JP2020063954A - Flow velocity measuring device, flow velocity distribution measurement system, fluid control system, and flow velocity measurement method - Google Patents

Abstract

To acquire velocity distribution in a depth direction in a flow field with a simple configuration, by achieving easy handling, and without traversing a probe relative to the depth direction.SOLUTION: The main part of a flow velocity measuring device 1 is comprised of a probe 2 including an emission part 10 and a variable-focus lens system 20, an observation part 30, and a control part 40, and is configured to acquire velocity distribution Vp in a depth direction Dd in a flow field Ff. The emission part 10 emits two laser beams L1, L2 in parallel at a predetermined interval in a direction orthogonal to the depth direction Dd. The variable-focus lens system 20 can change a focal distance fl, and allows the two laser beams L1, L2 emitted from the emission part 10 to cross with the focal distance fl. The observation part 30 observes scattered light Ls when a particle P of fluid to be observed passes through an interference fringe generated in an area in which the two laser beams L1, L2 cross.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a flow velocity measuring device, a flow velocity distribution measuring system, a fluid control system and a flow velocity measuring method.

Scattered light is generated when minute particles flowing in a fluid such as gas or liquid pass through an interference fringe formed in a region where two laser beams intersect. The frequency of this scattered light is displaced with respect to the frequency of the original laser light due to the Doppler effect of light. It is known that the frequency shift is proportional to the passage speed of particles. The frequency of scattered light is converted into an electrical signal through a light receiving element typified by a photodetector (photodiode), and used for oscilloscope and data collection. If it is acquired using the board, the velocity of particles can be estimated.
This is the principle of speed measurement using a laser Doppler velocity meter (LDV: Laser Doppler Velocity). Since LDV is a method that uses light, it is a measurement method that has a high time resolution and is characterized in that absolute calibration is not necessary. Further, since the velocity can be acquired by irradiating only light without inserting a sensor or the like into the flow path or the air passage to be measured, this is a non-invasive (non-contact) measurement method.
Based on the above characteristics, LDV is a microscale for biochemical analysis represented by micro-total analysis systems (μTAS) and lab-on-a-chip from large-scale flow fields around transportation equipment such as automobiles and railways. This is one of the typical velocity measurement methods used for velocity measurement in a wide scale flow field up to a minute scale flow field in a chip.

  In many cases, an LDV device is composed of two probes, an irradiation probe for irradiating a laser beam toward a flow path and a probe incorporating a light receiving element for receiving scattered light. In addition, there has been developed a device in which a light receiving element is incorporated in an irradiation probe to perform laser light irradiation to data acquisition with one probe.

On the other hand, since the LDV is a method (point measurement) of measuring the velocity only in the area where two laser beams intersect, the amount of information that can be acquired regarding the flow field is small.
In the flow field to be measured, it is necessary to mechanically traverse the device in order to acquire velocity as a distribution such as velocity in the flow direction, the height direction, and the depth direction.
Further, the two lasers are condensed by a lens attached to the laser irradiation port of the irradiation probe and intersect each other. Therefore, this intersection position is also determined by the focal length of the lens, and depending on the device, the distance (working distance) from the irradiation port to the intersection position may become very large.
Furthermore, depending on the measurement target, it is necessary to consider the traverse amount and working distance of the device itself, which limits the degree of freedom of the installation space of the device, and accordingly the measurement target to which the device is applied is limited. There was a problem of being lost.

  A technique capable of acquiring the velocity distribution in the depth direction in the flow field by the LDV without traversing the probe in the depth direction is disclosed in, for example, Non-Patent Document 1 and Non-Patent Document 2.

"Monochromatic heterodyne fiber-optic profile sensor for spatially resolved velocity measurements with frequency division multiplexing", Applied Optics, 44 (13), pp. 2501-2510, 2005. "Axial scanning laser Doppler velocimeter using wavelength change without moving mechanism in sensor probe", Optics Express, 19 (7), pp. 5960-5969, 2011.

