Method for judging the similarity of cavitation damage effects of cavitation bubbles of different scales

Abstract

The present invention discloses a method for judging the similarity of cavitation damage effects of cavitation bubbles of different scales, including: controlling electric pulse to induce cavitation bubbles and obtaining the radius of cavitation bubbles induced by electric pulse, performing the operation of cavitation bubbles hitting a first specimen according to a first preset condition, and obtaining the size of cavitation pits of the first specimen after cavitation damage occurs to the first specimen; controlling ultrasonic wave to induce cavitation bubble cloud and obtaining the characteristic radius of cavitation bubble cloud induced by ultrasonic wave, performing the operation of cavitation bubble cloud hitting a second specimen according to a second preset condition, and obtaining the size of cavitation pits of the second specimen after cavitation damage occurs to the second specimen; respectively calculating and comparing the microscopic cavitation damage effect of cavitation bubbles induced by electric pulse and the macroscopic cavitation damage effect of cavitation bubble cloud induced by ultrasonic wave, so as to judge the similarity of cavitation damage effects of cavitation bubbles of different scales. The present invention provides technical support for the practice of cavitation protection engineering and the development of anti-cavitation materials.

Description

Technical Field

[0001] The invention relates to the technical field of cavitation monitoring, and in particular to a method for judging the similarity of cavitation damage effects of cavitation bubbles of different scales. Background Art

[0002] Cavitation is a hydrodynamic phenomenon that is widely present in many fields such as water conservancy, shipbuilding, chemical industry, medical treatment and acoustics. The most common engineering problem caused by cavitation is the cavitation damage caused by the collapse of cavitation bubbles near the solid surface. Cavitation is the result of the combination of the destructive effect of cavitation and the ability of boundary materials to resist cavitation. The cavitation problem involves complex knowledge such as unsteady flow and the reaction of specific materials on the solid surface, including fluid mechanics, material mechanics and physical chemistry. Most of the research on the anti-cavitation performance of materials uses cavitation as a research method, and pays less attention to the intrinsic mechanism of cavitation itself. Although many empirical methods have been applied to engineering to calculate the potential cavitation risk of known structures, there are still a large number of basic issues related to the underlying mechanism that remain unresolved, and the cavitation mechanism is still controversial.

[0003] The collapse of cavitation bubbles is a violent process. During the collapse of cavitation bubbles, shock waves and microjets are generated in the fluid area near the collapse point. Due to the small size and short period of cavitation bubbles, it is difficult to observe the entire process of interaction between cavitation bubbles and boundaries under normal conditions. The movement and change process of cavitation bubbles has very complex dynamic characteristics. Due to the uncertainty and randomness of the appearance time and spatial position of migratory cavitation bubbles in moving water, and the extremely fast development and collapse of cavitation bubbles, it is difficult to capture the entire process of their movement and change. Therefore, studying the interaction process between cavitation bubbles and boundaries in still water is a more common method in the study of cavitation dynamics, such as electric pulse-induced cavitation bubbles and laser pulse-induced cavitation bubbles. Among them, electric pulse-induced cavitation bubbles are due to the rapid expansion of water vapor formed by the instantaneous high temperature between the discharge electrodes to form cavitation bubbles.

[0004] The principle of ultrasonic induced cavitation bubbles is similar to the principle of cavitation bubble formation in water conservancy and hydropower engineering, but different from the principle of electric pulse induced cavitation bubbles. Due to the concentrated ultrasonic energy, the liquid can vibrate violently. When the ultrasonic wave reaches a certain intensity, cavitation will occur in the liquid. Ultrasonic cavitation refers to the tiny gas nuclei existing in the liquid, which are excited to form cavitation bubbles under the pressure of the ultrasonic environment field, thereby continuously generating, oscillating, and accumulating sound field energy. When the energy reaches a certain threshold, the cavitation bubbles collapse and close sharply, and a series of dynamic processes such as shock waves are generated when they collapse and close. Ultrasonic waves propagating in the liquid, due to the alternating positive and negative pressures, cause a large number of tiny gas nuclei in the liquid to expand, thereby forming cavitation bubble clouds. These cavitation bubble clouds grow rapidly and then collapse, causing fierce collisions between the liquids, thereby generating pressures of up to thousands to tens of thousands of atmospheres. Ultrasonic cavitation has the effect of cleaning or cavitation damage on the test pieces placed in it. Ultrasonic cavitation is widely used in manufacturing, metallurgy, chemical industry and other fields, such as ultrasonic cleaning, emulsification, catalysis, electroplating and sewage treatment.

