Device and method for detecting dynamic characteristics of cavitation in closed hexagonal tube

Abstract

The invention discloses a device and a method for detecting dynamic characteristics of a cavitation bubble in a closed hexagonal tube, and relates to the technical field of photoelectric detection.According to the method, through combination of a concave-convex lens group, a beam expander and a circular diaphragm, a central area with uniform laser intensity distribution is intercepted as a detection light beam, and a cubic beam splitter and a reflector are combined to detect the dynamic characteristics of the cavitation bubble in the closed hexagonal tube; a detection area is constructed in the closed hexagonal tube; the light is reflected by the cubic beam splitter, converged to the photoelectric sensor by the focusing lens and displayed by the oscilloscope; and analyzing the electric signal obtained by the oscilloscope to obtain the maximum cavitation radius and the pulsation period of the cavitation in the closed hexagonal tube. According to the method, the problem that the dynamic characteristics of a large cavitation bubble or a cavitation bubble generated at a non-central position in the closed hexagonal pipe are difficult to detect is solved, and the method is simple to operate and low in cost.

Description

Technical Field

[0001] The invention relates to the field of photoelectric detection technology, and in particular to a device and method for detecting cavitation dynamic characteristics in a closed hexagonal tube. Background Art

[0002] Cavitation corrosion, or cavitation for short, is a common wear phenomenon in hydraulic structures, which seriously affects the service life of hydraulic structures such as sluices, reservoirs, and levees. How to prevent cavitation from damaging hydraulic structures is one of the hot topics of experts and scholars in the field of hydraulic engineering. At present, relevant anti-cavitation research is mainly concentrated in the field of materials, such as: using lasers and other means to modify the material itself to give it excellent anti-cavitation properties; or constructing a coating with excellent anti-cavitation properties on the surface of the base material to achieve the effect of anti-cavitation. Among them, the coating method is more economical and widely used, and the protection period can reach more than ten years. However, compared with the service life of hydraulic structures, the current protection period of the coating is still insufficient. my country encourages water conservancy projects to adopt diversified anti-corrosion measures. It is of great practical significance to explore other anti-cavitation means and further extend the service life of hydraulic structures through a combination of multiple methods. In fact, since confined space and wall structure can have a greater impact on cavitation jets, the use of similar surface structures can achieve the effect of anti-cavitation, thereby extending the service life of hydraulic structures, but there are currently no reports on related engineering applications. Honeycomb structure is one of the common structures in nature. When a similar structure is used on the surface of a hydraulic structure, the structure of its closed hexagonal tube can limit the dynamic behavior of cavitation, thereby achieving an anti-cavitation effect. Therefore, it is necessary to conduct experimental research on the dynamic characteristics of cavitation in closed hexagonal tubes.

[0003] The maximum bubble radius and pulsation period of the cavitation bubble are two key parameters that characterize the dynamic characteristics of the cavitation bubble. In the field of cavitation detection, common detection methods mainly include high-speed photography based on photography, Schlieren method, etc., as well as beam deflection method and beam transmission method based on detection beam. The former focuses on real-time morphological measurement of cavitation with high spatial resolution, but in order to achieve high temporal resolution measurement at the same time, it is often necessary to equip a very expensive high-speed camera. The latter focuses on high-temporal resolution measurement of cavitation, but it is difficult to simultaneously detect the entire morphology of the cavitation bubble. For detecting the dynamic characteristics of cavitation in a closed hexagonal tube, the high-speed photography method equipped with a high-speed camera is undoubtedly the best solution, however, the cost is too high; and the beam deflection method or beam transmission method based on the detection beam will encounter measurement limitations, namely: when the cavitation is generated in a non-central position in a closed hexagonal tube or the cavitation size exceeds the side length of the regular hexagon of the hexagonal tube cross-section, such as Figure 1As shown in the figure, since the detection beam can only be perpendicular to the two walls of the hexagonal tube, it will be refracted when it hits the adjacent wall (the detection beam in the dotted box in the figure), which will lead to the failure of the detection principle. How to accurately detect the dynamic characteristics of cavitation in a closed hexagonal tube at a lower cost has become a problem. Summary of the invention

