JP2012002665A - Fluctuation image analysis method and fluctuation image analysis system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluctuation image analysis method and a fluctuation image analysis system capable of improving SNR with a simple constitution and highly precisely acquiring unsteady fluid phenomena.SOLUTION: This fluctuation image analysis system consecutively acquires, with time, images of an object 1 to be measured which is applied with pressure-sensitive paint and where the intensity of the light emission on the surface is changed by a change in the pressure, and at the same time, measures, with time, the pressure to be a reference on the surface of or adjacent to the object 1 to be measured. A pressure fluctuation having a predetermined frequency is extracted by a band-pass filter based on a time change in the measured reference pressure. A phase of each image in the extracted pressure fluctuation period is acquired based on the time when each image is acquired. Each image is distributed to a plurality of phase bands based on the acquired phase of each image, and the plurality of images included in each phase band are averaged to acquire an average image for every phase band.

Description

  The present invention relates to a variation image analysis method and a variation image analysis system.

  Conventionally, in order to measure unsteady fluid phenomena, unsteady velocity field measurement using dynamic particle image velocimetry (PIV) has been performed, which is helpful for understanding unsteady fluid phenomena. Yes. However, the fluid force that the fluid is actually applying to the object cannot be known only by the information on the velocity field. In order to know the fluid force applied to an object, it is important to know local pressure fluctuations caused by vortex advection and discharge. For this reason, there is a demand for practical use of unsteady pressure-sensitive paint measurement, which is a surface measurement technique for unsteady pressure fields.

  However, it is very difficult to apply pressure-sensitive paint (PSP) technology (for example, see Non-Patent Document 1) to a phenomenon that is unsteady and has a small amount of pressure fluctuation from the viewpoint of responsiveness and signal-to-noise ratio (SNR). is there. Even if the unsteady phenomenon is a periodic phenomenon, it often has a wide range of fluctuation frequencies, and the amplitude and vibration center are not constant. For this reason, it is difficult to improve the SNR by simple addition averaging.

  In order to solve such a problem, as a non-stationary PSP technique including image measurement and analysis of the obtained image, a so-called phase-lock method (for example, non-patent literature) that can be applied to a periodic phenomenon. 2) and the FFT method (see, for example, Non-Patent Document 3 or Patent Document 1) have been developed.

A pressure-sensitive paint (PSP) is a paint composed of a dye that emits phosphorescence when irradiated with excitation light and a polymer as a binder. Oxygen quenching in which the emission intensity of the dye changes depending on the surrounding oxygen concentration. ) Is an optical oxygen molecular sensor that utilizes a phenomenon called “). Since there is a correlation between the pressure acting on the surface of the object coated with the pressure-sensitive paint and the oxygen concentration, a pressure value can be obtained. In the wind tunnel test, the pressure P is calculated from the light emission intensity ratio I _ref / I of the pressure-sensitive paint between the reference state (generally no wind) and the ventilation using the Stern-Volmer relational expression (1). be able to.
I _ref / I = A + B · P / P _ref (1)
Here, the subscript ref represents a reference state, and A and B are Stern-Volmer coefficients.

JP 2008-82735 A

Bell, J. H., Schairer, E. T., Hand, L. A., and Mehta, R. D., “Surfacepressure measurements using luminescent coatings”, Annual Review of Fluid Mechanics, 2001, 33, p.155-206 Yorita, D., Narumi, T., Nagai, H., and Asai, K., “Unsteady PSP Technique for Measuring Naturally-Disturbed Periodic Phenomena, AIAA2010-307, 2010 Nakakita, K., “Unsteady Pressure Distribution Measurement around 2D-Cylinders Using Pressure-Sensitive Paint”, AIAA 2007-3819, 2007

  The phase lock method and the FFT method have been tried to be applied to a wide band phenomenon and a phenomenon having fluctuations. However, when applied to such a phenomenon, the phase lock method has problems that the measurement system becomes complicated and the phase cannot be resolved with sufficient accuracy. On the other hand, the FFT method has a problem that the image processing method becomes complicated.