[0005] Currently, ultrasonically induced cavitation bubble clouds are widely used in multiple engineering fields. However, due to randomness and uncertainty, there is a lack of correlation between the macroscopic characterization of cavitation damage and its microscopic principles. The basis of each theoretical model and the actual results lack mutual verification and support, making it difficult to provide technical support for cavitation protection engineering practice and anti-cavitation material development. Summary of the invention

[0006] Therefore, the present invention provides a method for judging the similarity of the cavitation damage effects of cavitation bubbles of different scales. It can establish the relationship between the microscopic mechanism and macroscopic effect of cavitation erosion based on the correlation between the cavitation bubble collapse characteristics and the cavitation effect of the specimen, and expand the results of the electric pulse induced cavitation bubble mechanism test to the ultrasonic cavitation application research, providing technical support for the practice of cavitation protection engineering and the development of anti-cavitation materials, so as to solve the problems raised in the above background technology.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] The embodiment of the present invention provides a method for determining the similarity of cavitation damage effects of cavitation bubbles of different scales, including:

[0009] Controlling the electric pulse to induce cavitation bubbles and obtaining the radius Re of the cavitation bubbles induced by the electric pulse, performing an operation of the cavitation bubbles striking the first specimen according to the first preset condition, and obtaining the cavitation pit size re of the first specimen after the first specimen is cavitated;

[0010] Control the ultrasonic wave to induce the generation of cavitation bubble cloud and obtain the characteristic radius Ru of the cavitation bubble cloud induced by the ultrasonic wave, perform the operation of the cavitation bubble cloud striking the second test piece according to the second preset condition, and obtain the cavitation pit size ru of the second test piece after the second test piece is cavitated;

[0011] The micro-scale cavitation damage effect of cavitation bubbles induced by electric pulses and the macro-scale cavitation damage effect of cavitation bubble clouds induced by ultrasound were calculated respectively, among which the micro-scale cavitation damage effect Ee = re / Re, and the macro-scale cavitation damage effect Eu = ru / Ru;

[0012] By comparing the micro-scale cavitation damage effect Ee and the macro-scale cavitation damage effect Eu, the similarity of the cavitation damage effects of cavitation bubbles of different scales can be judged.

[0013] Optionally, by using an electric pulse induced cavitation bubble system, single cavitation bubbles of controllable size can be stably generated in still water. The electric pulse induced cavitation bubble system consists of a power supply, a resistor, a capacitor and a three-phase switch. The process of electric pulse inducing cavitation bubbles includes: controlling the power supply to charge the capacitor or discharge the capacitor through the three-phase switch, and transmitting the discharge current to the discharge electrode through a high-power cable, so as to generate instantaneous high temperature to form cavitation bubbles.

[0014] Optionally, the process of obtaining the radius Re of the cavitation bubble induced by the electric pulse includes:

[0015] The pixel count of the cavitation bubble image and the actual scale photo are calibrated to obtain the proportional relationship between the scale photo and the image pixels;

[0016] A high-speed camera and a scale are used to record scale photos of cavitation bubbles induced by electric pulses under actual working conditions. Based on the above proportional relationship, the number of pixels is calculated to convert it into actual size to obtain the radius Re of the cavitation bubble induced by the electric pulse.

[0017] Optionally, the operation of causing the cavitation bubble to strike the first specimen is performed according to a first preset condition, including: pre-marking the striking area of ​​the cavitation bubble on the first specimen, and precisely controlling the cavitation bubble to collapse in the striking area according to the first preset condition, wherein the first preset condition is to quantitatively control the relative position of the cavitation bubble and the first specimen according to a dimensionless distance formula.

[0018] Alternatively, the dimensionless distance formula γ is:

[0019] γ=D / Re max

[0020] Where D is the distance from the centroid to the surface of the first specimen when the cavitation bubble expands to its maximum, Re max It is the maximum radius of cavitation bubbles induced by electric pulse.

[0021] Optionally, a large number of cavitation bubbles are generated by using an ultrasonic cavitation system to form a cavitation bubble cloud. The ultrasonic cavitation system is composed of a power supply, a control host, a transducer, a horn, and a constant temperature cooling water circulation system, wherein the amplifier, the ultrasonic frequency converter and the power regulator are all integrated in the control host. The process of ultrasonic induction to generate a cavitation bubble cloud includes: the amplifier in the control host converts the civil electricity input by the power supply into alternating electrical energy through the ultrasonic frequency converter, and then matches the alternating electrical energy with the transducer through the power regulator. The transducer converts the electrical energy into mechanical energy to drive the longitudinal mechanical vibration of the horn. When the end of the horn is immersed in the water, the high-frequency vibration of the horn induces cavitation in the lower water body, thereby generating a cavitation bubble cloud composed of a large number of cavitation bubbles.

[0022] Optionally, the process of obtaining the characteristic radius Ru of the cavitation bubble cloud induced by ultrasound includes: photographing the cavitation bubble cloud using a high-speed camera in combination with a macro lens, and obtaining the characteristic radius Ru of the cavitation bubble cloud by statistically analyzing the size distribution of the cavitation bubbles.

[0023] Optionally, the operation of causing the cavitation bubble cloud to strike the second specimen is performed according to a second preset condition, including: pre-marking the striking area of ​​the cavitation bubble cloud on the second specimen, and according to the second preset condition, precisely controlling the collapse of the cavitation bubble cloud in the striking area. The second preset condition is to control the operating time of the ultrasonic cavitation system to ensure that relatively mild cavitation damage is generated on the surface of the second specimen, so that the cavitation pits are more evenly distributed on the surface of the second specimen.

[0024] Optionally, the process of obtaining the cavitation pit size re of the first specimen and the cavitation pit size ru of the second specimen includes:

[0025] After the cavitation damage occurs, the first test piece and the second test piece are cleaned respectively, dried at a constant temperature, and then placed in a dryer to stand;

[0026] The first specimen and the second specimen after standing were sliced ​​and sampled respectively, and a high-performance scanning electron microscope was used to record the cavitation pit size re of the first specimen when the cavitation bubble was hit by electric pulse and the cavitation pit size ru of the second specimen when the cavitation bubble cloud was hit by ultrasonic wave.

