JP6986265B2 - Measurement system - Google Patents

Description

The present invention relates to a measuring system, particularly a measuring system for measuring the wall shear stress of a fluid.

A measuring system for measuring the wall shear stress of a fluid is known. As a method for measuring the wall surface shear stress of a fluid, for example, a method of estimating the wall surface shear stress based on a flow velocity (indirect measurement method) and a method of directly measuring the wall surface shear stress using a strain gauge (direct measurement method) are available. be. Since the indirect measurement method presupposes the establishment of a universal law between the flow velocity and the wall surface shear stress, the wall surface shear stress cannot be measured in the case of a multiphase flow such as a bubble flow. Further, in the direct measurement method, since the time resolution of the strain gauge is low, it is not possible to measure a sudden change in the wall surface shear stress when a turbulent burst phenomenon or the like occurs.

Therefore, the development of a measurement system for measuring the wall shear stress of a fluid using a laser measurement system with high time resolution is underway. For example, in Patent Document 1, a light generation unit that generates laser light, a spectroscopic unit that divides laser light, a focusing lens that focuses the divided laser light, and laser light focused on the focal point collide with suspended particles. Disclosed is a measurement system comprising a frequency analyzer that detects the Doppler frequency from the scattered light produced thereby.

Japanese Unexamined Patent Publication No. 2009-22716

The measurement system of Patent Document 1 receives scattered light scattered by suspended particles of a fluid, detects the Doppler frequency of the scattered light, and calculates the wall surface shear stress based on the Doppler frequency. In other words, the floating of the fluid. The wall shear stress is indirectly measured based on the movement of the particles. Therefore, the measuring system of Patent Document 1 has a problem that the wall surface shear stress cannot be measured when the suspended particles in the fluid do not exist, and the momentary change in the wall surface shear stress due to turbulence or bubbles cannot be measured.

The present invention has been made based on such a background, and an object of the present invention is to provide a measurement system capable of directly measuring the wall shear stress of a fluid from the flow of the fluid and having high time resolution.

In order to achieve the above object, the measurement system according to the present invention is
A measurement system that measures the wall shear stress of a fluid.
A light emitting means that emits scattered light and
The first through hole and the second through hole through which the scattered light from the light emitting means is passed are included, and the first through hole moves in the flow direction of the fluid according to the wall shear stress of the fluid. The second through hole is a sensation means that is held at a fixed position even if the wall shear stress of the fluid changes.
A light receiving means for receiving a beat signal obtained by the interference of scattered light passing through the first through hole and the second through hole with each other.
An arithmetic means for calculating the wall shear stress of the fluid based on the frequency of the beat signal received by the light receiving means, and
To prepare for.

The sensation means
It is equipped with a fluid contact plate that is arranged in contact with the fluid and moves in the flow direction of the fluid in response to the shear stress on the wall surface of the fluid.
The first through hole may be configured to move in the flow direction of the fluid in conjunction with the fluid contact plate.

The sensation means
Supporting means fixed in place with respect to the object for measuring wall shear stress,
An elastically deformable means for elastic deformation, in which one end is supported by the support means, the other end is fixed to the fluid contact plate, and the fluid contact plate is suspended from the support means.
May be provided.

The sensitive means includes a housing for accommodating the elastic deformation means and the fluid contact plate inside.
The fluid contact plate may be arranged adjacent to the lower end of the housing so as to come into contact with the fluid together with the lower end of the housing.

A first optical path forming portion in which the first through hole is formed is fixed to the elastic deformation means.
A second optical path forming portion in which the second through hole is formed may be fixed to the housing.

The second optical path forming portion includes an opening formed adjacent to the second through hole.
The first optical path forming portion is arranged on the back side of the second optical path forming portion.
The opening is formed so that scattered light can pass through the first through hole even when the first optical path forming portion moves according to the wall shear stress of the fluid. good.

The first optical path forming portion and the second optical path forming portion are provided on the light emitting means side of the housing.
The light receiving means side of the housing may be provided with a transmitting portion capable of transmitting scattered light that has passed through the first optical path forming portion and the second optical path forming portion to the outside.

The measuring system is a measuring system for measuring the wall shear stress of a liquid.
The sensing means is configured so that the liquid enters the housing from between the fluid contact plate and the housing.
The measurement system supplies a gas into the housing so that the liquid level of the liquid that has entered the housing is located below the first through hole and the second through hole, and the liquid level of the liquid. It may be further provided with an air supply means for pressurizing.

The elastic deformation means is a pair of wires arranged side by side in the flow direction of the fluid.
One wire is fixed to the side end of the upper surface portion of the fluid contact plate, and the other wire is the side end of the upper surface portion of the fluid contact plate, which is opposite to the portion to which the one wire is fixed. It may be fixed to the side.

The light emitting means
Laser light source and
A rotary scattering plate that scatters the laser light emitted from the laser light source,
A motor that rotates the rotary scattering plate around the central axis at a constant angular velocity,
May be provided.

The rotational scattering plate and the motor may be connected to each other via a turning belt so that the rotation of the motor can be transmitted to the rotational scattering plate.

The light receiving means is
A lens system that generates a beat signal by focusing the scattered light that has passed through the first through hole and the second through hole at an intersection.
A scatterer that is arranged to include the intersection and scatters the beat signal generated by the lens system.
A photodetector that detects the intensity of the beat signal scattered by the scatterer,
May be provided.

According to the present invention, the first through hole and the second through hole through which the scattered light from the light emitting means is passed are included, and the first through hole is in the flow direction of the fluid according to the wall shear stress of the fluid. The second through hole is provided with a sensing means that moves and is held in a fixed position even if the wall shear stress of the fluid changes. Therefore, the wall surface shear stress of the fluid can be measured directly from the flow of the fluid, and a measurement system with high time resolution can be provided.

It is a front view which shows the structure of the measurement system which concerns on Embodiment 1 of this invention. It is a top view which shows the structure of the measurement system which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the structure of the light emitting device which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the structure of the sensation apparatus which concerns on Embodiment 1 of this invention. It is a front view which shows the structure of the sensation apparatus which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the structure of the light receiving device which concerns on Embodiment 1 of this invention. It is a figure which shows the optical path of a signal light and a reference light when a fluid does not flow. It is a figure which shows the optical path of a signal light and a reference light when a fluid is flowing. It is sectional drawing which shows the structure of the sensation apparatus which concerns on Embodiment 2 of this invention. It is sectional drawing which shows the structure of the light emitting device which concerns on Embodiment 3 of this invention. It is a figure which shows the structure of the experimental apparatus in Example 1. FIG. It is a figure which shows the experimental condition in Example 1. FIG. It is a graph which shows the relationship between the Reynolds number and the time average value of a friction stress coefficient in a single phase flow. It is a graph which shows the relationship between the Reynolds number in a bubble flow, and the time average value of a friction stress coefficient. It is a graph which shows the time change of the wall surface shear stress in a single phase flow. It is a graph which shows the time change of the wall surface shear stress in a bubble flow. (A) is a perspective view of the experimental ship in Example 2, and (b) is a cross-sectional view of the experimental ship of (a). (A) is a figure which shows the experimental condition of a single phase flow in Example 2, and (b) is a figure which shows the experimental condition of a bubble flow in Example 2. FIG. It is a graph which shows the relationship between the velocity of an experimental ship and the wall shear stress in a single phase flow. It is a graph which shows the relationship between the void ratio in a bubble flow, and the wall surface shear stress ratio.

