JP2857239B2 - Method and apparatus for measuring flow velocity distribution - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention provides a method for processing a flow field by visualizing a television image of the flow field visualized by a tracer injection method.
The present invention relates to a method and an apparatus for measuring a three-dimensional flow velocity distribution.

(Prior Art) For example, a method of visualizing a flow field by injecting a tracer into a fluid in order to know a flow velocity distribution of a flow field created by a flow of a fluid in a passage or the like is known. In order to quantitatively obtain the flow velocity information in the flow field visualized in this way as distribution data, the visualized flow field state is converted into a video signal using a television camera, and the image obtained thereby is obtained. For the data, two frame images are created from each field image in the frame image, and the trajectory image formed by the same tracer in each image is the inclination angle of the thin line obtained by the thinning process. A method has been proposed to measure the distribution of flow velocity from the amount of movement between two frame images of the flow trace image formed by the same tracer, estimated from the information of the flow and the length (Flow Visualization, Vol. 9 , No.34, No.
379 to 382). Since this method deals with only one frame of television image, it has a feature that the applicable range is wider than that of a method which deals with two or more frames of television image.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional method, a tracking process is performed in which the inclination angle and the length are obtained from the result of the thinning processing of the trail image, and the trail image is estimated using the result. Therefore, if noise is superimposed on the image, the tracking processing result is greatly affected by the noise, and there is a problem that a large error occurs in the measurement result of the flow velocity. In order to reduce this error, in order to visualize the flow, a good illumination condition is required, and the particle size of the tracer particles must be selected and used within a certain range. This is because the lengths of the fine lines of the trace images of particles having different particle diameters after the thinning process are different even if the lengths of the trace images are equal. Therefore, there is a problem that these points must be overcome in order to put the above-mentioned conventional technology into practical use.

Also, the method of calculating the inclination angle and length of the trail image includes:
Although there is a method using Hough transform or the like, it is not practical because the processing time is long, and it is considered that the influence of image noise is likely to occur. Therefore, a problem may occur in terms of reliability of the measurement result. is there.

The object of the invention is therefore to reduce the effects of noise,
It is an object of the present invention to influence a method and an apparatus for measuring a flow velocity distribution, which can measure a flow velocity distribution state more accurately.

(Means for Solving the Problems) A feature of the method of the present invention for solving the above problems is that visualization of a desired flow field is performed by injecting a tracer, and the flow field image information of the flow field is used. A method of measuring a two-dimensional flow velocity distribution of the flow field, wherein a first step of capturing the visualized flow field using a television camera of an interlaced scanning image pickup tube type without a shutter to obtain a television image signal; A second step of determining the correspondence of the trail images between the respective field image data by a logical AND operation of the respective field image data constituting one frame of the television image signal, and the second step of obtaining the second step; And a third step of calculating a flow velocity vector for each of the pair of trace image data.

Another feature of the present invention is a flow velocity distribution measuring apparatus that measures a two-dimensional flow velocity distribution of a flow field based on a television image signal of the flow field visualized by injecting a tracer. And a means for obtaining a pair of field image data constituting one frame in response to an output signal from the television camera without a shutter for capturing a desired flow field. A logical operation means for performing a logical product operation between the pair of field image data and outputting data indicating a correspondence relationship between the trail images respectively indicated by the two image data, and a corresponding function according to the operation result of the logical operation means Calculating means for calculating each barycentric position of a pair of trajectory images and calculating a movement vector of the calculated barycentric position A.

(Operation) When a flow field visualized by a television camera of a non-shutter interlaced scanning image pickup tube type is photographed, 1
A pair of field image data constituting a frame is obtained. One field image data can be obtained, for example, based on a first field signal, and the other field image data can be obtained, for example, based on a second field signal. By performing one frame of scanning with this television camera, the obtained first field signal and second field signal have a time lag with their scanning periods partially overlapping, and therefore, Each of the trace images indicated by the field image data and the respective trace images indicated by the other field image data are displaced in the flow direction by the movement length of the tracer particles corresponding to the time lag. Obtained as two images.