[0004] In order to overcome the above-mentioned technical problems, the purpose of the present invention is to provide a low-cost device and method for detecting the dynamic characteristics of cavitation in a closed hexagonal tube, which solves the problem that it is difficult to detect the dynamic characteristics of larger cavitations or cavitations generated in non-central positions in a closed hexagonal tube. The invention is also suitable for detecting the dynamic characteristics of cavitations in non-transparent closed hexagonal tubes.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a detection device for the dynamic characteristics of cavitation in a closed hexagonal tube, comprising a laser for projecting a detection beam, a detection device is provided on one side of the laser, the detection device comprises a concave-convex lens group, a first adjustable circular aperture, a beam expander, a second adjustable circular aperture, a cubic beam splitter, a closed hexagonal tube and a reflector, and the various components are coaxially installed in sequence along the direction of the detection beam projected by the laser, the closed hexagonal tube is installed in a transparent container containing a transparent liquid provided on one side of the cubic beam splitter, the closed end of the closed hexagonal tube is closed by a reflector, and the reflecting surface of the reflector is kept perpendicular to the detection beam projected by the laser and the axial direction of the closed hexagonal tube;

[0006] The detection device also includes a focusing lens, an interference filter, a photoelectric sensor and an oscilloscope, wherein the focusing lens, the interference filter and the photoelectric sensor are coaxially mounted in sequence on the other side of the cubic beam splitter, and the mounting directions of the focusing lens, the interference filter and the photoelectric sensor are kept perpendicular to the direction of the detection beam projected by the laser, and the output end of the photoelectric sensor is connected to any input end of the oscilloscope;

[0007] The incident surface of the cubic beam splitter is kept perpendicular to the direction of the detection light beam projected by the laser. After being dispersed by the cubic beam splitter for the first time, the detection light beam is emitted as two mutually perpendicular light beams, wherein the projection direction of one beam is in the same direction as the emission direction of the laser, and the other beam is projected in the direction opposite to the direction of the focusing lens; after being reflected by the reflector, the detection light beam in the same direction as the emission direction of the laser is dispersed by the cubic beam splitter for the second time, and is emitted as two mutually perpendicular light beams, wherein the projection direction of one beam is opposite to the emission direction of the laser, and the other beam is projected toward the focusing lens.

[0008] Preferably, the light intensity distribution of the detection light beam projected by the laser is Gaussian distribution.

[0009] Preferably, the laser power stability of the detection light beam projected by the laser is not less than ±2.5%.

[0010] Preferably, the central wavelength of the light that can be transmitted through the interference filter is consistent with the wavelength of the laser.

[0011] Based on the above detection device, the present invention also provides a method for detecting the dynamic characteristics of cavitation in a closed hexagonal tube, the detection method comprising the following steps:

[0012] S1, using a concave-convex lens group to expand the detection beam projected by the laser;

[0013] S2. Under the premise that no obvious optical diffraction occurs, adjust the first adjustable circular aperture so that the diameter of the circular detection light beam passing through the first adjustable circular aperture is reduced to less than 1.2 mm;

[0014] S3, using a beam expander to expand the detection beam projected by the laser;

[0015] S4, adjusting the second adjustable circular aperture so that the diameter of the circular detection beam passing through the second adjustable circular aperture is smaller than the inner diameter of the closed hexagonal tube, and measuring the diameter of the detection beam at this time as D;

[0016] S5, adjusting the position of the closed hexagonal tube so that the circular detection light beam passing through the second adjustable circular aperture enters the closed hexagonal tube, and the detection light beam reflected by the reflector inside the closed hexagonal tube coincides with the detection light beam incident on the closed hexagonal tube;

[0017] S6. Adjust the position of the cubic beam splitter so that the direction in which the detection beam reflected by the reflector in the closed hexagonal tube is reflected again by the cubic beam splitter is perpendicular to the direction in which the detection beam is emitted by the laser. Then, place the focusing lens, interference filter, and photoelectric sensor in the direction of the reflected detection beam, and ensure that each optical element is coaxial and at the same height as the cubic beam splitter.

[0018] S7. By adjusting the position of the photoelectric sensor, the detection beam passing through the focusing lens is focused on the photosensitive element of the photoelectric sensor. At this time, the signal voltage value of the oscilloscope reaches the maximum, which is recorded as V max ;

[0019] S8. Use a shield to completely block the detection beam passing through the focusing lens, and record the signal voltage value of the oscilloscope at this time as V min , remove the obstruction;

[0020] S9. Use an external high-energy laser transmitter to focus the high-energy laser on a position not close to the edge of the detection beam irradiation area in the closed hexagonal tube. The signal voltage waveform of the oscilloscope at this time is recorded as V(t). The relationship between the bubble radius of the cavitation bubble and time R(t) is:

[0021] Preferably, the concave-convex lens group can expand the detection light beam projected by the laser by n times, wherein n is a positive integer not less than 30.