  The present invention has been made paying attention to such a problem, and provides a variation image analysis method and a variation image analysis system that can increase the SNR with a simpler configuration and accurately grasp an unsteady fluid phenomenon. The purpose is to do.

  In order to achieve the above object, a variation image analysis method according to the present invention includes an image acquisition step of continuously acquiring images of a measurement object whose intensity of light emission on a surface changes due to a change in a first physical quantity, over time. In parallel with the image acquisition step, a reference data acquisition step for measuring the second physical quantity at or near the surface of the measurement object over time, and a time change of the second physical quantity measured in the reference data acquisition step The second physical quantity extracted in the fluctuation extraction step based on the fluctuation extraction step of extracting the fluctuation of the second physical quantity having a predetermined frequency, and the time when each image was acquired in the image acquisition step And a phase determination step for obtaining the phase of each image in the fluctuation period.

  The variation image analysis system according to the present invention includes an image acquisition unit that continuously acquires, over time, an image of a measurement target in which the intensity of light emission on the surface changes due to a change in the first physical quantity, and an image acquired by the image acquisition unit. In parallel with the acquisition, a reference sensor that measures the second physical quantity at or near the surface of the measurement object over time, and a predetermined frequency based on a time change of the second physical quantity measured by the reference sensor. Analysis means for extracting a change in the second physical quantity and obtaining a phase of each image in a fluctuation cycle of the second physical quantity based on a time when each image is obtained by the image obtaining means. And

  The variation image analysis method and the variation image analysis system according to the present invention can determine the phase of each image in one cycle of the variation having a predetermined frequency of the second physical quantity. By rearranging the images in the order of the obtained phases or averaging and rearranging the images for each predetermined phase width, the second physical quantity having a predetermined frequency has a first frequency within one cycle. It is possible to easily grasp a change in one physical quantity.

  Therefore, by measuring the physical quantity that changes in relation to the change of the first physical quantity as the second physical quantity, paying attention to the fluctuation of the predetermined frequency even if the phenomenon has a broadband phenomenon or fluctuation. The periodic change of the first physical quantity can be grasped with an image. As described above, the variation image analysis method and the variation image analysis system according to the present invention can increase the SNR with a simpler configuration than the phase lock method and the FFT method, and can accurately grasp an unsteady fluid phenomenon.

  The image acquisition means for continuously acquiring the image to be measured only needs to have a photographing speed and resolution capable of measuring the change in the first physical quantity, and is composed of, for example, a CMOS high-speed camera. The first physical quantity may be any physical quantity that can be measured by a change in the surface of the measurement target such as the intensity of light emission. The first physical quantity includes, for example, pressure, temperature, and the like that can be measured by applying a pressure-sensitive paint or a temperature-sensitive paint to the surface of the measurement target.

  The second physical quantity may be any physical quantity that is considered to change in relation to the change in the first physical quantity, and includes, for example, pressure, sound, flow velocity, force, displacement, and the like. The reference sensor for measuring the second physical quantity over time may be any sensor as long as it can extract a variation of the second physical quantity having a desired frequency. Moreover, even if it is directly installed on the surface of the measurement object, it may be installed in the vicinity of the measurement object without touching the measurement object. It may be installed in multiple places. The predetermined frequency of interest may be one or plural.

  The variation image analysis method according to the present invention divides one cycle into a plurality of phase bands, distributes each image to each phase band based on the phase of each image obtained in the phase determination step, It is preferable to have an image averaging process step of averaging a plurality of included images to obtain an averaged image for each phase band.

  In the variation image analysis system according to the present invention, the analysis unit divides one cycle into a plurality of phase bands, distributes each image to each phase band based on the phase of each image, and includes a plurality of included in each phase band. It is preferable to average these images to obtain an averaged image for each phase band.

  By obtaining an averaged image for each phase band, changes that differ from period to period, changes that are shorter than the width of the phase band, changes that differ from the predetermined frequency, etc. can be made relatively small, and fluctuations in the predetermined frequency SNR can be further increased. In order to increase the analysis accuracy, it is preferable that the image is distributed without deviation in each phase band, and it is preferable that the phase of the image is distributed evenly in each phase band. The averaged image can be obtained by, for example, simply averaging a plurality of images included in each phase band, or adding and weighting each image according to the position of each image in the phase band. It can be obtained by doing.

