CN1800820A - Pollutant gas concentration field measurement method in environmental wind tunnel - Google Patents

Abstract

The invention discloses a measurement method for polluted gas concentration by environmental wind tunnel. Wherein, the opposite measurement comprises: an environmental wind tunnel, a laser and a polarization light device both for tunnel irradiation, a digital camera with same spectral-response characteristic as the laser to collect the gas concentration data, and a computer connected to the camera for digital image collection, display and treatment for the tunnel. The measurement method comprises: irradiating the polluted gas diffusion field with laser source, collecting speckle figure of smog article with camera, and obtaining the relative quantitative concentration field by digital image processing technique. This invention can obtain the instantaneous concentration distribution of polluted gas and the time variation.

Description

Pollutant gas concentration field measurement method in environmental wind tunnel

Technical field

The present invention relates to green technology, particularly relate to the measuring technique of environmental wind tunnel dusty gas concentration field in a kind of environmental protection technology.

Background technology

Along with rapid economy development, the improving constantly of living standards of the people, energy resource consumption constantly increases, the also corresponding increase of disposal of pollutants.Because zero disposal of pollutants is difficult to accomplish, therefore, reduces disposal of pollutants as much as possible, make rational planning for and layout and environmental improvement become the task of top priority.

Under the existing energy of China, technology and economics dictate, only depend on improvement can not solve atmosphere polluting problem fully to pollutant itself; The diffusion of pollutant in atmosphere arranged by meteorological condition also, different meteorological conditions, and the ground pollution substrate concentration that same pollution source discharging is caused can differ tens times and even hundred times.Therefore, one of the reality of utilizing the activity of meteorological condition restriction pollution source just to become to prevent and remedy pollution, effective way, and the research of contamination rule is key wherein.

The mechanism research of environmental pollution diffusion, need on a large scale, the prompting message of non-permanent contamination concentration field, the instantaneous concentration field that experiment measuring obtains not only can be directly used in the mechanism of contamination under non-permanent, unstable, the rapid separated flow situation of research, can also provide sufficient data for numerical evaluation, environmental planning etc.At present, in environmental wind tunnel dusty gas concentration field measurement, also desirable without comparison measuring method.

No matter pollutant convection current diffusion research adopts any research method, all wishes to obtain the concentration of contamination, special wishes to obtain that instantaneous concentration distributes and history over time.In environmental wind tunnel dusty gas measurement of concetration, existing method generally be measure single-point (as the single-point sampled measurements), finite point (measuring) or zonule as multi-point sampling (have only several centimetres, survey area is 10 ^-4m ²Magnitude, employing be FLOW VISUALIZATION technology of new generation such as laser-induced fluorescence (LIF), laser molecule flow field detection technique).

Environmental wind tunnel generally is a low speed (wind speed is less than 10m/s), (the test section cross section is at 1m for large scale ²More than) wind-tunnel.Because the restriction of measuring method itself, the single-point of concentration or finite point are measured can only provide concentration data limited in the flow field; In addition, the existence meeting fluid flow of measuring sonde produces interference to a certain degree, and existing zonule concentration measuring method also can't carry out the measurement of concentration field in environmental wind tunnel.

Summary of the invention

At the defective that exists in the above-mentioned prior art, technical matters to be solved by this invention provides a kind of concentration field measurement that can carry out, and can obtain that the dusty gas instantaneous concentration distributes and the pollutant gas concentration field measurement method in environmental wind tunnel of history over time.

In order to solve the problems of the technologies described above, a kind of pollutant gas concentration field measurement method in environmental wind tunnel provided by the present invention, it is characterized in that the environmental wind tunnel dusty gas concentration field measurement device that described concentration field measurement method uses comprises environmental wind tunnel, the laser instrument and the sheet electro-optical device that are used for described environmental wind tunnel irradiation, the digital camera that is used for described environmental wind tunnel dusty gas concentration data collection that spectral response characteristic and described laser instrument optical maser wavelength are complementary, the digital image acquisition that is used for described environmental wind tunnel that connects described digital camera, show, the computing machine of handling;

Pollutant gas concentration field measurement method in environmental wind tunnel of the present invention is with light source irradiation dusty gas diffusion field, gather the speckle image of smoke particle with digital camera, obtain the number concentration field by digital image processing techniques, number concentration is meant the quantity of smoke particle in the unit volume; The measuring process of concentration field measurement method is as follows:

1) at first utilize standard particle (size evenly, in water, do not dissolve, not sedimentation) carry out system calibrating, determine measuring error;

2) in environmental wind tunnel, discharge simulating pollution gas, the control contamination gas scale of construction;

3) utilize the laser sheet optical irradiation to need the zone of measuring;

4) adjust digital parameters (adjusting in real time), make image reach best by software;

5) carry out image acquisition and storage in real time;

6), obtain the concentration field of large-scale pollution gas and change the statistical relationship of concentration etc. in time by digital imaging processing software.

