A method and device for detecting and measuring particle size of atmospheric cloud and fog fields

Abstract

The present invention discloses a method for particle detection and particle size measurement in an atmospheric cloud field: a parallel light beam is used to illuminate a particle detection area. When a particle passes through the particle detection area, the particle illuminated by the parallel light beam generates particle scattered light; a part of the particle scattered light and the parallel light beam enter a digital camera, and another part of the particle scattered light triggers a photodetector to generate a pulse trigger signal; another part of the parallel light beam is collected; the digital camera is controlled to record a particle hologram according to the pulse trigger signal; the particle hologram is reconstructed to obtain a focused image of the particle, and the particle size information is obtained according to the focused image. The present invention also discloses a device using the above method: a particle detection and holographic shooting system, a particle detection and holographic shooting system, and a control and data processing system. The method and device provided by the present invention greatly improve the efficiency of particle sampling and measurement.

Description

Technical Field

[0001] The invention relates to multiphase flow particle measurement, and in particular to a method and a device for detecting particles and measuring particle sizes in an atmospheric cloud field of a wind turbine. Background Art

[0002] Atmospheric cloud fields are closely related to many fields in nature and industry, such as atmospheric environment meteorological detection in nature, and wind power generation, aircraft flight, etc. in industry. Taking wind power generation as an example, the droplet particles in the wind field have an important impact on the icing of wind turbine blades. For example, in some high-latitude and high-altitude areas, the temperature is low and the humidity is high. Wind turbines are prone to ice in these areas, which has a great impact on the integrity of their blades, thereby greatly reducing the operating performance and power generation efficiency of the units. In addition, ice formation can also cause unbalanced blade loads, which seriously endangers the operating safety of the unit and reduces the service life of the unit. Therefore, the icing of wind turbines has become an imminent problem in the wind power industry.

[0003] At present, the monitoring of icing conditions at home and abroad is mainly through judging the blade speed of wind turbines or combining power parameters for judgment. For example, the invention patent with publication number CN 108223307 A judges the icing condition of wind turbines by measuring the current wind speed and unit speed and comparing them with the preset wind speed threshold and speed threshold. The shortcoming of this type of technology is that it cannot take corresponding prevention and control measures before the wind turbine freezes, and can only make corresponding judgments when the speed and power drop. We hope to analyze the meteorological reasons for the icing of wind turbines and take corresponding measures before the units freeze, so as to minimize the impact of icing on the operation of wind turbines.

[0004] Wind turbine icing is mainly caused by the deposition of frozen drizzle, wet snow or icy fog, clouds, frost and other water vapor condensates when the temperature is below freezing. In general, it can be divided into freezing fog icing and rainfall icing. Among them, liquid water content and median volume diameter of water droplets are two important parameters of icing climate conditions. The liquid water content in low-altitude clouds and fog is generally less than 0.3g / m3. The median volume diameter of water droplets is a representative value that divides the small water droplets in clouds and fog into two equal parts. For cumulus and stratus clouds, the median volume diameter of water droplets is generally between 10 and 50μm; the median volume diameter of water droplets in fog is generally 15 to 50μm. Studies have shown that the typical median volume diameter of water droplets in common icing meteorological conditions on the ground is about 25μm. These different particle parameters will have a direct impact on the icing situation. Corresponding de-icing measures need to be taken for different icing conditions. Therefore, it is necessary to monitor and analyze the size, quantity and distribution of air particles in the wind turbine area to provide data basis for subsequent icing analysis of wind turbines.

[0005] When measuring sparse particle fields such as wind turbine wind farms, if the free exposure photography mode of a digital camera is used, the sampling efficiency is low, which is not conducive to subsequent data processing. Summary of the invention

[0006] The purpose of the present invention is to provide a method and device for holographic real-time measurement of the particle size of atmospheric cloud particles; the method and device provided by the present invention greatly improve the efficiency of particle sampling and measurement.

[0007] In order to achieve the above-mentioned purpose, the present invention adopts the following specific technical solutions.

