CN104614342B - Three-dimensional reconstruction measurement method of air refractive index under high-temperature airflow disturbance - Google Patents

Abstract

The invention relates to a three-dimensional reconstruction measurement method of an air refractive index under high-temperature airflow disturbance, and belongs to the technical field of pneumatic optical measurement and three-dimensional reconstruction. The method comprises the following steps that a three-dimensional reconstruction measurement system of the air refractive index under airflow disturbance is established firstly; at least two CCD cameras and speckle background plates the number of which is the same with that of the CCD cameras are adopted; the CCD cameras are used for photographing the speckle background plates by penetrating through a measured air field from different angles in the same plane, so that a speckle image is obtained; because an air convection disturbance refractive index is changed non-uniformly, the speckle image photographed by the cameras is distorted; deflection angles of light penetrating through the measured air field from the different angles are obtained by adopting a digital image correlation method; the three-dimensional distribution of the refractive index of the measured air field is obtained by calculation by adopting a three-dimensional reconstruction algorithm, and therefore, the real-time measurement of the airflow disturbance is realized. According to the method, the three-dimensional real-time measurement of the air refractive index under the high-temperature airflow disturbance is realized; the device is simple, flexible, and simple and convenient to operate; and the three-dimensional reconstruction measurement method is applied to measuring the airflow disturbance conditions in real time under severe air convection disturbance conditions in engineering.

Description

Air refraction three-dimensionalreconstruction measuring method under a kind of high temperature gas flow disturbance

Technical field

The present invention relates to a kind of acquisition under high temperature gas flow disturbance by digital image correlation technique passes through air field light Deflection angle disturbs air field refractive index distributed in three dimensions method to reconstruct, and belongs to Pneumatic optical measurement and three-dimensional reconstruction field.

Background technology

Optical means is widely used in deformation measurement due to having the advantages that noncontact, measurement of full field.But it is big in high temperature Under compression ring border, carry out deformation measurement using optical means and face many difficulties, wherein the difficult problem for facing is that flow perturbation is tight Optical imagery is disturbed again.It is general more than 200 DEG C, air agitation will the deformation of severe jamming optical method for measuring, and with Temperature is raised, the aggravation of air agitation severe degree.Measure especially for high-precision deformation under high temperature, it is necessary to remove air agitation Interference.A kind of method is to vacuumize, but for large scale structure deformation measurement, particularly practical implementation in, it is to vacuumize very much What difficulty was accomplished.Another kind of method is exactly the disturbance rule for providing air under high temperature in real time, for optical method for measuring deformation, is needed Real-time air refraction distributed in three dimensions is obtained, thus calculate that air agitation in deformation measurement causes to optical imagery is abnormal Become, measurement deformation process in remove the amount of distortion that air agitation is caused, so as to realize high temperature under remove air agitation mesh 's.

From the problem of backprojection image reconstruction three-dimensional spatial distribution physical quantity, it is theoretical that mathematician Radon provides in theory it The one-dimensional Fourier transform of parallel projection under a certain visual angle of base center Slice Theorem, i.e. measured body image is equal to the image One center slice of two-dimensional Fourier transform, around 180 degree image difference Angles Projections result is obtained, and is become through inverse Fourier Change and be obtained measured object space distribution information.For the disturbance of high temperature downstream, find a kind of simple and reliable method to obtain Light rebuilds the refractive index distributed in three dimensions of air field through the projection information behind disturbance air field, is to realize that deformation is surveyed under high temperature The key of air agitation situation is obtained in amount.

Measurement people real-time for air agitation are in the early time using schlieren method and laser interference method, but schlieren method can only be qualitative The substantially situation of air agitation is provided, laser interference subtraction unit is complicated, poor anti jamming capability, cannot meet essence in engineer applied Really measurement high temperature gas flow disturbs lower air refraction.Digital Image Correlation Method is a kind of contactless optical wide variety of now Learn measurement deformation method, because device is simple, simple operation, strong antijamming capability the characteristics of, the method is applied to engineering field Using.

The content of the invention

The purpose of the present invention is to propose to a kind of high temperature gas flow disturbs lower air refraction three-dimensionalreconstruction measuring method, the method Prior art can be overcome not enough, it is adaptable to Practical Project in-site measurement, realize that the lower air refraction of high temperature gas flow disturbance is three-dimensional real When measurement of full field.

