Periodic pressure field measurement system and method based on the stacking life of pressure-sensitive coatings

Abstract

The present invention discloses a periodic pressure field measurement system based on the superposition life of pressure-sensitive coatings, including a test piece, a pulse light source, a camera, a synchronizer and a computer. The test surface of the test piece is evenly sprayed with pressure-sensitive coatings; the pulse light source is directly opposite to the test surface of the test piece and is arranged in the center relative to the test surface; the pulse light source is connected to the synchronizer; the camera is fixed above the pulse light source, and the lens of the camera is aimed at the test surface of the test piece, so that the test surface of the test piece completely falls into the lens of the camera; the camera is respectively connected to the synchronizer and the computer. The present invention also discloses a periodic pressure field measurement method of pressure-sensitive coatings based on the superposition life method. The beneficial effects of the present invention are: based on the relationship between the fluorescence lifetime and pressure of the pressure-sensitive coating, the present invention collects a sequence of fluorescence images of the pressure-sensitive coating with a high signal-to-noise ratio under high-frequency pulsating pressure through a stroboscopic light source and a low-frame-rate CCD camera, and obtains the dynamic pressure distribution of the entire domain according to the measurement principle of the life method, which can effectively reduce the system error.

Description

Technical Field

[0001] The present invention belongs to the technical field of pressure-sensitive coating measurement, and in particular relates to a periodic pressure field measurement system and method based on the stacking life of the pressure-sensitive coating. Background Art

[0002] As one of the three thermal parameters (pressure, temperature, flow) of automatic control, pressure plays a very important role in measurement and control. There are many ways to measure pressure, but each pressure measurement method requires calibration of the measuring equipment in order to obtain measurement data, such as the functional relationship between electrical signals, optical signals, etc. and pressure, as well as the characteristics of the measurement system such as sensitivity.

[0003] Optical pressure-sensitive paint pressure measurement technology (PSP) based on computer vision and image processing technology is an important breakthrough in non-contact flow display technology. Compared with the current traditional dot matrix measurement technology in China, optical pressure-sensitive measurement technology can make up for the damage to the model and the interference to the flow field caused by pressure probe holes, pressure sensors, etc., as well as the complexity of traditional data transmission methods. In addition, this measurement technology greatly improves the measurement range and has the advantages of non-contact, continuous measurement, relatively low test cost, and time saving. It has been favored by a large number of experimental workers. The basic principle of optical pressure-sensitive pressure measurement technology is: evenly cover the surface of the model to be measured with pressure-sensitive paint, which is composed of photosensitive molecules and a matrix that can permeate oxygen. When excited by light of a specific wavelength, the photosensitive molecules in the paint gain energy from the originally stable ground state and transition to a high-energy excited state. The photosensitive molecules in the unstable excited state are collided with oxygen molecules diffused from the measured surface, lose the energy of the excited state, and deactivate back to the ground state. This process does not produce radiated light, which leads to a decrease in luminescence intensity, forming an "oxygen quenching" phenomenon. The greater the concentration of oxygen molecules, that is, the greater the pressure in the atmosphere, the stronger the quenching effect of oxygen, and the darker the light emitted by the coating under a certain wavelength of light. Therefore, under light irradiation, the luminescence intensity of the pressure-sensitive coating can reflect the pressure value on the surface of the model under test. By taking an image of the surface of the model under test under light irradiation and analyzing the image, the pressure distribution on the surface of the model under test can be obtained. With the development of fast response optical pressure-sensitive coatings (Fast PSP), this technology has expanded from the original steady-state flow field measurement to dynamic flow field measurement, especially periodic flow field. As the response time of the coating gradually shortens, it can be used to measure high-frequency fluctuating pressure fields.

