Non-intrusive vortex center pressure measuring method and system based on cavitation dynamics

Abstract

The invention relates to a non-intrusive vortex center pressure measuring method and system based on cavitation dynamics. The non-intrusive vortex center pressure measuring method based on cavitation dynamics comprises the following steps: filtering and degassing a fluid to be measured to reduce the concentration of free gas in the fluid to be measured; generating a vortex to be measured; irradiating the to-be-measured fluid on a path through which the to-be-measured vortex flows by using laser to form cavitation bubbles; carrying out high-speed photography on the cavitation bubbles, and recording the size change of the cavitation bubbles growing or collapsing at the vortex center after the cavitation bubbles are captured by the vortex to be detected; the cavitation bubbles are observed, the condition that the cavitation bubbles grow or collapse in the vortex center is judged, and the vortex center pressure is obtained through inversion calculation in combination with a corresponding cavitation bubble kinetic equation. The non-intrusive vortex center pressure measurement method based on cavitation dynamics has the advantages of high precision, strong anti-interference capability and reliable result.

Description

Technical Field

[0001] The present invention relates to the field of vortex pressure measurement, and particularly to a non-invasive method and system for measuring the pressure at the center of a vortex based on cavitation dynamics. Background Art

[0002] Vortices are common phenomena in fluid flow, and the pressure at their center is an important parameter characterizing the intensity, stability, and energy distribution of vortices. By measuring the pressure at the center of a vortex, the formation mechanism, evolution law, and its impact on the flow can be better understood. From the perspective of engineering applications, the pressure fluctuations at the center of a vortex may cause flow instability, leading to equipment vibration or noise. For example, in aerospace, ship, and pipeline engineering, the changes in the pressure at the center of a vortex may be closely related to fluid-induced vibration and noise. Therefore, in the design of fluid machinery (such as pumps, turbines, compressors, etc.), the pressure information at the center of a vortex can help engineers optimize the flow passage design, evaluate the flow stability, and take measures to suppress vibration, reduce energy loss, and improve equipment efficiency. In the prior art, the pressure information at the vortex center is usually measured by an intrusive pressure sensor close to the vortex.

[0003] However, the intrusive pressure measurement method will destroy the vortex structure and it is difficult to accurately measure the pressure at the center of the vortex; even if the sensor is arranged on the periphery of the vortex, it may also interfere with the flow and change the characteristics of the vortex. In recent years, the technology of reconstructing the pressure field based on particle image velocimetry (PIV) inversion has provided a new idea for measuring the vortex pressure. However, this technology reconstructs the pressure based on the partial derivative operation of the velocity field. During this process, the tiny measurement error of the velocity field will be amplified exponentially, seriously affecting the accuracy of the final pressure field data. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a non-invasive method and system for measuring the pressure at the center of a vortex based on cavitation dynamics, which have the advantages of high accuracy, strong anti-interference ability, and reliable results.

[0005] The present invention provides a non-invasive method for measuring the pressure at the center of a vortex based on cavitation dynamics, including the following steps:

[0006] S1 Add the fluid to be measured into the container to be measured, filter and degas the fluid to be measured to reduce the concentration of free gas in the fluid to be measured;

[0007] S2 Generate a vortex to be measured in the container to be measured; irradiate the fluid to be measured with a laser on the path where the vortex to be measured flows through to form cavitation bubbles;

[0008] While S3 generates the cavitation bubbles, simultaneously perform high-speed photography on the cavitation bubbles to record the size change of the cavitation bubbles during growth or collapse after being captured by the vortex under test at the vortex center;

[0009] S4: Observe the cavitation bubbles, judge the situation of the cavitation bubbles growing or collapsing at the vortex center, and combine the corresponding cavitation dynamics equation to calculate the vortex center pressure through inverse calculation.

[0010] The non-invasive vortex center pressure measurement method based on cavitation dynamics of the present invention introduces cavitation bubbles, detects the size change and change time of the cavitation bubbles during growth or collapse at the vortex center, and calculates the vortex center pressure through inverse calculation; there is no need to perform invasive detection on the vortex under test, improving the anti-interference ability of the system.

