JP3718686B2 - Plane and space time-series fluid velocity measurement system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fluid velocity measurement system, and more specifically, a high-repetition double-pulse laser or a double-pulse laser system combining two pulse lasers or a continuous-wave laser light source and laser light oscillated from the laser light source into a sheet shape A conversion device (laser sheet generation system), a high-speed video camera equipped with a CCD image sensor or a CMOS image sensor, a scattered light image of particles mixed in the fluid to be measured by the high-speed video camera, or a spatial image of the fluid Time-series fluid velocities in plane and space, provided with arithmetic means for synchronously capturing gray images and obtaining time-series velocities from two consecutive scattered light images or spatial fluid gray images obtained by the imaging It relates to a measurement system.
[0002]
[Prior art]
Fluid velocity measurement methods include a method of measuring the velocity at one or several points in space with high time resolution, such as a hot-wire anemometer and laser Doppler anemometer, A particle image velocimeter (hereinafter referred to as PIV) that obtains images of such scattered light, etc., obtains the moving distance of particles or particle groups from particle images that differ for a minute time, and measures the fluid velocity in a two-dimensional plane. ) Hot wire velocimeters and laser Doppler velocimeters can measure fluid velocity with high temporal resolution, but they can only be measured at one or several points in space and simultaneously measure fluid velocity in space. I can't. In contrast, PIV can measure fluid velocity in a plane or space, but can only obtain fluid velocity at a certain moment or a large time interval, and its time resolution is very low. In addition, a vector containing a very large error (hereinafter referred to as an error vector) exists in the velocity field by PIV. The error vector is generated when particles are out of the laser sheet or flow into the laser sheet due to the velocity component and vorticity component perpendicular to the laser sheet. Therefore, the occurrence cannot be avoided, and a very large error is included.
[0003]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a highly accurate plane and space time-series fluid velocity measurement system having both high time resolution and spatial resolution, which has been impossible in the past.
[0004]
[Means for Solving the Problems]
The above object of the present invention is to provide a time-series fluid in a plane and space, which includes an image acquisition system having a high-speed video camera equipped with a laser light source, a laser sheet generating optical system, and one or a plurality of CCD image sensors. A velocity measurement system, wherein laser light oscillated from the light source is converted into a sheet-like laser by the laser sheet generating optical system, the sheet-like laser is irradiated to a fluid to be measured, and the light source and the image acquisition system are synchronized. The scattered light image by the particles in the fluid to be measured or the spatial grayscale image of the fluid is continuously photographed by the high-speed video camera at a minute time interval, and the velocity is obtained by cross-correlation from two temporally continuous images. A vector is calculated, and the time series velocity at each velocity definition point is Fourier-transformed for each obtained velocity vector distribution. Cutoff filter, or subjected to a low pass filter, by inverse Fourier transform, it is accomplished by time-series fluid velocity measurement system of the plane and space, characterized in obtaining a final time sequence rate.
[0005]
In addition, the above-described object of the present invention is to use a CCD image sensor as a CCD image sensor by using a CCD image sensor having 512 × 512 pixels or more and capable of photographing at 1 kHz or more, or using a CMOS image sensor instead of the CCD image sensor. Or by using a CMOS image sensor capable of photographing at 1 kHz or more with 512 × 512 pixels or more as the CMOS image sensor, or using a pulse laser of 100 Hz or more as the laser light source, The time interval between double pulses can be varied by performing imaging by synchronizing the light source and the image acquisition system so that laser beams of equal intervals are included one by one in one frame, or as the laser light source. Using a double pulse laser of 100 Hz or higher, the front side in two consecutive frames By combining the two lasers with a frequency of 100 Hz or more, by taking a picture in synchronism so that one laser beam enters each of the latter half of the frame and the first half of the rear frame, or instead of the double pulse laser, By using a laser system in which the interval between pulses emitted continuously from each other is variable, or using a continuous wave laser as the laser light source, the laser is continuously oscillated, and the camera shutter is opened and closed at regular intervals. By obtaining a particle image, or by directly applying a low-pass filter to the time series data in calculating the velocity vector, obtaining a final time series velocity, or the velocity vector distribution. In contrast, the time series data is Fourier-transformed and cut in frequency space. By applying an off-filter or low-pass filter and performing inverse Fourier transform, the velocity vector information at the time missing due to measurement errors, etc., or by interpolating the velocity vector information between measurement times, the final time-series velocity Or by using two high-speed video cameras, and adding two wings so that the Shine flag condition where the image plane, the lens main plane, and the extension line of the sheet plane intersect at one point is used. By arranging and shooting synchronously so that they perform exactly the same operation, two image pairs can be obtained simultaneously from different angles, and the movement amount vector at each speed definition point is calculated from the image pairs taken by each camera Then, correct the trapezoidal distortion of the image by observing from an angle, and match the speed definition points of the two cameras to make the angle difference between the two cameras To obtain time-series data of a three-dimensional velocity vector in a plane, by measuring a three-dimensional velocity in a plane using stereo projection, or one or more of the high-speed video cameras and a laser sheet generating optical system It is more effectively achieved by installing the moving speed of one axis on the moving shaft of one axis or more on a moving device having 0.5 m / s or more.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
A plane and space time-series fluid velocity measuring system according to the present invention will be described below with reference to the drawings. FIG. 1 shows an outline of an embodiment of a time-series fluid velocity measuring system for plane and space according to the present invention.