  In the variation image analysis method according to the present invention, the first physical quantity is composed of pressure, the measurement object is formed by applying a pressure-sensitive paint on the surface, and the second physical quantity is pressure, sound, flow velocity, force or displacement. The fluctuation extracting step includes applying a bandpass filter having the predetermined frequency as a center frequency to the second physical quantity, or time-differentiating the second physical quantity to obtain the predetermined frequency. You may extract the fluctuation | variation of the said 2nd physical quantity which has.

  In the fluctuating image analysis system according to the present invention, the first physical quantity includes pressure, the measurement object is formed by applying a pressure-sensitive paint on a surface, and the reference sensor includes a pressure sensor, a microphone, a flow rate sensor, a force The analysis means comprises a sensor or a displacement sensor, and the analyzing means applies a bandpass filter having the predetermined frequency as a center frequency to the second physical quantity, or time-differentiates the second physical quantity, and The fluctuation of the second physical quantity having a frequency of may be extracted.

  By using the pressure sensitive paint, it is possible to accurately grasp an unsteady fluid phenomenon accompanied by pressure fluctuation. Moreover, the fluctuation | variation of the 2nd physical quantity which has a significant desired frequency can be easily extracted by using a band pass filter and a time differentiation. In order to obtain sufficient analysis accuracy, the pressure-sensitive paint is preferably composed of a material having sufficient sensitivity to a predetermined frequency variation and a sufficiently fast response time.

  In the variation image analysis method according to the present invention, the predetermined physical value among the variations of the first physical quantity based on the averaged image obtained in the image averaging process step at an arbitrary position of the measurement target is determined. There may be provided a position variation determining step for obtaining a phase deviation from the amplitude of the variation at the frequency and the variation of the second physical quantity extracted in the variation extracting step.

  In the variation image analysis system according to the present invention, the analysis unit is configured to detect, with respect to an arbitrary position of the measurement target, at the predetermined frequency among variations in the first physical quantity based on the averaged image at the position. And the phase shift from the fluctuation of the second physical quantity may be obtained.

  By obtaining the amplitude and phase shift of the fluctuation of the predetermined frequency at an arbitrary position of the measurement object, the fluctuation of the first physical quantity at that position can be grasped in detail. By obtaining the amplitude and phase shift of the fluctuation of the predetermined frequency for all the positions of the measurement object, the fluctuation of the first physical quantity of the measurement object can be grasped in detail. In addition, by representing the deviation of the amplitude and phase as an image, it can be easily grasped visually. The deviation of the amplitude and the phase can be obtained for each position of the measurement object, for example, by approximating the fluctuation of the first physical quantity with a sine wave.

  According to the present invention, it is possible to provide a variation image analysis method and a variation image analysis system capable of increasing the SNR with a simpler configuration and accurately grasping an unsteady fluid phenomenon.

