JP2009222716A - Focus-variable optical flow velocity measurement device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical flow velocity measurement device capable of easily changing a focal distance of a laser beam to measure velocity of a fluid. <P>SOLUTION: An aperture of a lens is quickly and correctly varied with low power by means of a fluid lens for focusing the laser beam, thereby facilitating measurement of flow velocity and shearing stress in a structure boundary layer in a flow field. The optical flow velocity measurement device can be downsized by integrating an optical array containing the fluid lens through the use of diode laser light as a laser light source. In addition, the optical flow velocity measurement device can be inserted into the surface of a structure to use it as a surface flow field measurement sensor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical flow velocity measuring apparatus with variable focus. More specifically, a variable-focus optical velocity measuring device capable of easily changing the focal length of a laser beam in order to measure the flow velocity flowing around a structure in a flow field, shear stress, and the like. About.

  In recent years, with the development of optical measurement techniques, LDV (Laser Doppler Velocimeter) systems, which are flow velocity measuring devices that use the Doppler effect, have been widely used for flow field flow velocity measurement.

  As a general measurement method for measuring the flow velocity, a probe equipped with a focusing lens is installed so that a focus is formed on an external measuring device of a flow field equipped with a visible window, and laser light Is used to measure the flow velocity by detecting the scattered light of the flowing particles. In order to move the measurement point, the probe is mechanically moved using a transfer device or the like. The probe is moved according to the position of the measurement point in this way because the focal length of the focusing lens is fixed.

On the other hand, the flow velocity information in the boundary layer region of the structure in the flow field in the flow velocity measurement is very important in engineering. FIG. 1 is a schematic diagram illustrating the velocity gradient of the boundary layer shown on the surface of the structure in the flow field. As shown in FIG. 1, a boundary layer 30 having a velocity gradient U (y) exists up to a certain region on the structure surface 10 due to the influence of the shear frictional force of the surface. Within the boundary layer 30, the closer to the structure due to the shear frictional force with the structure, the gradual speed decreases and the flow velocity at the structure surface 10 becomes “0”. At a position away from a certain region on the surface, there is a region where the influence of the shearing force on the surface is small and the flow velocity U ₀ is similar. In particular, it is known that the velocity gradient is linear in the region of the lower boundary layer 20, and in the case of a Newtonian fluid, the surface shear stress of the structure is linearly proportional to the velocity gradient. Therefore, accurate measurement of the flow velocity in the y direction in the boundary layer 30 is very important not only for obtaining information on the surface shear stress but also the flow velocity distribution around the structure.

  In such a boundary layer, there may be a case where a large number of measurement points should be secured within 1 mm of the surface as a region adjacent to the surface of the structure. Accordingly, since an LDV system having an elaborate resolution is required, there is a limit depending on an existing general LDV system or a measurement method using the LDV system.

  Recently, small LDV systems suitable for such applications have been developed and their use is gradually expanded. For example, MSE in the United States developed a mini LDV by miniaturizing a probe using a semiconductor laser, and uses it for measuring a boundary layer flow velocity. Further, in order to measure the surface shear stress of the structure closer to the surface, a dedicated measuring device for shear stress that is attached to the surface of the structure in an integrated manner has been developed. However, these measuring devices have a fixed focal length of the laser focusing lens. Therefore, in the case of the mini LDV, the mechanical transfer device must still be used. The measurement position can only be fixed.

  As a general example of such a conventional LDV, FIG. 2 shows a schematic diagram of a small LDV probe integrated with a low-power small diode laser, particularly when the focal length of the focusing lens is not long. Looking at the operating principle, when the power 131 for generating laser light is supplied to the LDV probe 100 aimed at the measurement position of the flow field, laser light is generated from the diode light generation unit 130, which is connected to the spectroscopic unit 150. The light is split into parallel light 132 by the reflecting mirror 151 and transmitted to the focusing lens 110. The laser beam focused on the measurement point 133, that is, the focal length y by the focusing lens forms a fringe, and the suspended particles 101 passing through this region scatter the laser beam.