[0007]
The laser light oscillated from the laser light source 1 is converted into a sheet shape by a laser sheet generating optical system 11 having 2 to 7 and is irradiated to a fluid to be measured. The laser sheet generating optical system 11 includes cylindrical lenses 2, 3, 6, 7, a galvanometer scanner 4, and an off-axis object mirror 5. The laser sheet can be scanned by operating the galvanometer scanner 4, thereby enabling three-dimensional measurement. The test section 8 is irradiated with the laser light converted into a sheet shape. Images of the scattered light of the laser light irradiated on the test section are taken at short intervals by the image acquisition system 9. The photographed image data is sent to the image analysis portion of the system control and image analysis system 10 and subjected to arithmetic processing such as Fourier transform, cross-correlation method, and filtering. The system control and image analysis system 10 can use a personal computer.
[0008]
The laser light source system 1 and the image acquisition system 9 are synchronized, and the synchronization method is changed depending on the type of light source as shown in FIG. In any of FIGS. 2A to 2C, the right direction shows the change over time. In a camera frame, each pulse represents a camera frame. In the camera shutter, the H level of the pulse indicates that the shutter is open, and the L level of the pulse indicates that the shutter is closed. In the laser oscillation, the H level of the pulse indicates that the laser is oscillating, and the L level of the pulse indicates that the laser is not oscillating. FIG. 2A shows a synchronization method using a continuous wave laser. The laser keeps oscillating and takes a picture by opening and closing the camera shutter. (B) shows a synchronization method when a pulse laser is used as a light source. The shutter is opened before the laser is oscillated, and the shutter is closed after the laser is oscillated after a certain period of time. In (A) and (B), synchronous imaging is performed so that equally-spaced laser beams are included one by one in one frame of the camera. (C) shows a synchronization method when a laser light source having a performance equivalent to that of the double pulse laser or a combination of two pulse lasers is used as the light source. In (C), two consecutive frames are synchronously photographed so that one laser beam enters each of the second half of the previous frame and the first half of the subsequent frame. When imaging is performed at such timing, the time interval between particle images obtained from successive frames becomes the time interval between pulses, and thus the time interval can be dramatically shortened.
[0009]
FIG. 3 shows a system configuration diagram in the case of using one continuous wave laser or one pulse laser and one image acquisition device. The laser oscillated from the laser light source system 1 is converted into a sheet shape by the laser sheet generating optical system 11 and irradiated to the test section 8. In the embodiment shown in FIG. 3, the pipe of the test section 8 is made of acrylic to ensure the internal visibility. Tracer particles 12 are mixed in advance in the fluid in the pipe, and the image of the laser scattered light from the tracer particles 12 is captured by the image acquisition system 9 to acquire a particle image.
[0010]
In the embodiment of FIG. 3, one Ar ⁺ ion laser is used as the laser light source system 1, one high-speed CCD camera is used as the image acquisition system 9, and polyethylene (specific gravity 0.92) having an average particle diameter of 12 μm is used as the tracer particles 12. In use, images were taken with the image frame and laser timing diagram of FIG. In this embodiment, as shown in FIG. 4, the laser beam is continuously oscillated, and the frame interval and the exposure time are set by the internal shutter of the high-speed CCD camera.
[0011]
In addition, since the mixed layer is a flow field in which an average flow exists, if the size of the microscopic inspection region is too small, particles move out of the microscopic inspection region during the double pulse of the laser beam, and the particle pattern Correlation is lost. For this reason, when measuring a high-speed flow, the size of the minute inspection region must be increased. However, in order to increase the spatial resolution of the PIV, the dilemma that the size of the minute inspection region must be decreased. There is. In order to solve these problems and obtain a velocity vector with high spatial resolution, the present embodiment employs a velocity vector calculation method according to the following steps (1) to (4).