In the step 6) of concentration field measurement method, when with continuous laser sheet rayed, the average exposure of single smoke particle

$\stackrel{\‾}{\mathrm{\ϵ}}=\frac{{\mathrm{\λ}}^2\mathrm{P\δt}\underset{\mathrm{\Ω}}{\∫}(i_1\left(\mathrm{\θ}\right)+i_2\left(\mathrm{\θ}\right))\mathrm{d\Ω}}{{\mathrm{\π}}^3(M^2{d}_p^2+{2.44}^2{(1+M)}^2{f}^{\#2}{\mathrm{\λ}}^2)\mathrm{\Δy\Δz}}$

In the formula, i ₁(θ), i ₂Being strength function (θ), is the scattering amplitude function S ₁(θ), S ₂(θ) mould square; D is the diameter of scattering particle; λ is the incident light wavelength; Ω is the solid angle of digital camera lens; M is the enlargement factor of imaging system; f ^#Be the aperture ratio of imaging system lens, i.e. f-number; The sheet optical thickness is Δ z, then at sheet light zone Δ y * Δ z; The power of light device is P, and the time shutter is δ t;

For continuous wave laser, in the time shutter, the average exposure of speckle image satisfies

$\⟨\stackrel{\‾}{\mathrm{\ϵ}}\⟩=\frac{C\left({\stackrel{\→}{x}}_i\right)\mathrm{\Δz}}{M^2}\frac{1}{k^2}\∫I_0\mathrm{dt}\underset{\mathrm{\Ω}}{\∫}(i_1\left(\mathrm{\θ}\right)+i_2\left(\mathrm{\θ}\right))\mathrm{d\Ω}$

$=\frac{C\left({\stackrel{\→}{x}}_i\right)}{M^2}\frac{\mathrm{P\δt}}{\mathrm{\Δy}}\frac{1}{k^2}\underset{\mathrm{\Ω}}{\∫}(i_1\left(\mathrm{\θ}\right)+i_2\left(\mathrm{\θ}\right))\mathrm{d\Ω}>K{\mathrm{\ϵ}}_0$

In the formula, On sheet light face

The number concentration at some place, k=2 π/λ, K are constant, ε ₀Minimum sensitive volume for film or photoelectronic imaging equipment;

After measured zone, time shutter, imaging parameters and smoke particle size are determined, no matter adopt pulsed laser or continuous wave laser, the average exposure of speckle and all linear funtcional relationship of the quantity of smoke particle, promptly

$\⟨\stackrel{\‾}{\mathrm{\ϵ}}\⟩\∝C\left({\stackrel{\→}{x}}_i\right)$

At the zone line of Hurter and Driffield curve, the gray scale of digital picture and smoke particle speckle intensity have the better linearity relation, thereby also there is linear approximate relationship in the number concentration of the gray scale of digital picture and smoke particle

$G\∝K\⟨\stackrel{\‾}{I}({\stackrel{\→}{X}}_i,t)\⟩=K^{1}C\left({\stackrel{\→}{x}}_i\right)$

In the formula, G is a gradation of image, K, K ¹Be constant,

Be the average intensity of smoke particle i on the picture plane, Be the coordinate vector of smoke particle i on the picture plane, t is the time.

So just set up the relation between measured zone, particle size, laser power, particle scattering characteristic and the digital camera trait-treatment interaction.

Utilize pollutant gas concentration field measurement method in environmental wind tunnel provided by the invention, owing to adopt and utilize particle scattering, speckle statistical property and digital image processing techniques, proposed the instantaneous concentration field measurement method that imaging of particle speckle and digital image processing techniques combine innovatively.On the basis of satisfying approximate uncorrelated single scattering hypothesis, set up the relative populations concentration of dusty gas particle and the linear relationship between the speckle intensity from the statistical significance; Set up the linear approximate relationship between the relative populations concentration of digital picture gray scale and dusty gas particle, thereby the shortcoming that measuring method itself restriction that has overcome single-point, finite point or zonule in the existing method is brought, and can carry out the measurement of large-scale pollution gas concentration field, can obtain that the dusty gas instantaneous concentration distributes and history over time.

