CN113586312A - Top cover inner cavity design method for reducing vertical vibration hazard of top cover of water turbine - Google Patents
Top cover inner cavity design method for reducing vertical vibration hazard of top cover of water turbine Download PDFInfo
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- CN113586312A CN113586312A CN202111047003.7A CN202111047003A CN113586312A CN 113586312 A CN113586312 A CN 113586312A CN 202111047003 A CN202111047003 A CN 202111047003A CN 113586312 A CN113586312 A CN 113586312A
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- top cover
- water
- vertical vibration
- inner cavity
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
- F03B—MACHINES OR ENGINES FOR LIQUIDS
- F03B11/00—Parts or details not provided for in, or of interest apart from, the preceding groups, e.g. wear-protection couplings, between turbine and generator
- F03B11/04—Parts or details not provided for in, or of interest apart from, the preceding groups, e.g. wear-protection couplings, between turbine and generator for diminishing cavitation or vibration, e.g. balancing
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/20—Hydro energy
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Hydraulic Turbines (AREA)
Abstract
The invention discloses a top cover inner cavity design method for reducing vertical vibration hazard of a top cover of a water turbine, which comprises the following steps: increasing the distance between the top cover and the crown of the rotating wheel so as to reduce the flow velocity gradient between each layer of the water body between the static top cover and the rotating wheel and increase the thickness of the water layer; the rib plates on the lower end surface of the top cover and the outer end surface of the upper part of the rotating wheel and all devices causing unevenness are eliminated, so that the upper surface and the lower surface of the cavity space of the top cover are kept flat and smooth; the bulge that can't eliminate adds and shelters from, avoids sheltering from the stirring of internals to rivers through sheltering from to reduce the interior rivers velocity of flow of intermediate layer, and then alleviate top cap vertical oscillation. The design method of the top cover inner cavity for reducing the vertical vibration hazard of the top cover of the water turbine reduces the flow velocity between the top cover and the crown of the runner, reduces the desludging vortex and the water flow cavitation, and reduces or even eliminates the cavitation cavity, thereby reducing the amplification effect of the cavitation cavity on the pressure pulsation and reducing the vertical vibration hazard of the top cover.
Description
Technical Field
The invention relates to the technical field of hydraulic machinery, in particular to a top cover inner cavity design method for reducing vertical vibration hazards of top covers of a mixed-flow water turbine and a mixed-flow reversible water pump water turbine.
Background
The hydraulic mechanical equipment such as the mixed-flow water turbine, the mixed-flow reversible pump water turbine and the like often encounters severe hydraulic vibration which is mainly characterized in that the vertical vibration of the top cover is severe and the noise is severe and exceeds the standard. The vibration of the units can cause the strong vibration of the plant, even cause the cracking of walls or floors in serious conditions, and bring great threat to the safe and stable operation of the power station.
Disclosure of Invention
The invention aims to provide a top cover inner cavity design method for reducing vertical vibration damage of a top cover of a water turbine, which is used for reducing the violent vibration of the top cover of a mixed flow water turbine and a mixed flow reversible pump water turbine in the operation process.
The invention provides a top cover inner cavity design method for reducing vertical vibration hazard of a top cover of a water turbine, wherein the water turbine comprises a mixed flow water turbine and a mixed flow reversible pump water turbine, and the design method comprises the following steps:
increasing the distance between the top cover and the crown of the rotating wheel so as to reduce the flow velocity gradient between each layer of the water body between the static top cover and the rotating wheel and increase the thickness of the water layer;
the rib plates and other bulges on the surface of the lower end surface of the top cover and the outer end surface of the upper part of the rotating wheel are eliminated, so that the upper surface and the lower surface of the inner cavity space of the top cover are kept smooth;
the bulge which can not be eliminated is additionally provided with the shielding part, and the shielding part is prevented from stirring water flow through shielding, so that the flow velocity of the water flow in the interlayer is reduced, the desludging vortex is reduced, the water flow cavitation is reduced or even eliminated, and the vertical vibration of the top cover is reduced.
Specifically, the minimum value of the distance between the top cover and the runner crown is not less than 50 mm-150 mm, and the distance between the top cover and the runner crown is not more than 200 mm.
More specifically, when the francis turbine or the francis turbine is selected as a large unit, the minimum value of the distance between the head cover and the runner crown is 150mm, and when the francis turbine or the francis turbine is selected as a small unit, the minimum value of the distance between the head cover and the runner crown is 50 mm.
Compared with the prior art, the invention has the beneficial effects that:
the invention discloses a top cover inner cavity design method for reducing vertical vibration hazard of a top cover of a water turbine, which comprises a mixed flow water turbine and a mixed flow reversible water pump water turbine, is designed according to the principle of the cavitation cavity on pressure pulsation amplification, and is equivalent to the fact that an amplifier capable of amplifying pressure pulsation amplitude is removed, namely the cavitation cavity is removed, so that the vertical vibration of the top cover can be greatly reduced. The top cover inner cavity design method for reducing the vertical vibration hazard of the top cover of the water turbine, disclosed by the invention, is simple and clear to operate, only needs to design the structural member in the top cover inner cavity space perfectly, saves money and labor and is easy to realize.