Technical scheme is as follows：

Air refraction three-dimensionalreconstruction measuring method under a kind of high temperature gas flow disturbance, it is characterised in that methods described includes Following steps：

1) air refraction three-dimensionalreconstruction measuring system under flow perturbation is set up, the system includes：M CCD camera and m are individual Speckle background board, CCD camera is identical with speckle background board quantity, and CCD camera and speckle background board are arranged in tested air field Centered on same plane circumference on, the circle diameter is D, and is equally spaced, each CCD camera through tested air field just To a speckle background board, m is the positive integer more than or equal to 2；

2) before tested air field is heated, correspondence is shot simultaneously through tested air field with m described CCD camera Speckle background board, shoot the speckle image that obtains as reference picture；

3) tested air field is heated to into more than 200 DEG C, a certain moment is with m described CCD camera in heating process Corresponding speckle background board is shot simultaneously through heated tested air field, shoots the speckle image and step 2 for obtaining) in Reference picture is contrasted, and CCD camera and speckle background board place plane are set to Oxy planes, and number is used in z-axis direction perpendicular to Oxy planes Word image correlation method calculates on each the speckle background board caused due to air agitation speckle image distortion position along the z-axis direction Move field v；

4) m CCD camera is spaced in the same plane 180 °/m angles, and through tested air field speckle background board meter is shot Corresponding m angle speckle image z-axis direction displacement field is calculated, v is remembered respectively₁,v₂,...,v_m, arrived by obtaining 0 with spline interpolation The speckle image displacement field v of 180 degree unspecified angle θ_θ, θ ∈ (0, π)；

5) by step 4) obtain 0 to 180 degree unspecified angle θ speckle image displacement field v_θ, by following formula：

Calculate tested air field (3) air refraction n partial derivatives along the z-axis directionThree-dimensional spatial distribution, wherein j for void Number unitS_θ(ω) it is speckle image displacement field v_θFourier transformation value,t =x cos θ+y sin θs, x, y, z be respectively put on speckle image along x-axis, y-axis, the space coordinates of z-axis, ω is that Fourier becomes Independent variable is changed, D is the distance of the speckle background board that CCD camera shoots to correspondence；

6) tested air field edge air is set in constant temperature, its air refraction is n_o, by above-mentioned tested air field air Refractive index n partial derivative along the z-axis directionSubstitute into following formula：

The distributed in three dimensions of air refraction n is inscribed when calculating the measurement, whereinFor tested air field Air refraction z-axis Directional partial derivativeAlong the integration of z-axis, in not repeat step 3 in the same time)～when 6) can obtain corresponding Inscribe the lower air refraction distributed in three dimensions of high temperature gas flow disturbance.

The CCD camera number is preferably 2～10, and positioned at circumference the same side.The speckle background board is surface spray Apply and make the flat board for having random speckle.

The present invention compared with prior art, with advantages below and high-lighting effect：Obtained using Digital Image Correlation Method Light is taken from different perspectives through the deflection angle of tested air field, tested air field refraction is calculated by three-dimensional reconstruction algorithm Rate distributed in three dimensions.The method is capable of achieving the whole audience, real-time, online, the non-intervention measurement of the lower air refraction of high temperature gas flow disturbance, Strong antijamming capability, device is simple, simple operation, it is adaptable to measure under engineering site complex environment.

Description of the drawings

Fig. 1 is the lower air refraction three-dimensionalreconstruction measuring system structural representation of high temperature gas flow disturbance of the present invention.

Fig. 2 is a kind of available background speckle.

Fig. 3 is that light passes through tested air field deviation principle schematic.

Fig. 4 is the tested air field refractive index principle schematic of three-dimensionalreconstruction.

In figure：The CCD cameras of 1a- first；The CCD cameras of 1b- second；The CCD cameras of 1c- the 3rd；The CCD cameras of 1d- the 4th；2a- First speckle background board；2b- the second speckle background boards；The speckle background boards of 2c- the 3rd；The speckle background boards of 2d- the 4th；The tested skies of 3- Gas field.

Specific embodiment

The specific embodiment of the present invention is further illustrated below in conjunction with the accompanying drawings, but protection of the invention should not be limited with this Scope.