[0027] Optionally, the first specimen and the second specimen are cast using a rectangular or cylindrical mold, wherein the surface length of the first specimen is not less than 5 times the radius Re of the cavitation bubble induced by the electric pulse, or the radius is not less than 3 times the radius Re of the cavitation bubble induced by the electric pulse, and the thickness is not less than 1.5 times the radius Re of the cavitation bubble induced by the electric pulse; the surface length of the second specimen is not less than 2 times the radius of the amplitude transformer, or the radius is not less than 1.5 times the radius of the amplitude transformer, and the thickness is not less than 10 times the characteristic radius Ru of the cavitation bubble cloud.

[0028] The technical solution of the present invention has the following advantages:

[0029] The method for judging the similarity of cavitation damage effects of cavitation bubbles of different scales provided by the present invention comprises: controlling electric pulse to induce cavitation bubbles and obtaining the radius of cavitation bubbles induced by electric pulse, performing an operation of causing cavitation bubbles to strike a first specimen according to a first preset condition, and obtaining the size of cavitation pits of the first specimen after cavitation damage occurs to the first specimen; controlling ultrasonic wave to induce cavitation bubble clouds and obtaining the characteristic radius of cavitation bubble clouds induced by ultrasonic wave, performing an operation of causing cavitation bubble clouds to strike a second specimen according to a second preset condition, and obtaining the size of cavitation pits of the second specimen after cavitation damage occurs to the second specimen; respectively calculating the microscopic cavitation damage effect of cavitation bubbles induced by electric pulse and the macroscopic cavitation damage effect of cavitation bubble clouds induced by ultrasonic wave and comparing them to judge the similarity of cavitation damage effects of cavitation bubbles of different scales. Through the method provided by the present invention, the relationship between the microscopic mechanism and macroscopic effect of cavitation erosion can be established based on the correlation between the cavitation bubble collapse characteristics and the cavitation effect of the specimen, and the results of the electric pulse induced cavitation bubble mechanism test can be expanded to the ultrasonic cavitation application research, providing technical support for the practice of cavitation protection engineering and the development of anti-cavitation materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 A schematic flow chart of a method for determining the similarity of cavitation damage effects of cavitation bubbles of different scales provided in an embodiment of the present invention;

[0032] Figure 2 Schematic diagram of the structure of the electric pulse induced cavitation bubble impact test piece system provided in an embodiment of the present invention

[0033] Figure 3 A schematic diagram of the process of formation and evolution of cavitation bubbles induced by electric pulses and impacting a test piece provided in an embodiment of the present invention;

[0034] Figure 4 A schematic structural diagram of an ultrasonic cavitation system provided in an embodiment of the present invention;

[0035] Figure 5 A schematic diagram showing that the morphology of the cavitation bubble cloud clusters provided in an embodiment of the present invention presents periodic changes on the lower side of the horn;

[0036] Figure 6 (A)-6(B) Schematic diagram of the sample surface micromorphology provided in the embodiments of the present invention. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only an embodiment of a part of the present invention, not all embodiments, and is not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concepts disclosed in the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of the present invention.

[0038] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] The embodiment of the present invention provides a method for determining the similarity of the cavitation damage effects of cavitation bubbles of different scales, such as Figure 1 As shown, the method includes:

[0040] Step S1: Control the electric pulse to induce cavitation bubbles and obtain the radius Re of the cavitation bubbles induced by the electric pulse, perform the operation of the cavitation bubbles striking the first specimen according to the first preset condition, and obtain the cavitation pit size re of the first specimen after the first specimen is cavitated.

[0041] In an embodiment of the present invention, a single cavitation bubble of controllable size is stably generated in still water by using an electric pulse-induced cavitation bubble system. The electric pulse-induced cavitation bubble system is composed of a power supply, a resistor, a capacitor, and a three-phase switch. The power supply is controlled by the three-phase switch to charge or discharge the capacitor, and the discharge current is transmitted to the discharge electrode through a high-power cable to generate instantaneous high temperature to form cavitation bubbles. The pixel number of the cavitation bubble picture and the actual scale photo are calibrated to obtain the proportional relationship between the scale photo and the pixel of the picture; then a high-speed camera is used in conjunction with a scale to record the scale photo of the cavitation bubble induced by the electric pulse under actual working conditions, and the actual size is converted into the actual size by measuring the pixel number based on the above proportional relationship to obtain the radius Re of the cavitation bubble induced by the electric pulse.

[0042] In this embodiment, the operation of the cavitation bubble striking the first specimen according to the first preset condition includes: pre-marking the striking area of ​​the cavitation bubble on the first specimen, and precisely controlling the cavitation bubble to collapse in the striking area according to the first preset condition. The first preset condition is to quantitatively control the relative position of the cavitation bubble and the first specimen according to the dimensionless distance formula. The dimensionless distance formula γ is:

[0043] γ=D / Re max

[0044] Where D is the distance from the centroid to the surface of the first specimen when the cavitation bubble expands to its maximum, Re max It is the maximum radius of cavitation bubbles induced by electric pulse.