  The scattered light 142 generates a frequency shift (Doppler effect) corresponding to the velocity of the suspended particles, and a part of the scattered light 142 returns and is focused by the light receiving lens 120 in the probe. The focused optical signal is transmitted 141 to the frequency analyzer through the optical cable 140. By detecting the Doppler frequency from the frequency analyzer, the suspended particles, that is, the flow velocity at the measurement point can be confirmed.

  Since the general laser beam focusing lens 110 of the system has a fixed focal length y, the entire probe 100 must be moved in order to change the measurement point along the y direction. A separate mechanical transfer device must be coupled. Therefore, an additional transfer device is required, which increases the volume of the device, and there is a problem that there is a limitation in the rapid and accurate driving of the probe transfer.

  Such a problem is caused because the focal length of the focusing lens is fixed as described above, and the probe itself needs to be transported. For this reason, it is difficult to quickly measure the flow velocity, which is troublesome, and there is a problem that the efficiency of the flow velocity measurement is poor.

The present invention is for solving the above-mentioned problems, and a first object of the present invention is to make the LDV probe a small surface-integrated sensor type, and only by the flow velocity in the boundary layer on the surface of the structure. In other words, the focal point of the laser beam focusing lens can be arbitrarily changed to enable measurement of the surface shear stress.
A second object of the present invention is to apply not only a flow velocity measurement at an arbitrary position around a structure but also a surface shear stress measurement by applying an LDV system that realizes variable focus in the flow velocity measurement. Is to be able to do so.

In addition, the third object of the present invention is to realize a miniaturization of the measurement sensor by performing the flow velocity measurement at an arbitrary position around the structure without providing a separate mechanical transfer means, and to quickly and accurately It is to ensure operation.
In addition, a fourth object of the present invention is to provide a highly efficient optical flow velocity measuring apparatus that can rapidly measure the flow velocity by changing the focal point of the laser beam focusing lens at any time and can be dramatically improved. Is to provide.

  In order to achieve the above-mentioned object of the present invention, an optical flow velocity measuring apparatus according to a preferred embodiment of the present invention is divided into a light generation unit that generates laser light, and a spectroscopic unit that divides the laser light into a plurality of light sources. A focusing lens that is an insulator including a fluid lens containing a polar and a non-polar fluid therein so as to form a focal point by focusing the light source and outputting it to a position where the flow velocity is to be measured; A unit embodying variable focus that adjusts the focal length by changing the spherical surface of the focusing lens, a light receiving lens that receives and focuses the scattered light of the laser beam on which the focus is formed, and a Doppler frequency of the focused scattered light And a calculation unit for calculating the flow velocity.

  The spectroscopic unit includes a spectroscopic unit that splits the generated laser light and a reflecting mirror that reflects a part of the split laser light and changes its path, and the arithmetic unit is a frequency analyzer. The flow rate is calculated by detecting the Doppler frequency.

Here, the unit that implements the variable focus can apply an electromotive force to the focusing lens to change the radius of curvature of the focusing lens. For this purpose, the focusing lens contains the first and second liquids. The first and second liquids have the same specific gravity but are not mixed with each other, so that they form an interface.
At this time, it is preferable that the first liquid is a conductive liquid and the second liquid is an insulating liquid.

In the optical flow velocity measuring device according to a preferred embodiment of the present invention, the focusing lens is made of a transparent and stretchable material, and the spherical surface of the lens changes according to the amount of liquid contained in the focusing lens. To be able to.
At this time, it is preferable that the unit that implements the variable focus changes the spherical surface of the focusing lens by adjusting the amount of liquid contained in the focusing lens. To this end, the unit that implements the variable focus includes an introduction tube for introducing a liquid into the focusing lens, a discharge tube for discharging the liquid introduced into the focusing lens, and the liquid. And a pump for flowing the fluid.