Description of drawings

Fig. 1 is the theory diagram of image measurement structure of computer-oriented internal memory of the concentration field measurement system of the embodiment of the invention;

Fig. 2 is that the hardware of the concentration field measurement system of the embodiment of the invention is formed schematic block diagram;

Fig. 3 is the ultimate principle imaging synoptic diagram of pollutant gas concentration field measurement method in environmental wind tunnel of the present invention.

Embodiment

Below in conjunction with description of drawings embodiments of the invention are described in further detail, but present embodiment is not limited to the present invention, every employing analog structure of the present invention, similarity method and similar variation thereof all should be listed protection scope of the present invention in.

The structure of the employed measuring system of a kind of pollutant gas concentration field measurement method in environmental wind tunnel provided by the present invention, comprise the hardware and software two large divisions, wherein hardware components is to realize image acquisition and record, software section be realize the control in the gatherer process and measure after data processing.

The principle of the image measurement structure of the computer-oriented internal memory of concentration field measurement system connects the microcomputer display module by video camera through image digitazation module, microcomputer interface module, microcomputer memory module as shown in Figure 1.

1) hardware components of concentration field measurement system:

Optical imaging apparatus,

The industrial digital video camera.The characterisitic parameter that should consider when selecting optical imaging apparatus according to measurement requirement mainly contains: photoelectricity transfer characteristics, spectral response, dynamic range, dark current, resolution and electronic shutter etc.

The time shutter of environmental wind tunnel concentration field image measurement is controlled by electronic shutter, according to the concentration field measurement principle, surpass the minimum resolution of measuring for fear of speckle displacement in the time shutter, select the longest needed aperture time according to measurement requirement.For example the smoke particle rate of propagation is 1m/s, when measurement space resolution is 0.5mm, requires electronic shutter speed less than 1/2000s, if the smoke particle rate of propagation is bigger, requires electronic shutter speed littler (less than 1/10000s).

Digitizer,

For the image that obtains high resolving power, high refresh rate or the image of other specific (special) requirements, adopt the non-standard video image pick-up card.

Computing machine,

Computing machine in the concentration field measurement is used for managing whole testing device, can adjust measurement parameter by computing machine, as measuring frame frequency, Measuring Time and storage time etc.Simultaneously can manage the image that measures, handle and analyze, computing machine can be PC, microprocessor, also can be workstation.Do on the image plate that high-speed real-time handles at need processors such as lossless image processor, image accelerator, DSP can be housed.

Light source

In environmental wind tunnel concentration field measurement system, light source is one of visual plant that influences the measuring system cost.Measure the concentration in a certain cross section, need sheet light; When measuring IC, require whole contamination field to be illuminated.Because laser has characteristics such as monochromaticity is good, the coherence is good, beam collimation precision height, so concentration field measurement is selected laser sheet optical.

To measure the hardware system total optimization in order making in the concentration field measurement process, not only to require optical maser wavelength and digital camera spectral response characteristic to mate mutually, also require light source and illumination to mate mutually.If optical maser wavelength and digital camera spectral response characteristic do not match, then video camera can be worked under lower efficient.If light source and illumination do not match, then video camera can be operated in nonlinear area, produces bigger nonlinearity erron.

2) the software systems part of concentration field measurement system:

Based on unified modeling language (Unified Modeling Language, UML) and the method for soft project, adopt modular design, each module adopts Object-oriented Programming Design (Object-Oriented Programming, OOP), use Microsoft Visual C++, developing instruments such as Microsoft Visual Fortran, Adobe Photoshop, utilization software bus method for designing has realized software systems.

Software systems design around hardware communication and 2 of data processing emphatically, mainly comprise following modules: digital camera and laser instrument control module, the image pick-up card control module, image capture module, CONCENTRATION DISTRIBUTION module on the free hand drawing line, scheme a little to go up the CONCENTRATION DISTRIBUTION module more, CONCENTRATION DISTRIBUTION module on many figure lines, isoline/equivalence district module, information entropy and nonlinear characteristic module, various analysis result output modules, the Digital Image Processing module, picture format is resolved and memory module, image management module, the match of data fields and interpolating module, the Fourier transform module, the wavelet transformation module, system help module, software systems log management module and software version control module etc.In addition, also have modules commonly used such as the zone of image inverse, the background that turns black and image sequence obtains.

