A synchronous measurement method for velocity and temperature fields combining a three-color mask single camera and liquid crystal

Abstract

The present invention provides a method for synchronously measuring velocity and temperature fields by combining a three-color mask single camera with liquid crystal, which relates to the technical field of flow field observation. The method includes: screening thermochromic liquid crystal particles to obtain tracer particles; detecting a three-dimensional flow field of the tracer particles and acquiring a three-color mask color image through a three-color mask single camera; performing three-dimensional position reconstruction on the three-color mask color image through a three-view image separation technique to obtain a three-dimensional velocity field; performing color temperature calibration processing on the three-color mask color image to obtain a two-dimensional temperature image; and fitting the three-dimensional velocity field and the two-dimensional temperature image to obtain a three-dimensional velocity-temperature field. This method realizes synchronous high-precision measurement of the velocity field and the temperature field through three-dimensional particle tracking technology and the color temperature characteristics of thermochromic liquid crystal.

Description

Technical Field

[0001] The present invention relates to the technical field of flow field observation, and particularly to a method for synchronously measuring velocity and temperature fields by combining a three-color mask single camera with liquid crystal. Background Art

[0002] In the study of fluid mechanics, the accurate measurement of velocity fields and temperature fields is crucial for understanding fluid behavior. Currently, separate flow field velocity measurement methods and temperature measurement methods have been relatively mature. In the prior art, generally, devices such as hot wires or laser Doppler velocimeters are used to measure the velocity of a single point in fluid flow, and methods such as thermocouples or laser-induced fluorescence are used to measure the temperature of each point in fluid flow.

[0003] However, traditional measurement methods often can only measure velocity or temperature separately, and it is difficult to obtain the spatial distribution information of both simultaneously. Moreover, the technology for synchronously measuring flow field velocity and temperature is still in the development stage, and existing flow field velocity and temperature synchronous measurement methods have technical problems such as limited measurement range, large velocity measurement and temperature measurement errors. Therefore, it is very necessary to design a method for synchronously measuring velocity and temperature fields by combining a three-color mask single camera with liquid crystal. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for synchronously measuring velocity and temperature fields by combining a three-color mask single camera with liquid crystal, so as to achieve synchronous high-precision measurement of velocity fields and temperature fields through three-dimensional particle tracking technology and the color temperature characteristics of thermochromic liquid crystal.

[0005] To achieve the above purpose, the present invention provides the following solution:

[0006] A method for synchronously measuring velocity and temperature fields by combining a three-color mask single camera with liquid crystal, comprising the following steps:

[0007] Screen thermochromic liquid crystal particles to obtain tracer particles;

[0008] Perform three-dimensional flow field detection on the tracer particles, and obtain a three-color mask color image through a three-color mask single camera;

[0009] Perform three-dimensional position reconstruction on the three-color mask color image through a three-view image separation technique to obtain a three-dimensional velocity field;

[0010] Perform color temperature calibration processing on the three-color mask color image to obtain a two-dimensional temperature image;

[0011] Fit the three-dimensional velocity field and the two-dimensional temperature image to obtain a three-dimensional velocity-temperature field.

[0012] Optionally, the particle size range of the tracer particles is 100 µm - 110 µm.

[0013] Optionally, three-view image separation technology is used to reconstruct the three-dimensional position of the three-color mask color image to obtain a three-dimensional velocity field, including:

[0014] Perform a calibration operation on the three-color mask color image to obtain a calibrated image;

[0015] Use the method of iterative particle reconstruction to perform initial fitting on the first distribution image and the second distribution image of the calibrated image respectively to obtain a first trajectory and a second trajectory; the first distribution image is the first four frames of the calibrated image, and the second distribution image is the images subsequent to the fourth frame in the calibrated image;

[0016] Reconstruct and fit the first trajectory and the second trajectory to obtain a three-dimensional velocity field.

