CN113484201A - Method and device for particle detection and particle size measurement in atmospheric cloud and mist field - Google Patents
Method and device for particle detection and particle size measurement in atmospheric cloud and mist field Download PDFInfo
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Abstract
The invention discloses a method for detecting particles and measuring particle size in an atmospheric cloud and fog field, which comprises the following steps: illuminating a particle detection region with a collimated light beam, the particles illuminated by the collimated light beam producing particle scattered light as the particles pass through the particle detection region; one part of the particle scattered light and the parallel light beam enters the digital camera, and the other part of the particle scattered light triggers the photoelectric detector to generate a pulse triggering signal; another part of the parallel beam is collected; controlling a digital camera to record the particle hologram according to the pulse trigger signal; and reconstructing the particle hologram to obtain a focused image of the particles, and obtaining particle size information of the particles according to the focused image. The invention also discloses a device adopting the method, which comprises the following steps: particle detection and holography system, particle detection and holography system and control and data processing system. The method and the device provided by the invention greatly improve the particle sampling and measuring efficiency.
Description
Technical Field
The invention relates to multiphase flow particle measurement, in particular to a method and a device for particle detection and particle size measurement of an atmospheric cloud and mist field of a wind turbine.
Background
The atmospheric cloud field is closely related to the nature and various fields in the industry, such as atmospheric environment weather detection in the nature, wind power generation in the industry, aircraft flight and the like. Taking wind power generation as an example, liquid droplet particles in a wind field have an important influence on icing of a wind turbine blade. For example, in some high-latitude and high-altitude areas, the temperature is low, the humidity is high, and the wind generating set is easy to freeze in the areas, so that the integrity of the blades of the wind generating set is greatly influenced, and the running performance and the generating efficiency of the wind generating set are greatly reduced. In addition, icing can also cause unbalanced blade loads, thereby causing serious damage to the operation safety of the unit and reducing the service life of the unit. Therefore, icing of the wind driven generator becomes an urgent problem in the wind power industry.
At present, the icing condition is monitored at home and abroad mainly by judging the rotating speed condition of blades of a wind generating set or by combining power parameters, for example, the invention patent with publication number of CN 108223307A, and the icing condition of the wind generating set is judged by measuring the current wind speed and the rotating speed of the set and comparing the current wind speed and the rotating speed with a preset wind speed threshold and a preset rotating speed threshold. The technology has the defects that corresponding prevention and control measures cannot be taken before the wind driven generator is frozen, and corresponding judgment can be only made when the rotating speed and the power are reduced. The method is expected to take corresponding measures before the wind generating set freezes by analyzing the meteorological reasons of the icing of the wind generating set, so that the influence of the icing on the operation of the wind generating set can be reduced to the maximum extent.
The icing of the wind turbine is mainly formed by deposition of frozen fine rain, wet snow or frozen fog, cloud, frost and other water vapor condensates when the temperature is below the freezing point. Broadly, there are divided into frozen fog icing and rainfall type icing. The liquid water content and the median volume diameter of the water droplets are two important parameters of icing climatic conditions. The liquid water content in the low-altitude cloud and mist is generally less than 0.3g/m 3. The water droplet median volume diameter is a representative number that divides the water droplets in the cloud into two equal portions. For the cumulant cloud and the layer cloud, the median volume diameter of water drops is generally between 10 and 50 mu m; the median volume diameter of the water droplets of the mist is generally 15 to 50 μm. Studies have shown that typical water droplet median volume diameters for normal ice-forming meteorological conditions on the ground are around 25 μm. These different particle parameters have a direct effect on icing conditions. Corresponding deicing measures are required to be taken for different icing conditions, so that the particle size, the number and the distribution condition of air particles in the wind driven generator region need to be monitored and analyzed, and a data basis is provided for the subsequent icing analysis of the wind driven generator.
When the wind field of the wind turbine is measured in the sparse particle field, if a digital camera free exposure photographing mode is adopted, the sampling efficiency is low, and the later-stage data processing is not facilitated.
Disclosure of Invention
The invention aims to provide a method and a device for holographic real-time measurement of the particle size of atmospheric cloud and mist particles; the method and the device provided by the invention greatly improve the particle sampling and measuring efficiency.
In order to achieve the purpose, the invention adopts the following specific technical scheme.
