JPH0682332A - Visualizing method and tracking method for minute tracer particle - Google Patents

Abstract

PURPOSE:To visualize minute tracer particles excellently and to obtain the physical quantity of a flowing place accurately and quantitatively even if a flow speed is very high. CONSTITUTION:An irradiation time dt1 with laser light in the first field 1 is set long. Irradiation times dt2-dt4 in the second field 2 are set shorter than the irradiation time dt1 in the first field. Even if the size of the tracer particle, whose image is to be picked up, is minute, the flowing track of the minute tracer particle is formed on the image of the first field. The instantaneous image of the tracer particle is obtained on the second field. The fact that the tracer-particle images, which are picked up at a first time T1, become two or more and four or less is utilized. Thus, the position of the starting point is positively detected even if the size of the tracer particle is minute.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for visualizing micro tracer particles and a method for tracking the same, and more particularly to a method for visualizing micro tracer particles and a method for tracking the micro tracer particles at high speed.

[0002]

2. Description of the Related Art As is well known, attempts to grasp a flow by a flow field visualization method have been made for a long time.
The tuft method and the direct injection method are well known.

Among these methods, the wall surface tracing method is a method in which oil or the like is applied to the surface of an object and the flow state, direction, speed, etc. are obtained from the streak pattern caused by the flow. Also,
The tuft method is a method in which a large number of threads are stretched on the surface of an object and the flow is measured from the degree of flutter. Further, the direct injection method involves placing a dye in the stream and visualizing the dye trail.

The above-mentioned conventional visualization method is as follows.
There was a problem as described below. That is, it is difficult to measure the flow in the space away from the surface of the object by the wall tracing method. Further, the tuft method has a problem that it is difficult to measure an arbitrary cross section. Further, the above direct injection method has a problem in that the velocity of the dye on the trace can be grasped, but the entire flow region cannot be visualized at one time.

By the way, in recent years, visualization of the entire flow region at once and calculation of physical quantities such as flow velocity and flow function,
The interest in calculating the temporal change of physical quantity over the flow region is extremely strong. In addition, interest in visualizing an arbitrary cross section in the flow region, and visualization of not only the velocity of water alone but also the velocity of bubbles in water, for example, has become remarkably strong.

[0006] As an attempt to enable such visualization, the paper "The Japan Society of Mechanical Engineers (B), Vol. 55, 50"
No. 9 (1989-1), pages 107 to 114 have been proposed. In this method, tracer particles are mixed in a flow field, and the tracer particles are irradiated with continuous light or strobe light to image-process the trace.

In image processing, for example, an image is input from a television camera, its frame information is converted into field information, and field information for four consecutive times is subjected to image processing (only one of even or odd fields). , Track the trajectories of individual particles. Then, the flow field is visualized from the traces of the individual tracer particles to obtain various physical quantities.

[0008]

In the method described in the above-mentioned paper, it is necessary to increase the distance between the camera and the subject when the flow velocity of the fluid is high. As a result, there is a problem that an error occurs in the calculation of the center of gravity of particles during image processing.

Further, in the above method, the frame is formed from two field images, but there is a problem that the tracer particle image cannot be detected with small tracer particles. That is, when the tracer particle image in the television space is 1 pixel or less, there is a problem that the tracer particle image itself cannot be measured.

Further, in the case of the conventional tracer particle tracking method, it was premised that the fluid did not behave in a complicated manner for continuous 3/60 seconds. However, the fluid may behave in a complicated manner when, for example, an obstacle is present.

When following a flow path having a complicated flow as described above, it is possible to follow the flow path if the flow velocity is slow. However, if the flow velocity is high, the physical quantity of the flow field can be obtained accurately and quantitatively. There was a problem that I could not do it. In view of the above problems, the present invention makes it possible to satisfactorily visualize fine tracer particles and to accurately and quantitatively determine a physical quantity of a flow field even when the flow velocity is very high. To aim.

[0012]

A method for visualizing minute tracer particles according to the present invention comprises mixing tracer particles having a predetermined particle diameter into a fluid and spreading laser light spread in a sheet form in the same frame in a television camera signal. 1 in the first field and 2 to 6 in the second field are intermittently irradiated into the fluid, and scattered light or fluorescence of the tracer particles due to the irradiation of the laser light is recorded in the frame accumulation system. In a method of visualizing tracer particles which is imaged by a television camera, a laser beam irradiation time in the first field is set to be long to form a trace of tracer particles on an image, and in the second field. Irradiation time is set shorter than the irradiation time in the first field, and an instantaneous particle image is obtained in the second field. Unishi to have.

