JP3132841B2 - Adjustment of the natural frequency of the disk of the radiation impeller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting a natural frequency of a double-disc disk comprising a back and a front disk of a pump-turbine runner so as to be away from an excitation frequency.

[0002]

2. Description of the Related Art In a pumped storage power plant, a so-called pump turbine is widely used, which generates power as a water turbine at the time of falling water and reverses the power at the time of pumping to be used as a pump.

FIG. 1 shows an example of the shape of a runner of a Francis type pump-turbine. First, the basic dimensions of the runner 1, such as the entrance / exit diameter, the entrance / exit width, and the number of blades, are determined based on the design points of the pump turbine. Next, dynamic and static strength calculations are performed in consideration of the number of revolutions, materials, results, and the like, and the thickness of each part such as the crown (back disc) 2 and the band (front disc) 3 of the runner 1 is calculated. Is determined. If the shape of the runner is determined, the natural vibration of the runner 1 is also determined. The number of blades of the runner defines a vibration mode to be excited by a combination with the number of blades of guide vanes provided outside the runner when used as a water wheel.

[0004]

However, recent pump-turbines have been designed to have a high head, a large capacity, and a high speed in order to improve the economical efficiency. Therefore, the energy density acting on the runner has been increased. And vibration due to fluctuations in water pressure has become a problem. In particular, as for the runner, which is the main component, the vibration frequency has increased due to the increase in speed, whereas the specific speed of the runner has decreased due to the high drop, and the shape of the runner has been flattened. The rise in the natural frequency of the disk is relatively low.

In a conventional machine of less than 400 m class, this natural frequency is in a region higher than the vibration frequency, so the vibration frequency is given by the product of the rotation speed of the pump turbine and the number of blades of the guide heane. The resonance phenomenon between the disk and the natural frequency given by the required wall thickness determined from the strength aspect of the runner did not occur, but as described above, the runner was increased due to the higher head and the higher speed of the pump turbine. Since the rate of increase of the natural frequency of the disk is smaller than the rate of increase of the excitation frequency, these frequencies have come close to each other, and a resonance phenomenon has appeared.

The present invention has been made in view of the above circumstances, and has as its object to provide an adjustment method for changing the natural frequency of a runner in order to avoid resonance with an excitation frequency.

In order to achieve the above object, according to the present invention, adjustment of primary and secondary natural frequencies for changing the overall wall thickness of a crown and a band of a pump-turbine runner, and a wall only for an outer peripheral portion of the crown and a band. the thickness combination of the primary and secondary solid <br/> chromatic frequency adjustments changing, so separating the primary and secondary natural frequency of the disc of the radial flow impeller from excitation frequency by both adjustment Thus, there is provided a method for adjusting a natural frequency of a disk of a radiation impeller.

[0008]

In the adjustment for changing the overall wall thickness of the crown and the band of the pump turbine runner, the natural frequency can be increased by increasing the wall thickness and decreased by decreasing the wall thickness. In the adjustment for changing the thickness of only the outer periphery of the crown and the band, the natural frequency can be reduced or increased by increasing or decreasing the thickness. By designing these adjustments in combination, the natural frequency is changed to be higher above the excitation frequency and lower below the excitation frequency without compromising the runner strength.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for adjusting the natural frequency of a disk of a radiation impeller according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows an adjustment for changing the entire thickness of the crown and the band of the pump-turbine runner, and FIG. 2 shows an adjustment for changing the thickness of only the outer peripheral portions of the crown and the band. In the runner 1 shown in these figures, the crown (rear disk) 2, the band (front disk) 3, and the runner blades 4 are integrally formed of cast steel or stainless steel.

The blade thickness t _V of the pump-turbine runner needs to be sufficiently thick to withstand the stress generated by the centrifugal force. On the basis of this thickness, conventionally, the crown 2 and the band 3 have almost the same thickness. It is thick. Here, if the natural frequency predicted in the state determined as described above is close to the excitation frequency, a resonance phenomenon may occur. In such a case, the natural frequency is separated from the excitation frequency. Adjust as follows. One of them is the method shown in FIG.

According to the method of changing the natural frequency shown in FIG. 1, the crown 2 and the band 3
The natural frequency can be adjusted in the direction of increasing the natural frequency by increasing the thickness of the crown 2, and conversely, the natural frequency can be reduced by reducing the thickness of the crown 2 and the band 3 as indicated by the two-dot chain line. Can be adjusted in any direction.