A method for particle detection and particle size measurement in an atmospheric cloud and mist field comprises the following steps:
(1) illuminating a particle detection region with a collimated light beam, the particles illuminated by the collimated light beam producing particle scattered light as the particles pass through the particle detection region;
(2) one part of the particle scattered light and the parallel light beam enters the digital camera, and the other part of the particle scattered light triggers the photoelectric detector to generate a pulse triggering signal; another portion of the parallel beam is collected.
(3) Controlling a digital camera to record a particle hologram according to the pulse trigger signal obtained in the step (2);
(4) reconstructing the particle hologram obtained in the step (3) to obtain a focused image of the particles, and obtaining particle size information according to the focused image.
In the step (4), the method for obtaining particle size information from the focused image is as follows:
where d is the diameter of the particle, n is the number of pixels covered by the focused image, δ is the focused image pixel size, and π is the circumferential ratio.
The invention also provides a device for detecting the particles in the atmospheric cloud mist field and measuring the particle size by adopting the method, which comprises the following steps:
the particle detection system comprises a laser beam expanding parallel system, a particle detection area and a particle detection area, wherein the laser beam expanding parallel system generates parallel light beams to irradiate the particle detection area, and when particles exist, the particles generate particle scattering light;
the particle detection and holographic shooting system comprises a digital camera, and is used for judging whether particles exist in a particle detection area or not, when the particles exist, part of particle scattering light enters the digital camera and records a particle hologram in the particle detection area under the control of the control and data processing system;
the control and data processing system comprises a photoelectric detector, and the other part of the scattered light of the particles triggers the photoelectric detector to generate a pulse triggering signal; the control and data processing system controls the digital camera to shoot the particle hologram by using the pulse trigger signal generated by the photoelectric detector, and reconstructs and processes the particle hologram to obtain the particle size of the particles.
The laser beam expanding parallel system comprises a laser, a plano-concave lens, a spatial filter, a convex lens and a reflector; laser generated by the laser is expanded by the plano-concave lens and filtered by the spatial filter to remove impurity light, then the laser passes through the convex lens to form parallel beams, and the parallel beams are reflected by the reflecting mirror to enter the particle detection area.
The spatial filter comprises an objective lens and a pinhole, and the center of the pinhole is positioned at the front focus of the convex lens.
The particle detection and holographic shooting system comprises a beam splitter, a plano-convex lens, a reflector with holes, a photoelectric detector and a digital camera; when particles exist in the particle detection area, particle scattering light can be generated after the parallel light beams pass through the particles, the particle scattering light and the parallel light beams jointly enter the beam splitter and are divided into two parts, and one part of the particle scattering light and one part of the parallel light beams enter the digital camera; the other part of the particle scattered light is converged by the plano-convex lens and then enters the photoelectric detector through reflection of the perforated reflector to generate a pulse trigger signal; the other part of the parallel light beams are focused by the plano-convex lens to a central hole in the reflector with the hole and then absorbed by the light shield.
A telecentric lens is arranged on the digital camera. The digital camera is in an external trigger mode and is connected with an upper computer, and shooting of the digital camera can be controlled through software programming. The photoelectric detector generates a pulse signal and then transmits the pulse signal to a control and data processing system in an upper computer to control a digital camera to shoot a particle hologram; and an appropriate exposure time can be selected based on the intensity of light entering the digital camera. .
The middle of the reflector with the hole is provided with an inclined hole which forms an angle of 45 degrees with the reflector surface and has a size of 1-3 mm.
The distance between the photosensitive area of the photoelectric detector and the center of the reflector with the hole is 20-60mm, and the effective detection area is 10-100mm2。
Specifically, in a particle detection and holography system: when a particle is irradiated by an incident parallel light beam through the particle detection region, a particle scattering light (non-parallel light) is generated, wherein the incident parallel light beam is focused at a central hole of a perforated mirror obliquely arranged at 45 degrees by using the converging action of a plano-convex lens on the parallel light, and the converged parallel light beam passes through the central hole to be collected by a light shield and does not enter a photodetector, so that the photodetector does not respond when the particle detection region is free from particles. After the particle scattered light passes through the plano-convex lens, because the incident angle can change, the particle scattered light can not be focused on the central hole of the reflector with the hole, so that part of the scattered light enters the lens area of the photoelectric detector through the reflection of the reflector with the hole, the photoelectric detector is triggered to generate a pulse voltage signal with a corresponding amplitude, and the signal is used as a trigger to control the digital camera to record a holographic picture.