Hereinafter, embodiments of the measurement system according to the present invention will be described in detail with reference to the drawings. In each drawing, the same or equivalent parts are designated by the same reference numerals. Further, in each embodiment, a Cartesian coordinate system is used in which the flow direction of the fluid is the X axis, the axis perpendicular to the X axis and extending on the horizontal plane is the Y axis, and the vertical direction is the Z axis.

(Embodiment 1)
The configuration of the measurement system 1 according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 6. The measurement system 1 according to the first embodiment is an apparatus for measuring the wall surface shear stress of a fluid by detecting a beat signal of light that changes with a change in the wall surface shear stress of the fluid by using a heterodyne interference method. be.

The heterodyne interferometry is a signal light by interfering a signal light, which is the light to be measured, with a reference light, which is light having a slightly different phase, to generate a beat signal, and detecting the obtained beat signal with a detector. It is a method of acquiring information such as the phase of light. Since the frequency of light is very high, it is not possible to obtain information such as the phase of signal light simply by directly detecting the light with a detector, but by converting the signal light into a beat signal using reference light, the signal light can be obtained. Information such as phase can be acquired.

Hereinafter, in order to facilitate understanding, a case of measuring the wall surface shear stress of water in a pipeline having a rectangular cross section in which a fluid flows uniformly will be described as an example, but the measurement system 1 according to the first embodiment will be described. However, the flow of the fluid whose wall surface shear stress can be measured is not limited to the flow of water, and the object of measuring the wall surface shear stress is not limited to the pipeline having a rectangular cross section.

FIG. 1 is a front view showing the configuration of the measurement system 1. The measurement system 1 receives a light emitting device 10 that scatters laser light and radiates it as scattered light, and a receiver that changes an optical path formed by a part of the scattered light emitted from the light emitting device 10 according to the wall shear stress of the fluid. It includes a sensing device 20 and a light receiving device 30 that receives scattered light that has passed through the sensing device 20.

The light emitting device 10, the sensitive device 20, and the light receiving device 30 are installed side by side in the Y-axis direction on the support plate 40 and fixed. The support plate 40 is, for example, a plate made of a steel material, and may be installed on a base, a pier, the ground, or the like. The measurement system 1 is configured such that the scattered light scattered and emitted from the light emitting device 10 passes through the sensitive device 20 and enters the light receiving device 30. Below the sensation device 20 and the support plate 40, a pipeline 50 (object) having a rectangular cross section through which a fluid flows in the X-axis direction is installed. A part of the sensation device 20 is inserted into an opening 51 provided in the upper surface portion of the pipeline 50, and the lower end portion thereof is arranged so as to come into contact with the fluid flowing through the pipeline 50.

FIG. 2 is a plan view showing the configuration of the measurement system 1. The dotted line in FIG. 2 shows an optical path of scattered light emitted from the light emitting device 10 and an optical path of signal light and reference light incident on the light receiving device 30. A part of the scattered light scattered and emitted by the light emitting device 10 is incident on the sensitive device 20.

The sensation device 20 includes a mechanism that directly senses a change in the wall surface shear stress of the fluid. The sensation device 20 forms a signal light whose optical path changes according to a change in the wall shear stress of the fluid and a reference light whose optical path is constant invariant from a part of the incident scattered light. The signal light is provided in the sensitizer 20 and is formed by a first pinhole that moves in the X-axis direction in response to a change in the wall shear stress of the fluid, and the reference light is provided in the sensitizer 20 and receives. It is formed by a second pinhole fixed at a predetermined position of the sensor 20.

Then, the signal light and the reference light incident on the light receiving device 30 are focused at one intersection and interfere with each other at the intersection to generate a beat and generate a beat signal of light. The measurement system 1 can calculate the wall surface shear stress of the fluid by detecting the frequency of the beat signal.

FIG. 3 is a cross-sectional view of the light emitting device 10 observed from above. The light emitting device 10 is an example of a light emitting means that emits scattered light having a uniform phase at a single wavelength by scattering the laser light. The light emitting device 10 rotates a laser light source 11 that emits laser light, a rotatable rotary scattering plate 12 that is irradiated with laser light from the laser light source 11 and scatters the laser light, and a rotary scattering plate 12 around a central axis. A motor 13 for causing the laser and a housing 14 for accommodating each portion are provided.

The laser light source 11 is, for example, a laser light source that emits a laser beam having a red wavelength. The red wavelength is merely an example, and the laser light emitted by the laser light source 11 may be light of any wavelength as long as the frequency of the beat signal of the light is a measurable value.

The rotary scattering plate 12 is, for example, a disk-shaped member made of frosted glass formed by mixing fine particles with a glass material. The rotary scattering plate 12 converts the laser light incident from the laser light source 11 into scattered light having various frequencies and scatters the laser light. It is desirable that the rotational scattering plate 12 has a uniform distribution of fine particles inside in order to improve the measurement accuracy of the wall surface shear stress of the fluid. The laser light emitted to the rotating scattering plate 12 during rotation is scattered in all directions, but travels mainly in the direction in which the laser light is emitted.

The motor 13 is, for example, a servomotor that rotates the rotary scattering plate 12. The motor 13 is controlled by a control device (not shown) to rotate the rotary scattering plate 12 at a constant angular velocity. The rotation axis of the motor 13 is fixed to the central axis of the rotation scattering plate 12, that is, the axis oriented perpendicular to the rotation scattering plate 12 through the center point of the rotation scattering plate 12.

In order to improve the measurement accuracy of the wall surface shear stress of the fluid, it is desirable to fix the rotary scattering plate 12 to the rotary axis of the motor 13 so that the central axis of the rotary scattering plate 12 coincides with the rotary axis of the motor 13 as much as possible. .. When the central axis of the rotational scattering plate 12 coincides with the rotational axis of the motor 13, the laser light emitted from the laser light source 11 suppresses the fluctuation of the rotational scattering plate 12, so that the fluctuation of scattered light scattering is suppressed. As a result, the measurement accuracy of the wall surface shear stress of the fluid can be improved.

The housing 14 is formed in a cubic shape, and has a transmission portion 14a capable of transmitting scattered light on a side surface portion. The transmission portion 14a is formed of a glass plate or a transparent resin plate, and is fitted and fixed to an opening provided in a side surface portion of the housing 14. A part of the scattered light scattered by the rotary scattering plate 12 is radiated to the outside through the transmission portion 14a.