It is a perspective view which shows the fluctuation | variation image analysis system of embodiment of this invention. It is a flowchart which shows the fluctuation | variation image analysis method of embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a perspective view showing a three-dimensional prism model that is a measurement target of a variation image analysis method and a variation image analysis system according to an embodiment of the present invention, and FIG. It is the graph which shows the (a) time-sequential waveform of the pressure fluctuation by a reference | standard sensor of the fluctuation | variation image analysis method and fluctuation | variation image analysis system of embodiment of this invention, (b) It is a graph which shows an amplitude spectrum. (A) A graph showing a time series waveform of pressure fluctuations by a reference sensor of the fluctuation image analysis method and fluctuation image analysis system according to the embodiment of the present invention, and (b) a time series waveform of pressure fluctuations after application of a bandpass filter. FIG. 4C is a graph showing a pulse signal of shooting timing of the high-speed camera. It is the averaged image of the pressure in the side surface of the three-dimensional prism model calculated | required for every 12 phase bands divided | segmented into 30 deg of the fluctuation image analysis method and fluctuation image analysis system of embodiment of this invention. Pressure fluctuation (black circle in the figure) at the center of the three-dimensional prism model obtained from the averaged image and pressure fluctuation obtained by the reference sensor in the fluctuation image analysis method and fluctuation image analysis system of the embodiment of the present invention It is a graph which shows (the solid line in a figure). (A) An image showing the amplitude (pressure ratio) of fluctuation at 150 Hz obtained on the side surface of the three-dimensional prism model of the fluctuation image analysis method and fluctuation image analysis system of the embodiment of the present invention, and (b) 150 Hz of the reference sensor. It is an image which shows the shift | offset | difference of the phase from a pressure fluctuation. It is the averaged image of the pressure on the flat plate calculated | required for every 12 phase bands divided | segmented every 30 degrees of the fluctuation | variation image analysis method and fluctuation | variation image analysis system of embodiment of this invention. From the fluctuation image analysis method and fluctuation image analysis system according to the embodiment of the present invention, (a) an image showing the fluctuation amplitude (pressure ratio) of 150 Hz obtained on a flat plate, (b) from the pressure fluctuation of 150 Hz of the reference sensor. (C) an image showing the amplitude (pressure ratio) of the fluctuation at 300 Hz, and (d) an image showing the phase deviation from the pressure fluctuation at 300 Hz of the reference sensor.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 10 show a variation image analysis method and a variation image analysis system according to an embodiment of the present invention.
As shown in FIG. 1, the fluctuation image analysis system 10 includes an image acquisition unit 11, a reference sensor 12, and an analysis unit 13.

  As shown in FIG. 1, the measuring object 1 of the fluctuation image analysis system 10 is formed by applying a pressure-sensitive paint on the surface. The pressure-sensitive paint is composed of a material having sufficient sensitivity and sufficiently fast response time with respect to a change in frequency to be measured. The measurement object 1 is configured such that the intensity of light emission on the surface changes according to the change in the pressure of the first physical quantity.

  As shown in FIG. 1, the image acquisition means 11 includes two ultraviolet LEDs (UV-LEDs) 21 for exciting the pressure-sensitive paint and a high-speed camera 22. The image acquisition unit 11 continuously acquires images of the measurement target 1 with the high-speed camera 22 while irradiating the measurement target 1 with light of the ultraviolet LED 21 to emit pressure-sensitive paint. The high-speed camera 22 is composed of a camera having a photographing speed and resolution capable of measuring a change in pressure of the measurement object 1 to be measured. The high-speed camera 22 can output the image capturing timing as a pulse signal.

  As shown in FIG. 1, the reference sensor 12 includes a pressure transducer that can measure the pressure of the second physical quantity, and is attached to the surface of the measuring object 1. The reference sensor 12 measures the pressure on the surface of the measuring object 1 with time in parallel with the image acquisition by the image acquisition means 11. The reference sensor 12 can measure a pressure fluctuation at a frequency to be measured. In addition to the pressure, the reference sensor 12 is a microphone, a flow rate sensor, or a force sensor that can measure a sound, a flow rate, a force, and a displacement that change in association with a change caused by the pressure-sensitive paint measured by the image acquisition unit 11. A displacement sensor may be used. Moreover, the reference sensor 12 may be installed in the vicinity of the measuring object 1, and may be installed in one place or may be installed in a plurality of places.

  As shown in FIG. 1, the analysis means 13 includes a data logger 23 and an analysis unit 24. The data logger 23 is connected to the high-speed camera 22 and the reference sensor 12, and can record an image acquired by the high-speed camera 22 and pressure data measured by the reference sensor 12 in a simultaneous series. . In addition, the data logger 23 can record the pulse signal of the photographing timing from the high-speed camera 22 in the same series.

  The analysis unit 24 includes a computer and is connected to the data logger 23. The analysis unit 24 can analyze the data recorded in the data logger 23. The analysis unit 24 extracts a pressure fluctuation having a desired frequency based on the time change of the pressure data measured by the reference sensor 12. At this time, the analysis unit 24 extracts a pressure fluctuation having a desired frequency by applying a bandpass filter whose center frequency is a desired frequency to the pressure data, or by time-differentiating the pressure data. It is supposed to be.