The device comprises a double-arm type cylindrical shell, a laser beam expanding parallel system is positioned in a cylindrical arm at one end, a particle detection and holographic shooting system and a control and data processing system are positioned in a cylindrical arm at the other end, and a particle detection area is positioned between the two cylindrical arms. The particle detection area is positioned between the laser emission arm and the holographic shooting arm, so that the particles can not be blocked from falling in the longitudinal direction, and the interference to the flow field can be reduced in the transverse direction. And the structure can furthest lighten the influence of the instrument on the flow field of the particle detection area.
The problem mainly solved by the invention is that aiming at the problem that the sampling efficiency of the traditional measurement method of the sparse particle field, namely the atmospheric cloud and fog field, is too low, a trigger signal is generated by utilizing the response of a photoelectric sensor to particle scattering light to control a camera to shoot a particle hologram, so that the sampling efficiency is improved; and only when the particle exists in the particle detection area, the digital camera can record the particle information, so that the sampling efficiency of a sparse particle field is improved, the particle targeted measurement is realized, and redundant data can be greatly reduced.
Drawings
FIG. 1 is a schematic structural diagram of an apparatus provided by the present invention;
FIG. 2 is a particle hologram in an embodiment;
FIG. 3 is a focused image of the particles reconstructed in the example;
the system comprises a laser 1, a plano-concave lens 2, a spatial filter 3, a convex lens 4, a reflector 5, an optical window 6, a parallel light beam 7, a particle to be detected 8, a particle scattering light 9, a beam splitter 10, a convex lens 11, a perforated reflector 12, a light stop 13, a photoelectric detector 14, a telecentric lens 15, a digital camera 16, an upper computer 17, a laser emission arm 18, a holographic shooting arm 19 and a particle detection area 20, wherein the laser is a laser, the laser emission arm 8, the holographic shooting arm 10 and the particle detection area 20;
Detailed Description
In order to make the objects, 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 with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The present invention is in no way limited to any specific configuration and algorithm set forth below, but rather covers any modification, replacement or improvement of elements, components or algorithms without departing from the spirit of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
As shown in fig. 1, the optical path structure of the entire apparatus will be explained below.
The whole optical system needs to have the characteristics of high precision and high stability, and preferably, all the optical components adopt a cage structure so as to improve the connection stability of all the parts.
The device for detecting particles and measuring particle size in an atmospheric cloud and mist field provided by the embodiment adopts a double-arm cylindrical shell, and comprises cylindrical arms at two ends, namely a laser emission arm 18 and a holographic shooting arm 19; the particle detection zone 20 is located between two cylindrical arms.
In the laser emission arm 18, the light-emitting hole of the laser 1, the plano-concave lens 2, the spatial filter 3, the convex lens 4 and the reflector 5 are coaxially arranged and connected with a cage bar and a cage plate by utilizing a cage, wherein the center position of the pinhole of the spatial filter 3 is coincided with the focus of the convex lens 4, and the included angle between the mirror surface of the reflector 5 and the central axis in the horizontal direction is 45 degrees. The laser 1, the plano-concave lens 2, the spatial filter 3, the convex lens 4 and the reflector 5 form a laser beam expanding parallel system.
In the holographic shooting arm 19, a reflector 5, a light-transmitting window 6, a beam splitter 10, a convex lens 11 and a perforated reflector 12 are coaxially arranged in the center and are connected with a cage bar and a cage plate by the same method, and the perforated reflector 12 forms an included angle of 135 degrees with the central axis. In addition, the digital camera 16 is embedded into the cage cube where the beam splitter 10 is located through the sleeve by the telecentric lens 15; 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 concentric. The photodetector 14 is connected via a sleeve to a right angle optics turret on which the apertured mirror 12 is located. The light shield 13 is used for filtering emergent light in the inclined hole of the reflector with the hole. The particle detection and holographic shooting system consists of a beam splitter 10, a lens 11, a reflector 12 with a hole, a photoelectric detector 14, a telecentric lens 15 and a digital camera 16.
In the hologram arm 19, the photodetector 14 and the digital camera 16 are both connected to an upper computer 17, and the upper computer 17 includes a control and data processing system.
And finally, calibrating and fixing the whole light path structure by adopting a plurality of supports.
The specific operation of detecting the particle size of the particles in the air region by using the device is as follows:
s1, irradiating the particle detection area by using the parallel light beam, wherein when the particles pass through the particle detection area, the particles irradiated by the parallel light beam generate particle scattered light;
s1-1, the laser 1 outputs visible light wave band laser with adjustable power of 0-1000 mW. Considering the exposure setting of the digital camera 16 and the sensitivity of the photodetector 14 together, the laser 1 is preferably a semiconductor laser, the laser 1 power being 0.5W and the wavelength being 532 nm.