[0022] Preferably, the beam expander expands the detection beam projected by the laser by no less than 10 times.

[0023] Compared with the prior art, the invention has the following beneficial effects: compared with the traditional method, the invention solves the problem that it is difficult to detect the dynamic characteristics of larger cavitation or cavitation generated in a non-central position in a closed hexagonal tube. Through the combination of a concave-convex lens group, a beam expander and a circular aperture, the central area with a relatively uniform laser light intensity distribution is intercepted as a detection beam, and a detection area is constructed in the closed hexagonal tube in combination with a cubic beam splitter and a reflector; after being reflected by the beam splitter, it is converged to a photoelectric sensor by a focusing lens and displayed by an oscilloscope; the electrical signal obtained by the oscilloscope is analyzed, and the high time resolution measurement of the maximum bubble radius and pulsation period of the cavitation in the closed hexagonal tube can be achieved. The method of the invention is simple to operate and low in cost. At the same time, the invention is also suitable for the detection of the dynamic characteristics of cavitation in a non-transparent closed hexagonal tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0025] In the attached picture:

[0026] Figure 1 Schematic diagram of cavitation in a closed hexagonal tube of the present invention;

[0027] Figure 2 is an exploded view of the detection device of the present invention;

[0028] Figure 3 It is a signal voltage waveform diagram obtained by the oscilloscope in the present invention for measuring the cavitation dynamics characteristics in a closed hexagonal tube;

[0029] Figure 4 In the present invention, Figure 3 The relationship between the cavitation radius and time in the closed hexagonal tube obtained by analysis;

[0030] Numbers in the figure: 1. Laser; 2. Concave-convex lens group; 3. First adjustable circular aperture; 4. Beam expander; 5. Second adjustable circular aperture; 6. Cube beam splitter; 7. Closed hexagonal tube; 8. Reflector; 9. Transparent container; 10. Focusing lens; 11. Interference filter; 12. Photoelectric sensor; 13. Oscilloscope. DETAILED DESCRIPTION

[0031] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0032] like Figure 2 As shown in the exploded view of the detection device, a detection device for the dynamic characteristics of cavitation in a closed hexagonal tube is shown, wherein illustrations (a)-(e) are cross-sectional views of the detection beam at the positions indicated by the corresponding arrows, and the line of sight of the cross-sectional view is along the -x axis direction.

[0033] The detection device includes a laser 1 for projecting a detection beam, and a concave-convex lens group 2, a first adjustable circular aperture 3, a beam expander 4, a second adjustable circular aperture 5, a cubic beam splitter 6, a closed hexagonal tube 7, a reflector 8, and a transparent container 9 containing a transparent liquid are coaxially installed in sequence along the direction of the detection beam projected by the laser 1; wherein the reflector 8 is installed at the bottom of one closed end of the closed hexagonal tube 7, and the reflecting surface is kept perpendicular to the axial direction of the detection beam projected by the laser 1 and the closed hexagonal tube 6; the closed hexagonal tube 7 is placed in the transparent container 9 containing a transparent liquid.

[0034] The detection device also includes a focusing lens 10, an interference filter 11, a photoelectric sensor 12 and an oscilloscope 13. The focusing lens 10, the interference filter 11 and the photoelectric sensor 12 are coaxially installed on the cubic beam splitter 6 in sequence, and the installation direction of the focusing lens 10, the interference filter 11 and the photoelectric sensor 12 is perpendicular to the direction of the detection beam projected by the laser 1, wherein the output end of the photoelectric sensor 12 is connected to the input end of the oscilloscope 13.

[0035] The incident surface of the cubic beam splitter 6 is kept perpendicular to the direction of the detection light beam projected by the laser 1. After being dispersed by the cubic beam splitter 6 for the first time, the detection light beam is emitted as two mutually perpendicular light beams, wherein the projection direction of one beam is in the same direction as the emission direction of the laser 1, and the other beam is projected in the direction opposite to the direction of the focusing lens 10; after the detection light beam in the same direction as the emission direction of the laser 1 is reflected by the reflector 8, it is dispersed by the cubic beam splitter 6 for the second time and emitted as two mutually perpendicular light beams, wherein the projection direction of one beam is opposite to the emission direction of the laser 1, and the other beam is projected toward the focusing lens 10.