As described above, when each stream image showing the movement trajectory of the same tracer particle in a pair of field images obtained by scanning with the non-shutter interlaced image pickup television camera is overlapped when configured as an image of one frame. Will have. Therefore, by finding the overlap between the trace images, it is possible to associate the trace images with the same tracer particles between different field image data. This association is performed based on the result of the logical product operation of the two field image data, and the respective barycentric positions of the corresponding pair of trajectory images are calculated. Can be measured. By performing the above measurement at an appropriate place in the flow field, the distribution of the flow velocity in the flow field can be measured.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the flow field of the fluid 2 visualized by injecting appropriate tracer particles 3 such as nylon 12 particles into the fluid 2 in a water tank 1 made of transparent glass by the method of the present invention. 1 shows a configuration of a flow velocity distribution measurement system 10 for measurement. Flow velocity distribution measurement system 10
Is provided with a television camera 11 for converting the visualized image of the flow field into a television video signal, and a video output signal VS from the television camera 11 Data processing using the signal processing device 13 and the computer 14 of the
Two-dimensional flow velocity distribution data of the fluid 2 in the inside is obtained.

The television camera 11 is a video tube television camera of a 2: 1 interlace scanning system without a shutter, and outputs an image of a field of view captured by the television camera 11 as a corresponding video signal. Therefore, an image of one frame obtained by this is obtained by combining a set of field images. The relationship between the trail images indicated by these field images is as follows.

That is, when the field of view captured by the television camera 11 is scanned in an interlaced manner, first, the field of view is scanned by scanning along the odd-numbered scanning lines, and an odd field signal is obtained. In this case, since there is no shutter, the above-described scanning is performed while each tracer is moving. Next, the same field of view is scanned by scanning along the even-numbered scanning lines, and an even-numbered field signal is obtained.

As shown in FIG. 6 (a), the interlaced scanning is performed in synchronization with the vertical synchronizing pulse output every 1/60 second, and the scanning of the odd field is performed for a time length of 1/30 second. When executed in the slot T _1, the even field scanning corresponding thereto is performed in the time length of the time slot T ₂ of the same 1/30 second. Therefore, in this case, the time slot T ₁ and T _2, are overlapped by 1/60 second.

Odd field signal obtained in the time slot T ₁ in this manner is a video signal shown in Figure No. 6 (b)
Fitted to VS time slot A, whereas the even field signal obtained in the time slot T ₂ are fitted to the time slot B of the video signal VS shown in Figure No. 6 (b), television picture in this way A signal is created.

Returning to FIG. 1, the video signal VS is input to the signal processing device 13, where it is separated into an odd field video signal VS ₁ and an even field video signal VS _2, the signal VS _1, VS ₂ computer 14 , Where image data processing for flow velocity distribution measurement is performed according to a predetermined processing program.

FIG. 2 is a functional diagram showing the contents of the image data processing executed in the computer 14. The image data processing executed in the computer 14 will be described based on this functional diagram. Odd field video signal
VS ₁ and the even field video signal VS ₂
respectively given to a and the second calculation means 14b, each signal VS _1, VS ₂
, The flow image data D ₁ and D _{2 for} one frame are obtained.

Nagareato image data D _1, for example as shown in FIG. 7 (a), based on the odd field video signal VS ₁ with every other scan line ,,,, ... image information, the scanning line ,,, Scan lines as the contents of ...
Is interpolated using the content of the image data, and is created as data indicating image information of one frame shown in FIG. 7 (b).

On the other hand, the trail image data D ₂ is an even-field video signal.
Based on the image information of the scanning lines included in VS ₂ ,..., 1 is obtained by interpolation similar to the interpolation shown in FIG.
It is created as data indicating image information for a frame.

Therefore, in this case resulting stream marker image, as shown in 4 (a), flow according to data D ₂ based on the odd field flow marker image x and an even field image data according to the data D ₁ based on the image information The trace image y is displaced along the flow direction of the fluid 2, and only a part of these overlaps.

