Pressure static calibration method based on cavitation collapse and R-P equation

Abstract

The invention relates to a pressure static calibration method based on cavitation collapse and an R-P equation. In order to solve the problem of calibration result deviation caused by a traditional static calibration method of a high-dynamic-performance pressure sensor, the method provided by the invention takes transient pressure shock waves released in a cavitation collapse process as an excitation source, and the pulse width of the pressure shock waves released in the process is about 1 microsecond; the frequency band blank of microsecond-level static calibration is filled, a first-time cavitation collapse pressure peak value obtained through calculation in combination with a Rayleigh-Plesset equation and a dissipation formula of pressure shock waves in liquid is compared with a first-time cavitation collapse pressure peak value received by a pressure sensor, a pressure peak value difference value at the moment is obtained and serves as a peak value compensation error of the pressure sensor, and the frequency band compensation error of the microsecond-level static calibration is calculated. And completing calibration.

Description

Technical Field

[0001] The present invention relates to the technical field of static pressure calibration, and in particular to a pressure static calibration method based on cavitation collapse and RP equation. Background Art

[0002] High-dynamic pressure sensors play an irreplaceable role in critical areas such as assessing explosion shock wave pressure, monitoring engine flow pressure, and evaluating turbocharger performance. To ensure the accuracy and reliability of these precision sensors, they require not only regular dynamic calibration to verify their transient response characteristics, but also static calibration to ensure accurate measurements under various operating conditions.

[0003] The traditional static calibration method of high dynamic performance pressure sensor relies on loading devices such as weights and piston pressure gauges, which has the following problems: First, due to the insufficient frequency of the excitation source and the pulse width of only milliseconds, the pressure change rate of the pressure-sensitive element of the high dynamic performance pressure sensor during the slow loading process is much lower than the transient impact encountered by the high dynamic performance sensor in actual application. The internal mechanical friction and elastic deformation have sufficient time to respond to the pressure change, which is insufficient to fully stimulate and evaluate the ultimate performance of the sensor, resulting in significant deviations when used according to the static calibration results; Second, high dynamic performance pressure sensor

[0004] Long-term static loading will seriously affect the actual service life of the pressure sensor. Third, in static calibration, there are multiple pressure transmission links in the process of transmitting pressure excitation to the pressure-sensitive surface of the sensor. This will introduce uncertainty and response delay in the mechanical structure transmission, resulting in errors in the calibration results.

[0005] In order to solve the problems existing in the above-mentioned static calibration method, it is necessary to propose a new technical solution to overcome the shortcomings of the existing static calibration method for high dynamic performance pressure sensors. Summary of the Invention

[0006] In order to solve the problem of calibration result deviation caused by traditional static calibration methods of high dynamic performance pressure sensors, the present invention proposes a pressure static calibration method based on cavitation collapse and RP equation. The transient pressure shock wave released during the cavitation collapse process is used as the excitation source. The pulse width of the pressure shock wave released during the process is about 1 μs, filling the frequency band gap of microsecond static calibration. The first cavitation collapse pressure peak value calculated by combining the Rayleigh-Plesset equation and the dissipation formula of pressure shock wave in liquid is compared with the first cavitation collapse pressure peak value received by the pressure sensor to obtain the pressure peak difference at this time, which is used as the peak compensation error of the pressure sensor to complete the calibration.

[0007] The present invention comprises the following steps:

[0008] Step 1. Position the pressure sensor to be calibrated in the liquid medium in the experimental container;

[0009] Step 2. Using a laser, emitting laser pulses toward a predetermined position near the pressure-sensitive surface of the pressure sensor to be calibrated, so as to generate cavitation bubbles in the liquid medium;

[0010] Step 3. When the cavitation bubble collapses, a pressure shock wave is released. The pressure shock wave acts on the pressure-sensitive surface of the pressure sensor to be calibrated, and a dynamic pressure acquisition device acquires pressure waveform data of the pressure sensor to be calibrated.