Detailed Description
The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
The research finds that the vertical vibration of the unit such as a mixed-flow water turbine and a mixed-flow reversible pump turbine is not greatly related to the conventional problems of hydraulic imbalance, electromagnetic imbalance and mechanical imbalance such as the pressure pulsation of an eccentric vortex band, the static imbalance and the dynamic imbalance of a water turbine generator set, and the substantial reason is the additional pressure pulsation derived from the expansion-contraction cycle of cavitation cavities such as a blade vortex and a large-load drum vortex. The cavitation pressure was very low (2339 Pa absolute cavitation at 20 ℃ C.) and very close to 0Pa absolute. In the low pressure range near 0Pa, pressure changes of less than 2.5kPa (from 0Pa to 2340Pa absolute) may cause the body of water to undergo a phase transition from liquid to gas, from gas to liquid. Particularly, when the liquid state is changed from the gas state to the liquid state, the cavitation cavity (hereinafter referred to as the "cavitation cavity") formed by the cavitation bubble group originally occupies a certain space, and when the liquid state is instantly changed from the gas state of water vapor to the liquid state water, the occupied space is greatly reduced, and the change is close to the change from the existence to the nonexistence, and a large amount of vacated space can be occupied by the surrounding water body. The converging bodies of water produce large impact forces and thus derive the new pressure pulsations. The pressure pulsation propagates around in a compressional wave (longitudinal wave) mode, can enter an inner cavity space (hereinafter referred to as a top cover inner cavity) between the top cover and the top cover through a sealing gap between the outer edge of the top cover of the runner and the top cover, propagates and applies the pressure pulsation to the lower end surface of the inner side of the top cover to cause vertical vibration of the top cover, and further propagates the vibration to other structures of the unit and plants.
In fact, the density wave will be attenuated continuously in the process of propagation, and especially some pressure waves formed at the water outlet side of the runner are propagated from the low-pressure side to the high-pressure side, so that the power of the pressure waves is greatly reduced. If the space under the roof is completely filled with water, too strong vibration is not usually caused. However, if the water body in the space generates cavitation due to high flow velocity, the cavitation cavity generates much violent pressure pulsation under the influence of the pressure pulsation transmitted to the space, and the vibration is greatly amplified. When the low pressure of the pressure pulsation is transmitted into the inner cavity space of the top cover, the cavitated cavity group is further expanded, the volume of the cavitated cavity is increased, and downward suction or pulling force is applied to the top cover; when pressure waves are transmitted under high pressure, the cavitation cavity is contracted, the volume of the cavity is greatly reduced and even is completely collapsed, and the water body quickly rushes into the inner cavity of the top cover and applies upward huge impulsive force to the top cover. The larger the volume of the cavitation cavity, the greater the impact force generated when the cavity collapses, and the greater the amplification of the aforementioned derivative pressure pulsations. This cyclic motion produces a strong, amplified periodic strong vertical vibration.
Therefore, if the flow velocity of the water flow in the inner cavity of the top cover is reduced to avoid cavitation, the transmitted pressure pulsation cannot be amplified due to the existence of the cavitation cavity, and the vertical vibration caused by the cavitation cavity is greatly reduced. In order to reduce the speed of water flow existing in an interlayer space above the lower part of a top cover and the upper crown of a rotating wheel, the design of increasing the distance between the top cover and the upper crown of the rotating wheel, canceling rib plates on the lower end surface of the top cover and the outer end surface of the upper part of the rotating wheel and all devices which can cause unevenness, improving surface finish and the like is provided, so that the loss of a rotating disc caused by the rotation of the rotating wheel is reduced, the flow rate of water rotating along with the rotating wheel is reduced, the effect of increasing the pressure in the top cover is achieved, the cavitation of the water in the top cover is reduced or even eliminated, namely an amplifier for amplifying pressure pulsation is removed, and the vertical vibration of the top cover and other devices can be greatly reduced.
Example 1
Embodiment 1 provides a method for designing a top cover inner cavity for reducing vertical vibration hazard of a top cover of a water turbine, where the water turbine includes a francis turbine and a francis reversible pump turbine, and the method includes:
the first measure is as follows: the distance between the top cover and the crown of the rotating wheel is increased so as to reduce the flow velocity gradient between each layer of the water body between the static top cover and the rotating wheel and increase the thickness of the water layer.
Specifically, the minimum value of the distance between the top cover and the runner crown is not less than 50 mm-150 mm, wherein the minimum value of the distance between the top cover and the runner crown is determined according to the selected water turbine, when the selected francis turbine or francis turbine is a large unit, the minimum value of the distance between the top cover and the runner crown is 150mm, and when the selected francis turbine or francis turbine is a small unit, the minimum value of the distance between the top cover and the runner crown is 50 mm. However, no matter the selected water turbine is a large unit or a small unit, the distance between the top cover and the runner crown does not exceed 200 mm.