[0012]
(1) A velocity vector is calculated in a large inspection area (96 × 96 pixels).
[0013]
(2) Apply a low-pass filter under the periodic boundary condition to remove the error vector.
[0014]
{Circle around (3)} A correlation function between images taken continuously in a small minute inspection region (32 × 32 pixels) is calculated, and a velocity vector with high spatial resolution is calculated.
[0015]
(4) Apply a low-pass filter to remove error vectors.
[0016]
FIG. 5 is a typical particle image, where the bright areas show particles. FIG. 6 shows an example of a velocity vector in a plane obtained from two consecutive particle images, and the state of the plane flow field can be visually grasped from this figure.
[0017]
FIG. 7 is a velocity power spectrum obtained from the Fourier transform of one point of time-series velocity data measured under the above conditions. It can be seen that the spectrum rises in the high frequency range and non-physical signals are detected. This indicates the presence of an error vector. In conventional particle image measurement, error vectors are removed by applying only a low-pass filter based on spatial resolution in a two-dimensional plane, but the error vectors cannot be completely removed. Therefore, in this embodiment, a temporal low-pass filter is applied in addition to a spatial low-pass filter, and error vectors are further removed. FIG. 8 shows a power spectrum of speed obtained by applying a cutoff filter in the frequency space and removing an error vector. FIG. 9B shows the final velocity vector distribution obtained by performing the inverse Fourier transform after applying the cutoff filter in the frequency space, and FIG. 9A shows the case where the cutoff filter is not applied. Is the final velocity vector distribution.
[0018]
FIG. 10 shows a system configuration using a double pulse laser system combining two pulse laser light sources 13 and one high-speed camera. By using two pulsed lasers 13 as the laser light source 1 and synchronizing the laser oscillation by the laser synchronization system 14, it is possible to perform imaging at the timing shown in FIG. 2C. It is possible to dramatically shorten the time interval.
[0019]
The embodiment of FIG. 11 uses a double pulse laser system similar to the embodiment of FIG. 10 as the laser light source system 1, uses two high-speed cameras as the image acquisition system 9, and uses the laser light source system 1 and the laser sheet generation optics. A system configuration in which a system and an 11 image acquisition system 9 are installed on a uniaxial movable device 15 is shown. With this system configuration, it is possible to measure a velocity vector in a three-dimensional space.
[0020]
10 and 11, the jet flow by the lob nozzle 17 is used as the test section 8.
[0021]
【The invention's effect】
According to the planar and spatial time-series fluid velocity measuring system according to the present invention, the spatial velocity of the planar or spatial fluid velocity that can be obtained only at about 15 Hz with the conventional particle image velocimetry system is high up to 100 Hz to 4 kHz or more. It is possible to measure with high accuracy while maintaining In addition, by measuring with high time resolution of 100 Hz or higher, a technique for obtaining final speed data by removing errors from time-series planes or speed data in space using characteristics of time-series. In addition, a technique for measuring the velocity vector in the three-dimensional space by installing the image acquisition device and the laser sheet optical system on one movable device is possible.
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of an entire system.
FIG. 2 is a timing diagram of a camera frame and a laser in various laser light sources.
FIG. 3 is a diagram showing a system configuration when one continuous wave laser or one pulse laser and one high-speed camera are used.
FIG. 4 is a diagram illustrating a timing diagram of a shutter.
FIG. 5 is a view showing a typical particle image taken.
FIG. 6 is a diagram showing in-plane velocity vectors obtained from two consecutive particle images.
FIG. 7 is a diagram showing a velocity power spectrum obtained from a Fourier transform of a point of time-series velocity data.
FIG. 8 is a diagram showing a power spectrum of speed obtained by applying a cutoff filter in a frequency space and removing an error vector.
FIG. 9 shows a final velocity vector distribution (B) obtained by performing an inverse Fourier transform after applying a cutoff filter in a frequency space and a final velocity vector distribution (B) obtained without applying a cutoff filter. It is a figure which shows A).
FIG. 10 is a diagram showing a system configuration when a double pulse laser system combining two pulse lasers and one high-speed camera are used.
FIG. 11 is a diagram showing a system configuration when a double pulse laser system in which two pulse lasers are combined and two high-speed cameras are arranged on a single-axis movable device.
