Speed and temperature field synchronous measurement method based on combination of three-color mask single camera and liquid crystal

Abstract

The invention provides a three-color mask single camera and liquid crystal combined speed and temperature field synchronous measurement method, and relates to the technical field of flow field observation, the method comprises the following steps: screening thermochromic liquid crystal particles to obtain tracer particles; performing three-dimensional flow field detection on 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 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; and fitting the three-dimensional velocity field and the two-dimensional temperature image to obtain a three-dimensional velocity-temperature field. According to the method, synchronous high-precision measurement of the velocity field and the temperature field is realized through the three-dimensional particle tracking technology and the color temperature characteristic of the thermochromic liquid crystal.

Description

Technical Field

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

[0002] In fluid mechanics research, accurate measurement of velocity field and temperature field is crucial to understanding fluid behavior. At present, separate flow field velocity measurement methods and temperature measurement methods are relatively mature. In the existing technology, the velocity of a single point in the fluid flow is generally measured based on devices such as hot wire or laser Doppler velocimeters, and the temperature of each point in the fluid flow is measured using methods such as thermocouples or laser induced fluorescence.

[0003] However, traditional measurement methods can only measure velocity or temperature separately, and it is difficult to obtain the spatial distribution information of both at the same time. In addition, the technology for synchronous measurement of flow field velocity and temperature is still in the development stage. The existing synchronous measurement methods of flow field velocity and temperature have technical problems such as limited measurement range and large errors in velocity and temperature measurement. Therefore, it is very necessary to design a synchronous measurement method of velocity and temperature field using a three-color mask single camera combined 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 of a three-color mask single camera combined with liquid crystal, so as to realize synchronous high-precision measurement of velocity field and temperature field through three-dimensional particle tracking technology and the color temperature characteristics of thermochromic liquid crystal.

[0005] To achieve the above object, the present invention provides the following solutions: A method for synchronously measuring velocity and temperature fields of a three-color mask single camera combined with liquid crystal comprises the following steps: Screening thermochromic liquid crystal particles to obtain tracer particles; Conduct three-dimensional flow field detection on tracer particles and obtain three-color mask color images through a three-color mask single camera; The three-dimensional position of the three-color mask color image is reconstructed through three-view image separation technology to obtain the three-dimensional velocity field; Perform color temperature calibration on the three-color mask color image to obtain a two-dimensional temperature image; The three-dimensional velocity field and the two-dimensional temperature image are fitted to obtain the three-dimensional velocity-temperature field.

[0006] Optionally, the tracer particles have a particle size ranging from 100µm to 110µm.

[0007] Optionally, the three-dimensional position of the three-color mask color image is reconstructed by three-view image separation technology to obtain a three-dimensional velocity field, including: Performing a calibration operation on the three-color mask color image to obtain a calibration image; The first distribution image and the second distribution image of the calibration image are respectively initially fitted by 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 fourth subsequent frame of the calibration image; The first trajectory and the second trajectory are reconstructed and fitted to obtain a three-dimensional velocity field.

[0008] Optionally, performing a calibration operation on the three-color mask color image to obtain a calibration image includes: Separating the three-color mask color image according to color channels to obtain a first image; Performing interpolation and demosaicing processing on the original image in sequence to obtain a second image; Performing color crosstalk correction on the second image to obtain a third image; A volume calibration operation is performed on the third image to obtain a calibration image.

[0009] Optionally, color temperature calibration is performed on the three-color mask color image to obtain a two-dimensional temperature image, including: Perform color space transformation on the three-color mask color image to obtain a saturated image; Obtain the central hue value of the query window in the saturated image through the Gaussian curve; Repeatedly obtain the central hue value for multiple times, and obtain a color temperature calibration curve according to the central hue value; A two-dimensional temperature image is obtained according to the color temperature calibration curve.

[0010] Optionally, obtaining the central hue value of the query window in the saturated image through a Gaussian curve includes: At a preset calibration temperature, the saturated image is calibrated through the interrogation window to obtain the interrogation window; A one-dimensional Gaussian curve is determined according to the hue distribution of the query window, and the central hue value is obtained through the one-dimensional Gaussian curve.