Further, the tracer particle tracing method of the present invention is such that tracer particles having a particle diameter of 2 mm or less and 1 μm or more are mixed in a fluid, and a laser beam spread in a sheet shape is used in the first field of a television camera signal. Once, and in the second field, two or more but six or less are intermittently irradiated into the fluid, and the scattered light or fluorescence of the tracer particles by the irradiation of the laser light is framed. The second process of capturing an image with a storage-type television camera and the first of the previous frames of the outputs of the television camera
The output of the field and the output of the second field of the previous frame are used as the image information of the first field of the previous frame on the recording, and the output of the second field of the previous frame and the output of the first field of the subsequent frame are set. A third process of performing frame accumulation of light such as image information of the second field of the previous frame on recording and recording on a recording medium;
Using one frame image obtained by the third process and the image of the first field thereof, all tracer particles existing in the image of the first field are set as candidates for the starting point tracer particles, and the frame Fourth processing of setting a search area of a predetermined size centered on the tracer particle as a starting point candidate in the image of the first field on the image, and detecting the number of tracer particles existing in each of the search areas If there are 2 or more and 4 or less tracer particles, the fifth process of determining the tracer particles as tracer particles imaged by the laser beam irradiated at the first time, and the irradiation at the first time are performed. Tracer particles imaged with laser light are erased from the frame image, and imaged with laser light emitted at the first time. The sixth processing of registering the center of gravity of the tracer particles relating to the search area in which the tracer particles are detected as the starting point position of the tracer particles, and the second time to the fourth processing with the registered tracer particle position as the starting point. The seventh process of tracing the position of the tracer particle at the time on the frame image and determining the path of the same particle, and the tracer particle position at the second time and the fourth time detected by the seventh process. And the eighth process of calculating the velocity vector based on the time interval between these tracer particle positions.

[0014]

In the method for visualizing minute tracer particles of the present invention, tracer particles having a predetermined particle size are mixed in the fluid, and the laser light spread in a sheet shape is applied to the first field of the same frame in the television camera signal. One and two or more but six or less in the second field are intermittently irradiated into the fluid, and the scattered light or fluorescence of the tracer particles due to the irradiation of the laser light is imaged by a frame accumulation type television camera. In this case, the irradiation time of the laser light in the first field is set to be long and
The irradiation time in the field is set shorter than the irradiation time in the first field so that traces of the tracer particles can be formed on the image of the first field even if the size of the tracer particles is minute. Together with the second
In the field, an instantaneous tracer particle image is obtained so that the tracer particles imaged at time 1 can be easily and reliably imaged.

Further, in the tracer particle tracking method of the present invention, the tracer particle image taken at the first time is imaged at 2 or more and 4 or less, thereby utilizing the above tracer particle images. Even if the size is very small, the starting point position can be surely specified.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for visualizing micro tracer particles and a method for tracking the same according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an example of the illumination code of the intermittent irradiation timing LLS of the laser light sheet.

As is apparent from FIG. 1, in this embodiment, the instantaneous illumination is performed once in the latter half of the first field and three times in the first half of the second field. The irradiation time T ₁ and irradiation time dt ₁ of the laser light sheet LLS can be controlled in units of 1H (63.56 μs) according to the flow velocity. Moreover, the number of irradiations can be appropriately selected.

The television camera adopts the frame integration method as shown in FIG. That is, the light from the flow field is accumulated in the first field photosensor for 1/30 seconds from the start of the first field to the end of the second field. Further, for the element of the second field, light is accumulated for 1/30 seconds from the start of the second field to the end of the first field of the next frame.

Therefore, using the above-mentioned illumination code, the tracer particle images illuminated at times T ₁ and T ₅ are:
It is recorded only on the photo sensor of the first field. On the other hand, the tracer particle images illuminated at the times T ₂ , T ₃ , and T ₄ are stored in the photosensors of both fields because the time of frame integration overlaps.

In this embodiment, the representative position of each tracer particle is defined as the center of gravity of the particle image. Further, the velocity is calculated by using the position of the center of gravity of the particle image from time T ₂ to time T ₄ when the position of the center of gravity is highly accurate. Irradiation of the laser light sheet LLS based on the illumination code is carried out in successive television frames. The output of this television camera is transferred to and recorded in a recording device as an NTSC standard composite signal.

FIG. 2 shows a visualization system including an optical system, an image input / recording device and their control devices. In this embodiment, the laser light source 1 is a 4 W argon laser. The laser light passes through the acousto-optic cell (AOM) 2, and the primary scattered light of the laser scattered by the Doppler effect with the plane wave of the ultrasonic wave therein is guided to the optical fiber 4 via the slit 3. That is, by performing on / off control of the acousto-optic cell 2, it is possible to perform intermittent pulse illumination on the flow field within a short time.