[0004] However, in the prior art, the fast response optical pressure-sensitive coating pressure measurement technology mainly has the following problems:

[0005] As the frequency of measuring flow field pressure gradually increases, the camera exposure time is required to be shortened to meet the needs of high-frequency pressure field measurement. When the camera exposure time is shortened, it will directly lead to a decrease in the amount of light entering the camera, resulting in a lower signal-to-noise ratio (SNR) of the fluorescent image captured by the camera, reducing the accuracy of the pressure calibration of the pressure-sensitive coating, which is not conducive to obtaining high-resolution pressure measurement results; the main function of the filter in the measurement system is to filter out the light emitted by the light source, but the excitation degree of PSP coating is low, which belongs to weak light technology, and the filtering effect of the filter is limited, and the light intensity of the light source cannot be completely filtered out, resulting in both PSP coating luminescence components and light source luminescence components in the final image. Subsequent image processing technology and data processing technology cannot eliminate this effect, resulting in a low signal-to-noise ratio of the measurement result. Summary of the invention

[0006] The purpose of the present invention is to provide a periodic pressure field measurement system and method based on the stacking life of pressure-sensitive coatings with a high signal-to-noise ratio in view of the deficiencies in the prior art.

[0007] The technical solution adopted by the present invention is: a periodic pressure field measurement system based on the stacking life of pressure-sensitive coatings, including a test piece, a pulse light source, a camera, a synchronizer and a computer, wherein the test surface of the test piece is evenly sprayed with pressure-sensitive coating; the pulse light source is directly opposite to the test surface of the test piece; the pulse light source is connected to the synchronizer; the camera is fixed above the pulse light source, and the lens of the camera is aimed at the test surface of the test piece so that the test surface of the test piece completely falls into the lens of the camera; the camera is respectively connected to the synchronizer and the computer.

[0008] According to the above solution, the camera is a CCD camera.

[0009] According to the above solution, the pulse light source is arranged centrally relative to the test surface.

[0010] The present invention also provides a method for measuring a periodic pressure field based on the stacking life of a pressure-sensitive coating, the method comprising the following steps:

[0011] Step 1, providing the components of the periodic pressure field measurement system of the pressure-sensitive coating as described above;

[0012] Step 2: Evenly spray the pressure sensitive coating onto the test surface of the test piece;

[0013] Step 3: Direct the pulse light source toward the test surface of the test piece, and then install the camera above the pulse light source so that the camera lens is directed toward the test surface of the test piece;

[0014] Step 4: The camera turns on the modulation mode and divides the pressure field with a period of T into n parts evenly in time. The phase of the pressure field in the i-th time period is φ i, the corresponding phases in each time period are φ1, φ2…φ n ;

[0015] Step 5: Place the pressure-sensitive coating periodic pressure field measurement system in a light-free environment for experiment, and start the pressure field measurement of the PSP coating after the experimental pressure field meets the periodic change;

[0016] Step 6: Use the synchronizer to adjust the pulse light source so that the pulse width it emits is tp and the number of times it emits light at phase φ1 is M;

[0017] Step 7, the computer controls the camera through the synchronizer, so that the camera takes images after the pulse light source emits light for tp time; the camera selects the modulation mode, sets the modulation mode times to M times, and the camera single exposure time is t1. The modulation mode accumulates the life luminous intensity of M times of PSP coating time t1, records it with the computer, and outputs the image I1;

[0018] Step 8: Set the camera delay so that the camera starts to expose after the pulse light source emits light for tp+t1 time; select the camera modulation mode, set the modulation mode times to m / 2 times, and the exposure time to t2. The modulation mode accumulates the life luminous intensity of the M times PSP coating for time t2, records it with a computer, and outputs the image I2;

[0019] Step 9: The computer divides the grayscale values ​​of the same pixels of image I1 and image I2 to obtain image I1 / I2, and then restores the pressure information of phase φ1 according to the PSP coating image light intensity and pressure calibration formula;

[0020] Step 10. According to the periodicity of the pressure field and the spatial-temporal relationship of the phase, a synchronizer is used to adjust the pulse light source to emit light in other phases. By repeating steps 6 to 9, the pressure variation process at n moments in a cycle can be obtained, thus realizing dynamic measurement of pressure.