[0008] A method for detecting and measuring particle sizes of atmospheric cloud and fog particles comprises the following steps:

[0009] (1) Using a parallel light beam to illuminate the particle detection area, when the particles pass through the particle detection area, the particles illuminated by the parallel light beam generate particle scattered light;

[0010] (2) A portion of the particle scattered light and the parallel light beam enters the digital camera, another portion of the particle scattered light triggers the photodetector to generate a pulse trigger signal; another portion of the parallel light beam is collected.

[0011] (3) controlling a digital camera to record a particle hologram according to the pulse trigger signal obtained in step (2);

[0012] (4) Reconstruct the particle hologram obtained from step (3) to obtain a focused image of the particle, and obtain the particle size information based on the focused image.

[0013] In step (4), the method for obtaining particle size information based on the focused image is:

[0014]

[0015] Where d is the diameter of the particle, n is the number of pixels covered by the focused image, δ is the pixel size of the focused image, and π is the circumference of a circle.

[0016] The present invention also provides a device for detecting particles in an atmospheric cloud field and measuring particle sizes using the above method, the device comprising:

[0017] A laser beam expansion parallel system, wherein the laser beam expansion parallel system generates a parallel light beam to illuminate the particle detection area, and when particles exist, the particles generate particle scattered light;

[0018] A particle detection and holographic shooting system, including a digital camera, is used to determine whether there are particles in the particle detection area. When particles are present, a portion of the scattered light of the particles enters the digital camera and records a particle hologram of the particle detection area under the control of the control and data processing system;

[0019] The control and data processing system includes a photoelectric detector. Another part of the scattered light of the particle triggers the photoelectric detector to generate a pulse trigger signal. The control and data processing system uses the pulse trigger signal generated by the photoelectric detector to control a digital camera to take a particle hologram, and reconstructs and processes it to obtain the particle size.

[0020] The laser beam expansion parallel system comprises a laser, a plano-concave lens, a spatial filter, a convex lens and a reflector; the laser generated by the laser is expanded by the plano-concave lens and filtered by the spatial filter to remove impurity light, then passes through the convex lens to form a parallel beam, and is reflected by the reflector into the particle detection area.

[0021] The spatial filter comprises an objective lens and a pinhole, wherein the center of the pinhole is located at the front focus of the convex lens.

[0022] The particle detection and holographic shooting system includes a beam splitter, a plano-convex lens, a reflector with a hole, a photoelectric detector and a digital camera; when there are particles in the particle detection area, a parallel light beam will generate particle scattered light after passing through the particles, and the particle scattered light and the parallel light beam enter the beam splitter together and are divided into two parts, and a part of the particle scattered light and the parallel light beam enter the digital camera; another part of the particle scattered light is converged by the plano-convex lens and then reflected by the reflector with a hole to enter the photoelectric detector to generate a pulse trigger signal; another part of the parallel light beam is focused on the central hole in the reflector with a hole through the plano-convex lens and then absorbed by the light block.

[0023] The digital camera is provided with a telecentric lens. The digital camera is in external trigger mode and connected to a host computer. The shooting of the digital camera can be controlled by software programming. The photodetector generates a pulse signal and transmits it to the control and data processing system in the host computer to control the digital camera to shoot the hologram of the particles; and the appropriate exposure time can be selected according to the light intensity entering the digital camera.

[0024] The middle of the perforated reflector is provided with an oblique hole which is 45 degrees to the reflector surface and has a size of 1-3 mm.

[0025] The photosensitive area of ​​the photodetector is 20-60mm away from the center of the holed reflector, and the effective detection area is 10-100mm 2 .

[0026] Specifically, in the particle detection and holographic shooting system: when a particle passes through the particle detection area and is illuminated by an incident parallel light beam, particle scattered light (non-parallel light) will be generated, wherein the incident parallel light beam is focused on the central hole of a perforated reflector placed at a 45-degree inclination by utilizing the convergence effect of a plano-convex lens on parallel light, and the converged parallel light beam passes through the central hole and is collected by a light block and will not enter the photodetector, so that the photodetector will not respond when there are no particles in the particle detection area. After the particle scattered light passes through the plano-convex lens, the incident angle will change and it will not be focused on the central hole of the perforated reflector, so that part of the scattered light will be reflected by the perforated reflector into the lens area of ​​the photodetector, triggering the photodetector to generate a pulse voltage signal of a corresponding amplitude, which is used as a trigger to control the digital camera to record a holographic image.