The flow velocity gradient between each layer of the water body between the static top cover and the rotating runner is reduced, so that the flow shedding is reduced, and the water flow cavitation is reduced; the thickness of the water layer is increased, even if the lower layer is cavitated, the non-cavitated water body on the upper layer still keeps liquid state, and the liquid on the layer can generate certain buffer effect on the impact water flow when the cavitation cavity is collapsed.
And step two: the rib plates and other bulges on the surface of the lower end surface of the top cover and the outer end surface of the upper part of the rotating wheel are eliminated, so that the upper surface and the lower surface of the inner cavity space of the top cover are kept smooth;
specifically, the surface other protrusions include bolts, pipelines and the like, and the embodiments of eliminating the surface other protrusions on the lower end surface of the top cover and the upper part of the rotating wheel are as follows: the outcrop bolt is changed into the countersunk bolt, and the exposed installation of the pipeline is changed into the concealed installation.
Wherein, the upper and lower two surfaces in top cap inner chamber space keep level and smooth, help reducing the rivers along with the runner rotational speed, increase rivers pressure, alleviate or avoid the water cavitation, alleviate or eliminate the amplification effect to transmitting pressure pulsation.
Taking the third step: the bulge which can not be eliminated is additionally provided with the shielding part, and the shielding part is prevented from stirring water flow through shielding, so that the flow velocity of the water flow in the interlayer is reduced, the desludging vortex is reduced, the water flow cavitation is reduced or even eliminated, and the vertical vibration of the top cover is reduced.
Specifically, the non-removable protrusions include exposed bolts, pipes, and ribs.
Research results show that cavitation cavities of cavitation groups generated after water body cavitation have the following effects and influences in pressure pulsation propagation: (1) the pressure pulsation amplitude can be amplified, the low-pressure part of the transmitted pressure pulsation can expand the cavitation cavity, the high-pressure part can contract and even collapse the cavitation cavity, the expansion-contraction of the cavitation cavity can cause the leaving-gathering movement of surrounding water bodies to the cavitation cavity, the collapse of the cavity can also cause the collision of water bodies on two sides, and huge impact force is generated on the top cover. (2) The larger the cavitation cavity volume, the greater its amplification of the pressure pulsations. (3) The high-speed water flow in the inner cavity space of the top cover is mainly concentrated at the outer edge, and the cavitation cavity is also concentrated in the outer ring space; when the cavitation cavity is contracted or collapsed under high pressure, a large amount of water passes through the labyrinth gaps at the outer edge of the rotating wheel to 'rush' towards the cavitation cavity, and an upward impact force is applied to the top cover to cause the top cover to vibrate vertically.
Therefore, the cavitation of the water flow in the inner cavity of the top cover can be reduced or even eliminated as long as measures are taken to reduce the flow velocity between the top cover and the rotating wheel and reduce the desludging vortex, thereby greatly reducing the effect of amplifying pressure pulsation and reducing the vertical vibration of the top cover.
Although the invention has been described in detail above with reference to a general description and specific examples, it will be apparent to one skilled in the art that modifications or improvements may be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.
Claims (5)
1. A design method of a top cover inner cavity for reducing vertical vibration hazard of a top cover of a water turbine, wherein the water turbine comprises a mixed flow water turbine and a mixed flow reversible pump water turbine, and is characterized by comprising the following steps:
the distance between the top cover and the crown of the rotating wheel is increased so as to reduce the flow velocity gradient between each layer of the water body between the static top cover and the rotating wheel and increase the thickness of the water layer.
2. The method for designing a header inner cavity for reducing the vertical vibration hazard of a hydraulic turbine header as recited in claim 1, further comprising:
the rib plates and other bulges on the surface of the lower end surface of the top cover and the outer end surface of the upper part of the rotating wheel are eliminated, so that the upper surface and the lower surface of the inner cavity space of the top cover are kept flat and smooth.
3. The method for designing a roof cavity for reducing the vertical vibration hazard of a hydraulic turbine roof as claimed in claim 2, further comprising the following steps:
the bulge which can not be eliminated is additionally provided with the shielding part, and the shielding part is prevented from stirring water flow through shielding, so that the flow velocity of the water flow in the interlayer is reduced, the desludging vortex is reduced, the water flow cavitation is reduced or even eliminated, and the vertical vibration of the top cover is reduced.
4. The method of claim 1, wherein the design of the inner cavity of the header is such that the vertical vibration of the header is reduced,
the minimum value of the distance between the top cover and the runner crown is not less than 50 mm-150 mm, and the distance between the top cover and the runner crown is not more than 200 mm.
5. The method of designing a head cavity for mitigating the vertical vibration hazards of a hydraulic turbine head as set forth in claim 4, wherein the minimum value of the spacing between said head and said runner crown is determined based on the selected hydraulic turbine,
when the selected water turbine is a large unit, the minimum value of the distance between the top cover and the runner crown is 150mm,
when the selected water turbine is a small unit, the minimum distance between the top cover and the runner crown is 50 mm.
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| CN202111047003.7A CN113586312B (en) | 2021-09-07 | 2021-09-07 | Top cover inner cavity design method for reducing vertical vibration hazard of top cover of water turbine |
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2021
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