[0045] In a specific embodiment, a schematic diagram of the structure of a system for electric pulse-induced cavitation bubbles striking a specimen is provided. Figure 2 As shown, the circuit part of the low-voltage DC pulse generator is the electric pulse induced cavitation bubble system. When the low-voltage DC pulse generator is performing electric pulse induced cavitation bubble impact on the test piece, the discharge electrode is placed in a transparent glass tank filled with water. On one side of the glass tank is a soft light source, and on the other side is a high-speed camera for photographing cavitation bubbles. The high-speed camera is connected to a computer to transmit the photographed impact phenomenon and analyze it.

[0046] Specifically, according to the radius Re of the cavitation bubble induced by the electric pulse, the space required for the support platform, wires, discharge electrodes, etc. arranged in the glass water tank, and the space required for manual operation, the lower limit of the size of the glass water tank is determined, that is, the length × width × height size is not less than 50Re × 50Re × 50Re, which is only used as an example and is not limited to this. The glass water tank is filled with distilled water with extremely low impurity and gas nucleus content, and the discharge electrode and the specimen are supported by a plexiglass plate fixed in the glass water tank. In order to ensure that the liquid surface and the side wall of the glass water tank do not affect the evolution of the cavitation bubble, the discharge electrode is placed in the center of the glass water tank, 20Re below the liquid surface, and the specimen is fixed below the discharge electrode. It should be noted that if the discharge electrode is placed within 20Re, the air on the liquid surface can be regarded as an infinite air bubble boundary, which will affect the evolution process of the cavitation bubble; if it exceeds 20Re, the cavitation bubble is considered to be in an unbounded domain, and the evolution process of the cavitation bubble is not affected by various boundary conditions. The pressure of the water surface in the glass water tank is atmospheric pressure, and the water temperature is maintained at 25.0±1.0℃. It should be noted that the indoor temperature is constant at 25℃, and distilled water is sealed in bottles and placed indoors to make the distilled water consistent with the room temperature. During the operation, a thermometer is placed in the glass water tank to monitor the water temperature. When the temperature exceeds the range, the operation is paused and continued after the water temperature returns to normal.

[0047] In a specific embodiment, the process of generating cavitation bubbles by electric pulses includes: the voltage inputted by the low-voltage DC pulse generator is 220V AC, the three-phase switch is turned upward to the charging state, the charging indicator light is on, and the power supply starts to charge two 4000μF capacitors in parallel. The voltmeter indicates the voltage across the capacitor, and the DC voltage outputted by the power supply is 100-1000V by adjusting the resistor. After judging that the capacitor is fully charged by the ammeter and the indicator light, the three-phase switch is turned downward to the ready-to-discharge state, and the current stored in the low-voltage DC pulse generator is transmitted to the discharge electrode through a high-power cable (380V, 1000A), that is, an instantaneous high temperature is generated at the overlap point of the discharge electrode, and the discharge electrode will stably induce cavitation bubbles of a certain size according to the currently set voltage. The discharge electrode is a pair of pure copper wires (diameter is 0.08mm). Since the radius Re of the cavitation bubble induced by the electric pulse is much larger than the radius of the discharge electrode, the influence of the discharge electrode on the cavitation bubble can be ignored. By adjusting the voltage value of the power supply output, spherical cavitation bubbles of different radii can be stably obtained. It should be noted that the specific values ​​involved in the above description are only used as examples and are not limited thereto, and can be adaptively modified according to actual applications.

[0048] The pixel points and real size of the current high-speed camera setting parameters are calibrated to obtain the radius Re of the cavitation bubble induced by the electric pulse. The specific method is to place the scale at the focus of the high-speed camera, that is, the position where the cavitation bubble will appear, record the scale photo under this working condition, and calculate the actual size represented by a single pixel during image processing. Since the clarity of the image boundary varies with different shooting conditions, the measurement accuracy can generally reach the micron level. Figure 3 A single pixel corresponds to 0.01 mm, that is, the ratio between the scale photo and the image pixel is 1 pixel corresponds to 0.01 mm. The specimen size is 50×50×12 mm 3 The evolution of cavitation bubble formation and the whole process of hitting the specimen at the dimensionless distance γ of 1.24 can be clearly observed. Under the effect of soft light source, the photos taken by high-speed camera are clearer.

[0049] By controlling the voltage at 120V, the size of the cavitation bubble Re induced each time is 8.00mm±0.10mm. The fine control of the electric pulse induced cavitation bubble system can achieve the technical requirement of "pointing and hitting" by changing the position of the discharge electrode overlap point; each time the cavitation bubble hits the specimen, mark the corresponding position of the specimen so that it can be accurately positioned under a high-performance scanning electron microscope. The distance range in which the cavitation bubble can hit the specimen satisfies γ<2, and the dimensionless distance γ range is 1.10-1.30. By precisely controlling the position of the discharge electrode and hitting each specimen 100 times, complete coverage of the γ range can be achieved, wherein the cavitation bubble hitting the specimen needs to cause cavitation damage. The cavitation bubble hitting area is pre-marked on the specimen. The hitting area should be smaller than the size of the high-performance scanning electron microscope sample. The discharge electrode is precisely positioned to control the collapse of the cavitation bubble in the hitting area.

