CN110260945A - Total-reflection type gas-liquid interface Method of flow visualization and gas-liquid interface location recognition method - Google Patents
Total-reflection type gas-liquid interface Method of flow visualization and gas-liquid interface location recognition method Download PDFInfo
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Abstract
The invention discloses a kind of total-reflection type gas-liquid interface Method of flow visualization and gas-liquid interface location recognition methods.Total-reflection type gas-liquid interface Method of flow visualization of the invention, by the way that area source of the white screen illuminated by light source as imaging is arranged in liquid side, the light that white screen diffusing reflection issues is with the angular illumination more than or equal to the cirtical angle of total reflection to gas-liquid interface, incident light can be totally reflected on gas-liquid interface, light will not pass through gas-liquid interface and refract to gas side, greatly enhance the intensity of reflected light, on the other hand, the light of gas side cannot be refracted into liquid side and propagate along the direction of aforementioned reflected light, reduce invalid information.Then make the direction of the shooting direction face reflected light of camera, to take the gas-liquid interface image of high contrast, invalid information is not included in image, substantially so as to quickly and accurately identify the position of gas-liquid interface on the basis of the high-contrast image of acquisition.Also, total-reflection type gas-liquid interface Method of flow visualization of the invention still can obtain the detailed information of all interface locations when having spray of water or having droplet.
Description
Technical field
The present invention relates to hydrodynamic calculations fields, particularly, are related to a kind of total-reflection type gas-liquid interface FLOW VISUALIZATION side
Method, in addition, further relating to a kind of gas-liquid interface location recognition method using above-mentioned total-reflection type gas-liquid interface Method of flow visualization.
Background technique
Particle image velocimetry (PIV) is a kind of measurement method being commonly used in hydrodynamic calculations, it can measure certain
The instantaneous velocity field of fluid in a region, principle are to sow the trace particle moved with fluid micellar in a fluid,
Two photos are shot in short time, and shooting area can be calculated by the variation of trace particle position on photo in two moment
The inside speed of fluid micellar everywhere (this speed is the speed in plane, i.e., there are two component).Wherein most important calculating side
Method is to separate the picture into several fritters (query window), calculates the fritter at moment earlier above and photo is bright between the fritter at moment compared with after
The related coefficient of degree, the position of related coefficient peak value indicate the speed of fluid micellar near fluid respective queries window.Particle figure
Picture, which tests the speed, to be had the advantages that interference is small, can measure certain region all position and speeds in the same time.
And gas-liquid interface identification is vital link in particle image velocimetry, the accuracy of gas-liquid interface recognition result
Directly affect the precision of particle image velocimetry.At present in gas-liquid interface identification process frequently with imaging technique are as follows: use
Natural light or illuminated by surface light source directly use camera in gas-liquid interface with photographs interface shape.But everywhere due to interface
Intensity of reflected light difference is smaller, and the contrast of the interface image of acquisition is poor, meanwhile, the light that position below liquid level comes out
More than can be by interfacial refraction to interface, to be got off by cameras record, this adds increased invalid informations, therefore can not be accurate
Identify gas-liquid interface position.Therefore, the image that the Method of flow visualization used in existing gas-liquid interface identification process obtains
Contrast is poor and contains more invalid information and leads to not the position for accurately identifying gas-liquid interface.
Summary of the invention
The present invention provides a kind of total-reflection type gas-liquid interface Method of flow visualization and gas-liquid interface location recognition method, with
The contrast for solving the image of the Method of flow visualization used in existing gas-liquid interface identification process acquisition is poor and contain
The technical issues of more invalid information is so as to cause that can not accurately identify gas-liquid interface position.
According to an aspect of the present invention, a kind of total-reflection type gas-liquid interface Method of flow visualization, including following step are provided
It is rapid:
Step S100: area source of the white screen that setting is illuminated by light source in liquid side as imaging, white screen diffusing reflection hair
Light out is with the angular illumination more than or equal to the cirtical angle of total reflection to gas-liquid interface；
Step S200: in liquid side, setting camera is for shooting gas-liquid interface, the shooting direction face reflected light of camera
Direction.
Further, the total-reflection type gas-liquid interface Method of flow visualization is further comprising the steps of:
Step S300: the perspective distortion for the image that amendment camera takes.
Further, the surface of the white screen is curved surface, light source is arranged in the near focal point of white screen, and light source will not hide
Light of the gear white screen to liquid level.
Further, camera using shifting lens shaft or moves adapter axis or moves axis adapter ring or reflective mirror.
Further, the step S3 specifically:
At interface, following close region places reference of the latticed object of reference as perspective correction before shooting interface
Object calculates one from the image of the object of reference illumination front and back taken with image of the cameras record object of reference before and after illumination
Then the coordinate conversion relation of rank or high-order reuses the original image that coordinate conversion relation amendment camera takes.
The present invention also provides a kind of gas-liquid interface location recognition methods, have trace particle to deposit suitable for gas-liquid interface two sides
The case where,
The following steps are included:
Step S1: sowing trace particle in gas and liquid respectively, and sheet laser is then arranged and is illuminated, wherein liquid
Area source of the white screen that the setting of body side is illuminated by light source as imaging, the light that white screen diffusing reflection issues are all-trans with being more than or equal to
The angular illumination of critical angle is penetrated to gas-liquid interface；
Step S2: respectively using two high speed cameras shooting trace particle images in the two sides of gas-liquid interface, etc. time intervals
It exposes, and the camera for being located at interface two sides is respectively demarcated, wherein the shooting direction of the two of liquid side high speed camera
The direction of face reflected light；
Step S3: the initial time interface position in two obtained images of camera of identification shooting interface area above
It sets；
Step S4: the obtained image in the same time of two cameras of shooting interface area above is pre-processed；
Step S5: the gas-liquid interface position in then each frame image is identified；
Step S6: time-space smooth operation is carried out to gas-liquid interface position to obtain the two of shooting interface area above
Gas-liquid interface position in the obtained image of platform camera；
Step S7: it is obtained according to the gas-liquid interface position in two obtained images of camera of shooting interface area above
Shoot the gas-liquid interface position in two obtained images of camera of interface following region.