[0011] Optionally, a color temperature calibration curve is obtained according to the central hue value, including: Determine the calibration point of the interrogation window by the central hue value; Based on the calibration points, a color temperature calibration curve is determined by fitting the function.

[0012] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: the present invention provides a method for synchronously measuring the velocity and temperature field of a three-color mask single camera combined with a liquid crystal, the method comprising: screening thermochromic liquid crystal particles to obtain tracer particles; performing three-dimensional flow field detection on the tracer particles, and obtaining a three-color mask color image through a three-color mask single camera; reconstructing the three-color position of 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0014] Figure 1 It is a flow chart of the method for synchronously measuring the velocity and temperature fields according to an embodiment of the present invention; Figure 2 A flowchart of three-dimensional position reconstruction according to an embodiment of the present invention; Figure 3 is a color temperature calibration flow chart of an embodiment of the present invention; Figure 4 is a query window histogram of an embodiment of the present invention; Figure 5 is a color temperature calibration curve diagram of an embodiment of the present invention; Figure 6 The extraction efficiency and ghost particle result diagram of an embodiment of the present invention; Figure 7 This is a graph showing particle distance results before and after reconstruction according to an embodiment of the present invention. DETAILED DESCRIPTION

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] like Figure 1As shown, the present invention provides a method for synchronously measuring the velocity and temperature field of a three-color mask single camera combined with a liquid crystal, comprising the following steps: Step 100: Screening thermochromic liquid crystal particles to obtain tracer particles; Specifically, the screened thermochromic liquid crystal (TLC) particles have a particle size distribution in the range of 100µm-110µm, and the screened particles are used as tracer particles.

[0018] It should be noted that the screened particles have a narrow size distribution, can reliably detect single particles, and no bright reflection ring appears around the particle core. The particles can reflect as much color information as possible, that is, the temperature 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.

[0019] Step 200: performing three-dimensional flow field detection on the tracer particles, and acquiring a three-color mask color image through a three-color mask single camera; Specifically, the process of three-dimensional flow field detection is: to prepare a measurement flow field of thermochromic liquid crystal (TLC) particle emulsion, to illuminate the tracer particles with a high-energy white LED array light source, and to use a three-color mask single color camera to obtain a time-series particle three-color mask color image of the tracer particles in the measurement flow field.

[0020] More specifically, the array light source of this embodiment uses a three-band white light laser with a beam power of 3W and wavelengths of 450nm, 532nm and 650nm. A customized three-color mask is installed in front of a ZEISS Milvus2 / 100M lens and connected to a RevealerM120 color camera.

[0021] More specifically, the water tank for measuring the flow field of this embodiment is made of a 15 mm thick acrylic plate, with dimensions of 1000 mm long, 500 mm wide and 500 mm high. 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 of the jet circular nozzle is D=10 mm. The measurement area is located 0.1D to the left of the nozzle, and the measurement volume is defined as 2D*2D*0.4D distributed along the x, y, and z directions. TLC particles (Hallcrest, R18C6) are used as tracer particles and temperature indicating particles with a diameter of 100-110 μm, and a water-ethylene glycol mixture with a mass mixing ratio of 7:3 is used as the fluid, and the concentration of the particles is approximately 0.025 PPP. The temperature of the cold fluid in the water tank was room temperature, the temperature of the flow field was measured to be 18°C ​​before the measurement began (measured with a thermocouple thermometer), and then the temperature of the hot fluid in the nozzle was set to 20°C to form a temperature difference.

[0022] Step 300: Reconstruct the three-dimensional position of the three-color mask color image by three-view image separation technology to obtain a three-dimensional velocity field; the specific steps are as follows: Figure 2 As shown, including: Step 301: performing a calibration operation on the three-color mask color image to obtain a calibration image; specifically comprising: Separating the three-color mask color image according to color channels to obtain a first image; Specifically, the three-color mask color image is separated by color channels in the RGB space to obtain three color-separated first images.

[0023] Performing interpolation and demosaicing processing on the original image in sequence to obtain a second image; Specifically, in this embodiment, dual three-color interpolation, bilinear interpolation, pattern recognition interpolation or deep learning interpolation method is used to perform demosaic hole interpolation on the separated first image to obtain the second image.