  The analysis unit 24 converts all images acquired by the image acquisition unit 11 from an image of emission intensity to an image of pressure using Expression (1). Next, the analysis unit 24 obtains the phase of each image in the fluctuation cycle of the pressure data having a desired frequency based on the time when each image is acquired by the image acquisition unit 11.

  The analysis unit 24 divides one period into a plurality of phase bands, distributes each image to each phase band based on the obtained phase of each image, averages a plurality of images included in each phase band, and outputs each phase An averaged image for each band is obtained. At this time, the analysis unit 24 obtains an averaged image by averaging the plurality of images included in each phase band. The analysis unit 24 can output the averaged images obtained in the order of the phase bands.

  Further, the analysis unit 24, for all the positions of the measurement object 1, among the pressure fluctuations based on the averaged image at each position, the amplitude of the fluctuation at a desired frequency and the desired frequency by the reference sensor 12 The phase shift from the pressure fluctuation is obtained. At this time, the analysis unit 24 obtains a deviation in amplitude and phase by approximating the pressure fluctuation of the averaged image with a sine wave for each position of the measurement object 1. The analyzing unit 24 can output the obtained amplitude and phase shifts as an image.

  The variation image analysis method according to the embodiment of the present invention can be implemented by the variation image analysis system 10. As shown in FIG. 2, in the variation image analysis method according to the embodiment of the present invention, first, the image of the measurement object 1 coated with the pressure-sensitive paint is continuously acquired over time by the image acquisition unit 11. ("PSP images"; step 31) In parallel with this, the pressure on the surface of the measuring object 1 is measured over time by the reference sensor 12 ("Reference signal"; step 32). Next, the analysis means 13 extracts a pressure fluctuation having a desired frequency from the time change of the pressure data measured by the reference sensor 12 (“Conditioned signal”; step 33). At this time, since a band-pass filter and time differentiation are used, it is possible to easily extract significant pressure fluctuations passing through a desired frequency band by removing high-frequency noise and low-frequency bias fluctuations included in the data.

The analysis unit 13 converts all images acquired by the image acquisition unit 11 into pressure images using Expression (1) (“Pressure images”; step 34). At this time, only the pressure fluctuation component can be obtained by using an averaged image of all acquired images as the reference image (I _ref ) of the emission intensity. Moreover, the influence of the temperature change of the measuring object 1 and the light deterioration of the pigment can be reduced, and the position correction of the deformation of the measuring object 1 is not necessary.

  Next, the phase of each image in the fluctuation cycle of the pressure data having a desired frequency is obtained by the analyzing unit 13 based on the time when each image is acquired by the image acquiring unit 11 (“Phase categorized images”; step 35). . Based on the obtained phase of each image, each image is distributed to each phase band obtained by dividing one period, and a plurality of images included in each phase band are averaged to obtain an averaged image for each phase band ( “Phase-averaged images”; step 36). At this time, by obtaining an averaged image, changes different from period to period, changes different from the desired frequency, and the like can be made relatively small, and the SNR for fluctuations in the desired frequency can be increased. In addition, it is possible to easily grasp the change in pressure on the surface of the measuring object 1 within one cycle of fluctuation having a desired frequency.

  Furthermore, the analysis means 13 makes the amplitude of the fluctuation at a desired frequency out of the pressure fluctuations based on the averaged image at each position and the desired frequency by the reference sensor 12 for all the positions of the measuring object 1. The phase shift from the pressure fluctuation is obtained. Thereby, pressure fluctuations can be grasped in detail for all positions of the measuring object 1.

  As described above, according to the variation image analysis method and the variation image analysis system 10 according to the embodiment of the present invention, paying attention to the variation of a predetermined frequency even if the phenomenon has a wide-band phenomenon or fluctuation, A periodic change in pressure on the surface of the measuring object 1 can be easily grasped with an image. Further, since the pressure sensitive paint is used, it is possible to accurately grasp the unsteady fluid phenomenon accompanied by the pressure fluctuation. The variation image analysis method and the variation image analysis system 10 according to the present invention can increase the SNR with a simpler configuration than the phase lock method and the FFT method, and can accurately grasp an unsteady fluid phenomenon.