[0036] The present invention adopts a laser 1 and a series of optical elements to construct a circular light beam with relatively uniform light intensity distribution in a closed hexagonal tube 7 as a detection light, and at the exit of the closed hexagonal tube 7, the detection light beam returned by the reflector 8 is divided into two beams of light by a cubic beam splitter 6, one of which is converted into an electrical signal by a photoelectric sensor 12 after passing through a series of optical elements and received by an oscilloscope 13; by analyzing and processing the electrical signal received by the oscilloscope 13, a relationship diagram of the change of the cavitation radius in the closed hexagonal tube 7 with time can be obtained, thereby realizing the measurement of the maximum bubble radius and the pulsation period of the cavitation in the closed hexagonal tube 7.

[0037] As an example, the light intensity distribution of the detection light beam projected by the laser 1 is a Gaussian distribution.

[0038] As an example, the laser power stability of the detection beam projected by the laser 1 is not less than ±2.5%.

[0039] As an example, the central wavelength of the light that can be transmitted through the interference filter 11 is consistent with the wavelength of the laser 1 .

[0040] The present invention also proposes a method for detecting the dynamic characteristics of cavitation in a closed hexagonal tube, which is applied to the above-mentioned detection device. The detection method comprises the following steps:

[0041] S1, using a concave-convex lens group 2 to expand the detection beam projected by the laser 1, and the beam expansion multiple is not less than 30 times;

[0042] S2. Under the premise that no obvious optical diffraction occurs, adjust the first adjustable circular aperture 3 so that the diameter of the circular detection light beam passing through the first adjustable circular aperture 3 is reduced to less than 1.2 mm;

[0043] S3, using a beam expander 4 to expand the detection beam projected by the laser 1, with the beam expansion factor being not less than 10 times;

[0044] S4, adjusting the second adjustable circular aperture 5 so that the diameter of the circular detection beam passing through the second adjustable circular aperture 5 is slightly smaller than the inner diameter of the closed hexagonal tube 7, and measuring the diameter of the detection beam at this time as D;

[0045] S5, adjusting the position of the closed hexagonal tube 7 so that the circular detection light beam passing through the second adjustable circular aperture 5 just completely enters the closed hexagonal tube 7, and the detection light beam reflected by the internal reflector 8 of the closed hexagonal tube 7 coincides with the detection light beam incident on the closed hexagonal tube 7;

[0046] S6. Adjust the position of the cubic beam splitter 6 so that the direction in which the detection light beam reflected by the reflector 8 in the closed hexagonal tube 7 is reflected again by the cubic beam splitter 6 is perpendicular to the direction in which the detection light beam is emitted by the laser 1. Then, place the focusing lens 10, the interference filter 11, and the photoelectric sensor 12 in the direction in which the detection light beam is reflected, and ensure that these optical elements are coaxial and at the same height as the cubic beam splitter 6.

[0047] S7. By adjusting the position of the photoelectric sensor 12, the detection light beam passing through the focusing lens 10 is focused on the photosensitive element of the photoelectric sensor 12. At this time, the signal voltage value of the oscilloscope 13 reaches the maximum, which is recorded as V max ;

[0048] S8. Use a shield to completely block the detection beam passing through the focusing lens 10. The signal voltage value of the oscilloscope 13 at this time is recorded as V min , remove the obstruction;

[0049] S9. Use an external high-energy laser transmitter to focus the high-energy laser on a position not close to the edge of the detection beam irradiation area in the closed hexagonal tube. The signal voltage waveform of the oscilloscope 13 at this time is recorded as V(t). The relationship between the bubble radius of the cavitation bubble and time R(t) is:

[0050]

[0051] Here, an example is presented to further describe the above detection method in detail, which specifically includes the following steps:

[0052] Step 1: According to Figure 2 The detection device shown in the figure builds an optical detection system, wherein the laser 1 uses a He-Ne laser (wavelength 632.8nm, spot diameter 0.8mm, light intensity distribution is Gaussian distribution, power stability is ±2.5%); the concave-convex lens group 2 uses a concave-convex lens group that can expand the detection light beam by 30 times; the beam expander 4 uses a 10-fold beam expander; the cubic beam splitter 6 uses a cubic beam splitter with a transmission and reflection ratio of 1:1; in order to facilitate the use of high-energy laser focusing to produce cavitation, the closed hexagonal tube 7 uses a transparent glass hexagonal tube with an inner diameter of 10mm, one end of which is closed with a reflector 8 to form a closed hexagonal tube 7; the transparent container 9 uses a glass cubic water tank with a side length of 10cm, and the interior of the glass cubic water tank is filled with deionized water; the entire closed hexagonal tube 7 is placed in the transparent container 9;