[0024] Performing color crosstalk correction on the second image to obtain a third image; Specifically, single light hole images of two light holes in a three-color mask single camera are taken respectively to obtain images of three colors. The images of these three light holes are used as calibration images for color crosstalk correction. The linear relationship between the calibration image and other color channels is obtained by a first-order fitting method. Color crosstalk correction is performed on the second image according to the linear relationship to remove ghost pixels in the image.

[0025] A volume calibration operation is performed on the third image to obtain a calibration image.

[0026] Specifically, this embodiment obtains the two-dimensional position information of the third image through a plane calibration plate, and then moves the plane calibration plate along the depth of field direction to determine the two-dimensional position information of different depths of field. The three-dimensional position is obtained through the depth of field position and its two-dimensional position information, thereby obtaining 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 calibration image according to the conversion relationship.

[0027] Step 302: Initially fitting the first distribution image and the second distribution image of the calibration image respectively by 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 fourth subsequent frame of the calibration image; Specifically, the trajectory of the first four frames of the calibration image is initially fitted by an iterative particle reconstruction method to obtain a first trajectory. The subsequent frame images of the calibration image except the first four frames are also initially fitted to obtain a second trajectory. The parameters in the preliminary fitting process include: a two-dimensional particle search range of pixels, a ghost particle intensity threshold, a two-dimensional line of sight search range of voxels, and a three-dimensional line of sight search range of voxels.

[0028] Step 303: reconstruct and fit the first trajectory and the second trajectory to obtain a three-dimensional velocity field.

[0029] Specifically, this embodiment reconstructs and fits the first trajectory and the second trajectory through a shake-the-box (STB) method, wherein the parameters in the reconstruction and fitting process include: voxel jitter range, maximum single-frame displacement of voxel particles, particle intensity subtraction ratio, and ghost particle intensity threshold.

[0030] Step 400: Perform color temperature calibration on the three-color mask color image to obtain a two-dimensional temperature image. The specific steps are as follows: Figure 3 As shown, including: Step 401: performing color space transformation on the three-color mask color image to obtain a saturated image; 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 saturated image in the HSL color space.

[0031] Step 402: Obtain the central hue value of the query window in the saturated image through a Gaussian curve; Specific as Figure 4 As shown, the preset calibration temperature in this embodiment is 20°C, and a query window of 100×100 pixels is used to calibrate the saturated image at 20°C, and multiple query windows of 100×100 pixels are obtained. The hue (H) distribution of the query window is represented by a histogram, and a one-dimensional Gaussian curve is determined according to the edge profile of the histogram, and the central hue value Hc is obtained by the one-dimensional Gaussian curve, and the central hue value Hc 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.

[0032] Step 403: repeatedly obtaining the central hue value for multiple times, and obtaining a color temperature calibration curve according to the central hue value; Specific as Figure 5 As shown, the calibration points of all inquiry windows are obtained, and based on all the obtained calibration points, the color temperature calibration curve is determined by fitting function. The black dots in the figure are the values ​​of the calibration points, and the curve is the color temperature calibration curve.

[0033] Step 404: Obtain a two-dimensional temperature image according to the color temperature calibration curve.

[0034] 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 comparing the color temperature calibration curve and a two-dimensional temperature image can be generated.

[0035] Step 500: Fit the three-dimensional velocity field and the two-dimensional temperature image to obtain a three-dimensional velocity-temperature field.

[0036] Specifically, by mapping the three-dimensional velocity field of the two-dimensional temperature image to the three-dimensional space, several three-dimensional temperature values ​​can be obtained, thereby obtaining a three-dimensional velocity-temperature field combining velocity and temperature.

[0037] Another embodiment of the present invention uses a three-color mask single camera with a resolution of 1280*1024 pixels. 2 , the camera area used is 1240*984pixel 2 , the pixel size is 0.004mm, and the radius of the circumscribed circle of the three mask hole centers is 32mm. First, the calibration image is generated using ray tracing technology, and the three-dimensional tracer particles are projected onto the two-dimensional image plane to achieve particle reconstruction to obtain the three-view calibration information of the three-color mask. Subsequently, a group of particles are randomly generated in the measurement volume, and the projection of the particles at each view angle is calculated using the calibration information to determine the image coordinates of the particle center. Gaussian distribution is applied to the image coordinates to generate a particle image with a diameter of 3 pixels. Finally, the measured flow field is moved frame by frame according to the set motion form.