  An optical flow velocity measuring device according to a preferred embodiment of the present invention includes a light generation unit that generates laser light, a spectroscopic unit that divides the laser light into a plurality of light sources, and a flow rate obtained by focusing the divided light sources. A focusing lens, which is an insulator including a fluid lens containing a fluid that can be moved in and out so as to form a focal point by outputting to a position to be measured, and a tensile force coupled to the focusing lens to the focusing lens And a unit embodying variable focus for applying a compressive force, a light receiving lens that receives and scatters the scattered light of the laser beam on which the focus is formed, detects a Doppler frequency of the focused scattered light, and calculates a flow velocity. And an arithmetic unit. At this time, an actuator that generates the tensile force and / or compressive force, and the converging lens is extended by using the tensile force and / or compressive force generated by connecting the actuator and the converging lens, or A coupling unit that changes the spherical surface of the focusing lens by pulling.

  At this time, it is preferable that the actuator includes at least one of a voice coil motor (VCM) and a piezoelectric element.

  According to the present invention, the LDV probe can be measured quickly and accurately without a separate mechanical transfer device for transferring the probe according to the flow velocity distribution around the surface of the structure in the flow field. In addition to forming a mold, the focal point of the laser beam focusing lens can be arbitrarily changed so that not only the flow velocity in the boundary layer on the surface of the structure but also the surface shear stress can be measured.

In addition, by applying the LDV system that realizes variable focus in the flow velocity measurement, not only the flow velocity measurement at an arbitrary position around the structure but also the surface shear stress can be measured by one measuring device. is there.
In addition, since a separate mechanical transfer device is not required, the probe can be easily downsized, and a measurement sensor integrated with a structure can be realized.

It is a schematic diagram which shows distribution of the flow velocity in the surface boundary layer of the structure in a flow field. It is a schematic diagram of the conventional mini LDV system. It is the block diagram which showed the optical flow velocity measuring apparatus which concerns on 1st Embodiment of this invention. It is the block diagram which showed the action | operation mechanism in which a focal distance changes in the optical flow velocity measuring apparatus which concerns on 1st Embodiment of this invention. It is a schematic diagram for demonstrating the mechanism of the spherical surface change of the focusing lens which concerns on 1st Embodiment of this invention. It is the block diagram which showed the probe of the optical flow velocity measuring apparatus which concerns on 2nd Embodiment of this invention. It is the block diagram which showed the action | operation mechanism in which a focal distance changes in the optical flow velocity measuring apparatus which concerns on 2nd Embodiment of this invention. It is a schematic diagram for demonstrating the mechanism of the spherical surface change of the condensing lens which concerns on 2nd Embodiment of this invention. It is a schematic diagram for demonstrating the mechanism of the spherical surface change in the focusing lens which is a deformation | transformation embodiment of 2nd Embodiment of this invention. It is a schematic diagram which shows the drive power with respect to a LDV probe, a fluid lens, and a laser beam generator, and the form of signal input / output. It is a schematic diagram which shows the form of the other drive power and signal input / output with respect to FIG.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited or limited by the present embodiment. For reference, in the following description, since the configuration and function are almost the same, elements that are handled in the same way are identified by the same reference numerals.

FIG. 3 is a schematic diagram showing the configuration of the probe of the optical flow velocity measuring apparatus according to the first embodiment of the present invention.
As shown in the drawing, the probe 200 of the optical flow velocity measuring device contains a light generation unit 230 for generating laser light therein. In addition, a spectroscopic unit 250 that divides the laser light generated by the light generation unit 230 into two is housed, and a focusing lens 210 for forming a focal point of the output laser light, and the input laser light are collected. A light receiving lens 220 is accommodated.

  First, a focusing lens 210 which is a core technical feature of the present invention is a fluid lens in which a fluid is contained inside a lens instead of a general fixed focus lens in order to arbitrarily change the focus of the focusing lens. It is characterized by being.