[0050] Step S2: Control the ultrasonic wave to induce the generation of cavitation bubble cloud and obtain the characteristic radius Ru of the cavitation bubble cloud induced by the ultrasonic wave, perform the operation of the cavitation bubble cloud striking the second specimen according to the second preset condition, and obtain the cavitation pit size ru of the second specimen after the second specimen is cavitated.

[0051] In the embodiment of the present invention, a large number of cavitation bubbles are generated by using an ultrasonic cavitation system to form a cavitation bubble cloud, such as Figure 4 As shown, the ultrasonic cavitation system consists of a power supply, a control host, a transducer, a horn, and a constant temperature cooling water circulation system, wherein the amplifier, ultrasonic frequency converter and power regulator are all integrated in the control host. The amplifier in the control host converts the civil electricity input by the power supply into alternating electric energy through the ultrasonic frequency converter, and then matches the alternating electric energy with the transducer through the power regulator. The transducer converts the electric energy into mechanical energy to drive the longitudinal mechanical vibration of the horn. When the end of the horn is immersed in the water in the beaker, the high-frequency vibration of the horn induces cavitation in the lower water body, generating a cavitation bubble cloud composed of a large number of cavitation bubbles. Specifically, the ultrasonic cavitation system also includes a phase-locked frequency automatic tracker, which should be noted that the phase-locked frequency automatic tracker is also integrated in the control host. Since the transducer of the ultrasonic cavitation system will continue to heat up when it runs for a long time, causing the optimal frequency to fluctuate, on the one hand, the temperature is continuously controlled by using a constant temperature cooling water circulation system, and on the other hand, the transducer is kept at the optimal frequency during operation by using a phase-locked frequency automatic tracker. Without a phase-locked frequency automatic tracker, the ultrasonic frequency converter needs to be adjusted manually continuously, which is costly and inefficient.

[0052] In this embodiment, the process of obtaining the characteristic radius Ru of the cavitation bubble cloud induced by ultrasonic waves includes: using a high-speed camera in combination with a macro lens to photograph the cavitation bubble cloud, and obtaining the characteristic radius Ru of the cavitation bubble cloud by statistically analyzing the size distribution of the cavitation bubbles. Specifically, a high-speed camera in combination with a macro lens is used to photograph the cavitation bubble cloud. Most of the cavitation bubbles in the cavitation bubble cloud are close to the surface of the horn after formation. The farther away from the horn, the fewer the cavitation bubbles are, and the overall distribution is conical; further observe the morphology of the cavitation bubble cloud on the lower side of the horn and the size of each cavitation bubble, and obtain the characteristic radius Ru of the cavitation bubble cloud by statistically analyzing the size distribution of the cavitation bubbles. It should be noted that the overall size of the cavitation bubble decreases with the increase of the distance from the lower side of the transformer. Therefore, a fitting curve of the relationship between the radius of the cavitation bubble and the distance from the lower side of the transformer can be obtained. Referring to the dimensionless distance formula γ of the cavitation bubble induced by electric pulse, its value range is 1.10-1.30, and γ=1.20 is taken. The intersection of the oblique line and the fitting curve is the characteristic radius value Ru.

[0053] In this embodiment, the operation of the cavitation bubble cloud striking the second specimen is performed according to the second preset condition, including: pre-marking the striking area of ​​the cavitation bubble cloud on the second specimen, and according to the second preset condition, precisely controlling the cavitation bubble cloud to collapse in the striking area. The second preset condition is to control the operation time of the ultrasonic cavitation system, which is used to ensure that a relatively mild cavitation damage occurs on the surface of the second specimen, so that the cavitation pits are more evenly distributed on the surface of the second specimen. It should be noted that if the operation time of the ultrasonic cavitation system is greater than the preset operation time, the cavitation pits on the surface of the specimen will overlap or accumulate, making it difficult to obtain the actual cavitation pit size results under a high-performance scanning electron microscope. The preset operation time is set based on actual needs and is not limited here.

[0054] In a specific embodiment, the ultrasonic cavitation system can achieve 10-100KHz frequency and 0-500W power adjustment through a power regulator. Considering that the horn radiation head will experience rapid loss during high-power operation, and the cavitation bubble cloud is weaker during low-power operation, after multiple pre-strikes, it is determined that the equipment power used is 300W, the ultrasonic transducer operating frequency is 20.0±0.2KHz, the beaker liquid level is 100.0±2.0mm, the liquid medium is deionized water, the water temperature can be controlled to be constant at 25±2℃ through a circulating water cooling system, and the specimen size is 20×20×2mm 3 The distance between the specimen and the radiating surface at the end of the horn is 2.0±0.1mm.