[0011] Step 4. Using an image acquisition device to record the dynamic process of the cavitation bubble from generation to collapse;

[0012] Step 5. Calculate the theoretical pressure value at the pressure sensing surface of the pressure sensor when the first cavitation bubble collapses based on the transient radius data of the cavitation bubble acquired by the image acquisition device, the Rayleigh-Plesset equation, and the dissipation formula of the pressure shock wave in the liquid;

[0013] Step 6. Collecting the peak pressure value measured by the pressure sensor to be calibrated when the cavitation bubble collapses for the first time;

[0014] Step 7. Calculating the difference between the theoretical pressure value and the measured pressure peak value;

[0015] Step 8. Use the difference as a correction coefficient to compensate for the peak error of the pressure sensor to be calibrated to complete the calibration.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The present invention uses the transient pressure shock wave released during the cavitation collapse process as the excitation source, which can quickly act on the pressure-sensitive surface of the pressure sensor to be calibrated. Compared with standard instruments such as piston pressure gauges, which require complex pressure transmission links, the present invention avoids the calibration error caused by the uncertainty introduced by pressure transmission and the response delay.

[0018] (2) The present invention combines the Rayleigh-Plesset equation and the dissipation formula of pressure shock waves in liquids to calculate the peak value of the theoretical shock wave pressure on the pressure-sensitive surface of the sensor to be calibrated, and can directly trace the evolution of shock wave pressure and cavitation radius and time domain characteristics.

[0019] (3) The present invention uses the transient pressure shock wave released during the cavitation collapse process as the excitation source. The pulse width of the excitation source is only 1 μs, which achieves a breakthrough of three orders of magnitude compared to the millisecond requirement for the static calibration time of the current pressure sensor.

[0020] (4) The present invention utilizes nanosecond pulsed lasers to generate cavitation bubbles of different sizes with good repeatability, meeting the calibration requirements of different pressure sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present application will be further described below with reference to the accompanying drawings:

[0022] Figure 1 Schematic diagram of the pressure static calibration device based on cavitation collapse and RP equation;

[0023] Figure 2 Flow chart of the pressure static calibration method based on cavitation collapse and RP equation;

[0024] Figure 3 is the theoretical pressure curve of laser-induced cavitation;

[0025] Figure 4 It is a curve diagram of shock wave pressure received by the measured pressure sensor;

[0026] Figure numerals: 1. pressure sensor to be calibrated; 2. charge amplifier; 3. dynamic acquisition card; 4. first light source; 5. second light source; 6. light homogenizer; 7. high-speed camera; 8. delay trigger; 9. pulse laser; 10. beam expansion and focusing optical path; 11. host computer; 12. experimental water tank; 13. cavitation. DETAILED DESCRIPTION

[0027] The present application will be further described below with reference to the accompanying drawings and examples.

[0028] like Figure 1 As shown, a pressure static calibration device based on cavitation collapse and RP equation includes a pulse laser, a delay trigger, a pressure acquisition device, an optical path device, an image acquisition device and an experimental water tank.

[0029] The delayed trigger 8 is electrically connected to the pulse laser 9, which generates a laser beam by triggering the pulse laser 9 to generate a cavitation bubble 13 in the experimental water tank 12. The cavitation bubble 13 then undergoes a growth-collapse process and releases a collapse shock wave during the first collapse.

[0030] The pressure acquisition device includes a pressure sensor to be calibrated 1, a charge amplifier 2, and a dynamic acquisition card 3.

[0031] The signal output port of the pressure sensor to be calibrated 1 is electrically connected to the charge amplifier 2, which converts the charge signal of the pressure sensor to be calibrated 1 into a voltage signal and amplifies it. The charge amplifier 2 is electrically connected to the dynamic acquisition card 3, which converts the voltage signal into a digital signal and transmits the digitized shock wave pressure data in real time to the host computer 11 for analysis and processing.