[0021] According to the above scheme, the modulation mode means that the camera can control the start and end time of the camera's photosensitive chip through external trigger signals multiple times during the exposure period. Each time the photosensitive chip receives a photon, it is converted into an electrical signal and accumulated in the memory. After the exposure time is over, the accumulated signals are combined and converted into the grayscale value of the image.

[0022] According to the above scheme, in step nine, the image intensity and pressure calibration formula is: Where A and B are calibration coefficients, Pref is the reference pressure, Iref1 and Iref2 are two images obtained by using the pressure-sensitive coating superposition life method under the reference pressure; the calibration coefficient is determined in the calibration chamber; by repeatedly adjusting the pressure P, a series of univariate equations related to A and B are obtained, and A and B are finally determined by the least squares method, and the pressure information can be restored by this formula.

[0023] The beneficial effects of the present invention are:

[0024] The present invention is based on the relationship between the fluorescence lifetime and pressure of the pressure-sensitive coating. A sequence of fluorescence images of the pressure-sensitive coating with a high signal-to-noise ratio under high-frequency pulsating pressure is collected by a stroboscopic light source and a low-frame-rate CCD camera. The global dynamic pressure distribution is obtained according to the lifetime measurement principle, which can effectively reduce the system error. Through timing control, the light source is avoided. Compared with the traditional measurement system, no filter is needed to filter out the light source. Only the PSP light is contained in the captured image, thereby improving the signal-to-noise ratio of the optical pressure-sensitive coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of a specific embodiment of the present invention.

[0026] Figure 2 Schematic diagram of the control timing of the camera in this embodiment.

[0027] Among them: 1. Camera; 2. Pulse light source; 3. Synchronizer; 4. PSP coating; 5. Test piece; 6. Computer. DETAILED DESCRIPTION

[0028] In order to better understand the present invention, the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0029] like Figure 1 A periodic pressure field measurement system based on the stacking life of pressure-sensitive coatings is shown, comprising a test piece 5, a pulse light source 2, a camera 1, a synchronizer 3 and a computer 6, wherein the test surface of the test piece 5 is evenly sprayed with a pressure-sensitive coating (hereinafter referred to as PSP coating 4); the pulse light source 2 is directly facing the test surface of the test piece 5; the pulse light source 2 is connected to the synchronizer 3; the camera 1 is fixed above the pulse light source 2, and the lens of the camera 1 is aimed at the test surface of the test piece 5, so that the test surface of the test piece 5 completely falls into the lens of the camera 1; the camera 1 is respectively connected to the synchronizer 3 and the computer 6.

[0030] In this embodiment, the camera 1 is a CCD camera; the pulse light source 2 faces the test surface of the test piece 5 and is arranged in the center relative to the test surface.

[0031] In the present invention, the pulse light source 2 is used to emit light to the test surface of the test piece 5; the camera 1 is used to capture images; the synchronizer 3 is used to control the light emission timing of the pulse light source 2 and the pulse width of the pulse light source 2. The computer 6 is used to control the parameters of the camera 1 and save image data.

[0032] A method for measuring the periodic pressure field of a pressure-sensitive coating based on a superposition lifetime method comprises the following steps:

[0033] Step 1: Provide the components of the periodic pressure field measurement system of the pressure-sensitive coating as described above.

[0034] Step 2: spray the pressure sensitive coating evenly onto the test surface of the test piece 5.

[0035] Step 3: direct the pulse light source 2 toward the test surface of the test piece 5 to ensure that the pulse light source irradiates evenly; then install the camera 1 above the pulse light source 2 so that the lens of the camera 1 is aligned with the test surface of the test piece 5 .

[0036] Step 4: Camera 1 turns on the modulation mode. In order to capture the dynamic changes of the pressure field, the pressure field with a period of T is evenly divided into n parts in time. The phase corresponding to the pressure field in the i-th time period is φ i , the corresponding phases in each time period are φ1, φ2…φ n .

