JP2015161639A - Visualized fluid flow velocity measuring method and visualized fluid flow velocity measuring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To alleviate or reduce the load and data analysis time of an arithmetic processor for acquiring a three-dimensional velocity vector or three velocity components of a visualized fluid by a tomographic PIV measurement method.SOLUTION: A particle distribution at each time (t, t+Δt) in a three-dimensional space (α) is reconstructed (S3) on the basis of two-dimensional image data obtained by imaging a fluid by imaging devices (1-4), and three-dimensional luminance information on the two consecutive time is obtained. A slice region (β) of a predetermined thickness obtained by dividing the three-dimensional space (α) is set, and a particle distribution in the slice region (β) is extracted from the three-dimensional luminance information (S4). The particle distribution in the slice region (β) is projected onto a plurality of virtual projection planes, and a plurality of virtual two-dimensional particle images at the two consecutive time is generated (S6). On the basis of a two-dimensional motion vector of particles in a plurality of image planes obtained by executing two-dimensional PIV to the plurality of two-dimensional particle images, a three-dimensional velocity vector or three velocity components of a visualized fluid in the three-dimensional space (α) are acquired (S7, S8, S11).

Description

  The present invention relates to a flow velocity measurement method and a flow velocity measurement system for a visualization fluid, and more specifically, a flow field of a visualization fluid formed by visualizing a fluid with a group of fine particles is photographed by an imaging device, and the visualization fluid 3 The present invention relates to a flow velocity measurement method and a flow velocity measurement system for measuring a dimensional velocity vector or a three velocity component.

  A visualization measurement technique is known in which tracer particles for visualizing a fluid are mixed as a marker into a fluid flow and the fluid velocity of a flow field is measured. In the direct imaging method known as the visualization fluid measurement technology, the tracer particles are separated by a minute time interval (for example, by double exposure imaging or high-speed camera imaging, frame imaging using a pulse laser and a digital CCD camera). By continuously photographing at intervals of 1 ms), the moving distance of the particles is measured. The velocity of the particles is calculated by dividing the distance traveled by the time interval.

  PIV (Particle Image Velocimetry), which is known as a kind of visualization fluid measurement technology, is a measurement technique that is widely used as a direct imaging method for examining the velocity distribution of such visualization fluid. The PIV measurement method irradiates a fluid with a laser sheet light, captures fine particles with a size of about 10 μm contained in the fluid by continuous photographing at minute time intervals (time t and time t + Δt), and determines the velocity of the particle or particle group. This is a flow velocity measuring method that is obtained by image analysis and thereby measures a flow velocity distribution and the like. According to such a PIV measurement method, it is possible to measure two in-plane velocity components in the laser sheet light.

  A stereo PIV measurement method is known as a measurement technique for obtaining three velocity components in laser sheet light (two-dimensional). In the stereo PIV measurement method, fine particles in a fluid are continuously photographed at a minute time interval by at least two CCD cameras that photograph visualization fluids from different angular directions, and based on the parallax of a plurality of camera images, This is a flow velocity measurement method in which the three-dimensional movement amount is obtained by image analysis, and thereby, the velocity three components (x-axis, y-axis, and z-axis directions) of the visualization fluid are measured.

  Such PIV measurement method or stereo PIV measurement method is described in, for example, Japanese Patent Application Laid-Open Nos. 2011-247601 and 2004-286733 (Patent Documents 1 and 2).

  As another flow velocity measurement method for measuring the three components of the velocity of the visualization fluid, the visualization fluid is irradiated with a band-shaped and three-dimensional laser beam of a predetermined thickness having a square or rectangular cross section, and the visualization fluid is photographed from different angular directions. Image at least three CCD cameras, and reconstruct the particle distribution in the three-dimensional space based on the image data of the particle image obtained by the imaging, and the three-dimensional velocity of the visualization fluid in the three-dimensional space. A tomographic PIV measuring method for measuring a vector or a three-speed component is known (JP 2005-91364 A, JP 2013-217902 A, etc.). The tomographic PIV measurement method is a measurement technique that can measure a three-dimensional flow velocity distribution of a fluid efficiently and with high accuracy by fusing CT (Computed Tomography) technology and PIV technology. Typically, four CCD cameras are used for imaging, and each camera simultaneously captures particulates in the fluid at each of two consecutive times (t and t + Δt). The stereo PIV technique is a two-dimensional measurement technique, whereas the tomographic PIV technique is advantageous in that it is a three-dimensional measurement technique.

JP2011-247601A JP 2004-286733 A JP 2005-91364 A JP 2013-217902 A

  However, in the tomographic PIV measurement method, the storage device that constitutes the image analysis device of the measurement system uses three-dimensional data such as three-dimensional particle distribution data and three-dimensional voxel group luminance data as analysis data. In order to store and save, a storage section or storage means having an excessive storage capacity must be possessed. In addition, since a large amount of operation load is imposed on the arithmetic processing devices constituting the measurement system for data analysis of a large amount of three-dimensional data, the arithmetic processing device can analyze data for a relatively long time for arithmetic processing. It takes time. For this reason, in the tomographic PIV measurement method, a high-performance and large-capacity electronic device must be employed as a storage device and an arithmetic processing unit. As a result, the initial equipment cost of the measurement system increases, and the system The configuration tends to be complicated.

  In addition, 3D data such as 3D particle distribution data and 3D voxel group luminance data are different from actual particle images captured by the camera. In addition, it is difficult to evaluate or recognize visually or sensoryly, and the validity of reconstruction of three-dimensional data based on particle images cannot be confirmed visually or sensorially.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an arithmetic processing device for acquiring a three-dimensional velocity vector or a three-velocity component of a visualization fluid by a tomographic PIV measurement method. An object of the present invention is to provide a flow velocity measurement method and a flow velocity measurement system that can reduce or shorten the load and data analysis time.

