JPS6036968A - Method for measuring flow rate - Google Patents

Abstract

PURPOSE:To enable determination of a two-dimensional flow rate distribution at a high speed with simple software by storing periodically the information on particle groups into a sheet of an image memory and subjecting the same to Fourier transform. CONSTITUTION:A fluid contg. particles is contained in a water tank 1 and the image thereof is picked up by a television camera 2. Positive and negative pulse trains are generated by a predetermined number from a clock pulse generator 8 according to the signal from a controller. An A/D converter 3 digitized the image for one image plane when the positive or negative pulse is generated. The digitized image data is added and stored successively in an picture memory 5. A coder 4 gives positive and negative codes to the image data according to the positive and negative of the pulse. Therefore the image of the water tank contg. the particles is written into the picture memory by the certain positive pulse and the image of that time is subtracted by the succeeding negative pulse. The image of a static object such as the water tank or the like is canceled and only the images 10 of the moving particles is given the positive or negative code and line up at intervals along the track.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a flow velocity measurement method using a particle mixing method, and particularly to a flow velocity measurement method and apparatus suitable for determining a two-dimensional flow velocity distribution in a fluid.

[Background of the invention]

In the conventional two-dimensional flow velocity distribution measurement method using the particle mixing method, small particles of several micrometers to several tens of micrometers with the same specific gravity as the fluid but different optical properties are mixed into a transparent fluid, and the velocity of the fluid is determined from the photographic image. I was watching. This method involved exposing a film to light for a certain amount of time to create an image of the trajectory of the particles, and calculating the velocity of the fluid from the length of this trajectory. In this method, the trajectory of each individual particle had to be measured, which required a huge amount of effort. Furthermore, if the direction of the flow was not known, it was necessary to devise measures such as changing the brightness of the lighting over time to give the trajectory directionality.

In order to save a huge amount of effort, methods have been developed that use a television camera and image memory instead of taking photographs.

In this method, images of particles at two different times are recorded in two image memories, and through computer processing, the distance traveled by the particles between the two times is calculated, and the flow velocity is determined from this. In this method, it is necessary to recognize a large number of particles ii one by one, and also to recognize the correspondence between two images. Furthermore, the image includes not only images of the particles but also images of the structure of the flow path.

In order to separate the gold particles from these images and track their movement between the two images, the computer program becomes extremely complex and requires a long processing time.

[Purpose of the invention]

An object of the present invention is to provide a means for determining a two-dimensional flow velocity distribution in a short time using only one image memory and using simple software.

[Summary of the invention]

The present invention periodically stores image data of a particle group from a television camera in one image memory. At this time, by alternately inverting the sign of the data, images of stationary objects, that is, structures, are removed, and by applying Fourier transformation to the tracks of the obtained particle groups, the two-dimensional flow velocity distribution of the fluid is obtained. It is.

[Embodiments of the invention]

An embodiment of the present invention will be described using FIGS. 1 to 5. As shown in Fig. 1, this embodiment includes a water tank l in which the flow velocity distribution is to be measured, and a television camera 2 that captures the movement of particle groups in the tank.
2. A/D that digitizes the output signal of the TV camera
Converter 3, encoder 4 that signs the output of the A/D converter
, an image memory 5 that stores the image signal output from the encoder.
, a Fourier transformer 6 that performs high-speed Fourier transform on the image data recorded in the image memory, a CRT 7 that displays the transformed results, and a clock pulse generator 8 that synchronizes these devices, controlling the overall operation. It consists of a controller 9.

This embodiment operates as follows. There is a fluid mixed with a single particle in the water tank l, and the shadow team is seen by a TV camera 2.
2 is filming. In response to signals from the controller, the clock pulse generator 8 generates a predetermined number of positive and negative pulse trains as shown in FIG. When a pulse with a positive magnitude or a negative value is generated, the A/D converter 3 digitizes the image for one screen. This digitized image data is stored in the image memory 5 by being added one after another, and at this time, the encoder 4 assigns a positive or negative sign to the image data according to the positive or negative sign of the pulse. Therefore, a certain positive pulse writes an image of the aquarium containing particles into the image memory;
The next negative pulse will subtract the image at that time. Since the number of positive pulses and the number of negative pulses are equal, the image of a stationary object such as a water tank is canceled, and only the image lO of the moving particle is given alternating positive and negative signs as shown in Figure 3. They are arranged in a row along the trajectory. The pulse train generated from the pulse generator is arranged so that the interval between positive and negative pulses is T+ / To = l / 4, so the track also has an interval force of 1 / 4 between positive and negative points, and has directionality. Since the pulse generation period is known, the flow velocity can be determined by calculating the distance between the points of this track.