[0037] In the present invention, the modulation mode of camera 1, that is, camera 1 can control the start and end time of photosensitivity of the photosensitive chip of camera 1 multiple times through an external trigger signal during exposure. Each time the photosensitive chip receives a photon, it is converted into an electrical signal and accumulated in a memory. After the exposure time ends, the accumulated signals are merged and converted into the grayscale value of the image.

[0038] Step 5: Place the pressure sensitive coating periodic pressure field measurement system in a dark environment for experiment. After the experimental pressure field meets the periodic variation, start the pressure field measurement of the PSP coating 4. Figure 2 shown.

[0039] In the present invention, a lightless environment refers to that the camera 1 takes images with the lens cover opened and closed respectively, and the exposure time is 1 minute. When the grayscales of the two images are the same, it is considered that the environment is lightless.

[0040] Step 6: Use the synchronizer 3 to adjust the pulse light source 2 so that the pulse width it emits is tp (about 1ms, to excite the PSP coating 4 to the strongest luminous state as much as possible), and the number of luminous times at phase φ1 is M. The pulse light source timing is as follows: Figure 2 shown.

[0041] In the present invention, the method for determining the number of luminescence times M is: ensuring the number of luminescence times when the image grayscale is close to the grayscale value corresponding to the full well capacity of the camera; after the number of luminescence times is determined, the number of luminescence times of all image acquisitions remains unchanged.

[0042] Step seven, computer 6 controls camera 1 through synchronizer 3, so that camera 1 takes images after pulse light source 2 emits light for tp time, ensuring that camera 1 shields pulse light source 2 from emitting light without a filter; camera 1 selects modulation mode (i.e., camera 1 can control the start and end time of the light-sensitive chip through an external trigger signal multiple times during exposure, and each time the photosensitive chip receives a photon, it is converted into an electrical signal and accumulated in the memory, and after the exposure time is over, the accumulated signals are merged and converted into the grayscale value of the image), sets the modulation mode number to M times, and the single exposure time of camera 1 is t1. The modulation mode accumulates the life luminous intensity of PSP coating 4 for M times of time t1, records it with computer 6, and outputs image I1. Camera 1 exposure sequence I1 is as follows Figure 2 shown.

[0043] Step 8: Set the delay of camera 1 so that camera 1 starts to expose after pulse light source 2 emits light for tp+t1 time; camera 1 selects modulation mode, sets the modulation mode times to M times, and the exposure time to t2. The modulation mode accumulates the life luminous intensity of M times of PSP coating 4 for time t2, records it with computer 6, and outputs image I2. Camera 1 exposure timing I2 is as follows Figure 2 shown.

[0044] Step nine, the computer divides the grayscale values ​​of the same pixels of image I1 and image I2 to obtain image I1 / I2, and then restores the pressure information of phase φ1 according to the PSP coating 4 image light intensity and pressure calibration formula.

[0045] In the present invention, the image intensity and pressure calibration formula is: Where A and B are calibration coefficients, Pref is the reference pressure, and Iref1 and Iref2 are two images obtained by using the pressure-sensitive coating superposition life method under the reference pressure. The calibration coefficient is determined in the calibration chamber; by repeatedly adjusting the pressure P, a series of one-variable equations related to A and B are obtained, and A and B are finally determined by the least squares method, and the pressure information can be restored by this formula. Both Pref and can be measured experimentally.

[0046] Step 10: According to the periodicity of the pressure field and the spatial-temporal relationship of the phase, the synchronizer 3 is used to adjust the pulse light source 2 to emit light at other phases. By repeating steps 6 to 9, the pressure variation process at n moments in a cycle can be obtained, thereby realizing dynamic measurement of pressure.

[0047] In the present invention, the single exposure times t1 and t2 of the camera 1 are determined according to the characteristics of the PSP coating 4 .