  It is another object of the present invention to provide a flow velocity measurement method and a flow velocity measurement system that can reduce the storage capacity of a storage device in such a flow velocity measurement method and flow velocity measurement system.

In order to achieve the above object, the present invention is obtained by imaging a two-time particle image separated by a minute time interval with a plurality of imaging devices that image visualization fluid visualized by a group of microparticles. In the flow velocity measurement method for a visualization fluid, the particle distribution in the three-dimensional space is reconstructed based on the image data of the particle image, and the three-dimensional velocity vector or the three velocity component of the visualization fluid in the three-dimensional space is measured.
Reconstructing the particle distribution at each time in the three-dimensional space based on the two-dimensional image data imaged by the imaging device to obtain continuous two-time three-dimensional luminance information (S3);
Setting a slice region of a predetermined thickness obtained by dividing the three-dimensional space, extracting a particle distribution inside the slice region from the three-dimensional luminance information, and projecting the particle distribution onto a plurality of virtual projection planes A step (S4, S6) of generating a plurality of virtual two-dimensional particle images at two consecutive times,
Based on a two-dimensional movement vector of particles in a plurality of image planes obtained by executing a two-dimensional PIV on the plurality of two-dimensional particle images, a three-dimensional velocity vector or a three-velocity component of the visualization fluid in the three-dimensional space is obtained. There is provided a flow velocity measuring method characterized by having a step (S7, S8, S11) of acquiring.

The present invention also captures two continuous time particle images separated by a minute time interval by a plurality of imaging devices that image visualization fluid visualized by a group of microparticles, and converts the image data of the particle images obtained by the imaging into image data. In the flow velocity measurement method of the visualization fluid, the particle distribution in the three-dimensional space is reconstructed based on the three-dimensional velocity vector or the three-velocity component of the visualization fluid in the three-dimensional space.
A slice region having a predetermined thickness formed by dividing the three-dimensional space is set, and the particle distribution at each time in the slice region is reconstructed based on the two-dimensional image data imaged by the imaging device, and the slice region Obtaining three-dimensional luminance information at two consecutive times (S3 ', S5'),
A step of generating a plurality of virtual two-dimensional particle images at two consecutive times by projecting the particle distribution inside the slice region on a plurality of virtual projection planes based on the three-dimensional luminance information (S6);
Based on two-dimensional movement vectors of particles in a plurality of image planes obtained by executing two-dimensional PIV on a plurality of the two-dimensional particle images, a three-dimensional velocity vector or a three-velocity component of the visualization fluid in the slice region is acquired. (S7, S8) to perform,
Collecting, integrating, or synthesizing information of the three-dimensional velocity vector or three-velocity component in each slice region to obtain a three-dimensional velocity vector or three-velocity component of the visualization fluid in the three-dimensional space (S11). A flow velocity measuring method characterized by the above is provided.
Preferably, in the step of obtaining the three-dimensional luminance information, a weighting factor for specifying the three-dimensional luminance information in the slice region by weighted accumulation is calculated and stored based on the pixels of the two-dimensional image. In the step of generating the two-dimensional particle image, the particle distribution in the slice region is projected onto the virtual projection plane according to the weighting factor.

  According to the above configuration of the present invention, the three-dimensional space in which the particle distribution is reconstructed is divided into slice regions, and the particle distribution in the slice region is extracted from the three-dimensional luminance information. The particle distribution in the slice region is projected onto a plurality of virtual projection planes, and a plurality of virtual two-dimensional particle images at two consecutive times are generated. Two-dimensional PIV is performed on a plurality of two-dimensional particle images, and two-dimensional movement vectors of the particles in the plurality of image planes obtained thereby are obtained. Based on the two-dimensional movement vectors thus obtained, three-dimensional A three-dimensional velocity vector or three velocity component of the visualization fluid in space is obtained. In other words, the arithmetic processing unit does not perform arithmetic processing on the three-dimensional voxel group luminance data, but only performs arithmetic processing on the two-dimensional pixel group luminance data. Time is reduced or shortened. Therefore, according to the flow velocity measuring method or the flow velocity measuring system having the above configuration, the analysis time of the arithmetic processing device can be shortened and the measurement can be speeded up.

  Further, according to the above configuration of the present invention, the two-dimensional particle image obtained by projecting the particle group in each slice region is a particle image that can be directly compared with a normal PIV particle image photographed with sheet light illumination. The validity of particle imaging by the imaging device can be evaluated, and the validity of reconstruction of the three-dimensional luminance information can be visually confirmed.

  Furthermore, according to the above configuration of the present invention, it is possible to arbitrarily select a line-of-sight direction capable of performing the stereo PIV analysis with the highest accuracy in the process of projecting the particle distribution of each slice region onto the virtual projection plane. Therefore, it is possible to achieve high measurement accuracy.

From another viewpoint, the present invention is arranged to image a visualization fluid visualized by a group of microparticles, and a plurality of imaging devices that capture particle images at two consecutive times separated by a minute time interval, and the imaging device The flow velocity of the visualization fluid having the arithmetic processing unit for reconstructing the particle distribution in the three-dimensional space based on the image data obtained by the above and calculating the three-dimensional velocity vector or the three velocity component of the visualization fluid in the three-dimensional space In the measurement system,
The arithmetic processing unit is configured to reconstruct the particle distribution at each time in the three-dimensional space based on the two-dimensional image data imaged by the imaging device and obtain three-dimensional luminance information at two consecutive times. 3D luminance information acquisition means (S3)
Setting a slice region of a predetermined thickness obtained by dividing the three-dimensional space, extracting a particle distribution inside the slice region from the three-dimensional luminance information, and projecting the particle distribution onto a plurality of virtual projection planes By means of two-dimensional particle image generation means (S4, S6) for generating a plurality of virtual two-dimensional particle images at two consecutive times,
A two-dimensional PIV is performed on the plurality of two-dimensional particle images, and a three-dimensional velocity vector or three velocities of the visualization fluid in the three-dimensional space is obtained based on the two-dimensional movement vectors of the particles in the plurality of image planes obtained by the two-dimensional PIV. Provided is a flow velocity measurement system characterized by having calculation means (S7, S8, S11) for calculating components.