FIG. 4 is a cross-sectional view of the sensitive device 20 cut along the XZ plane. The sensitizing device 20 is an example of a sensitizing means that changes the optical path of the scattered light emitted from the light emitting device 10 according to the wall surface shear stress of the fluid. The sensory device 20 includes a cylindrical housing 21, a support portion 22 fixed to the upper end portion of the housing 21, a pair of wires 23 fixed to the support portion 22 and suspended from the support portion 22, and a fluid. A fluid contact plate 24, which is supported by the tips of the pair of wires 23 so as to be in contact with each other and moves in the flow direction of the fluid according to the shear stress on the wall surface of the fluid, is provided.

The housing 21 is a member that houses each part of the sensing device 20 inside. The housing 21 is a cylindrical member made of a metal material such as stainless steel. The housing 21 is provided at the lower end thereof and includes a flange 21a that can be installed on the support plate 40.

The flange 21a is a disk-shaped member made of stainless steel or the like, and includes a plurality of through holes 21b arranged at intervals on the same circumference. The through hole 21b is formed at a position where a bolt can be inserted and coincides with the female screw hole of the support plate 40. Therefore, the bolt is inserted into the through hole 21b, and the bolt is screwed into the female screw hole of the support plate 40, so that the flange 21a is detachably fixed to the support plate 40.

FIG. 5 is a front view showing a state in which the sensitive device 20 is observed from the light emitting device 10 side, that is, from the same direction as in FIG. An opening is formed in the side surface portion of the housing 21, and a second optical path forming portion 26 forming an optical path for reference light is fixed to the opening. The second optical path forming portion 26 is, for example, a plate-shaped member formed of a metal material.

The second optical path forming portion 26 includes a second pinhole (second through hole) 26a and an opening 26b formed adjacent to the second pinhole 26a. The second pinhole 26a is, for example, a circular through hole formed through the Y-axis direction, and passes a part of the incident scattered light to form an optical path of the reference light. The opening 26b is, for example, a circular through hole formed so as to penetrate in the Y-axis direction.

A first optical path forming portion 25 is arranged on the back surface side of the opening portion 26b. The first optical path forming portion 25 is formed so as to penetrate in the Y-axis direction, and includes a first pinhole (first through hole) 25a that forms an optical path for signal light when scattered light is incident. The opening 26b is provided so that scattered light is incident on the first pinhole 25a even when the first optical path forming portion 25 arranged on the back surface side moves in the X-axis direction due to the wall shear stress of the fluid. , The first pinhole 25a is formed so as to be always visible from the outside.

Returning to FIG. 4, another opening is provided in the side surface portion of the housing 21, which is located on the opposite side of the first optical path forming portion 25 and the second optical path forming portion 26. A transmission portion 27 capable of transmitting laser light is fixed to this opening. The transmission portion 27 is formed of, for example, a glass plate or a transparent resin plate. Therefore, the signal light formed by the scattered light passing through the first pinhole 25a and the reference light formed by the scattered light passing through the second pinhole 26a are both transmitted portions. It is emitted to the outside of the housing 21 through 27.

The support portion 22 is an example of a support means that is fixed to the upper end portion of the housing 21 and supports the wire 23. The support portion 22 is a cap-shaped member formed of, for example, a metal material such as stainless steel. The support portion 22 includes a circular upper surface portion and a cylindrical side surface portion extending downward from the side end portion of the upper surface portion. The support portion 22 is fixed to the upper part of the housing 21 by means such as welding and tightening.

The wire 23 is an example of elastically deformable means in which one end is fixed to the support portion 22 and the other end is fixed to the fluid contact plate, and the fluid contact plate 24 is suspended from the support portion 22. The wire 23 is composed of, for example, a piano wire. The wire 23 includes a first wire 23a and a second wire 23b. The first wire 23a and the second wire 23b are arranged side by side in the fluid flow direction (X-axis direction).

The first optical path forming portion 25 is fixed to the first wire 23a by means such as adhesion and welding. The first optical path forming portion 25 is a plate-shaped member arranged on the YZ plane, and moves in the X-axis direction following the deformation of the first wire 23a.

The tip of the wire 23 is fixed to the upper surface of the fluid contact plate 24 by means such as adhesion. In order to accurately measure the wall shear stress of the fluid, it is desirable that the tip of the wire 23 is firmly fixed to the fluid contact plate 24 so as not to bend.

The mechanical properties (eg, spring constant) of the wire 23 are determined by the user in consideration of the type of fluid to be measured, temperature, magnitude of wall shear stress, fluctuation range, steepness, presence of bubbles and turbulence, and the like. Select as appropriate. For example, when measuring a low stress field, it is desirable that the spring coefficient of the wire 23 is large, and when measuring a high stress field, it is desirable that the spring coefficient of the wire 23 is small.

It is desirable that the wire 23 has a sufficient length so that the movement of the first optical path forming portion 25 in the Z-axis direction can be ignored even when the fluid contact plate 24 moves in the X-axis direction. When a piano wire is used for the wire 23, the length of the wire 23 is, for example, about 10 cm to about 30 cm.

The fluid contact plate 24 is a plate-shaped member that comes into direct contact with the fluid and moves in the flow direction (X-axis direction) of the fluid in response to the wall shear stress from the fluid. The fluid contact plate 24 is a disk-shaped member formed of a lightweight and rigid material, for example, a metal material such as stainless steel. The fluid contact plate 24 is formed, for example, with dimensions having an outer diameter of 10 mm and a thickness of 0.2 mm.

The outer diameter and thickness of the fluid contact plate 24 are arbitrary values in consideration of the type of fluid, the magnitude of wall shear stress, the fluctuation range, steepness, the presence or absence of bubbles or turbulence, the ease of metal processing, and the like. Can be set to. The fluid contact plate 24 is preferably in the range of, for example, an outer diameter of 5 mm to 20 mm and a thickness of 0.1 mm to 1.0 mm. When the outer diameter of the fluid contact plate 24 is small, the local wall surface shear stress can be measured, which is suitable for measuring the wall surface shear stress of turbulent flow. Further, when the outer diameter of the fluid contact plate 24 is large, the overall tendency of the wall surface shear stress can be effectively measured.

FIG. 6 is a cross-sectional view of the light receiving device 30 observed from above. The light receiving device 30 is an example of a light receiving means that causes two scattered lights that have passed through the sensitive device 20 to interfere with each other and receives a beat signal obtained from the scattered light that interferes with each other.

The light receiving device 30 is scattered by a lens system 31 that collects scattered light that has passed through the sensitive device 20 at one intersection to generate a beat signal, a scattering body 32 that scatters the beat signal, and a scattering body 32. It is provided with a photodetection element 33 that receives a light-receiving beat signal. Each part of the light receiving device 30 is installed in the housing 34.