In the embodiments of the invention, the employed 0.4 * 0.5=0.2m of pollutant gas concentration field measurement method in environmental wind tunnel ²The concentration field measurement system is the measuring system of picture of computer-oriented internal memory, its hardware is formed as shown in Figure 2, the laser instrument that comprise environmental wind tunnel, is used for the irradiation of described environmental wind tunnel and sheet electro-optical device, spectral response characteristic and described laser instrument optical maser wavelength are complementary is used for digital camera (optical imaging apparatus) that described environmental wind tunnel makes a video recording, be connected digital image acquisition that described video camera is used for described environmental wind tunnel, the computing machine of demonstration, processing, and embodiments of the invention are specific as follows:

Optical imaging apparatus:

Optical imaging apparatus is selected Basler 601f high resolving power, face battle array, is lined by line scan, CMOS black and white numeral digital camera, its video is output as the IEEE1394 signal, resolution of video camera is 659 * 493, valid pixel is 640 * 480, Pixel Dimensions 9.9 * 9.9 μ m, imageing sensor is 1/2 inch, and maximum frame per second is 60fps during full resolution;

Time shutter control, brightness, gain and power supply all pass through 1394 controls and supply with.For there not being the image of compression, minimum exposure times 20 μ s, sensitivity minimization are 21ux to output image entirely.The maximum smoke particle speed that can measure is about 5m/s;

Camera lens is selected NSK AVENIR CCTV LENS (16mm, F1.2, manual iris, C interface).

Laser instrument and sheet electro-optical device:

Power is that 0.5W-1W is adjustable continuously, 532nm end face pump Pu semiconductor solid state laser.Laser divergence angle less than 4mrad, output stability less than ± 3%, natural air cooled; With integrated photosystem, the sheet beam waist is at laser instrument outlet 1.5-2.0m place, and the sheet optical thickness is about 1mm, and sheet beam waist position forms the irradiation area of at least 700 * 700cm.

The smoke particle size Selection:

Measured zone is 0.2m ², use the 1W laser instrument, the smoke particle diameter selects 0.5 μ m more satisfactory, can satisfy the requirement of approximate uncorrelated single scattering, and the cost performance of measuring system is higher.

The error estimation of measuring system:

Can be obtained by the measuring system error analysis, be 0.2m for measured zone ²The concentration field measurement system, when particle diameter was 0.5 μ m, because the speckle intensity that causes of particle scattering is changed to 4.32% with respect to the maximum of average, promptly the maximum of concentration was changed to 4.32%, is equivalent to grey scale change 11 in theory.Along with the increase of smoke particle size, the measuring error that particle scattering causes can increase thereupon;

Calculate because measuring process speckle intensity is difficult to carry out accurate Theory, therefore, the measuring method error also is difficult to estimation, and the measuring method error is generally determined by test;

In fact because the uneven distribution of measured zone sheet light light intensity can make measuring error further increase;

During actual tests, the smoke particle diameter can not be identical, but the result who measures thinks to have the number concentration of identical particle diameter.

The method of inspection of measuring system:

Inspection principle is as follows: in large-scale glass container, the distilled water that adds pure (through filtering), the standard particle (supposing not precipitation, cohesion etc.) that takes a morsel adds in the container, is mixed with to have certain density sample, stirs the particle concentration in the sample is evenly distributed.

According to adding standard particle quantity difference, can prepare that various concentration differences, its relative value can determine for the sample of measuring the verification use.The variable concentrations sample that obtains of preparation as stated above is that the particle by identical material and identical size is constituted, and good correlativity and homogeneity are arranged.Evenly distribute owing to standard particle in the check test, and do not change in time, when therefore measuring the time shutter is not strict with.

Under the identical condition of measurement parameter, to different standard solution, utilize designed concentration field measurement system to carry out concentration field measurement respectively, according to resulting measurement result, can carry out accuracy and error-tested to measuring system.

