A rotating blade surface pressure-deformation synchronous measurement system and method

Abstract

The present invention relates to a synchronous measurement system and method for pressure-deformation on the surface of a rotating blade, the system comprising a binocular camera, a light source, a digital delay generator, a photoelectric speed sensor, a counter and a PSP coating. The method comprises the following steps: preparing a PSP coating with marking points on the surface of the blade to be measured; after the binocular camera and the light source are aligned with the blade to be measured, binocular positioning is performed and a phase-locked phase is obtained; under the target speed and the turning speed, after the binocular camera shutter is controlled to open, the light source is triggered to flash in the phase-locked phase; after the image accumulates sufficient intensity, the counter is disconnected and the shutter is closed; the binocular positioning parameters and the PSP coating characteristic curve are substituted, and the obtained image is aligned and reconstructed in three dimensions to obtain the three-dimensional pressure-deformation value of the blade surface. The beneficial effects of the present invention are: at the same time, the high signal-to-noise ratio and high definition of the image of the rotating model are guaranteed to facilitate the high-precision recognition of binocular features and the effective extraction of PSP signals, so as to realize the synchronous measurement of pressure-deformation parameters.

Description

Technical Field

[0001] The invention relates to the field of fluid-solid coupling test measurement of aircraft engines, and in particular to a synchronous measurement system and method for surface pressure and deformation of a rotating blade. Background Art

[0002] Rotating blades are components that directly perform functional conversion between aircraft engines and air, and their aerodynamic performance directly affects the operating efficiency and working stability of aircraft engines. Compared with cold blades (blades in a stationary state), hot blades (blades in a rotating state) not only bear huge centrifugal forces, but also are subject to the reaction force of the air, namely aerodynamic loads. Under the influence of these two main factors, hot blades will undergo changes in shape, such as "lengthening" in the radial direction and "thinning" in the circumferential direction. After the blade shape changes from cold to hot, the position and size of the blade's effect on the airflow are also changed. Therefore, there is a performance deviation between cold and hot blades of rotating blades directly due to deformation problems. Measuring the aerodynamic force and deformation of hot blades is of great value for blade pre-deformation design.

[0003] Rotor blades are characterized by high-speed movement. Traditional pressure measurement technology based on pressure sensors has problems such as installation difficulties, data transmission difficulties, and tester modification when applied to the surface of rotating models. Blade strain measurement based on strain gauges also has the above limitations and can only obtain local deformation.

[0004] Pressure Sensitive Paint (PSP) is a method for measuring model surface pressure based on optical signals. With the advantages of non-contact measurement, no modification of the measured model and full-area measurement, PSP technology has been widely used in rotating model surface pressure measurement at home and abroad. Digital image correlation (DIC) deformation measurement refers to a method of obtaining model deformation parameter measurement by imaging the measured model before and after deformation and using binocular stereo vision technology to track the displacement of specific pixels on the image before and after deformation; it also has the advantages of non-contact measurement, no modification of the measured model and full-area measurement, and has good application potential in rotor blade deformation measurement.

[0005] Chinese invention patent CN115615589A proposes a rotating model global pressure measurement system and method, which accumulates multiple short-term light emission of PSP coating in a long exposure image of a camera, thereby obtaining a high signal-to-noise ratio image on the basis of ensuring a low signal-to-noise ratio image. The system and method have high speed adaptability, but the method can only measure the pressure parameters on the blade surface and cannot obtain deformation parameters.

[0006] Chinese patent CN114152210A proposes a method for synchronously measuring the three-dimensional continuous distribution of pressure and deformation on the surface of a high-speed aircraft. This technology realizes the measurement of surface pressure and deformation of a motion model by performing DIC measurement and PSP measurement independently at the same time. However, this technology does not realize the combination of DIC method and PSP technology, and the measured pressure cannot be directly mapped to the deformation model. In addition, the large amount of speckle required by the DIC technology will interfere with the PSP luminescence and reduce the spatial resolution of the PSP measurement.