[0055] The specific operation process of ultrasonic-induced cavitation bubble cloud is divided into the following steps:

[0056] Step 1: The specimen was cleaned with deionized water and anhydrous ethanol and placed in a dryer for 12 hours;

[0057] Step 2: Fix the specimen on the loading platform below the horn radiation surface with a residue-free double-sided tape, inject 250 ml of deionized water into the beaker, and align the horn radiation surface with the center of the specimen with a spacing of 2.0 mm;

[0058] Step 3: Turn on the ultrasonic equipment, first roughly adjust the equipment power until you can hear the sound, then adjust the transducer operating frequency, and when the amplitude transformer resonates best, turn on the tracking frequency switch, and finally fine-tune the equipment power to the preset value;

[0059] Step 4: The ultrasonic equipment is shut down every 60 minutes, the waste water is poured out, the test piece is removed, and then the next test piece is loaded and started according to steps 2 and 3;

[0060] Step 5: The removed specimens were washed with deionized water and anhydrous ethanol in turn, dried at 25°C for 10 min, placed in a dryer for 12 h, and then placed in a sample bag and stored away from light.

[0061] Install a macro lens on the high-speed camera and increase the shooting speed (no less than 400,000 frames per second) to observe the morphology of the cavitation bubble cloud and the size distribution of the cavitation bubble under the working horn. Since the vibration of the horn generates an alternating positive and negative ultrasonic field, the morphology of the cavitation bubble cloud under the horn changes periodically, such as Figure 5 By counting the size of each cavitation bubble in the cavitation bubble cloud in each complete cycle (no less than 30 in each cycle and no less than 10 complete cycles), it can be obtained that the radius of the cavitation bubble is between 0.08mm and 0.21mm, and the characteristic radius Ru of the cavitation bubble cloud is 0.15mm.

[0062] In this embodiment, the process of obtaining the cavitation pit size re of the first specimen and the cavitation pit size ru of the second specimen includes: cleaning the first specimen and the second specimen after cavitation damage, and placing them in a dryer for standing after drying at a constant temperature. In a specific embodiment, distilled water and anhydrous ethanol can be used to remove tiny debris attached to the surface of the above specimens to avoid affecting the observation effect of observing the microscopic morphology of the sample surface using a high-performance scanning electron microscope, and the cleaned specimen is placed at a constant temperature of 25°C for 10 minutes for drying, and then placed in a dryer for 12 hours. This is only used as an example, and adaptive modifications are made according to actual applications.

[0063] In this embodiment, the first specimen and the second specimen after being left to stand are sliced ​​and sampled respectively, and a high-performance scanning electron microscope is used to record the cavitation pit size re of the first specimen of the sample struck by electric pulse induced cavitation bubbles and the cavitation pit size ru of the second specimen of the sample struck by ultrasonic induced cavitation bubble cloud. In a specific embodiment, the specimens are sliced ​​and sampled, and different specimens have different sampling requirements. Specifically, for the first specimen struck by electric pulse induced cavitation bubbles, the sample size should be larger than the cavitation bubble strike area pre-marked on the first specimen during sampling. For the second specimen struck by ultrasonic induced cavitation bubble cloud, the second specimen will leave circular cavitation damage marks on the surface. The area affected by the cavitation bubble cloud on the second specimen is roughly divided into the cavitation core area, the cavitation transition area and the non-cavitation area. When sampling, 1 / 4 of the second specimen is intercepted to obtain the cavitation transition area and the non-cavitation area. A high-performance scanning electron microscope is used to observe the microscopic morphology of the sample surface. The maximum chamber pressure of 500Pa in the low vacuum mode can image even the most demanding insulators.

[0064] It should be noted that in order to clearly observe the deformation of the specimen and quantify the deformation response of the specimen after cavitation, the specimen material is required to have properties such as homogeneity, transparency, stability, hydrolysis resistance and easy plasticity. The specimen material solidifies under heating conditions, has low viscosity, good fluidity, good electrical insulation, and does not contain solvents, does not yellow, has good hydrolysis stability and return performance. In addition, the shape and size of the specimen are also strictly required. In an embodiment of the present invention, the first specimen and the second specimen are cast with a rectangular or cylindrical mold, wherein the surface length of the first specimen is not less than 5 times the cavitation bubble radius Re induced by the electric pulse, or the radius is not less than 3 times the cavitation bubble radius Re induced by the electric pulse, and the thickness is not less than 1.5 times the cavitation bubble radius Re induced by the electric pulse; the second specimen, the surface length is not less than 2 times the amplitude rod radius, or the radius is not less than 1.5 times the amplitude rod radius, and the thickness is not less than 10 times the characteristic radius Ru of the cavitation bubble cloud.

[0065] In the embodiment of the present invention, the process of preparing the test piece mainly includes the following steps:

[0066] Step 1: Mix, mix and stir according to different mass ratios. Place a glass beaker that has been rinsed with distilled water and alcohol and dried on an analytical balance, peel it and pour two liquid silica gels A and B into it according to the mass ratio. The total volume should not exceed 1 / 3 of the glass beaker. After weighing, take out the beaker, place it on a clean and flat workbench, and stir it at a constant speed in one direction for 30 minutes using a clean glass rod.

[0067] Step 2: Exhaust. It is necessary to remove the air bubbles that are involved and trapped during the mixing process by vacuuming. Place the glass beaker in a vacuum oven to extract air. When the pressure vacuum gauge reading is less than -0.8 bar, turn off the vacuum pump and seal the vacuum oven. During the vacuuming process, the rubber will expand and even overflow the beaker. Therefore, when the rubber expands to about 2 / 3 of the beaker, stop vacuuming and let it stand for about 10 minutes before continuing. After reaching the predetermined vacuum degree, let it stand for about 1 hour, wait for the bubbles to float to the upper side of the rubber, and then let air return to the standard atmospheric pressure. Repeat the above process several times until there are almost no bubbles in the rubber.

