Flow velocimeter

Abstract

To provide a flow velocimeter capable of relatively easily measuring an ensemble average value of passage flow velocities near the surface.SOLUTION: A flow velocimeter 10 for measuring the flow velocity of a stream passing through a water conduit, comprises: a resistance plate 11 drooped below a water surface in the water conduit; a support unit 12 for supporting the resistance plate 11 from above the water surface; a measurement unit 13 for measuring a change of the support unit 12 based on the resistive force of fluid acting on the resistance plate 11; and an arithmetic unit 14 for calculating a flow velocity on the basis of the value measured by the measurement unit 13. The support unit 12 is a length-adjustable cantilever secured to the measurement unit 13 at one end and having the resistance plate 11 attached on the other end side.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a current meter that measures the flow velocity of a flow passing through a waterway. [Background technology]

[0002] In recent years, as environmental problems have become more serious, power generation devices that use natural energy to generate electricity have been attracting attention. In particular, in order to evaluate the performance of devices for recovering surface tidal energy, such as devices with open undershot water turbines installed on a floating body, a simple method is required to measure the flow velocity of the water flowing through the waterway that the floating body constitutes.

[0003] Known current meters include a propeller current meter that has a propeller that rotates in proportion to the speed of the flow and detects the rotation of the propeller, and a current meter that uses the Doppler effect of ultrasonic waves.

[0004] For example, Patent Document 1 describes a flow velocity meter having a sensor unit for measuring fluid equipped with a vane wheel having multiple propellers that rotate as a fluid passes through it, a coupling unit for airtightly connecting to a pipe through which the fluid passes, and a calculation and display unit for calculating and displaying the results measured by the sensor unit.

[0005] Patent Document 2 describes a flow velocity measurement device for measuring the flow velocity in a flow path, the flow velocity measurement device comprising an ultrasonic sensor for transmitting ultrasonic waves into the flow path and receiving echo signals from within the flow path, an ultrasonic transmitting / receiving unit for driving the ultrasonic sensor at a predetermined frequency and receiving echo signals from the ultrasonic sensor, an analog / digital converter for the echo signal from the ultrasonic transmitting / receiving unit, and a control unit connected to the ultrasonic transmitting / receiving unit and the analog / digital converter for operating the ultrasonic transmitting / receiving unit at a repeating period to receive the echo signal from the analog / digital converter.

[0006] However, propeller-type current meters and current meters using the Doppler effect have problems in terms of ease of handling and measurement of flow velocities near the surface. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2004-132729 A [Patent Document 2] JP 2020-190444 A Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above problems of the conventional technology, an object of the present invention is to provide a current meter that can measure the ensemble average value of passing flow velocities near a surface relatively easily. [Means for solving the problem]

[0009] One aspect of the present invention is a current meter that measures the flow speed of a flow passing through a water channel, and comprises a resistance plate suspended below the water surface of the water channel, a support section that supports the resistance plate above the water surface, a measuring section that measures changes in the support section based on the resistance of the fluid acting on the resistance plate, and a calculation section that calculates the flow speed based on the value measured by the measuring section, wherein the support section is a length-adjustable cantilever with one end fixed to the measuring section and the resistance plate attached to the other end.

[0010] In this case, in one aspect of the present invention, the measurement unit may be a piezoelectric torque sensor.

[0011] In one aspect of the present invention, the resistance plate may be maintained at a predetermined depth by a float provided on the upper part, and the support part may be equipped with a mechanism for rotating the resistance plate so that it faces a predetermined direction relative to the direction of flow.

