and accepting the performance of the prototype machine on the premise of meeting certain similarity conditions. This places very high demands on the accuracy of the model test.
For a high specific speed hydraulic machine as shown in fig. 1, the flow passing member geometry increases accordingly due to its low head (head) and high flow rate. The draft tube diffuser section of the high specific speed hydraulic mechanical model is large in geometric dimension, so that in order to ensure the hydraulic and structural performance of the high specific speed hydraulic machine, the local rigidity of the area is generally improved in a mode of additionally arranging the buttress in the draft tube diffuser section, and the situation that the flow channel geometric shape of the area of the high specific speed hydraulic mechanical model is seriously deformed due to insufficient rigidity is prevented.
Although the method of additionally installing the buttresses can be adopted to improve the rigidity of the high specific speed hydraulic mechanical model draft tube diffusion section part with relatively weak local rigidity, the draft tube elbow cannot adopt the mode of additionally installing the buttresses to improve the local rigidity due to the hydraulic power, the structure and the process, the downstream side 10 of the draft tube elbow is of a thin-wall plate structure, the local rigidity is weak, and the water body continuously and repeatedly acts on the elbow tube wall at the vortex band frequency under the partial load working condition, so that the vibration with the same frequency as the vortex band can possibly occur in the area of the downstream side 10 of the elbow tube wall under the condition of relatively strong vortex band energy. At this time, due to the interaction between the elbow wall and the water body, the pressure pulsation measurement values obtained by the pressure pulsation measurement point 11 on the elbow downstream side and the pressure pulsation measurement points on the periphery thereof may be greatly deviated from the actual values.
In view of the above, a detection method is needed to be developed, which can timely detect the lack of the local rigidity of the elbow of the high specific speed hydraulic machine, so as to ensure the accuracy and reliability of the test result of the hydraulic machine model.
The invention content is as follows:
the invention discloses a method for judging the insufficient rigidity of the downstream side of an elbow of a high specific speed hydraulic mechanical model, which can ensure the test result of the hydraulic mechanical model to be accurate and reliable, and the technical scheme is as follows:
1) starting a computer acquisition system;
2, enabling the high specific speed hydraulic mechanical model to run under partial working conditions;
3) keeping the operation condition of the high specific speed hydraulic mechanical model stable, and collecting a pressure pulsation signal at a pressure pulsation measuring point at the downstream side of an elbow of the high specific speed hydraulic mechanical model;
4) carrying out frequency domain analysis on a pressure pulsation signal at a pressure pulsation measuring point on the downstream side of the elbow of the high specific speed hydraulic mechanical model through fast Fourier transform;
5) a band elimination filter is adopted to ignore the conversion frequency component in the pressure pulsation signal frequency domain at the pressure pulsation measuring point at the downstream side of the elbow of the high specific speed hydraulic mechanical model, namely, a band elimination filter is constructed, the cut-off frequency of the low frequency band is set as the conversion frequency minus 0.5 Hz, and the cut-off frequency of the high frequency band is set as the conversion frequency plus 0.5 Hz, so that the conversion frequency component in the pressure pulsation signal frequency domain at the pressure pulsation measuring point at the downstream side of the elbow of the hydraulic mechanical model is eliminated, and finally, the purpose that the conversion frequency component is attenuated and ignored and other characteristic frequencies are not influenced is realized;
6) if the energy distribution in the frequency domain of the pressure pulsation signal at the pressure pulsation measuring point at the downstream side of the elbow of the high specific speed hydraulic mechanical model presents the following characteristics:
firstly, the main frequency is the frequency of a vortex band;
second, frequency doubling of the vortex band frequency occurs, i.e., 2 frequency doubling of the vortex band frequency, 3 frequency doubling of the vortex band frequency, and 4 frequency doubling of the vortex band frequency;
thirdly, the frequency doubling energy of the vortex band frequency is gradually reduced, namely the energy corresponding to the frequency doubling of 2, the frequency doubling of 3 and the frequency doubling of 4 of the vortex band frequency is gradually reduced; it can be determined that the stiffness of the elbow downstream side of the high specific speed hydro-mechanical model is insufficient.
