CN107860667B - Intermittent supersonic sand erosion test bed and test method - Google Patents
Intermittent supersonic sand erosion test bed and test method Download PDFInfo
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- 238000000034 method Methods 0.000 claims abstract description 34
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- 238000005488 sandblasting Methods 0.000 claims abstract description 13
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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Abstract
The invention discloses an intermittent supersonic sand erosion test bed which comprises an air source system, a sand supply device, a sand blasting device, a test cabin and a shooting system, wherein the air source system is connected with the sand supply device; the high-pressure gas cylinder and the gas storage tank are used as gas sources for supplying high-pressure gas, so that the filling pressure value of the high-pressure gas cylinder to the gas storage tank can be accurately controlled, and the lowest starting pressure of the Laval tube for forming supersonic air flow can be ensured. The Laval pipe is adopted as an accelerating device, and the Laval pipe is designed to be a curved surface so that high-quality air flow can be formed and sand grains in the sand mixing pipe can be accelerated along a straight line in the pipeline as far as possible, so that collision with the pipe wall is avoided, and the problem that the sand grains are broken due to collision with the pipe wall in the accelerating process is solved well.
Description
Technical Field
The invention relates to the field of fine particle transportation and powder transportation in a pressure environment, and also relates to the field of sand blasting tests.
Background
At present, published literature data shows that few devices can intermittently emit one or a few sand grains at a time to impact a test piece in a supersonic speed state by using normal-temperature gas as a power medium, and the existing high-speed sand grain erosion device can hardly avoid the sand grains from colliding or scraping with the pipe wall and breaking in the acceleration process, so that the shape of the test sand grains is difficult to master, and further, test input variables can not be controlled. To realize intermittent supersonic sand erosion and possibly avoid the sand from contacting the wall surface in the process of pipeline acceleration, the following technical problems are faced: firstly, how to use normal temperature gas to accelerate sand grains to supersonic speed state and avoid the sand grains from colliding with the pipe wall as far as possible. In order to make sand particles reach a supersonic speed state, a common method is to mix the sand particles with normal-temperature high-pressure gas, and then pass the mixed gas-sand two-phase flow through a laval tube to accelerate the sand particles to the supersonic speed state. However, when the gas and sand pass through the laval pipe in two phases, the sand is difficult to avoid colliding with the wall surface of the converging section of the laval pipe, i.e., to avoid crushing of the sand. If the position where the sand and the supersonic air flow are merged is adjusted to be behind the Laval pipe, a second problem is faced: how to combine the sand grains with the supersonic main air flow in time and reduce the influence on the flow speed and the quality of the main air flow as much as possible. The air flow behind the Laval pipe reaches a supersonic speed state, and if the sand discharging mode and the sand discharging opening are not properly designed, the formed supersonic speed air flow is easily interfered by a bypass with high static pressure, so that sand grain acceleration is influenced. Third, how to create an inexpensive gas source that can continuously provide high pressure dry gas. If the air source is required to provide high-pressure air which can be continued for a certain time, the general method is to adopt a high-power air compressor to convey compressed air to an air storage tank; however, compressors that can provide high pressure gas are expensive and can be too costly to perform general experimental studies.
One way is to convey high-pressure gas to the driving section of the shock tube through a high-pressure gas bottle, when a pressure sensor monitors that the pressure of the driving section and the driven section of the shock tube reaches a certain value, the inflation valve is closed first, then the aluminum film for separating the driving section and the driven section of the shock tube is blasted, and at the moment, the high-pressure gas in the driving section of the shock tube quickly passes through the driven section, so that shock waves are generated, and the gas flow is supersonic. The formed supersonic air flow carries the material which is placed behind the shock tube by the tinfoil to accelerate the material, and the material is finally sprayed to the to-be-tested piece. The method has some disadvantages: first, the device is not highly secure. Because the pressure resistance of the aluminum film material has certain dispersibility, if the aluminum film is not broken under the control operation condition of testers, serious potential safety hazard is brought to the testers. Second, the device makes it difficult to bring the sand grains to a supersonic state. Because the device adopts the supersonic air flow generated by the shock tube and the method that the shock wave pushes the particles to accelerate, according to the knowledge of fluid mechanics, the shock wave reduces the effect of the air flow on the acceleration of the particles in the process that the supersonic air flow in the pipeline accelerates the particles; more importantly, the flow following performance of the sand is poor, the supersonic airflow generated by the device cannot be continued, the acceleration of the sand is continuously reduced along with the increase of the stroke, and the stroke of the sand acceleration in the device is short, which means that the sand is difficult to reach the sound velocity and difficult to cross the sound velocity.