[0017] Optionally, perform a calibration operation on the three-color mask color image to obtain a calibrated image, including:

[0018] Separate the three-color mask color image by color channel to obtain a first image;

[0019] Perform interpolation operation and demosaicing on the original image in sequence to obtain a second image;

[0020] Perform color crosstalk correction on the second image to obtain a third image;

[0021] Perform volume calibration operation on the third image to obtain a calibrated image.

[0022] Optionally, perform color temperature calibration processing on the three-color mask color image to obtain a two-dimensional temperature image, including:

[0023] Perform color space transformation on the three-color mask color image to obtain a saturation image;

[0024] Obtain the central hue value of the interrogation window in the saturation image through a Gaussian curve;

[0025] Obtain the central hue value multiple times and obtain a color temperature calibration curve based on the central hue value;

[0026] Obtain a two-dimensional temperature image based on the color temperature calibration curve.

[0027] Optionally, obtain the central hue value of the interrogation window in the saturation image through a Gaussian curve, including:

[0028] At a preset calibration temperature, calibrate the saturation image through the interrogation window to obtain an interrogation window;

[0029] Determine a one-dimensional Gaussian curve according to the hue distribution of the interrogation window and obtain the central hue value through the one-dimensional Gaussian curve.

[0030] Optionally, obtain a color temperature calibration curve based on the central hue value, including:

[0031] Determine the calibration points of the interrogation window through the central color tone value;

[0032] Based on the calibration points, determine the color temperature calibration curve through a fitting function.

[0033] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: The method for synchronously measuring the velocity temperature field by combining a three-color mask single camera and liquid crystal provided by the present invention includes: screening thermochromic liquid crystal particles to obtain tracer particles; detecting the three-dimensional flow field of the tracer particles, and obtaining a three-color mask color image through a three-color mask single camera; performing three-dimensional position reconstruction on the three-color mask color image through a three-view image separation technology to obtain a three-dimensional velocity field; performing color temperature calibration processing on the three-color mask color image to obtain a two-dimensional temperature image; fitting the three-dimensional velocity field and the two-dimensional temperature image to obtain a three-dimensional velocity-temperature field. Description of the Drawings

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0035] Figure 1 It is a flowchart of the method for synchronously measuring the velocity temperature field according to the embodiment of the present invention;

[0036] Figure 2 It is a flowchart of the three-dimensional position reconstruction according to the embodiment of the present invention;

[0037] Figure 3 It is a flowchart of the color temperature calibration according to the embodiment of the present invention;

[0038] Figure 4 It is a histogram of the interrogation window according to the embodiment of the present invention;

[0039] Figure 5 It is a color temperature calibration curve graph according to the embodiment of the present invention;

[0040] Figure 6 It is a result graph of the extraction efficiency and ghost particles according to the embodiment of the present invention;

[0041] Figure 7 It is a result graph of the particle distance before and after reconstruction according to the embodiment of the present invention. Detailed Embodiments

[0042] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0043] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0044] As Figure 1 shown, the present invention provides a method for synchronous measurement of velocity and temperature fields by combining a three-color mask single camera with liquid crystal, including the following steps:

[0045] Step 100: Screen the thermochromic liquid crystal particles to obtain tracer particles;

[0046] Specifically, screen out the thermochromic liquid crystal (TLC) particles with a particle size distribution in the range of 100 µm - 110 µm, and use the screened particles as tracer particles.

[0047] It should be noted that the screened particles have a narrow size distribution, can reliably detect individual particles, and there is no bright reflection ring around the particle core. This enables the particles to reflect as much color information as possible, that is, the temperature indication range should be large, and the temperature-color gradient should be as smooth as possible to ensure the accuracy of temperature measurement. And the particles have neutral buoyancy in the liquid.

[0048] Step 200: Perform three-dimensional flow field detection on the tracer particles, and obtain a three-color mask color image through a three-color mask single camera;

[0049] Specifically, the process of three-dimensional flow field detection is as follows: Make a measurement flow field of a thermochromic liquid crystal (TLC) particle emulsion, irradiate the tracer particles with a high-energy white LED array light source, and use a three-color mask single color camera to obtain the sequential particle three-color mask color images of the tracer particles in the measurement flow field.