The lens system 31 includes a parallel lens 31a and a condenser lens 31b. The parallel lens 31a refracts the signal light that has passed through the first pinhole 25a and the reference light that has passed through the second pinhole 26a so as to travel in an optical path parallel to each other. The condenser lens 31b focuses the signal light and the reference light that have passed through the parallel lens 31a so as to intersect at one intersection.

The scatterer 32 is arranged so as to include an intersection of the signal light and the reference light, and scatters the light that has passed through the lens system 31. The scatterer 32 is made of frosted glass containing fine particles, like the rotary scattering plate 12, for example. Since the optical path of the signal light changes according to the change in the wall shear stress of the fluid, it is difficult to predict the traveling direction of the beat signal. Therefore, by scattering the beat signal using the scatterer 32, a part of the beat signal can be reliably incident on the photodetection element 33.

The photodetection element 33 is a sensor that detects the intensity of the beat signal of scattered light and outputs a signal corresponding to the intensity of the bead signal. The photodetector 33 is, for example, a photoelectric effect type photodetector. The photodetection element 33 is an amplifier that amplifies a weak beat signal, and a bandpass that extracts a signal in a specific frequency band (for example, about 90 Hz to about 150 Hz) from the amplified beat signal in order to eliminate the influence of noise. It is electrically connected to a filter and a data logger that stores the filtered beat signal. The beat signal stored in the data logger is transmitted to an arithmetic unit (not shown) via a wired or wireless communication circuit, and is used for calculating the wall shear stress of the fluid.

The range of a specific frequency band extracted by the bandpass filter as a signal is empirically set by repeating the experiment. Further, the first pinhole 25a and the second pinhole 26a and the lens system 31 are positioned with each other so that the beat frequency becomes about 50 kHz to about 150 kHz when no fluid is flowing in the pipeline 50. There is.

The housing 34 is formed in a cubic shape, and has a transmitting portion 34a capable of transmitting laser light on its side surface portion. The transmission portion 34a is formed of a glass plate or a transparent resin plate, and is fitted and fixed to the opening of the side surface portion. The scattered light that has passed through the sensation device 20 passes through the transmission portion 34a and enters the inside of the housing 34.

The arithmetic unit receives a signal generated by processing the beat signal detected by the photodetection element 33, acquires the frequency of the beat signal (hereinafter referred to as the beat frequency) from the received signal, and obtains the frequency of the beat signal (hereinafter referred to as the beat frequency) from the beat frequency on the wall surface of the fluid. This is an example of a calculation means for calculating shear stress. The arithmetic unit is, for example, a general-purpose computer and includes a memory for storing a program and a processor for executing the program stored in the memory. The above is the configuration of the measurement system 1.

Next, with reference to FIGS. 7 and 8, the mechanism by which the measurement system 1 according to the first embodiment measures the wall surface shear stress of the fluid will be described. Hereinafter, the sensing device 20 is installed in the pipeline 50 so that the fluid contact plate 24 is in contact with the fluid in the pipeline 50 and moves in the flow direction (X-axis direction) according to the flow of the fluid. It is assumed that there is.

FIG. 7 is a diagram showing an optical path of signal light and reference light when the fluid in the pipeline 50 is not flowing. First, the laser light emitted from the laser light source 11 is incident on the rotating scattering plate 12 rotating at a constant angular velocity ω. Next, the scattered light scattered by the rotary scattering plate 12 passes through the transmission portion 14a, and a part of the scattered light is radiated toward the sensitive device 20. Then, the scattered light radiated from the light emitting device 10 passes through the first pinhole 25a and the second pinhole 26a of the sensing device 20, so that the signal light and the reference light are formed.

Next, the signal light from the first pinhole 25a and the reference light from the second pinhole 26a pass through the transmission portion 34a of the light receiving device 30, and enter the inside of the light receiving device 30. The signal light and the reference light incident on the light receiving device 30 are focused by the lens system 31, and when they intersect at one intersection, they interfere with each other and are converted into a beat signal of light. Since the scatterer 32 is arranged at the intersection of the signal light and the reference light, the converted beat signal is scattered and finally received by the photodetection element 33.

To explain the generation of the beat signal in more detail, the signal light passing through the first pinhole 25a and the reference light passing through the second pinhole 26a were radiated from the rotational scattering plate 12 in different directions. Since it is formed using scattered light, each has a different frequency. When the signal light and the reference light having different frequencies interfere with each other, a beat is generated and a beat signal is generated.

_{The beat frequency f d1} in the initial state when the wall surface shear stress of the fluid is not generated is expressed by the following equation. However, f ₁ is the frequency of the reference light, f ₂ is the wavelength of the signal light when the wall surface shear stress of the fluid is not generated, and r is the radius of the portion of the rotary scattering plate 12 to which the laser light is irradiated. λ is the wavelength of light, and φ is the angle (scattering angle) between the scattered light incident on the first pinhole 25a and the scattered light incident on the second pinhole 26a.
f _d1 = | f ₁ −f ₂ | = 2ωr / λ × sin (φ / 2)… (1)

FIG. 8 is a diagram showing an optical path of signal light and reference light when a fluid is flowing in the pipeline 50. In FIG. 8, since the wall surface shear stress acts on the fluid contact plate 24 due to the fluid flow, the fluid contact plate 24 moves in the fluid flow direction (X-axis direction) as compared with FIG. 7. Along with this, the first wire 23a supporting the fluid contact plate 24 is deformed and moves in the X-axis direction. Therefore, the first pinhole 25a of the first optical path forming portion 25 fixed to the first wire 23a moves in the X-axis direction according to the wall surface shear stress of the fluid.

At this time, the signal light that has passed through the first pinhole 25a is incident on the parallel lens 31a at an angle different from the signal light in the case of FIG. 7 (shown by the solid line in FIG. 8) as shown by the dotted line in FIG. .. Since the position of the first pinhole 25a changes, the optical path length from the first pinhole 25a of the signal light to the intersection changes, so that the phase of the signal light at the intersection also changes. Since the second pinhole 26a is arranged so that the relative positional relationship with the light receiving device 30 is constant, the phase of the reference light at the intersection does not change even if the wall shear stress of the fluid changes. .. Therefore, when the wall shear stress of the fluid is generated, the phase difference between the signal light and the reference light changes. This change in phase difference changes the beat frequency of the beat signal generated by the interference of scattered light.