[0011] Further, the step S4 includes:

[0012] S41 If the cavitation bubble grows at the vortex center, the following formula is used to calculate the vortex center pressure;

[0013]

[0014] Wherein, R is the radius of the cavitation bubble, t is the time, is the rate of change of the cavitation bubble radius, p v is the saturated vapor pressure of the fluid, p c is the vortex center pressure, ρ L is the fluid density.

[0015] Further, the step S4 includes:

[0016] S42 If the cavitation bubble collapses at the vortex center, the following formula is used to calculate the vortex center pressure;

[0017]

[0018] Wherein, t c is the time experienced by the cavitation bubble from the start of collapse to the minimum size, R0 is the radius of the cavitation bubble at the start of collapse, ρ L is the fluid density, p v is the saturated vapor pressure of the fluid, p c is the vortex center pressure.

[0019] Further, in the step S1, reduce the free gas concentration in the fluid under test until no spontaneous cavitation occurs in the vortex under test.

[0020] Further, in the step S1, filter the fluid under test and / or perform heating and evaporation to reduce the free gas concentration in the fluid under test.

[0021] Further, in the step S2, the size of the cavitation bubble is adjusted by adjusting the intensity and irradiation time of the laser radiation.

[0022] A non-invasive vortex center pressure measurement system based on cavitation dynamics, which is used for the non-invasive vortex center pressure measurement method based on cavitation dynamics described above, includes: a container to be measured, a vortex generator for generating a vortex, a high-speed photography device, and a laser generating device; the vortex generator is arranged in the container to be measured, and the fluid to be measured forms a to-be-measured vortex after flowing through the vortex generator; the high-speed photography device is arranged beside the container to be measured and faces the container to be measured; the laser generating device is arranged beside the container to be measured, and the laser emitted by the laser generating device is injected into the container to be measured and irradiates the fluid to be measured in the container to be measured to form a cavitation bubble.

[0023] Further, it further includes a laser adjustment device, and the laser emitted by the laser generating device is injected into the container to be measured after passing through the laser adjustment device; the laser adjustment device is used to adjust the focusing position of the laser emitted by the laser generating device; the laser generating device can adjust the intensity and irradiation time of the laser.

[0024] Further, at least two transparent windows are provided on the container to be measured; the high-speed photography device takes pictures inside the container to be measured through one of the transparent windows; the laser emitted by the laser generating device is injected into the container to be measured through the other transparent window.

[0025] Further, it further includes a synchronization device, and the synchronization device is electrically connected to the high-speed photography device and the laser generating device respectively. When the synchronization device detects the start of the laser generating device, the synchronization device sends a synchronization signal to the high-speed photography device to make the high-speed photography device start synchronously.

[0026] For better understanding and implementation, the present invention will be described in detail below with reference to the accompanying drawings. Description of the Drawings

[0027] Figure 1 It is a flowchart of the non-invasive vortex center pressure measurement method based on cavitation dynamics according to the embodiment of the present application;

[0028] Figure 2 It is a schematic diagram of the non-invasive vortex center pressure measurement system based on cavitation dynamics according to the embodiment of the present application;

[0029] Figure 3 It is a schematic diagram of the vortex generated by water flowing through a hydrofoil according to the embodiment of the present application;

[0030] Figure 4 It is a schematic diagram of the change of the radius R with time t during the cavitation bubble growth collected in Embodiment 2 of the present application.

[0031] In the accompanying drawings, the technical features represented by each reference numeral are as follows:

[0032] 1. Container to be measured; 2. Vortex generator; 3. High-speed photography device; 4. Laser generating device; 5. Laser adjusting device; 6. Synchronizing device. Detailed implementation manners

[0033] In the prior art, in order to measure the pressure at the vortex center, it is usually measured by an intrusive pressure sensor or a technique for inverting the pressure field based on particle image velocimetry (PIV). However, the above measurement methods have low anti-interference ability, are prone to generate large errors, and seriously affect the accuracy of the finally measured pressure data.