One method is to adopt an airflow ejection mode, a Laval pipe is utilized to form a supersonic airflow under a certain airflow total pressure, an ejection effect is formed by the supersonic airflow, so that a negative pressure is formed in a local area of the supersonic airflow, and sand grains are sucked into a main airflow to accelerate the main airflow, thereby realizing sand blasting. The method has some disadvantages: first, it is difficult for this method to accelerate the sand particles to sonic velocity. According to the knowledge of fluid mechanics and gas dynamics, one of the necessary conditions for ejection is that the inner diameter of the ejection flow pipe is smaller than that of the downstream pipe, so that the speed of the small pipe flows through the large pipe diameter is inevitably reduced on the premise that the total pressure of the airflow is not changed, and therefore, for sand grains with poor follow-up flow performance, the sand grains are difficult to accelerate to a supersonic speed state by an ejection method. Second, this method does not avoid the sand particles from colliding with the pipe wall during acceleration and causing breakage. Because the sand throwing mode is that sand grains are sucked into the main air flow through negative pressure formed by ejection, and the stress of the sand grains is extremely uneven, the sand grains are difficult to ensure to be accelerated straightly along the axial direction, and the scraping collision between the sand grains and a straight pipeline is difficult to avoid; the test grit is a friable material that breaks upon impact with the pipe wall, thereby affecting test integrity.
One method is to mix sand and high-pressure air flow, and then make the two-phase flow of air and sand pass through the Laval pipe together, so that the formed supersonic air flow can accelerate the sand, and finally make it reach supersonic speed state. The method has the following disadvantages: in the method, the gas phase in the gas-sand two-phase flow needs to cross from the subsonic speed to the hypersonic speed, so that the sand with poor flow following performance can be accelerated to the supersonic speed. According to the relevant knowledge of the design of the Laval tube, if the airflow reaches hypersonic speed in a short stroke, the ratio of the inner diameter of the contraction starting end face of the Laval tube to the inner diameter of the throat of the Laval tube with a slightly larger numerical value is selected, which means that the difference between the inner diameter of the contraction starting end face of the contraction section of the Laval tube and the inner diameter of the throat of the Laval tube is larger. When the mixed gas-sand two-phase flow in the high-pressure area passes through the Laval pipe, sand cannot be prevented from colliding with the wall surface of the contraction section of the Laval pipe, and the collision with a certain speed inevitably causes the crushing of the sand, so that the requirement of a single sand supersonic erosion test cannot be met.
Therefore, a new technical solution is needed to solve the above problems.
Disclosure of Invention
The purpose of the invention is as follows: the invention provides an intermittent supersonic sand erosion test bed which can accelerate sand particles to a supersonic speed state by simply depending on normal-temperature dry high-pressure gas and can well solve the problem that the sand particles collide with a pipe wall in the acceleration process to cause breakage.
The invention also provides a test method using the test bed.
