CN102435414B - Method of decompression test of air entrainment and cavitation alleviation model - Google Patents
Method of decompression test of air entrainment and cavitation alleviation model Download PDFInfo
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- CN102435414B CN102435414B CN201110214269.6A CN201110214269A CN102435414B CN 102435414 B CN102435414 B CN 102435414B CN 201110214269 A CN201110214269 A CN 201110214269A CN 102435414 B CN102435414 B CN 102435414B
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Abstract
The invention belongs to the technical field of the prevention of cavitation damage and destruction of high-flowrate outlet structures, and relates to a method of a decompression test of an air entrainment and cavitation alleviation model. A device of the decompression test of the air entrainment and cavitation alleviation model comprises a decompression tank, a vacuum pump, and the air entrainment and cavitation alleviation model which is provided with an air entrainment facility, wherein the vacuum pump is connected with the decompression tank through a vacuum pumping pipeline of the vacuum pump; the air entrainment and cavitation alleviation model is positioned in the decompression tank; the air entrainment facility is connected with a ventilation pipe; the ventilation pipe of the air entrainment facility is led to the outer part of the decompression tank; air is sucked from an ordinary pressure environment, but the air entrainment and cavitation alleviation model is still in a vacuum environment of the decompression tank; and the vacuum degree of the decompression tank is equal to a theoretical value of a traditional decompression test. By adopting the method, the problem that the ventilatory capacity of the model of the decompression test is dissimilar to that of a prototype is solved, the air entrainment and cavitation alleviation effect of the prototype engineering is scientifically reflected, and the method has an important reference value for the design and the optimization of air entrainment and cavitation alleviation measures of the high-flowrate outlet structures.
Description
Technical field
The invention belongs to the technical field that prevents high flow rate outlet structure escape works cavitation erosion, relate to a kind of air mixing corrosion reducing model decompression test method.
Background technology
Along with the raising of dam construction technique and the fast development of China's water resources and hydropower construction cause, China's high dam construction is developed to the 300m level stage from the nearly 100m level starting, flood discharge flow velocity is corresponding be developed to current 50m/s from 20 early stage～30m/s more than, consequent high-velocity flow problem becomes increasingly conspicuous, the possibility that serious cavitation erosion occurs outlet structure escape works increases gradually, the safe operation of serious threat engineering, thereby enjoy engineering circles and researchist's concern.
At present, for the protection of high water head flood discharging tunnel cavitation erosion, only adopt ensure wall flatness and use anti-cavitation corrosion material method oneself can not finely meet the demands, facts have proved, air mixing corrosion reducing is the engineering measure of a kind of economical and effective and technical feasibility.In engineering, conventionally adopt at present the method that aeration groove/bank is set on outlet structure escape works flow-passing surface to carry out air mixing corrosion reducing, two kinds of aeration and side wall aerations bottom these air entraining facilitieses can be divided into according to residing position, its effect is the aeration concentrater that increases outlet structure escape works bottom and side wall place.Due to high-velocity flow the complex nature of the problem, the corrosion inhibitor effect of air entraining facilities is also difficult to simulate by mathematical model at present, conventionally adopts vacuum experiment to prove.
Tradition decompression test theory thinks, general flow cavitation occurs in serious negative pressuren zone, and normal pressure test, high negative pressure easily produces the problem of virtual negative pressure, so atmospheric pressure must reduce according to model scale in model test.Specific Principles is that decompression model adopts gravity similarity design, keeps in test model to equate with the cavitation number of prototype, that is:
（1）
In formula ,-flow cavitation number;
-atmospheric pressure;
equal pressure when-calculating section part;
-pressure for vaporization;
-mean velocity in section;
-acceleration of gravity.
Can obtain the air pressure that decompression cabinet inner model should control is:
（2）
-model scale.
In vacuum experiment process, obtain atmospheric pressure value decompression cabinet in the institute accordingly variation of pressure for vaporization by (2) formula according to the water temperature of working in decompression cabinet at any time
.
Vacuum tightness in decompression cabinet is:
（3）
In formula,
for testing laboratory's atmospheric pressure.
According to above test method, as model non-cavitating phenomenon, prototype is without cavitation erosion.