Fig. 2 shows a typical frequency domain characteristic of a pressure pulsation signal measured at a pressure pulsation measuring point at the downstream side of an elbow under a partial load of a high specific speed hydro-mechanical model when the stiffness of the elbow is sufficient, wherein the horizontal axis of a coordinate system represents a corresponding frequency value f, and the vertical axis represents an energy value E corresponding to a corresponding frequency. In the partial load working condition, namely the vortex band area of the hydraulic machine, in the frequency domain diagram of the tail pipe pressure pulsation of the high specific speed hydraulic machine model, the energy corresponding to the rotating frequency and the vortex band frequency is the highest. The frequency of the vortex is the rotation frequency of the high specific speed hydraulic mechanical model, and the frequency of the vortex is the frequency of the vortex generated by the draft tube around the rotation axis of the hydraulic mechanical model under partial working conditions of the high specific speed hydraulic mechanical model, and is generally one quarter to one third times of the frequency of the high specific speed hydraulic mechanical model. For a high specific speed hydro-mechanical model with reasonable design, under partial load, the energy corresponding to the vortex band frequency should account for a large proportion of the total energy of the frequency domain, and no frequency doubling of the frequency occurs. And once the area with insufficient rigidity exists at the downstream side of the elbow pipe of the high specific speed hydraulic mechanical model, the elbow pipe wall of the area can generate forced vibration with the same frequency as the vortex band under the continuous and repeated action of the vortex band frequency. The higher the energy of the vortex band, the more violent the oscillation of the elbow wall.
According to the vibration theory, the amplitude of the object in forced vibration is determined by the natural frequency of the object and the frequency of the vibration source: the closer the natural frequency of the object is to the frequency of the vibration source, the larger the amplitude of the forced vibration of the object is; the greater the difference between the natural frequency of the object itself and the frequency of the vibration source, the smaller the amplitude of the forced vibration of the object. In the high specific speed hydraulic mechanical model elbow with the downstream side insufficient rigidity area, the lower the rigidity of the downstream side area, the lower the corresponding natural frequency. The frequency of the vortex band as a vibration source is only one fourth to one third of the frequency of the rotation frequency of the hydraulic machine, and the absolute value is very low. The frequency value of the vortex belt as a vibration source is very close to that of the area with insufficient rigidity at the downstream side of the elbow pipe which does forced vibration, and finally the phenomenon of serious forced vibration can occur. In addition, the appearance is that the local part at the downstream side of the elbow of the high specific speed hydraulic mechanical model has obvious vibration inductance, and the appearance in a pressure pulsation signal frequency domain measured at a pressure pulsation measuring point at the downstream side of the elbow is higher harmonics of the appearance frequency of the vortex band, as shown in fig. 3.
The technical effects are as follows:
the invention discloses a method for judging the local insufficient rigidity at the downstream side of an elbow of a high specific speed hydraulic mechanical model, which does not need to additionally arrange a measuring point, performs routine pressure pulsation measurement, and simultaneously accurately judges the local insufficient rigidity at the downstream side 10 of the elbow wall by performing spectrum analysis on a pressure pulsation measuring point signal at the downstream side 11 of the elbow of the high specific speed hydraulic mechanical model through the characteristic phenomenon of higher harmonic of a vortex frequency 2 when the local insufficient rigidity at the downstream side 10 of the elbow wall of the high specific speed hydraulic mechanical model is used, thereby adopting a local reinforcement measure to improve the local rigidity at the downstream side 10 of the elbow wall of the high specific speed hydraulic mechanical model, and further theoretically improving the accuracy of the pressure pulsation measurement at the downstream side 11 of the elbow of the high specific speed hydraulic mechanical model.
Description of the drawings:
FIG. 1 is a schematic view of a high specific speed hydraulic mechanical model elbow
FIG. 2 is a typical frequency domain characteristic of a pressure pulsation signal measured at a pressure pulsation measuring point at the elbow downstream side under partial load of a high specific speed hydraulic mechanical model when the elbow stiffness is sufficient, which is disclosed by the invention
FIG. 3 is a typical frequency domain characteristic of a pressure pulsation signal measured at a pressure pulsation measurement point at the elbow downstream side under partial load of a high specific speed hydraulic mechanical model when the stiffness at the elbow downstream side is insufficient, disclosed by the invention
FIG. 4 is a typical frequency domain characteristic of a pressure pulsation signal measured at a pressure pulsation measurement point at the elbow downstream side under partial load of a high specific speed hydraulic mechanical model when the stiffness at the elbow downstream side is insufficient under the condition of neglecting the frequency conversion, disclosed by the invention
The specific implementation mode is as follows:
a method for judging the insufficient rigidity of the downstream side of an elbow of a high specific speed hydraulic mechanical model comprises the following concrete implementation steps:
1) starting a computer acquisition system;
2, enabling the high specific speed hydraulic mechanical model to run under partial working conditions;