In these documents, it is necessary to use a plurality of devices such as an acousto-optic device which is very expensive, and to appropriately adjust the frequencies of a plurality of laser beams and their passing positions (Non-Patent Document 1), and a plurality of diffractions. It is described that, among diffracted lights generated from the grating, appropriate light is selectively crossed so that the optical system must be strictly adjusted (Non-Patent Document 2).
Therefore, not only a special device has to be used, but also highly skilled technology is required for adjusting the position of the laser beam, etc., and it is hard to say that this is a device and technology that anyone can easily handle.

  In view of the circumstances as described above, an object of the present invention is to measure the flow velocity with a simple configuration, easy handling, and capable of acquiring the velocity distribution in the depth direction in the flow field without traversing the probe in the depth direction. An object is to provide an apparatus, a flow velocity distribution measuring system, a fluid control system, and a flow velocity measuring method.

  In order to achieve the above-mentioned object, a flow velocity measuring device according to an embodiment of the present invention is capable of changing a focal length and an emission part that emits two laser beams, and emits two laser beams emitted from the emission part. A variable focus lens system to intersect, and an observation unit for observing scattered light generated when particles flowing in a fluid to be measured pass through an interference fringe formed in an area where the two laser beams intersect. Have.

  A flow velocity distribution measurement system according to an aspect of the present invention is a flow velocity distribution measurement system that measures a flow velocity distribution of a fluid near a wall. This system is configured by embedding the flow velocity measuring device having the above configuration in the wall such that a region where two laser beams emitted from the emission unit intersect is located near the wall.

  A fluid control system according to an aspect of the present invention includes an influence imparting unit, a flow velocity measuring device having the above configuration, and a control unit. The influence imparting unit influences the flow of the fluid flowing in the vicinity of the wall. The flow velocity measuring device is configured to be embedded in the wall around the influence imparting unit so that a region where the two laser beams emitted from the emitting unit intersect is located near the wall. The control unit controls the influence of the influence imparting unit on the flow of the fluid based on the flow velocity of the fluid measured by the flow velocity measuring device.

  A flow velocity measuring method according to an aspect of the present invention is an object to be measured by emitting two laser beams and intersecting the two laser beams emitted via a variable focus lens system capable of changing a focal length. The scattered light generated when the particles existing in the fluid pass through the interference fringe formed in the region where the two laser beams intersect is observed.

  According to the present invention, it is possible to acquire the velocity distribution in the depth direction in the flow field without traversing the probe in the depth direction with a simple configuration and easy handling.

It is a block diagram showing a schematic structure of flow velocity measuring device 1 concerning one embodiment of the present invention. It is a figure which shows an example of a concrete structure of the emission part 10, the variable focus lens system 20, and the observation part 30 which concern on this embodiment. It is a schematic perspective view for demonstrating the principle of a laser Doppler anemometer. It is a schematic front view for demonstrating the principle of a laser Doppler anemometer. FIG. 6 is a diagram for explaining the action of the liquid lens 21. It is a figure (1) for demonstrating the change of spatial resolution with respect to the change of a focal length. It is a figure (the 2) for demonstrating the change of spatial resolution with respect to the change of a focal length. 6 is a graph showing an example of changes in spatial resolution with respect to changes in focal length. It is a schematic diagram showing composition of flow velocity distribution measuring system 100 concerning other embodiments of the present invention. It is a graph which shows the relationship between the distance from a wall, and a flow velocity. It is a schematic diagram showing composition of fluid control system 200 concerning another embodiment of the present invention. FIG. 1 shows a schematic perspective view of a mother wing 301 of an aircraft and a flap 302 that is deployable relative to the mother wing 301. It is a figure for demonstrating the application example of the flow velocity measuring device which concerns on this embodiment, and has shown the state which looked at the emission part and the observation part through the liquid lens 21.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Flow velocity measuring device according to one embodiment>
FIG. 1 is a block diagram showing a schematic configuration of a flow velocity measuring device 1 according to an embodiment of the present invention. As shown in FIG. 1, the flow velocity measuring device 1 includes a probe 2 including an emitting unit 10 and a variable focus lens system 20, an observing unit 30, and a control unit 40 as main components, and the flow direction Ff includes a depth direction. The flow velocity distribution Vp of Dd is acquired. The probe 2 of the flow velocity measuring device 1 according to the present embodiment shares both the illumination probe and the light receiving probe, but the present invention is not limited to this, and the illumination probe and the light receiving probe may be separate.
The emitting unit 10 emits two laser beams L1 and L2 in parallel at a predetermined interval in a direction orthogonal to the depth direction Dd. The two laser beams L1 and L2 are typically the same light source and have the same frequency and phase.