The technical scheme is as follows: in order to achieve the purpose, the invention can adopt the following technical scheme:
an intermittent supersonic sand erosion test bed comprises an air source system, a sand supply device, a sand blasting device, a test cabin and a shooting system;
the gas source system comprises a high-pressure gas cylinder, a gas storage tank communicated with the high-pressure gas cylinder, a pressure regulating valve connected with the high-pressure gas cylinder and used for controlling the output of high-pressure gas, and a first valve body connected with the gas storage tank;
the sand supply system comprises a first three-way pipe connected with the first valve body, an extension pipe connected with one outlet of the first three-way pipe and extending horizontally, a straight pipe connected with the extension pipe and extending horizontally from the extension pipe, a laval pipe connected with the straight pipe, a sand mixing pipe connected with the laval pipe, a sand accelerating pipe connected with the sand mixing pipe, a gas guide pipe connected with the other outlet of the first three-way pipe, a second three-way pipe communicated with the outlet of the gas guide pipe, a straight pipe communicated with the outlet of the second three-way pipe and extending downwards, a sand discharging pipe communicated with the lower end of the straight pipe, and a sand mixing pipe communicated with the lower end of the sand discharging pipe; an inlet of the second three-way pipe, which extends upwards relative to the outlet, is a sand inlet; the contraction section of the Laval pipe is connected with the outlet of the straight pipe, and the expansion section of the Laval pipe is connected with the sand mixing pipe; the accelerating tube extends into the test chamber;
a test piece clamp positioned at the orifice of the accelerating tube is arranged in the test chamber;
the shooting system comprises a high-speed camera and a light source, wherein the high-speed camera and the light source are respectively positioned on two sides of the test chamber.
Has the advantages that: compared with the prior art, the beneficial effects of the technical scheme are as follows:
1. the high-pressure gas bottle and the gas storage tank are used as gas sources for supplying high-pressure gas, so that the filling pressure value of the high-pressure gas bottle to the gas storage tank can be accurately controlled, and the lowest starting pressure of the Laval tube for forming supersonic air flow can be ensured. In addition, the high-pressure gas cylinder can be directly filled with drier air and can be used by circularly filling gas;
2. the design that the Laval pipe is a curved surface can form supersonic air flow with good quality and the axial velocity gradient of which is approximately zero on the end face of the outlet of the expansion section, so that sand in the sand mixing pipe can be accelerated along a straight line in the pipeline as far as possible, further collision with the pipe wall is avoided, and the problem that the sand collides with the pipe wall in the acceleration process to cause breakage is solved well.
Furthermore, a sand inlet of the second three-way pipe is connected with a ball valve, and a pneumatic ball valve is connected between the straight pipe and the sand discharging pipe.
Furthermore, a third three-way pipe fitting is arranged between the pressure regulating valve and the air storage tank, and an inlet of the third three-way pipe fitting is connected with the pressure regulating valve, one outlet of the third three-way pipe fitting is connected with the air storage tank, and the other outlet of the third three-way pipe fitting is connected with the pressure sensor.
Furthermore, an electromagnetic valve is connected between the inlet of the third three-way pipe fitting and the pressure regulating valve.
Furthermore, the lower side of the test chamber is connected with a translation guide rail and a lifting device.
Further, the first valve body is also an electromagnetic valve.
The test method using the intermittent supersonic sand erosion test bed provided by the invention can adopt the following technical scheme:
(1) and placing a test piece: clamping a test piece on a test piece clamp and setting an erosion angle through the test piece clamp; turning on and adjusting the high-speed camera and the light source;
(2) placing sand grains: putting sand grains into a sand supply system from a sand inlet; sand grains fall on the upper end surface of the pneumatic ball valve along with gravity;
(3) filling high-pressure gas into the gas storage tank: setting the pressure value of gas to be filled in the gas storage tank; opening the high-pressure gas cylinder, and setting the pressure regulating valve to the pressure required by the test; filling gas into the gas storage tank;
(4) releasing the pressure gas to complete the erosion test: an electromagnetic valve is connected between the inlet of the third three-way pipe fitting and the pressure regulating valve; when the air storage tank reaches the set pressure, the first valve body, the electromagnetic valve and the pneumatic ball valve are opened simultaneously, sand grains at the upper end of the pneumatic ball valve are converged into the main air flow in the sand mixing pipe and sprayed to a test piece through acceleration of the acceleration pipe, and the erosion process of single sand is completed;
(5) recording the incident and rebound test parameters of the sand grains in the erosion test process: the high-speed camera triggers the shooting record of the electromagnetic valve when the electromagnetic valve is opened, and then records the impact speed, the rebound speed and the angle of sand grains and the phenomenon generated in the whole erosion process in a shooting picture playback mode.