The laser light emitted from the tip of the optical fiber 4 is formed as a laser light sheet LLS having a thickness of several mm by the two cylindrical lenses 5. The acousto-optic cell 2 and the TV camera 6 (CCD camera) are connected to the external control device 7
To control the vertical / horizontal synchronization (VD /
The irradiation timing of the laser light sheet LLS with respect to (HD) is set. In addition, the recording / playback device 8 (for example, S
The operation timing of the VHS system recording / reproducing device is also controlled by the synchronization signal Sync provided from the external control device 7.

By the way, in the speed measurement of the tracer particle image, the size of the tracer particle may be equal to or smaller than the spatial resolution of the image on the image depending on the setting of the experimental conditions.

[0024] In such conditions, the lighting code laser light sheet LLS is the irradiation time dt ₁ set slightly longer in time T _1, thereby to form a flow trace of tracer particles on the image. On the other hand, at the times T ₂ , T ₃ and T ₄ , the irradiation time dt is set short so that an instantaneous particle image can be obtained. In this lighting code, the above lighting is repeated at intervals of one frame. That is, irradiation from time T ₅ is performed in the same manner as in the third frame to the first frame.

FIG. 3 shows a frame image when tracer particles having a spatial resolution similar to that of a television camera are traced by the above illumination code, and two temporally continuous field images after field separation / interpolation. It is shown schematically. These images have the following features. That is, (1) the position of the tracer particles obtained at time T ₁ is detected only by the photosensor of the first field, and therefore, the position of the tracer particle exists only in the image of the first field and does not exist on the scanning line of the second field. .

(2) The positions of the tracer particles at times T _{2 to} T ₄ can be detected by the photosensor in either the first field or the second field by frame integration. The accuracy of position measurement of these particles is determined only by the image resolution of the visualization space.

Next, one embodiment of the tracer particle tracking method of this embodiment will be described with reference to FIG. 4 schematically showing the tracer particle tracking method and the flow chart of FIG. 5 showing the tracking operation. . Here, an example is shown in which tracer particles having a size of 1 pixel are traced using one frame image G and the interpolation image G1 of the first field thereof. In the following description, the tracer particles obtained in the processed image G of FIG. 4A will be referred to as a, b, c, d, and e, and the processed image G of the first field of FIG.
Tracer particles m, n, and o obtained from No. 1 are used. The tracer particle tracking algorithm is shown below.

As shown in FIG. 5, first, at step P1, all tracer particles (m,
n, o) are candidates for the starting point tracer particle. Next, proceeding to step P2, a search area having a radius of 2 pixels centered on the tracer particle (m, n, o) of the image G1 is set on the image G. However, the set position of the tracer particle m is the gravity center position mg of the trail.

After setting the search areas in this way, the process proceeds to step P3 to detect whether or not there are tracer particles in each search area. Then, when only one tracer particle exists in this region, it is determined that the tracer particle is not exposed at time T ₁ .

On the other hand, when there are 2 or more and 4 or less tracer particles (if there are 2 to 4 pixels having a certain threshold value or more), the tracer particles exposed at the time T ₁ during the irradiation time dt. Is determined. This determination condition is based on the fact that the tracer particle image having a pixel resolution has a trace with a maximum width of 2 pixels. For example, in the image G of FIG. 4, two tracer particles a and b are present in the area of √2 pixels from the mg position. However, since only the particles of c and e exist in the tracer particles (n, o), respectively, it is determined that the particles irradiated by the image G at the time T ₁ are a and b.

Next, in step P5, the particles a and b are deleted from the image G, and the mg position of the image G1 is registered as the starting point position of the tracer particles. Then, when the registration of the start point position is completed, the process proceeds to step P6, and the particles of time T _{2 to} T ₄ are traced on the image G with mg as the start point to determine the route of the same particle.

Next, in step P7, the velocity vector is calculated. This velocity vector is calculated at time T ₂ and T
₄ tracer particle positions and their time intervals dT (= T
_4- T ₂ ) and calculated.

FIG. 6 is a flowchart for explaining an algorithm of an example of tracer particle tracking. Also,
FIG. 7 is an explanatory diagram schematically showing an algorithm for tracing tracer particles. As shown in FIG. 6, first, step P1
In, processing is performed with the tracer particle as the starting point. In this case, for example, mg in FIG. 4B is used as the starting point tracer particle. Thereby, for example, the tracer particles with the symbol A1 in FIG. 7 are set as the starting point tracer particles.