  This fluid lens is an optical technology that has been actively studied recently, and by using the electrowetting phenomenon to generate a voltage difference between the conductive liquid and the container, by changing the curvature of the liquid spherical surface, A method of changing the focal length of the lens is adopted. In addition, a method of adjusting the focal length of the fluid lens by changing the spherical surface of the liquid container by injecting liquid into a flexible transparent container to increase or decrease the amount of the liquid is also used.

  At this time, in the method of generating a voltage difference between the conductive liquid and the container, the liquid inside the fluid lens contains polar and nonpolar fluids respectively, and the spherical surface of the liquid container is formed by an insulator, The applied voltage difference changes the surface tension of the polar liquid, resulting in the liquid container changing shape and changing the focal length.

  In addition, the fluid lens is easy to downsize, and has an advantage that the focus can be changed quickly and accurately even with small power. By applying such a variable focus function of the fluid lens to the LDV system, the probe itself is integrally mounted on the measurement structure without the need for mechanical transfer means, and not only the flow velocity in the surrounding boundary layer, Up to surface shear stress can be measured.

  Next, the light generation unit 230 will be described. The light generation unit 230 can generate laser light using a diode. The laser light source for measurement can generate laser light of a specific frequency band by various generating means such as He-Ne and Ar-ion, and can be selectively used according to the purpose of use.

  The laser light generated by the light generating unit 230 is equally divided by a spectroscopic unit 250 (beam splitter) and sent to the focusing lens 210. Any suitable optical system can be used to adjust the beam path during this process.

Next, the operation mechanism of this apparatus will be described.
First, the laser light generated by the light generation unit 230 is split into parallel light 232 and reflected light by the spectroscopic unit 250. The reflected light is reflected by the reflecting mirror 251, and the parallel light and the reflected light pass through the focusing lens 210 in parallel with each other.

  As described above, the focusing lens 210 is a fluid lens, and is adjusted so that the first measurement point 233 is focused by forming the spherical surface 208 by the applied electromotive force 211. The laser beam focused on the first measurement point 233, that is, the focal length y1, forms a fringe, and the floating particles 201 passing through this region scatter the laser beam. The scattered light 242 generates a frequency shift (Doppler effect) corresponding to the velocity of the suspended particles, and a part of the scattered light 242 returns and is focused by the light receiving lens 220 in the probe. The focused optical signal is transmitted 241 to the frequency analyzer through the optical cable 240. By detecting the Doppler frequency from this frequency analyzer, the flow velocity at the first measurement point 233 is confirmed.

  At this time, when measuring the velocity of other suspended particles by changing the focal length y1, that is, when measuring the flow velocity at the changed y-direction position, the electromotive force applied to the focusing lens 210. By appropriately changing 211, the spherical surface 209 of the fluid lens is changed as shown in FIG. 4 so that the focal length y2 is formed at another position 234 to be measured.

  Thereafter, the flow velocity at the second measurement point 234 can be confirmed by focusing the scattered light 242 of the suspended particles 201 of the laser beam through the same mechanism as in FIG. 3 and detecting the Doppler frequency. By changing the focal length of the focusing lens 210 through such a method, the flow velocity distribution in the boundary layer around the structure surface 10 (see FIG. 1) can be measured. Since the surface shear stress of the structure can be measured by measuring, the measurement variables separately measured by the conventional flow velocity measuring device and the surface shear stress measuring device can be measured by one measuring device. .

  To restate the core feature of the present invention, the focal length is changed by applying an electromotive force to the focusing lens and changing the spherical surface of the liquid lens. Such an operating mechanism is illustrated in FIG.

  According to FIG. 5, the fluid lens is filled with a liquid having an appropriate optical property in a cylindrical container 210 whose upper and lower sides are sealed by transparent insulators 204 and 205, but the upper part is filled with a conductive liquid 202. In addition, the lower part is filled with an insulating liquid. At the same time, the two liquids have the same specific gravity, but maintain the property of not being mixed with each other, and the two liquids each form a boundary surface. At this time, when a potential difference is applied between the conductive liquid 202 and the lower panel (transparent insulator) 205, the radius of curvature of the boundary between the two liquids changes. Such a phenomenon is called an electrowetting phenomenon. By changing the voltage here, the radius of curvature of the fluid lens can be controlled as shown by 208 and 209 shown in FIG. Become.

