Disclosure of Invention
The invention aims to solve the problem of low accuracy of a method for determining a cavitation phenomenon at a runner blade by means of visual inspection.
A method for determining cavitation initial position of a runner blade of an axial flow model water turbine comprises the following steps:
s1, starting an axial flow type model water turbine;
s2, adjusting the operation condition of the axial-flow model water turbine to enable the runner blades of the axial-flow model water turbine to be in an uncovitated state;
s3, keeping the operation condition of the axial flow type model water turbine stable, and collecting a runner chamber vibration signal;
s4, calculating the spectral power distribution of the vibration signal of the runner chamber of the axial-flow model water turbine;
s5, determining the energy distribution trend dividing point frequency of the axial flow type model water turbine runner chamber vibration signal spectral power distribution;
s6, representing the energy distribution trend of the axial flow model water turbine runner chamber vibration signal spectral power distribution by using the energy distribution trend dividing point frequency of the axial flow model water turbine runner chamber vibration signal spectral power distribution;
s7, determining axial flow type model water turbine runner chamber vibration signal spectral power distribution
The difference omega of the phase angles of the vibration signal energy change gradients of the runner chambers of the axial flow model water turbines on two sides of the frequency of the energy distribution trend dividing point;
s8, gradually reducing the cavitation coefficient of the axial flow type model water turbine, and repeating the step S3 to the step S7 under different cavitation coefficients until obvious cavitation phenomenon occurs to the runner blade of the axial flow type model water turbine;
s9, determining the cavitation position of the runner blade of the axial flow type model water turbine:
assuming that the cavitation coefficient is changed for m times, the difference between the cavitation coefficient and the phase angle of the vibration signal energy change gradient of the axial flow model water turbine runner chamber on two sides of the corresponding energy distribution trend dividing point frequency is respectively recorded as (sigma) according to the sequence of the cavitation coefficient from large to small 1 ,ω 1 ),(σ 2 ,ω 2 ),…,(σ m ,ω m ) Wherein σ is a cavitation coefficient;
calculating the difference of the phase angles of the vibration signal energy change gradients of the runner chambers of the axial-flow model water turbines on two sides of the energy distribution trend dividing point frequency corresponding to the adjacent cavitation coefficients
When in use
The cavitation phenomenon does not occur on the runner blade of the axial flow model water turbine; when the temperature is higher than the set temperature
When the axial flow model water turbine runner blade is in operation, the axial flow model water turbine runner blade is indicated to have cavitation; when in use
And is
Time, point
The initial position of the axial flow model water turbine runner blade cavitation is obtained.
Further, the energy distribution trend dividing point frequency of the axial flow model turbine runner chamber vibration signal spectral power distribution of S5 is as follows:
in the formula: f. of B : the energy distribution trend dividing point frequency (Hz) of the axial flow model water turbine runner chamber vibration signal spectrum power distribution; f. of T : rotational frequency (Hz) of the axial flow model turbine; z R : the number of the rotating wheel blades of the axial flow model water turbine; z is a linear or branched member G : the number of guide vanes of the axial flow model water turbine; r is the maximum common divisor of the movable guide vane number and the fixed guide vane number of the axial-flow type model water turbine; n: and (4) the coefficient.
Further, the determination process of the coefficient n is as follows:
if the greatest common divisor R =1 of the movable guide vane number and the fixed guide vane number of the axial-flow type model water turbine, taking n as 1.5-1.8; if the greatest common divisor R of the number of the movable guide vanes and the number of the fixed guide vanes of the axial-flow type model water turbine is not equal to 1, n is 4.2-8.6.
Further, in S7, the process of determining the difference between the phase angles of the energy variation gradients of the runner chamber vibration signals of the axial flow model turbine on both sides of the energy distribution trend dividing point frequency of the axial flow model turbine runner chamber vibration signal spectral power distribution includes the following steps:
in the formula: ω: the difference of phase angles of vibration signal energy change gradients of runner chambers of the axial flow model water turbines on two sides of the frequency of an energy distribution trend dividing point;
the left axial flow type model water turbine runner chamber vibration signal energy variation gradient of the energy distribution trend division point frequency is obtained;
right side of energy distribution trend division point frequencyAnd the axial flow model water turbine runner chamber vibration signal energy variation gradient.
Further, the
In the formula:
omega corresponding to adjacent cavitation coefficients
i The difference, i =1,2, \ 8230;, m-1.
Has the advantages that:
the invention provides a concept of an energy distribution trend boundary point of axial flow model water turbine runner chamber vibration signal spectral power distribution representing energy distribution rule change in axial flow model water turbine runner chamber vibration signal spectral power distribution for the first time, and accordingly defines a judgment basis of a phase angle difference of axial flow model water turbine runner chamber vibration signal energy change gradients on two sides of the energy distribution trend boundary point frequency of axial flow model water turbine runner chamber vibration signal spectral power distribution, and provides a method for judging the initial position of an axial flow model water turbine runner blade. The method for determining the axial flow model water turbine runner blade cavitation has the advantages of having a unified quantifiable standard and ensuring the accuracy of determining the axial flow model water turbine runner blade cavitation.
