A method for measuring the dynamic pressure of non-axisymmetric collapse of cavitation bubbles based on constantan filaments

Abstract

The present invention discloses a method for measuring the dynamic pressure of the non-axisymmetric collapse of cavitation bubbles based on constantan filaments. The present invention uses the constantan filament as a pressure-sensitive unit and connects it to a dynamic acquisition device using a Huygens bridge circuit. The dynamic acquisition device provides a DC power supply voltage for the constantan filament. A pulsed laser generates pulsed laser light, which generates cavitation bubbles in a container containing pure water through a beam expansion and focusing optical system. The pressure generated by the collapse of the cavitation bubbles acts on the constantan filament, and the voltage signal generated is collected by the dynamic pressure acquisition device. The measured voltage signal is multiplied by the known sensitivity coefficient of the constantan filament to obtain the strain of the constantan filament stimulated by the collapse of the cavitation bubble. The obtained strain is then multiplied by the elastic modulus of the constantan filament to obtain the dynamic pressure of the non-axisymmetric collapse of the cavitation bubble. By using the constantan filament as both a pressure sensor and a slender wall, the present invention can measure the dynamic pressure generated by the collapse of cavitation bubbles near a slender, high-curvature, non-planar wall.

Description

Technical Field

[0001] The present invention relates to the measurement of dynamic pressure of cavitation bubbles in water or aqueous solution on a slender solid wall surface, specifically to the measurement of transient impact force values ​​of cavitation bubbles on a filament wall surface, belonging to the technical field of underwater dynamic pressure detection. Background Art

[0002] The problem of bubble collapse has always been a hot topic in the field of fluid mechanics research, and cavitation bubble technology has been widely used in many fields such as industrial production, water treatment, biopharmaceuticals, and life sciences. Cavitation occurs when the internal pressure of a fluid drops to a certain critical value, and the liquid inside the fluid vaporizes or the bubbles acting as gas nuclei rapidly expand outward, resulting in the formation of a large number of bubbles. When there is a wall nearby, the bubbles will collapse asymmetrically, and a unilateral concave appear on the bubble surface during collapse, resulting in local high temperature and high pressure, and a jet. The dynamic pressure of the shock wave generated by the bubble collapse acts on the wall, which will impact the wall and cause cavitation, which is particularly common on hydraulic machinery impellers. When ultrasonic cleaning is performed in the field of biochemistry research, the dynamic pressure of cavitation bubbles generated by cleaning filamentous equipment such as microprobes is currently unclear, and it is a hot topic worthy of study by fluid researchers.

[0003] In recent years, most studies on bubble collapse have been based on macroscopic bubbles, with diameters exceeding millimeters. However, in practical applications utilizing the bubble collapse effect, micron-sized bubbles are used. Current methods for measuring cavitation bubble pressure primarily include pressure-sensitive paper, hydrophones, and piezoresistive sensors. These methods all involve dynamic pressure measurements of cavitation bubbles near flat walls or free collapse, and the sensors generate significant disturbances. The wall environment in which cavitation bubbles occur is complex, necessitating the development of new, stable, and reliable methods for measuring the dynamic pressure of cavitation bubbles near non-planar walls to accurately measure the dynamic pressure of cavitation bubbles near walls of varying shapes.

[0004] Generally, free collapse and near-plane cavitation collapse occur in axisymmetric spherical and axisymmetric non-spherical forms, respectively. However, non-axisymmetric cavitation collapse is a unique mode of cavitation collapse induced by filamentary walls and is a common cavitation collapse process encountered during optical fiber and microprobe measurements. For example, ultrasonic cleaning of filamentary instruments such as microprobes can damage the probes, altering their internal structure and reducing their lifespan. The dynamic pressure of ultrasonically generated cavitation bubbles is currently unknown, and quantitatively measuring and controlling the intensity of ultrasonic cavitation is of practical significance. Summary of the Invention

[0005] To address the difficulty of using pressure-sensitive paper, hydrophones, and piezoresistive sensors to measure the dynamic pressure of non-axisymmetric cavitation collapse near slender walls, the present invention proposes a method using a constantan filament as a dynamic pressure sensor to measure the dynamic pressure of laser-induced cavitation bubbles near slender, high-curvature, non-planar walls. This method avoids the inherent changes in the bubble collapse morphology that occur with conventional sensors such as piezoresistive sensors due to the large wall size. Cavitation bubbles near the surface of the constantan filament undergo non-axisymmetric collapse. The constantan filament acts as both a sensing element and the equivalent of the slender wall, enabling the measurement of the dynamic pressure of non-axisymmetric cavitation bubble collapse on the slender wall.