With the occurrence of the wall shear stress of the fluid, the first pin hole 25a is moved in the X-axis direction, the frequency of the signal light changes from f ₂ to f _3, the scattering angle by changing the phi 'from phi , The beat signal growls. _{The beat frequency f d2} at the time of measuring the wall surface shear stress of the fluid is expressed by the following equation.
f _d2 = | f ₁ −f ₃ | = 2ωr / λ × sin (φ'/2)… (2)

Further, the difference between the wall shear stress τ _w of the fluid and the bead frequency (f _d2- f _d1 ) has the relationship shown in the following equation. However, the coefficient k is a coefficient determined by repeating the experiment. For example, when a piano wire is used as the wire 23, the coefficient when using the gravitational unit system is k = 0.0317, and the coefficient when using the International System of Units (SI) is k = 3.964.
τ _w = k × (f _d2- f _d1 )… (3)

When the fluid is flowing in the pipeline, the arithmetic unit can calculate the wall surface shear stress of the fluid by using the equation (3) from the beat frequency changed according to the shear stress of the fluid. Further, when the wall surface shear stress of the fluid is not generated, the beat frequency f _d2 at the time of measuring the wall surface shear stress of the fluid matches the beat frequency f _{d1 in the} initial state (f _d2 = f _d1 ). Can be calculated using Eq. (3) as the wall shear stress τ _{w of the fluid is zero.}

As described above, the measurement system 1 according to the first embodiment includes a first pinhole 25a and a second pinhole 26a through which scattered light from the light emitting device 10 is passed, and the first pinhole 25a is a first pinhole 25a. The second pinhole 26a is provided with a sensing device 20 that moves in the flow direction of the fluid according to the wall shear stress of the fluid and is maintained at a constant position even if the wall shear stress of the fluid changes. Therefore, the measurement system 1 can directly measure the wall shear stress of the fluid from the flow of the fluid, and can realize a high time resolution that can cope with turbulent flow and bubble flow.

Further, the measurement system 1 according to the first embodiment includes a fluid contact plate 24 which is arranged so as to be in contact with the fluid and moves in the flow direction of the fluid according to the wall shear stress of the fluid. Therefore, the fluid contact plate 24 can directly sense the wall shear stress of the fluid from the flow of the fluid, and as a result, the wall shear stress of the fluid can be measured accurately.

Further, the measurement system 1 according to the first embodiment includes a pair of elastically deformable wires 23 that suspend the fluid contact plate 24 from the support portion 22 fixed to the measurement target. Therefore, the weight of the measurement system 1 can be reduced, and the fluid contact plate 24 can easily follow the flow of the fluid. As a result, the wall shear stress of the fluid can be measured more accurately.

(Embodiment 2)
The configuration of the measurement system according to the second embodiment of the present invention will be described with reference to FIG. 9. Unlike the measurement system 1 according to the first embodiment, the measurement system according to the second embodiment is different from the measurement system 1 according to the first embodiment, in order to measure the wall surface shear stress of the mixed phase flow containing bubbles and the like, from the upper part of the sensitizing device 20 into the housing 21. It is configured to supply gas. In the second embodiment, it is assumed that the fluid for which the wall surface shear stress is to be measured is a liquid such as seawater or groundwater flowing in the pipeline 50.

FIG. 9 is a cross-sectional view of the sensitive device 20 cut along the XZ plane as in FIG. 4, and shows a state in which a part of the liquid has penetrated into the housing 21 from below the sensitive device 20. For ease of understanding, the second optical path forming portion 26 and the second pinhole 26a are shown by dotted lines. The sensation device 20 is formed so that liquid can enter the housing 21 from between the inner surface of the housing 21 and the outer peripheral surface of the fluid contact plate 24. Since the wire 23 is immersed in the liquid that has entered the housing 21, the vibration of the wire 23 that affects the measurement result of the wall surface shear stress is suppressed.

The support portion 22 of the sensation device 20 includes a through hole 22a that penetrates from the upper surface portion to the lower surface portion. The through hole 22a is connected to an air supply device 29 that supplies gas into the housing 21 via a tube 28 capable of supplying air. The air supply device 29 includes, for example, a compressor, a syringe, and the like.

The air supply device 29 supplies gas into the housing 21 so that the liquid that has entered the housing 21 does not enter the path of the laser beam, in other words, the liquid level of the liquid that has entered the housing 21 is the first. This is an example of an air supply means that pressurizes the liquid level of the liquid so as to be located below the pinhole 25a of the first pinhole 25a and the pinhole 26a of the second pinhole 26a. More specifically, the air supply device 29 positions the liquid level of the liquid that has entered the housing 21 between the upper surface portion of the fluid contact plate 24 and the first pinhole 25a and the second pinhole 26a. The liquid level of the liquid is pressurized by supplying a gas into the housing 21 so as to hold the liquid. The gas supplied by the air supply device 29 is, for example, air, nitrogen gas, or the like.

The air supply device 29 is provided in the housing 21 in order to hold the position of the liquid level of the liquid in the housing 21 between the upper surface portion of the fluid contact plate 24 and the first pinhole 25a and the second pinhole 26a. The gas is pressurized at a constant pressure (eg, about 14 to about 131 kPa). By holding the gas in the housing 21 at a constant pressure, the position of the liquid level of the liquid in the housing 21 changes slightly according to the change in the surrounding environment, but the upper surface portion of the fluid contact plate 24 and the first one. It is held between the pinhole 25a and the second pinhole 26a.

The side wall surface of the housing 21 is transparent extending in the Z-axis direction from the vicinity of the lower end portion of the housing 21 to the vicinity of the second pinhole 26a so that the user can visually recognize the liquid level position of the liquid in the housing 21. An observation window may be provided.

When a liquid containing bubbles or the like infiltrates into the housing 21 and enters the path of the laser light radiated from the light emitting device 10, the bubbles or the like block the path of the laser light and scatter the laser light, resulting in wall shear stress. It may affect the measurement accuracy. However, since the measurement system according to the second embodiment is configured as described above, there is no possibility that bubbles or the like block the path of the laser beam, and the wall surface shear stress is high even in a mixed phase flow containing the bubbles or the like. It can be measured with accuracy.

Further, in the measurement system according to the second embodiment, since the wire 23 is configured to be immersed in the liquid that has penetrated into the housing 21, the vibration of the wire 23 can be suppressed by the presence of the liquid. As a result, the noise included in the wall surface shear stress of the liquid can be reduced, and the wall surface shear stress can be measured with high accuracy.

(Embodiment 3)
The configuration of the measurement system according to the third embodiment of the present invention will be described with reference to FIG. 10. Unlike the measurement systems according to the first and second embodiments, the measurement system according to the third embodiment transfers power from the rotation shaft of the motor 13 to the rotation shaft of the rotation scattering plate 12 via a power transmission means such as a turning belt. It is configured to communicate to.

FIG. 10 is a cross-sectional view showing the configuration of a light emitting device 10 including a turning belt 15 and a pulley 16. The turning belt 15 and the pulley 16 are examples of power transmission means for transmitting power from the rotation shaft of the motor 13 to the rotation shaft of the rotation scattering plate 12. The turning belt 15 is a belt that can be deformed along the circumference of the pulley 16. The turning belt 15 is made of a material that is deformable along the circumference of a pulley 16 such as rubber or elastomer and is rigid enough to transmit power.