The present invention proposes a kind of lower air refraction three-dimensionalreconstruction measuring method of high temperature gas flow disturbance, its concrete steps：

1) air refraction three-dimensionalreconstruction measuring system under flow perturbation is initially set up, the system includes：M CCD camera With m speckle background board, CCD camera is identical with speckle background board quantity, and CCD camera and speckle background board are arranged in tested sky On same plane circumference centered on gas field 3, and it is equally spaced, the circle diameter is set to D, each CCD camera is through tested Just to a speckle background board, m is the positive integer more than or equal to 2 for air field, preferably 2～10；As embodiment, the present invention As a example by 4 CCD cameras and 4 speckle background boards, CCD camera and speckle background board be arranged in same plane, with tested sky On circumference centered on gas field 3, and it is equally spaced, each CCD camera passes through tested air field just to a speckle background board, Speckle background board is that surface spraying makes the flat board (as shown in Figure 1) for having random speckle.

2) before tested air field 3 is heated, 4 CCD cameras shoot corresponding speckle simultaneously through tested air field 3 Background board, shoots the speckle image for obtaining as reference picture.

3) more than 3 to 200 DEG C of the tested air field of heating, a certain moment passes through heating with 4 CCD cameras in heating process Afterwards tested air field 3 shoots correspondence speckle background board simultaneously, shoot obtain in the speckle image that obtains and previous step with reference to figure As contrast, CCD camera and speckle background board place plane are set to Oxy planes, and digital picture is used in z-axis direction perpendicular to Oxy planes Correlation technique calculates on each the speckle background board caused due to air agitation speckle image distortion displacement field v along the z-axis direction.

4) 4 CCD cameras are spaced in the same plane 45 ° of degree angles and shoot the calculating of speckle background board through tested air field 3 4 angle z direction displacement speckle displacement fields of correspondence are obtained, v is remembered respectively₁,v₂,v₃,v₄, by obtaining 0 to 180 with spline interpolation The speckle displacement field v of degree unspecified angle θ_θ, θ ∈ (0, π) inscribe tested air field refractive index n during by being calculated the measurement Distributed in three dimensions, in not repeat step 3 in the same time)～inscribe air refraction under high temperature gas flow disturbance when 4) can obtain corresponding Distributed in three dimensions.

The operation principle of the present invention is as follows：

As shown in figure 3, light passes through tested air field, due to air refraction non-uniform Distribution, there is deviation, folding in light Firing angle is φ, and by geometrical relationship, deflection angle Oyz plane components are φ_z, its with speckle image along the z-axis direction displacement field v just like Lower relation：

Wherein D/2 is air field to be measured to distance between speckle background board.Rolled over air by optical analysis deflection of light Penetrating relation between rate is：

Wherein n is air refraction,For refractive index n partial derivative in the z-direction, then simultaneous (I) and (II) formula：

B is tested air field areas diameter, as shown in figure 4, light from direction through dissipating that tested air field is clapped Spot displacement field v_θ(t, z) is equivalent to air refraction partial derivativeProjection under the view directions, by Central slice theorem, should The one-dimensional Fourier transform of parallel projection is equal in (III) formula by product air refraction partial derivativeTwo-dimensional Fourier transform A center slice.In acquisition θ is from 0 to 180 degree after all angles projection, can be obtained by inverse Fourier transform and be accumulated Air refraction partial derivativeDistributed in three dimensions：

Wherein j is imaginary unitS_θ(ω) it is speckle image displacement field v_θFourier transformation value,T=x cos θ+y sin θs, x, y, z be respectively on speckle image put along x-axis, y-axis, z The space coordinates of axle.In embodiment, we choose at equal intervals 4 angles with 4 CCD cameras in the range of θ is from 0 to 180 degree Measurement speckle image displacement along the z-axis direction, is designated as 0 degree of v₁, 45 degree of v₂, 90 degree of v₃, 135 degree of v₄, by symmetry, in 180 degree angle The speckle image of shooting displacement v along the z-axis direction₅Obtained by following formula：

v₅=v₁ (Ⅴ)

By v₁、v₂、v₃、v₄、v₅The 0 speckle displacement field v for arriving 180 degree unspecified angle is obtained with spline interpolation_θ, that is, obtain sky Gas refractive index partial derivativeAlong θ angles from 0 to 180 degree direction projection speckle displacement field v_θThe one-dimensional Fourier transform of (t, z)Bring (IV) formula into and obtain air refraction partial derivativeDistributed in three dimensions.If tested air Field edge air is in constant temperature, and refractive index is n at this_o, by above-mentioned air refraction partial derivativeIntegrate so as to obtain height along z-axis The corresponding air refraction distributed in three dimensions for measuring moment tested air field under wet flow disturbance：

In formulaFor tested air field air refraction partial derivativeAlong the integration of z-axis.