Detailed Description
The first specific implementation way is as follows:
the method for determining the cavitation initial position of the runner blade of the axial flow model water turbine in the embodiment comprises the following steps of:
1. starting the axial flow type model water turbine;
2. adjusting the operation condition of the axial flow type model water turbine to enable the runner blades of the axial flow type model water turbine to be in an uncovitalized state;
3. keeping the operation condition of the axial flow model water turbine stable, and collecting a runner chamber vibration signal;
4. calculating the spectral power distribution of the vibration signal of the runner chamber of the axial-flow model water turbine;
5. determining the energy distribution trend dividing point frequency of the axial flow type model water turbine runner chamber vibration signal spectrum power distribution;
the frequency of the energy distribution trend dividing point of the axial flow type model water turbine runner chamber vibration signal spectrum power distribution is calculated according to the following formula:
in the formula: f. of B : the energy distribution trend dividing point frequency (Hz) of the axial flow model water turbine runner chamber vibration signal spectrum power distribution; f. of T : rotational frequency (Hz) of the axial flow model turbine; z R : the number of the rotating wheel blades of the axial flow model water turbine; z G : the number of guide vanes of the axial flow model water turbine; r is the maximum common divisor of the movable guide vane number and the fixed guide vane number of the axial-flow type model water turbine; n: the coefficient generally has a value range of: if R =1, n is 1.5-1.8; if R is not equal to 1, n is 4.2-8.6;
6. representing the energy distribution trend of the axial flow model water turbine runner chamber vibration signal spectral power distribution by using the energy distribution trend dividing point frequency of the axial flow model water turbine runner chamber vibration signal spectral power distribution;
in the power distribution of the vibration signal spectrum of the runner chamber of the axial-flow model water turbine, the variation trend of energy is continuous, the low-frequency region shows the trend of the steep drop of the energy value along with the rise of the frequency of the vibration signal of the runner chamber, the amplitude of the energy value in the high-frequency region, which is reduced along with the rise of the frequency of the vibration signal of the runner chamber, is much smaller, an obvious boundary point exists between the low-frequency region and the high-frequency region, and the boundary point is the frequency of the energy distribution trend boundary point of the power distribution of the vibration signal spectrum of the runner chamber of the axial-flow model water turbine;
7. determining the difference of phase angles of vibration signal energy change gradients of the runner chambers of the axial-flow model water turbines on two sides of the energy distribution trend dividing point frequency of the vibration signal spectrum power distribution of the runner chambers of the axial-flow model water turbines; the method specifically comprises the following steps:
in the formula: ω: the difference of phase angles of vibration signal energy change gradients of runner chambers of the axial flow model water turbines on two sides of the frequency of an energy distribution trend dividing point;
the left axial flow type model water turbine runner chamber vibration signal energy variation gradient of the energy distribution trend division point frequency is obtained;
the energy variation gradient of the vibration signal of the runner chamber of the axial-flow model water turbine on the right side of the frequency of the energy distribution trend division point is obtained;
8. acquiring axial flow model water turbine runner chamber vibration signals under different cavitation coefficients:
gradually reducing the cavitation coefficient of the axial flow type model water turbine, and repeating the step 3 to the step 7 under different cavitation coefficients until the impeller blade of the axial flow type model water turbine generates obvious cavitation;
9. determining the cavitation position of the runner blade of the axial-flow model water turbine:
assuming that the cavitation coefficient is changed for m times, the difference between the cavitation coefficient and the phase angle of the vibration signal energy change gradient of the axial flow model water turbine runner chamber on two sides of the corresponding energy distribution trend dividing point frequency is respectively marked as (sigma) according to the sequence of the cavitation coefficient from large to small 1 ,ω 1 ),(σ 2 ,ω 2 ),…,(σ m ,ω m ) And sigma is a cavitation coefficient, and the difference of phase angles of vibration signal energy change gradients of the runner chambers of the axial flow model water turbines on two sides of the energy distribution trend dividing point frequency corresponding to the adjacent cavitation coefficients is calculated as follows:
in the formula:
omega corresponding to adjacent cavitation coefficients
i The difference, i =1,2, \8230, m-1;
when in use
The cavitation phenomenon does not occur on the runner blade of the axial flow model water turbine; when the temperature is higher than the set temperature
When the cavitation phenomenon occurs, the cavitation phenomenon occurs on the runner blade of the axial flow type model water turbine; when the temperature is higher than the set temperature
And is
Time, point
Namely the initial position of the axial flow model water turbine runner blade cavitation;
10. and closing the axial flow model water turbine.