Pollutant gas concentration field measurement method in environmental wind tunnel of the present invention is with light source irradiation dusty gas diffusion field, gather the speckle image of smoke particle with digital camera, obtain the number concentration field by digital image processing techniques, number concentration is meant the quantity of smoke particle in the unit volume.The concrete steps of concentration field measurement method:

1) at first utilize standard particle (size evenly, in water, do not dissolve, not sedimentation) carry out system calibrating, determine measuring error;

2) in environmental wind tunnel, discharge simulating pollution gas, the control contamination gas scale of construction;

3) utilize the laser sheet optical irradiation to need the zone of measuring;

4) adjust digital camera parameter (adjusting in real time), make image reach best by software;

5) carry out image acquisition and storage in real time;

6), obtain concentration field and concentration changes with time, the statistical relationship etc. of large-scale pollution gas by digital imaging processing software.

The ultimate principle of pollutant gas concentration field measurement method in environmental wind tunnel of the present invention:

Utilize particle scattering, speckle statistical property and digital image processing techniques, proposed the instantaneous concentration field measurement method that imaging of particle speckle and digital image processing techniques combine innovatively.On the basis of satisfying approximate uncorrelated single scattering hypothesis, set up the relative populations concentration of dusty gas particle and the linear relationship between the speckle intensity from the statistical significance; Set up the linear approximate relationship between the relative populations concentration of digital picture gray scale and dusty gas particle.

During continuous laser sheet rayed, the average exposure of single smoke particle

$\stackrel{\‾}{\mathrm{\ϵ}}=\frac{{\mathrm{\λ}}^2\mathrm{P\δt}\underset{\mathrm{\Ω}}{\∫}(i_1\left(\mathrm{\θ}\right)+i_2\left(\mathrm{\θ}\right))\mathrm{d\Ω}}{{\mathrm{\π}}^3(M^2{d}_p^2+{2.44}^2{(1+M)}^2{f}^{\#2}{\mathrm{\λ}}^2)\mathrm{\Δy\Δz}}---\left(1\right)$

In the formula, i ₁(θ), i ₂Being strength function (θ), is the scattering amplitude function S ₁(θ), S ₂(θ) mould square; D is the diameter of scattering particle; λ is the incident light wavelength; Ω is the solid angle of digital camera camera lens; M is the enlargement factor of imaging system; f ^#Be the aperture ratio of imaging system lens, i.e. f-number; The sheet optical thickness is Δ z, then at sheet light zone Δ y * Δ z; The power of light device is P, and the time shutter is δ t;

For continuous wave laser, in the time shutter, the average exposure of speckle image satisfies

$\⟨\stackrel{\‾}{\mathrm{\ϵ}}\⟩=\frac{C\left({\stackrel{\→}{x}}_i\right)\mathrm{\Δz}}{M^2}\frac{1}{k^2}\∫I_0\mathrm{dt}\underset{\mathrm{\Ω}}{\∫}(i_1\left(\mathrm{\θ}\right)+i_2\left(\mathrm{\θ}\right))\mathrm{d\Ω}$

$=\frac{C\left({\stackrel{\→}{x}}_i\right)}{M^2}\frac{\mathrm{P\δt}}{\mathrm{\Δy}}\frac{1}{k^2}\underset{\mathrm{\Ω}}{\∫}(i_1\left(\mathrm{\θ}\right)+i_2\left(\mathrm{\θ}\right))\mathrm{d\Ω}>K{\mathrm{\ϵ}}_0$ (2)

In the formula,

On sheet light face The number concentration at some place, k=2 π/λ, K are constant, ε ₀Minimum sensitive volume for film or photoelectronic imaging equipment;

After measured zone, time shutter, imaging parameters and smoke particle size are determined, no matter adopt pulsed laser or continuous wave laser, the average exposure of speckle and all linear funtcional relationship of the quantity of smoke particle, promptly

$\⟨\stackrel{\‾}{\mathrm{\ϵ}}\⟩\∝C\left({\stackrel{\→}{x}}_i\right)---\left(3\right)$

At the zone line of Hurter and Driffield curve, the gray scale of digital picture and smoke particle speckle intensity have the better linearity relation, thereby also there is linear approximate relationship in the number concentration of the gray scale of digital picture and smoke particle

$G\∝K\⟨\stackrel{\‾}{I}({\stackrel{\→}{X}}_i,t)\⟩=K^{1}C\left({\stackrel{\→}{x}}_i\right)---\left(4\right)$

In the formula, G is a gradation of image, K, K ¹Be constant, Be the average intensity of smoke particle i on the picture plane, Be the coordinate vector of smoke particle i on the picture plane, t is the time.