According to traditional decompression test theory, vacuum tightness and model scale in decompression cabinet
closely related.Large guide (
=40 left and right) in model test, identical in order to reach flow cavitation number, test must be carried out under condition of high vacuum degree (similar vacuum tightness is greater than 95%).Current air mixing corrosion reducing model decompression test method as shown in Figure 2, that whole air mixing corrosion reducing model is placed in to decompression cabinet 7, air mixing corrosion reducing model comprises base plate 1, aeration hole 3, bottom air entraining facilities 5 and snorkel 4, the snorkel 4 of air entraining facilities 5 is also arranged in the vacuum environment of decompression cabinet 7 inside, current and current ambient air are pumped, therefore the air entrainment of air entraining facilities is far smaller than prototype, corrosion inhibitor effect that can not actual response air entraining facilities.Taking the power station model test of making a pilgrimage to a temple on a famous mountain greatly as example, these model scale=40, similar vacuum tightness 96% left and right, the facility of ventilating in model test is from the inner air inlet of decompression cabinet, and now in casing, most air are drawn out of, current move substantially in without air ambient, in water, almost without aeration, in model, observed cavitation noise, but the Hydraulic Prototype Observation in June, 2002 shows, there is not cavitation erosion in prototype operation, decompression test result and prototype are dissimilar.
Calculate formula and also can find out from above decompression cabinet vacuum tightness, as reduced the vacuum tightness of vacuum experiment, increase the throughput of air entraining facilities in reduced pressure atmosphere, only have the as far as possible little model scale of employing, increase moulded dimension.For example, by similar vacuum degree control, 90%, corresponding model scale is about
=12 left and right, 200～300m high dam model height will reach 20～30m, and for current large-scale and even huge model tests of hydraulic engineering, this method is uneconomic, is also unpractical.Even if similar vacuum tightness is reduced to 90%, its air entrainment is also far smaller than the air entrainment under normal pressure.
In sum, whole model is placed in vacuum environment by traditional air mixing corrosion reducing model decompression test method, and air entraining facilities is air inlet from decompression cabinet, cannot meet model similar to the throughput of prototype, and test findings is difficult to react the air mixing corrosion reducing effect of prototype.
Summary of the invention
Technical matters to be solved by this invention is: for above prior art existent defect, propose a kind of air mixing corrosion reducing model decompression test method, can solve the dissimilar problem of air entraining facilities throughput in decompression test.
The technical scheme that the present invention solves above technical matters is:
Air mixing corrosion reducing model decompression test method, the device of air mixing corrosion reducing model decompression test comprises decompression cabinet, vacuum pump and is provided with the air mixing corrosion reducing model of air entraining facilities, vacuum pump is connected with decompression cabinet by vacuum pump pump-line, air mixing corrosion reducing model is positioned at decompression cabinet, is connected to snorkel on air entraining facilities; The snorkel of air entraining facilities is passed to decompression cabinet outside, air inlet from atmospheric pressure environment, but air mixing corrosion reducing model is still in the vacuum environment in decompression cabinet, the theoretical value that the vacuum tightness of decompression cabinet is traditional decompression test.
The technical scheme that the present invention further limits is:
Aforesaid air mixing corrosion reducing model decompression test method, air entraining facilities is bottom air entraining facilities, its build be choose bank, fall bank, aeration groove, differential bank or wherein the two, three's combined air entraining facilities.
Aforesaid air mixing corrosion reducing model decompression test method, air entraining facilities is side wall air entraining facilities, its build is for choosing bank, sudden expansion or the two combined air entraining facilities.
Aforesaid air mixing corrosion reducing model decompression test method, air entraining facilities is bottom aeration and the combined air entraining facilities of side wall aeration.
Advantage of the present invention is: the invention solves decompression test model and the dissimilar problem of prototype throughput, scientifically react the air mixing corrosion reducing effect of prototype engineering, there is important reference value for the design and optimization of high flow rate outlet structure escape works air mixing corrosion reducing measure.
Brief description of the drawings
Fig. 1 a is that bottom aeration is that the snorkel of choosing bank and aeration groove combination form is arranged schematic diagram.
Fig. 1 b is that bottom aeration is that the snorkel of choosing bank pattern is arranged schematic diagram.
Fig. 1 c is that bottom aeration is the snorkel layout schematic diagram of choosing bank, falling bank and aeration groove combination form.
Fig. 1 d is that the snorkel of bottom aeration and the combined air entraining facilities of side wall aeration is arranged schematic diagram.
Fig. 1 e is that the snorkel of bottom aeration and the combined air entraining facilities of side wall aeration is arranged schematic diagram.