The present invention is also arranged to image a visualization fluid visualized by a group of microparticles, and a plurality of imaging devices that capture particle images at two consecutive times separated by a minute time interval, and the imaging device In a flow measurement system for a visualization fluid having a processing device for reconstructing a particle distribution in a three-dimensional space based on image data and calculating a three-dimensional velocity vector or a three-velocity component of the visualization fluid in the three-dimensional space,
The arithmetic processing unit sets a slice region having a predetermined thickness obtained by dividing the three-dimensional space, and re-analyzes the particle distribution at each time in the slice region based on the two-dimensional image data captured by the imaging device. Three-dimensional luminance information acquisition means (S3 ′, S5 ′) constructed to obtain three-dimensional luminance information at two consecutive times,
Two-dimensional particle image generation means (S6) for generating a plurality of virtual two-dimensional particle images at two consecutive times in the slice region by projecting the particle distribution inside the slice region onto a plurality of virtual projection planes; ,
A two-dimensional PIV is performed on a plurality of the two-dimensional particle images, and a three-dimensional velocity vector or a three-velocity component of the visualization fluid in the slice region is obtained based on two-dimensional movement vectors of the particles in the plurality of image planes obtained by the two-dimensional PIV. First calculating means (S7, S8) for calculating
Second calculation means (S11) for collecting, integrating or synthesizing the information of the three-dimensional velocity vector or the three velocity components in each slice region to obtain the three-dimensional velocity vector or the three velocity components of the visualization fluid in the three-dimensional space. A flow velocity measurement system characterized by comprising:
Preferably, the three-dimensional luminance information acquisition means calculates and stores a weighting factor for specifying the three-dimensional luminance information in the slice region by weighted accumulation based on the pixels of the two-dimensional image, The two-dimensional particle image generation unit projects the particle distribution in the slice region onto the virtual projection plane according to the weighting factor.

  In the above configuration of the present invention, the reconstruction of the three-dimensional luminance information, the generation of a virtual two-dimensional particle image, the calculation of the two-dimensional PIV, the three-dimensional velocity vector, or the three-velocity component are executed in units of slice regions. The information of the three-dimensional velocity vector or the three velocity components in each slice region is collected, integrated, or synthesized to obtain the three-dimensional velocity vector or the three velocity components of the visualization fluid in the three-dimensional space. According to such a configuration, the storage device configuring the measurement system only needs to have a storage capacity for storing the three-dimensional luminance information of each slice region, and thus the storage capacity of the storage device can be reduced. That is, according to the above-described configuration of the present invention, not only the advantages of shortening the analysis time, visual confirmation of the validity of the reconstruction and increasing the accuracy of the measurement, but also the storage of the storage device constituting the measurement system. Since the capacity can be further reduced, the initial equipment cost of the measurement system can be further reduced, and the system configuration can be further simplified.

  According to the flow velocity measurement method and flow velocity measurement system of the present invention, the load on the arithmetic processing unit and the data analysis time for acquiring the three-dimensional velocity vector or the three velocity components of the visualization fluid by the tomographic PIV measurement method are reduced or shortened. be able to.

  Further, according to the flow velocity measuring method and flow velocity measuring system of the present invention in which reconstruction of three-dimensional luminance information, generation of a two-dimensional particle image, calculation of a two-dimensional PIV, a three-dimensional velocity vector, or a three-velocity component is executed in units of slice regions. For example, the load on the arithmetic processing unit and the data analysis time can be reduced or shortened, and the storage capacity of the storage device can be reduced.

FIG. 1 is a schematic perspective view schematically showing a configuration of a measurement unit of a flow velocity measurement system according to a preferred embodiment of the present invention. FIG. 2A is a perspective view showing the structure of the calibration plate and the support column arranged in the measurement channel in the initial setting of the measurement system, and FIG. 2B shows the pattern of the reference points of the calibration plate. It is a top view. 3A is a plan view of the calibration plate shown in FIG. 2, and FIG. 3B is a bottom view of the calibration plate. FIG. 4A is a particle image photographed at two consecutive times by a CCD camera, and FIG. 4B is an enlarged image of the particle image photographed by the CCD camera. FIG. 5 is an enlarged perspective view showing a photographing target area of the CCD camera. FIG. 6A is image data illustrating a two-dimensional particle image obtained by projecting the particle distribution in the slice region onto the virtual projection plane, and FIG. 6B is a plurality of two-dimensional particle images. It is a schematic perspective view which illustrates the three-dimensional velocity vector of the visualization fluid obtained based on this. FIG. 7 is a flowchart showing a flow velocity measuring method according to a preferred embodiment of the present invention. FIG. 8 is a flowchart showing another flow velocity measuring method according to a preferred embodiment of the present invention.

  According to a preferred embodiment of the present invention, the slice region is a space obtained by equally dividing the three-dimensional space. Preferably, the slice region is a space that traverses the flow path of the visualization fluid in parallel with the optical axis of the laser light irradiated to the visualization fluid.

  In one embodiment of the present invention, the virtual projection plane is a plane orthogonal to the optical axis of the imaging device.