[0050] More specifically, the array light source in this embodiment uses a three-band white light laser with a beam power of 3W and wavelengths of 450 nm, 532 nm, and 650 nm respectively. Install the customized three-color mask in front of the ZEISS Milvus2 / 100M lens and connect it to the Revealer M120 color camera.

[0051] More specifically, the water tank for measuring the flow field in this embodiment is made of 15-mm-thick acrylic plates, with dimensions of 1000 mm in length, 500 mm in width, and 500 mm in height. The half stroke of the piston is set to 13 mm, and the driving frequency f is 0.25 Hz. The Strouhal number of the flow field is 0.77, and the Reynolds number is 32. The diameter D of the jet circular nozzle is 10 mm. The measurement area is located at 0.1D to the left of the nozzle, and the measurement volume is defined as 2D*2D*0.4D distributed in the x, y, and z directions. TLC particles (Hallcrest, R18C6) are used as tracer particles and temperature-sensitive particles, with a diameter of 100 - 110 µm. A water-ethylene glycol mixture with a mass mixing ratio of 7:3 is used as the fluid, and the particle concentration is approximately 0.025 PPP. Among them, the temperature of the cold fluid in the water tank is at room temperature. Before the measurement starts, the temperature of the flow field is measured to be 18 °C (measured with a thermocouple thermometer), and then the temperature of the hot fluid in the nozzle is set to 20 °C to form a temperature difference.

[0052] Step 300: Perform three-dimensional position reconstruction on the three-color mask color image through the three-view image separation technique to obtain a three-dimensional velocity field; the specific steps are as Figure 2 shown, including:

[0053] Step 301: Perform a calibration operation on the three-color mask color image to obtain a calibrated image; specifically including:

[0054] Separate the three-color mask color image by color channel to obtain a first image;

[0055] Specifically, separate the three-color mask color image in the RGB space by color channel to obtain three color-separated first images.

[0056] Perform an interpolation operation and a demosaicing process on the original image in sequence to obtain a second image;

[0057] Specifically, in this embodiment, the double-three-color interpolation, bilinear interpolation, pattern recognition interpolation, or deep learning interpolation method is used to perform demosaicing hole interpolation on the separated first image to obtain a second image.

[0058] Perform color crosstalk correction on the second image to obtain a third image;

[0059] Specifically, separately take single-aperture images that block two light-transmitting apertures in the single-camera with an occluded three-color mask to obtain images of three colors. Use these three-aperture images as the calibration images for color crosstalk correction. Use the first-order fitting method to obtain the linear relationship between the calibration image and other color channels, and perform color crosstalk correction on the second image according to the linear relationship to remove the ghost pixels in the image.

[0060] Perform a volume calibration operation on the third image to obtain a calibrated image.

[0061] Specifically, in this embodiment, the two-dimensional position information of the third image is obtained through a planar calibration board, and then the planar calibration board is moved along the depth of field direction to determine the two-dimensional position information at different depths of field. The three-dimensional position is obtained from the depth of field position and its two-dimensional position information, so as to obtain the conversion relationship between the two-dimensional image coordinates and the three-dimensional world coordinates of the third image, and the third image is converted into a calibrated image according to the conversion relationship.

[0062] Step 302: Perform initial fitting on the first distribution image and the second distribution image of the calibrated image respectively through the method of iterative particle reconstruction to obtain a first trajectory and a second trajectory; the first distribution image is the first four frames of the calibrated image, and the second distribution image is the subsequent images after the fourth frame in the calibrated image;

[0063] Specifically, the trajectory of the first four frames of the calibrated image is initially fitted through the method of iterative particle reconstruction to obtain a first trajectory. The subsequent frame images of the calibrated image except the first four frames are also initially fitted to obtain a second trajectory. Among them, the parameters in the preliminary fitting process include: the two-dimensional particle search range of pixels, the ghost particle intensity threshold, the two-dimensional line-of-sight search range of voxels, and the three-dimensional line-of-sight search range of voxels.

