JPH0223820B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a flow field observation device using an optical interference method that can non-contactly measure a three-dimensional density distribution in a fluid flow field.

(Prior Art) Among the flow field observation methods used as verification means for research and development of fluid dynamics, optical interferometry is used as a non-contact density distribution observation method. As this optical interference method, Matsuha-Zehnder interferometry, direct light transmission type laser holographic interferometry, and diffused light transmission type laser holographic interferometry have been used.

The optical arrangement of these interferometry methods is shown in Figures 4 to 6.
As shown in the figure.

FIG. 4 shows the Matsuha-Zehnder interferometry, in which the incident light 40 is split into two beams by a beam splitter 44, one beam 41 is transmitted through the observation area 43,
Interference occurs with the other beam that passes through a space that is not disturbed.

FIG. 5 shows a direct light transmission type laser holographic interferometry, in which the incident laser beam is split by a beam splitter 51, and the measurement light 49 is transmitted through a lens 5.
3 and 55, the beam diameter is expanded, passes through a measurement area 57, becomes diverging light by a lens 54, and interferes with the obliquely incident reference light 50 to record a hologram on a photosensitive material 56.

FIG. 6 shows a diffused light transmission type laser holographic interferometry, in which an incident laser beam 58 is split by a beam splitter 61, and the measurement light passes through a lens 63 and becomes diffused light 59 by a diffuser plate 65 to form a measurement area 6.
7 and interferes with a reference beam 60 that is obliquely incident through a lens 64, thereby recording a hologram on a photosensitive material 66. The observable angle at this time is indicated by Θ.

The observable angular range of the measurement region obtained by these interferometry methods is narrow, and the three-dimensional distribution of the flow field cannot be observed as is. In order to observe the three-dimensional distribution, as shown in FIG. 7, it is necessary to measure the projected amount of the measurement area 68 over an angular range in which φ usually ranges from 0° to 180°.
At this time, it goes without saying that projection information must be acquired correctly regarding the geometrical relationships of the measurement space. For flow fields with several planes of symmetry, the observation angle range required for measurement is reduced, but in the case of bilaterally symmetric flow fields, which are relatively common in test cases, the minimum φ ranges from 0° to 90°. observation is required.

For this reason, attempts have been made to make it easier to measure the density distribution of a three-dimensional flow field by expanding the observation angle of the above-mentioned diffused light transmission type laser holographic interferometry.

FIG. 9 shows an example of this, in which a light diffusing plate 78 and a hologram recording photosensitive material 79 are placed on the circumference including the measurement area 74.
from diagonally below the light diffusing plate 78,
The beam from the laser light source 75 is expanded and illuminated by a lens 76, a portion of which illuminates a light diffusing plate 78 as diffused measurement light, and a portion of which passes through an undisturbed space outside the measurement area and directly illuminates the photosensitive material. 79 as a reference beam, thereby recording and storing changes in the state of the optical wavefront caused by changes in density within the measurement area on the photosensitive material 79 as a hologram. This method is characterized by an extremely simple structure, but no specific observation examples have been reported, and this method alone has problems with the laser beam being irradiated from only one direction and the light diffusing plate. Considering the scattering characteristics of , it is effective only near the center of the diffuser plate, and it is impossible to obtain a wide observation angle.

FIG. 10 shows another example in which the observation angle range is expanded.
A light diffusing plate 85 is placed on the side, and three sheets of photosensitive material 86-1, 8 are placed at 45° intervals on the opposite side across the measurement area.
6-2 and 86-3 are installed to enable simultaneous observation in directions from 0° to 90°. 80 is a pulse laser, 81 is a gas laser, 83 1 to 5 are beam splitters, and 84 1 to 9 are plane mirrors. However, with this method, the observable angle of the hologram that can be recorded with each photosensitive material is not so wide;
It is not possible to perform continuous observation in the angular range of 0° to 90° with only three holograms. Furthermore, as shown in the figure, this method also has the disadvantage of requiring a complex optical system and many optical elements.

What is particularly important when measuring a three-dimensional flow field using laser holography interferometry is that the projection amount in each direction must be associated with the positional relationship in the space to be measured. This is because, when collecting projection data, it is necessary to match the reference point in the space to be measured with the reference point in the interferogram to be acquired, and to keep the magnification of the figure constant during acquisition. However, in the above-mentioned known examples, no technical means for this association is used.