So just set up the relation between measured zone, particle size, laser power, particle scattering characteristic and the digital camera trait-treatment interaction.

In the environmental wind tunnel during dusty gas concentration field measurement t with the speckle image of camera acquisition smoke particle, obtain the number concentration field with light source irradiation dusty gas diffusion field by digital image processing techniques.Number concentration is meant the quantity of smoke particle in the unit volume.

During concentration field measurement, shine a certain cross section with laser sheet optical, measured is two-dimensional concentration field.Here in fact the two-dimensional concentration field of indication still is the concentration field in the three dimensions, just in the three dimensions of measuring, the yardstick (length and width reach several meters of zero points) of the other relatively length and width bidimensional of the yardstick (thickness of laser sheet optical is about about 1mm) of thickness dimension is very little.

The measurement major parameter is selected

Select simulating pollution gas (being smoke particle): come simulating pollution gas with soot (as the granule after the burnings such as mosquito-repellent incense, joss sticks and candles, cigarette) in the environmental wind tunnel.The particle diameter of soot is littler than smoke particle, and followability is good, does not have sedimentation and does not pollute the environment wind tunnel window and wall.

Measuring accuracy and error: as required, cost and measuring principle select.Measured zone, particle size, laser power, particle scattering characteristic and digital camera trait-treatment interaction.

The selection of measured zone: at first satisfy environmental wind tunnel and measure and cost requirement, according to measuring accuracy and measuring principle, the object distance when selecting measured zone and measurement.Along with the variation of measured zone and object distance, the scattering angle of smoke particle, scattering particle change greatly to the distance and bearing angle at digital camera center in the same visual field.The influence of the implicit measured zone of formula (1) and formula (2), along with the variation of measured zone, the scattering properties of the scattering angle smoke particle of particle changes.Therefore, the selection of measured zone will be seen the measuring accuracy that needs.

As shown in Figure 3, suppose that X is the sheet optical propagation direction, Y is the electric field intensity direction.Video camera is d to the distance (object distance) of film stock optical plane, the position that film stock optical plane (being object plane) is gone up arbitrarily any for (x, y), the coordinate center is the shooting center, then the optional position (x, the viewing distance of y) locating (being the distance of scattering particle) to the digital camera center square

r ²＝f(x，y)＝x ²+y ²+d ² (5)

(x, y) the center scattering angle of the relative video camera of smoke particle at some place on the object plane

$\mathrm{\θ}={\cos }^{-1}\frac{x}{\sqrt{x^2+y^2+r^2}}---\left(6\right)$

Optional position on the sheet optical plane (x, the position angle of y) locating

By formula (5)-(7) as can be known, along with the variation of measured zone and measurement object distance, in same measured zone, the scattering angle of the smoke particle of diverse location, position angle and smoke particle all can change to the distance at digital camera center.

If object distance is 2m, measured zone is 0.2m ²The time, measured zone inscattering angle variation range is 6.7 °; Measured zone is 0.5m ²The time, scattering angle changes about 9 °.Along with the increase of measuring object distance, the variation of same measurement range scattering angle reduces, for 0.2m ²Measured zone, when object distance was 2.5m, scattering angle was changed to 4.5 °.

When the measurement object distance is big (as 2m), along with the increase of measurement range, scattering particle is little to the variation of shooting point distance, when measured zone reaches 0.5m ²The time, scattering particle to the shooting point variable in distance also in 3%.If object distance is 2.5m, scattering particle to the shooting point variable in distance in 2%.Take object distance during concentration field measurement and be generally about 2.5m, can ignore the influence of scattering particle to the shooting point variable in distance this moment.

Along with the variation of measured zone and measurement object distance, the azimuthal variation of smoke particle is also very big.When incident light was natural light, the position angle of scattering particle did not have influence to scattering properties but by scattering theory as can be known.

The size of simulation smoke particle is selected: during large-range measuring, in order to improve measuring accuracy, require scattered light intensity less in the scattering angle variation range, the scattered light intensity pulsation do not occur.The influence of smoke particle is in formula (1)-(2).Because this method has provided measurement range, laser power, video camera and imaging parameters etc. and smoke particle diameter mutual relationship, therefore, when design concentration field measurement hardware system, by calculating the best of breed that can select between them.The calculating of the scattered light intensity of smoke particle shows, when the concentration field measurement, smoke particle diameter, measured zone there are higher requirement, scattering angle changes one regularly, smoke particle diameter too conference causes measuring error, and too little meeting makes the measurement mechanism hardware costs too high.Therefore, for certain measured zone (scattering angle changes certain), the smoke particle diameter has an optimum value.