Fig. 1 f is that the snorkel of bottom aeration and the combined air entraining facilities of side wall aeration is arranged schematic diagram.
Fig. 2 is traditional air mixing corrosion reducing model decompression test method schematic diagram.
Fig. 3 is air mixing corrosion reducing model decompression test method schematic diagram of the present invention.
Fig. 4 is for choosing bank type bottom air mixing corrosion reducing model decompression test method schematic diagram.
Fig. 5 is the combination corrosion inhibitor model decompression test method schematic diagram of choosing bank type bottom aeration and choosing bank type side wall aeration.
Cavitation noise oscillogram when Fig. 6 is air hole Close All.
Cavitation noise oscillogram when Fig. 7 is air hole from the inner air inlet of decompression cabinet.
Fig. 8 is the cavitation noise oscillogram of air hole during from decompression cabinet external feed stream.
Fig. 9 is the cavitation noise oscillogram of air hole during from decompression cabinet external feed stream.
Figure 10 is the cavitation noise oscillogram of air hole during from decompression cabinet external feed stream.
Figure 11 is the cavitation noise oscillogram of air hole during from decompression cabinet external feed stream.
In above-mentioned figure, 1 is base plate, and 2 is side wall, 3 is aeration hole, and 4 is snorkel, and 5 is bottom air entraining facilities, 6 is side wall air entraining facilities, 7 is decompression cabinet, and 8 is vacuum pump pump-line, and 9 is vacuum pump, 10 is throughput by-pass valve control, 11 is air flowmeter, and arrow F represents water (flow) direction, and arrow A represents airflow direction.
Embodiment
embodiment 1
The present embodiment is a kind of air mixing corrosion reducing model decompression test method, as shown in Figure 3, the device of air mixing corrosion reducing model decompression test comprises decompression cabinet 7, vacuum pump 9 and is provided with the air mixing corrosion reducing model of air entraining facilities, vacuum pump 9 is connected with decompression cabinet 7 by vacuum pump pump-line 8, air mixing corrosion reducing model is positioned at decompression cabinet 7, is connected to snorkel 4 on air entraining facilities; The snorkel of air entraining facilities 4 is passed to decompression cabinet 7 outsides, air inlet from atmospheric pressure environment, but air mixing corrosion reducing model is still in the vacuum environment in decompression cabinet, the theoretical value that the vacuum tightness of decompression cabinet is traditional decompression test.Snorkel 4 is provided with throughput by-pass valve control 10 and air flowmeter 11.
Air entraining facilities is bottom air entraining facilities, its build be choose bank, fall bank, aeration groove, differential bank or wherein the two, three's combined air entraining facilities; Air entraining facilities is side wall air entraining facilities, and its build is for choosing bank, sudden expansion or the two combined air entraining facilities; Air entraining facilities is bottom aeration and the combined air entraining facilities of side wall aeration.Fig. 1 a is that bottom aeration is that the snorkel of choosing bank and aeration groove combination form is arranged schematic diagram; Fig. 1 b is that bottom aeration is that the snorkel of choosing bank pattern is arranged schematic diagram; Fig. 1 c is that bottom aeration is the snorkel layout schematic diagram of choosing bank, falling bank and aeration groove combination form; Fig. 1 d is that the snorkel of bottom aeration and the combined air entraining facilities of side wall aeration is arranged schematic diagram, and wherein bottom aeration is for choosing bank and falling bank combination form, and side wall aeration is for choosing bank pattern; Fig. 1 e is that the snorkel of bottom aeration and the combined air entraining facilities of side wall aeration is arranged schematic diagram, and wherein bottom aeration is for falling bank pattern, and side wall aeration is sudden expansion pattern; Fig. 1 f is that the snorkel of bottom aeration and the combined air entraining facilities of side wall aeration is arranged schematic diagram, and wherein bottom aeration is differential bank and aeration groove combination form, and side wall aeration is for choosing bank and sudden expansion combination form.
In Fig. 4, model is arranged in decompression cabinet inner vacuum environment, but the snorkel of choosing bank type bottom air entraining facilities is connected to decompression cabinet outside, air inlet from atmospheric pressure environment, and air inflow is controlled by valve 10, and corresponding throughput numerical value is read from air flowmeter 11.In Fig. 5, model is arranged in decompression cabinet inner vacuum environment, air entraining facilities is the combination form of choosing bank type bottom aeration and choosing bank type side wall aeration, snorkel is connected to decompression cabinet outside, air inlet from atmospheric pressure environment, air inflow is controlled by valve 10, and corresponding throughput numerical value is read from air flowmeter 11.