FIG. 3 shows the change rate of the natural frequency with respect to the change rate of the thickness t _C of the crown 2 and the change rate of the thickness t _B of the band 3. According to FIG. 3, the change rate of the natural frequency with respect to the change rate of the thickness of the crown 2 and the band 3 is 1
The second order is larger than the second order.

The adjustment method shown in FIG. 2 utilizes the characteristics of the vibration mode of the disk natural frequency. That is, regarding the vibration mode of the natural frequency of the disk, the lower-order mode is the crown 2
The band 3 is a mode in which the entire band swings, and the higher mode adjusts the natural frequency by utilizing the mode in which the outer peripheral portion swings locally.

For example, D is the diameter of the disk, δ is the crown 2
Assuming that the change length of the thickness at the outer peripheral portion of the band 3 is to be changed, the thickness of the outer peripheral portion is changed in the range of the outer peripheral portion δ / (D / 2) ≦ 0.1 to 0.2. When the wall thickness is increased, the effect of the additional mass is obtained for the low-order natural frequency, the frequency is reduced, and for the high-order mode, the rigidity is enhanced, and the frequency is increased. If the thickness is reduced, the frequency increases in the low-order mode and decreases in the high-order mode. FIG. 4 shows the relationship between the change rate of the natural frequency and the change rate of the outer peripheral plate thickness t _{Ct of the} crown 2 and the outer peripheral plate thickness t _Bt of the band 3.

FIGS. 5 and 6 show an outer peripheral portion δ / (D / 2) ≦
In the range of 0.1 to 0.2, an example is shown in which a portion of the outer peripheral portion of the crown 2 and the band 3 which has the effect of the added mass is obliquely cut to increase the natural frequency. In this case, the primary and secondary natural frequencies both have characteristics that change in the same direction.

By combining the above adjustment methods, it is possible to arbitrarily change the natural frequencies of all the discs and separate them from the excitation frequencies. That is, as shown in FIG.
The primary frequency is lower and the secondary frequency can be changed to a higher frequency.

The amount of change in the thickness of each part differs each time depending on the degree of avoidance of the natural frequency and the excitation frequency which are determined as a result. The degree of avoidance between the natural frequency and the excitation frequency is set such that the resonance point at the primary and secondary frequencies of the natural frequency is ± 10% from the excitation frequency from the viewpoint of setting the stress at resonance to 以下 or less. %.

[0019]

According to the present invention, the vibration frequency is multiplied.
Since the natural frequency of the number can be changed by design actions , not only can resonance be avoided, but also
Operating point (excitation frequency) by separating the next natural frequency
It is important to further reduce the vibration of the pump turbine to improve the reliability of the pump turbine runner.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an adjustment method according to the present invention.

FIG. 2 is an explanatory diagram showing an adjustment method according to the present invention.

FIG. 3 is a diagram showing a change rate of a natural frequency with respect to a change rate of a wall thickness of a crown and a band of a pump turbine runner.

FIG. 4 is a diagram showing a change rate of a natural frequency with respect to a change rate of a wall thickness of a crown and a band of a pump-turbine runner.

FIG. 5 is an explanatory view in the case of adjusting the outer periphery of a crown and a band by cutting.

FIG. 6 is a diagram showing a change rate of a natural frequency in a case where an outer peripheral portion of a crown and a band is cut and adjusted.

FIG. 7 is a diagram showing the effect of the adjustment method of the present invention.

[Explanation of symbols]

 1 Runner 2 Crown (back disc) 3 Band (front disc)

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor, Sumihiro Iwasaki 2-1-1, Shinhama, Arai-machi, Takasago-shi, Hyogo Mitsubishi Heavy Industries, Ltd. Inside Takasago Works (56) References JP-A-57-195874 (JP, A)

Claims (1)

(57) [Claims] 1. A primary varying order 1 changing the thickness entire pump-turbine runner crown and band and a secondary natural frequency of adjusting the thickness of the outer peripheral portion only of the crown and band
And the adjustment of the secondary natural frequency, and by adjusting both, the primary and secondary natural frequencies of the disk of the radiation impeller are separated from the excitation frequency. How to adjust the natural frequency.