Further, the step S3 specifically includes the following steps:
Step S31: if gas motion speed is much larger than liquid motion speed, the brightness of each pixel takes phase in plurality of pictures
Answer the reckling of position brightness；Otherwise this step is skipped；
Step S32: gray scale morphology is carried out to picture and opens operation several times；
Step S33: setting luminance threshold identifies the particle in liquid, obtains bianry image；
Step S34: operation is carried out out several times to bianry image, then carries out closed operation several times；
Step S35: being arranged height number y0 according to the interfacial level in image, and making the height and position at interface be in height should
The straight line of numerical value is hereinafter, height is set as 0 in the part of y0 or more；
Step S36: the highest position of height in all nonzero values of each column pixel in record bianry image, if certain column does not have
Nonzero value exists, then records the position of the last one pixel of the column, obtain a sequence；
Step S37: median filtering and gaussian filtering process are carried out to sequence, obtain the position at interface；
Step S38: the average value of two camera obtained photo median surfaces position is calculated；
Step S39: then setting amount of bias moves up initial interface position according to amount of bias.
Further, the step S5 specifically includes the following steps:
Step S51: the image obtained for pretreatment, setting luminance threshold identify the particle in liquid to obtain binary map
Picture；
Step S52: operation is carried out out several times to bianry image, then carries out closed operation several times；
Step S53: the interface of previous frame image is translated up into 15 pixels as line of demarcation, line of demarcation area above two-value
Image values are set as 0；
Step S54: the highest position of height in all nonzero values of each column pixel in record bianry image, if certain column does not have
Nonzero value exists, then the position of the column the last one pixels and the smaller value of former frame interface same position is recorded, to obtain
One sequence；
Step S55: median filtering is carried out to sequence and gaussian filtering obtains the position at interface；
Step S56: the position at interface is moved up according to amount of bias.
Further, the step S6 specifically includes the following steps:
Step S61: it is separated by the cross correlation value that several frames calculate interface location between every two frame；
Step S62: peak position is found after multiple cross correlation values are added；
Step S63: step S61 and step S62 is repeated for all computable moment, obtains the time sequence of boundary velocity
Column；
Step S64: the time series based on obtained boundary velocity does locking phase average computation to interface location；
Step S65: time-space smooth operation is done to the boundary position at all moment, obtains smoothed out boundary position
Time-space sequence.
Further, the step S7 specifically includes the following steps:
Step S71: will be obtained by two cameras of shooting interface following region according to coordinate conversion relation obtained by calibrating
Image the image under physical space coordinates system is transformed to from original image；
Step S72: whether the interface location in image obtained by two cameras after checking coordinate transform is overlapped, if not weighing
It closes, then self-calibration is carried out to two cameras of shooting interface following region；
Step S73: zooming in and out boundary position time-space sequence and interpolation is to adapt to the shooting by coordinate transform
Two obtained images of camera of interface following region；
Step S74: the temporarily initial offset of given interface location shows two cameras by space on a picture
The image of transformation and interface position temporary after offset, the image of two cameras occupies different Color Channels respectively, defeated
The video being made of out the picture of different moments；
Step S75: the difference of the interface location and the interface location reacted by particle brightness in picture fixed tentatively in observation video
It is different, and according to the offset of difference modification interface location；
Step S76: repeating step S74 and step S75, until particle brightness is anti-in the temporary position in interface and picture
The interface location reflected is overlapped.
The invention has the following advantages:
Total-reflection type gas-liquid interface Method of flow visualization of the invention, by liquid side be arranged illuminated by light source it is white
Shield the area source as imaging, the light that white screen diffusing reflection issues is with the angular illumination more than or equal to the cirtical angle of total reflection to gas-liquid
Interface, incident light can be totally reflected on gas-liquid interface, and light will not pass through gas-liquid interface and refract to gas side, greatly
The intensity of reflected light is enhanced, on the other hand, the light of gas side cannot be refracted into liquid side and along aforementioned reflection
The direction of light is propagated, and invalid information is reduced.Then in liquid side setting camera for shooting gas-liquid interface, the shooting of camera
The direction of direction face reflected light, to take the gas-liquid interface image of high contrast, it is invalid not include substantially in image
Information, so as to quickly and accurately identify the position of gas-liquid interface on the basis of the high-contrast image of acquisition.Also,
Total-reflection type gas-liquid interface Method of flow visualization of the invention still can obtain institute's bounded when having spray of water or having droplet
The detailed information of face position.
In addition, gas-liquid interface location recognition method of the invention, divides in gas and liquid respectively spread trace particle first,
Then by respectively using two high speed cameras to shoot trace particle image in the two sides of gas-liquid interface, shooting circle is then identified
The interface location of initial time in two obtained images of camera of face area above, then again to all figures in the same time
As being pre-processed, when identifying the gas-liquid interface position in subsequent each frame image, then being carried out to obtained gas-liquid interface position
M- space smoothing, to obtain all gas-liquid interfaces in two obtained images of camera of shooting interface area above
Position is finally shot further according to the gas-liquid interface position in two obtained images of camera of shooting interface area above
Shoot the gas-liquid interface position in two obtained images of camera of interface following region.Know gas-liquid interface position of the invention
Other method can accurately identify the position of gas-liquid interface in the presence of there are particle in gas-liquid interface two sides, and identify quasi-
Exactness is high, the nearly wall measurement process that can be perfectly suitable in particle image velocimetry.Also, gas-liquid interface position of the invention
Recognition methods is when shooting the image of gas-liquid interface following region using the total-reflection type gas-liquid interface stream in first embodiment
Dynamic display methods, the contrast of the image of the gas-liquid interface following region taken is higher, clarity is more preferable, the invalid letter for including
Breath is seldom, the gas-liquid interface position in image so as to which gas-liquid interface following region is fast and accurately identified.
Other than objects, features and advantages described above, there are also other objects, features and advantages by the present invention.
Below with reference to figure, the present invention is described in further detail.
Detailed description of the invention
The attached drawing constituted part of this application is used to provide further understanding of the present invention, schematic reality of the invention
It applies example and its explanation is used to explain the present invention, do not constitute improper limitations of the present invention.In the accompanying drawings:
Fig. 1 is the flow diagram of the total-reflection type gas-liquid interface Method of flow visualization of first embodiment of the invention.