Further, the camera adopts a shutter time not less than 1.5 mu s and a shooting frame rate of more than 50000 frames, and for the lens, an amplifying lens or a 100mm macro lens is required; the shooting system adopts a shooting method that a light source directly shines on a high-speed camera.
Further, a third three-way pipe fitting is arranged between the pressure regulating valve and the gas storage tank, an inlet of the third three-way pipe fitting is connected with the pressure regulating valve, one outlet of the third three-way pipe fitting is connected with the gas storage tank, the other outlet of the third three-way pipe fitting is connected with a pressure sensor, and the pressure sensor is simultaneously connected with a pressure release valve; when the pressure sensor senses that the pressure reaches a set value, the electromagnetic valve is closed; if the gas filling speed is too high, the pipeline gas pressure is higher than the set value, and the pressure relief valve slowly relieves the pressure of the gas in the gas storage tank to the set value.
Drawings
FIG. 1 is a schematic view of the overall structure of the test stand of the present invention;
FIG. 2 is a schematic of a test chamber system of the present invention;
FIG. 3 is a cross-sectional view of a sand supply mechanism and a sand blasting gun according to the present invention;
FIG. 4 is a cross-sectional view of the air supply system of the present invention.
Detailed Description
The following describes the embodiments of the present invention with reference to fig. 1 to 4.
Fig. 1 is a general structural view of the present invention. The left side of the air source system 3 comprising a high-pressure air bottle 41, an air storage tank 35, an electromagnetic valve 39 and a pressure sensor 38 is provided with a sand blasting mechanism 2 consisting of a sand supply mechanism, a supersonic sand blasting gun and the like; the sand blasting mechanism 2 is fixed on a support frame 5 through bolts, and the support frame 5 and a gas storage tank of the gas source system 3 are both placed on a test table 4; a test chamber system 1 is composed of a test piece clamp, a test chamber and a slide rail; the test chamber lifting mechanism consists of a worm gear lead screw lifter 9, a lead screw 11, a synchronous shaft 7, a screw post 8 and a hand crank 10; the test chamber system 1 is placed on a lifting mechanism, and the lifting mechanism is fixed on a test table 6. The test table 6 is placed on the left side of the test table 4.
Fig. 2 is a schematic structural diagram of the test chamber and the shooting system. The test piece clamp 31 is fixed inside the test chamber 30 through a bolt; the upper end and the lower end of the slide rail 34 are respectively connected with the test chamber 30 and the lifting mechanism; the high-speed camera 33 and the high-power LED light source 32 are respectively arranged at two sides of the test chamber.
FIG. 3 is a schematic view of the sand supply mechanism and the supersonic sand-blasting gun. The left side of the electromagnetic valve 25 is connected with a first three-way pipe 26, the left side of the first three-way pipe 26 is connected with an expansion pipe 27, and a copper pipe clamping sleeve 24 is connected above the first three-way pipe 26; the left side of the expansion pipe 27 is connected with a straight pipe 28, the left side of the straight pipe 28 is connected with the contraction section of a laval pipe 29, the left side of the laval pipe 29 is connected with a sand mixing pipe 16, and the left side of the sand mixing pipe 16 is connected with a sand accelerating pipe 15; a thin copper pipe 23 is connected above the copper pipe clamping sleeve 24, the left side of the thin copper pipe 23 is connected with a clamping sleeve 22, and the left side of the clamping sleeve 22 is connected with a second three-way pipe fitting 20; the upper side of the second tee pipe fitting 20 is connected with a manual ball valve 21, the lower side of the second tee pipe fitting 20 is connected with a straight pipe 19, the lower side of the straight pipe 19 is connected with a pneumatic ball valve 18, the lower side of the pneumatic ball valve 18 is connected with a sand discharging pipe 17, and the lower side of the sand discharging pipe 17 is connected with a sand mixing pipe 16.