[0027] The device includes a double-arm cylindrical housing, a laser beam expansion parallel system is located in the cylindrical arm at one end, a particle detection and holographic shooting system and a control and data processing system are located in the cylindrical arm at the other end, and a particle detection area is located between the two cylindrical arms. The particle detection area is located between the laser emission arm and the holographic shooting arm, which can prevent particles from falling in the longitudinal direction and reduce interference with the flow field in the lateral direction. In addition, the above structure can reduce the influence of the instrument itself on the flow field in the particle detection area to the greatest extent.

[0028] The main problem that the present invention solves is the low sampling efficiency of traditional measurement methods for sparse particle fields such as atmospheric cloud fields. The response of photoelectric sensors to particle scattered light is used to generate a trigger signal to control the camera to capture a particle hologram, thereby improving the sampling efficiency. The digital camera will only record particle information when particles exist in the particle detection area, thereby improving the sampling efficiency of sparse particle fields, achieving targeted measurement of particles, and greatly reducing redundant data. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of the structure of the device provided by the present invention;

[0030] Figure 2 is a particle hologram in the embodiment;

[0031] Figure 3 is a focused image of particles reconstructed in the embodiment;

[0032] Among them, 1 is a laser, 2 is a plano-concave lens, 3 is a spatial filter, 4 is a convex lens, 5 is a reflector, 6 is an optical window, 7 is a parallel light beam, 8 is a particle to be measured, 9 is particle scattered light, 10 is a beam splitter, 11 is a convex lens, 12 is a reflector with a hole, 13 is a light block, 14 is a photoelectric detector, 15 is a telecentric lens, 16 is a digital camera, 17 is a host computer, 18 is a laser emission arm, 19 is a holographic shooting arm, and 20 is a particle detection area; DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The present invention is by no means limited to any specific configuration and algorithm proposed below, but covers any modification, replacement and improvement of the elements, components and algorithms without departing from the spirit of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0034] Example 1

[0035] like Figure 1 As shown, the optical path structure of the entire device is explained below.

[0036] The entire optical system needs to have the characteristics of high precision and high stability. Preferably, all optical components adopt a cage structure to improve the connection stability of each part.

[0037] The device for atmospheric cloud field particle detection and particle size measurement provided in this embodiment adopts a double-arm cylindrical housing, including cylindrical arms at both ends, namely a laser emitting arm 18 and a holographic shooting arm 19; the particle detection area 20 is located between the two cylindrical arms.

[0038] In the laser emitting arm 18, the laser 1 light exit hole, the plano-concave lens 2, the spatial filter 3, the convex lens 4 and the reflector 5 are coaxially placed and connected by cage rods and cage plates, wherein the pinhole center position of the spatial filter 3 coincides with the focus of the convex lens 4, and the angle between the mirror surface of the reflector 5 and the horizontal central axis is 45°. The laser 1, the plano-concave lens 2, the spatial filter 3, the convex lens 4 and the reflector 5 constitute a laser beam expansion parallel system.

[0039] In the holographic shooting arm 19, the reflector 5, the light window 6, the beam splitter 10, the convex lens 11 and the reflector with a hole 12 are coaxially placed at the center, and are also connected by cage rods and cage plates. The angle between the reflector with a hole 12 and the central axis is 135°. In addition, the digital camera 16 is embedded in the cage cube where the beam splitter 10 is located through the telecentric lens 15 via a sleeve; wherein the telecentric lens 15 is coaxially connected to the lens of the digital camera 16. The beam splitter 10, the telecentric lens 15 and the digital camera 16 are coaxial in the center. The photodetector 14 is connected to the right-angle optical adjustment frame where the reflector with a hole 12 is located via a sleeve. The light block 13 is used to filter the outgoing light from the oblique hole of the reflector with a hole. The beam splitter 10, the lens 11, the reflector with a hole 12, the photodetector 14, the telecentric lens 15 and the digital camera 16 constitute a particle detection and holographic shooting system.

[0040] In the holographic shooting arm 19, the photoelectric detector 14 and the digital camera 16 are both connected to a host computer 17, which includes a control and data processing system.