  The fluctuation image analysis method and the fluctuation image analysis system 10 according to the embodiment of the present invention are applied to a periodic pressure fluctuation field generated on the side surface of the three-dimensional prism model 51 shown in FIG. The effectiveness was evaluated. As shown in FIG. 3, the three-dimensional prism model 51 has a square cross section of 40 mm in length and 40 mm in width, and has a height of 100 mm. The three-dimensional prism model 51 is hollow inside. The pressure-sensitive paint (PSP) is applied to one entire side surface of the three-dimensional prism model 51. A removable test plate 51a having a width of 30 mm, a height of 100 mm, and a thickness of 5 mm is embedded in the coating surface of the pressure-sensitive paint. There is no step between the three-dimensional prism model 51 and the test plate 51a. A pressure transducer (manufactured by Kulite Semiconductor Products, Inc .; product name “XCL-152”) as a reference sensor 12 is attached to the center of the meter side surface.

  The pressure-sensitive paint is made of a highly responsive Polymer / Ceramic PSP (PC-PSP) having a sufficiently fast response time for fluctuations of several hundred Hz or less. The pressure-sensitive paint is applied to the side surface of the three-dimensional prism model 51 by spraying. The pressure-sensitive paint uses PtTFPP as a pigment and has a sensitivity to pressure of 0.5% / kPa.

  Using this three-dimensional prism model 51, a wind tunnel test was conducted. The wind tunnel used in the wind tunnel test is an air suction type, and the temperature rise due to ventilation is relatively small, so it is suitable for experiments using pressure sensitive paint. The three-dimensional prism model 51 is fixed to a turn table having a diameter of 250 mm on a flat plate 52. In this test, a pressure-sensitive paint was applied also on the turntable, and the periodic pressure fluctuation field generated on the flat plate 52 on which the three-dimensional prism model 51 was installed was also measured. The main flow velocity was 50 m / s, and the model yaw angle was 0 deg so that the measurement surface was parallel to the flow.

  As shown in FIG. 1, the measurement of the pressure-sensitive paint surface by the high-speed camera 22 and the pressure measurement by the pressure transducer of the reference sensor 12 were performed in parallel. Here, the UV LED 21 uses a product name “LEDH576-395” having a peak wavelength of 395 nm; the product name “LEDH576-395”, and the high-speed camera 22 has a resolution of 12-bit CMOS high-speed camera (Photo) Ron, product name “FASTCAM SA5”) was used. The shooting speed of the high-speed camera 22 was 1000 frames / s, and 23,000 luminescent images of pressure-sensitive paint during ventilation were acquired. The exposure time per image was set to 0.99 ms. Thus, the obtained luminescent image is an average image having a phase width of 54 deg of the fluctuation phenomenon. The data logger 23 was manufactured by Yokogawa Electric Corporation; the product name “WE7000” was used, and the sampling rate was 10 kHz.

  FIG. 4 shows a time-series waveform and an amplitude spectrum of the pressure fluctuation generated on the side surface of the three-dimensional prism model 51 measured by the pressure transducer of the reference sensor 12. As shown in FIG. 4B, the basic component of the pressure fluctuation generated on the side surface of the three-dimensional prism model 51 is sinusoidal vibration with a frequency of 150 Hz. However, as shown in FIG. 4A, the amplitude, period, and zero point have fluctuations. A 1-octave bandpass filter having a center frequency of 150 Hz was applied to the pressure fluctuation shown in FIG. The pressure fluctuation of 150 Hz obtained by this is shown in FIG.

All images acquired by the high-speed camera 22 were converted from a light emission intensity image into a pressure image using Equation (1). As shown in FIG. 5, the respective phases of the obtained pressure images were determined using the pressure transducer data. Here, first, the point at which the sign of the pressure fluctuation shown in FIG. 5B changes from negative to positive is defined as the fluctuation starting point (phase 0 deg), and one period of fluctuation is determined. Here, the phase theta _image included in each image, the length T _j of one cycle, the time difference t _i from variation start point of the immediately preceding,
θ _image = t _i / T _j × 360 [deg] (2)
Can be defined. Using this equation (2), the phases of all the images were obtained.