The variable focus lens system 20 can change the focal length f and intersects the two laser beams L1 and L2 emitted from the emitting unit 10 at the focal length f. The variable focus lens system 20 is also called a varifocal lens, and is typically a liquid lens whose focal length can be controlled by voltage control. The variable focus lens system 20 according to the present embodiment may be other than the liquid lens as long as it is an optical system capable of changing the focal length f. For example, the varifocal lens system 20 may be an optical system including a plurality of lenses, and a part of which is moved along the optical axis to continuously change the focal length.
When the observation unit 30 passes through the interference fringes formed in the region where the particles P in the fluid to be measured, typically, the two laser beams L1 and L2 intersect, that is, the region of the focal length f. This is for observing the scattered light Ls generated in 1 through the variable focus lens system 20.
The control unit 40 functions as a calculation unit and estimates the flow velocity of the fluid based on the frequency of the scattered light Ls observed by the observation unit 30. The control unit 40 also controls the operations of the emission unit 10, the variable focus lens system 20, and the observation unit 30. For example, the control unit 40 controls the emission unit 10 to emit the laser beams L1 and L2, electrically controls the varifocal lens system 20 to control the focal length of the varifocal lens system 20, and the observation unit. Control is performed so that scattered light Ls is received from 30. The control unit 40 can be typically configured by a PC (personal computer).

FIG. 2 is a diagram showing an example of a specific configuration of the emission unit 10, the variable focus lens system 20, and the observation unit 30 according to this embodiment. The flow velocity measuring device 1 according to the present embodiment is not limited to this configuration.
In FIG. 2, reference numeral 11 is a laser light source such as a semiconductor laser, reference numeral 12 is a beam splitter that splits the laser light L from the laser light source 11, and reference numeral 13 is a prism that reflects one laser light L2 split by the beam splitter 12. Is. A mirror may be used instead of the prism. The emission unit 10 is composed of the laser light source 11, the beam splitter 12, and the prism 13, and converts the laser light L emitted from the laser light source 11 into two laser lights L1 and L2 via the beam splitter 12 and the prism 13. Branch and emit. The frequency of the laser light emitted by the laser light source 11 is not particularly limited.
Reference numeral 21 is a liquid lens, and in the flow velocity measuring device 1 according to the present embodiment, the variable focus lens system 20 is composed of this liquid lens 21. The focal length f of the liquid lens 21 is controlled by voltage control using the control unit 40 (see FIG. 1) as described above.
Reference numeral 31 is a condenser lens that collects the scattered light Ls that has passed through the liquid lens 21, reference numeral 32 is an optical fiber whose light receiving port is located at the focal position of the liquid lens 21, and 33 is the scattered light Ls that is passed through the optical fiber 32. It is a photodetector that receives light. In the flow velocity measuring device 1 according to the present embodiment, the observation unit 30 is composed of at least the condenser lens 31, the optical fiber 32, and the photodetector 33.

The flow velocity measuring device 1 configured in this manner functions as a laser Doppler velocity meter (LDV: Laser Doppler Velocity). The principle of this laser Doppler anemometer will be briefly described with reference to FIGS. 3A and 3B.
As shown in FIGS. 3A and 3B, when the particle P in the flow field Ff passes through the interference fringe Fr generated by the interference of the two laser beams L1 and L2, the scattered light Ls corresponding to the light and shade of the interference fringe. Occurs. At this time, the scattered light Ls becomes stronger or weaker due to the Doppler effect of light. The photodetector 33 of the observation unit 30 converts the optical signal of the scattered light Ls into an electric signal, and the control unit 40 obtains the frequency when the interference fringes pass. Since this method uses light, the signal at the moment when the optical signal is emitted can be obtained. Therefore, the time resolution is high.
The flow velocity U of the particle P is determined by the following equation by the Doppler frequency f _dp and the interval d between the interference fringes Fr.
U = f _dp d
Therefore, it can be said that the flow velocity measuring device 1 according to the embodiment adopting the LDV is a non-invasive (non-contact) measuring method with high time resolution.