Fig. 4 is a schematic structural diagram of the air source system. The left side of a high-pressure gas cylinder 41 is connected with a pressure regulating valve 40, the left side of the pressure regulating valve 40 passes through a section of straight pipe and then is connected with an electromagnetic valve 39, the left side of the electromagnetic valve is connected with a third three-way pipe 42, and the upper part of the third three-way pipe 42 passes through a section of straight pipe and then is connected with the lower part of a three-way pipe 36; an electromagnetic valve 37 above the tee joint 36, and the right side of the tee joint 36 is connected with a pressure sensor 38; the left side of the third tee pipe 42 is connected with the air storage tank 35, and the left side of the air storage tank 35 is connected with the electromagnetic valve 25.
On the basis of disclosing the structure of the intermittent supersonic erosion test bed, the patent further explains the design method and the test method of the test bed.
The operation steps of the invention are as follows:
the first step is as follows: and placing a test piece. Clamping a test piece on a clamp 31, and setting an erosion angle by adjusting an inclined plate of the clamp 31; aligning the test piece to the sandblasting muzzle by adjusting the test chamber slide rail 34 and the lifting hand crank 10 to a specified distance of the test; the high speed camera 33 and the LED light source 32 are turned on and adjusted.
The second step is that: sand grains are placed. Opening the manual ball valve 21, and putting sand into a sand supply system from the manual ball valve; the sand will fall with gravity onto the upper end face of the pneumatic ball valve 18 and then close the manual ball valve 21.
The third step: and filling high-pressure gas into the gas storage tank. Setting the pressure value of the gas to be filled in the gas storage tank 35; opening the high-pressure gas cylinder 41, and setting the pressure regulating valve 40 to the pressure required by the test; opening the electromagnetic valve 39 to fill the gas tank 35 with gas; when the pressure sensor 38 senses that the pipeline pressure reaches a set value, the electromagnetic valve 39 is closed; if the gas filling speed is too fast, the gas pressure in the pipeline is higher than the set value, the electromagnetic valve 37 completes the opening and closing action in a very short time, and the pressure is relieved to the set value.
The fourth step: releasing the pressure gas to complete the erosion test. When the air storage tank 35 reaches the set pressure, the electromagnetic valve 25, the electromagnetic valve 39 and the pneumatic ball valve 18 are opened simultaneously, and at the moment, sand grains at the upper end of the pneumatic ball valve 18 are converged into the main air flow in the sand mixing pipe 16 and are accelerated by the accelerating pipe 15 to be sprayed to a test piece, so that the erosion process of single sand is completed.
The fifth step: incident and rebound test parameters of the sand grains were recorded during the erosion test. The high-speed camera 33 triggers the electromagnetic valve 25 to shoot and record at the same time of opening, and records the impact speed, rebound speed and angle of sand grains and phenomena generated in the whole erosion process in a shooting picture playback mode.