  Preferably, the flow path of the visualization fluid has a circular flow path cross section, and a circular calibration plate disposed in the flow path is used to obtain a calibration image in order to obtain a relationship between image coordinates and physical coordinates. . The calibration plate has an orthogonal lattice array index disposed in the central circular region and an annular array index disposed circumferentially in the outer peripheral region. By arranging the indicators of the outer peripheral area in a pattern corresponding to the shape of the outer peripheral surface of the flow path in this way, the image distortion in the vicinity of the flow path wall is appropriately corrected to obtain the relationship between the image coordinates and the physical coordinates, Coordinate information optimal for the shape of the measurement region can be acquired efficiently.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic perspective view schematically showing a configuration of a measurement unit of a flow velocity measurement system according to a preferred embodiment of the present invention.

  A flow velocity measurement system according to the present invention is a tomographic stereo PIV system (hereinafter referred to as “TSPIV”) that efficiently and highly accurately measures a three-dimensional flow velocity distribution of fluid by fusing CT (Computed Tomography) technology and stereo PIV technology. System ")). The TSPIV system includes a cylindrical body 10 having a perfectly circular cross section that forms a visualization flow path of a visualization fluid (gas) P into which fine particles (tracer particles) are injected. The size of the fine particles is, for example, about 10 μm. The cylindrical body 10 has a tube wall 11 made of transparent resin or transparent glass, and the upper and lower portions of the cylindrical body 10 are connected to a supply path and a discharge path (not shown) for the fluid P.

  The TSPIV system includes a light source (not shown) including a laser head and an optical system device, an image processing device (not shown) including a storage device, an arithmetic processing device, an image display (display) device, and various input / output devices. Z). The band-shaped and three-dimensional laser light L irradiated by the light source is irradiated in a direction orthogonal to the central axis of the cylindrical body 10. In this example, the central axis of the cylindrical body 10 is oriented in the vertical direction, and the optical axis of the laser light L is oriented in the horizontal direction. The laser light L has a rectangular or rectangular cross section with a width W and a height H, the width W of the laser light L is larger than the inner diameter D of the cylindrical body 10, and the vertical flow path in the cylindrical body 10 is a laser. It is perpendicular to the optical axis of the light L and is included in the laser light L within the range of the height H. The height H of the laser light L is set to a predetermined dimension of about several mm to several cm, for example, a predetermined value within a range of 5 to 10 mm. The visualization fluid flows through the flow path in the cylindrical body 10 downward or upward (downward in this example).

  The CCD cameras 2 and 3 are disposed above the laser light L, and the CCD cameras 1 and 4 are disposed below the laser light L. The optical axes of the CCD cameras 1 to 4 are inclined at a predetermined angle with respect to the central axis of the cylindrical body 10, and the CCD cameras 1 to 4 photograph fine particles in the fluid P from four directions having different angles. Are positioned as follows.

  FIG. 2A is a perspective view illustrating the structure of the calibration plate 20 and the support column 21 disposed in the cylindrical body 10, and FIG. 2B is a plan view illustrating the index pattern of the calibration plate 20. FIG. 3A is a plan view of the calibration plate 20, and FIG. 3B is a bottom view of the calibration plate 20.

  The calibration plate 20 is for performing calibration of the CCD cameras 1 to 4 that specify in advance the relationship between the image coordinates of the CCD cameras 1 to 4 and the physical coordinates of the space in the flow path. The calibration plate 20 is inserted into the cylindrical body 10 after the positions of the CCD cameras 1 to 4 are fixed, and removed after the camera calibration operation is completed. FIG. 2A shows a state where the calibration plate 20 and the support column 21 are assembled. The calibration plate 20 and the column 21 are made of a metal member having a black surface, and the top of the column 21 is fitted into the notch 22 of the calibration plate 20 to support the calibration plate 20 horizontally.

  As shown in FIG. 2B, the calibration plate 20 has a configuration in which a white index (a reference point 23 shown in FIG. 3) is arranged at predetermined positions on a circular upper surface and a circular lower surface on a black background surface. The background color and the reference point color need only differ greatly in brightness, and therefore it is possible to arrange a black circular reference point on the white background. As shown in FIG. 3, the reference point 23 is arranged at the same upper and lower positions on each surface (upper surface and lower surface) of the calibration plate 20. The reference point 23 includes a reference point 23a of an orthogonal lattice arrangement disposed in the central circular region, and an annular array of reference points 23b disposed in the circumferential direction in the outer peripheral region. The reference points 23a and 23b are basically circular contour indicators having the same diameter, but the specific reference points 23c arranged in the central region to indicate the XY directions are more than the reference points 23a and 23b. Have a large diameter.

  By arranging the reference points 23b in the outer peripheral area in a pattern corresponding to the shape of the inner peripheral surface of the tube wall 11 in this way, image coordinates and physical properties are prevented so that an image transmitted through the tube wall 11 is not distorted. The relationship of coordinates (projection function) can be obtained appropriately.

  When the calibration plate 20 is used to obtain the relationship between the image coordinates and the physical coordinates and the initial setting of the TSPIV system is completed, the visualization fluid P containing fine particles is supplied into the cylindrical body 10 from the supply path (not shown). The visualization fluid P flows through the flow path in the cylindrical body 10 and flows out to the discharge path (not shown).

  Imaging by the CCD cameras 1 to 4 is simultaneously performed at two times (time t, t + Δt) separated by a minute time interval Δt. FIG. 4A is a particle image taken at time t and time t + Δt by the CCD cameras 1 to 4. FIG. 4B is an enlarged image of the particle image taken at time t by the CCD camera 1. FIG. 5 is an enlarged perspective view showing the photographing target area α of the CCD cameras 1 to 4.

  The group of fine particles moving through the flow path in the cylindrical body 10 reflects the laser light L in the imaging target region α and is captured by the CCD cameras 1 to 4 as particle images as shown in FIG. By applying MART (Multiplicative Algebraic Reconstruction Technique) to the particle image, it is possible to reconstruct the particle distribution in the three-dimensional space at different times (t and t + Δt). From the reconstructed three-dimensional luminance information, a three-dimensional array using the voxel group (three-dimensional) as element data is obtained. In this reconstruction process, the luminance of each pixel of the particle image (two-dimensional) is represented by weighted addition of the luminance of the voxel group that is the source of the luminance, and a weighting coefficient is calculated.