[Explanation of symbols]
1 Laser light source system 2 Cylindrical lens (a)
3 Cylindrical lens (b)
4 Galvanometer / Scanner 5 Axial object mirror 6 Cylindrical lens (c)
7 Cylindrical lens (d)
8 Test section 9 Image acquisition system 10 System control and image analysis system (PC)
11 Laser sheet generation optical system 12 Tracer particle 13 Pulse laser light source 14 Laser synchronization system 15 Single-axis movable device 16 Laser synchronization system 17 Rob nozzle

Claims (12)

A planar and spatial time-series fluid velocity measurement system comprising an image acquisition system having a laser light source, a laser sheet generation optical system, and a high-speed video camera equipped with one or a plurality of CCD image sensors, The laser light oscillated from the light source is converted into a sheet-like laser by the laser sheet generating optical system, the sheet-like laser is irradiated to a fluid to be measured, the light source and the image acquisition system are synchronized, and the time interval is small, The scattered light image by the particles in the fluid to be measured or the spatial grayscale image of the fluid is continuously captured by the high-speed video camera, and the velocity vector is obtained by calculating the velocity vector from the two temporally continuous images by the cross-correlation method. For each velocity vector distribution, the time series velocity at each velocity definition point is Fourier transformed, and the cutoff filter is used in the frequency space. Or subjected to low-pass filter, by inverse Fourier transform, the time series fluid velocity measurement system of the plane and space, characterized in that to obtain a final time sequence rate. 2. The planar and spatial time-series fluid velocity measurement system according to claim 1, wherein a CCD image sensor capable of photographing at 1 kHz or more with 512 × 512 pixels or more is used as the CCD image sensor. The planar and spatial time-series fluid velocity measurement system according to claim 1, wherein a CMOS image sensor is used in place of the CCD image sensor as the image acquisition system. The planar and spatial time-series fluid velocity measurement system according to claim 3, wherein a CMOS image sensor having a number of image sensors of 512 × 512 pixels or more and capable of photographing at 1 kHz or more is used as the CMOS image sensor. As the laser light source, using a pulse laser of 100 Hz or more,
The planar and spatial time-series fluid according to any one of claims 1 to 4, wherein imaging is performed by synchronizing the light source and the image acquisition system so that laser beams at equal intervals enter one frame at a time. Speed measurement system. As the laser light source, a double pulse laser of 100 Hz or more with a variable time interval between double pulses is used, and in two consecutive frames, one laser beam is emitted in each of the second half of the front frame and the first half of the rear frame. 5. The planar and spatial time-series fluid velocity measurement system according to claim 1, wherein photographing is performed in synchronization with each other so as to be performed. 7. A time-series fluid in a plane and a space according to claim 6, wherein a laser system is used in which two pulse lasers of 100 Hz or more are combined instead of the double pulse laser, and the interval of pulses alternately and continuously emitted from each is variable. Speed measurement system. 5. The plane and space time according to claim 1, wherein a continuous wave laser is used as the laser light source to continuously oscillate a laser, and a particle image is obtained by opening and closing a camera shutter at a predetermined time interval. Series fluid velocity measurement system. 9. The plane and space time-series fluid velocities according to claim 1, wherein a final time-series velocity is obtained by directly applying a low-pass filter to the time-series data in the calculation of the velocity vector. Measuring system. Velocity vector information at the time lost due to measurement error, etc. by Fourier transforming the time-series data with respect to the velocity vector distribution, applying a cut-off filter or low-pass filter in the frequency space, and performing inverse Fourier transform 9. The planar and spatial time-series fluid velocity measurement system according to any one of claims 1 to 8, wherein a final time-series velocity is obtained by interpolating velocity vector information between measurement times. Two high-speed video cameras are used, and the two cameras are arranged with a tilt so that the Shine flag condition where the image plane, the lens main plane, and the extension line of the sheet plane meet at one point is satisfied, and the same operation By capturing images synchronously, two image pairs were obtained from different angles at the same time, moving amount vectors at each speed definition point were calculated from the image pairs captured by each camera, and observed obliquely. A plane using stereo projection that corrects the trapezoidal distortion of the image and matches the speed definition points of the two cameras to obtain time-series data of the three-dimensional velocity vector in the plane from the angle difference between the two cameras. The planar and space time-series fluid velocity measurement system according to any one of claims 1 to 10, wherein three-dimensional velocity measurement is performed. 12. One or more of the high-speed video cameras and a laser sheet generating optical system are installed on a movable device having a moving speed of 0.5 m / s or more on one or more movable axes. The planar and space time-series fluid velocity measurement system according to any one of the above.

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