[0012] In one embodiment of the present invention, the resistance plate may be a thin plate having a thickness of less than 0.5 mm on the surface facing the flow, and the length of the side facing the flow may be 5 mm or less. Effect of the Invention

[0013] In this way, according to the present invention, a current meter can be provided that can measure the ensemble average value of passing flow velocities near the surface relatively easily. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic diagram showing a configuration of a current meter according to an embodiment of the present invention. [Diagram 2] FIG. 13 is a diagram showing the relationship between the measurement flow velocity range and the flat plate length in the present invention. [Diagram 3] FIG. 3(A) is an external view of a cantilever-type current meter used in an embodiment of the present invention, and FIG. 3(B) is a schematic diagram showing the configuration of a resistance plate and a support part in the embodiment of the present invention. [Figure 4] FIG. 1 is a diagram showing an observation state in an embodiment of the present invention. [Diagram 5] FIG. 13 shows the results of a calibration experiment in an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The flow meter according to the present invention will be described in detail below. Note that the present invention is not limited to the following examples, and can be modified as desired without departing from the gist of the present invention.

[0016] Fig. 1 is a schematic diagram showing the configuration of a current meter according to one embodiment of the present invention. One aspect of the present invention is a current meter 10 for measuring the flow velocity of a flow passing through a waterway, comprising a resistance plate 11 suspended below the water surface of the waterway, a support section 12 for supporting the resistance plate 11 above the water surface, a measurement section 13 for measuring a change in the support section 12 based on the drag of the fluid acting on the resistance plate 11, and a calculation section 14 for calculating the flow velocity based on the value measured by the measurement section 13, wherein the support section 12 is a length-adjustable cantilever having one end fixed to the measurement section 13 and the resistance plate 11 attached to the other end.

[0017] The resistance plate 11 is a flat resistor that is suspended below the water surface of the waterway, and the current meter 10 according to the present invention calculates the flow velocity by detecting the fluid resistance generated in this resistance plate 11. There are no particular limitations on the material of the resistance plate 11, but since it will be suspended in seawater, it is preferable to use a metal or the like that has corrosion resistance and rust prevention properties.

[0018] The support part 12 supports the resistance plate 11 from above the water surface. In addition, in the present invention, the support part 12 is characterized as being a length-adjustable cantilever with one end fixed to the measuring part 13 and the resistance plate 11 attached to the other end. In this way, the length of the resistance plate 11 attached to the tip of the cantilever can be adjusted so that it is at a desired depth position. Fluid resistance generated in the resistance plate 11 causes changes such as deflection in the cantilever, which is the support part 12.

[0019] The measuring unit 13 measures the change in the support part 12 based on the drag of the fluid acting on the resistance plate 11. The measuring unit 13 may be, for example, a photographing device such as a camera that observes the amount of deflection of the support part 12 (cantilever) due to the drag of the fluid acting on the resistance plate 11. In one aspect of the present invention, the measuring unit 13 is preferably a piezoelectric (piezo) torque sensor. By using a piezoelectric (piezo) torque sensor, a moment proportional to the drag of the fluid acting on the resistance plate 11 can be converted into an electrical signal in the measuring unit 13 (torque sensor) and sent.

[0020] The calculation unit 14 calculates the flow velocity based on the value measured by the measurement unit 13. The flow velocity is calculated, for example, using the following formula.

[0021] As an example, when the measuring unit 13 is a piezoelectric torque sensor, the input torque is given by the following equation (1).

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[0022] At this time, the fluid force Fd acting on the resistance plate 11 is expressed by the formula (2).

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[0023] In addition, the resistance coefficient around the resistive plate in the laminar flow region, C d is obtained by equation (3).

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[0024] Therefore, since the torque M measured by the measuring unit 13 can be expressed as a function of the fluid velocity V, the fluid velocity V can be obtained by performing the above calculation in the calculation unit 14. When calculating the fluid flow velocity V, it is desirable to store in the calculation unit 14 a coefficient for obtaining the flow velocity V and a coefficient for correcting errors by performing a calibration test in advance.

[0025] In one embodiment of the present invention, the resistance plate 11 is maintained at a predetermined depth by having a float 21 provided on the upper part, and it is preferable that the support part 12 is equipped with a mechanism 22 that rotates the resistance plate 11 so that it faces a predetermined direction relative to the direction of flow.

