JP4720192B2 - Ultrasonic flow measurement method - Google Patents

Description

  The present invention relates to a flow rate measurement technique for measuring the flow velocity distribution and flow rate of a fluid flowing in an inclined pipe with a height difference, and in particular, flows in an inclined pipe with a height difference, such as a hydraulic iron pipe in a hydropower station or the like. The present invention relates to an ultrasonic flow rate measuring method for measuring a flow rate distribution and a flow rate of a fluid.

  Conventionally, as a flowmeter for measuring the flow rate of a fluid flowing in a pipe, as shown in Japanese Patent Laid-Open No. 2000-97742 (Patent Document 1), an ultrasonic wave is irradiated to a fluid to be measured, and an ultrasonic Doppler shift is performed. The Doppler type ultrasonic flowmeter that measures the flow velocity distribution of the fluid using the flow rate and measures the flow rate, and as shown in Japanese Patent Laid-Open No. 2003-344131 (Patent Document 2), from the reflector included in the fluid There is a correlation type ultrasonic flowmeter that measures the flow velocity distribution and flow rate of a fluid by using a correlation method from a time change of a reflected ultrasonic echo signal.

  A conventional ultrasonic flowmeter receives an ultrasonic echo signal reflected by a reflector existing in a fluid to be measured, measures a flow velocity distribution of the fluid, and measures a flow rate from the flow velocity distribution. In order to measure the flow rate of the fluid, it is necessary that a sufficient amount of reflectors exist in the fluid to be measured.

  If there is not enough reflector in the fluid to be measured, as shown in Japanese Patent Laid-Open No. 8-62007 (Cited document 3), a gas is directly injected into the fluid as a reflector using a pump. Accordingly, as described in JP-A-6-294670 (Patent Document 4), bubbles due to cavitation are generated in the fluid to be measured by the ultrasonic reflector, and a reflector made of the generated bubbles is supplied. ing.

Using a conventional ultrasonic flowmeter at a hydroelectric power plant, a pumped-storage power plant, etc., measuring the flow velocity distribution of the fluid flowing in an inclined pipe (hydraulic iron pipe) with a difference in height, and trying to measure the flow rate, Since it is installed on the slope of the mountainside, it is necessary to measure the flow velocity distribution and the flow rate of the fluid flowing in the inclined pipe. The conventional ultrasonic flowmeter has a problem that the flow velocity distribution and flow rate of the fluid cannot be measured accurately and accurately due to the pressure difference of the fluid due to the height difference.
JP 2000-97742 A JP 2003-344131 A JP-A-8-62007 JP-A-6-294670

  When measuring the flow velocity distribution and flow rate of fluid flowing in a pipe (hydraulic iron pipe) in a hydropower plant, etc., an inclined pipe is installed along the slope of the mountainside, so an ultrasonic flow meter is installed in the middle of the inclined pipe. However, when an attempt is made to supply the bubbles constituting the reflector from the upstream side of the ultrasonic flowmeter, the difference in level between the bubble supply site and the flow rate measurement site appears as a pressure difference of the fluid. Work to make it smaller. As a result, the bubble supplied at the bubble supply site becomes small at the flowmeter measurement site, and the volume ratio of the bubble as a reflector to the fluid [the volume occupied by the bubble in the fluid containing a certain amount of bubbles is in the whole fluid. The volume ratio (ratio)] is also reduced.

  Bubbles 1 act as shown in FIG. 6 in the fluid flowing in the inclined pipes arranged along the height difference. The bubble 1 flows along the fluid flow velocity Va (the fluid flow velocity in the axial direction of the inclined pipe 2), and a vertical rising velocity Vb is generated by buoyancy. For this reason, the fluid of the actual bubble 1 becomes the velocity vector Vt. As a result, the fluid flow velocity measured by the ultrasonic velocimeter appears as V, which is different from the actual fluid flow velocity Va. When measuring the flow velocity of the fluid from the ultrasonic reflection echo using the bubble 1 as a reflector with an ultrasonic flowmeter, it is difficult to measure the accurate flow velocity distribution of the fluid due to the movement of the bubbles due to buoyancy. there were.