[0038] Extraction efficiency R by particles f , the ratio of ghost particles R g and the distance D between the particles before and after reconstruction f The effect of the method of the present invention was verified. f It indicates the proportion of screened particles to all particles, R g Indicates the ratio of ghost particles to all reconstructed particles.

[0039] like Figure 6 As shown in the figure, the three-color mask technology using a three-color mask single color camera can screen out more than 85% of TLC particles when the particle concentration is 0.05PPP, and the proportion of ghost particles is less than 15%. Figure 7 As shown, the distance between particles before and after reconstruction is less than 0.3 voxels, indicating that the particles have a high matching accuracy.

[0040] The beneficial effects of the present invention are as follows: 1. The three-color mask technology improves the image contrast and reduces the image color distortion; 2. Through the screening of TLC particles, the temperature range of the particles is guaranteed and the smoothness of the color temperature calibration curve is improved; 3. By transforming the image from RGB color space to HSL color space, it is ensured that the hue distribution is only sensitive to color components, and the accuracy of the color temperature calibration curve is improved.

[0041] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0042] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A three-color mask single camera combined with liquid crystal speed and temperature field synchronous measurement method, characterized in that: The steps include: Screening thermochromic liquid crystal particles to obtain tracer particles; Performing three-dimensional flow field detection on the tracer particles, and acquiring a three-color mask color image through a three-color mask single camera; Reconstructing the three-dimensional position of the three-color mask color image by 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; The three-dimensional velocity field and the two-dimensional temperature image are fitted to obtain a three-dimensional velocity-temperature field.

2. The method for synchronously measuring velocity and temperature fields of a three-color mask single-camera combined with liquid crystal according to claim 1, characterized in that: The particle size of the tracer particles ranges from 100µm to 110µm.

3. The method for synchronously measuring velocity and temperature fields of a three-color mask single-camera combined with liquid crystal according to claim 1, characterized in that: The three-dimensional position of the three-color mask color image is reconstructed by three-view image separation technology to obtain a three-dimensional velocity field, including: Performing a calibration operation on the three-color mask color image to obtain a calibration image; Performing initial fitting on the first distribution image and the second distribution image of the calibration image respectively by 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 fourth subsequent frame of the calibration image; The first trajectory and the second trajectory are reconstructed and fitted to obtain the three-dimensional velocity field.

4. The method for synchronously measuring velocity and temperature fields of a three-color mask single-camera combined with liquid crystal according to claim 3, characterized in that: Performing a calibration operation on the three-color mask color image to obtain a calibration image includes: Separating the three-color mask color image according to color channels to obtain a first image; Performing interpolation and demosaicing processing on the original image in sequence to obtain a second image; Performing color crosstalk correction on the second image to obtain a third image; A volume calibration operation is performed on the third image to obtain the calibration image.

5. The method for synchronously measuring velocity and temperature fields of a three-color mask single-camera combined with liquid crystal according to claim 1, characterized in that: Performing color temperature calibration processing on the three-color mask color image to obtain a two-dimensional temperature image includes: Performing color space transformation on the three-color mask color image to obtain a saturated image; Obtaining the central hue value of the query window in the saturated image through a Gaussian curve; Repeating to obtain the central hue value for multiple times, and obtaining a color temperature calibration curve according to the central hue value; The two-dimensional temperature image is obtained according to the color temperature calibration curve.

6. The method for synchronously measuring velocity and temperature fields of a three-color mask single-camera combined with liquid crystal according to claim 5, characterized in that: Obtaining the central hue value of the query window in the saturated image through a Gaussian curve includes: At a preset calibration temperature, calibrating the saturated image through an inquiry window to obtain the inquiry window; A one-dimensional Gaussian curve is determined according to the hue distribution of the inquiry window, and the central hue value is obtained through the one-dimensional Gaussian curve.

7. The method for synchronously measuring velocity and temperature fields of a three-color mask single-camera combined with liquid crystal according to claim 6, characterized in that: A color temperature calibration curve is obtained according to the central hue value, including: Determining a calibration point of the interrogation window by means of the central hue value; Based on the calibration points, the color temperature calibration curve is determined by a fitting function.

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