[0048] The contents not described in detail in this specification belong to the prior art known to the professional and technical personnel in this field. Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it is still possible for the technical solutions described in the aforementioned embodiments to be modified or some of the technical features thereof to be replaced by equivalents by the technical personnel in this field. However, 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 method for measuring periodic pressure field based on the stacking life of pressure-sensitive coating, characterized in that: The method comprises the following steps: Step 1, providing components of a periodic pressure field measurement system based on the stacking life of a pressure-sensitive coating; Step 2: Evenly spray the pressure sensitive coating onto the test surface of the test piece; Step 3: Direct the pulse light source toward the test surface of the test piece, and then install the camera above the pulse light source so that the camera lens is directed toward the test surface of the test piece; Step 4: The camera turns on the modulation mode and divides the pressure field with a period of T into n parts evenly in time. The phase of the pressure field in the i-th time period is The corresponding phases in each time period are Step 5: placing the pressure-sensitive coating periodic pressure field measurement system in a light-free environment for experiment, and starting the pressure field measurement of the pressure-sensitive coating after the experimental pressure field meets the periodic change; Step 6: Use the synchronizer to adjust the pulse light source so that the pulse width it emits is tp, and the phase The number of times M is emitted; Step 7, the computer controls the camera through the synchronizer, so that the camera takes an image after the pulse light source emits light for tp time; the camera selects the modulation mode, sets the modulation mode times to M times, and the camera single exposure time is t1. The modulation mode accumulates the life luminous intensity of the pressure sensitive coating for M times of time t1, records it with the computer, and outputs the image I1; Step 8: Setting the camera delay so that the camera starts to expose after the pulse light source emits light for tp+t1 time; the camera selects the modulation mode, sets the modulation mode times to M times, and the exposure time to t2. The modulation mode accumulates the life luminous intensity of the pressure sensitive coating for M times of t2, records it with a computer, and outputs the image I2; Step 9: The computer divides the grayscale values ​​of the same pixels of the images I1 and I2 to obtain the image I1 / I2, and then restores the pressure information of the phase φ1 according to the light intensity and pressure calibration formula of the pressure sensitive coating image; Step 10: According to the periodicity of the pressure field and the time-space relationship of the phase, a synchronizer is used to adjust the pulse light source to emit light in other phases, and steps 6 to 9 are repeated to obtain the pressure change process at n moments in a cycle, thereby realizing dynamic measurement of pressure; The periodic pressure field measurement system based on the stacking life of pressure-sensitive coatings includes a test piece, a pulse light source, a camera, a synchronizer and a computer. The test surface of the test piece is evenly sprayed with pressure-sensitive coatings; the pulse light source is directly opposite to the test surface of the test piece and is arranged in the center relative to the test surface; the pulse light source is connected to the synchronizer; the camera is fixed above the pulse light source, and the lens of the camera is aimed at the test surface of the test piece so that the test surface of the test piece completely falls into the lens of the camera; the camera is respectively connected to the synchronizer and the computer.

2. The periodic pressure field measurement method according to claim 1, characterized in that: Modulation mode means that the camera can control the start and end time of the camera's photosensitive chip through external trigger signals multiple times during exposure. Each time the photosensitive chip receives a photon, it is converted into an electrical signal and accumulated in the memory. After the exposure time is over, the accumulated signals are combined and converted into the grayscale value of the image.

3. The periodic pressure field measurement method according to claim 1, characterized in that: In step nine, the image intensity and pressure calibration formula is: Where A and B are calibration coefficients, Pref is the reference pressure, Iref1 and Iref2 are two images obtained by using the pressure-sensitive coating superposition life method under the reference pressure; the calibration coefficient is determined in the calibration chamber; by repeatedly adjusting the pressure P, a series of univariate equations related to A and B are obtained, and A and B are finally determined by the least squares method, and the pressure information can be restored by this formula.

4. The periodic pressure field measurement method according to claim 1, characterized in that: The camera is a CCD camera.

5. The periodic pressure field measurement method according to claim 1, characterized in that: The pulse light source is arranged centrally relative to the test surface.

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