The purpose of the invention is realized as follows:
in the first step of the above operation, the angle of the test piece fixing plate in the test fixture 31 is adjusted to achieve the purpose of erosion research at different erosion angles. The front, the back and the left of the test chamber 30 adopt optical plane glass with the thickness of 10mm and good light transmittance; the purpose of this is: on one hand, good light transmission conditions can be provided for the movement of shooting sand grains, and the visual field of a camera is not obstructed; on one hand, the protection can be provided for the tester during sand blasting, and the personal safety of the operator caused by the rebound of the supersonic sand particles through the test piece is avoided. The high-power LED light source 32, the high-speed camera 33, the crescent test piece clamp 31 and the test chamber 30 with high-light-transmission optical glass on four sides form a test shooting system together. Because the grain size of the sand used in the test is small, usually in the range of 0.3 mm-0.6 mm, when the sand moves at the supersonic speed of 340-500 m/s, the erosion process is required to be shot and recorded, and the difficulty is very high. In order to solve the problem of shooting by erosion of supersonic sand grains, the camera adopts a shutter time not less than 1.5 mu s and a shooting frame rate of more than 50000 frames, and for a lens, an amplifying lens or a 100mm macro lens is required. Because the requirement of the shooting parameters on the lens light-entering amount is extremely high, the shooting system adopts a shooting method that the high-power LED lamp 32 just shines the high-speed camera 33, so that the process of sand erosion is captured and recorded by the camera in a light projection mode. Because different inclination's erosion test is carried out, when the inclined plate angular adjustment, the height and the distance of test piece and sandblast muzzle also change along with it, for eliminating this influence factor, through adjusting test cabin slide rail 34 and control elevating system's crank 10 in order to ensure that test piece and sandblast muzzle relative position do not change under the different inclination.
In the second step of the above operation, the purpose thereof is to put sand grains into the sand supply mechanism.
In the third step of the above operation, it is necessary to set the pressure value in the air tank 35 so that the sand grains can obtain different erosion rates by releasing the air at different pressures. In order to accelerate sand grains to a supersonic speed state by gas, high-pressure gas is needed to be used as a gas source; the pressure value of the filling gas of the industrial high-pressure gas cylinder is over 10MPa, so that the gas can be supplied to the gas storage tank 35 by the high-pressure gas cylinder 41, the requirement of the test on the high-pressure gas can be met, the high-pressure gas cylinder can be recycled, and the price is low. In order to keep the gas pressure in the gas storage tank 35 at a set value, firstly, a pressure regulating valve is arranged at the output end of the high-pressure gas cylinder 41, so that the gas pressure output by the gas cylinder 41 can be roughly controlled; then, an electromagnetic valve 39 responsible for supplying air to the air storage tank 35, a sensor 38 responsible for sensing real-time inflation pressure and an electromagnetic valve 37 responsible for pressure relief are arranged between the air storage tank 35 and the high-pressure air bottle 41; the design and working logic is as follows: after the pressure value of the air storage tank 35 to be inflated is set, the electromagnetic valve 39 is opened, the high-pressure air bottle 41 starts to inflate the air storage tank 35, and when the pressure sensor 38 senses that the pipeline pressure reaches the set value, the electromagnetic valve 39 is closed; if the gas filling speed is too fast, which causes the pipeline gas pressure to be higher than the set value, the solenoid valve 37 completes the opening and closing action in a very short time, aiming at slowly releasing the pressure of the gas in the gas storage tank to the set value. The opening and closing time of the electromagnetic valve is usually within 0.8s, the action is quicker, and therefore, the electromagnetic valve is suitable to be used as a slow pressure relief element.
In the fourth step of the above operation, when the pressure in the air storage tank 35 reaches the set value, the electromagnetic valve 25, the electromagnetic valve 39 and the pneumatic ball valve 18 are simultaneously opened, and at this time, the high-pressure air in the air storage tank 35 rapidly passes through the laval pipe 29 of the sand blasting gun to form hypersonic air flow; on one hand, a gas branch flow led out from the thin copper pipe 23 is used for balancing the total pressure of the gas at the upper end and the lower end of the pneumatic ball valve 18, so that sand at the upper end of the valve 18 can fall into the sand mulling pipe 16 along with the self gravity when the valve 18 is opened to be converged with the main gas flow; on the other hand, the branch is led out from the gas high-pressure end and connected to the upper end of the pneumatic ball valve 18, when the valve 18 is opened, the gas flow speed at the upper end of the valve 18 is low, and supersonic gas flow is formed in the sand mixing pipe 16 at the lower end, so that the static pressure at the upper end of the valve 18 is higher than that at the lower end, and at the moment when the valve 18 is opened, the sand grains are subjected to downward force in the direction of the static pressure of the gas besides the action of self gravity, and the two flows enable the sand grains to rapidly pass through the sand discharging pipe 17 and to be timely merged with the supersonic gas flow in the sand mixing pipe 16 to enter the expansion-type accelerating. In order to reduce the influence of the air flow in the sand supply mechanism composed of the valve 21, the thin copper pipe 23, the valve 18, the sand discharge pipe 17 and other components on the supersonic main air flow in the sand mixing pipe 16 in the sand discharge process as much as possible, on one hand, the air pressure balance pipe 23 is required to divide the air flow as little as possible, so that a pressure-resistant thin copper pipe with the inner diameter of 5mm is selected; on the other hand, the inner wall of the sand discharge pipe 17 adopts a conical surface design, and the communication hole between the inner wall and the sand mixing pipe is as small as possible, and the invention adopts a small hole with the inner diameter of 4mm, which is large enough for sand grains falling by about 0.5mm, and does not bring difficulty to processing.