[0006] The technical solution adopted by the present invention to solve the technical problem is:

[0007] The constantan filament is used as a pressure sensitive unit and is connected to a dynamic acquisition device using a Huygens bridge circuit. The dynamic acquisition device provides a DC power supply voltage to the constantan filament.

[0008] A nanosecond pulse laser generates pulsed laser light, which generates cavitation bubbles in a container filled with pure water through a beam expansion and focusing optical system. The pressure generated by the collapse of the cavitation bubbles acts on the surface of the constantan filament, causing slight deformation of the surface of the constantan filament. The voltage signal generated is collected by a dynamic pressure acquisition device.

[0009] The strain of the constantan wire stimulated by the collapse of the cavitation bubble can be obtained by multiplying the measured voltage signal by the known sensitivity coefficient of the constantan wire. The obtained strain is then multiplied by the elastic modulus of the constantan wire to obtain the non-axisymmetric collapse dynamic pressure of the cavitation bubble.

[0010] Furthermore, it also includes a high-precision three-dimensional displacement platform, which is arranged under a container filled with pure water; by adjusting the high-precision three-dimensional displacement platform, the dynamic pressure of cavitation bubble collapse at different distances can be obtained.

[0011] Furthermore, it also includes a digital delay trigger, which is connected to the nanosecond pulse laser and the dynamic pressure acquisition device by signal.

[0012] Furthermore, it also includes an ultra-high-speed camera for observing the collapse process of cavitation bubbles, and the ultra-high-speed camera is connected to the digital delay trigger.

[0013] Furthermore, the diameter of the constantan filament is 0.005 mm to 0.2 mm.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] (1) The present invention uses the constantan filament as both a pressure sensor and a slender wall surface, and can measure the dynamic pressure generated by the collapse of cavitation bubbles near a slender high-curvature non-planar wall surface with high precision.

[0016] (2) The cavitation bubbles generated in the present invention undergo non-axisymmetric collapse, which has a high guiding value for studying such collapse.

[0017] (3) The dynamic pressure of cavitation bubble collapse under different conditions can be obtained by adjusting the location of cavitation bubble generation, the size of cavitation bubble, and the time triggering is precisely controllable.

[0018] (4) Based on the response waveform of the pressure sensor and the evolution of the gas-liquid interface during the non-axisymmetric collapse of the cavitation bubble, it is found that during the collapse process, a pressure peak is generated when the cavitation bubble collapses, and the step time of the pressure peak is in the microsecond order. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the constantan filament pressure sensor system based on laser-induced cavitation.

[0020] Figure 2 Schematic diagram of the position of the laser-generated cavitation bubbles and the constantan filament pressure sensor.

[0021] Figure 3a The dynamic evolution diagram of the cavitation bubble with dimensionless distance γ = 0.872 at different times.

[0022] Figure 3b Schematic diagram of the pressure-time variation curve measured by the constantan filament pressure sensor when γ=0.872.

[0023] Figure 4a The dynamic evolution diagram of the cavitation bubble with dimensionless distance γ = 0.635 at different times.

[0024] Figure 4b Schematic diagram of the pressure-time variation curve measured by the constantan filament pressure sensor when γ=0.635.

[0025] Figure 5a The dynamic evolution diagram of the cavitation bubble with dimensionless distance γ = 0.512 at different times.

[0026] Figure 5b Schematic diagram of the pressure-time variation curve measured by the constantan filament pressure sensor when γ=0.512.

[0027] Figure 6 This is the side view dynamic evolution diagram of the cavitation bubble with γ=0.62.

[0028] Figure 7 is the dimensionless distance γ and the peak pressure P max relationship diagram.

[0029] Figure 8Schematic diagram of the pressure-time variation curve measured when the constantan filament is fixed near a plane wall.

[0030] Figure 9 Schematic diagram of the pressure-time variation curve measured by the piezoresistive sensor. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to the accompanying drawings and examples.