Next, the process proceeds to step P2, where the area Length1 having a predetermined size centered on the tracer particle A1 is used.
Tracer particles within are searched for as tracer particles at time 2. By this search, for example, the tracer particles of C in FIG. 4 are searched. After searching for the tracer particles at time 2 in this way, the position of the tracer particles at time 3 is then estimated in step P3. Thereby, for example, the position S1 of FIG. 7 is estimated as the moving position of the tracer particles at time 3.

Then, it is determined whether or not there is a tracer particle corresponding to the tracer particle at time 3 within the range of Length2 with the estimated position S1 at time 3 as the center (step P4). By this determination, if there is a corresponding tracer particle, the process proceeds to step P5, and it is determined whether or not a predetermined condition is satisfied. If there is no corresponding tracer particle, the process proceeds to step P9 to perform a process starting from another tracer particle, and then to step P1.
Return to.

The condition determination in step P5 is, for example, when the tracer particle shown by A3 in FIG. 7 is the corresponding tracer particle, the line connecting A2 and S1 and the line connecting A2 and A1.
This is performed by determining whether or not the angle θ formed by the line connecting 3 and 3 is smaller than 20 °. If the angle θ is larger than 20 °, the process returns to step P1 via step P9.

As a result of the determination in step P5, A3 is time 3
If the condition as the tracer particle of is satisfied, the process proceeds to step P6, and the position of the tracer particle at time 4 is estimated. From this estimation, for example, S2 in FIG. 7 is estimated as the tracer particle position at time 4. In this way time 4
After the position of the tracer particle is estimated, it is determined whether or not there is a corresponding tracer particle as the tracer particle at time 4 in Length3 centered on the position of S2.

When it is determined in step P7 that the tracer particles A4 in FIG. 7 correspond to the tracer particles at time 4, the process proceeds to step P8, and it is determined whether the tracer particles A4 satisfy the predetermined condition. I do. If it is determined that the predetermined condition is not satisfied, the process returns to step P1 via step P9.

The determination condition of step P8 is to determine whether or not the angle θ formed by the line connecting A3 and S2 and the line connecting A3 and A4 in FIG. 7 is larger than 20 °. To do. When it is determined that the angle θ is larger than 20 °, the process returns to step P1 via step P9. If it is determined that the angle θ is smaller than 20 °, the process proceeds to step P7 in FIG. 5 to calculate the velocity vector. The calculation of the velocity vector is performed by calculating the tracer particle positions at time 2 and time 4 and the pulse interval T ₂ as described above.
It is performed based on and T _4.

In this embodiment, the tracer particles are traced in this manner, so that even when fine tracer particles are used and the output of the light source is limited, the tracer particles are not limited to the space of the television camera 6. If it can be sensed in the range of resolution, it can be visualized well and can be tracked.

Next, in order to confirm the practicality and usefulness of the present invention, the velocity was measured in a flow field accompanied by separation behind the back step. Then, the accuracy of this system was evaluated by comparing the measurement result of this system with the measurement result of the laser Doppler velocimeter.

The flow field to be measured is the turbulent flow in the channel having the back step shown in FIG. The step height h is 0.05m, and one side is 0.1m upstream of the step.
A 1.5 m long rectangular tube with a square cross section of (2 h) is attached.

A rectangular tube having a rectangular section of 0.1 m × 0.15 m and a length of 2.0 m is attached downstream. The step expansion rate is 1.5. The flow is rectified by a 5 mm mesh rectifying network installed at a position of 0.5 m (10 h) upstream of the step, and a stepping inlet part is provided by a tripping wire having a diameter of 2.0 mm installed on the pipe wall immediately downstream of the rectifying network. The shape of the velocity distribution is determined.

Nylon 12 having an average particle size of 50 μm and a specific gravity of 1.02 was used as the tracer particles. The measurement cross section was an xy cross section (z / h = 0) at the center of the pipeline, and this cross section was irradiated with LLS having a thickness of 2 mm from the upper portion of the pipeline, and an image was input by the television camera 6 from the direction perpendicular to the measurement cross section. Step upstream 3h
From step to 9h on the downstream side into a 3h x 3h area
Each area was photographed with one TV camera (total of four). Image spatial resolution is 0.31m
m / pixel. A main flow region, shear region, recirculation region, etc. are mixed in the set measurement region, and a wide flow velocity range exists. In this experiment, three levels of illumination codes as shown in Table 1 were used, and 300 frames of image data were collected and processed by each code.