Here, as shown in FIG. 4, the flow velocity measuring device 1 according to the present embodiment employs the liquid lens 21, and the focal length f of the liquid lens 21 is set in the depth direction Dd under the control of the control unit 40. Can be changed. For example, the dotted line in FIG. 4 indicates the laser lights L1 and L2 when the liquid lens 21 is controlled so that the focal length becomes long. Further, the chain double-dashed line in FIG. 4 shows the laser beams L1 and L2 when the liquid lens 21 is controlled so that the focal length becomes short.
Since the LDV having the conventional configuration has a fixed focus, it is necessary to move the probe in the depth direction Dd in order to acquire the flow velocity in the depth direction Dd with respect to the probe. That is, in the LDV having the conventional configuration, it is necessary to move the device itself, so that the device is spatially restricted. On the other hand, in the flow velocity measuring device 1 according to the present embodiment, since the LDV has the configuration using the liquid lens 21, the focal length can be electrically controlled, and the measurement position can be changed without moving the probe. be able to. Therefore, spatial restrictions on the depth direction Dd are reduced. Further, even in the case where it is difficult to spatially move the device, the flow velocity distribution Vp in the depth direction Dd can be acquired without moving the device. Further, the flow velocity distribution in the depth direction Dd in the flow field Ff can be instantaneously measured.

<About spatial resolution>
The flow velocity measuring device 1 according to the present embodiment can change the focal length by using the liquid lens 21, but the spatial resolution changes with the change in the focal length.

As shown in FIG. 5, the wavelengths of the laser beams L1 and L2 are λ, the intervals and δ of the laser beams L1 and L2, the focal length of the liquid lens 21 is f, and the laser beams L1 and L2 after passing through the liquid lens 21 are Letting each beam diameter be D, the beam waist diameter φ, which is the intersection width of the laser lights L1 and L2 shown in FIG.
φ = 4λf / πnD = 4λf / πD (n is a refractive index, and n = 1 in the air)
And φ corresponds to the diameter (x * y) of the measurement volume.

The beam intersection angle θ is
θ = tan ⁻¹ (0.5δ / f)
And the fringe space (interference fringe spacing) Δx is
Δx = λ (2nsinθ) = λ (2sinθ)
And the probe volume length (the length of the portion where the laser beams L1 and L2 intersect) l is
l = φ / sin θ
Is.
The size of the probe volume 1 is the spatial resolution. Since the value of θ changes with the change of the focus, it can be said that the volume length l also changes with the change of the focus. Therefore, when l becomes small, the space can be measured minutely, and the spatial resolution increases. On the other hand, when l becomes large, the space cannot be measured very finely, so that the spatial resolution decreases.

<About spatial resolution and uncertainty>
The flow velocity measuring device 1 according to this embodiment employs a configuration in which the liquid lens 21 is used to change the focal length. Therefore, for example, when performing measurement while changing the focal length f of the liquid lens 21, the smaller the value of the probe volume length 1, the higher the spatial resolution in the depth direction Dd. That is, the value of θ increases as the value of the focal length f decreases, and the value of sin θ increases accordingly, and the volume length l of the probe decreases. In other words, the spatial resolution in the depth direction Dd where the focal length f becomes short is high, and the flow velocity near the probe can be acquired with high accuracy.
On the other hand, as shown in FIG. 7, the probe volume increases as the focal length f increases. That is, the resolution is reduced. At this time, since the flow velocity is uniquely determined within the probe volume at any measured position, if the flow velocity has a distribution within the probe volume, the distribution is uncertain with respect to the average value of the flow velocity at the measuring point. Expressed as
As shown in FIG. 7, the change in the spatial resolution with respect to the change in the focal length f is at most about 2% even if the focus changes by about 10 mm. Therefore, even if the configuration in which the focal length is changed by using the liquid lens 21 as in the flow velocity measuring device 1 according to the present embodiment is adopted, the uncertainty of the measurement itself is not so long as the focal length is not significantly changed during the measurement. It is not expected to grow much. Note that, in FIG. 7, calculation is performed assuming that the original beam diameter D = 1 mm and the beam interval δ = 15 mm as preconditions.