[0064] Step 303: Reconstruct and fit the first trajectory and the second trajectory to obtain a three-dimensional velocity field.

[0065] Specifically, in this embodiment, the first trajectory and the second trajectory are reconstructed and fitted through the Shake-The-Box (STB) method. Among them, the parameters in the reconstruction and fitting process include: the voxel jitter range, the maximum single-frame displacement of particles in voxels, the particle intensity subtraction magnification, and the ghost particle intensity threshold.

[0066] Step 400: Perform color temperature calibration processing on the three-color mask color image to obtain a two-dimensional temperature image; the specific steps are as Figure 3 shown, including:

[0067] Step 401: Perform color space transformation on the three-color mask color image to obtain a saturation image;

[0068] Specifically, in this embodiment, the three-color mask color image is transformed from the original RGB color space to the hue-saturation-lightness (HSL) color space to obtain a saturation image in the HSL color space.

[0069] Step 402: Obtain the central hue value of the interrogation window in the saturation image through a Gaussian curve;

[0070] Specifically, as Figure 4As shown, the preset calibration temperature in this embodiment is 20°C. At 20°C, a saturation image is calibrated using an interrogation window of 100×100 pixels, and multiple interrogation windows of 100×100 pixels are obtained. The hue (H) distribution of the interrogation window is represented by a histogram. A one-dimensional Gaussian curve is determined based on the edge contour of the histogram, and the central hue value Hc is obtained through the one-dimensional Gaussian curve. The central hue value is used as the calibration point. In this embodiment, the anchor point (x0, y0) of the image is (800, 600), and the central hue value Hc is 2488.

[0071] Step 403: Repeatedly obtain the central hue value multiple times, and obtain a color temperature calibration curve based on the central hue value;

[0072] Specifically, as Figure 5 shown, obtain the calibration points of all interrogation windows. Based on all the obtained calibration points, determine the color temperature calibration curve through a fitting function. The black dots in the figure are the values of the calibration points, and the curve is the color temperature calibration curve.

[0073] Step 404: Obtain a two-dimensional temperature image based on the color temperature calibration curve.

[0074] Specifically, the data described by the color temperature calibration curve has negligible uncertainty and can be used to convert the hue value to temperature. Therefore, the temperature of all TLC particles can be obtained by referring to the color temperature calibration curve, and a two-dimensional temperature image is generated.

[0075] Step 500: Fit the three-dimensional velocity field and the two-dimensional temperature image to obtain a three-dimensional velocity-temperature field.

[0076] Specifically, mapping the two-dimensional temperature image three-dimensional velocity field into three-dimensional space can obtain several three-dimensional temperature values, thereby obtaining a three-dimensional velocity-temperature field combining velocity and temperature.

[0077] Another embodiment of the present invention uses a three-color mask single camera with a resolution of 1280*1024pixel 2 , and the camera area used is 1240*984pixel 2 , the pixel size is 0.004mm, and the radius of the circumscribed circle of the centers of the three mask holes is 32mm. First, use ray tracing technology to generate a calibration image, project the three-dimensional tracer particles onto the two-dimensional image plane, and realize particle reconstruction to obtain the calibration information of three perspectives of the three-color mask. Subsequently, a group of particles is randomly generated within the measurement volume, and the projection of the particles in each perspective is calculated through the calibration information to determine the image coordinates of the particle centers. Apply a Gaussian distribution to the image coordinates to generate a particle image with a diameter of 3 pixels. Finally, the measured flow field moves frame by frame according to the set motion form.

[0078] Through the particle extraction efficiency Rf , the ratio R of ghost particles g and the distance D between particles before and after reconstruction f verified the effectiveness of the method of the present invention. Among them, R f represents the ratio of the filtered particles to all particles, and R g represents the ratio of ghost particles to all particles after reconstruction.