[0026] Regarding the float 21, for example, as shown in Fig. 1, the float 21 is attached to the upper part of the resistance plate 11. If the float 21 is installed on the upper end of the resistance plate 11 as shown in Fig. 1, the float 21 will be in a floating state above the water surface, so the position of the resistance plate 11 will be maintained near the water surface. Also, if it is desired to maintain the resistance plate 11 at a predetermined depth below the water surface, a gap of approximately the same length as the desired depth may be provided between the resistance plate 11 and the float 21. For example, if it is desired to maintain the resistance plate 11 at a water depth of 50 mm, the float 21 may be provided at a position 50 mm above the resistance plate 11.

[0027] In addition, as shown in FIG. 1, the rotating mechanism 22 may be configured such that the support part 12A, one end of which is fixed to the measuring part 13, and the support part 12B, one end of which is fixed to the resistor plate 11, are formed of separate members, and the two support parts 12A and 12B are connected by a joint structure, so that the support part 12B on the resistor plate 11 side can rotate and slide up and down with respect to the support part 12A on the measuring part 13 side. As an example, as shown in FIG. 1, the rotating mechanism 22 may be configured such that the end of the support part 12B on the resistor plate 11 side is formed into a coil shape and passed through the end of the support part 12A on the measuring part 13 side. It is preferable to provide a stopper 23 or the like at the end of the support part 12A on the measuring part 13 side so that the end of the support part 12B on the resistor plate 11 side does not come off.

[0028] With this configuration, it is possible to have a float structure that automatically follows and slides along the up and down fluctuating water surface, and it is also possible to have a structure that automatically follows and rotates along changes in the flow direction from side to side, making it possible to create a current meter that automatically follows the surface of fluctuating water levels.

[0029] In addition, when the support part 12 is capable of sliding up and down, the length L of the cantilever also varies. Therefore, in a flow meter 10 according to one embodiment of the present invention, the distance L may be calculated from measurements using a range finder or from images from a camera or the like, and the input value may be corrected in the calculation part 14 as appropriate.

[0030] In one embodiment of the present invention, the resistance plate 11 is a thin plate with a thickness of less than 0.5 mm on the surface facing the flow, and the length of the side along the flow is preferably 5 mm or less. With regard to the resistance plate 11 of the present invention, the thickness of the surface facing the flow is less than 0.5 mm, so that it can be regarded as a thin plate, and therefore the drag acting on the surface perpendicular to the flow can be ignored.

[0031] FIG. 2 is a diagram showing the relationship between the measurement flow velocity range and the length of the plate in the present invention. The horizontal axis is the flow velocity (m / s), and the vertical axis is the Reynolds number, and each graph shows the flow direction dimension of the resistance plate 11 (the length of the side along the flow) of 5 mm, 4 mm, 3 mm, 2 mm, and 1 mm, respectively. As shown in FIG. 2, the region where the Reynolds number is less than 10,000 (Re<10,000) can be considered as a laminar flow region with few turbulent components, so by making the flow direction dimension of the resistance plate 11 5 mm or less, the flow around the resistance plate 11 can be made into a laminar flow region in the measurement range (2 m / s or less). Also, as can be seen from FIG. 2, for example, by making the flow direction dimension of the resistance plate 11 3 mm, the measurement range can be adjusted to the high-speed side up to 3 m / s. Thus, in one embodiment of the present invention, it is preferable to adjust the flow direction dimension of the resistance plate 11 to a laminar flow region with a Reynolds number of less than 10,000 depending on the incoming flow velocity range to be measured. By setting the Reynolds number to fall within the laminar flow region of less than 10,000, the oscillation frequency of the resistance plate 11 becomes sufficiently small, making it possible to obtain the time-averaged amount of movement by simple image processing.

[0032] The depth length of the resistance plate 11 may be appropriately set depending on the object for which the flow velocity is to be measured. For example, in the case of a device in which the above-mentioned open-type undershot water turbine is installed on a floating body, the required positional average of the flow velocity can be measured by setting the length to about the tip of the water turbine blades.

[0033] As described above, according to the present invention, the measurement flow velocity range can be set by adjusting the cantilever length of support part 12, and the length of the cantilever to which resistor plate 11 is attached can be adjusted depending on the sensitivity of the sensor to be detected, so that a detectable torque is applied to measuring part 13, making it possible to measure the ensemble average value of the passing flow velocities near the surface relatively easily. EXAMPLES

[0034] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples in any way.