The correction of measurement data:, then do not have background noise basically in the darkroom if experiment is carried out; Otherwise background noise can be eliminated by background image, and background image is the image when not having smoke particle, and measurement image subtracting background image can obtain ground unrest and proofread and correct.Secondly, the uneven distribution of sheet light (being generally Gaussian distribution) can cause edge's intensity lower, in order to obtain relative concentration field accurately, can proofread and correct by reference picture.Reference picture is the image of measured zone when being full of uniform smoke particle.Image after the image of measuring can obtain proofreading and correct divided by reference picture, this method not only can be eliminated the influence of light intensity uneven distribution, can also eliminate the influence of camera optics system defect.

The measuring accuracy of pollutant gas concentration field measurement method in environmental wind tunnel of the present invention and analysis of measurement errors:

Measurement precision analysis:

1) spatial accuracy

If measured zone, that is imaging viewing field is W * H, resolution of video camera is M * N, then imaging system image object plane resolution is

$R_x=\frac{W}{M},R_y=\frac{H}{N}---\left(8\right)$

In the formula, R _xBe image x directional resolution, R _yBe image y directional resolution.

Image object plane resolution is the greatest factor of decision optical measurement precision, if each pixel is represented several square millimeters of object plane, then measuring accuracy is the millimeter magnitude.Therefore design concrete measuring task, at first will determine this image object plane resolution, and then definite resolution of video camera and visual field size.

2) time precision

The time precision of environmental wind tunnel concentration field measurement is the number of image frames of gathering the unit interval, establishes video camera per second output N frame, then temporal resolution t _MaxFor

$t_{\max }=\frac{1}{N}---\left(9\right)$

t _MaxIt also is the maximum permission time shutter.

Time precision is meant the number of image frames that the video camera per second is exported, and it is not the real exposure time of image.The time shutter of in fact every width of cloth image is very short, and generally in millisecond even microsecond level, well below the sampling time, with respect to sampled measurements, what can think the digital picture measurement is the instantaneous concentration field.

Having only very little portion of time in every width of cloth image of video camera output is effective exposure time, and other time does not produce any influence to imaging, is bled off by video camera.Therefore, strictly speaking, what the video camera shooting obtained is not the time consecutive image, but takes piece image every a bit of time.

Overlapping for fear of data during concentration field measurement, the distance of smoke particle motion can not be too big in the time shutter, otherwise the doubling of the image can occur, causes measuring error.

3) relative concentration precision

During concentration field measurement, even do not consider the influence that scattering angle, position angle and shooting distance change, the gray scale of digital picture can not reflect the number concentration of smoke particle fully.And the digital picture gray scale has certain span, and value also must be integer.For 8 gray level images, on a two field picture, can only tell 256 kinds of different gray scales, relative accuracy is 1/256.Along with the increase of digital picture gray scale figure place, relative accuracy improves thereupon, but the shared storage area of image can be increasing, the also corresponding increase of video camera cost.

Analysis of measurement errors,

1) measuring method error,

Be subjected to the restriction of photoelectric recording sensitivity minimization, not all speckle picture can both be recorded, could imaging when having only the intensity of picture to surpass the sensitivity minimization of photoelectric recording equipment.In minimum resolution element, if number of particles less than minimum source density, then can not imaging, measuring method error that Here it is.The big more measuring method error of minimum source density is big more, and it is the restricted one of the main reasons of absolute quantity concentration field measurement.

The sensitivity minimization of different incident intensities, particle diameter and recording medium, minimum source density difference, measuring method error are also different.The sensitivity minimization that improves incident intensity, increase particle diameter or photoelectronic imaging equipment can both improve measuring accuracy.

2) influence of smoke particle

The concentration field measurement theoretical analysis be based upon smoke particle identical, be entirely on the spherical hypothesis, standard particle such in the actual tests can not obtain.Therefore, the number concentration of measurement just equivalence be the relative populations concentration of a certain particle diameter.

3) other

Flashing is qualitative, the precision of the noise of the geometric distortion error of imaging system, imaging system, scattering noise, A/D conversion.