A set of track image data D ₁ , D ₂ thus obtained
The logical product computing means given 14c, wherein each flow mark image and the other Nagareato image data D ₂ according to one Nagareato image data D ₁
AND operation is performed with each of the trail images according to. Then, the combination data indicating the combination of the trajectory images having the logical product image according to the logical product operation result is obtained by the flow velocity vector calculating means 14d.
Given to.

The velocity vector calculation unit 14d, further Nagareato image data D _1, and D ₂ is given, the center of gravity of the flow trace image based on these is calculated. Further, a movement vector of the position of the center of gravity in each flow image pair based on the combination data indicating the combination of the flow images is calculated as a flow velocity vector at that point. Based on the flow velocity vector data indicating the calculated flow velocity vector, the two-dimensional flow velocity distribution of the fluid 2 in the visual field captured by the television camera 11 is measured.

Next, the memory in the computer 14 shown in FIG.
The image processing operation will be described in more detail based on the flowchart of the image processing program stored in the storage unit 15.

When the execution of the image processing program 20 is started, first,
In step 21 and the odd field video signal VS ₁ and an even field video signal VS ₂ is taken into the computer 14, Nagareato image data D _1, D ₂ showing the Nagareato image follow these signals are created respectively in step 22 You.

Nagareato image data D ₁ corresponds to the odd-numbered field image shown in FIG. 4 (b), whereas, Nagareato image data D ₂ corresponds to the even-numbered field image shown in FIG. 4 (c). In the following description, referred to as 1 time th Nagareato image an image represented by Nagareato image data D _1, referred to as an image two times th Nagareato image represented by Nagareato image data D _2.

FIGS. 4D and 4E show the first time and the second time.
Each of the trail images at the time is shown in detail.

Next, the process proceeds to step 23, where each stream image data
Data processing for binarizing the image represented by D ₁ and D ₂ is performed. In the data processing for the binarization, each data D ₁ , D ₂
Is converted into a binary image, and as a result, binarized data Da and Db indicating a binarized trajectory pattern are obtained.

In the next step 24, unnecessary information is removed, that is, noise removal processing is performed based on the binary data Da and Db. This process removes the data of the trail image connected to the frame of the image at all from each trail image.

Noise removal processing of the trail image periphery due to expansion and contraction.

A process of removing a stream image having a number of pixels equal to or less than a predetermined number as noise.

Is included. However, it goes without saying that other appropriate noise removal processing may be performed in addition to or in place of some of them.

Next, in step 25, labeling 1a, 1b, 1c,..., 2a, 2b, 2c,... Is applied to each of the trail images at the first time and the second time left as a result of the noise removal processing in step 24. (See FIGS. 4 (d) and 4 (e)), calculation of the center of gravity and calculation of the area are performed for all the labeled flow trajectory images.

Thereafter, the process proceeds to step 26, where the logical product is calculated between each of the trail images at the first time and each of the trail images at the second time. Next, in step 27,
As a result of the logical product operation, combination data having a value and indicating a combination of the label of the trail image at the first time and the label of the trail image at the second time is obtained. For example, when the trace image of the label 1a and the trace image of the label 2a are in a correspondence relationship and in the positional relationship shown in FIG. 5, the result of the logical product of these trace images is indicated by hatching in FIG. Represents the area of the overlapped portion, and if this area is greater than zero, it is assumed that both trace images are trace images formed by the same tracer particle.
Therefore, in this case, combination data indicating one set of trail images indicated by the labels 1a and 2a is obtained. This calculation is performed for all the combinations, and the combinations of the trail images are determined.

In step 28, in order to determine whether each combination of the trail images obtained as described above is valid or not, it is checked whether or not the following conditions are satisfied.

(A) Each of the trail images is combined with only one of the trail images at the other time.

(B) The difference between the areas of one set of trail images must be within 20%.

(C) A straight line connecting the centers of gravity of a set of trace images passes through a logical product image obtained by these.

Only combination data that satisfies each of the conditions (a) to (c) is taken as correct combination data, and combination data that does not satisfy any one of the conditions (a) to (c) is removed.