3) keeping the operation condition of the high specific speed hydraulic mechanical model stable, and collecting a pressure pulsation signal at a pressure pulsation measuring point 11 at the downstream side of an elbow of the high specific speed hydraulic mechanical model;
4) carrying out frequency domain analysis on a pressure pulsation signal at a pressure pulsation measuring point 11 on the downstream side of an elbow of the high specific speed hydraulic mechanical model through fast Fourier transform;
5) a band elimination filter is adopted to ignore the frequency conversion component in the pressure pulsation signal frequency domain at the pressure pulsation measuring point 11 at the downstream side of the elbow of the high specific speed hydraulic mechanical model, namely, a band elimination filter is constructed, the cut-off frequency of the low frequency band is set as the frequency conversion minus 0.5 Hz, and the cut-off frequency of the high frequency band is set as the frequency conversion plus 0.5 Hz, so that the frequency conversion component in the pressure pulsation signal frequency domain at the pressure pulsation measuring point 11 at the downstream side of the elbow of the hydraulic mechanical model is eliminated, and finally, the purpose that the frequency conversion component is attenuated and ignored, and other characteristic frequencies are not influenced is realized;
6) if the energy distribution in the frequency domain of the pressure pulsation signal at the pressure pulsation measuring point 11 at the downstream side of the elbow of the high specific speed hydraulic mechanical model presents the following characteristics:
firstly, the main frequency is the vortex band frequency 2;
secondly, frequency doubling of the vortex band frequency 2 occurs, namely 2 frequency doubling 3 of the vortex band frequency, 3 frequency doubling 4 of the vortex band frequency and 4 frequency doubling 5 of the vortex band frequency;
thirdly, the frequency doubling energy of the vortex band frequency is gradually reduced, namely the energy corresponding to the frequency doubling of 2 of the vortex band frequency by 3, the frequency doubling of 3 of the vortex band frequency by 4 and the frequency doubling of 4 of the vortex band frequency by 5 is gradually reduced; it can be determined that the stiffness of the elbow downstream side of the high specific speed hydro-mechanical model is insufficient.
Claims (1)
1. A method for judging the insufficient rigidity of the downstream side of an elbow of a high specific speed hydraulic mechanical model is characterized in that: the method comprises the following steps:
1) starting a computer acquisition system;
2, enabling the high specific speed hydraulic mechanical model to run under partial working conditions;
3) keeping the operating condition of the high specific speed hydraulic mechanical model stable, and collecting a pressure pulsation signal at a pressure pulsation measuring point (11) at the downstream side of an elbow of the high specific speed hydraulic mechanical model;
4) performing frequency domain analysis on a pressure pulsation signal at a pressure pulsation measuring point (11) at the downstream side of an elbow of the high specific speed hydraulic mechanical model through fast Fourier transform;
5) a band elimination filter is adopted to ignore the frequency conversion component in the pressure pulsation signal frequency domain at the lateral pressure pulsation measuring point (11) at the downstream side of the elbow of the high specific speed hydraulic mechanical model, namely a band elimination filter is constructed, the cut-off frequency of the low frequency band is set as the frequency conversion minus 0.5 Hz, the cut-off frequency of the high frequency band is set as the frequency conversion plus 0.5 Hz, the frequency conversion component in the pressure pulsation signal frequency domain at the lateral pressure pulsation measuring point (11) at the downstream side of the elbow of the hydraulic mechanical model is eliminated, so that the frequency conversion component is attenuated and ignored, and other characteristic frequencies are not influenced;
6) if the energy distribution in the frequency domain of the pressure pulsation signal at the pressure pulsation measuring point (11) at the downstream side of the elbow of the high specific speed hydraulic mechanical model presents the following characteristics:
firstly, the main frequency is the vortex band frequency (2);
second, frequency doubling of the vortex band frequency (2) occurs, i.e., 2 frequency doubling (3) of the vortex band frequency, 3 frequency doubling (4) of the vortex band frequency, and 4 frequency doubling (5) of the vortex band frequency;
thirdly, the frequency doubling energy of the vortex band frequency is gradually reduced, namely the energy corresponding to the frequency doubling of 2 (3), the frequency doubling of 3 (4) and the frequency doubling of 4 (5) of the vortex band frequency is gradually reduced; it is determined that the stiffness of the elbow downstream side of the high specific speed hydro-mechanical model is insufficient.
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| CN100582705C (en) * | 2008-11-21 | 2010-01-20 | 清华大学 | Determination method of horizontal hydraulic load at rotary wheel of water turbine-generator set |
| CN102353516A (en) * | 2011-09-29 | 2012-02-15 | 中国海洋大学 | Method for determining time-domain pulsating drag force of deepwater riser |
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2020
- 2020-01-09 CN CN202010020768.0A patent/CN111175018B/en active Active
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| CN201133321Y (en) * | 2007-12-27 | 2008-10-15 | 东方电机股份有限公司 | Small runner crown exit port mixed flow turbine runner |
| CN100582705C (en) * | 2008-11-21 | 2010-01-20 | 清华大学 | Determination method of horizontal hydraulic load at rotary wheel of water turbine-generator set |
| CN102353516A (en) * | 2011-09-29 | 2012-02-15 | 中国海洋大学 | Method for determining time-domain pulsating drag force of deepwater riser |
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