[0032] like Figure 1 As shown, this embodiment includes a nanosecond pulse laser 1, an LED focused light source 2, a container 3 placed on a high-precision three-dimensional displacement platform, a constantan filament pressure sensor 4 (composed of a constantan filament and a Huygens bridge circuit), a dynamic pressure acquisition device 5, a computer 6, an ultra-high-speed camera 7, a digital delay trigger 8, and a beam expansion and focusing optical path system 9.

[0033] A constantan filament is used as a pressure-sensitive unit and is connected to a dynamic acquisition device using a Huygens bridge circuit. The dynamic acquisition device provides a DC power supply voltage for the constantan filament. A nanosecond pulse laser generates pulsed laser light, which generates cavitation bubbles in a container containing pure water through a beam expansion and focusing optical system. The pressure generated by the collapse of the cavitation bubbles acts on the surface of the constantan filament, causing slight deformation of the constantan filament surface. The generated voltage signal is collected by the dynamic pressure acquisition device. The laser, the dynamic pressure acquisition device and the ultra-high-speed camera are connected via a digital delay trigger, so that the dynamic pressure acquisition device operates synchronously when the cavitation bubbles generated by the laser collapse.

[0034] The strain of the constantan wire stimulated by the collapse of the cavitation bubble can be obtained by multiplying the measured voltage signal by the known sensitivity coefficient of the constantan wire. The obtained strain is then multiplied by the elastic modulus of the constantan wire to obtain the non-axisymmetric collapse dynamic pressure of the cavitation bubble.

[0035] like Figure 2 As shown, a digital delay trigger triggers a nanosecond pulse laser to generate pulsed laser light. A beam expansion and focusing optical system generates cavitation bubbles in a container of pure water. A constantan filament 403 is mounted on a support 404, which is placed in the container. Laser light 401, passing through the beam expansion and focusing optical system, generates cavitation bubbles 402 in the container of pure water. The high-precision three-dimensional displacement platform is adjusted to generate cavitation bubbles 402 at a specific location on the constantan filament pressure sensor.

[0036] The dimensionless distance γ is defined as: the maximum radius R during the expansion of the cavitation bubble max The ratio of the distance L from the center of the cavitation bubble to the pressure sensing surface of the pressure sensor is the dimensionless distance γ, that is:

[0037]

[0038] After a short period of expansion, the cavitation bubble begins to collapse under the action of the inertia of the surrounding water and produces a jet, as shown in the schematic diagram. Figure 3a As shown in the figure, after the cavitation bubble is generated, it begins to expand. Under the action of the constantan filament, the cavitation bubble begins to deform and expand in the direction away from the constantan filament. The bubble reaches its maximum expansion at t = 60 μs. Due to the pressure gradient, the bubble begins to collapse inward, and at t = 140 μs, a jet begins to form, directed toward the constantan filament, followed by a symmetrical jet. The cavitation bubble acts on the constantan filament, and the output signal of the constantan filament pressure sensor is collected by a dynamic pressure acquisition device, generating the pressure sensor's response waveform.

[0039] The ultra-high-speed image acquisition device is controlled by a time-delay trigger to collect accurate digital image information of the evolution of the gas-liquid interface during the collapse of cavitation bubbles. Figure 3a , Figure 4a , Figure 5a as well as Figure 6 , the non-axisymmetric collapse of the cavitation bubble can be observed. Figure 8 The dynamic pressure data of cavitation bubble collapse measured when the constantan filament is fixed near a plane wall. Figure 9 The dynamic pressure data of cavitation bubble collapse measured by piezoresistive sensor. Figure 8 and Figure 9 By comparing the dynamic pressure data of cavitation bubble collapse measured near the constantan filament, it is found that the cavitation bubble is affected by the wall near the plane wall and measures a dynamic pressure with multiple pressure peaks, while the dynamic pressure with a single pressure peak is measured near the slender high-curvature non-planar wall of the constantan filament. Therefore, for the non-axisymmetric collapse of cavitation bubbles near the slender high-curvature non-planar wall, it is necessary to select a sensor that does not interfere with its collapse. Combining the response waveform of the measured pressure sensor and the digital image information, it is known that the pressure peak P generated by the cavitation bubble during the collapse process is max , and the peak pressure P max The step time is in microseconds.