  For the reconstructed three-dimensional luminance information at time t and time t + Δt, the particle distribution of the slice region β having a predetermined thickness defined at an arbitrary position is extracted. FIG. 5 illustrates a slice region β having a thickness h. The slice area β is a circular flat space obtained by equally dividing a three-dimensional space (that is, the imaging target area α) in the cylindrical body 10 irradiated with the laser light L in parallel with the optical axis of the laser light L. It traverses the flow path of the visualization fluid parallel to the optical axis of the light L. The thickness h of the slice region β is set to, for example, a predetermined value within the range of the height H × 1/5 to the height H × 1/10 of the laser light L, and each slice region β It is set by dividing evenly over the entire height H.

  The particle distribution in the slice region β is projected onto a plurality of virtual projection planes defined in an arbitrary plurality of line-of-sight directions by applying the above-described calculation processing using a weighting coefficient, and as a result, continuous 2 optimal for stereo PIV is obtained. A plurality of virtual particle images at time (t and t + Δt) are generated. In this example, the virtual projection plane is a plane orthogonal to the optical axes of the CCD cameras 1 to 4. FIG. 6A is image data illustrating a virtual particle image projected on the virtual projection plane.

  Two-dimensional PIV is performed on the virtual projection image generated as the particle image of the particle group located in each slice region β, and the two-dimensional movement vector of the particle in each image plane obtained thereby, and the slice region β The least square method is applied to the relational expression established between the three-dimensional velocity vector in, the separately generated camera parameter and the two-time time interval Δt, and the three-dimensional velocity vector in the slice region β is calculated. By executing such a process for all slice regions β, the three-dimensional velocity vector of the visualization fluid P in the target physical space (imaging target region α) can be acquired. FIG. 6B is a schematic perspective view illustrating a three-dimensional velocity vector in the imaging target region α obtained by the above process.

  As described above, according to such a TSPIV system, three-dimensional voxel group data using voxel groups (three-dimensional) as element data is converted into a plurality of two-dimensional particle images to which two-dimensional PIV can be applied. The That is, in the TSPIV system, image data captured by the CCD cameras 1 to 4 is not processed as three-dimensional voxel group data, but two-dimensional virtual particle images to which two-dimensional PIV can be applied. The two-dimensional PIV is executed on a plurality of virtual particle images (projected images) at two consecutive times (t and t + Δt), thereby obtaining a motion vector (two-dimensional) of the particle image. As described above, the application of the least square method regarding the relational expression established between the movement vector, the separately generated camera parameter, the time interval Δt of two times, and the three-dimensional velocity vector of the particle group allows the particle group 3 A dimensional velocity vector is obtained. By considering this as a flow velocity distribution, a three-dimensional flow velocity distribution is obtained.

  According to such a TSPIV system, the data to be calculated by the arithmetic processing unit is not the three-dimensional voxel group luminance data but the two-dimensional pixel group luminance data. Data processing time is greatly reduced or shortened (it is reduced or shortened by about one to two digits). For this reason, it is possible to shorten the analysis time of the arithmetic processing unit and speed up the measurement.

  In addition, since the particle image obtained by projecting the particle group in each slice region β is a particle image that can be directly compared with a normal PIV particle image captured by sheet light illumination, the validity of capturing the particle image is evaluated. And the validity of the reconstruction can be confirmed visually.

  Furthermore, in the projection of the particle group in each slice region β, it is possible to select a line-of-sight direction capable of performing the stereo PIV analysis with the highest accuracy, so that it is possible to achieve high measurement accuracy.

  Next, the flow velocity measuring method of the present invention will be described based on a flowchart showing the image analysis process of the TSPIV system.

  FIG. 7 is a flowchart showing a flow velocity measuring method according to a preferred embodiment of the present invention.

  As shown in FIG. 7, the CCD cameras 1 to 4 simultaneously photograph particles in the photographing target region α at two different times (time t, t + Δt) (S (step) 1). This photographing is photographing in three directions and two consecutive times of particles in the fluid by three or more imaging devices.

For each particle image captured by the CCD cameras 1 to 4 at each photographing time (time t, t + Δt), the luminance value of each pixel is expressed by weighted accumulation of the luminance of the particle group in the three-dimensional space that is the source. The weighting coefficient w _ij of the following formula is calculated (S2).

  In the above equation, I (xi, yi) represents the luminance of the pixel of each coordinate (xi, yi) in the two-dimensional coordinates (xi, yi) of the two-dimensional image captured by the CCD cameras 1 to 4. I is a pixel number in each two-dimensional image. E (Xj, Xj, Xj) represents the luminance of a voxel having three-dimensional coordinates (Xj, Xj, Xj), where j is a voxel number. Note that voxel is a volume element, and pixel is a normal lattice unit representing two-dimensional image data, whereas voxel is a normal lattice unit in a three-dimensional space. The fact that the luminance E (Xj, Xj, Xj) shows a relatively high value means that there is a relatively large amount of particles that reflect the laser beam at the j-th voxel j having the coordinates (Xj, Xj, Xj). It means to do.

At each photographing time (time t, t + Δt), MART (Multiplicative Algebraic Reconstruction Technique) is applied to the particle images of all the CCD cameras 1 to 4 using a weighting coefficient w _ij, and the three-dimensional luminance distribution information of the particles at each time Is reconstructed (S3).

  The imaging target area α is equally divided into slice areas β having a predetermined thickness perpendicular to an arbitrary axial direction (in this example, the central axis of the flow path), and reconstructed three-dimensionally at two times (time t, t + Δt). The luminance distribution is divided into a three-dimensional luminance distribution of the slice region β (S4).