[0041] Finally, multiple brackets are used to calibrate and fix the entire optical path structure.

[0042] The specific operation of using the above device to detect the particle size of air area is as follows:

[0043] S1. Use a parallel light beam to illuminate the particle detection area. When the particles pass through the particle detection area, the particles illuminated by the parallel light beam generate particle scattered light;

[0044] S1-1, laser 1 outputs 0-1000mW adjustable visible light band laser. Taking into account the exposure setting of the digital camera 16 and the sensitivity of the photodetector 14, preferably, laser 1 is a semiconductor laser with a power of 0.5W and a wavelength of 532nm.

[0045] S1-2, the laser is then expanded by a plano-concave lens 2, and then filtered to remove impurity light by a spatial filter 3. Preferably, the focal length of the plano-concave lens 2 is -50 mm, the objective lens is 20X, and the pinhole aperture is 150 μm.

[0046] S1-3, the pinhole center of the spatial filter 3 is located at the front focus of the convex lens 4, which can make the original divergent light beam become a parallel light beam after being filtered by the spatial filter 3. Preferably, the focal length of the convex lens 4 is 50mm, and the spatial filter 3 is adjusted so that the spot diameter of the parallel light beam generated by the convex lens 4 is about 1cm, so as to ensure the laser intensity.

[0047] S1-4. Subsequently, the parallel light beam 7 is reflected by the reflector 5 and then enters the particle detection area 20 through the optical window 6, irradiating the particles 8 passing through the particle detection area 20 and generating particle scattered light 9. Preferably, the width of the particle detection area 20 is set to 30-100 mm.

[0048] S2, part of the particle scattered light and the parallel light beam enters the digital camera, another part of the particle scattered light triggers the photodetector to generate a pulse trigger signal; another part of the parallel light beam is collected:

[0049] S2-1, after the particle scattered light 9 and the incident parallel light beam 7 pass through the optical window 6, they are divided into two parts by the beam splitter 10, and one part is incident into the digital camera 16 equipped with the telecentric lens 15. Preferably, the beam splitter 10 has a beam splitting ratio of 5:5. The digital camera 16 is set to an external trigger mode. The host computer 17 is equipped with software for controlling the digital camera, which can control the digital camera 16 to shoot a hologram.

[0050] S2-2, another part of the parallel light beam 7 passing through the beam splitter 10 is converged to the perforated reflector 12 whose center is at the focus of the convex lens through the convex lens 11 close to the beam splitter 10, and then is absorbed by the light block 13 through the light hole. There is an oblique hole in the middle of the perforated reflector, which is convenient for completely filtering the light entering the light hole to prevent the subsequent triggering of the photodetector 14 from being affected. Preferably, the focal length of the convex lens 11 is 35 mm, and the central hole of the perforated reflector 12 is an oblique hole with a size of 1-3 mm and an angle of 45° with the reflector surface.

[0051] S2-3, another part of the particle scattered light 9 passing through the beam splitter 10 will not be focused in the oblique hole of the perforated reflector 12 after passing through the convex lens 11, but a part of it will be reflected to the photodetector 14. The photodetector can quickly and sensitively sense the light signal to generate a voltage pulse signal and transmit the signal to the host computer. Preferably, the photosensitive area of ​​the photodetector is 20-60mm away from the center of the perforated reflector, and the effective detection area is 10-100mm 2 , so that the scattered light from particles at different positions can be detected.

[0052] S3, controlling the digital camera to record the particle hologram according to the pulse trigger signal:

[0053] Each time the host computer 17 collects an electrical signal, it controls the digital camera 16 to take a hologram. The particle hologram taken will be stored in the host computer, such as Figure 2 Preferably, the response frequency of the photodetector 14 is not less than 1 kHz so as to respond quickly to the particles.

[0054] S4, reconstructing the obtained particle hologram to obtain a focused image of the particle, and obtaining particle size information according to the focused image;

[0055] The photographed hologram is reconstructed and reproduced to obtain the morphology of the measured particle, as shown in Figure 3. Analyze the particle image in the holographic reconstruction image, the number of pixels occupied by the particle image is n, and the pixel size is δ. The particle size d can be calculated.