[0007] The paper "Simultaneous pressure and deformation field measurement on helicopter rotor blades using a grid-pattern pressure-sensitive paint system" published in the journal "Measurement", Chinese patent CN114354036B and Chinese patent CN113155399B all proposed a synchronous measurement technology for the surface deformation and pressure of rotating parts based on the PSP life method and considering the DIC concept, and explored the feasibility of integrating the PSP technology with the speckle marker technology. However, the PSP measurement technology based on the life method adopted by it does not have outstanding advantages in image signal-to-noise ratio and motion blur control when facing high wheel rim speed, and cannot adapt to high-speed model measurement.

[0008] At present, PSP technology and DIC method have been used for preliminary exploration of rotating blade surface pressure and deformation measurement, respectively. However, the fusion of the two methods easily makes it difficult to identify image features, and faces serious limitations of image motion blur on high-speed rotating models. Solving the limitations of image motion blur and image signal-to-noise ratio at high speeds of rotating models and developing measurement systems and methods are of great value for high-precision synchronous measurement of rotating blade surface pressure and deformation. Summary of the invention

[0009] The purpose of the present invention is to overcome the difficulties in applying existing pressure measurement technology and deformation measurement technology to rotating blades, and to develop a high signal-to-noise ratio, high-definition, full-range measurement and non-invasive rotating blade surface pressure-deformation synchronous measurement system and method.

[0010] One aspect of the present invention provides a rotating blade surface pressure-deformation synchronous measurement system, the scheme of which is:

[0011] (1) A rotating blade pressure-deformation synchronous measurement system, specifically comprising: a binocular camera, a digital delay generator, a photoelectric speed sensor, a computer, a light source, a reflective sticker, a pressure sensitive coating, and a counter;

[0012] (2) The surface of the blade being tested is evenly sprayed with pressure-sensitive paint. After the pressure-sensitive paint is sprayed, a certain number of marking points are evenly arranged on the paint surface;

[0013] (3) A reflective sticker is pasted on the rotating shaft of the blade to be measured, and the photoelectric speed sensor is aligned with the reflective sticker. Every time the blade to be measured rotates one circle, the reflective sticker can reflect the active light of the photoelectric speed sensor, so that the photoelectric speed sensor generates a speed signal and transmits it to the digital delay generator; the phase of the blade to be measured that can generate a speed signal is called the phase-locked phase;

[0014] (4) The binocular camera is equipped with a lens and a filter to form a binocular vision image acquisition module. Its focal length and field of view are sufficient to achieve full-area acquisition of the PSP luminous intensity on the model surface. The binocular camera is connected to the computer via a data cable to transmit the captured images in real time. The light source irradiation area is sufficient to cover the PSP coating, achieving full-area excitation of the PSP coating.

[0015] (5) The digital delay generator is connected to the binocular camera and the light source through data lines, and can freely control the synchronous opening and closing of the binocular camera shutter, control the light source to flash, and form a timing control; the counter is connected to the light source through a data line, and can record the number of flashes.

[0016] Preferably, the filter is a bandpass filter, which passes a wavelength adapted to the excitation spectrum of the pressure sensitive coating;

[0017] Preferably, the light source is a cold light source with an externally triggered stroboscopic function, and the stroboscopic light stability is better than 99.5%;

[0018] Preferably, the digital delay generator has two independent signal output channels CH1 and CH2, and one external trigger signal input channel Trig;

[0019] Another aspect of the present invention provides a method for synchronously measuring pressure and deformation on the surface of a rotating blade, the method comprising the following steps:

[0020] Step 1: Provide and install the above rotating blade pressure-deformation synchronous measurement system;

[0021] Step 2: Make the blade under test rotate at the target speed. After the operation is stable, control the binocular camera shutter to open synchronously. After a short delay time, each time the blade under test reaches the phase-locked phase, control the light source to briefly strobe, so as to control the motion blur length; the counter synchronously counts the stroboscopic light; when the image accumulates enough intensity in the phase-locked phase, after a short delay time, control the binocular camera shutter to close synchronously, the exposure time is T, and the counter counts N, so as to obtain a set of binocular operation images under the phase-locked phase;