The invention provides a concept of an energy distribution trend boundary point of axial flow model water turbine runner chamber vibration signal spectral power distribution representing the change of an energy distribution rule in axial flow model water turbine runner chamber vibration signal spectral power distribution for the first time, and accordingly defines a judgment basis of a difference of phase angles of axial flow model water turbine runner chamber vibration signal energy change gradients on two sides of the energy distribution trend boundary point frequency of axial flow model water turbine runner chamber vibration signal spectral power distribution, and accordingly provides a method for judging the initial position of an axial flow model water turbine runner blade. Through repeated experimental research on the axial-flow model water turbine, the change trend of the phase angle difference along with the cavitation coefficient of the vibration signal energy change gradient of the axial-flow model water turbine runner chamber on two sides of the energy distribution trend boundary point frequency of the axial-flow model water turbine runner chamber vibration signal spectrum power distribution representing the energy distribution change rule in the axial-flow model water turbine runner chamber vibration signal spectrum power distribution for determining the initial position of the axial-flow model water turbine runner blade cavitation occurrence is firstly found in the whole world, as shown in fig. 1. By using the characteristic that the initial occurrence position (point 1) of the axial flow model water turbine runner blade cavitation reflected in the graph 1 is the maximum value of the phase angle difference of the energy variation gradient of the axial flow model water turbine runner chamber vibration signal energy on two sides of the energy distribution trend dividing point frequency of the axial flow model water turbine runner chamber vibration signal spectral power distribution, the occurrence position of the axial flow model water turbine runner blade cavitation can be very accurately determined. Meanwhile, the difference of the phase angles of the vibration signal energy variation gradients of the runner chambers of the axial-flow model water turbine on the two sides of the energy distribution trend boundary point frequency of the vibration signal spectral power distribution of the runner chambers of the axial-flow model water turbine on the left and right sides of the point 1 where the initial cavitation occurs on the runner blades of the axial-flow model water turbine is monotonously changed along with the change of the cavitation coefficient, namely, the difference of the phase angles of the vibration signal energy variation gradients of the runner chambers of the axial-flow model water turbine on the two sides of the energy distribution trend boundary point frequency of the vibration signal spectral power distribution of the runner chambers of the axial-flow model water turbine on the right side of the point 1 shows a trend rising along with the reduction of the cavitation coefficient; on the left side of the point 1, under the condition that the runner blades of the axial flow model water turbine are cavitated, the difference of phase angles of the vibration signal energy change gradients of the runner chambers of the axial flow model water turbine on two sides of the division point frequency of the energy distribution trend of the vibration signal spectral power distribution of the runner chambers of the axial flow model water turbine presents a trend of being reduced along with the reduction of cavitation coefficients.
The method requires the axial-flow model water turbine to respectively acquire the vibration signals of the runner chamber of the axial-flow model water turbine under different cavitation coefficients in the interval from non-cavitation to severe cavitation. And calculating the difference of phase angles of vibration signal energy change gradients of the runner chambers of the axial-flow model water turbine on two sides of the energy distribution trend dividing point frequency of the vibration signal spectral power distribution of the runner chambers of the axial-flow model water turbine, which represents the energy distribution rule in the vibration signal spectral power distribution of the runner chambers of the axial-flow model water turbine after acquisition. Generally, the difference of phase angles of vibration signal energy change gradients of the runner chambers of the axial flow model water turbine on two sides of an energy distribution trend dividing point frequency of vibration signal spectral power distribution of the runner chambers of the axial flow model water turbine representing an energy distribution law in vibration signal spectral power distribution of the runner chambers of the axial flow model water turbine shows a trend which changes along with a cavitation coefficient monotonously on the left and right sides of a point 1 where initial cavitation of runner blades of the axial flow model water turbine occurs: on the right side of the point 1, the difference of phase angles of vibration signal energy change gradients of the runner chambers of the axial-flow model water turbines on two sides of the dividing point frequency of the energy distribution trend of the vibration signal spectral power distribution of the runner chambers of the axial-flow model water turbines shows a trend of rising along with the reduction of the cavitation coefficient; on the left side of the point 1, the difference of phase angles of the energy change gradients of the axial flow model turbine runner chamber vibration signal energy on two sides of the dividing point frequency of the energy distribution trend of the axial flow model turbine runner chamber vibration signal spectral power distribution shows a trend of decreasing with the decrease of the cavitation coefficient. Therefore, the position of the model water turbine runner blade cavitation can be determined as long as the maximum value of the curve that the difference of the phase angles of the vibration signal energy change gradients of the axial flow model water turbine runner chamber on two sides of the energy distribution trend dividing point frequency of the axial flow model water turbine runner chamber vibration signal spectral power distribution representing the energy distribution rule in the axial flow model water turbine runner chamber vibration signal spectral power distribution is along with the change of the cavitation coefficient can be found.
The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it is therefore intended that all such changes and modifications be considered as within the spirit and scope of the appended claims.