CN-121980989-A - Method for determining pressure pulsation in no-leaf area of steady-state working condition of variable-speed water pump turbine

Abstract

The invention provides a method for determining pressure pulsation in a no-leaf area of a steady-state working condition of a variable-speed water pump water turbine, which comprises the following steps of S1, determining working condition points and boundary conditions; S2, calculating pressure pulsation, S3, carrying out dimensionless treatment on the pressure pulsation, S4, extracting amplitude corresponding to the passing frequency of the blade, and S5, carrying out conversion fitting on the amplitude corresponding to the passing frequency of the blade. Under a certain opening degree, the pressure pulsation (including rated rotation speed) under five rotation speed working conditions is calculated, then according to a fitted curve, the amplitude of the steady-state operation working condition pressure pulsation of the water turbine under the passing frequency of the blade can be predicted, calculation of each working condition is not needed, multiple tests are not needed, calculation resources and test cost are saved, the efficiency of the working point corresponding to the rated rotation speed is highest in a variable speed range under the same opening degree condition of each working condition point, the pressure pulsation is almost minimum, the working condition pressure pulsation after the rotation speed is changed is increased, and the working condition of the pressure pulsation increase can be well predicted.

Inventors

• YANG ZHIYAN
• ZHANG BAOYONG
• LI CHENGJUN
• FANG JIE
• CAO CHUNJIAN

Assignees

• 中国电建集团华东勘测设计研究院有限公司

Dates

Publication Date

20260505

Application Date

20251223

Claims (6)

1. 1. A method for determining pressure pulsation in a no-leaf area of a steady-state working condition of a variable-speed water pump turbine is characterized by comprising the following steps: S1, determining working condition points and boundary conditions, namely establishing a three-dimensional calculation area for a water pump turbine unit section, setting a volute inlet and a draft tube outlet as pressure boundary conditions, setting a rotating speed direction as a water turbine direction, and taking different values including rated rotating speeds; S2, pressure pulsation calculation, namely setting pressure pulsation monitoring points in a bladeless area, adopting a Steady method to calculate a Steady-state working condition, taking a flow field after calculation stabilization as an initial working condition of a Transient method, and finally calculating and outputting pressure pulsation data of the bladeless area under the Transient method; s3, pressure pulsation dimensionless treatment, namely respectively selecting pressure pulsation data which show stable trend or periodic fluctuation in each working condition to carry out dimensionless treatment; s4, extracting corresponding amplitude values of the blade passing frequency, namely performing fast Fourier transform on the pressure pulsation after dimensionless operation under each working condition to obtain corresponding amplitude values of the blade passing frequency under each working condition; S5, carrying out amplitude transformation fitting on the blade passing frequency, namely selecting a relative rated rotation speed value as an abscissa in a plane coordinate system, taking the logarithm of the amplitude corresponding to the blade passing frequency under each working condition, and taking the logarithm as an ordinate to transform a fitting curve.
2. 2. The method according to claim 1, wherein the step S1 comprises the steps of: S11, selecting an opening line on a four-quadrant characteristic curve plane of the water pump turbine, and reading an n 11 value corresponding to an optimal efficiency point on the opening line; s12, according to the formula Setting n as a rated rotation speed, and calculating a corresponding water head H according to the existing diameter D of the rotating wheel, wherein the highest efficiency is shown under the working conditions that the water head is H and the rotation speed is 1.00n r ; S13, selecting a volute inlet total water head H 1 and a draft tube outlet total water head H 2 to enable H 1 -H 2 to be larger than H, namely considering the flow loss of the extension tube section under the condition that the water purifying head is H; S14, the rotation speed value is 0.90n r 、0.95n r 、1.00n r 、1.05n r 、1.10n r ,n r and is the rated rotation speed, and the rest conditions are kept unchanged.
3. 3. The method of claim 1, wherein the rotor rotation angle is no more than 1 ° per time step in the Transient method in step S2.
4. 4. The method of claim 1, wherein in step S3, the pressure pulsation data p in each working condition 1S with stable trend or periodic fluctuation is subjected to low-frequency filtering to obtain low-frequency data p ave , the peripheral speed v of the blade edge of the rotating wheel is obtained according to the rotating speed and the rotating wheel diameter, and the dimensionless pressure pulsation Cp is calculated as shown in the following formula: Cp=0.5*(p-p ave )/(ρv 2 ); Where ρ is the density of water.
5. 5. The method of claim 1, wherein in step S4, the method is characterized in that the non-dimensionalized pressure pulsation Cp is subjected to fast Fourier transform to obtain the amplitude corresponding to the blade passing frequency mf n in each working condition, and the blade passing frequency is calculated as follows: mf n ＝m*n 0 /60 Wherein m is the number of the rotating wheel blades, n 0 is the rotating speed, and the unit is r/min.
6. 6. The method according to claim 1, wherein the step S5 comprises the steps of: S51, taking ln logarithms of amplitudes a 0.90 ,a 0.95 ,a 1.00 ,a 1.05 ,a 1.10 corresponding to the passing frequency mf n of the blade under five working conditions with the rotating speed of 0.90n r 、0.95n r 、1.00n r 、1.05n r 、1.10n r to obtain A 0.90 ＝lna 0.90 ,A 0.95 ＝lna 0.95 ,A 1.00 ＝lna 1.00 ,A 1.05 ＝lna 1.05 ,A 1.10 ＝lna 1.10 ; S52, taking a value A in five working conditions as an ordinate, taking a relative rated rotation speed value as an abscissa, making a curve, taking A 1.00 as a symmetry center, making downward symmetrical transformation on A 0.90 ,A 0.95 , and performing linear fitting to obtain a final linear function result; And S53, obtaining an A value at any rotating speed according to the fitted function result.