(Objective of the Invention) The present invention arranges a light diffusing plate and a photosensitive material for hologram recording facing each other on the circumferential surface of a cylindrical frame surrounding a measurement area, and improves the irradiation of laser light to the light diffusing plate and the photosensitive material. An attempt is made to obtain a device that enables three-dimensional flow field observation using the holographic method by collecting images while always keeping the reference point of the collected image constant at the back of the photosensitive material loading section during hologram playback. It is something.

(Structure of the Invention) FIGS. 1 to 3 show an embodiment of the flow field observation device of the present invention. The device consists of a light source section (a), an optical element group (b), and a hologram recording section (c).

In the light source section A, a pulsed laser light source 1A and a continuous light emitting gas laser 1B are arranged so that the beams are emitted on the same optical axis by a light source switching mechanism 1C, and are selectively used depending on the purpose, such as the observation target or optical system adjustment. . In this case, in order to prevent image distortion during hologram reproduction, it is necessary to use the same light source for both hologram recording and reproduction.

Optical element group B consists of a measurement light optical system and a reference light optical system for irradiating the light diffusing plate 17 with laser light over as wide an angular range as possible and transmitting the diffused light to the measurement area. The optical system includes a beam splitter 7, reflecting mirrors 8, 9, 10, and a lens 1.
1 and 12, the incident beam is sent to the diffuser plate as diverging light having a mutually large angle. On the other hand, the light beam 3 for the reference light is transmitted to the beam splitter 6 and the reflecting mirror 1.
3, the reflection mirror 14 and the convex reflection mirror 15 placed in the space next to the cylindrical frame 16 convert it into a reference light wavefront Re with a uniform brightness distribution, and from the angle θr direction. It is guided to the recording surface 18.
At this time, the reference light wavefront needs to pass through a space without disturbance, and the measurement area FI in this case is limited to a triangular area surrounded by a chain line.

However, the reference light irradiation method is not limited to this.
This can be carried out by any suitable method, such as by irradiating the recording surface from behind according to the well-known method of holography. This reference light optical system is used not only in the hologram recording process but also in the reproduction process, and a minute positional shift of the optical element group causes a change in the position of the reproduced image, aberrations, etc., so it needs to have a solid structure. In addition, in the hologram reproduction process, since the measurement light is not needed, it is shut off by the shutter 2-S.

When configuring these optical systems, it is necessary to keep the following two points in mind.

(1) The difference in optical path length between the measurement light and reference light must be as small as possible. (2) The intensity ratio of the measurement light and reference light on the photosensitive material surface must be adjusted to the optimum value. Regarding the first point, use beam splitter 6 or later. It is only necessary to arrange the optical elements so that the length of each optical path is equal, and for the second point, neutral filters 2-F and 3-F for concentration adjustment are inserted in each optical path to adjust the intensity of both lights. Adjust the ratio.

As shown in detail in FIGS. 2 and 3, the hologram recording section C includes a light diffusing plate 17 and a band-shaped hologram recording photosensitive material (film) 18 on the side and half of the cylindrical frame 16 surrounding the measurement area FI, respectively. are placed opposite each other.

Further, an image recording device 21 for collecting a hologram reproduced image and its support stand 20 are attached to the back surface of the strip-shaped photosensitive material 18 so as to be movable along the back surface of the photosensitive material 18 by a guide 16-1.
In the figure, 16-2 is a film window, 19 is a film presser flexible plate 23 is a film window shutter guide, 24
Reference numeral 25 indicates a film window shutter, 25 a flexible plate fixing fitting for holding down a photosensitive material, and 26 a photosensitive material loading guide.
The strip-shaped photosensitive material 18 disposed over the film window 16-2 is a recording photosensitive material during hologram recording, and during reproduction, it is a hologram original on which optical information within the measurement area is recorded and developed.
The flexible film holding plate 19 is used to hold the film 18 in close contact with the cylindrical frame 16. One end of the flexible plate 19 is fixed by a fixing fitting 25, but when reproducing a hologram, this is removed and the film window is opened. Open 16-2. The film window shutter 24 is for preventing unnecessary environmental light from entering the unexposed film, and is moved along the guide 23 and kept open during observation recording. It is also opened during hologram playback.