Fig. 2 is that light source and camera are arranged in the total-reflection type gas-liquid interface Method of flow visualization of first embodiment of the invention
Schematic diagram.
Fig. 3 is the experimental provision schematic diagram of the total-reflection type gas-liquid interface Method of flow visualization of first embodiment of the invention.
Fig. 4 is the gas-liquid interface figure that the total-reflection type gas-liquid interface Method of flow visualization of first embodiment of the invention takes
Picture.
Fig. 5 is the gas-liquid interface image that the existing Method of flow visualization of first embodiment of the invention takes.
Fig. 6 is the flow diagram of the gas-liquid interface location recognition method of second embodiment of the invention.
Fig. 7 is respectively to be demarcated in step S2 in Fig. 6 of second embodiment of the invention to the camera of interface two sides
Schematic diagram.
Fig. 8 is the sub-process schematic diagram of the step S3 in Fig. 6 of second embodiment of the invention.
Fig. 9 is the sub-process schematic diagram of the step S4 in Fig. 6 of second embodiment of the invention.
Figure 10 is the sub-process schematic diagram of the step S5 in Fig. 6 of second embodiment of the invention.
Figure 11 is the sub-process schematic diagram of the step S6 in Fig. 6 of second embodiment of the invention.
Figure 12 is the sub-process schematic diagram of the step S7 in Fig. 6 of second embodiment of the invention.
Specific embodiment
The embodiment of the present invention is described in detail below in conjunction with attached drawing, but the present invention can be limited by following and
The multitude of different ways of covering is implemented.
As shown in Figure 1, Figure 2 and Figure 3, the first embodiment of the present invention provides a kind of total-reflection type gas-liquid interface FLOW VISUALIZATION
Method can provide the image of high contrast during identifying gas-liquid interface position, and almost only wrap in the image obtained
Containing one lateral reflection imaging of liquid, and gas side refraction light imaging is excluded, the invalid information contained in image is very
It is few, so as to quickly and accurately identify the position of gas-liquid interface from the image of high contrast.The total-reflection type gas-liquid interface
Method of flow visualization the following steps are included:
Step S100: area source of the white screen that setting is illuminated by light source in liquid side as imaging, white screen diffusing reflection hair
Light out is with the angular illumination more than or equal to the cirtical angle of total reflection to gas-liquid interface；
Step S200: in liquid side, setting camera is for shooting gas-liquid interface, the shooting direction face reflected light of camera
Direction.
It is appreciated that in the step S100, light source can choose laser, the illumination brilliant white screen that laser issues from
And diffusing reflection can occur in white screen, the light that diffusing reflection generates is with the angular illumination more than or equal to the cirtical angle of total reflection to gas-liquid
When interface, since the incidence angle of light is more than or equal to the cirtical angle of total reflection, it can be totally reflected at gas-liquid interface at this time, light
Gas-liquid interface will not be passed through and refract to gas side, it is very big to enhance the intensity of reflected light.Preferably, optimal photograph
Bright mode is that the light generated after diffusing reflection occurs for the white screen for directional light, can further strengthen the intensity of reflected light, have
Body are as follows: be the white screen of curved surface, such as spherical surface screen using surface, then light source is arranged in the near focal point of white screen, ensured simultaneously
Light source will not block white screen to the light of liquid level.
It is appreciated that in the step S200, due to the direction of the shooting direction face reflected light of camera, i.e. camera
Angle between sensitive chip and liquid level is equal to the incidence angle that the light that white screen diffusing reflection generates exposes to gas-liquid interface, therefore,
The light that total reflection generates can enter directly into camera, and since the intensity of total reflection light is very high, camera can be taken clearly
Clear interface image.In addition, preferably, in order to further increase the clarity of image, camera using move lens shaft or
Move adapter axis or move axis adapter ring or reflective mirror, so as to meet Scheimpflug (husky nurse law) condition at
Picture, obtained image more clean.
It is appreciated that preferably, the total-reflection type gas-liquid interface Method of flow visualization is further comprising the steps of:
Step S300: the perspective distortion for the image that amendment camera takes.
It is appreciated that in the step S300, due to perspective relation, the coordinate system on original image that camera is recorded
It is no longer rectangular coordinate system in physical space coordinates, it is therefore desirable to which perspective distortion is modified to the image that camera takes.
Detailed process are as follows: following close region places ginseng of the latticed object of reference as perspective correction at interface before shooting interface
It is calculated from the image of the object of reference illumination front and back taken according to object with image of the cameras record object of reference before and after illumination
Then the coordinate conversion relation of single order or high-order reuses the original image that coordinate conversion relation amendment camera takes.
In addition, preferably, needing in the case of larger for liquid regions area first by light source and camera mounted in streamline
It is placed into liquid in shape waterproof case.Furthermore it is also possible to which frosted glass is arranged at light source so that illuminating ray becomes more soft
With imaging effect is more preferable.
The present inventor also attempts to be imaged using following several method: 1, allowing light to pass perpendicularly through interface, then
It shoots the light after interfacial refraction and is formed by picture on screen, this method can directly shoot the image that screen locking is formed, i.e.,
Shadowing method can also add the edge of a knife in optical path, filter off reimaging, i.e. schlieren method after the lesser light of deviation rate；2, background line
Shadow method: figuratum background board is placed in interface side, generally uses compound particle as group, in interface other side shooting background
The pattern of plate passes through the anti-shape for releasing interface of the deformation of background plate pattern；3, X-ray scattering method.But shadowing method, schlieren method
It is all limited by interface undulation degree with background schlieren method, if interface undulation degree is too big, needs to shield or background board is close
Interface is so as to blur-free imaging, but in actual use, does not allow to shield or background board is too near to interface prevents from influencing
Experiment condition；And X-ray scattering rule is limited by experimental facilities, cost is larger, is difficult wide popularization and application.