[0056] This embodiment uses the method of triggering by the photoelectric detector to achieve real-time camera shooting of holograms when particles exist in the particle detection area, and keeps the digital camera on standby when no particles exist. This improves the efficiency of digital cameras in shooting holograms, greatly reduces the number of invalid holograms, and reduces the workload for subsequent data analysis.

Claims

1. A device for detecting and measuring particle size of atmospheric cloud and fog particles, characterized in that: The device comprises: A laser beam expansion parallel system, wherein the laser beam expansion parallel system generates a parallel light beam to illuminate the particle detection area, and when particles exist, the particles generate particle scattered light; A particle detection and holographic shooting system, including a digital camera, is used to determine whether there are particles in the particle detection area. When particles exist, a portion of the scattered light of the particles enters the digital camera and records a particle hologram of the particle detection area under the control of the control and data processing system; The control and data processing system includes a photoelectric detector, and another part of the scattered light of the particle triggers the photoelectric detector to generate a pulse trigger signal; the control and data processing system uses the pulse trigger signal generated by the photoelectric detector to control the digital camera to take a particle hologram, and reconstruct and process it to obtain the particle size; The particle detection and holographic shooting system comprises a beam splitter, a plano-convex lens, a reflector with a hole, a photoelectric detector and a digital camera; when particles exist in the particle detection area, a parallel light beam will generate particle scattered light after passing through the particles, and the particle scattered light and the parallel light beam enter the beam splitter together and are divided into two parts, and a part of the particle scattered light and the parallel light beam enter the digital camera; another part of the particle scattered light is converged by the plano-convex lens and then reflected by the reflector with a hole to enter the photoelectric detector to generate a pulse trigger signal; another part of the parallel light beam is focused on the central hole in the reflector with a hole by the plano-convex lens and then absorbed by the light block; The middle of the perforated reflector is provided with an oblique hole at an angle of 45° to the reflector surface, and the size is 1-3 mm; The photosensitive area of ​​the photodetector is 20-60mm away from the center of the holed reflector, and the effective detection area is 10-100mm 2 .

2. The device for detecting and measuring particle size of atmospheric cloud and fog particles according to claim 1, characterized in that: The laser beam expansion parallel system comprises a laser, a plano-concave lens, a spatial filter, a convex lens and a reflector; the laser generated by the laser is expanded by the plano-concave lens and filtered by the spatial filter to remove impurity light, then passes through the convex lens to form a parallel beam, and is reflected by the reflector into the particle detection area.

3. The device for detecting and measuring particle size of atmospheric cloud and fog particles according to claim 2, characterized in that: The spatial filter comprises an objective lens and a pinhole, wherein the center of the pinhole is located at the front focus of the convex lens.

4. The device for detecting and measuring particle size of atmospheric cloud and fog fields according to claim 1, characterized in that: The digital camera is provided with a telecentric lens.

5. The device for detecting and measuring particle size of atmospheric cloud and fog particles according to claim 1, characterized in that: The device includes a double-arm cylindrical shell, a laser beam expansion parallel system is located in the cylindrical arm at one end, a particle detection and holographic shooting system and a control and data processing system are located in the cylindrical arm at the other end, and a particle detection area is located between the two cylindrical arms.

6. The device for detecting and measuring particle size of atmospheric cloud and fog fields according to claim 1, characterized in that: The method for measuring by the device comprises the following steps: (1) Using a parallel light beam to illuminate the particle detection area, when the particles pass through the particle detection area, the particles illuminated by the parallel light beam generate particle scattered light; (2) A portion of the particle scattered light and the parallel light beam enters the digital camera, another portion of the particle scattered light triggers the photodetector to generate a pulse trigger signal; another portion of the parallel light beam is collected; (3) controlling a digital camera to record a particle hologram according to the pulse trigger signal obtained in step (2); (4) Reconstruct the particle hologram obtained from step (3) to obtain a focused image of the particle, and obtain the particle size information based on the focused image.

7. The device for detecting and measuring particle size of atmospheric cloud and fog particles according to claim 6, characterized in that: In step (4), the method for obtaining particle size information based on the focused image is: Where d is the diameter of the particle, n is the number of pixels covered by the focused image, δ is the pixel size of the focused image, and π is the circumference of a circle.

Images