In step 29, among the pair Nagareato image indicated by the combination data recognized the legitimacy, for example, as shown in FIG. 5, 2 times counted from the gravity center position W ₁ of Nagareato image of 1 time th vector VC toward the gravity center position W ₂ of the Nagareato image is calculated,
This vector VC is used as the flow velocity vector at this point of the fluid 2. In this way, the flow velocity vector is calculated as described above for the flow image pairs indicated by all the combination data.

As a result, the flow velocity vector at each position in the image becomes apparent, and in step 30, based on each flow velocity vector,
The flow velocity distribution is measured, and data indicating the result is output in an appropriate form. This data may be shown as an image on a display tube, for example, or the data may be printed out.

As described above, the apparatus shown in FIG. 1 uses the video output signal obtained by using the television camera of the interlaced scanning tube type without the shutter, so that the stream image at the first time obtained by each tracer particle is used. The correspondence between the trail image of the second time and the trail image of the second time image can be found very easily by calculating the logical product between them, so that it is hardly affected by noise. In addition, the flow velocity distribution can be measured extremely accurately by a simple process.

Note that, in the above embodiment, an imaging tube type television camera was used to capture a visualized image. However, as can be understood from the above description, an interlaced scanning television camera using a MOS type imaging device without a shunter was used. Even if it is used, exactly the same effect can be obtained.

(Effects of the Invention) According to the present invention, as described above, the correspondence between each trace image of one field image and each trace image of the other field image can be easily determined by a logical product operation of each image data. , And is not easily affected by noise or the like. Therefore, an excellent effect that extremely reliable flow velocity distribution measurement can be performed without a complicated algorithm is required.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of a flow velocity distribution measuring system according to the present invention, FIG. 2 is a functional diagram showing a configuration of a main part of the flow velocity distribution measuring system of FIG. 1, and FIG. 3 is a computer of FIG. 4 (a) to 4 (e) are diagrams showing a stream image for explaining image processing in the system of FIG. 1, and FIG. 5 is a flowchart showing the image processing program executed in FIG. FIG. 6 (a) and FIG. 6 (a) are explanatory diagrams for a logical product operation of a trail image executed in the system of FIG.
FIG. 7B is an explanatory diagram for explaining the configuration of an interlaced television video signal, and FIGS.
FIG. 2B is an explanatory diagram for explaining a method of creating one frame of trail image data by interpolation based on an odd-numbered field video signal. 2 fluid, 3 tracer, 10 flow velocity distribution measurement system, 11 television camera, VS video output signal, 13 separation device, 14 computer, 14a first computing means .. 14b... AND operation means, 14d... Velocity vector calculation means, VS ₁ ... Odd field video signal, VS ₂ ... Even field video signal, D ₁ , D _2. Trail image data.

Continuation of the front page (56) References JP-A-63-298065 (JP, A) JP-A-63-14586 (JP, A) “New edition of running water visualization handbook” P419-P422, 1986. Published by Asakura Shoten Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) G01P 13/00

Claims (2)

(57) [Claims] In a method for visualizing a desired flow field by injecting a tracer and measuring a two-dimensional flow velocity distribution of the flow field based on flow image information of the flow field, a visualized flow field is provided. And a first step of obtaining a television image signal by taking an image using a television camera of an interlaced scanning image pickup tube type without a shutter, and performing a logical product operation of each field image data constituting one frame of the television image signal. A second step of determining the correspondence of the trail images between the respective field image data, and a third step of calculating a flow velocity vector for each of the pair of trail image data obtained in the second step; A method for measuring a flow velocity distribution, comprising: 2. A flow velocity distribution measuring apparatus which measures a two-dimensional flow velocity distribution of a flow field based on a television image signal of the flow field visualized by injecting a tracer. A television camera of an interlaced scanning tube type without a shutter for photographing a flow field of a camera, means for obtaining a pair of field image data constituting one frame in response to an output signal from the television camera; A logical operation unit that performs a logical product operation between a pair of field image data and outputs data indicating a correspondence relationship between the trail images indicated by the two image data, and a pair of corresponding logical operation units according to the operation result of the logical operation unit Calculation means for calculating each position of the center of gravity of the trail image and calculating a movement vector of the calculated position of the center of gravity. Measuring device of the flow velocity distribution with.