[0032] The image acquisition device includes a first light source 4, a second light source 5, a light homogenizer 6, and a high-speed camera 7. The image information of the cavitation growth-collapse process is acquired by a frontal lighting imaging method.

[0033] The delay trigger 8 is connected to the image acquisition device and the pressure acquisition device to achieve synchronous acquisition of the cavitation bubble image and the pressure signal.

[0034] The static pressure calibration method based on cavitation collapse and RP equation is used to implement the process, such as Figure 2 As shown, a pulsed laser 9 is first triggered by a delayed trigger 8, generating a single pulsed laser beam that passes through a beam expansion and focusing optical path 10. The pulsed laser energy is evenly dispersed and then precisely focused to radiate at a predetermined location in the liquid medium in the experimental water tank 12, generating a cavitation bubble 13. The focal spot size of the pulsed laser is only about 100 microns. When the laser focusing performance meets the standard and the laser beam energy reaches the threshold of laser-induced cavitation, each single pulsed laser beam emitted by the pulsed laser will only produce a single cavitation bubble.

[0035] Since the cavitation releases most of its initial energy in the first collapse, and there is no flow field disturbance caused by the collapse of preceding cavitation bubbles, a high-intensity spherical shock wave can be formed (i.e., when the cavitation bubble collapses, it collapses in a spherical shape under the action of surface tension and releases a spherical pressure shock wave outward); at the same time, the first collapse pulse pressure generated in the laser-induced cavitation process under the same working conditions has good repeatability and stability, so the embodiment of the present application selects the first collapse pulse as the excitation source for pressure calibration.

[0036] The image acquisition device records the image information of the cavitation from growth to collapse, and calculates the theoretical pressure value of the first cavitation collapse received at the pressure sensing surface of the pressure sensor 1 to be calibrated based on the Rayleigh-Plesset equation and the dissipation formula of the pressure shock wave in the liquid.

[0037] When the pressure wave of the first cavitation collapse propagates to the pressure-sensitive surface of the pressure sensor 1 to be calibrated, the pressure sensor 1 to be calibrated cooperates with the charge amplifier 2 and the dynamic acquisition card 3 to collect the output signal obtained at this time, and obtains the pressure waveform of the pressure sensor 1 to be calibrated, and then obtains the pressure peak value of the pressure sensor 1 to be calibrated when the cavitation collapses for the first time.

[0038] The peak pressure value received by the pressure sensor 1 to be calibrated when the cavitation collapses for the first time is compared with the theoretical pressure value received by the pressure sensing surface of the pressure sensor 1 to be calibrated when the cavitation collapses for the first time. The obtained pressure difference is used as the peak compensation coefficient of the pressure sensor 1 to be calibrated to complete the static calibration.

[0039] Furthermore, the Rayleigh-Plesset equation and the dissipation formula of the pressure shock wave in the liquid in this application are as follows:

[0040] The dynamic changes in high-frequency pulse signals are often difficult to determine through theoretical models or numerical calculations. In the present embodiment, the Rayleigh-Plesset equation and the spherically symmetric shock wave propagation formula are used to calculate the dynamic pressure changes in the surrounding flow field caused by the "collapse pulse" during the laser-induced cavitation process by capturing the position changes of the cavitation bubble's gas-liquid interface and the bubble radius using a high-speed camera.

[0041] The Rayleigh-Plesset equation is as follows:

[0042]

[0043] Spherically symmetric shock wave propagation formula:

[0044]

[0045] Among them, P in represents the pressure inside the cavitation bubble; represents the pressure at an infinite distance from the bubble; ρ represents the density of the surrounding liquid; R(t) represents the radius of the bubble; μ represents the viscosity of the surrounding liquid; σ is the surface tension coefficient of the liquid; p (r, t) is the pressure at a distance r; c is the speed of sound in the liquid; α is the empirical dissipation coefficient, is the radial velocity of the cavitation bubble, is the radial acceleration of the cavitation bubble.