  That is, the spherical surfaces 208 and 209 of the lens can be easily changed in focal length while being deformed, as shown in FIGS. 3 and 4, so that the velocity gradient due to the shear stress can be easily measured. .

The second embodiment of the present invention will be described below with reference to FIGS.
FIG. 6 is a schematic diagram illustrating the configuration of the probe of the optical flow velocity measuring device according to the second embodiment of the present invention.
Detailed description of the same parts as those of the first embodiment is omitted for the sake of brevity.

  The difference from the first embodiment is that a liquid 302 filled in a bag of a transparent and flexible material is used in the method of driving the fluid lens 310 serving as the focusing lens 300 shown in FIG. 9 (see FIG. 8). ) To adjust the radius of curvature of the spherical surface of the liquid lens 310. That is, by discharging or introducing 311 the liquid 302 having optical properties through the tube and changing the shape of the spherical surfaces 308 and 309 of the fluid lens 310, the focal length is made shorter or longer like y1 and y2. Thus, the focus position of the measurement point is changed. FIG. 7 shows an example in which the focal position of the measurement point changes as the spherical shape changes in this way.

  FIG. 8 is a schematic diagram showing a fluid lens driving principle in which the radius of curvature of the spherical surface of the fluid lens 310 is changed by adjusting the amount of the liquid 302 filled in the bag made of a transparent and stretchable flexible material. It is.

  A liquid 302 having optical properties is discharged into a transparent and stretchable flexible container (liquid lens bag) 310 into which liquid can be introduced by discharging the liquid 302 through a tube connected to the periphery of the container. The focal length of the lens can be controlled by increasing or decreasing the radius of curvature 308, 309 of the container spherical surface. Liquid introduction and discharge pumps can include a variety of means operated by electrical and mechanical power.

  The spherical surface control for the focusing lens 300 shown in FIG. 9 can include a method other than the above method using liquid introduction / discharge. This will be described in more detail. FIG. 9 is a schematic diagram for explaining a spherical change mechanism in a focusing lens which is a modified embodiment of the second embodiment.

  As shown in FIG. 9, the fluid lens 300 is not a device that introduces and discharges liquid from the outside in a state where a certain amount of liquid 302 is filled in the liquid container 310, but the liquid container 310 in its peripheral part. In contrast, it is possible to adopt a configuration including a means capable of pulling in the radial direction or applying a contraction force to the surface. The actuator 440 for driving to apply the tension or contraction force may include various means operated by electric or mechanical power. The actuator 440 is connected to the focusing lens 300 and a connection unit (not shown), and the tensile force and / or compression force generated from the actuator 440 is transmitted to the focusing lens 300 through the connection unit. ing. The transmitted tensile force and / or compressive force changes the focal length y by changing the spherical surface of the focusing lens 300 by pulling or compressing the liquid container 310 constituting the focusing lens 300. It has become.

Further, the actuator 440 provides the tension / contraction force so that the liquid container 310 is driven in a direction perpendicular to the laser light projection direction so as to change the focal length y of the focusing lens 300. It is also possible to make it.
At this time, the actuator 440 is a linear motor, a voice coil motor (VCM), or a piezoelectric element that is generally used as a highly accurate position determination device. It is preferable to comprise at least one kind. However, it is not limited to these.

  FIG. 10 shows an LDV probe 200 including a fluid lens using an electrowetting phenomenon, power input units 211 and 231 for driving the fluid lens and the laser light generator, and a measurement light signal processing device 260. A block diagram is shown. The arrangement of each component device is not limited as shown in FIG. 10, and can be variously modified. That is, the laser light generator 230 in the probe 200, the external optical signal processor 260, or the like can be disposed inside or outside the probe 200.