Claims (3)

1. the lower air refraction three-dimensionalreconstruction measuring method of a kind of high temperature gas flow disturbance, it is characterised in that methods described include as Lower step：

1) air refraction three-dimensionalreconstruction measuring system under flow perturbation is set up, the system includes：M CCD camera and m speckle Background board, CCD camera is identical with speckle background board quantity, and CCD camera and speckle background board are arranged in and are with tested air field (3) On the same plane circumference at center, and it is equally spaced, the circle diameter is D, each CCD camera is just right through tested air field One speckle background board, m is the positive integer more than or equal to 2；

2) before tested air field (3) is heated, tested air field (3) is passed through with m described CCD camera while shooting right The speckle background board answered, shoots the speckle image for obtaining as reference picture；

3) tested air field (3) is heated to into more than 200 DEG C, a certain moment is saturating with m described CCD camera in heating process Heated tested air field (3) is crossed while shooting corresponding speckle background board, the speckle image and step 2 for obtaining is shot) Middle reference picture contrast, CCD camera and speckle background board place plane are set to Oxy planes, and z-axis direction is used perpendicular to Oxy planes Digital Image Correlation Method is calculated speckle image on each the speckle background board caused due to air agitation and is distorted along the z-axis direction Displacement field v；

4) m CCD camera is spaced in the same plane 180 °/m angles, and through tested air field (3) speckle background board meter is shot Corresponding m angle speckle image z-axis direction displacement field is calculated, v is designated as respectively₁,v₂,...,v_m, by obtaining 0 with spline interpolation To the speckle image displacement field v of 180 degree unspecified angle θ_θ, θ ∈ (0, π)；

5) by step 4) obtain 0 to 180 degree unspecified angle θ speckle image displacement field v_θ, by following formula：

$\frac{\∂n}{\∂z}=\frac{\∂n(x,y,z)}{\∂z}=\underset{0}{\overset{\mathrm{\π}}{\∫}}\underset{-\mathrm{\∞}}{\overset{\mathrm{\∞}}{\∫}}{S}_{\mathrm{\θ}}\left(\mathrm{\ω}\right)\left|\mathrm{\ω}\right|e^{j2\mathrm{\π}\mathrm{\ω}(xcos\mathrm{\θ}+ysin\mathrm{\θ})}d\mathrm{\ω}d\mathrm{\θ}$

Calculate tested air field (3) air refraction n partial derivatives along the z-axis directionThree-dimensional spatial distribution, wherein j be imaginary number UnitS_θ(ω) it is speckle image displacement field v_θFourier transformation value,T= Xcos θ+ysin θ, x, y, z be respectively put on speckle image along x-axis, y-axis, the space coordinates of z-axis, ω be Fourier transformation from Variable, D is the distance of the speckle background board that CCD camera shoots to correspondence；

6) tested air field edge air is set in constant temperature, its air refraction is n_o, by above-mentioned tested air field air refraction N partial derivatives along the z-axis directionSubstitute into following formula：

$n=n(x,y,z)=n_o+\underset{0}{\overset{z}{\∫}}\frac{\∂n(x,y,z)}{\∂z}dz$

The distributed in three dimensions of air refraction n is inscribed when calculating the measurement, whereinFor tested air field air folding Penetrate rate z-axis Directional partial derivativeAlong the integration of z-axis, in not repeat step 3 in the same time)～height is inscribed when 6) can obtain corresponding Air refraction distributed in three dimensions under wet flow disturbance.

2. according to the lower air refraction three-dimensionalreconstruction measuring method of a kind of high temperature gas flow disturbance described in claim 1, its feature It is：In step 1) described in CCD camera number be 2～10, and positioned at circumference the same side.

3., according to the lower air refraction three-dimensionalreconstruction measuring method of a kind of high temperature gas flow disturbance described in claim 1 or 2, it is special Levy and be：In step 1) described in speckle background board be that surface spraying makes and has the flat board of random speckle.