  Further, the fact that the spatial resolution changes according to the focal length may be positively used as shown below.

<Velocity distribution measurement system according to one embodiment>
FIG. 8 is a schematic diagram showing the configuration of a flow velocity distribution measuring system 100 according to another embodiment of the present invention.
As shown in FIG. 8, the flow velocity distribution measurement system 100 measures the flow velocity distribution Vp of a fluid such as gas near the wall 101.

  In the flow velocity distribution measurement system 100, in the flow velocity measurement device 1 according to the above-described embodiment, a region where the two laser beams L1 and L2 emitted from the emission unit 10 (see FIG. 1) intersect is located near the wall 101. Thus, it is configured to be embedded in the wall 101.

  Here, the flow velocity distribution Vp has a smaller value as it gets closer to the vicinity of the wall 101, but as it gets closer to the vicinity of the wall 101, the focal length f becomes shorter and l becomes smaller, so that the spatial resolution becomes higher, and as shown in FIG. The uncertainty of the flow velocity near the wall 101 becomes smaller. That is, the width of the error bar becomes smaller. On the other hand, the flow velocity distribution Vp has a larger value as it gets farther from the vicinity of the wall 101, but as it gets farther from the vicinity of the wall 101, the focal length f becomes longer and l becomes larger, so that the spatial resolution becomes lower, and as shown in FIG. The uncertainty of the flow velocity near 101 becomes large. That is, the width of the error bar becomes large. In FIG. 9, the plotted points are the flow velocities (u) at points separated by a predetermined distance (z) from the vicinity of the wall 101, and the thin lines at the top, bottom, left, and right generated from the plotted points indicate the width of the error bar. . The vertical error bar is the error bar at the measurement position associated with the size of l, and the horizontal error bar is the flow velocity error bar.

  Further, in the LDV having the conventional configuration, in order to obtain the flow velocity distribution Vp near the wall 101, a highly accurate positioning device for moving the device is required. Further, although there has been a sensor having a size smaller than the value of the probe volume length 1 from the past, it is necessary to insert the sensor into the flow channel, which disturbs the flow.

  On the other hand, in the flow velocity distribution measurement system 100 according to the present embodiment, since the variable focus lens system is used, the flow velocity measurement device 1 is not moved, and since it is a non-invasive measurement method, the flow is not disturbed, The flow velocity distribution Vp near the wall 101 can be measured. In the flow velocity distribution measurement system 100 according to this embodiment, it has been confirmed that the focal length can be adjusted with an accuracy of 1 mm or less.

<Fluid control system according to one embodiment>
FIG. 10 is a schematic diagram showing the configuration of a fluid control system 200 according to still another embodiment of the present invention. Here, an example in which the fluid control system 200 is typically used in the wing of an aircraft is shown.
In FIG. 10, reference numeral 201 indicates a wing which is one mode of the wall, and reference numeral 202 indicates the upper surface of the wing 201. The left side of the figure is the front edge side of the blade 201.
The main part of the fluid control system 200 according to the present embodiment is mounted inside the blade 201.

  The fluid control system 200 is mainly composed of an influence imparting unit 210 that influences the flow of the fluid flowing in the vicinity of the blade 201 and the flow velocity measuring device 1 according to the above-described embodiment, and further the influence imparting unit 210. It has a synchronizer 220 for synchronizing the operations of the flow velocity measuring device 1 and the controller 230.

Here, the influence imparting section 210 can be configured by, for example, a blowing device that is embedded in the blade 201 and blows the fluid upward from the surface of the blade 201 at high speed. Note that the influence imparting unit 210 can be configured not only by the blowing device but also by, for example, a protruding device represented by a vortex generator, a dielectric barrier discharge plasma actuator, or the like.
The probe 2 of the flow velocity measuring device 1 is arranged so that the region where the two laser beams L1 and L2 emitted from the emission unit 10 intersect is located near the blade 201 on the rear end side of the blade 201 with respect to the influence imparting unit 210. And is embedded in the wing 201. The flow velocity measuring device 1 may be embedded in the blade 201 upstream of the influence imparting unit 210 instead of downstream.
The control unit 230 is composed of, for example, a PC, and controls the influence of the influence imparting unit 210 on the flow of the fluid based on the flow velocity of the fluid measured by the flow velocity measuring device 1. The synchronizer 220 and the control unit 230 may be arranged in the fuselage of the airframe.