Total-reflection type gas-liquid interface Method of flow visualization of the invention, by liquid side be arranged illuminated by light source it is white
Shield the area source as imaging, the light that white screen diffusing reflection issues is with the angular illumination more than or equal to the cirtical angle of total reflection to gas-liquid
Interface, incident light can be totally reflected on gas-liquid interface, and light will not pass through gas-liquid interface and refract to gas side, greatly
The intensity of reflected light is enhanced, then in liquid side setting camera for shooting gas-liquid interface, the shooting direction of camera is just
To the direction of reflected light, to take the gas-liquid interface image of high contrast, do not include invalid information in image substantially, from
And the position of gas-liquid interface can be quickly and accurately identified on the basis of the high-contrast image of acquisition.Also, it is of the invention
Total-reflection type gas-liquid interface Method of flow visualization still can obtain all interface locations when having spray of water or having droplet
Detailed information.Fig. 4 is the interface image that total-reflection type gas-liquid interface Method of flow visualization of the invention obtains, and Fig. 5 is using existing
The interface image for thering is technology to obtain, from the comparison of the two as can be seen that the interface image contrast of the invention obtained is higher, more clear
Clear, the invalid information for including is less, so as to more quickly and accurately identify the position of gas-liquid interface.
In addition, as shown in fig. 6, the second embodiment of the present invention also provides a kind of gas-liquid interface location recognition method, it is excellent
Choosing uses total-reflection type gas-liquid interface Method of flow visualization as in the first embodiment, passes through the total reflection of first embodiment
Formula gas-liquid interface Method of flow visualization obtains the image of high contrast, can be during measuring gas-liquid interface two sides velocity field
The position for identifying gas-liquid interface, is adapted to the case where interface two sides are with the presence of trace particle, and interface location identification
Accuracy is very high.The gas-liquid interface location recognition method the following steps are included:
Step S1: sowing trace particle in gas and liquid respectively, and sheet laser is then arranged and is illuminated；
Step S2: respectively using two high speed cameras shooting trace particle images in the two sides of gas-liquid interface, etc. time intervals
Exposure, and the camera for being located at interface two sides is respectively demarcated；
Step S3: the initial time interface position in two obtained images of camera of identification shooting interface area above
It sets；
Step S4: the obtained image in the same time of two cameras of shooting interface area above is pre-processed；
Step S5: the gas-liquid interface position in then each frame image is identified；
Step S6: time-space smooth operation is carried out to gas-liquid interface position to obtain the two of shooting interface area above
Gas-liquid interface position in the obtained image of platform camera；
Step S7: it is obtained according to the gas-liquid interface position in two obtained images of camera of shooting interface area above
Shoot the gas-liquid interface position in two obtained images of camera of interface following region.
It is appreciated that in the step S1, it is contemplated that particle follows the performance of fluid related with stokes number, it is ensured that
Tracing particle is good enough, needs the particle that diameter is sufficiently small, but on the other hand, in the image of cameras record, particle
Brightness and particle diameter it is square related, this requires particle radii again cannot be too small.Therefore, the present embodiment is using in gas
The lesser particle of partial size is sowed, and is sowed in a liquid using the biggish particle of partial size, the liquid near gas-liquid interface
It repeats to sow particle in body so that the region particle density is sufficiently large, so that it is guaranteed that while particle has enough followability, two
The respective brightness and partial size different from of the particle of kind partial size in the picture.Preferably, using diameter in gas is 1
μm or so smog as trace particle, using diameter in a liquid is 50 μm or so of hollow organic glass particle as tracer
Particle, wherein the trace particle in gas is injected by fan, and particle a part in liquid is injected deep position by funnel
It sets, another part is gently poured on liquid level.It is illuminated in measured zone setting sheet laser, specific set-up mode can be point
A sheet laser is not respectively set in the two sides of gas-liquid interface to be illuminated, the illumination direction of the area source of gas side is vertical
Downwards, the set-up mode of liquid side area source is specific such as first embodiment using the light source set-up mode in first embodiment
In step S100 described in, details are not described herein.Wherein, the color of two light sources can be different, consequently facilitating by optical filtering section
Point.
It is appreciated that this preferred embodiment uses time series three-dimensional particles image speed measurement method in the step S2
The velocity field of section two side areas is measured simultaneously, specifically respectively uses two high speed camera shooting trace particle figures in interface two sides
The region that picture, i.e. two cameras shoot gas-liquid interfaces or more, two cameras shoot gas-liquid interface regions below, then carry out etc.
Time interval exposure, i.e., shoot a series of pictures, and respectively marked in gas-liquid interface two sides in uniform time interval
It is fixed.As shown in fig. 7, specifically demarcating mode are as follows: it is required that the plane of the datum plane of gas-liquid interface two sides calibration and laser irradiation
It is overlapped, scaling board bottom edge is horizontal positioned, can there is distance, i.e., the two physical space coordinates systems demarcated between coordinate origin
In, vertically upward, z-axis is directly in scaling board front surface, and z=0 plane is overlapped, x, y, the direction z phase for the positive direction of the y-axis of the two
Together.In addition, preferably, plane where blocking measurement in shooting process in order to avoid the interface before plane where measurement
On interface, need the camera for shooting interface area above being inclined relative to horizontal setting, tilt angle is 10 ° or so.
It is appreciated that two cameras of shooting gas-liquid interface area above obtain when between camera and horizontal plane being in 10 ° or so of angle
To image in there are mainly two types of content: the particle in particle direct imaging, liquid in gas is imaged after interfacial refraction.
And the set-up mode step S200 as in the first embodiment for shooting two cameras of interface following region, therefore it is no longer superfluous herein
It states.Content there are mainly two types of shooting in two obtained images of camera of gas-liquid interface following region: area below gas-liquid interface
Domain trace particle scattering light is directly imaged in the camera, the scattering light of gas-liquid interface following region trace particle is reflected by interface
It is imaged in the camera afterwards.It is considered that the scattering light by reflection with gas-liquid interface distance with increasing, deformation and decoking phenomenon are cured
Add seriously, edge is also more fuzzy, and there are relationships between light intensity and scattering angle in Mie scattering, scatter light and irradiation light
Scattered light intensity is bigger when angle is smaller, so the particle of gas-liquid interface area above is brighter than the particle of interface following region
Degree is big, and fuzzyyer apart from the remoter particle in interface.Therefore, the present invention is obtained using two cameras of shooting gas-liquid interface area above
The image recognition interface location arrived, recognition result are more accurate.