FIG. 11 shows an LDV probe 300 including a fluid lens that utilizes adjustment of the amount of liquid in a liquid container made of a transparent flexible material, and power input devices 231 and 370 for driving the fluid lens and the laser light generator. The optical signal processing device 260 is shown. As in the case of FIG. 10, the arrangement of the constituent devices is not limited as shown in FIG. 11, and various modifications are possible.
That is, the laser light generator 230 in the probe 200, the external optical signal processing device 260, the liquid transfer pump 370, or the like can be disposed inside or outside the probe.

  As described above, the preferred embodiments of the present invention have been described with reference to the preferred embodiments of the present invention. Can be modified and changed.

202 Conductive liquid 203: Insulating liquid 210: Converging lens 220: Light receiving lens 230: Light generation unit 240: Optical cable 250: Spectroscopic unit 251: Reflecting mirror

Claims (11)

A light generation unit for generating laser light;
A spectroscopic unit for dividing the laser light into a plurality of light sources;
A focusing lens that is an insulator including a fluid lens containing a polar and a non-polar fluid therein so as to focus the divided light source and output it to a position to measure the flow velocity to form a focal point;
A unit embodying variable focus for changing the spherical surface of the focusing lens by changing the surface tension by applying an electromotive force to the polar fluid;
A light receiving lens that receives and focuses the scattered light of the laser beam on which the focal point is formed;
An arithmetic unit for detecting a Doppler frequency of the focused scattered light and calculating a flow velocity;
An optical flow velocity measuring device comprising: The spectroscopic unit is:
A spectroscopic unit for dividing the generated laser light;
A reflecting mirror that reflects part of the divided laser light and changes its path;
The optical flow velocity measuring device according to claim 1, comprising:   The optical flow velocity measuring apparatus according to claim 1, wherein the unit that implements the variable focal point applies an electromotive force to the focusing lens to change a radius of curvature of the focusing lens.   The focusing lens includes a first liquid and a second liquid, and the first liquid and the second liquid have the same specific gravity but are not mixed with each other, thereby forming a boundary surface. The optical flow velocity measuring apparatus as described.   The optical flow velocity measuring apparatus according to claim 4, wherein the first liquid is a conductive liquid, and the second liquid is an insulating liquid.   2. The optical flow velocity measurement according to claim 1, wherein the focusing lens is made of a transparent and stretchable material, and the spherical surface of the lens changes according to the amount of liquid contained in the focusing lens. apparatus.   The optical flow rate measuring apparatus according to claim 6, wherein the unit that implements the variable focus changes a spherical surface of the focusing lens by adjusting an amount of the liquid contained in the focusing lens. The unit embodying the variable focus is an introduction tube for introducing a liquid into the focusing lens;
A discharge tube for discharging the liquid introduced into the focusing lens;
A pump for flowing the liquid;
The optical flow velocity measuring device according to claim 7, comprising: A light generation unit for generating laser light;
A spectroscopic unit for dividing the laser light into a plurality of light sources;
A focusing lens that is an insulator including a fluid lens containing a fluid that can enter and exit to focus the divided light source and output the flow velocity to a position to be measured to form a focal point;
A unit embodying a variable focus that is coupled to the focusing lens to provide a tensile force and a compression force to the focusing lens;
A light receiving lens that receives and focuses the scattered light of the laser beam on which the focal point is formed;
An optical flow velocity measuring apparatus comprising: an arithmetic unit that detects a Doppler frequency of the focused scattered light and calculates a flow velocity. The unit embodying the variable focus is
An actuator that generates the tensile and / or compressive force;
A connecting unit that changes the spherical surface of the focusing lens by extending or pulling the focusing lens using the tensile force and / or compression force generated by connecting the actuator and the focusing lens;
The optical flow velocity measuring apparatus according to claim 9, comprising:   11. The optical flow velocity measuring apparatus according to claim 10, wherein the actuator includes at least one of a voice coil motor (VCM) or a piezoelectric element.

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