  In the fluid control system 200 configured as described above, the flow velocity measuring device 1 measures in real time scattered light generated from particles that follow a flow with a large velocity fluctuation on the surface of the blade 201, and the control unit 230 causes the Doppler signal to be detected. When a certain threshold is exceeded, the flow is controlled by, for example, blowing high-speed gas from the influence imparting unit 210 to add momentum to the flow on the surface of the blade 201. As a result, large fluctuations caused by the flow on the surface of the blade 201 can be suppressed. Then, in the system according to the present embodiment, the optical signal of the scattered light of the particles generated in the region where L1 and L2 intersect in time series is acquired, and based on the signal, blowing is performed, so that the surface of the wing 201 is It is possible to control the above flow in real time. By enabling real-time control, it becomes possible to more accurately suppress flow separation on the surface of the blade 201.

<Example of use of flow velocity measuring device according to this embodiment>
FIG. 11 shows a schematic perspective view of a mother wing 301 of an aircraft and a flap 302 provided so as to be deployable with respect to the mother wing 301. FIG. 11 shows a state in which the flap 302 is expanded.
Reference numeral 300 is a device in which the above-described flow velocity measuring device 1 itself is created by microfabrication (MEMS), and a plurality of them are arranged to form one MEMS sensor module. The MEMS sensor module 300 is embedded, for example, on the front edge side of the surface of the flap 302 so as to be parallel to the front edge. This position may not be directly observable from the surroundings even if the flap 302 is housed in the main wing 301 or the flap 302 is deployed from the main wing 301.

  Typically, in an environment such as a wind tunnel test room, and where the MEMS sensor module 300 is embedded in the flap 302 in a place surrounded by walls and without a measurement window, it passes between the main wing 301 and the flap 302. It is possible to acquire the velocity distribution of the air flow.

In the flow velocity measuring device 1 according to the present embodiment, it is possible to create an endoscope-like object and measure the flow velocity of a portion that cannot be reached by a person through the probe.
Further, the state of combustion can be measured by inserting the flow velocity measuring device 1 according to the present embodiment into a combustion engine of a moving automobile and measuring the movement of fine particles in the combustion engine.
Furthermore, the flow velocity measuring device 1 according to the present embodiment is inserted into the body through human skin, and the surface of the blood vessel is aligned with the blood vessel wall. For example, scattered light at the time of passage of interference fringes of red blood cells flowing in the blood vessel is acquired to determine the blood flow. The velocity distribution of can be measured.

<Application example of the flow velocity measuring device according to the present embodiment>
FIG. 12 is a diagram for explaining an application example of the flow velocity measuring device according to the present embodiment, and shows a state in which the emission part and the observation part are viewed through the liquid lens 21.
The flow velocity measuring device 401 according to this application example includes first and second emission units 10a and 10b as emission units, and first and second observation units 30a and 30b as observation units.
The first emitting portion 10a emits two laser beams L1 and L2, and the second emitting portion 10b intersects with a first straight line l1 that connects the two laser beams L1 and L2. The other two laser beams L3 and L4 which intersect in the same region as the region where the two laser beams L1 and L2 intersect are emitted from above l2. The first observation unit 30a observes the scattered light originating from the two laser beams L1 and L2, and the second observation unit 30b observes the scattered light originating from the other two laser beams L3 and L4. To do.

  For example, the laser beams emitted from the first and second emission units 10a and 10b have different wavelengths, and the first observation unit 30a is provided with a filter that allows only the laser beams L1 and L2 to enter the second observation unit. 30b is provided with a filter for entering only the laser beams L3 and L4, so that scattered light emitted from particles passing through the interference fringes can be observed separately.

  In the flow velocity measuring device 401 according to this application example, the direction of the fluid flowing on the surface of the wall and the flow velocity distribution of the fluid in the direction can be measured by the calculation in the control unit 40 (see FIG. 1).