It is appreciated that in the step S3, boundary in the image that two cameras of identification shooting interface area above obtain
The position in face needs that image is transformed to physical space coordinates according to coordinate mapping relations obtained by calibrating, it is therefore desirable to examine mark
Surely the coordinate mapping relations obtained are made whether accurately.Preferably, the gas-liquid interface location recognition method is in step S2
It further include step S23 between step S3,
Step S23: the brightness of the photo of two cameras in the same time Jing Guo coordinate transform is switched to the number in red green channel
Value is then combined with to showing on a picture, and judges whether the interface of two photos is overlapped.If coordinate obtained by calibrating reflects
Penetrate that relationship is accurate, at this moment the position of two picture median surfaces will be overlapped；If coordinate mapping relations inaccuracy obtained by calibrating,
The picture of two cameras interface location after changes in coordinates is not overlapped, then needs to carry out self-calibration to two cameras, it can
According to the distance of two picture median surface relative spot locations be arranged initial offset, i.e., respective point on the direction x and the direction y away from
From, then by the determining offset generally of these offsets, overall deviant is the average value of each point deviant.In order to ensure accurate
Property, the multipair picture that two cameras can be used carries out self-calibration, such as 100 pairs of pictures.
It is appreciated that also needing to execute following steps between the step S2 and step S3:
By the obtained image level overturning of two cameras for shooting interface area above, or interface or less area will be shot
Two cameras in domain obtained image level overturning, in order to by the figure of the image of interface following region and interface following region
As comparing.
There are two ways to being appreciated that in the step S3, identifying initial time interface location, the first is to use
It is manually entered after manual identified interface location, second is identified using algorithm.In order to ensure the accuracy of identification, the present embodiment
It is preferred that using second of recognition methods.Specifically, as shown in figure 8, the step S3 the following steps are included:
Step S31: if gas motion speed is much larger than liquid motion speed, under suitable sample frequency, each pixel
Brightness take the reckling of corresponding position brightness in plurality of pictures；If gas motion speed is not much larger than liquid motion speed,
Then skip this step；
Step S32: gray scale morphology is carried out to picture and opens operation several times, the particle in image in gas is eliminated and retains
Particle in liquid；
Step S33: setting luminance threshold identifies the particle in liquid, obtains bianry image；
Step S34: operation is carried out out several times to bianry image, then carries out closed operation several times；
Step S35: being arranged height number y0 according to the interfacial level in image, and making the height and position at interface be in height should
The straight line of numerical value is hereinafter, height is set as 0 in the part of y0 or more；
Step S36: the highest position of height in all nonzero values of each column pixel in record bianry image, if certain column does not have
Nonzero value exists, then records the position of the last one pixel of the column, obtain a sequence；
Step S37: median filtering and gaussian filtering process are carried out to sequence, obtain the position at interface；
Step S38: the average value of two camera obtained photo median surfaces position is calculated.
It is appreciated that in the step S31, if the movement velocity of gas is much larger than the movement velocity of liquid, i.e. gas
More than the average movement velocity of body is more order of magnitude greater than the average movement velocity of liquid, under suitable sample frequency, picture
Trace particle in middle gas has apparent movement, i.e., every frame is mobile to be greater than 1 pixel, and the trace particle in liquid is not obvious
Movement, i.e. every frame is mobile less than 1 pixel, then the sliding minimum value of 3 or 5 pictures in time series can be used, i.e., each
The brightness of pixel takes the reckling of 3 or 5 picture corresponding position brightness, then carries out subsequent step process.Otherwise, this step is skipped
Suddenly.
It is appreciated that gray scale morphology opens operation and refers to first carrying out gray scale morphology to picture in the step S32
Corrosion, then gray scale morphology expansion is carried out, retain the particle in liquid so as to eliminate the particle in picture in gas.
It is appreciated that in the step S33, due to particle brightness and its diameter it is square related, and in gas
Particle diameter is 1 μm or so, and the particle diameter in liquid is 50 μm or so, is identified so as to which a luminance threshold is arranged
Particle in liquid, such as the local brightness of 1 expression are higher than threshold value, and 0 indicates local brightness lower than threshold value.And it is possible to be arranged complete
The luminance threshold that office's threshold value, i.e. space use same size everywhere, also can be set the local threshold value of gradual change, i.e., different in space
There is different luminance threshold sizes in position, this depends on each imaging parameters, if using telephoto lens and large scale sensitive chip, figure
As fringe region overall brightness is likely less than central area, it at this moment can choose and reduce fringe region threshold value.
It is appreciated that first carrying out gray scale morphology corruption to bianry image obtained in step S33 in the step S34
Erosion carries out gray scale morphology expansion several times again, then carries out closed operation several times, i.e., first carries out gray scale morphology expansion and carry out again
Gray scale morphology corrodes several times.
It is appreciated that a height number y0 is arranged according to the interfacial level in bianry image in the step S35,
So that the height and position at interface is in the straight line that height is y0 hereinafter, and being highly set as 0 in the part of y0 or more.
It is appreciated that in the step S36, height is recorded in bianry image in all nonzero values of each column pixel most
The position of a high pixel, if not having the presence of nonzero value in a certain column pixel, i.e. the height and position of the column pixel exists
Height is the straight line of y0 or more, then the position of the last one pixel of the column pixel is recorded, to obtain a position sequence.
It is appreciated that in the step S38, in order to ensure the accuracy of identification, using obtained by two cameras of calculating
Photo median surface position average value as final initial interface position.
It is appreciated that since this algorithm is carried out again by the particle in identification liquid smoothly to reach identification interface
Purpose, and the trace particle in liquid always in gas-liquid liquid level hereinafter, therefore need to be arranged amount of bias, then further according to amount of bias to
Initial interface position obtained in upper moving step S38, to allow the interface location recognized and actual interface location to be overlapped,
Further improve the accuracy of identification.The amount of bias is obtained by actual picture test of many times.Therefore, the step S3
Further include step S39 after step S38:
Step S39: then setting amount of bias moves up initial interface position according to amount of bias.
It is appreciated that as shown in figure 9, the step S4 specifically includes the following steps:
Step S41: if gas motion speed is much larger than liquid motion speed, under suitable sample frequency, each pixel
Brightness take the reckling of corresponding position brightness in plurality of pictures；If gas motion speed is not much larger than liquid motion speed,
Then skip this step；
Step S42: the obtained photo in the same time of two cameras is synthesized into a photo；
Step S43: gray scale morphology is carried out to the photo of synthesis and opens operation several times, eliminates the particle in image in gas
And retain the particle in liquid.