[0079] As Figure 6 shown, when using the three-color mask technology of a three-color mask single-color camera, more than 85% of TLC particles can be screened out at a particle concentration of 0.05 PPP. At the same time, the proportion of ghost particles is less than 15%. As Figure 7 shown, the distance between particles before and after reconstruction is less than 0.3 voxels, indicating that the particles have a high matching accuracy.

[0080] The beneficial effects of the present invention are as follows:

[0081] 1. The contrast of the image is improved and the color distortion of the image is reduced by the three-color mask technology;

[0082] 2. By screening TLC particles, the temperature indication range of the particles is ensured and the smoothness of the color temperature calibration curve is improved;

[0083] 3. By transforming the image from the RGB color space to the HSL color space, it is ensured that the hue distribution is only sensitive to color components, and the accuracy of obtaining the color temperature calibration curve is improved.

[0084] In this specification, each embodiment is described in a progressive manner. The key points of each embodiment are the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other.

[0085] Specific examples are applied in the present invention to elaborate the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A synchronous measurement method for velocity and temperature fields combining a three-color mask single camera with liquid crystal, characterized in that It includes the following steps: Screen the thermochromic liquid crystal particles to obtain tracer particles; Perform three-dimensional flow field detection on the tracer particles and obtain a three-color mask color image through a three-color mask single camera; Perform three-dimensional position reconstruction on the three-color mask color image through a three-view image separation technique to obtain a three-dimensional velocity field; Perform color temperature calibration processing on the three-color mask color image to obtain a two-dimensional temperature image; Fit the three-dimensional velocity field and the two-dimensional temperature image to obtain a three-dimensional velocity-temperature field; Perform three-dimensional position reconstruction on the three-color mask color image through a three-view image separation technique to obtain a three-dimensional velocity field, including: Perform a calibration operation on the three-color mask color image to obtain a calibration image; Perform initial fitting on the first distribution image and the second distribution image of the calibration image respectively through an iterative particle reconstruction method to obtain a first trajectory and a second trajectory; the first distribution image is the first four frames of the calibration image, and the second distribution image is the images subsequent to the fourth frame of the calibration image; Reconstruct and fit the first trajectory and the second trajectory to obtain the three-dimensional velocity field; Perform a calibration operation on the three-color mask color image to obtain a calibration image, including: Separate the three-color mask color image according to color channels to obtain a first image; Perform an interpolation operation and a demosaicing process on the original image in sequence to obtain a second image; Perform color crosstalk correction on the second image to obtain a third image; Perform a volume calibration operation on the third image to obtain the calibration image.

2. The method for synchronously measuring the velocity and temperature fields by combining a three-color mask single camera with liquid crystal according to claim 1, wherein The particle size range of the tracer particles is 100 µm - 110 µm.

3. The method for synchronously measuring the velocity and temperature fields by combining a three-color mask single camera with liquid crystal according to claim 1, wherein Perform color temperature calibration processing on the three-color mask color image to obtain a two-dimensional temperature image, including: Perform a color space transformation on the three-color mask color image to obtain a saturation image; Obtain the central hue value of the interrogation window in the saturation image through a Gaussian curve; Obtain the central hue value multiple times and obtain a color temperature calibration curve according to the central hue value; Obtain the two-dimensional temperature image according to the color temperature calibration curve.

4. The method for synchronously measuring the velocity and temperature fields by combining a three-color mask single camera with liquid crystal according to claim 3, wherein Obtain the central hue value of the interrogation window in the saturation image through a Gaussian curve, including: Under a preset calibration temperature, calibrate the saturation image through an interrogation window to obtain the interrogation window; Determine a one-dimensional Gaussian curve according to the hue distribution of the interrogation window and obtain the central hue value through the one-dimensional Gaussian curve.

5. The method for synchronously measuring the velocity and temperature fields by combining a three-color mask single camera with liquid crystal according to claim 4, characterized in that Obtain a color temperature calibration curve according to the central hue value, including: Determine the calibration points of the interrogation window through the central hue value; Based on the calibration points, determine the color temperature calibration curve through a fitting function.

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