[0034] To solve the above problems, the inventors have found through research that by irradiating a vortex flow field with a laser, cavitation bubbles will be introduced into the vortex flow field. The internal pressure of the cavitation bubble is the saturated vapor pressure of the fluid. Thereafter, the cavitation bubble is captured by the vortex under the action of the vortex pressure field and enters the vortex center. According to the magnitude relationship between the pressure at the vortex center and the saturated vapor pressure of the fluid, when the pressure at the vortex center is less than the saturated vapor pressure of the fluid, the cavitation bubble grows and its volume increases under the action of the internal and external pressure difference; when the pressure at the vortex center is greater than the saturated vapor pressure of the fluid, the cavitation bubble collapses under pressure and its volume decreases. Whether the cavitation bubble grows or collapses, its size change follows the basic laws of cavitation dynamics, and the cavitation bubble itself will not have a great impact on the vortex.

[0035] Based on the above principle, the present invention proposes a non-intrusive method for measuring the pressure at the vortex center based on cavitation dynamics, which has high anti-interference ability.

[0036] Example 1

[0037] Please refer to Figure 1 , an embodiment of the present application provides a non-intrusive method for measuring the pressure at the vortex center based on cavitation dynamics.

[0038] Specifically, it includes the following steps:

[0039] S1: Add the fluid to be measured into the container to be measured, and perform sufficient filtration and degassing on the fluid to be measured to reduce the concentration of free gas in the fluid to be measured;

[0040] S2: Generate a vortex to be measured in the container to be measured; irradiate the path through which the vortex to be measured flows with a laser to form cavitation bubbles;

[0041] S3: While generating cavitation bubbles, synchronously perform high-speed photography on the cavitation bubbles, and record the size change and change time of the cavitation bubbles growing or collapsing at the vortex center after being captured by the vortex to be measured;

[0042] S4: Observe the cavitation bubbles and determine whether the cavitation bubbles grow or collapse at the vortex center. According to whether the cavitation bubbles grow or collapse, combined with the cavitation dynamics equation, the vortex center pressure is obtained through inverse calculation.

[0043] Further, step S4 specifically includes the following steps:

[0044] S41: If the cavitation bubbles grow at the vortex center, the following formula is used to calculate the vortex center pressure;

[0045]

[0046] In the formula, R is the cavitation bubble radius, t is the time, is the change rate of the cavitation bubble radius, p v is the saturated vapor pressure of the fluid, p c is the vortex center pressure, ρ L is the fluid density; in the formula, the saturated vapor pressure p v and the fluid density ρ L are known values; the change rate of the cavitation bubble radius is a detected value, and substituting it into the above formula and performing inverse calculation to obtain the vortex center pressure p c .

[0047] S42: If the cavitation bubbles collapse at the vortex center, the following formula is used to calculate the vortex center pressure;

[0048]

[0049] In the formula, t c is the time experienced by the cavitation bubble from the start of collapse to the minimum size, R0 is the radius of the cavitation bubble at the start of collapse, ρ L is the fluid density, p v is the saturated vapor pressure of the fluid, p c is the vortex center pressure; in the formula, the saturated vapor pressure p v and the fluid density ρ L are known values; the radius R0 of the cavitation bubble at the start of collapse and the time t c experienced by the cavitation bubble from the start of collapse to the minimum size are detected values, and substituting them into the above formula and performing inverse calculation to obtain the vortex center pressure p c .

[0050] Further, in step S1, the fluid to be measured is filtered and heated for evaporation to reduce the free gas concentration in the fluid to be measured until no spontaneous cavitation occurs in the vortex. To reduce the interference of self-cavitation formed due to the low pressure at the vortex center, the fluid to be measured needs to be fully filtered during the experiment, and methods such as heating and evaporation are used to reduce the concentration of dissolved gases.

[0051] Further, step S2 further includes: adjusting the size of cavitation bubbles by adjusting the intensity and irradiation time of laser radiation.