Cavitation noise oscillogram when Fig. 6 is air hole Close All is obviously seen and is had spike pulse signal from figure, illustrates and now has cavitation to occur.
Cavitation noise oscillogram when Fig. 7 is air hole from the inner air inlet of decompression cabinet is obviously seen and is had spike pulse signal from figure, illustrate and now has cavitation generation; Comparison of wave shape by Fig. 6 and Fig. 7 is analyzed known, extent of cavitation in two kinds of situations is substantially suitable, illustrate that air mixing corrosion reducing model decompression test method throughput traditional in high vacuum environment is very little, can think and ventilate hardly, in model, have cavitation phenomenon, and extent of cavitation is substantially suitable with stuffiness operating mode.
Fig. 8 is the cavitation noise oscillogram of air hole during from decompression cabinet external feed stream, and snorkel air inflow is 1.59m3/s; Fig. 9 is the cavitation noise oscillogram of air hole during from decompression cabinet external feed stream, and snorkel air inflow is 3.18m3/s; Figure 10 is the cavitation noise oscillogram of air hole during from decompression cabinet external feed stream, and snorkel air inflow is 4.76m3/s; Figure 11 is the cavitation noise oscillogram of air hole during from decompression cabinet external feed stream, and snorkel air inflow is 7.94m3/s.Fig. 8～Figure 11 explanation, when snorkel is from ambient atmosphere environment when air inlet, because air entrainment in water significantly increases, extent of cavitation obviously weakens, and in the time that snorkel air inflow reaches 7.94m3/s, aeration groove downstream is without obvious cavitation.
The present invention can also have other embodiment, and the technical scheme that the equal replacement of all employings or equivalent transformation form, within all dropping on the scope of protection of present invention.
Claims (1)
1. air mixing corrosion reducing model decompression test method, the device of described air mixing corrosion reducing model decompression test comprises decompression cabinet, vacuum pump and is provided with the air mixing corrosion reducing model of air entraining facilities, described vacuum pump is connected with described decompression cabinet by vacuum pump pump-line, described air mixing corrosion reducing model is positioned at described decompression cabinet, on described air entraining facilities, is connected to snorkel; It is characterized in that: the snorkel of described air entraining facilities is passed to described decompression cabinet outside, air inlet from atmospheric pressure environment, but air mixing corrosion reducing model is still in the vacuum environment in decompression cabinet, the theoretical value that the vacuum tightness of described decompression cabinet is traditional decompression test;
Described air entraining facilities is bottom air entraining facilities, side wall air entraining facilities or chooses bank type bottom aeration and choose the combination air entraining facilities of bank type side wall aeration, and the air hole of each air entraining facilities leads to decompression cabinet outside;
Described bottom aeration facility shape be choose bank, fall bank, aeration groove, differential bank or wherein the two, three's combined air entraining facilities, described side wall aeration facility shape is for choosing bank, sudden expansion or the two combined air entraining facilities;
Described air hole is during from decompression cabinet external feed stream, and snorkel air inflow is 1.59m
3/ s, 3.18 m
3/ s, 4.76 m
3/ s or 7.94 m
3/ s.
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| CN103290817B (en) * | 2013-06-26 | 2015-09-16 | 中国电建集团中南勘测设计研究院有限公司 | A kind of setting-out corrosion inhibitor structure of outlet structure escape works |
| CN104198208B (en) * | 2014-09-19 | 2016-08-24 | 中国航天科技集团公司川南机械厂 | A kind of rapid decompression assay device |
| CN107421846B (en) * | 2017-09-21 | 2023-03-14 | 水利部交通运输部国家能源局南京水利科学研究院 | Negative pressure type aeration concentration instrument and operation method thereof |
| CN108225728B (en) * | 2018-01-09 | 2020-06-02 | 水利部交通运输部国家能源局南京水利科学研究院 | Method for measuring and calculating relationship between jet velocity and air carrying capacity |
| CN108385603B (en) * | 2018-04-19 | 2024-01-19 | 长江水利委员会长江科学院 | Hydraulic model test device and method for aerated water flow narrow slit energy dissipater |
| CN109141818B (en) * | 2018-09-24 | 2023-06-27 | 天津大学 | Centralized threading method special for instrument and meter wires of hydraulic pressure reducing box |
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