Claims (2)

1, a kind of pollutant gas concentration field measurement method in environmental wind tunnel, it is characterized in that the computing machine of the digital camera that is used for the collection of described environmental wind tunnel dusty gas concentration data that the laser instrument that the environmental wind tunnel dusty gas concentration field measurement device that described concentration field measurement method uses comprises environmental wind tunnel, be used for described environmental wind tunnel dusty gas irradiation and sheet electro-optical device, spectral response characteristic and described laser instrument optical maser wavelength are complementary, the digital image acquisition that is used for described environmental wind tunnel that is connected described digital camera, demonstration, processing;

The measuring process of pollutant gas concentration field measurement method in environmental wind tunnel is as follows:

1) at first utilizes standard particle to carry out the demarcation of measuring system, determine measuring error;

2) in environmental wind tunnel, discharge specific simulating pollution gas, and the control contamination gas scale of construction;

3) utilize the laser sheet optical irradiation to need the zone of measuring, dusty gas diffusion field;

4) adjust the digital camera parameter, make image reach best;

5) carry out the collection and the storage of the speckle image of smoke particle in real time with digital camera;

6), obtain the concentration field of large-scale pollution gas and change the statistical relationship of concentration in time by digital imaging processing software.

2, pollutant gas concentration field measurement method in environmental wind tunnel according to claim 1 is characterized in that, in described step 6), and when continuous laser shines, the average exposure of single smoke particle

$\stackrel{\‾}{\mathrm{\ϵ}}=\frac{{\mathrm{\λ}}^2\mathrm{P\δt}\underset{\mathrm{\Ω}}{\∫}(i_1\left(\mathrm{\θ}\right)+i_2\left(\mathrm{\θ}\right))\mathrm{d\Ω}}{{\mathrm{\π}}^3(M^2{d}_p^2+{2.44}^2{(1+M)}^2{f}^{\#2}{\mathrm{\λ}}^2)\mathrm{\Δy\Δz}}$

In the formula, i ₁(θ), i ₂Being strength function (θ), is the scattering amplitude function S ₁(θ), S ₂(θ) mould square; D is the diameter of scattering particle; λ is the incident light wavelength; Ω is the solid angle of CCD camera lens; M is the enlargement factor of imaging system; f ^#Be the aperture ratio of imaging system lens, i.e. f-number; The sheet optical thickness is Δ z, then at sheet light zone Δ y * Δ z; The power of light device is P, and the time shutter is δ t;

For continuous wave laser, the smoke particle blur-free imaging, in the time shutter, the average exposure of speckle image will satisfy

$\⟨\stackrel{\‾}{\mathrm{\ϵ}}\⟩=\frac{C\left({\stackrel{\→}{x}}_i\right)\mathrm{\Δz}}{M^2}\frac{1}{k^2}{\∫I}_0\mathrm{dt}\underset{\mathrm{\Ω}}{\∫}(i_1\left(\mathrm{\θ}\right)+i_2\left(\mathrm{\θ}\right))\mathrm{d\Ω}$

$=\frac{C\left({\stackrel{\→}{x}}_i\right)}{M^2}\frac{\mathrm{P\δt}}{\mathrm{\Δy}}\frac{1}{k^2}\underset{\mathrm{\Ω}}{\∫}(i_1\left(\mathrm{\θ}\right)+i_2\left(\mathrm{\θ}\right))\mathrm{d\Ω}>K{\mathrm{\ϵ}}_0$

In the formula, On sheet light face The number concentration at some place, k=2 π/λ, K are constant, ε ₀Minimum sensitive volume for film or photoelectronic imaging equipment;

After measured zone, time shutter, imaging parameters and smoke particle size are determined, the average exposure of speckle and all linear funtcional relationship of the quantity of smoke particle, promptly

$\⟨\stackrel{\‾}{\mathrm{\ϵ}}\⟩\∝C\left({\stackrel{\→}{x}}_i\right)$

At the zone line of Hurter and Driffield curve, there are linear approximate relationship in the gray scale of digital picture and the number concentration of smoke particle

$G\∝K\⟨\stackrel{\‾}{I}({\stackrel{\→}{X}}_i,t)\⟩=K^{1}C\left({\stackrel{\→}{x}}_i\right)$

In the formula, G is a gradation of image, K, K ¹Be constant,

Be the average intensity of smoke particle i on the picture plane, Be the coordinate vector of smoke particle i on the picture plane, t is the time.

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