  Based on the obtained phase of each image, all 23,000 images are distributed in 30 deg increments to 12 phase bands, and a plurality of images included in each phase band are added and averaged for each phase band. 12 averaged images were obtained. The obtained averaged image for each phase band is shown in FIG. The direction in which the wind flows is from the left to the right of each image. As shown in FIG. 6, the pressure fluctuation field periodically generated on the side surface of the three-dimensional prism model 51 can be clearly visualized. This pressure fluctuation tends to become stronger toward the lower side of the three-dimensional prism model 51, and it can be confirmed that a region having a strong fluctuation appears locally at the bottom of the rear edge side of the three-dimensional prism model 51.

  FIG. 7 shows the pressure fluctuation (black circle in FIG. 7) at the center of the three-dimensional prism model 51 obtained from the averaged image of FIG. 6 and the pressure fluctuation obtained by the reference sensor 12. As shown in FIG. 7, by obtaining an averaged image, a sine fluctuation of pressure generated on the side surface of the three-dimensional prism model 51 is captured, and the measurement result of the reference sensor 12 is in good agreement with the measurement result. I understand that.

Next, with respect to all the positions on the side surface of the three-dimensional prism model 51, among the pressure fluctuations based on the averaged image at each position, the amplitude of the fluctuation of 150 Hz and the pressure fluctuation of the reference sensor 12 from 150 Hz. The phase shift was determined. Here, first, after binning the averaged image shown in FIG. 6 in an area of 5 × 5 pixels, the distribution of the amplitude A and the phase shift θ 0 is obtained by performing the sine wave approximation of Equation (3) on each pixel. Asked.
P / P _ref = A · sin (θ + θ ₀ ) + B (3)
Here, B is a bias component.

The distribution of the obtained amplitude A and phase shift θ ₀ is shown in FIG. As shown in FIG. 8, the pressure fluctuation generated on the side surface of the three-dimensional prism model 51 can be clearly grasped by visualizing the amplitude and phase distribution. As shown in FIG. 8A, it can be confirmed that a strong fluctuation occurs at the bottom of the rear edge side of the three-dimensional prism model 51. Further, as shown in FIG. 8B, in the phase distribution, a region where the phase is delayed by about 15 degrees can be confirmed in the vicinity of the trailing edge. This phase lag region seems to correlate with a region having a locally strong amplitude. These structures are considered to be caused by a complicated flow field around the three-dimensional prism model 51.

  Similarly, an averaged image of the periodic pressure fluctuation field generated on the flat plate 52 on which the three-dimensional prism model 51 is installed is obtained and shown in FIG. The direction in which the wind flows is from the left to the right of each image. The reference sensor 12 is installed on the lower side surface of each image. As shown in FIG. 9, it is captured that a symmetric region of negative pressure and positive pressure moves from the vicinity of the side surface of the three-dimensional prism model 51 to the downstream, and periodically generated on the flat plate 52. The pressure fluctuation field can be clearly visualized. It can be considered that the pressure fluctuation field shown in FIG. 9 is generated by alternately passing vortices generated from the front edge of the three-dimensional prism model 51.

For all the positions on the flat plate 52, the pressure fluctuation amplitude and phase shift shown in FIG. 9 are obtained and shown in FIG. Here, considering the passage of a pair of alternating vortices, the sinusoidal approximation is performed by the equation (4) including the component of the second harmonic to obtain the deviation of the amplitude and the phase.
P / P _ref = A ₁ · sin (θ + θ ₁ ) + A ₂ · sin (θ + θ ₂ ) + B (4)
Here, the subscripts 1 and 2 mean a fundamental wave (f = 150 Hz) component and a double wave (f = 300 Hz) component, respectively.

  As shown in FIG. 10A, it can be seen that pressure fluctuation occurs from the vicinity of the side surface of the three-dimensional prism model 51 to the downstream side. Behind the three-dimensional prism model 51, this variation is maximum. This amplitude distribution appears symmetrically with respect to the central axis of the model 51 in the flow direction. On the other hand, as shown in FIG. 10B, the phase has a distribution that is inverted by 180 degrees on the central axis. This indicates that two symmetrical pressure fluctuations occur with a half-cycle shift. As shown in FIGS. 10C and 10D, the second harmonic component appears only on the back surface of the three-dimensional prism model 51 through which both of the alternating vortices pass. Thus, the pressure fluctuation field induced when a pair of alternating vortices flows downstream can be clearly understood.