It is appreciated that the step S41 is consistent with above-mentioned steps S31, therefore details are not described herein.
It is appreciated that the step S42 specifically: the interface of previous frame image is translated up into 10 pixels as boundary
Line, line of demarcation area above compare two photos with the brightness of position, take brightness of the relatively low value as photomontage；Again will
The interface of previous frame image translates downwards 10 pixels as line of demarcation, and line of demarcation following region compares two photos with the bright of position
Degree, takes brightness of the relatively high value as photomontage；Two lines of demarcation intermediate region can from lower value to average value again to
High value gradual change can also take the average value of local brightness.
It is appreciated that the step S43 is consistent with above-mentioned steps S32, therefore details are not described herein.
It is appreciated that as shown in Figure 10, the step S5 specifically includes the following steps:
Step S51: the image obtained for pretreatment, setting luminance threshold identify the particle in liquid to obtain binary map
Picture；
Step S52: operation is carried out out several times to bianry image, then carries out closed operation several times；
Step S53: the interface of previous frame image is translated up into 15 pixels as line of demarcation, line of demarcation area above two-value
Image values are set as 0；
Step S54: the highest position of height in all nonzero values of each column pixel in record bianry image, if certain column does not have
Nonzero value exists, then the position of the column the last one pixels and the smaller value of former frame interface same position is recorded, to obtain
One sequence；
Step S55: median filtering is carried out to sequence and gaussian filtering obtains the position at interface；
Step S56: the position at interface is moved up according to amount of bias.
It is appreciated that the step S51 is consistent with above-mentioned steps S33, therefore details are not described herein, wherein luminance threshold is
The Luminance Distribution setting of two cameras of shooting interface area above is tested according to the group.
It is appreciated that the step S52 is consistent with above-mentioned steps S34, therefore details are not described herein.
It is appreciated that in the presence of there is no nonzero value in a certain column pixel, then it is last to record the column in the step 54
The position of one pixel and the smaller value of former frame interface same position, that is, take height the higher person in the two.
It is appreciated that step S55 is consistent with above-mentioned steps S37, therefore details are not described herein.
It is appreciated that the amount of bias is set in step S39 in the step S56.
It is appreciated that as shown in figure 11, the step S6 specifically includes the following steps:
Step S61: it is separated by the cross correlation value that several frames calculate interface location between every two frame；
Step S62: peak position is found after multiple cross correlation values are added；
Step S63: step S61 and step S62 is repeated for all computable moment, obtains the time sequence of boundary velocity
Column；
Step S64: the time series based on obtained boundary velocity does locking phase average computation to interface location；
Step S65: time-space smooth operation is done to the boundary position at all moment, obtains smoothed out boundary position
Time-space sequence.
It is appreciated that in the step S61, for example, selecting first frame and second frame according to chronological order, wherein second
Frame interface location is fixed, and first frame interface is moved in the x-direction, to obtain cross correlation value with the pass between first frame Interface Moving distance
System, then looks for the corresponding moving distance of cross-correlation peak value.Wherein, it is separated by the purpose that several frames calculate cross correlation value and allows for boundary
Face rate travel is slow, and increasing time interval can be improved precision.
It is appreciated that, in order to further increase precision, can choose multiple cross correlation value phases in the step S62
Peak position is found after adding.For example, selection one frame of first, two frame of first, three frame of first, three frame of one frame of second, two frame of second and second, wherein first two
Between the time between three frame of time interval, three frame of first and second between one frame of time interval and one frame of first and second of two frame of frame and second
Every identical, above-mentioned three groups double frame data interface location cross correlation values are calculated separately with the relationship between moving distance, then by three groups
Cross correlation value is added to obtain new interface location cross correlation value with the relationship between moving distance, finds corresponding cross-correlation peak value pair
The moving distance answered.In addition, the group number of superposition calculation can be selected as needed, it is not specifically limited herein.
It is appreciated that the Interface Moving distance in the unit time is boundary velocity, and interface in the step S63
Moving distance is obtained according to the position of cross-correlation peak value in step S61 and step S62.For it is all can calculate at the time of repetition
Step S61 and step S62, to obtain the time series of boundary velocity.Preferably, can also be adopted in the step S63
It is handled with time series of the smothing filtering to boundary velocity to reduce time series pulsating quantity, smothing filtering can be intermediate value
Filtering, gaussian filtering, Butterworth filtering etc..
Be appreciated that the step S64 specifically: note the t0 moment interface location be<s (<x>, t0)>, wherein<s>table
Show interfacial level,<x>indicates the abscissa sequence at interface, and<>indicates vector, interface location<s (<x>, t0)>indicate in t0
The interfacial level of certain point x0 column corresponding component in<s>in quarter<x>.Remember step S61 in it is middle calculate cross correlation value when
Between between be divided into △ t, it is<△ x (t0)>that the moment interface t0 moving distance in △ t is obtained after smooth.Then it is m- when note N is
Space smoothing radius, calculate s (<x>-N<Δ x (t0)>, t0-N Δ t)>,<s (<x>-(N-1)<Δ x (t0)>, t0-(N-1) Δ
T)>...,<s (<x>, t0)>,<s (<x>+(N-1)<Δ x (t0)>, t0+ (N-1) Δ t)>,<s (<x>+N<Δ x (t0)>, t0+N
The average value<s1 (<xe>, t0) of Δ t)>on<xe>>, wherein<xe>indicates the new horizontal seat obtained after extending<x>to two sides
Mark sequence.In addition, needing to carry out one-dimensional interpolation in the step S64, and average computation only uses the numerical value that interpolation obtains
The numerical value obtained without the use of extrapolation.Wherein, N is set as 30, in order to which interface location extends enough length to two sides.
It is appreciated that can reduce N when edge carries out time-space smooth operation in the step S65.Separately
Outside, in obtained smoothed out boundary position time-space sequence, the part for lacking data can be used interpolation and be counted
According to.So far, the interface location in image obtained by two cameras of shooting gas-liquid interface area above has been obtained.