One screen has many dot sequences showing the tracks of these particles. To easily handle this, the following method is used. The image in the image memory is divided into small regions 11 in which the flow can be considered uniform as shown in FIG. 4, and the flow velocity is determined for each small region. To do this, first calculate the sum of 12 image data in the vertical direction of the small area. Next, perform a Fourier transform on this. At this time, the flow velocity is determined from the frequency where the amplitude is maximum,
The direction of flow is determined from the phase relationship between this frequency and the harmonic frequency. That is, if f is the frequency at which the absolute value of the coefficient of the Fourier series is maximum, and the magnification ratio of the aquarium 1 and the image in the image memory is 'rM, then the horizontal component of the flow velocity can be calculated as 11. T here. is the time interval from one positive pulse to the next positive pulse, as shown in FIG.

On the other hand, the direction of flow is determined from the phase relationship. Let the Fourier coefficients at the maximum amplitude frequency be a, -1-b,i, and the coefficient ka2+b2'' at twice that frequency.The phase α of the fundamental wave is a, = tan''l) H/''+, The phase α2 of the harmonic is a2 = tan-'b2/a2. Since the pulse interval is larger from negative to positive than between positive and negative, as shown in Figure 5, when the velocity is positive, (flow is to the right), the phase of the harmonics is 180 degrees from the fundamental wave.
They are shifted by 1°, but if the velocity is negative, they are in phase. That is, if it is a positive direction, it is a negative direction.

By rotating the above method by 90 degrees, the component of the flow velocity in the vertical direction of the screen can be similarly determined. 1
Although there may be multiple particle images in one small region, the small region is kept small enough to be considered to have a uniform flow, so the particles within the small region have the same velocity and direction. Fourier transform has linearity, so even if there are multiple particles, the frequency,
The phase relationship remains unchanged. Therefore, it is not necessary to recognize individual particles.

By applying such operations to each small area, the flow velocity distribution over the entire screen can be adjusted. The flow velocity in each small area is converted into the size and direction of the arrow and displayed on the CRT 7.

When the 7-υ engineering conversion of the screen is completed, the controller 9 erases the contents of the image memory and prepares for the next measurement.

〔Effect of the invention〕

According to the present invention, by periodically storing information on particle groups in one image memory and performing Fourier transformation, it is possible to quickly obtain a two-dimensional flow velocity distribution using simple software. .

[Brief explanation of the drawing]

Fig. 1 is a diagram of the equipment configuration of an embodiment of the present invention, Fig. 2 is a diagram showing the cycle of data recording, Fig. 3 is a trajectory diagram of particles stored in the image memory, and Fig. 4 is a diagram of the image memory. FIG. 5 is a schematic diagram of the intensity distribution of the image data. 2...TV camera, 3...AD converter, 5...
Image memo +7-15...Fourier transformer, 8...Clock pulse generator, 9...Controller, 11...Small area of image memory. , 3 fig. 4 fig. 1

Claims (1)

[Scope of Claims] 1. A video recording medium comprising means for mixing particles to be used as a tracer into a fluid, detecting the position Rt of the mixed particles and generating a video signal, and a video information recording medium for storing the video signal. In a method of determining the fluid flow velocity by processing video information stored in an information recording medium, the video signals are periodically and the signs of the signals are alternately inverted and integrated onto one video information recording medium. A flow velocity measurement method characterized in that the flow velocity is determined by Fourier transforming the video information obtained. 2. In claim 1, it is provided that the cycle of synchronously inverting the sign of a video signal and integrating it on one video information recording medium is such that the signal is accumulated with the sign of the signal being positive, and then the signal is A flow velocity measurement method characterized in that the time taken to integrate the sign of the signal as negative and the time from the time of integration as the sign of the signal to the time of integration with the sign of the signal as positive are different. 3. A flow velocity measuring method according to claim 2, characterized in that the means for detecting the position of particles and generating a video signal is a television camera, and the video information recording medium for storing all the video signals is an image memory. .