  First, a specific slice region β is focused (S5), and the luminance I (xi, yi) of the pixel and the luminance E (Xj, Xj, voxel) of the pixel based on the three-dimensional luminance distribution information of the particles included in the slice region β. Xj) is used to generate a virtual two-dimensional image obtained by projecting the images of the CCD cameras 1 to 4 on the virtual projection plane (S6).

  The two-dimensional PIV is applied to the virtual two-dimensional image at two times (time t, t + Δt) generated in this way, and the two-dimensional movement vector of the particle on the virtual projection plane of each CCD camera 1 to 4 is calculated ( S7).

  Next, the least square method is applied to the relational expression established between the two-dimensional movement vector, the three-dimensional velocity vector of the particle, the separately generated camera parameter, and the time interval Δt of two times, and the three-dimensional particle A velocity vector is calculated (S8). The calculation of the three-dimensional velocity vector is executed for all slice regions β of the imaging target region α (S9: S10).

  After such image analysis and calculation processing are completed for all slice regions β, the three-dimensional velocity vectors calculated for each slice region β are integrated to obtain a particle velocity vector in the imaging target space α (S11). . If desired, a series of flow velocity measurement processes from photographing (S1) to obtaining the particle velocity vector (S11) of the CCD cameras 1 to 4 are repeatedly executed (S12, S13). Acquired serially. A series of flow velocity measurement processes ends when a prescribed number of two-time particle velocity data is obtained (S12).

  FIG. 8 is a flowchart showing another flow velocity measuring method according to a preferred embodiment of the present invention.

  The flow velocity measurement method shown in FIG. 7 reconstructs the particle distribution of the imaging target region α, obtains the three-dimensional luminance information of the entire region α, extracts the particle distribution in the slice region β from the three-dimensional luminance information, Although the virtual two-dimensional particle image is generated and the two-dimensional PIV is executed, only the particle distribution of each slice region β is reconstructed by using the flow velocity measurement method shown in FIG. After obtaining the three-dimensional luminance information, the flow velocity measurement method may be configured to generate a virtual two-dimensional particle image and execute the two-dimensional PIV.

As shown in FIG. 8, the slice region β is set based on the particle images at the respective photographing times (time t, t + Δt) obtained by photographing the particles in the photographing target region α by the CCD cameras 1 to 4 (S1). (S2 '). The specific slice region β is focused (S3 ′), the weighting coefficient w _ij (the above formula 1) is calculated and stored for the particle group of the specific slice region β (S4 ′), and each imaging time ( At time t, t + Δt), MART (Multiplicative Algebraic Reconstruction Technique) is applied from the particle images of all the CCD cameras 1 to 4 using the weighting coefficient w _ij, and the three-dimensional luminance distribution of the particles in the slice region β at each time Information is reconstructed and stored (S5 ′).

Based on the three-dimensional luminance distribution information of the particles included in the slice region β, the above-described virtual two-dimensional image is generated according to the weighting coefficient w _ij (S6), and the virtual time 2 thus obtained (time t, t + Δt) is obtained. A two-dimensional PIV is applied to the two-dimensional image, and a two-dimensional movement vector of particles on the virtual projection planes of the CCD cameras 1 to 4 is calculated (S7).

Next, the least square method is applied to the relational expression established between the two-dimensional movement vector, the three-dimensional velocity vector of the particle, the separately generated camera parameter, and the time interval Δt of two times, and the three-dimensional particle A velocity vector is calculated (S8). The process of calculating the weighting coefficient w _ij for the particle group in the slice region β (S4 ′) to calculating the three-dimensional velocity vector (S8) is performed for all slice regions β of the imaging target region α (S9: S10). .

  After such image analysis and calculation processing are completed for all slice regions β, the three-dimensional velocity vectors calculated for each slice region β are integrated, and particle velocity vectors in the entire imaging target space α are obtained (S11). ). If desired, a series of flow velocity measurement processes from photographing (S1) to obtaining the particle velocity vector (S11) of the CCD cameras 1 to 4 are repeatedly executed (S12, S13). Acquired serially. A series of flow velocity measurement processes ends when a prescribed number of two-time particle velocity data is obtained (S12).

  According to such a flow velocity measuring method, similar to the above-described embodiment, advantages such as shortening of the analysis time of the arithmetic processing device and high speed of measurement can be obtained. Moreover, in the above flow velocity measurement method, since reconstruction of the three-dimensional luminance information is executed in units of slice areas, the amount of information or the number of data of the three-dimensional luminance information to be stored in the image analysis process is reduced. The storage capacity of the device can be reduced.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications or changes can be made within the scope of the present invention described in the claims. Is possible.

  For example, in the above-described embodiment, the imaging target space is a cylindrical flow path having a perfect circular cross section, but may be designed as a flow path having various cross sectional forms such as a polygonal cross section, an elliptical cross section, and a triangular cross section. .

  In the above embodiment, four imaging devices (CCD cameras) are used for particle imaging. However, three or five or more imaging devices may be used for particle imaging.

  INDUSTRIAL APPLICABILITY The present invention is applied to a flow velocity measurement method and a flow velocity measurement system in which a flow field of a visualized fluid obtained by visualizing a fluid with a group of fine particles is photographed by an imaging device and a three-dimensional velocity vector or three velocity component of the visualized fluid is measured. The In particular, according to the present invention, a plurality of imaging devices that image visualization fluid visualized by a group of microparticles are used to capture two continuous time particle images separated by a minute time interval, and an image of a particle image obtained by imaging. The method is applied to a flow velocity measurement method and a flow velocity measurement system for a visualization fluid that reconstructs the particle distribution in the three-dimensional space based on the data and measures the three-dimensional velocity vector or the three velocity component of the visualization fluid in the three-dimensional space. The flow velocity measurement method and flow velocity measurement system of the present invention are a tomographic stereo PIV measurement method obtained by improving the tomographic PIV measurement method. According to the tomographic stereo PIV measurement method of the present invention, it is possible to reduce or shorten the load of the arithmetic processing unit and the data analysis time for acquiring the three-dimensional velocity vector or three-speed component of the visualization fluid. The practical effect of the invention is remarkable.