[0022] Step 3: Make the blade under test rotate at the turning speed. After the operation is stable, first control the binocular camera shutter to open synchronously. After a short delay time, each time the blade under test reaches the phase-locked phase, control the light source to perform a short stroboscopic light emission to control the motion blur length; the counter synchronously counts the stroboscopic light emission; when the image accumulates enough intensity in the phase-locked phase, after a short delay time, control the binocular camera shutter to close synchronously, the exposure time is T, and the counter counts N, thereby obtaining a set of binocular reference images under the phase-locked phase;

[0023] Step 4: Perform binocular positioning on the binocular camera to obtain the internal and external parameters of the binocular camera;

[0024] Step 5: Identify and match the markers on the binocular reference image and the binocular running image, and substitute the internal and external parameters of the binocular camera to calculate the deformation information between the binocular running image and the binocular blowing image. The binocular running image is aligned to the binocular reference image through the calculated deformation information, and the binocular reference image is compared with the aligned binocular running image to obtain the PSP light intensity ratio parameter of the blade surface.

[0025] Step 6: Substitute the calibration relationship of the pressure sensitive coating, convert the PSP light intensity ratio of the blade surface into pressure, and obtain the pressure parameters of the blade surface; thereby achieving synchronous measurement of the blade surface deformation and pressure parameters.

[0026] According to the above scheme, in step 2, it should be ensured that the image signal-to-noise ratio is not less than 30dB after the binocular camera is exposed for a time period of T. The signal-to-noise ratio calculation formula is:

[0027] SNR=20×lg(I2 / I1),

[0028] Among them, I2 is the grayscale of the measured blade surface on the image, and I1 is the grayscale of the area without the measured blade on the image.

[0029] According to the above scheme, in step 2 and step 3, the delay time is used to ensure that the binocular camera can completely capture the process of the PSP coating being stimulated by the light source N times and causing photoluminescence.

[0030] According to the above scheme, in step 2 and step 3, the calculation formula for the single stroboscopic light duration t of the light source is:

[0031] t=L / v,

[0032] Wherein, L is the given image motion blur control length, and v is the tip speed of the measured blade at the target speed, which can be calculated by the rotation radius and physical speed of the tip of the measured blade.

[0033] According to the above scheme, in step six, the calibration relationship of the pressure sensitive coating is:

[0034] I ref / I=A+B×P / P ref ,

[0035] Among them, Iref and I represent the PSP luminous intensity of the blade surface under the action of the local atmospheric pressure and the pressure to be measured on the blade surface at the target speed of the model under test, and the PSP luminous intensity of the blade surface under test in the reference image, respectively; A and B are the calibration coefficients of the PSP coating.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The present invention proposes a synchronous measurement method for rotating blade surface pressure-deformation based on PSP technology, which incorporates the advantages of the DIC method. By performing feature recognition and matching on PSP images with uniformly distributed marker points, the synchronous acquisition of pressure-deformation parameters on the rotating model surface can be achieved.

[0038] (2) The measurement technology involved in the present invention has the characteristics of non-invasive measurement and full-area measurement, and uses the method of stroboscopic light source to perform image accumulation enhancement, effectively reducing the motion blur length of the rotating image, and has the advantages of high definition and high signal-to-noise ratio. It is suitable for synchronous measurement of transient pressure-deformation on the surface of high-speed rotating models;

[0039] (3) The rotating blade surface pressure-deformation synchronous measurement system provided by the present invention has low requirements for binocular cameras, light sources, etc., and is low-cost and easy to obtain. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a schematic diagram of the rotating blade surface pressure-deformation synchronous measurement system proposed by the present invention;

[0041] Figure 2 A schematic diagram of the image processing flow in the rotating blade surface pressure-deformation synchronous measurement method proposed by the present invention;

[0042] Figure 3 Schematic diagram of a stationary PSP blade with marked points in this embodiment;

[0043] Among them: 1. Binocular camera; 2. Zoom lens; 3. Filter; 4. Light source; 5. Digital delay generator; 6. Photoelectric speed sensor; 7. Counter; 8. Reflective patch; 9. PSP coating; 10. Marking point; 11. Blade to be measured; 12. Computer. DETAILED DESCRIPTION

[0044] In order to better understand the present invention, the present invention is described in detail with reference to the accompanying drawings and specific implementation examples.