[0035] Fig. 3(A) is an external view of the cantilever-type current meter used in the embodiment of the present invention, and Fig. 3(B) is a schematic diagram showing the configuration of the resistor plate and the support part in the embodiment of the present invention. We adopted a method in which the flow resistance is detected by a plate-shaped resistor inserted into the water, and the deflection of the cantilever beam corresponding to the flow resistance is observed by a camera installed directly above it, as shown in Fig. 3(A).

[0036] As a calibration experiment, a set speed was increased and decreased in the range of 0 to 0.4 m / s in a circulating water tank with a depth of 800 mm. As shown in FIG. 3(B), the resistance plate and support were attached to the tip of a cantilever (length 300 mm, outer diameter 0.3 mm) made by bending a piano wire into a crank shape. The resistance plate (length in the flow direction 5 mm, length in the depth direction 20 mm, thickness 0.5 mm) was supported at the top end by a resin sleeve (inner diameter of the sleeve 0.8 mm, length 10 mm) so that it could rotate freely, allowing it to smoothly follow the main flow. In addition, the bottom end of the resistance plate was installed at a position 22 mm above the water surface. FIG. 4 shows the observation state in the embodiment.

[0037] In this example, the Reynolds number is in the laminar region (Re<2500 in the experimental range), and the drag coefficient C d can be calculated using equation (4).

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[0038] Figure 5 shows the results of a calibration experiment in an embodiment of the present invention. As shown in Figure 5, it was found that a cubic approximation of the measurement results, which relatively closely matched the theoretical values, could be used as the calibration formula. Note that the resistance plate at the tip of the cantilever slowly oscillates in the horizontal direction (x and y directions) during measurement, which is cited as the largest error factor. This can be addressed by extracting the maximum and minimum oscillations from a video of a certain period of time and taking the average value as the amount of movement.

[0039] Although one embodiment of the present invention and each example have been described in detail as above, it will be easily understood by those skilled in the art that many modifications are possible without substantially departing from the novel features and effects of the present invention. Therefore, all such modifications are intended to be included within the scope of the present invention.

[0040] For example, a term described at least once in the specification or drawings together with a different term having a broader meaning or the same meaning may be replaced with the different term anywhere in the specification or drawings. The configuration of the current meter is not limited to the one described in the embodiment and each example of the present invention, and various modifications are possible. [Industrial Applicability]

[0041] The inventors have developed a surface tidal power generation system that uses an open undershot water turbine in a waterway formed by a floating body as a system for effectively utilizing tidal energy, a type of renewable energy. The current meter according to the present invention can be used to evaluate the relationship between the typical waterway shape formed by the floating body and the passing current speed. [Explanation of symbols]

[0042] 10 Current meter, 11 Resistance plate, 12, 12A, 12B Support part, 13 Measurement part, 14 Calculation part, 21 Float, 22 Rotating mechanism, 23 Stopper

Claims

1. A current meter for measuring the flow velocity of a flow passing through a waterway, comprising: A resistance plate suspended below the water surface of the waterway; A support portion that supports the resistance plate above the water surface; a measurement unit that measures a change in the support unit based on a resistance force of a fluid acting on the resistance plate; A calculation unit that calculates a flow velocity based on the value measured by the measurement unit. Equipped with A current meter characterized in that the support part is a length-adjustable cantilever having one end fixed to the measuring part and the other end to which the resistive plate is attached.

2. 2. The current meter according to claim 1, wherein the measuring unit is a piezoelectric torque sensor.

3. The resistance plate is provided with a floating body on the upper part to maintain a predetermined depth, 3. The current meter according to claim 2, wherein the support portion includes a mechanism for rotating the resistance plate so that the resistance plate faces a predetermined direction relative to the direction of flow.

4. 4. The current meter according to claim 3, wherein the resistance plate is a thin plate having a thickness of less than 0.5 mm on the surface facing the flow, and a length of the side facing the flow is 5 mm or less.

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