1-4 CCD camera 10 cylindrical body 11 tube wall 20 calibration plate P visualization fluid L laser light α imaging target region β slice region

The present invention also captures two continuous time particle images separated by a minute time interval by a plurality of imaging devices that image visualization fluid visualized by a group of microparticles, and converts the image data of the particle images obtained by the imaging into image data. In the flow velocity measurement method of the visualization fluid, the particle distribution in the three-dimensional space is reconstructed based on the three-dimensional velocity vector or the three-velocity component of the visualization fluid in the three-dimensional space.
A slice region having a predetermined thickness formed by dividing the three-dimensional space is set, and the particle distribution at each time in the slice region is reconstructed based on the two-dimensional image data imaged by the imaging device, and the slice region Obtaining three-dimensional luminance information at two consecutive times (S3 ', S5'),
A step of generating a plurality of virtual two-dimensional particle images at two consecutive times by projecting the particle distribution inside the slice region on a plurality of virtual projection planes based on the three-dimensional luminance information (S6);
Based on two-dimensional movement vectors of particles in a plurality of image planes obtained by executing two-dimensional PIV on a plurality of the two-dimensional particle images, a three-dimensional velocity vector or a three-velocity component of the visualization fluid in the slice region is acquired. (S7, S8) to perform,
Collecting, integrating, or synthesizing information of the three-dimensional velocity vector or three-velocity component in each slice region to obtain a three-dimensional velocity vector or three-velocity component of the visualization fluid in the three-dimensional space (S11). A flow velocity measuring method characterized by the above is provided.
Preferably, in the step of obtaining the 3-dimensional luminance information, weighting factors for the three-dimensional luminance information specific of said slice region based on the pixel of the two-dimensional image is stored is calculated and the In the step of generating a two-dimensional particle image, the particle distribution in the slice region is projected onto the virtual projection plane according to the weighting factor.

The present invention is also arranged to image a visualization fluid visualized by a group of microparticles, and a plurality of imaging devices that capture particle images at two consecutive times separated by a minute time interval, and the imaging device In a flow measurement system for a visualization fluid having a processing device for reconstructing a particle distribution in a three-dimensional space based on image data and calculating a three-dimensional velocity vector or a three-velocity component of the visualization fluid in the three-dimensional space,
The arithmetic processing unit sets a slice region having a predetermined thickness obtained by dividing the three-dimensional space, and re-analyzes the particle distribution at each time in the slice region based on the two-dimensional image data captured by the imaging device. Three-dimensional luminance information acquisition means (S3 ′, S5 ′) constructed to obtain three-dimensional luminance information at two consecutive times,
Two-dimensional particle image generation means (S6) for generating a plurality of virtual two-dimensional particle images at two consecutive times in the slice region by projecting the particle distribution inside the slice region onto a plurality of virtual projection planes; ,
A two-dimensional PIV is performed on a plurality of the two-dimensional particle images, and a three-dimensional velocity vector or a three-velocity component of the visualization fluid in the slice region is obtained based on two-dimensional movement vectors of the particles in the plurality of image planes obtained by the two-dimensional PIV. First calculating means (S7, S8) for calculating
Second calculation means (S11) for collecting, integrating or synthesizing the information of the three-dimensional velocity vector or the three velocity components in each slice region to obtain the three-dimensional velocity vector or the three velocity components of the visualization fluid in the three-dimensional space. A flow velocity measurement system characterized by comprising:
Preferably, the 3-dimensional luminance information obtaining means, the said 3-dimensional luminance information of the slice area is calculated and store the weighting coefficients for particular based on the pixel of the 2-dimensional image, the two-dimensional particles The image generation means projects the particle distribution in the slice area onto the virtual projection plane according to the weighting factor.

Claims (13)