The pulley 16 includes a first pulley 16a provided at the tip of the rotation shaft of the motor 13, and a second pulley 16b provided at the base end of the rotation shaft of the rotation scattering plate 12. The first pulley 16a and the second pulley 16b are arranged on the same plane in the housing 14. A turning belt 15 is attached to the first pulley 16a and the second pulley 16b so as to mechanically connect them. Therefore, when the first pulley 16a is rotated by the motor 13, the rotation of the first pulley 16a is transmitted to the second pulley 16b via the turning belt 15, and the rotation scattering plate is accompanied by the rotation of the second pulley 16b. 12 rotates.

The rotation axis of the rotation scattering plate 12 to which the second pulley 16b is fixed is rotatably supported at two points, the tip end side and the base end side, with respect to the frame body 17 fixed to the housing 14. Therefore, the rotary scattering plate 12 can rotate around its rotation axis without wobbling. The frame body 17 supports the laser light source 11 together with the rotation axis of the rotation scattering plate 12. Therefore, the laser light emitted from the laser light source 11 is irradiated to a predetermined position of the rotary scattering plate 12.

When the rotary scattering plate 12 is directly fixed to the rotary shaft of the motor 13 as in the measurement systems of the first and second embodiments, the wobbling of the rotary shaft of the motor 13 due to the assembly accuracy of the motor 13 and the like is the rotary scattering plate. It affects the rotation of the 12 and may deteriorate the quality of the scattered light emitted from the rotating scattering plate 12. However, since the measurement system according to the third embodiment is configured as described above, the wobbling of the rotating shaft of the motor 13 is absorbed by the turning belt 15 and the pulley 16. Therefore, the rotary scattering plate 12 can be stably rotated around the rotation axis, and uniform emission of scattered light from the rotary scattering plate 12 can be realized. As a result, the wall surface shear stress of the fluid can be measured with high accuracy.

(Example 1)
Next, with reference to FIGS. 11 to 16, the results of verifying whether the measurement system 1 can accurately measure the wall surface shear stress of the fluid in the single-phase flow and the bubble flow are shown. In this verification, the wall shear stress of the fluid was measured in the internal flow in the horizontal channel.

FIG. 11 is a diagram showing an outline of the experimental device used in this verification. The channels extending to the left and right have a rectangular cross section and are made of a transparent acrylic resin so that bubbles can be visually recognized. Inside the channel, water supplied from the tank via a line pump flows from left to right. The total length of the channel is 6000 mm, the height is 20 mm, and the width is 160 mm. The measurement system 1 is located at a position 3750 mm away from the tip of the channel in order to measure the wall shear stress of the fluid in the region where the flow is sufficiently developed. A bubble injector for injecting bubbles into the channel is attached at a position 2250 mm from the tip of the channel.

FIG. 12 is a data table showing the experimental conditions of this verification. Re _m is the Reynolds number between parallel plates defined by the average flow velocity U _m. In this verification, the experiment was performed under the experimental conditions shown in FIG. In this verification, the line pump, by controlling using an inverter to vary the flow rate of the water flowing through the channel was properly changed Reynolds number Re _m.

In this verification, the beat signal of the light detected by the photodetection element 33 was analyzed by the following method. First, the beat signal detected by the photodetection element 33 was processed by a bandpass filter that passes a signal in the frequency band of 75 to 99 Hz, and then the strength of the processed signal was recorded in a data logger. Then, the beat signal stored in the data logger, short-time Fourier transform: by applying _{(Short Time Fourier Transform S T -FT} ), it was carried out frequency analysis. Specifically, the data of a total of 1048576 points acquired in this verification was summarized into 128 points each, and frequency analysis was performed for each 8192 section. As a result, a power spectrum up to 250 Hz was obtained at intervals of 256 μs in frequency increments of 3.9 Hz. The frequency of the beat signal in each section was obtained by averaging the frequencies of the top 10 power spectra in each section.

Figure 13 is a graph showing the relationship between the time average value of the friction coefficient Cf and the Reynolds number Re _m in the case of single-phase flow. Each plot is the average value of the frictional resistance coefficient Cf based on the values measured multiple times. The solid line is the value of the frictional resistance coefficient Cf calculated by the empirical formula of the flow between parallel plates by Dean shown below.

Dean's empirical formula is expressed as follows.
Re _m = √ (2 / Cf) × exp [0.41 (√ (2 / Cf) -2.4]… (4)

As shown in FIG. 13, the measured value of the frictional resistance coefficient Cf is in good agreement with the theoretical value of the frictional resistance coefficient Cf derived from Dean's empirical formula. If the Reynolds number Re _m is 6000 to 8000, the standard deviation is 24%, the Reynolds number Re _m if the 9000-22000, the standard deviation was 10%.

Incidentally, the frictional resistance coefficient Cf and the wall shear stress tau _w are known to satisfy the following expression. However, [rho is the density, _{u m} is flow rate.
Cf = 2τ _w / ρu _m … (5)

Considering the equation (5), the above experimental results show that the measurement system 1 can measure the wall surface shear stress τ _w within a systematic error of 10% in a single phase flow.

Figure 14 is a graph showing the relationship between the time average value of the friction coefficient Cf and the Reynolds number Re _m in the case of bubble flow. Each plot is the average value of the frictional resistance coefficient Cf measured multiple times. The solid line is the value of the frictional resistance coefficient Cf calculated by the empirical formula of the flow between parallel plates by Dean.

As shown in FIG. 14, the measured value of the frictional resistance coefficient Cf is in good agreement with the theoretical value of the frictional resistance coefficient Cf derived from Dean's empirical formula. If the Reynolds number Re _m is 6000 to 8000, the standard deviation was 27%. Moreover, Reynolds number Re _m if the 9000-22000, the standard deviation was within 10%. This indicates that the measurement system 1 can measure the wall surface shear stress τ _w within a systematic error of 10% even in a bubble flow.

15, in the single-phase flow Reynolds number Re 22000 is a graph showing the time variation of wall shear stress tau _w. From the waveform of FIG. 15, the existence of high frequency fluctuation and low frequency fluctuation can be confirmed. It is presumed that the high frequency fluctuation is caused by the electronic noise of the optical system. The low frequency fluctuation captures the change in the wall shear stress of the fluid. It can be confirmed that the wall surface shear stress changes like a spike due to the change in the vertical vortex structure of the turbulent flow. This indicates that the measurement system 1 can detect fluctuations in the wall surface shear stress due to turbulence.

16, in the bubble flow Reynolds number Re 22000 is a graph showing the time variation of wall shear stress tau _w outside the frictional resistance reduction effect region by fine bubbles. The void ratio of the bubble flow was 20% or less. The low-frequency fluctuation captures the change in the wall shear stress of the fluid, as in the case of single-phase flow. This indicates that the measurement system 1 can detect fluctuations in the wall shear stress due to the burst of bubbles.