[0045] References Figure 1As shown, this embodiment provides a rotating blade surface pressure-deformation synchronous measurement system, comprising:

[0046] Binocular camera 1: used to synchronously collect PSP binocular images;

[0047] Zoom lens 2: used to adjust the field of view of the measured leaf 11 of the PSP binocular image;

[0048] Filter 3: used to filter out interference light in non-PSP bands;

[0049] Light source 4: used to strobe and excite PSP coating;

[0050] Digital delay generator 5: used for timing triggering control of the binocular camera 1 and the light source 4;

[0051] Photoelectric speed sensor 6, reflective patch 8: used to detect the phase of the blade 11 to be measured, and generate an external trigger signal to control the digital delay generator 5 to start working;

[0052] Counter 7: used to record the number of stroboscopic light emission of the light source 4;

[0053] PSP coating 9: used for measuring the surface pressure of the blade 11 to be measured;

[0054] Measured blade 11: a measurement object in the embodiment;

[0055] Computer 12: used for controlling the binocular camera 1 and image post-processing;

[0056] This embodiment provides a rotating blade surface pressure-deformation synchronous measurement system, and the steps for constructing the system are as follows:

[0057] (1) spraying the PSP coating 9 uniformly on the surface of the blade 11 to be tested by air spraying;

[0058] As an optional implementation, the PSP coating is configured on-site, and an air spray gun is used to evenly spray the PSP coating 9 on the surface of the measured blade 11 .

[0059] (2) Using a marker pen, the marking points 10 are evenly arranged on the surface of the blade 11 to be tested, which is sprayed with the PSP coating 9. After the marking points are arranged, the blade 11 to be tested is as follows: Figure 3 As shown;

[0060] As an optional implementation, the marker pen used is a black oil-based marker pen; the marking points 10 can be evenly distributed over the entire surface of the blade.

[0061] (3) The measured blade 11 is rotated to the phase-locked phase, and the reflective sticker 8 is pasted on its rotating shaft; the photoelectric speed sensor 6 is aligned with the luminous sticker, so that each time the measured blade 11 rotates to the phase-locked phase, the photoelectric speed sensor 6 can be triggered by the reflective sticker; the photoelectric speed sensor 6 is connected to the Trig channel of the digital delay generator 5 through a data line.

[0062] As an optional implementation, the reflective sticker 8 can be pasted on the rotating shaft or on other non-target measurement blades. The reflective sticker 8 needs to be as far away from the measured blade 11 as possible; the marking points 10 can be evenly distributed over the entire blade surface; the Trig channel of the digital delay generator 5 is an external trigger signal input channel, which serves as a reference clock for the signal output channels CH1 and CH2 of the digital delay generator 5.

[0063] (4) The binocular camera 1, the zoom lens 2, and the filter 3 are connected together through a threaded interface and aimed at the measured blade 11; the binocular camera 1 is connected to the computer 12 and the CH2 channel of the digital delay generator 5 through a data line; the light source 4 is aimed at the measured blade 11, the light source 4 is connected to the counter 7 through a data line, and the counter 7 is connected to the CH1 channel of the digital delay generator 5 through a data line;

[0064] As an optional implementation, when installing the binocular camera 1, the aperture, focal length and magnification of the zoom lens 2 should be adjusted so that the measured blade 11 appears on the image of the computer 12 and occupies more than 50% of the pixels of the image; the light source 4 can fully excite the PSP on the surface of the measured blade 11; the physical dimensions of the zoom lens 2 and the filter 3 match the interface of the binocular camera 1.