A three-dimensional space based on image data of particle images obtained by imaging, by capturing a plurality of continuous two-time particle images with a minute time interval by a plurality of imaging devices that image visualization fluid visualized by a group of microparticles. In the flow velocity measurement method of the visualization fluid, the particle distribution in the inside is reconstructed, and the three-dimensional velocity vector or the three-velocity component of the visualization fluid in the three-dimensional space is measured.
Reconstructing the particle distribution at each time in the three-dimensional space based on the two-dimensional image data imaged by the imaging device to obtain three-dimensional luminance information at two consecutive times;
Setting a slice region of a predetermined thickness obtained by dividing the three-dimensional space, extracting a particle distribution inside the slice region from the three-dimensional luminance information, and projecting the particle distribution onto a plurality of virtual projection planes A step of generating a plurality of virtual two-dimensional particle images at two consecutive times,
Based on a two-dimensional movement vector of particles in a plurality of image planes obtained by executing a two-dimensional PIV on the plurality of two-dimensional particle images, a three-dimensional velocity vector or a three-velocity component of the visualization fluid in the three-dimensional space is obtained. A flow rate measuring method comprising: a step of acquiring. A three-dimensional space based on image data of particle images obtained by imaging, by capturing a plurality of continuous two-time particle images with a minute time interval by a plurality of imaging devices that image visualization fluid visualized by a group of microparticles. In the flow velocity measurement method of the visualization fluid, the particle distribution in the inside is reconstructed, and the three-dimensional velocity vector or the three-velocity component of the visualization fluid in the three-dimensional space is measured.
A slice region having a predetermined thickness formed by dividing the three-dimensional space is set, and the particle distribution at each time in the slice region is reconstructed based on the two-dimensional image data imaged by the imaging device, and the slice region Obtaining three-dimensional luminance information at two consecutive times
Generating a plurality of virtual two-dimensional particle images at two consecutive times by projecting a particle distribution inside the slice region on a plurality of virtual projection planes based on the three-dimensional luminance information;
Based on two-dimensional movement vectors of particles in a plurality of image planes obtained by executing two-dimensional PIV on a plurality of the two-dimensional particle images, a three-dimensional velocity vector or a three-velocity component of the visualization fluid in the slice region is acquired. And a process of
Collecting, integrating, or synthesizing information on the three-dimensional velocity vector or three-velocity component in each slice region to obtain a three-dimensional velocity vector or three-velocity component of the visualization fluid in the three-dimensional space. Flow velocity measurement method.   The flow velocity measurement method according to claim 1, wherein the slice region is a space obtained by equally dividing the three-dimensional space.   The said slice area | region is the space which crosses the flow path of the said visualization fluid in parallel with the optical axis of the laser beam irradiated to the said visualization fluid, The any one of Claim 1 thru | or 3 characterized by the above-mentioned. Flow velocity measurement method.   5. The flow velocity measurement method according to claim 1, wherein the virtual projection plane is a plane orthogonal to the optical axis of the imaging device. In the step of obtaining the three-dimensional luminance information, calculating and storing a weighting factor for specifying the three-dimensional luminance information in the slice region by weighted accumulation based on the pixels of the two-dimensional image;
3. The flow velocity measurement method according to claim 2, wherein, in the step of generating the two-dimensional particle image, the particle distribution in the slice region is projected onto the virtual projection plane according to the weighting factor. Based on image data obtained by a plurality of imaging devices that are arranged to image a visualization fluid visualized by a group of microparticles and that image particle images at two consecutive times separated by a micro time interval, and the imaging device In the flow velocity measurement system for a visualization fluid, the particle distribution in the three-dimensional space is reconstructed, and the visualization fluid flow velocity measurement system includes an arithmetic processing unit that calculates a three-dimensional velocity vector or a three-velocity component of the visualization fluid in the three-dimensional space.
The arithmetic processing unit is configured to reconstruct the particle distribution at each time in the three-dimensional space based on the two-dimensional image data imaged by the imaging device and obtain three-dimensional luminance information at two consecutive times. Three-dimensional luminance information acquisition means;
Setting a slice region of a predetermined thickness obtained by dividing the three-dimensional space, extracting a particle distribution inside the slice region from the three-dimensional luminance information, and projecting the particle distribution onto a plurality of virtual projection planes A two-dimensional particle image generating means for generating a plurality of virtual two-dimensional particle images at two consecutive times,
A two-dimensional PIV is performed on the plurality of two-dimensional particle images, and a three-dimensional velocity vector or three velocities of the visualization fluid in the three-dimensional space is obtained based on the two-dimensional movement vectors of the particles in the plurality of image planes obtained by the two-dimensional PIV. A flow velocity measurement system comprising a calculation means for calculating a component. Based on image data obtained by a plurality of imaging devices that are arranged to image a visualization fluid visualized by a group of microparticles and that image particle images at two consecutive times separated by a micro time interval, and the imaging device In the flow velocity measurement system for a visualization fluid, the particle distribution in the three-dimensional space is reconstructed, and the visualization fluid flow velocity measurement system includes an arithmetic processing unit that calculates a three-dimensional velocity vector or a three-velocity component of the visualization fluid in the three-dimensional space.
The arithmetic processing unit sets a slice region having a predetermined thickness obtained by dividing the three-dimensional space, and re-analyzes the particle distribution at each time in the slice region based on the two-dimensional image data captured by the imaging device. Three-dimensional luminance information acquisition means constructed and constructed to obtain three-dimensional luminance information at two consecutive times;
Two-dimensional particle image generation means for generating a plurality of virtual two-dimensional particle images at two consecutive times in the slice region by projecting the particle distribution inside the slice region onto a plurality of virtual projection planes;
A two-dimensional PIV is performed on a plurality of the two-dimensional particle images, and a three-dimensional velocity vector or a three-velocity component of the visualization fluid in the slice region is obtained based on two-dimensional movement vectors of the particles in the plurality of image planes obtained by the two-dimensional PIV. First computing means for computing
Second calculation means for collecting, integrating or synthesizing the information of the three-dimensional velocity vector or the three velocity components in each slice region to obtain the three-dimensional velocity vector or the three velocity components of the visualization fluid in the three-dimensional space; A flow velocity measurement system characterized by this.   The flow velocity measurement system according to claim 7 or 8, wherein the slice region is a space obtained by equally dividing the three-dimensional space.   The said slice area | region is the space which crosses the flow path of the said visualization fluid in parallel with the optical axis of the laser beam irradiated to the said visualization fluid, The any one of Claim 7 thru | or 9 characterized by the above-mentioned. Flow velocity measurement system.   The flow velocity measurement system according to claim 7, wherein the virtual projection plane is a plane orthogonal to the optical axis of the imaging device. The three-dimensional luminance information acquisition means calculates and stores a weighting factor for specifying the three-dimensional luminance information in the slice region by weighted accumulation based on the pixels of the two-dimensional image.
9. The flow velocity measurement system according to claim 8, wherein the two-dimensional particle image generation unit projects a particle distribution in the slice region onto the virtual projection plane according to the weighting factor.   The flow path of the visualization fluid has a circular flow path cross section, and a circular calibration plate disposed in the flow path is used to obtain a calibration image in order to obtain a relationship between image coordinates and physical coordinates, 7. The calibration plate according to claim 1, wherein the calibration plate has an index of an orthogonal lattice array disposed in a central circular region and an index of an annular array disposed in a circumferential direction in an outer peripheral region. The flow velocity measurement method according to item 1.

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