[0053] Step 2, adjusting the first adjustable circular aperture 3 so that the diameter of the circular detection light beam passing through the first adjustable circular aperture 3 is reduced to 1 mm;

[0054] Step 3, using a beam expander 4 to expand the detection beam projected by the laser 1, the diameter of the circular detection beam after expansion is 10 mm;

[0055] Step 4, adjust the second adjustable circular aperture 5 so that the diameter of the circular detection beam passing through the second adjustable circular aperture 5 is slightly smaller than the inner diameter of the closed hexagonal tube 7, and the detection beam diameter D is measured to be 9.5 mm at this time;

[0056] Step 5, adjusting the position of the closed hexagonal tube 7 so that the circular detection light beam passing through the second adjustable circular aperture 5 just completely enters the closed hexagonal tube 7, and the detection light beam reflected by the reflector 8 at one end of the closed hexagonal tube 7 coincides with the detection light beam incident on the closed hexagonal tube 7;

[0057] Step 6, adjust the position of the cubic beam splitter 6 so that the direction in which the detection beam reflected by the reflector at one end of the hexagonal tube 7 is reflected again by the cubic beam splitter 6 is perpendicular to the direction in which the detection beam is emitted by the laser 1, and then place the focusing lens 10, the interference filter 11, and the photoelectric sensor 12 in the direction of the reflected detection beam, and ensure that these optical elements are coaxial and at the same height as the cubic beam splitter;

[0058] Step 7: By adjusting the position of the photoelectric sensor 12, the detection beam passing through the focusing lens 10 is focused on the photosensitive element of the photoelectric sensor 12. At this time, the signal voltage value of the oscilloscope 13 reaches the maximum, which is recorded as V max =7.515mV;

[0059] Step 8: Use a shield to completely block the detection beam passing through the focusing lens 10, and record the signal voltage value of the oscilloscope 13 at this time as V min =0mV, remove the obstruction;

[0060] Step 9, use Nd:YAG high energy laser (pulse width of 7ns, wavelength of 1064nm) to focus on the position of the detection beam irradiation area not close to the edge in the closed hexagonal tube 7. At this time, the signal voltage waveform of the oscilloscope 13 is V(t), and the waveform diagram is as follows: Figure 3 As shown in the figure, the signal glitch in the dashed box is caused by plasma.

[0061] In this example, we use a concave-convex lens group 2 to first expand the detection beam with a diameter of 0.8 mm emitted by the laser 1 to 24 mm. Then, the first adjustable circular aperture 3 intercepts the area with a central diameter of 1 mm of the detection beam, and then passes through a 10x beam expander 4 and a second adjustable circular aperture 5 to obtain a detection beam with a diameter of 9.5 mm. The detection beam enters a closed hexagonal tube 7 with an inner diameter of 10 mm, and is reflected back through a reflector 8 along the original path, thereby constructing a detection area in the closed hexagonal tube 7. Since the He-Ne laser selected by the laser 1 has good Gaussian distribution characteristics of light intensity and power stability, the light intensity distribution in its central area has good spatial distribution uniformity after large-multiple expansion. Under this premise, based on the principle of laser transmission, the area of ​​the detection light blocked by the cavity is proportional to the loss of light intensity. Thus, the relationship between the cavity bubble radius R(t) and the signal voltage V(t) received by the oscilloscope 13 is established:

[0062]

[0063] Based on the above formula Figure 3 After analysis, we can get the relationship between the radius of the cavitation bubble in the closed hexagonal tube and time, as shown in Figure 4 It should be noted that for Figure 3 The burr in the dashed box should be modified to V before applying the above formula. max . Through Figure 4 Further analysis of the data can yield the maximum bubble radius and pulsation period of the cavitation. In this example, the maximum bubble radius of the first pulsation period of the cavitation is 1.423 mm, and the first pulsation period is 266 μs.