[0052] Please refer to Figure 2 , an embodiment of the present application further provides a non-invasive vortex center pressure measurement system based on cavitation dynamics for the above measurement method. The pressure measurement system of the present application includes a container to be measured 1, a vortex generator 2 for generating a vortex, a high-speed photography device 3, a laser generating device 4, a laser adjusting device 5, and a synchronization device 6. The vortex generator 2 is disposed in the container to be measured 1, and the fluid to be measured forms a vortex after flowing through the vortex generator 2. The high-speed photography device 3 is disposed beside the container to be measured 1 and faces the container to be measured 1 for photographing the cavitation bubbles in the container to be measured 1. The laser generating device 4 and the laser adjusting device 5 are disposed beside the container to be measured 1. The laser emitted by the laser generating device 4 enters the container to be measured 1 after passing through the laser adjusting device 5, irradiates the fluid to be measured in the container to be measured 1, and forms cavitation bubbles; the laser adjusting device 5 is used to adjust the focusing position of the laser emitted by the laser generating device 4; the laser generating device 4 can adjust the intensity and irradiation time of the laser, thereby changing the size of the cavitation bubbles; the synchronization device 6 is electrically connected to the high-speed photography device 3 and the laser generating device 4 respectively. When the synchronization device 6 detects the start of the laser generating device 4, the synchronization device 6 sends a synchronization signal to the high-speed photography device 3, so that the high-speed photography device 3 starts synchronously.

[0053] Further, at least two transparent windows are provided on the container to be measured; the high-speed photography device photographs the inside of the container to be measured through one of the transparent windows; the laser emitted by the laser generating device enters the container to be measured through the other transparent window.

[0054] Please refer to Figure 3 , in some embodiments, the vortex generator 2 is a hydrofoil. One end of the hydrofoil is provided with a curved leading edge, and the other end is provided with a sharp tapered trailing edge; the cross-section of the hydrofoil is spiral or curved airfoil-shaped. The hydrofoil can promote flow separation, so that the fluid flowing through the hydrofoil forms a vortex.

[0055] Example 2

[0056] Please refer to Figure 4 , an embodiment of the present application provides a specific embodiment of a non-invasive vortex center pressure measurement method based on cavitation dynamics, which specifically includes the following steps:

[0057] S1: Select water as the fluid to be measured, the experimental temperature is 20°C, use the vortex center pressure measurement system in Embodiment 1 as the measurement device, add water to the container to be measured 1, and perform sufficient filtration and degassing to reduce the free gas concentration in the water to below 1.5 ppm;

[0058] S2: Generate a vortex to be measured in the container 1 to be measured; irradiate the path through which the vortex to be measured flows with a laser to form cavitation bubbles;

[0059] S3: While generating cavitation bubbles, synchronously perform high-speed photography on the cavitation bubbles, and record the size changes and change times of the cavitation bubbles growing or collapsing at the vortex center after being captured by the vortex to be measured; in this embodiment, different experimental parameters are adopted for the same measuring device to generate vortices with different intensities, record the size changes of the cavitation bubbles during growth, and obtain experimental data 1 and experimental data 2;

[0060] S4: Observe that the cavitation bubbles grow at the vortex center after being captured by the vortex to be measured, and measure the radius change rates of experimental data 1 and experimental data 2 to be 0.92 and 0.65 m / s respectively; under the condition that the experimental temperature is 20 °C, the density ρ of water L = 1000 kg / m 3 , and the saturation vapor pressure p v = 2338 Pa; substitute the above data into the following formula;

[0061]

[0062] Obtain the vortex center pressures p c of two different vortices to be measured to be 1068 Pa and 1704 Pa respectively.

[0063] The non-invasive vortex center pressure measurement method and system based on cavitation dynamics of the present application calculates the vortex center pressure by measuring the size changes of cavitation bubbles. Compared with the prior art, it reduces the invasiveness to the vortex to be measured, improves the anti-interference ability of the overall system, and thus improves the accuracy of the test results.

[0064] The above-described embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and the present invention also intends to include these modifications and improvements.