Further, the image recording device 21 refers to a recording camera, a television camera, or the like used to record only necessary image information from a hologram reproduced image. This image recording device 21 is fixed to a support base 20,
It can be moved along the guide groove 16-1 together with the support stand to any desired position and fixed. The image recording device 21 and support stand 20 are also used when reproducing a hologram.

The entire hologram recording section C is fixed via a cylindrical frame 16 to a support base 22 having a height adjustment function.

This flow field observation device is used as follows.
First, the hologram recording section C is installed at an appropriate position surrounding the measurement area FI, and with this as a reference, the light source section and the optical element group B are arranged in this order to form the above-mentioned optical path.

Observation using double exposure laser holography interferometry is performed by the following operations.

(1) Setting the photosensitive material Unexposed photosensitive material (film) for hologram recording
is set at the film window 16-2 position by the guide 26.

(2) First exposure The shutter 24 in front of the film window is opened, and the first hologram recording is performed in the reference state of the measurement area.

(3) Second exposure A second hologram recording is performed under the experimental conditions. (4) Development The photosensitive material is developed to create a hologram.

(5) Reproduction Return the completed hologram to the original photosensitive material loading position, irradiate it with only the reference light, and record the hologram reproduction image using the image recording device 21 while moving along the guide 16-1. I'll keep going.

(6) From the acquired interference fringe image data, determine the projection amount in each peripheral direction, and calculate the density distribution of the measurement area from this.

(Effects of the Invention) The flow field observation device of the present invention has the following remarkable effects due to the above configuration.

(1) Since the diffuser plate is illuminated from multiple directions, the observation area is irradiated with diffused light with uniform intensity over a wide angular range, allowing for a wide observable angular range.

(2) Flow field observation with a wide observation angle can now be realized, expanding the scope of use of optical interferometry, which was previously limited to two-dimensional or axisymmetric flow field observation, to three-dimensional flow field observation. Can be expanded.

(3) Since projection information around the reference point of the measurement area can be collected at a constant magnification, it is expected that data collection time will be shortened and measurement accuracy will be improved.

(4) A relatively simple optical system allows continuous recording and measurement over a wide angular range.

[Brief explanation of drawings]

FIG. 1 is an optical layout diagram of one embodiment of the flow field observation device of the present invention, in which a is an overall side view and b is an overall side view of the device.
2 is a front view, a side view, and a side view showing a partial cross section of the other side of the hologram recording section, and FIG. 3 is a cross section taken along the line X-X in FIG. 2b. Front view showing, Fig. 4, Fig. 5, Fig. 6,
FIGS. 9 and 10 are optical layout diagrams of a known flow field observation device, and FIGS. 7 and 8 are explanatory diagrams of the relationship between observation directions and projection information required for three-dimensional observation. A: Light source section, 1A: Pulsed laser light source, 1B:
Continuous light emission is laser, 1C: Light source switching mechanism, B:
Optical element group, 6, 7: Beam splitter, 15:
Convex reflecting mirror, 11, 12: Beam expanding lens, 2
-S: Shutter for blocking measurement light, 2-F, 3-F:
Neutral filter, C: Hologram recording section, 16: Cylindrical frame, 16-2: Film window, 17: Light diffusing plate, 18: Strip-shaped photosensitive material, 19: Photosensitive material presser plate, 21: Image recording device, 22: Support stand, 24:
Film window shutters, 43, 57, 67, 68,
71, 74, 82, FI: measurement area, 65, 78,
85: Light diffusing plate, 70, 73: Projection amount in the direction of angle φ, 80, 81: Laser.

Claims (1)

[Claims] 1. A light diffusing plate and a band-shaped hologram recording photosensitive material are attached to opposing circumferential surfaces of a cylindrical framework surrounding a measurement area space, and the light diffusing plate is illuminated with laser light from multiple directions. A flow field observation device using a laser holography method that allows a wider observation viewing angle. 2. A light diffusing plate illuminated from multiple directions and a band-shaped hologram recording photosensitive material or a recorded hologram are attached to opposing circumferential surfaces of a cylindrical framework surrounding the measurement area space, and the photosensitive material or hologram mounting portion is A flow field observation device using a laser holography method, which has an image recording device mounted on the same cylinder frame behind the hologram and moving along the back surface of the hologram.