[0064] Finally, it should be noted that the above description is only a preferred example of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A device for detecting the dynamic characteristics of cavitation in a closed hexagonal tube, comprising a laser for projecting a detection beam, characterized in that: A detection device is provided on one side of the laser, and the detection device includes a concave-convex lens group, a first adjustable circular aperture, a beam expander, a second adjustable circular aperture, a cubic beam splitter, a closed hexagonal tube and a reflector, and each component is coaxially installed in sequence along the direction of the detection beam projected by the laser, the closed hexagonal tube is installed in a transparent container containing a transparent liquid and provided on one side of the cubic beam splitter, the closed end of the closed hexagonal tube is closed by a reflector, and the reflective surface of the reflector is kept perpendicular to the detection beam projected by the laser and the axial direction of the closed hexagonal tube; The detection device also includes a focusing lens, an interference filter, a photoelectric sensor and an oscilloscope, wherein the focusing lens, the interference filter and the photoelectric sensor are coaxially mounted in sequence on the other side of the cubic beam splitter, and the mounting directions of the focusing lens, the interference filter and the photoelectric sensor are kept perpendicular to the direction of the detection beam projected by the laser, and the output end of the photoelectric sensor is connected to any input end of the oscilloscope; The incident surface of the cubic beam splitter is kept perpendicular to the direction of the detection light beam projected by the laser. After being dispersed by the cubic beam splitter for the first time, the detection light beam is emitted as two mutually perpendicular light beams, wherein the projection direction of one beam is in the same direction as the emission direction of the laser, and the other beam is projected in the direction opposite to the direction of the focusing lens; after being reflected by the reflector, the detection light beam in the same direction as the emission direction of the laser is dispersed by the cubic beam splitter for the second time, and is emitted as two mutually perpendicular light beams, wherein the projection direction of one beam is opposite to the emission direction of the laser, and the other beam is projected toward the focusing lens.

2. The device for detecting cavitation dynamics characteristics in a closed hexagonal tube according to claim 1, characterized in that: The light intensity distribution of the detection light beam projected by the laser is Gaussian distribution.

3. The device for detecting cavitation dynamics characteristics in a closed hexagonal tube according to claim 1, characterized in that: The laser power stability of the detection light beam projected by the laser is not less than ±2.5%.

4. The device for detecting cavitation dynamics characteristics in a closed hexagonal tube according to claim 1, characterized in that: The central wavelength of the light that can be transmitted through the interference filter is consistent with the wavelength of the laser.

5. A method for detecting the dynamic characteristics of cavitation in a closed hexagonal tube, characterized in that: Applied to the detection device according to any one of claims 1 to 4, the detection method comprises the following steps: S1, using a concave-convex lens group to expand the detection beam projected by the laser; S2. Under the premise that no obvious optical diffraction occurs, adjust the first adjustable circular aperture so that the diameter of the circular detection light beam passing through the first adjustable circular aperture is reduced to less than 1.2 mm; S3, using a beam expander to expand the detection beam projected by the laser; S4, adjusting the second adjustable circular aperture so that the diameter of the circular detection beam passing through the second adjustable circular aperture is smaller than the inner diameter of the closed hexagonal tube, and measuring the diameter of the detection beam at this time as D; S5, adjusting the position of the closed hexagonal tube so that the circular detection light beam passing through the second adjustable circular aperture enters the closed hexagonal tube, and the detection light beam reflected by the reflector inside the closed hexagonal tube coincides with the detection light beam incident on the closed hexagonal tube; S6. Adjust the position of the cubic beam splitter so that the direction in which the detection beam reflected by the reflector in the closed hexagonal tube is reflected again by the cubic beam splitter is perpendicular to the direction in which the detection beam is emitted by the laser. Then, place the focusing lens, interference filter, and photoelectric sensor in the direction of the reflected detection beam, and ensure that each optical element is coaxial and at the same height as the cubic beam splitter. S7. By adjusting the position of the photoelectric sensor, the detection beam passing through the focusing lens is focused on the photosensitive element of the photoelectric sensor. At this time, the signal voltage value of the oscilloscope reaches the maximum, which is recorded as V max ; S8. Use a shield to completely block the detection beam passing through the focusing lens, and record the signal voltage value of the oscilloscope at this time as V min , remove the obstruction; S9. Use an external high-energy laser transmitter to focus the high-energy laser on a position not close to the edge of the detection beam irradiation area in the closed hexagonal tube. The signal voltage waveform of the oscilloscope at this time is recorded as V(t). The relationship between the bubble radius of the cavitation bubble and time R(t) is:

6. The method for detecting cavitation dynamic characteristics in a closed hexagonal tube according to claim 5, characterized in that: The concave-convex lens group expands the detection light beam projected by the laser by n times, wherein n is a positive integer not less than 30.

7. The method for detecting cavitation dynamics characteristics in a closed hexagonal tube according to claim 5, characterized in that: The beam expander expands the detection beam projected by the laser by no less than 10 times.

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