Claims

1. A non-invasive method for measuring the pressure at the center of a vortex based on cavitation dynamics, characterized in that Including the following steps: S1 Add the fluid to be measured into the container to be measured, filter and degas the fluid to be measured, so as to reduce the free gas concentration in the fluid to be measured; S2 Generate a vortex to be measured in the container to be measured; irradiate the fluid to be measured with a laser along the path through which the vortex to be measured flows to form cavitation bubbles; S3 While generating the cavitation bubbles, synchronously perform high-speed photography on the cavitation bubbles, and record the size change of the cavitation bubbles growing or collapsing at the vortex center after being captured by the vortex to be measured; S4 Observe the cavitation bubbles, judge the situation of the cavitation bubbles growing or collapsing at the vortex center, and combine the corresponding cavitation dynamics equation to inversely calculate the vortex center pressure through inversion calculation.

2. The non-invasive vortex center pressure measurement method based on cavitation dynamics according to claim 1, characterized in that The step S4 includes: S41 If the cavitation bubbles grow at the vortex center, calculate the vortex center pressure using the following formula; where R is the radius of the cavitation bubble, t is the time, is the rate of change of the cavitation bubble radius, p v is the saturated vapor pressure of the fluid, p c is the pressure at the vortex center, ρ L is the fluid density.

3. The non-invasive vortex center pressure measurement method based on cavitation dynamics according to claim 2, wherein The step S4 includes: S42 If the cavitation bubbles collapse at the vortex center, calculate the vortex center pressure using the following formula; where t c is the time elapsed from the start of the cavitation bubble collapse to the moment when its size reaches the minimum value, R0 is the radius of the cavitation bubble at the start of the collapse, ρ L is the fluid density, p v is the fluid saturated vapor pressure, p c is the vortex center pressure.

4. The non-invasive vortex center pressure measurement method based on cavitation dynamics according to claim 1, characterized in that: In the step S1, reduce the free gas concentration in the fluid to be measured until no spontaneous cavitation occurs in the vortex to be measured.

5. The non-invasive vortex center pressure measurement method based on cavitation dynamics according to claim 4, characterized in that: In the step S1, filter the fluid to be measured and / or heat and evaporate it to reduce the free gas concentration in the fluid to be measured.

6. The non-invasive vortex center pressure measurement method based on cavitation dynamics according to any one of claims 1-5, characterized in that: In the step S2, adjust the size of the cavitation bubbles by adjusting the intensity and irradiation time of the laser radiation.

7. A non-invasive vortex center pressure measurement system based on cavitation dynamics, which is used to implement the non-invasive vortex center pressure measurement method based on cavitation dynamics according to any one of claims 1-5, and is characterized in that, Including: A container to be measured, a vortex generator for generating a vortex, a high-speed photography device, and a laser generating device; The vortex generator is arranged in the container to be measured, and the fluid to be measured forms a vortex to be measured after flowing through the vortex generator; the high-speed photography device is arranged beside the container to be measured and faces the container to be measured; the laser generating device is arranged beside the container to be measured, and the laser emitted by the laser generating device is injected into the container to be measured to irradiate the fluid to be measured in the container to form cavitation bubbles.

8. The non-invasive vortex center pressure measurement system based on cavitation dynamics according to claim 7, characterized in that: It further includes a laser adjustment device, and the laser emitted by the laser generating device is injected into the container to be measured after passing through the laser adjustment device; the laser adjustment device is used to adjust the focusing position of the laser emitted by the laser generating device; the laser generating device can adjust the intensity and irradiation time of the laser.

9. The non-invasive vortex center pressure measurement system based on cavitation dynamics according to claim 8, characterized in that: At least two transparent windows are arranged on the container to be measured; the high-speed photography device photographs the inside of the container to be measured through one of the transparent windows; the laser emitted by the laser generating device is injected into the container to be measured through the other transparent window.

10. The non-invasive vortex center pressure measurement system based on cavitation dynamics according to claim 9, characterized in that: It further includes a synchronization device, and the synchronization device is electrically connected to the high-speed photography device and the laser generating device respectively. When the synchronization device detects the start of the laser generating device, the synchronization device sends a synchronization signal to the high-speed photography device to enable the high-speed photography device to start synchronously.

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