[0068] Step 3: Curing. Pour the degassed rubber into the prepared glass or polytetrafluoroethylene mold. The mold size is determined according to actual needs. After the mold is transferred into the vacuum oven, the vacuum oven is set to a predetermined temperature and cured under constant temperature conditions at normal pressure. When the preset time is reached, turn off the power of the vacuum oven and let the inside of the vacuum oven cool naturally to minimize temperature stress on the material caused by sudden temperature changes.

[0069] Step 4: Demolding: After the vacuum oven is completely cooled, take out the mold, separate the mold box from top to bottom, and then easily take out the specimen. Use scissors or a blade to remove the burrs, and then place it in a sample bag and store it at a constant temperature, sealed, and away from light.

[0070] Avoid touching the surface area of ​​the specimen to be tested with your fingers or other tools during the entire operation. The physical and mechanical properties of the specimens that have been strictly prepared and properly stored can be kept stable for more than 12 months.

[0071] Step S3: respectively calculate the micro-scale cavitation damage effect of cavitation bubbles induced by electric pulses and the macro-scale cavitation damage effect of cavitation bubble clouds induced by ultrasound, wherein the micro-scale cavitation damage effect Ee=re / Re, and the macro-scale cavitation damage effect Eu=ru / Ru.

[0072] Step S4: By comparing the microscopic cavitation damage effect Ee with the macroscopic cavitation damage effect Eu, the similarity of the cavitation damage effects of cavitation bubbles of different scales is determined.

[0073] In a specific embodiment, Figure 6 As shown, the sample was observed at 200 times magnification after the electric pulse induced cavitation bubble impact. Figure 6 In the circular area in (A), circular pits can be seen that are different from the surrounding textures. These are pits caused by the electric pulse-induced cavitation bubbles hitting the sample, and their size re is 80μm. The sample was observed under 500 times magnification when the ultrasonic-induced cavitation bubble cloud hit it. Figure 6The circular area in (B) is the pit where the ultrasonic wave-induced cavitation bubble cloud hits the sample, and its size ru is about 1.5μm-2μm. Combined with the cavitation bubble radius Re of 8.00mm and the characteristic radius Ru of the cavitation bubble cloud of 0.15mm, the effect of the electric pulse-induced cavitation bubble hitting the sample is Ee=re / Re, and after calculation, Ee is 0.010. The effect of the ultrasonic wave-induced cavitation bubble cloud hitting the sample is Eu=ru / Ru, and after calculation, Eu is 0.010-0.013.

[0074] In summary, the sizes of cavitation bubbles and cavitation bubble clouds induced by the two methods are very different. Each of them causes obvious pit deformation on the surface of the specimen, and the pit sizes are also very different. However, the effects Ee and Eu of the two methods on the samples are very close, indicating that although the two methods of inducing cavitation bubbles are different and the sizes are very different, the effects on the specimens are similar.

[0075] The present invention provides a method for judging the similarity of cavitation damage effects of cavitation bubbles of different scales. The method comprises striking a test piece with cavitation bubbles induced by electric pulses and striking a test piece with cavitation bubble clouds induced by ultrasonic waves, comparing the cavitation damage results of the test pieces, and using the microscopic morphology of the test piece surface and by comparing the characteristics of cavitation damage pits, judging whether the cavitation damage effects of two different scales of cavitation bubbles, microscopic cavitation bubbles and macroscopic cavitation bubble clouds, are similar, thereby establishing a connection from microscopic cavitation laws to macroscopic cavitation effects, and providing technical support for the engineering application of cavitation protection theory and the research and development of cavitation-resistant materials.

[0076] Obviously, the above embodiments are only examples for clear explanation, and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the invention.

Claims

1. A method for judging the similarity of cavitation damage effects of cavitation bubbles of different scales, characterized in that: include: Controlling the electric pulse to induce cavitation bubbles and obtaining the radius Re of the cavitation bubbles induced by the electric pulse, performing an operation of the cavitation bubbles striking the first specimen according to the first preset condition, and obtaining the cavitation pit size re of the first specimen after the first specimen is cavitated; Control the ultrasonic wave to induce the generation of cavitation bubble cloud and obtain the characteristic radius Ru of the cavitation bubble cloud induced by the ultrasonic wave, perform the operation of the cavitation bubble cloud striking the second test piece according to the second preset condition, and obtain the cavitation pit size ru of the second test piece after the second test piece is cavitated; The micro-scale cavitation damage effect of cavitation bubbles induced by electric pulses and the macro-scale cavitation damage effect of cavitation bubble clouds induced by ultrasound are calculated respectively, wherein the micro-scale cavitation damage effect Ee = re / Re, and the macro-scale cavitation damage effect Eu = ru / Ru; By comparing the micro-scale cavitation damage effect Ee and the macro-scale cavitation damage effect Eu, the similarity of the cavitation damage effects of cavitation bubbles of different scales can be judged.