It is appreciated that the interface location in image obtained by two cameras of shooting interface area above passes through above-mentioned step
Suddenly it obtains, it is now desired to which shooting interface following region is determined by position in physical space of obtained interface
Interface location in image obtained by two cameras.As shown in figure 12, the step S7 specifically includes the following steps:
Step S71: will be obtained by two cameras of shooting interface following region according to coordinate conversion relation obtained by calibrating
Image the image under physical space coordinates system is transformed to from original image；
Step S72: whether the interface location in image obtained by two cameras after checking coordinate transform is overlapped, if not weighing
It closes, then self-calibration is carried out to two cameras of shooting interface following region；
Step S73: zooming in and out boundary position time-space sequence and interpolation is to adapt to the shooting by coordinate transform
Two obtained images of camera of interface following region；
Step S74: the temporarily initial offset of given interface location shows two cameras by space on a picture
The image of transformation and interface position temporary after offset, the image of two cameras occupies different Color Channels respectively, defeated
The video being made of out the picture of different moments；
Step S75: the difference of the interface location and the interface location reacted by particle brightness in picture fixed tentatively in observation video
It is different, and according to the offset of difference modification interface location；
Step S76: repeating step S74 and step S75, until particle brightness is anti-in the temporary position in interface and picture
The interface location reflected is overlapped.
It is appreciated that boundary will be shot according to the coordinate conversion relation obtained by calibrating in step S2 in the step S71
Two obtained images of camera of face following region transform to the image under physical space coordinates system from original image.In addition,
Due to shooting interface following region image when using the total-reflection type gas-liquid interface Method of flow visualization in first embodiment,
The contrast of the image of acquisition is high, clarity is high, and the invalid information for including is seldom, so as to quickly and accurately carry out gas
The identification at liquid interface.
It is appreciated that in the step S72, obtained by two cameras using visual inspection shooting interface following region
Image in interface location whether be overlapped, interface location can substantially be judged by the particle brightness in image, if the two
Interface location be not overlapped, then need to shooting interface following region two cameras carry out self-calibration, the process of self-calibration with
Self-calibration process in above-mentioned steps S23 is consistent, therefore details are not described herein.
It is appreciated that in the step S73, due to the calibration of two cameras to shooting interface area above and to bat
The calibration for taking the photograph two cameras of interface following region is respectively individually to carry out, every millimeter of corresponding pixel in two groups of calibration relationships
Number is not necessarily identical, it is therefore desirable to zoom in and out to obtained boundary position time-space sequence and interpolation is to adapt to by sitting
Mark two obtained images of camera of transformed shooting interface following region.
It is appreciated that the initial offset of interface location is temporarily given, then in a picture in the step S74
Two cameras of upper display position temporary after offset by the image of spatial alternation and interface, the image difference of two cameras
Different Color Channels is occupied, in order to distinguish, finally exports the video being made of the picture of different moments.
It is appreciated that in the step S75, since the particle brightness of picture median surface area above is bigger, and boundary
The particle brightness of face following region is smaller, therefore, can significantly observe the interface location fixed tentatively in video and by picture
The difference of the interface location of middle particle brightness reaction.
It is appreciated that in the step S76, the interface position of the particle brightness reflection in the temporary position in interface and picture
It sets after being overlapped to get the position of the gas-liquid interface into two obtained images of camera of shooting interface following region.So far,
Gas-liquid interface position in all obtained images of camera has been obtained.
Present inventor also attempted to identify gas-liquid interface position using following three methods: 1, identifying interface
Reflective feature；2, fluorescent material is added in liquid, there are the regions of fluorescent material for identification；3, it identifies existing for trace particle
Region.But in the first method, the direction for needing that camera is enabled to shoot is concordant with interface reflective to promote to capture interface, still
Because gas-liquid interface is actually what height rose and fell, the problem of sight is blocked thus is had, is using three-dimensional particle
Especially severe is blocked when image speed measurement；And in the second approach, need two different colors of light source and three groups of shootings different
The camera of color content, whole system is more complicated, and cost is also very high, and common fluorescent dye (rhodamine B) is toxic
, it is detrimental to health；And the third method can not be suitable for the case where interface two sides are with the presence of particle at all, because of gas
In particle and liquid in particle be not easy to distinguish.
Therefore, present inventor proposes the gas-liquid interface location recognition method of the application preferred embodiment, first
Divide in gas and liquid respectively and spread trace particle, then by respectively using two high speed cameras to clap in the two sides of gas-liquid interface
Trace particle image is taken the photograph, then identifies the initial time in two obtained images of camera of shooting interface area above
Then interface location again pre-processes all images in the same time, identify the gas-liquid interface position in subsequent each frame image
It sets, then smooth to obtained gas-liquid interface position progress time-space, to obtain two phases of shooting interface area above
All gas-liquid interface positions in the obtained image of machine, finally further according to obtained by two cameras of shooting interface area above
Image in gas-liquid interface position obtain shooting shooting interface following region two obtained images of camera in gas-liquid
Interface location.Gas-liquid interface location recognition method of the invention, can be in the presence of there be particle in gas-liquid interface two sides
The position of gas-liquid interface is accurately identified, and recognition accuracy is high, the nearly wall that can be perfectly suitable in particle image velocimetry is surveyed
Amount process.In addition, gas-liquid interface location recognition method of the invention is used when shooting the image of gas-liquid interface following region
Total-reflection type gas-liquid interface Method of flow visualization in first embodiment, pair of the image of the gas-liquid interface following region taken
More preferable than Du Genggao, clarity, the invalid information for including is seldom, so as to which gas-liquid interface or less is fast and accurately identified
Gas-liquid interface position in the image in region.
The foregoing is only a preferred embodiment of the present invention, is not intended to restrict the invention, for the skill of this field
For art personnel, the invention may be variously modified and varied.All within the spirits and principles of the present invention, made any to repair
Change, equivalent replacement, improvement etc., should all be included in the protection scope of the present invention.
Claims (10)
1. a kind of total-reflection type gas-liquid interface Method of flow visualization, which is characterized in that
The following steps are included:
Step S100: area source of the white screen that setting is illuminated by light source in liquid side as imaging, what white screen diffusing reflection issued
Light is with the angular illumination more than or equal to the cirtical angle of total reflection to gas-liquid interface；
Step S200: in liquid side, setting camera is for shooting gas-liquid interface, the side of the shooting direction face reflected light of camera
To.