In the fourth step of the above operation, the high-pressure gas in the gas tank flows through the expansion pipe 27 and then through the laval pipe 29, so that: in order to meet the requirement of a supersonic sand test, the sand must be accelerated to a supersonic speed state by the hypersonic air flow, and to realize the hypersonic air flow, the Laval tube must have a relatively large contraction ratio, so that the air flow passes through expansion firstly. The laval pipe 29 adopts the design method of the curved surface, because the laval pipe with the smooth curved surface can form the supersonic airflow with good quality with the axial velocity gradient being approximately zero on the outlet end surface of the expansion section, the sand in the sand mixing pipe 16 can be accelerated in the pipeline 15 along a straight line as much as possible, and further the collision with the pipe wall is avoided. The reason why the sand accelerating tube 15 and the sand mulling tube 16 are designed to have the expanded surface is that: according to aerodynamic knowledge, high-pressure airflow is accelerated from subsonic velocity to sonic velocity in a throat of the Laval pipe, the airflow can cross into supersonic velocity from the sonic velocity in an expansion section of the Laval pipe, and the acceleration is kept continuously along with the stroke of the expansion section; therefore, the sand mixing pipe 16 and the accelerating pipe 15 both adopt an expanding surface to form a generalized Laval pipe together with the Laval pipe 29, so that the supersonic airflow at the outlet end surface of the Laval pipe 29 is further accelerated to a high supersonic speed, and then a large air drag force is continuously generated on sand grains, and finally the sand grains are accelerated to the supersonic speed.
The invention has convenient operation, stable and safe work; the gas supply device can intermittently supply high-pressure gas for a certain time; the sand supply device can timely converge sand grains into the supersonic main air flow, and can reduce the influence on the main air flow as much as possible; the Laval tube can form high-quality airflow with zero axial velocity gradient, so that sand grains move along the axis as far as possible and the collision between the sand grains and the tube wall is reduced; the expanding flow guide pipe can further accelerate the airflow at the tail end of the expanding section of the laval pipe, and further can add sand particles in a relatively short stroke to accelerate the airflow to an ultrasonic speed state.
In addition, the present invention has many specific implementations and ways, and the above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be construed as the protection scope of the present invention. All the components not specified in the present embodiment can be realized by the prior art.