Define a spike peaks exceeding 2.tau _w to remove noise components, FIG. 15, in the case of FIG. 16, and counts the number of spikes in the total measurement interval. In the case of single-phase flow, the number of spikes was 16, whereas in the case of bubble flow, the number of spikes was 17. Therefore, it can be understood that the frequency of burst occurrence outside the frictional resistance reduction effect region in the case of bubble flow is about the same as in the case of single-phase flow.

As described above, through this verification, it was confirmed that the measurement system 1 can measure the wall surface shear stress within 10% of the systematic error and can measure the peak of the wall surface shear stress due to the turbulent flow in the single phase flow. In addition, it was understood that the frequency of burst occurrence outside the frictional resistance reduction effect region in the case of bubble flow is about the same as in the case of single-phase flow. Therefore, it was confirmed that the measurement system 1 has a higher time resolution than the conventional measurement system.

(Example 2)
Next, with reference to FIGS. 17 to 20, whether or not the measurement system 1 can accurately measure the wall surface shear stress in the external flow was verified by towing the experimental ship equipped with the measurement system 1 in the towing tank. The results are shown.

17 (a) is a perspective view showing an acrylic experimental ship towed in a towed water tank, and FIG. 17 (b) is a cross-sectional view of the experimental ship of FIG. 17 (a). In FIG. 17A, the bow of the experimental ship is shown on the lower side, and the stern of the experimental ship is shown on the upper side. The towing tank has a length of 80 m, a width of 8 m, and a depth of 3.5 m. The bow of the experimental ship is provided with a bubble injector at a position 0.65 m from the bow to inject bubbles into the groundwater in the towed water tank toward the rear of the experimental ship. Further, at the stern of the experimental ship, a measurement system 1 for measuring the wall surface shear stress is provided at a position 3.35 m from the bow.

FIG. 18A is a data table showing experimental conditions when bubbles are not injected (single-phase flow), and FIG. 18B is a data table showing experimental conditions when bubbles are injected (bubble flow). Is. In this verification, the experimental ship was towed under the experimental conditions shown in FIGS. 18 (a) and 18 (b) with groundwater filled in the towed water tank for each of the single-phase flow and the bubble flow, and the wall surface of the fluid was towed. Shear stress was measured. In the case of bubble flow, the experimental vessel was towed at 1.5 m / s, 2.25 m / s, and 3.0 m / s, and the void ratio was changed for each speed of the experimental vessel to measure the wall surface shear stress. Porosity is the volume ratio of voids (air bubbles) contained in a unit volume of fluid.

FIG. 19 is a graph showing the relationship between the _{wall surface shear stress τ w} and the velocity U _{m of the} experimental ship in the case of a single-phase flow. Each point in the graph of FIG. 19 is data actually measured by the measurement system 1, and the solid line is a theoretical value based on the formula of Prandtl-Schlichting. The measurable range of the sensing device 20 (displacement meter) was 2.6 Pa to 12.4 Pa (standard deviation less than 3%). As shown in FIG. 19, when the external flow is a single-phase flow, it can be confirmed _{that the wall surface shear stress τ w increases as the flow velocity increases.}

FIG. 20 is a graph showing the relationship between the wall surface shear stress ratio τ _w / τ ₀ and the void ratio α _{δ in the case of bubble flow.} The wall surface shear stress τ ₀ is the wall surface shear stress when the void ratio α _{δ is zero.} As shown in FIG. 20, when the external flow is a bubble flow, it was confirmed that the higher the speed of the experimental ship, the more the frictional resistance reducing effect can be obtained. It was also confirmed that when the flow velocity is 3.0 m / s, the wall surface shear stress ratio τ _w / τ ₀ decreases as the amount of bubbles increases and the void ratio α _δ increases, and the effect of reducing frictional resistance can be obtained. did it.

As explained above, through this verification, it was confirmed that the wall surface shear stress can be measured in the external flow as well as in the internal flow. Further, it was confirmed that the frictional resistance reducing effect can be obtained as in the case of the internal flow by generating the bubble flow in the external flow.

(Modification example)
The present invention is not limited to the above embodiment, and the modifications described below are also possible.

In the above embodiment, the scattered light is formed by using the laser light emitted from the laser light source 11, but the present invention is not limited to this. For example, a light emitting diode or the like may be used as the light source.

In the above embodiment, the housing 21 of the sensing device 20 has a cylindrical shape, but the present invention is not limited to this. The housing 21 may be a cylindrical member having an elliptical or polygonal cross-sectional shape, as long as it can accommodate a pair of wires 23 and a fluid contact plate 24 inside. Further, even if the fluid enters the inside of the housing 21, it does not affect the measurement accuracy. Therefore, the cross-sectional shape of the housing 21 and the shape of the fluid contact plate 24 do not necessarily have to match, and the shapes are formed different from each other. You may.

In the above embodiment, the housing 21 and the support portion 22 are separate bodies, but the present invention is not limited to this. For example, the housing 21 and the support portion 22 may be integrally configured to form one housing.

In the above embodiment, the first pinhole 25a and the second pinhole 26a are used as the first through hole and the second through hole, but the present invention is not limited to this. The first through hole and the second through hole may be, for example, an elliptical or polygonal through hole, a slit or the like.

In the above embodiment, the opening 26b is a circular through hole, but the present invention is not limited to this. The opening 26b may have a shape that can be observed even if the first pinhole 25a moves in the X-axis direction, and may be, for example, rectangular or slit-shaped.

In the above embodiment, the transmission portion 27 made of a glass plate or a transparent resin plate is fixed to the opening of the housing 21, but the present invention is not limited to this. For example, the housing 21 may be left open to drain the fluid that has entered the housing 21.

In the above embodiment, the transmission portions 14a, 27, 34a are fixed to the openings of the housings 14, 21, 34, but the present invention is not limited to this. For example, the transmissive portions 14a, 27, 34a may be configured to be detachably attached to the opening. In this case, since dirt and the like can be removed by removing and cleaning the transmission portions 14a, 27, and 34a, it is possible to suppress a decrease in the measurement accuracy of the wall surface shear stress.

In the above embodiment, the fluid contact plate 24 is suspended by a pair of wires 23, but the present invention is not limited to this. As long as the fluid contact plate 24 is configured to move in the fluid flow direction without tilting from the fluid flow direction, the member supporting the fluid contact plate 24 may be any member, and the fluid contact plate 24 may be made of rubber or It may be supported by a member made of an elastoma.

In connection with the above modification, for example, a pair of plate-shaped elastic members made of rubber or elastomer may be arranged side by side in the X-axis direction so as to face the Y-axis direction. Since the plate-shaped elastic member faces the Y-axis direction, it is difficult to deform in the Y-axis direction and easily deforms in the X-axis direction, so that the wall surface shear stress of the fluid acting in the X-axis direction can be measured accurately. ..