[0045]

[Table 1]

FIG. 9 shows the result of tracer tracking performed by imaging with laser light irradiation by code 1 and FIG. 10 shows the result of tracer tracking by imaging by laser light irradiation by code 2. FIG. 11 shows the result of performing the tracer tracking, synthesizing the results in the same space with matching the time reference, and performing the grid point interpolation. As is clear from these results, it can be seen that the method for visualizing microtracer particles and the method for tracking the same of the present invention have high reliability.

[0047]

As is apparent from the above description, according to the present invention, it is possible to satisfactorily visualize fine tracer particles having a size of the pixel resolution. In addition, since the visualized micro tracer particles can be tracked well, it can be reliably tracked even when the above micro tracer particles move at high speed, and it is also suitable for measurement of complicated high-speed flow fields. can do.

[Brief description of drawings]

FIG. 1 is a timing diagram of intermittent irradiation of a laser light sheet according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an example of an optical system used for visualizing a flow.

FIG. 3 is a diagram showing an example of an image in which minute tracer particles are visualized.

FIG. 4 is a diagram showing tracer particle positions for explaining a tracer tracking algorithm.

FIG. 5 is a flowchart showing an example of a tracer tracking algorithm.

FIG. 6 is a flowchart showing an example of a tracer tracking algorithm.

FIG. 7 is a diagram schematically showing a tracer tracking algorithm.

FIG. 8 is a diagram showing an example of an experimental device used for actually performing visualization.

FIG. 9 is a diagram showing tracer tracking results obtained by irradiating a laser beam of code 1.

10 is a diagram showing a tracer tracking result obtained by irradiating a laser beam of code 2. FIG.

FIG. 11 is a diagram showing a result of performing the grid point interpolation by synthesizing the tracer tracking results as shown in FIGS. 9 and 10 in the same space while matching the time reference.

[Explanation of symbols]

1 Laser Light Source 2 Acousto-Optical Cell 3 Slit 4 Optical Fiber 5 Cylindrical Lens 6 Television Camera 7 External Control Device dt Laser Light Irradiation Time T ₁ First Time T ₂ Second Time T ₃ Third Time T ₄ Fourth time of

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichiro Tomino 1 Kimitsu, Kimitsu City Nippon Steel Corporation Kimitsu Steel Works

Claims (2)

[Claims] 1. Tracer particles having a predetermined particle diameter are mixed in a fluid, and one laser beam spread in a sheet shape is provided in a first field of a television camera signal, and two or more laser beams are provided in a second field. In the method for visualizing tracer particles, six or less are intermittently irradiated toward the fluid, and scattered light or fluorescence of the tracer particles due to the irradiation of the laser light is imaged by a frame accumulation type television camera. The irradiation time of the laser light in the first field is set to be long to form traces of tracer particles on the image, and the irradiation time in the second field is set to be shorter than the irradiation time in the first field. The method for visualizing tracer particles is characterized in that an instantaneous particle image is obtained in the second field. 2. Tracer particles having a particle diameter of 2 mm or less and 1 μm or more are mixed in a fluid, and a laser beam spread in a sheet shape is once in the first field and 2 in the second field in the television camera signal. A first process of intermittently irradiating six or more and six or less into the fluid, and a second process of capturing the scattered light or fluorescence of the tracer particles by the irradiation of the laser light with a frame accumulation type television camera.
Of the output of the television camera and the output of the first field of the previous frame and the output of the second field of the previous frame as image information of the first field of the previous frame on the recording, and Of the second field and the output of the first field of the subsequent frame as the image information of the second field of the previous frame in the recording, and the third processing of recording on the recording medium by performing frame accumulation of light. Using one frame image obtained by the third processing and the image of the first field thereof, all the tracer particles existing in the image of the first field are set as candidates for the starting point tracer particles, and A first search area having a predetermined size centered on the tracer particle that is the starting point candidate in the first field image is set on the frame image. And the number of tracer particles existing in each of the search areas is detected, and if there are 2 or more and 4 or less tracer particles, the tracer particles imaged by the laser beam irradiated at the first time are detected. And a fifth process of determining that the tracer particles imaged by the laser light emitted at the first time are erased from the frame image, and imaged by the laser light emitted at the first time. Sixth processing for registering the position of the center of gravity of the tracer particles related to the search area in which the tracer particles are detected as the start point position of the tracer particles, and the second to fourth times with the registered tracer particle position as the start point. The tracer particle positions are tracked on the frame image to determine the path of the same particle, and the tracer particle is detected by the seventh processing. And a tracer particle position at a second time, a tracer particle position at a fourth time, and an eighth process for calculating a velocity vector based on the time interval between these tracer particle positions. How to track particles.