[0046] In the embodiment, a delayed trigger triggers a pulsed laser, and a single pulse laser beam is focused at a preset position in the experimental water tank to generate a single cavitation bubble. The image acquisition device collects bubble dynamics image information from the generation to the collapse of the cavitation bubble. It is found that at the experimental recording time of 173 μs, the cavitation bubble expands to a maximum radius R = 1.255 mm. Combined with the Rayleigh-Plesset equation and the dissipation formula of the pressure shock wave in the liquid, the theoretical pressure change curve with time under this working condition is obtained as follows: Figure 3 As shown, the pressure peak P′ generated when the cavitation bubble first collapses is obtained. max =0.937MPa, the pressure acquisition device simultaneously obtains the pressure waveform from the growth to the collapse of the cavitation bubble as shown below Figure 4 As shown in the figure, the peak pressure P generated when the cavitation bubble collapses for the first time in the experiment is obtained. max =0.883MPa, and the difference between the two pressure peaks, 0.054MPa, is used as the correction coefficient of the pressure sensor to compensate for the peak error of the pressure sensor, thus completing the calibration of the pressure sensor.

[0047] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. Static pressure calibration method based on cavitation collapse and RP equation, characterized by The method comprises the following steps: Step 1. Position the pressure sensor to be calibrated in the liquid medium in the experimental container; Step 2. Using a laser, emitting laser pulses toward a predetermined position near the pressure-sensitive surface of the pressure sensor to be calibrated, so as to generate cavitation bubbles in the liquid medium; Step 3. When the cavitation bubble collapses, a pressure shock wave is released. The pressure shock wave acts on the pressure-sensitive surface of the pressure sensor to be calibrated, and a dynamic pressure acquisition device acquires pressure waveform data of the pressure sensor to be calibrated. Step 4. Using an image acquisition device to record the dynamic process of the cavitation bubble from generation to collapse; Step 5. Calculate the theoretical pressure value at the pressure sensing surface of the pressure sensor when the first cavitation bubble collapses based on the transient radius data of the cavitation bubble acquired by the image acquisition device, the Rayleigh-Plesset equation, and the dissipation formula of the pressure shock wave in the liquid; Step 6. Collecting the peak pressure value measured by the pressure sensor to be calibrated when the cavitation bubble collapses for the first time; Step 7. Calculating the difference between the theoretical pressure value and the measured pressure peak value; Step 8. Use the difference as a correction coefficient to compensate for the peak error of the pressure sensor to be calibrated to complete the calibration.

2. The static pressure calibration method according to claim 1, characterized in that: The laser is a nanosecond pulse laser, which is used to generate cavitation bubbles with set size and repeatability.

3. The static pressure calibration method according to claim 1 or 2, characterized in that: The dynamic pressure acquisition device includes a charge amplifier and a dynamic acquisition card, which is used to convert the charge signal of the pressure sensor to be calibrated into a voltage signal and amplify it, and convert the voltage signal into a digital signal.

4. The static pressure calibration method according to claim 3, characterized in that: The image acquisition device includes a high-speed camera for capturing bubble dynamics images from the generation to the collapse of cavitation bubbles.

5. The static pressure calibration method according to claim 4, characterized in that: It also includes a delay trigger, which is connected to the image acquisition device and the dynamic pressure acquisition device to achieve synchronous acquisition of cavitation bubble images and pressure signals.

6. The static pressure calibration method according to claim 1 or 2, characterized in that: The laser pulse has a pulse width of 1 microsecond and is used to generate an excitation source for microsecond-level static calibration.

7. The static pressure calibration method according to claim 1, characterized in that: The experimental container is an experimental water tank, and the laser pulse is focused on a predetermined position of the liquid medium in the experimental water tank.

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