Claims (3)
1. A test method using an intermittent supersonic sand erosion test bed comprises an air source system, a sand supply device, a sand blasting device, a test chamber and a shooting system;
the gas source system comprises a high-pressure gas cylinder (41), a gas storage tank (35) communicated with the high-pressure gas cylinder, a pressure regulating valve (40) connected with the high-pressure gas cylinder and used for controlling the output of high-pressure gas, and a first valve body (25) connected with the gas storage tank;
the sand supply system comprises a first three-way pipe (26) connected with a first valve body (25), an extension pipe (27) which is connected with one outlet of the first three-way pipe (26) and extends horizontally, a straight pipe (28) which is connected with the extension pipe (27) and extends from the extension pipe continuously and horizontally, a Laval pipe (29) which is connected with the straight pipe, a sand mixing pipe (16) which is connected with the Laval pipe, a sand grain accelerating pipe (15) which is connected with the sand mixing pipe, a gas leading pipe (23) which is connected with the other outlet of the first three-way pipe, a second three-way pipe (20) which is communicated with the outlet of the gas leading pipe, a straight pipe (19) which is communicated with the outlet of the second three-way pipe and extends downwards, a sand discharging pipe (17) which is communicated with the lower end of the straight pipe (19; an inlet of the second three-way pipe, which extends upwards relative to the outlet, is a sand inlet; the contraction section of the Laval pipe (29) is connected with the outlet of the straight pipe, and the expansion section of the Laval pipe (29) is connected with the sand mixing pipe; the accelerating tube (15) extends into the test chamber (30);
a test piece clamp (31) positioned at the orifice of the accelerating tube is arranged in the test chamber;
the shooting system comprises a high-speed camera (33) and a light source (32), wherein the high-speed camera and the light source are respectively positioned on two sides of the test chamber;
a sand inlet of the second three-way pipe (20) is connected with a ball valve (21), and a pneumatic ball valve (18) is connected between the straight pipe (19) and the sand discharging pipe (17); a third three-way pipe (42) is arranged between the pressure regulating valve (40) and the air storage tank (35), the inlet of the third three-way pipe is connected with the pressure regulating valve, one outlet of the third three-way pipe is connected with the air storage tank, and the other outlet of the third three-way pipe is connected with the pressure sensor (38);
the method is characterized by comprising the following steps:
(1) and placing a test piece: clamping a test piece on a test piece clamp (31) and setting an erosion angle through the test piece clamp; turning on and adjusting the high-speed camera (33) and the light source (32);
(2) placing sand grains: putting sand grains into a sand supply system from a sand inlet; sand grains fall on the upper end surface of the pneumatic ball valve (18) along with gravity;
(3) filling high-pressure gas into the gas storage tank: setting the value of the pressure of the gas to be filled in the gas storage tank (35); opening a high-pressure gas cylinder (41), and setting a pressure regulating valve (40) to a pressure required by a test; filling a gas tank (35) with gas;
(4) releasing the pressure gas to complete the erosion test: an electromagnetic valve (39) is connected between the inlet of the third three-way pipe fitting and the pressure regulating valve; when the gas storage tank (35) reaches the set pressure, the first valve body (25), the electromagnetic valve (39) and the pneumatic ball valve (18) are opened simultaneously,
at the moment, sand grains at the upper end of the pneumatic ball valve (18) are converged into the main air flow in the sand mixing pipe (16) and are accelerated by the accelerating pipe (15) to be sprayed to a test piece, and the erosion process of single sand is finished;
(5) recording the incident and rebound test parameters of the sand grains in the erosion test process: the high-speed camera (33) triggers the shooting and recording of the electromagnetic valve (39) when the electromagnetic valve is opened, and then records the impact speed, the rebound speed and the angle of the sand grains and the phenomenon generated in the whole erosion process in a shooting picture playback mode.
2. The assay method of claim 1, wherein: the camera adopts shutter time not less than 1.5 mu s and a shooting frame rate of more than 50000 frames, and for the lens, an amplifying lens or a 100mm macro lens is required; the shooting system adopts a shooting method that a light source (32) shines a light on a high-speed camera (33).
3. The test method according to claim 2, characterized in that: a third three-way pipe (42) is arranged between the pressure regulating valve (40) and the air storage tank (35), the inlet of the third three-way pipe is connected with the pressure regulating valve, one outlet of the third three-way pipe is connected with the air storage tank, the other outlet of the third three-way pipe is connected with a pressure sensor (38), and the pressure sensor (38) is simultaneously connected with a pressure release valve (37); when the pressure sensor senses that the pressure reaches a set value, the electromagnetic valve (39) is closed; if the gas filling speed is too high, and the pipeline gas pressure is higher than the set value, the pressure relief valve (37) slowly relieves the pressure of the gas in the gas storage tank to the set value.
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