Description

Method for determining pressure pulsation in no-leaf area of steady-state working condition of variable-speed water pump turbine Technical Field The invention belongs to the technical field of hydraulic machinery, and particularly relates to a method for determining pressure pulsation in a bladeless area of a steady-state working condition of a variable-speed water pump water turbine. Background With the rapid development of renewable energy sources, the demand for the stability of the power grid is also increasing, and pumped storage power stations become the safest stable regulator in the power grid due to their flexible regulation function and complementarity with renewable energy sources. The pumped storage power station has the characteristics of various running conditions and frequent condition conversion, and the core component of the pumped storage power station is difficult to maintain the optimal efficiency of a water pump turbine. When the working point is operated under the non-design condition, the internal flow state of the water pump turbine is complex, and the pressure pulsation is large, which can lead to the vibration of the unit. The existing water pump turbine pressure pulsation research is mainly concentrated on different positions in a unit, including a vaneless area, a vane passage and a draft tube, and the pressure pulsation characteristic is obtained qualitatively or quantitatively through an experimental method and a three-dimensional numerical simulation method. In order to further improve the operation efficiency of the unit under the non-design condition, reduce the dynamic load and reduce the pressure pulsation, the variable-speed water pump turbine becomes a hot research topic. It should be noted that the design theory of variable speed pump turbines is still based on the fixed speed unit theory, and further considers many other factors such as the variation range of the rotational speed, the lift and the power demand. Therefore, the research method of the constant speed unit is also of great significance to the speed change unit. The existing statistical and predictive research methods for the pressure pulsation of the vaneless area are less, the water pump turbine is generally tested through a model test in the design stage, and the pressure pulsation amplitude of all working conditions needing to be concerned is ensured to be controlled within a certain numerical range. In addition, there is also a method of counting pressure pulsation by extracting the corresponding amplitude of the characteristic frequency, as in document (Hu Jinhong. Water pump turbine S characteristics and pressure pulsation control study [ D ]. University of Wuhan, 2021.). However, the methods have great workload on one hand, concentrate on a constant speed unit on the other hand, and have little research on statistical prediction of pressure pulsation under certain opening degree and different rotating speeds of a speed unit. The existing method for counting pressure pulsation of steady-state working conditions of a water pump turbine is to obtain amplitude corresponding to passing frequency of blades by carrying out frequency domain analysis on pressure pulsation at a measuring point of a no-blade area in each working condition, taking logarithm of the amplitude, and then carrying out linear fitting on unit rotating speed of each working condition and the logarithm of the amplitude to obtain an approximate linear rule. The following disadvantages still exist: 1) In the prior researches, the rotation speed is fixed, the opening degree of the guide vane is changed, and the water head is changed, so that different characteristics are obtained by changing the opening degree of the guide vane at the fixed rotation speed. The existing method only obtains the characteristics under different guide vane opening degrees, but the characteristics under different rotating speeds are required to be obtained for the variable speed water pump turbine; 2) In the existing research, because the rotating speed is fixed, when the pressure pulsation is dimensionless, only the water head effect can be considered, and the influence of the rotating speed cannot be considered; 3) The jump of the working point is large in the existing research, and the curve fitting cannot be completely linearly approximated. Disclosure of Invention The main purpose of the invention is to provide a method for determining the pressure pulsation of the no-leaf area of the steady-state working condition of the variable-speed water pump water turbine aiming at the problems. For this purpose, the above object of the present invention is achieved by the following technical solutions: a method for determining pressure pulsation in a bladeless area of a steady-state working condition of a variable-speed water pump turbine comprises the following steps: S1, determining working condition points and boundary conditions, namely establishing a three-dimens