In the above embodiment, the piano wire is used as the wire 23, but the present invention is not limited to this. For example, a stainless wire, a hard steel wire, an iron wire, or the like may be used as the wire 23. Further, the number of wires 23 is two, but the present invention is not limited to this, and for example, three or more wires may be used.

In the above embodiment, the light emitting device 10, the sensitive device 20, and the light receiving device 30 are provided with separate housings, but the present invention is not limited to this. For example, each configuration of the light emitting device 10, the sensitive device 20, and the light receiving device 30 may be housed in one housing and unitized.

In the third embodiment, the turning belt 15 and the pulley 16 have been exemplified as the power transmission means, but the present invention is not limited to this. For example, as the power transmission means, a turning belt made of a metal chain and a gear engaged with the metal chain may be used.

In the above embodiment, the case where the measurement system 1 is fixed to the pipeline 50 having a rectangular cross section and the wall surface shear stress of the fluid (internal flow) in the conduit 50 is measured has been exemplified. Not limited. For example, the measurement system 1 may be fixed to the outer panel of a ship to measure the wall shear stress of the fluid (external flow) acting on the outer panel of the ship.

In connection with the above modification, the convection velocity of the ship can be derived based on the wall shear stress of the fluid acting on the outer panel of the ship. Conventionally, the ground speed of a ship has been measured, but the measurement of the convection speed of a ship in transit has not been realized. When the power source such as the engine mounted on the ship is controlled by using the derived convection speed, the fuel consumption can be improved. In particular, when the ship is a large ship such as a tanker, fuel efficiency can be significantly improved.

Further, a technique of injecting fine bubbles into the turbulent boundary layer in order to reduce the frictional resistance with the sea surface of the ship is known, but by using the measurement system 1, the contact field with the sea surface of the ship is known. A detailed demonstration experiment of the frictional resistance reduction phenomenon due to bubbles becomes possible. Therefore, by conducting a demonstration experiment using the measurement system 1 for each ship, it is possible to optimize the amount, position, timing, etc. of fine bubbles flowing into the turbulent boundary layer.

The above embodiments are examples, and the present invention is not limited thereto, and various embodiments are possible without departing from the spirit of the invention described in the claims. The components described in each embodiment and modification can be freely combined. The present invention also includes inventions equivalent to those described in the claims.

1 Measurement system 10 Light emitting device 11 Laser light source 12 Rotating scattering plate 13 Motors 14, 21, 34 Housings 14a, 27, 34a Transmissive part 15 Turning belt 16 Pulley 16a First pulley 16b Second pulley 17 Frame 20 Sensing device 21a Flange 21b Through hole 22 Support part 23 Wire 23a First wire 23b Second wire 24 Fluid contact plate 25 First light path forming part 25a First pinhole 26 Second light path forming part 26a Second pinhole 26b, 51 Opening 28 Tube 29 Air feeder 30 Light receiving device 31 Lens system 31a Parallel lens 31b Condensing lens 32 Scatterer 33 Photodetection element 40 Support plate 50 Pipeline

Claims (12)

A measurement system that measures the wall shear stress of a fluid.
A light emitting means that emits scattered light and
The first through hole and the second through hole through which the scattered light from the light emitting means is passed are included, and the first through hole moves in the flow direction of the fluid according to the wall shear stress of the fluid. The second through hole is a sensation means that is held at a fixed position even if the wall shear stress of the fluid changes.
A light receiving means for receiving a beat signal obtained by the interference of scattered light passing through the first through hole and the second through hole with each other.
An arithmetic means for calculating the wall shear stress of the fluid based on the frequency of the beat signal received by the light receiving means, and
A measurement system equipped with. The sensation means
It is equipped with a fluid contact plate that is arranged in contact with the fluid and moves in the flow direction of the fluid in response to the shear stress on the wall surface of the fluid.
The first through hole is configured to move in the fluid flow direction in conjunction with the fluid contact plate.
The measurement system according to claim 1. The sensation means
Supporting means fixed in place with respect to the object for measuring wall shear stress,
An elastically deformable means for elastic deformation, in which one end is supported by the support means, the other end is fixed to the fluid contact plate, and the fluid contact plate is suspended from the support means.
To prepare
The measurement system according to claim 2. The sensitive means includes a housing for accommodating the elastic deformation means and the fluid contact plate inside.
The fluid contact plate is arranged adjacent to the lower end of the housing so as to be in contact with the fluid together with the lower end of the housing.
The measurement system according to claim 3. A first optical path forming portion in which the first through hole is formed is fixed to the elastic deformation means.
A second optical path forming portion in which the second through hole is formed is fixed to the housing.
The measurement system according to claim 4. The second optical path forming portion includes an opening formed adjacent to the second through hole.
The first optical path forming portion is arranged on the back side of the second optical path forming portion.
The opening is formed so that scattered light can pass through the first through hole even when the first optical path forming portion moves according to the wall shear stress of the fluid.
The measurement system according to claim 5. The first optical path forming portion and the second optical path forming portion are provided on the light emitting means side of the housing.
On the light receiving means side of the housing, a transmitting portion capable of transmitting scattered light that has passed through the first optical path forming portion and the second optical path forming portion is provided.
The measurement system according to claim 5 or 6. The measuring system is a measuring system for measuring the wall shear stress of a liquid.
The sensing means is configured so that the liquid enters the housing from between the fluid contact plate and the housing.
The measurement system supplies a gas into the housing so that the liquid level of the liquid that has entered the housing is located below the first through hole and the second through hole, and the liquid level of the liquid. Further equipped with an air supply means to pressurize,
The measurement system according to any one of claims 4 to 7. The elastic deformation means is a pair of wires arranged side by side in the flow direction of the fluid.
One wire is fixed to the side end of the upper surface portion of the fluid contact plate, and the other wire is the side end of the upper surface portion of the fluid contact plate, which is opposite to the portion to which the one wire is fixed. Fixed to the side,
The measurement system according to any one of claims 3 to 8. The light emitting means
Laser light source and
A rotary scattering plate that scatters the laser light emitted from the laser light source,
A motor that rotates the rotary scattering plate around the central axis at a constant angular velocity,
To prepare
The measurement system according to any one of claims 1 to 9. The rotational scattering plate and the motor are connected to each other via a turning belt so that the rotation of the motor can be transmitted to the rotational scattering plate.
The measurement system according to claim 10. The light receiving means is
A lens system that generates a beat signal by focusing the scattered light that has passed through the first through hole and the second through hole at an intersection.
A scatterer that is arranged to include the intersection and scatters the beat signal generated by the lens system.
A photodetector that detects the intensity of the beat signal scattered by the scatterer,
To prepare
The measurement system according to any one of claims 1 to 11.

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