  The variation image analysis method and the variation image analysis system according to the present invention are used for wind tunnel experiments using a scale model or a real object in the transportation field of automobiles, high-speed railways, airplanes, and the construction field of buildings and bridges. Can do. The present invention can also be used in the field of sports engineering for rotating machines such as compressors and propellers, fluid machines such as blowers and air conditioners, and golf balls.

DESCRIPTION OF SYMBOLS 10 Fluctuating image analysis system 11 Image acquisition means 12 Reference sensor 13 Analysis means 21 Ultraviolet LED
22 High-speed camera 23 Data logger 24 Analysis unit

Claims (8)

An image acquisition step of continuously acquiring an image of a measurement object whose intensity of light emission on the surface changes due to a change in the first physical quantity;
In parallel with the image acquisition step, a reference data acquisition step of measuring the second physical quantity at or near the surface of the measurement object over time;
A fluctuation extracting step of extracting a fluctuation of the second physical quantity having a predetermined frequency based on a time change of the second physical quantity measured in the reference data acquisition step;
A phase determination step for obtaining a phase of each image in a variation period of the second physical quantity extracted in the variation extraction step based on a time at which each image is acquired in the image acquisition step.
Characteristic variation image analysis method.   One period is divided into a plurality of phase bands, each image is allocated to each phase band based on the phase of each image obtained in the phase determination step, and a plurality of images included in each phase band are averaged. The variation image analysis method according to claim 1, further comprising an image averaging process step of obtaining an averaged image for each phase band. The first physical quantity comprises pressure,
The measurement object is formed by applying a pressure-sensitive paint on the surface,
The second physical quantity comprises pressure, sound, flow velocity, force or displacement,
In the fluctuation extracting step, the second physical quantity is applied with a bandpass filter having the predetermined frequency as a center frequency, or the second physical quantity is time-differentiated to obtain the first physical quantity having the predetermined frequency. 2 Extracting fluctuations in physical quantities
The variation image analysis method according to claim 1 or 2, characterized in that:   Of the variation of the first physical quantity based on the averaged image obtained in the image averaging processing step at that position for an arbitrary position of the measurement object, the amplitude of the variation at the predetermined frequency, and 3. The variation image analysis method according to claim 2, further comprising a position variation determination step for obtaining a phase shift from the variation of the second physical quantity extracted in the variation extraction step. Image acquisition means for continuously acquiring, over time, images of a measurement object in which the intensity of light emission on the surface changes due to a change in the first physical quantity;
In parallel with the image acquisition by the image acquisition means, a reference sensor that measures the second physical quantity at or near the surface of the measurement object over time,
Based on the time variation of the second physical quantity measured by the reference sensor, the variation of the second physical quantity having a predetermined frequency is extracted, and each image is obtained based on the time when each image is obtained by the image obtaining means. Having an analysis means for obtaining a phase in a fluctuation period of the second physical quantity,
Characteristic variation image analysis system.   The analysis unit divides one cycle into a plurality of phase bands, distributes the images to the phase bands based on the phase of each image, averages the plurality of images included in each phase band, and The fluctuation image analysis system according to claim 5, wherein an averaged image is obtained. The first physical quantity comprises pressure,
The measurement object is formed by applying a pressure-sensitive paint on the surface,
The reference sensor comprises a pressure sensor, a microphone, a flow rate sensor, a force sensor or a displacement sensor,
The analysis means applies the bandpass filter having the predetermined frequency as a center frequency to the second physical quantity, or time-differentiates the second physical quantity to have the second frequency having the predetermined frequency. Extracting the fluctuations in physical quantities,
The fluctuation image analysis system according to claim 5 or 6, characterized in that The analysis means, for an arbitrary position of the measurement object, among the fluctuations of the first physical quantity based on the averaged image at the position, the amplitude of the fluctuation at the predetermined frequency, and the second The fluctuation image analysis system according to claim 6, wherein a phase shift from a change in physical quantity is obtained.