[0040] The present invention can generate pressures of different sizes by adjusting the dimensionless distance γ, thereby obtaining the dynamic pressure generated by the collapse of cavitation bubbles induced by laser near a slender, high-curvature non-planar wall.

[0041] The pulse laser is a nanosecond pulse laser.

[0042] The dynamic pressure acquisition device is a dynamic signal acquisition card.

[0043] The response waveform is a pressure-time image.

[0044] The pressure sensor is at the millisecond level or microsecond level.

[0045] The cavitation bubbles are random cavitation bubbles.

[0046] The constantan filament has a diameter of 0.005 mm to 0.2 mm and a length of 0.01 m to 1 m.

[0047] The sampling rate of the dynamic acquisition card is 1 kHz to 1 MHZ.

[0048] The fluid can be a Newtonian or non-Newtonian fluid.

[0049] An example is given to illustrate: by adjusting the dimensionless distance γ, the pressure generated by cavitation bubbles near a slender, high-curvature non-planar wall under different working conditions is measured. Figure 3b 、 Figure 4b 、 Figure 5b When γ=0.872, P max =7.297MPa,γ=0.635 max =8.654MPa,γ=0.512 max =11.480MPa. Compared with sensors such as fiber optic hydrophones, the cavitation bubble collapse pressure near the solid wall measured by fiber optic hydrophones at different dimensionless distances is around 1-2MPa. The cavitation bubble collapse pressure measured by the constantan filament pressure sensor is more accurate and has more reference value. Combined with the ultra-high-speed image acquisition device, digital image information of the gas-liquid interface evolution process during the cavitation bubble collapse process is simultaneously collected to measure the dynamic pressure when the cavitation bubble collapses non-axisymmetrically near the constantan filament and generates a jet. After statistically analyzing the measured data, the following is obtained: Figure 7 The dimensionless distance γ and the peak pressure P max As the dimensionless distance γ increases, the pressure peak P max This method is of great value in the fields of underwater equipment cavitation analysis and dynamic pressure detection technology.

[0050] The present invention is not limited to the above-mentioned embodiments. All equivalent changes and modifications made within the scope of the present invention should fall within the scope of the present invention.

Claims

1. A method for measuring the dynamic pressure of cavitation bubble non-axisymmetric collapse based on constantan filaments, characterized by: A constantan filament is used as a pressure-sensitive unit and is connected to a dynamic acquisition device using a Huygens bridge circuit. The dynamic acquisition device provides a DC power supply voltage to the constantan filament. The constantan filament serves as a sensing element and also as an equivalent of a slender wall. A nanosecond pulse laser generates pulsed laser light, which generates cavitation bubbles in a container filled with pure water through a beam expansion and focusing optical system. The pressure generated by the collapse of the cavitation bubbles acts on the surface of the constantan filament, causing slight deformation of the surface of the constantan filament. The voltage signal generated is collected by a dynamic pressure acquisition device. The strain of the constantan wire stimulated by the collapse of the cavitation bubble can be obtained by multiplying the measured voltage signal by the known sensitivity coefficient of the constantan wire. The obtained strain is then multiplied by the elastic modulus of the constantan wire to obtain the non-axisymmetric collapse dynamic pressure of the cavitation bubble. It also includes a digital delay trigger, which is connected to the nanosecond pulse laser and the dynamic pressure acquisition device; The sampling rate of the dynamic pressure acquisition device is 1 kHz to 1 MHz; The diameter of the constantan filament is 0.005mm~0.2mm.

2. The method for measuring the non-axisymmetric collapse dynamic pressure of cavitation bubbles based on constantan filaments according to claim 1, characterized in that: It also includes a high-precision three-dimensional displacement platform, which is arranged under a container filled with pure water. By adjusting the high-precision three-dimensional displacement platform, the dynamic pressure of cavitation bubble collapse at different distances can be obtained.

3. The method for measuring the non-axisymmetric collapse dynamic pressure of cavitation bubbles based on constantan filaments according to claim 1, characterized in that: It also includes an ultra-high-speed camera for observing the collapse process of cavitation bubbles. The ultra-high-speed camera is connected to the digital delay trigger.

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