S1-2, the laser light is then expanded by the plano-concave lens 2, and then filtered by the spatial filter 3 to remove impurity light. Preferably, the focal length of the plano-concave lens 2 is-50 mm, the objective lens is selected to be 20X, and the pinhole aperture is 150 μm.
S1-3, the center of the pinhole of the spatial filter 3 is located at the front focal point of the convex lens 4, so that the original diverging light beam filtered by the spatial filter 3 can become a parallel light beam. Preferably, the focal length of the convex lens 4 is 50mm, and the spatial filter 3 is adjusted to make the spot diameter of the parallel light beam generated by the convex lens 4 be about 1cm, so as to ensure the laser intensity.
S1-4, the collimated light beam 7 is then reflected by the mirror 5 and then incident in parallel to the particle detection region 20 through the optical window 6, illuminating the particles 8 passing through the particle detection region 20 and producing particle scattered light 9. Preferably, the width of the particle detection zone 20 is set to 30-100 mm.
S2, enabling one part of the particle scattered light and the parallel light beams to enter the digital camera, and triggering the photoelectric detector to generate a pulse triggering signal by the other part of the particle scattered light; another part of the parallel beam is collected:
s2-1, the particle scattered light 9 and the incident parallel light beam 7 pass through the optical window 6, and are divided into two parts by the beam splitter 10, and one part is incident on the digital camera 16 equipped with the telecentric lens 15. Preferably, the beam splitting ratio of the beam splitter 10 is 5: 5. The digital camera 16 is set to the external trigger mode. The upper computer 17 is equipped with software for controlling the digital camera, and can control the digital camera 16 to shoot the hologram.
S2-2, the other part of the parallel light beam 7 which penetrates through the beam splitter 10 is converged on a perforated reflector 12 with the center at the focus of a convex lens through a convex lens 11 which is tightly attached to the beam splitter 10, and then is absorbed by a light shield 13 through a light through hole. The mirror with the hole is provided with an inclined hole in the middle, so that light emitted into the light through hole can be filtered completely, and the influence on the triggering of the follow-up photoelectric detector 14 is prevented. Preferably, the focal length of the convex lens 11 is 35mm, and the central hole of the reflector 12 with holes is an inclined hole with the size of 1-3mm and 45 degrees with the reflector surface.
S2-3, another portion of the particles scattered light 9 transmitted through the beam splitter 10, which is not focused in the inclined hole of the holey mirror 12 through the convex lens 11, is partially reflected to the photodetector 14. The photoelectric detector can quickly and sensitively sense an optical signal so as to generate a voltage pulse signal and transmit the signal to an upper computer. Preferably, photovoltaicThe distance between the light sensing area of the detector and the center of the reflector with the hole is 20-60mm, and the effective detection area is 10-100mm2So that scattered light from particles at different locations can be detected.
S3, controlling the digital camera to record the particle hologram according to the pulse trigger signal:
the upper computer 17 controls the digital camera 16 to shoot the hologram once when the upper computer collects the electric signal once. The shot particle hologram will be stored in the upper computer, as shown in fig. 2. Preferably, the response frequency of the photodetector 14 is not lower than 1kHz to perform a fast response to particles.
S4, reconstructing the obtained particle hologram to obtain a focused image of the particles, and obtaining particle size information according to the focused image;
and reconstructing the shot hologram so as to obtain the morphology of the detected particles, as shown in FIG. 3. Analyzing the particle image in the holographic reconstruction image, wherein the number of pixels occupied by the particle image is n, and the pixel size is delta
The particle size d can be calculated.
The embodiment can realize that the camera shoots the hologram in real time when the particles exist in the particle detection area by the method of triggering generated by the photoelectric detector, and the digital camera is kept in a standby state when no particles exist. Therefore, the efficiency of shooting the hologram by the digital camera is improved, the number of invalid holograms is greatly reduced, and the workload is reduced for later data analysis.