[0065] This embodiment provides a method for synchronously measuring pressure and deformation on the surface of a rotating blade, which specifically includes the following steps:

[0066] Step 1: Provide and construct the above rotating blade surface pressure-deformation synchronous measurement system;

[0067] Step 2: Set the light source 4 to the rising edge external trigger mode, and the light emission mode is stroboscopic light emission; set the binocular camera 1 to the rising edge external trigger mode; close the external trigger signal input channel Trig of the digital delay generator 5;

[0068] In this embodiment, the test rotation speed of the blade under test is 4440 rpm (corresponding to the wheel rim speed v=217 m / s), and the motion blur length is specified as L<0.5 mm;

[0069] Step 3, set the CH1 channel waveform of the digital delay generator 5 to pulse wave mode, the output number is 1, the high level width is set to t, and the trigger mode is selected as automatic continuous trigger; manually trigger the binocular camera 1 for long exposure until the image signal-to-noise ratio is greater than 30dB; after the binocular camera 1 ends the exposure, read the counter count N, and calculate the exposure time T of the binocular camera 1; change the trigger mode setting of the CH1 channel of the digital delay generator 5 to external signal trigger, and set the first delay trigger time; set the CH2 channel waveform of the digital delay generator 5 to pulse wave mode, the frequency is set to 2T, the output number is 1, the trigger mode is selected as external signal trigger, and the first delay trigger time is set to 0; the counter preset count value is N, and a circuit is formed after the count exceeds N;

[0070] In this embodiment, t=2.3 μs, N=9000, T=42 ms, and the delay time is 10 μs.

[0071] Step 4, turn on the measured blade 11 and adjust it to reach the target speed. During this process, each time the measured blade 11 rotates to the phase-locked phase, the photoelectric speed sensor will send a trigger signal to the Trig port of the digital delay generator 5; the Trig port of the digital delay generator 5 is pre-set to a closed state in step 2, and the binocular camera 1, the light source 4 and the counter 7 are all in a to-be-triggered state; after the measured blade 11 runs stably, turn on the Trig port of the digital delay generator 5, and the CH1 and CH2 channels of the digital delay generator 5 send trigger signals to the binocular camera 1 and the light source 4 according to preset values; the binocular camera 1 first opens the shutter to collect a binocular image with an exposure time of T, and the light source 4 starts to flash continuously after the delay time following the trigger signal received by the Trig port of the digital delay generator 5; the counter 7 counts synchronously, and the count value reaches the preset value N Then, the signal transmission between the digital delay generator 5 and the light source 4 is interrupted; the binocular camera 1 closes the shutter synchronously after the delay time, thereby obtaining a set of binocular operation images and storing them in the computer 12;

[0072] Step 5, close the blade 11 to be measured, and rotate the blade 11 to the phase-locked phase after it is completely still; change the trigger mode of the CH1 channel of the digital delay generator 5 to automatic continuous triggering; manually trigger the Trig port of the digital delay generator 5 once, and the CH1 and CH2 channels of the digital delay generator 5 send trigger signals to the binocular camera 1 and the light source 4 according to the preset values, and the binocular camera 1 first opens the shutter to collect a binocular image with an exposure time of T, and the light source 4 starts to flash continuously following the trigger signal of CH1 of the digital delay generator 5 after the delay time; the counter 7 counts synchronously, and interrupts the signal transmission between the digital delay generator 5 and the light source 4 after the count value reaches the preset value N; the binocular camera 1 closes the shutter synchronously after the delay time, thereby obtaining a set of binocular reference images, and storing them in the computer 12;

[0073] Step 6: Figure 2 As shown, the relative position and parameters of the system are kept unchanged, and the binocular image acquisition system composed of the binocular camera 1, the zoom lens 2, and the filter 3 is binocularly calibrated using a calibration plate to obtain the internal and external parameters of the binocular image acquisition system;

[0074] Step seven, identify and match the marking points on the binocular image surface; on the one hand, bring in the internal and external parameters of the binocular image acquisition system to solve the deformation relationship between the binocular images; on the other hand, align the binocular reference image with the binocular running image according to the matched marking points, bring in the calibration parameters of the PSP coating 9 after ratio processing, and calculate the pressure distribution on the blade surface; map the two aspects of data to each other, and obtain the synchronous pressure-deformation data of the rotating blade surface.