<Other>
The present invention is not limited to the above-described embodiments, and can be modified and carried out within the scope of the technical idea thereof, or can be applied and carried out. And, it goes without saying that the scope of these implementations also belongs to the technical scope of the present invention.

1: Flow velocity measuring device 10: Emitting unit 11: Laser light source 12: Beam splitter 13: Prism 20: Variable focus lens system 21: Liquid lens 30: Observing unit 31: Condensing lens 33: Photo detector 40: Control unit 100: Flow velocity distribution Measuring system 101: Wall 200: Fluid control system 210: Influence giving part 230: Control part 401: Flow velocity measuring device D: Beam diameter Dd: Depth direction Ff: Flow field Fr: Interference fringe L: Laser light L1: Laser light L2: Laser light L3: Laser light L4: Laser light Ls: Scattered light P: Particle U: Flow velocity Vp: Flow velocity distribution f: Focal length fdp: Doppler frequency l: Probe volume l1: First straight line l2: Second straight line λ: Wavelengths of the laser beams L1 and L2 θ: Crossing angle δ: Beam interval φ: Beam waist diameter

Claims (10)

An emission part for emitting two laser beams,
A variable focus lens system capable of changing the focal length and intersecting two laser beams emitted from the emission unit;
When a particle flowing in a fluid to be measured passes through an interference fringe formed in an area where the two laser beams intersect, an observation section for observing scattered light generated in that area, Measuring device.   The flow velocity measuring device according to claim 1, wherein the variable focus lens system is a liquid lens whose focal length can be controlled by voltage control.   The observation unit observes scattered light generated when particles in the fluid pass through an interference fringe generated in a region where the two laser beams intersect, via the variable focus lens system. The flow velocity measuring device according to.   The emitting portion has a laser light source, a beam splitter for splitting the laser light from the laser light source, and a prism for reflecting one of the laser light split by the beam splitter, and the laser light emitted from the laser light source. 5. The flow velocity measuring device according to claim 1, wherein the laser light is split into the two laser beams and emitted through the beam splitter and the prism. The observation unit has a condenser lens that condenses the scattered light through the variable focus lens system, and a light receiving port is located at a focal position of the condensing lens, and receives the scattered light through the light receiving port. The flow velocity measuring device according to claim 1, 2, 3, or 4, comprising a photo detector. The flow velocity measuring device according to claim 1, further comprising a calculation unit that estimates the flow velocity of the fluid based on the frequency of the scattered light. In addition to the two laser beams, the emission unit is in the same region as the region where the two laser beams intersect from a second straight line orthogonal to the first straight line connecting the two laser beams. Emits the other two laser beams that intersect at
The observation section separately observes scattered light originating from the two laser beams and scattered light originating from the other two laser beams. The flow velocity measuring device described. A flow velocity distribution measuring system for measuring the flow velocity distribution of a fluid near a wall,
The emission part that emits two laser beams, the variable focus lens system that can change the focal length and intersects the two laser beams emitted from the emission part, and the particles in the fluid to be measured are A flow velocity measuring device having an observation part for observing scattered light generated when passing through an interference fringe formed in an area where the two laser lights intersect, the two laser lights emitted from the emitting part are A flow velocity distribution measuring system embedded in the wall so that an intersecting region is located near the wall. An influence imparting portion that influences the flow of the fluid flowing near the wall,
The emission part that emits two laser beams, the variable focus lens system that can change the focal length and intersects the two laser beams emitted from the emission part, and the particles that flow in the fluid to be measured are And an observation unit for observing scattered light generated when passing through an interference fringe formed in a region where the two laser beams intersect, and the two laser beams emitted from the emission unit intersect with each other. A flow velocity measuring device embedded in the wall upstream or downstream of the impact imparting unit so that the region is located near the wall,
And a controller that controls the influence of the influence imparting unit on the flow of the fluid based on the flow velocity of the fluid measured by the flow velocity measuring device. Emits two laser beams,
The two emitted laser beams are crossed via a variable focus lens system capable of changing the focal length,
A flow velocity measuring method for observing scattered light generated when particles flowing in a fluid to be measured pass through an interference fringe formed in a region where the two laser beams intersect.

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