Claims (10)
1. A method for particle detection and particle size measurement in an atmospheric cloud and mist field is characterized by comprising the following steps:
(1) illuminating a particle detection region with a collimated light beam, the particles illuminated by the collimated light beam producing particle scattered light as the particles pass through the particle detection region;
(2) one part of the particle scattered light and the parallel light beam enters the digital camera, and the other part of the particle scattered light triggers the photoelectric detector to generate a pulse triggering signal; another part of the parallel beam is collected;
(3) controlling a digital camera to record a particle hologram according to the pulse trigger signal obtained in the step (2);
(4) reconstructing the particle hologram obtained in the step (3) to obtain a focused image of the particles, and obtaining particle size information according to the focused image.
2. The method for particle detection and particle size measurement in atmospheric cloud and fog fields as claimed in claim 1, wherein in step (4), the method for obtaining particle size information from 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 focused image pixel size, and π is the circumferential ratio.
3. An apparatus for particle detection and particle size measurement in an atmospheric cloud and mist field, the apparatus comprising:
the particle detection system comprises a laser beam expanding parallel system, a particle detection area and a particle detection area, wherein the laser beam expanding parallel system generates parallel light beams to irradiate the particle detection area, and when particles exist, the particles generate particle scattering light;
the particle detection and holographic shooting system comprises a digital camera, and is used for judging whether particles exist in a particle detection area or not, when the particles exist, part of particle scattering light enters the digital camera and records a particle hologram in the particle detection area under the control of the control and data processing system;
the control and data processing system comprises a photoelectric detector, and the other part of the scattered light of the particles triggers the photoelectric detector to generate a pulse triggering signal; the control and data processing system controls the digital camera to shoot the particle hologram by using the pulse trigger signal generated by the photoelectric detector, and reconstructs and processes the particle hologram to obtain the particle size of the particles.
4. The atmospheric cloud and mist field particle detection and particle size measurement device of claim 3, wherein the laser beam expanding parallel system comprises a laser, a plano-concave lens, a spatial filter, a convex lens and a reflector; laser generated by the laser is expanded by the plano-concave lens and filtered by the spatial filter to remove impurity light, then the laser passes through the convex lens to form parallel beams, and the parallel beams are reflected by the reflecting mirror to enter the particle detection area.
5. The atmospheric cloud mist field particle detection and particle size measurement device of claim 4, wherein the spatial filter comprises an objective lens and a pinhole, the center of the pinhole is located at the front focal point of the convex lens.
6. The atmospheric cloud field particle detection and particle size measurement device of claim 3, wherein said particle detection and holography system comprises a beam splitter, a plano-convex lens, a mirror with holes, a photodetector and a digital camera; when particles exist in the particle detection area, particle scattering light can be generated after the parallel light beams pass through the particles, the particle scattering light and the parallel light beams jointly enter the beam splitter and are divided into two parts, and one part of the particle scattering light and one part of the parallel light beams enter the digital camera; the other part of the particle scattered light is converged by the plano-convex lens and then enters the photoelectric detector through reflection of the perforated reflector to generate a pulse trigger signal; the other part of the parallel light beams are focused by the plano-convex lens to a central hole in the reflector with the hole and then absorbed by the light shield.
7. The atmospheric cloud and mist field particle detection and particle size measurement device of claim 6, wherein the digital camera is provided with a telecentric lens.
8. The atmospheric cloud and mist field particle detection and particle size measurement device of claim 6, wherein the perforated mirror is provided with an inclined hole in the middle at an angle of 45 degrees with respect to the mirror surface, and the size of the inclined hole is 1-3 mm.
9. The atmospheric cloud and mist field particle detection and particle size measurement device of claim 6, wherein the light sensing area of the photodetector is 20-60mm from the center of the perforated mirror, and the effective detection area is 10-100mm2。
10. The atmospheric cloud and mist field particle detection and particle size measurement device of claim 3, wherein the device comprises a double-armed cylindrical housing, the laser beam-expanding parallel system is located in the cylindrical arm at one end, the particle detection and holography system and the control and data processing system are located in the cylindrical arm at the other end, and the particle detection region is located between the two cylindrical arms.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| CN116297040A (en) * | 2023-05-17 | 2023-06-23 | 中国人民解放军国防科技大学 | Three-dimensional fog drop measuring device and method based on digital coaxial holographic imaging |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116297040A (en) * | 2023-05-17 | 2023-06-23 | 中国人民解放军国防科技大学 | Three-dimensional fog drop measuring device and method based on digital coaxial holographic imaging |
| CN116297040B (en) * | 2023-05-17 | 2023-08-18 | 中国人民解放军国防科技大学 | Three-dimensional fog drop measuring device and method based on digital coaxial holographic imaging |
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