2. total-reflection type gas-liquid interface Method of flow visualization as described in claim 1, which is characterized in that
The total-reflection type gas-liquid interface Method of flow visualization is further comprising the steps of:
Step S300: the perspective distortion for the image that amendment camera takes.
3. total-reflection type gas-liquid interface Method of flow visualization as described in claim 1, which is characterized in that
The surface of the white screen is curved surface, light source is arranged in the near focal point of white screen, and light source will not block white screen to liquid level
Light.
4. total-reflection type gas-liquid interface Method of flow visualization as described in claim 1, which is characterized in that
Camera is using shifting lens shaft or moves adapter axis or moves axis adapter ring or reflective mirror.
5. total-reflection type gas-liquid interface Method of flow visualization as described in claim 1, which is characterized in that
The step S3 specifically:
At interface, following close region places object of reference of the latticed object of reference as perspective correction before shooting interface, uses
Image of the cameras record object of reference before and after illumination, from take object of reference illumination front and back image in calculate single order or
Then the coordinate conversion relation of high-order reuses the original image that coordinate conversion relation amendment camera takes.
6. a kind of gas-liquid interface location recognition method, suitable for gas-liquid interface two sides with the presence of trace particle the case where, it is special
Sign is,
The following steps are included:
Step S1: sowing trace particle in gas and liquid respectively, and sheet laser is then arranged and is illuminated, wherein liquid one
Area source of the white screen that side setting is illuminated by light source as imaging, the light that white screen diffusing reflection issues are faced with being more than or equal to total reflection
The angular illumination at boundary angle is to gas-liquid interface；
Step S2: respectively using two high speed cameras shooting trace particle images in the two sides of gas-liquid interface, etc. time intervals exposure,
And the camera for being located at interface two sides is respectively demarcated, wherein the shooting direction face of the two of liquid side high speed camera is anti-
Penetrate the direction of light；
Step S3: the initial time interface location in two obtained images of camera of identification shooting interface area above；
Step S4: the obtained image in the same time of two cameras of shooting interface area above is pre-processed；
Step S5: the gas-liquid interface position in then each frame image is identified；
Step S6: time-space smooth operation is carried out to obtain two phases of shooting interface area above to gas-liquid interface position
Gas-liquid interface position in the obtained image of machine；
Step S7: it is shot according to the gas-liquid interface position in two obtained images of camera of shooting interface area above
Gas-liquid interface position in two obtained images of camera of interface following region.
7. gas-liquid interface location recognition method as described in claim 1, which is characterized in that
The step S3 specifically includes the following steps:
Step S31: if gas motion speed is much larger than liquid motion speed, the brightness of each pixel takes corresponding positions in plurality of pictures
Set the reckling of brightness；Otherwise this step is skipped；
Step S32: gray scale morphology is carried out to picture and opens operation several times；
Step S33: setting luminance threshold identifies the particle in liquid, obtains bianry image；
Step S34: operation is carried out out several times to bianry image, then carries out closed operation several times；
Step S35: being arranged height number y0 according to the interfacial level in image, and making the height and position at interface is highly being the numerical value
Straight line hereinafter, height in the part of y0 or more is set as 0；
Step S36: the highest position of height in all nonzero values of each column pixel in record bianry image, if certain arranges no non-zero
Value exists, then records the position of the last one pixel of the column, obtain a sequence；
Step S37: median filtering and gaussian filtering process are carried out to sequence, obtain the position at interface；
Step S38: the average value of two camera obtained photo median surfaces position is calculated；
Step S39: then setting amount of bias moves up initial interface position according to amount of bias.
8. gas-liquid interface location recognition method as claimed in claim 7, which is characterized in that
The step S5 specifically includes the following steps:
Step S51: the image obtained for pretreatment, setting luminance threshold identify the particle in liquid to obtain bianry image；
Step S52: operation is carried out out several times to bianry image, then carries out closed operation several times；
Step S53: the interface of previous frame image is translated up into 15 pixels as line of demarcation, line of demarcation area above bianry image
Numerical value is set as 0；
Step S54: the highest position of height in all nonzero values of each column pixel in record bianry image, if certain arranges no non-zero
Value exists, then the position of the column the last one pixels and the smaller value of former frame interface same position is recorded, to obtain one
Sequence；
Step S55: median filtering is carried out to sequence and gaussian filtering obtains the position at interface；
Step S56: the position at interface is moved up according to amount of bias.
9. gas-liquid interface location recognition method as claimed in claim 8, which is characterized in that
The step S6 specifically includes the following steps:
Step S61: it is separated by the cross correlation value that several frames calculate interface location between every two frame；
Step S62: peak position is found after multiple cross correlation values are added；
Step S63: step S61 and step S62 is repeated for all computable moment, obtains the time series of boundary velocity；
Step S64: the time series based on obtained boundary velocity does locking phase average computation to interface location；
Step S65: doing time-space smooth operation to the boundary position at all moment, obtains m- when smoothed out boundary position
Spatial sequence.
10. gas-liquid interface location recognition method as claimed in claim 9, which is characterized in that
The step S7 specifically includes the following steps:
Step S71: two obtained figures of camera of interface following region will be shot according to coordinate conversion relation obtained by calibrating
As transforming to the image under physical space coordinates system from original image；
Step S72: whether the interface location in image obtained by two cameras after checking coordinate transform is overlapped, if not being overlapped,
Self-calibration is carried out to two cameras of shooting interface following region；
Step S73: zooming in and out boundary position time-space sequence and interpolation is to adapt to the shooting interface by coordinate transform
Two obtained images of camera of following region；
Step S74: the temporarily initial offset of given interface location shows that two cameras pass through spatial alternation on a picture
Image and the interface temporary position after offset, the image of two cameras occupies different Color Channels respectively, output by
The video of the picture composition of different moments；
Step S75: the difference of the interface location and the interface location reacted by particle brightness in picture fixed tentatively in observation video, and
The offset of interface location is modified according to difference；
Step S76: repeating step S74 and step S75, until particle brightness reflection in the temporary position in interface and picture
Interface location is overlapped.
Priority Applications (1)
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