[0075] Typical embodiments of the present invention are described above in detail.

Claims

1. A synchronous measurement system for pressure and deformation on the surface of a rotating blade, characterized in that: Including binocular camera, lens, filter, digital delay generator, photoelectric speed sensor, computer, light source, reflective sticker, pressure sensitive paint, counter; Prepare a PSP coating with uniform marking points on the surface of the blade to be tested; The reflective sticker is pasted on the rotating shaft of the blade to be measured, and the photoelectric speed sensor is aligned with the reflective sticker so that the phase of the blade to be measured is the phase-locked phase; the photoelectric speed sensor generates a speed signal in the phase-locked phase; The binocular camera is matched with the lens and the filter in size and is fixedly connected. Its focal length and field of view are sufficient to realize the full-area image acquisition of the measured blade. The data interface of the binocular camera is connected to the computer through a data cable to transmit the captured image in real time. The irradiation area of ​​the light source is sufficient to cover the entire area of ​​the measured blade to realize the full-area excitation of the PSP coating. The signal input channel of the digital delay generator is connected to the photoelectric speed sensor to continuously receive the speed signal; the signal output channel 1 of the digital delay generator is connected to the external trigger interface of the light source via the counter; the signal output channel 2 of the digital delay generator is connected to the external trigger interface of the binocular camera; The digital delay generator can freely control the synchronous opening and closing of the binocular camera shutter, control the light source to strobe, and form a timing control by setting the signal parameters of the signal output channel; the counter can record the number of strobe times and cut off the signal transmission between the digital delay generator and the light source after reaching a preset value.

2. A method for synchronously measuring pressure and deformation on the surface of a rotating blade, characterized in that: The following steps are involved: Step 1: providing the rotating blade pressure-deformation synchronous measurement system according to claim 1; Step 2: Make the blade under test run at the target speed. After the running is stable, control the binocular camera shutter to open synchronously. After a short delay, control the light source to flash briefly after the blade under test reaches the phase-locked phase, and the counter counts synchronously. When the image accumulates enough intensity in the phase-locked phase, the counter stops counting and disconnects. After a short delay, control the binocular camera shutter to close synchronously, and record the exposure time of the binocular camera, so as to obtain a set of binocular running images. Step 3: Make the blade under test run at the turning speed. After the running is stable, preset the exposure time of the binocular camera and the counter value to be consistent with step 2; control the binocular camera shutter to open synchronously, and after a short delay time, control the light source to flash briefly after the blade under test reaches the phase-locked phase; count synchronously until it becomes open circuit; after a short delay time, the binocular camera shutter automatically closes synchronously, thereby obtaining a set of binocular reference images; Step 4: adjust the measured blade to the phase-locked phase, perform binocular positioning on the binocular camera, and obtain the internal and external parameters of the binocular camera; Step 5: Identify and match the marking points on the binocular reference image and the binocular running image, bring in the internal and external parameters of the binocular camera, calculate the deformation parameters between the binocular running image and the binocular blowing image, align the binocular reference image to the binocular running image through the calculated deformation parameters, compare the binocular running image with the aligned binocular reference image, and obtain the three-dimensional PSP light intensity ratio of the measured blade surface; Step 6: Substitute the calibration relationship of the pressure sensitive coating into the measured blade surface PSP light intensity ratio into a pressure parameter, thereby achieving synchronous measurement of the blade surface deformation and pressure parameters.

3. The method for synchronously measuring pressure and deformation on the surface of a rotating blade according to claim 2, characterized in that: In step 2, the signal-to-noise ratio of the image captured by the binocular camera should be no less than 30dB. The signal-to-noise ratio calculation formula is: SNR = 20 × lg (I2 / I1), Among them, I2 is the grayscale of the measured blade surface on the image, and I1 is the grayscale of the area without the measured blade on the image.

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