2. The method for judging the similarity of cavitation damage effects of cavitation bubbles of different scales according to claim 1, characterized in that: By using an electric pulse-induced cavitation bubble system, single cavitation bubbles of controllable size are stably generated in still water. The electric pulse-induced cavitation bubble system is composed of a power supply, a resistor, a capacitor and a three-phase switch. The process of electric pulse-induced cavitation bubble generation includes: controlling the power supply to charge the capacitor or discharge the capacitor through the three-phase switch, and transmitting the discharge current to the discharge electrode through a high-power cable, so as to generate instantaneous high temperature to form cavitation bubbles.

3. The method for judging the similarity of cavitation damage effects of cavitation bubbles of different scales according to claim 2, characterized in that: The process of obtaining the cavitation bubble radius Re induced by the electric pulse includes: The pixel count of the cavitation bubble image and the actual scale photo are calibrated to obtain the proportional relationship between the scale photo and the image pixels; A high-speed camera and a scale are used to record scale photos of cavitation bubbles induced by electric pulses under actual working conditions. Based on the above proportional relationship, the number of pixels is calculated to convert it into actual size to obtain the radius Re of the cavitation bubble induced by the electric pulse.

4. The method for judging the similarity of cavitation damage effects of cavitation bubbles of different scales according to claim 1, characterized in that: The operation of causing the cavitation bubble to strike the first specimen according to the first preset condition includes: pre-marking the striking area of ​​the cavitation bubble on the first specimen, and precisely controlling the cavitation bubble to collapse in the striking area according to the first preset condition, wherein the first preset condition is to quantitatively control the relative position of the cavitation bubble and the first specimen according to a dimensionless distance formula.

5. The method for judging the similarity of cavitation damage effects of cavitation bubbles of different scales according to claim 4, characterized in that: The dimensionless distance formula γ is: γ=D / Re max Where D is the distance from the centroid to the surface of the first specimen when the cavitation bubble expands to its maximum, Re max It is the maximum radius of cavitation bubbles induced by electric pulse.

6. The method for judging the similarity of cavitation damage effects of cavitation bubbles of different scales according to claim 1, characterized in that: A large number of cavitation bubbles are generated by using an ultrasonic cavitation system to form a cavitation bubble cloud. The ultrasonic cavitation system is composed of a power supply, a control host, a transducer, a horn, and a constant temperature cooling water circulation system, wherein an amplifier, an ultrasonic frequency converter, and a power regulator are all integrated in the control host. The process of ultrasonic wave inducing the generation of cavitation bubble clouds includes: the amplifier in the control host converts the civil electricity input by the power supply into alternating electric energy through the ultrasonic frequency converter, and then matches the alternating electric energy with the transducer through the power regulator. The transducer converts the electric energy into mechanical energy to drive the longitudinal mechanical vibration of the horn. When the end of the horn is immersed in the water body, the high-frequency vibration of the horn induces cavitation in the lower water body, thereby generating a cavitation bubble cloud composed of a large number of cavitation bubbles.

7. The method for judging the similarity of cavitation damage effects of cavitation bubbles of different scales according to claim 6, characterized in that: The process of obtaining the characteristic radius Ru of the cavitation bubble cloud induced by ultrasound includes: photographing the cavitation bubble cloud using a high-speed camera in combination with a macro lens, and obtaining the characteristic radius Ru of the cavitation bubble cloud by statistically analyzing the size distribution of the cavitation bubbles.

8. The method for judging the similarity of cavitation damage effects of cavitation bubbles of different scales according to claim 6, characterized in that: The operation of striking the second specimen with a cavitation bubble cloud according to the second preset condition includes: pre-marking the striking area of ​​the cavitation bubble cloud on the second specimen, and according to the second preset condition, precisely controlling the collapse of the cavitation bubble cloud in the striking area. The second preset condition is to control the operating time of the ultrasonic cavitation system to ensure that relatively mild cavitation damage is generated on the surface of the second specimen, so that the cavitation pits are more evenly distributed on the surface of the second specimen.

9. The method for judging the similarity of cavitation damage effects of cavitation bubbles of different scales according to claim 1, characterized in that: The process of obtaining the cavitation pit size re of the first specimen and the cavitation pit size ru of the second specimen comprises: After the cavitation damage occurs, the first test piece and the second test piece are cleaned respectively, dried at a constant temperature, and then placed in a dryer to stand; The first specimen and the second specimen after standing were sliced ​​and sampled respectively, and a high-performance scanning electron microscope was used to record the cavitation pit size re of the first specimen when the cavitation bubble was hit by electric pulse and the cavitation pit size ru of the second specimen when the cavitation bubble cloud was hit by ultrasonic wave.

10. The method for judging the similarity of cavitation damage effects of cavitation bubbles of different scales according to claim 6, characterized in that: The first specimen and the second specimen are cast using a rectangular or cylindrical mold, wherein the thickness of the first specimen is not less than 1.5 times the radius Re of the cavitation bubble induced by the electric pulse, the surface length is not less than 5 times the radius Re of the cavitation bubble induced by the electric pulse or the radius is not less than 3 times the radius Re of the cavitation bubble induced by the electric pulse; the thickness of the second specimen is not less than 10 times the characteristic radius Ru of the cavitation bubble cloud, the surface length is not less than 2 times the radius of the horn or the radius is not less than 1.5 times the radius of the horn.

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