  In addition, even if we intend to supply enough bubbles from the bubble supply site into the inclined pipe, the bubbles that are reflectors have a size and volume density suitable for measuring flow velocity distribution and flow rate in the actual flow rate measurement site. In some cases, it was difficult to accurately and accurately measure the flow velocity distribution and flow rate of the fluid flowing in the inclined pipe with an ultrasonic anemometer.

  The present invention has been made in consideration of the above-described circumstances, corrects the influence of bubble buoyancy on the fluid flow velocity, and determines the pressure difference of the fluid due to the height difference between the bubble supply site and the flow rate measurement site. It is an object of the present invention to provide an ultrasonic flow rate measuring method capable of accurately and accurately measuring the flow velocity distribution and the flow rate of a fluid flowing in an inclined pipe even when there is a gas flow.

  The present inventor, while repeating measurement experiments of the flow velocity distribution and the flow rate of the fluid flowing in the inclined pipe with a difference in height, applies a plurality of measurement lines from the ultrasonic flowmeter to the fluid flowing in the inclined pipe. Obtained from multiple measurement lines by detecting the ultrasonic echo reflected from the reflector of the bubbles contained in the fluid. By knowing that the fluid deceleration component due to buoyancy can be extracted by processing with simultaneous flow velocities, the effect on the flow velocities caused by the buoyancy of bubbles is corrected, and the flow velocity distribution of the fluid flowing in the inclined pipe is accurately determined. The present invention has been completed by finding that high-accuracy ultrasonic flow measurement is possible by measuring with high accuracy.

In order to solve the above-described problem, an ultrasonic flow rate measuring method according to the present invention uses ultrasonic waves to calculate the flow velocity distribution and flow rate of a fluid flowing in a pipe inclined along a height difference. In the measuring method using the method, the step of supplying bubbles to the fluid flowing in the inclined pipe by the bubble supplying means provided on the upstream side of the ultrasonic flowmeter, and the flow velocity distribution of the fluid supplied with the bubbles are measured. In addition, an ultrasonic transmission step for transmitting ultrasonic waves from the ultrasonic flowmeter to the fluid flowing in the inclined pipe along a plurality of measurement lines, and the transmitted ultrasonic waves are applied to the fluid flowing in the inclined pipe. The ultrasonic echo reflected by the reflector of the bubbles contained in the fluid is received and signal-processed, the flow velocity distribution in the plurality of measurement lines of the fluid flowing in the inclined pipe is measured, and the flow rate is measured. And a flow velocity distribution, the flow rate measuring step, in the flow velocity distribution, the flow meter measurement step, using a flow rate distribution in the plurality of measuring lines, the influence of the flow rate by floating movement of the bubbles in the fluid flowing through the inclined pipe Is a method of correcting the above.

In order to solve the above-described problem, the ultrasonic flow rate measurement method according to the present invention includes a flow rate distribution / flow meter measurement step in which the flow rate distribution in the plurality of measurement lines is as described in claim 2. This is a method of correcting the influence on the flow velocity due to the rising motion of bubbles in the fluid flowing in the inclined pipe by making simultaneous the equations relating to the flow speed at the same distance from the pipe center on each measurement line.

Furthermore, in order to solve the above-described problem, an ultrasonic flow rate measuring method according to the present invention is transmitted from a plurality of ultrasonic transducers of an ultrasonic flow meter in the ultrasonic transmission step as described in claim 3. comprising a plurality of ultrasonic measurement lines being, at least one measurement line, a method of forming an ultrasonic transducer mounted perpendicular to the tube axis direction at the center angle zero angle to the inclined pipe, also claim As described in 4 , the bubble supply means is a method for supplying bubbles to the fluid flowing in the pipe at a position separated by 10 times or more of the pipe inner diameter on the upstream side of the ultrasonic flowmeter.

  In the ultrasonic flow rate measurement method according to the present invention, the flow velocity of the fluid along a plurality of measurement lines is processed in parallel, thereby correcting the influence on the flow velocity due to the rising motion of the bubbles, and the flow of the fluid flowing in the inclined pipe. When the flow velocity distribution is measured accurately and in a timely manner to enable high-accuracy ultrasonic flow measurement, and there is a fluid pressure difference due to the height difference between the bubble supply part and the flow measurement part. In addition, it is possible to accurately and accurately measure the flow velocity distribution and the flow rate of the fluid flowing in the inclined pipe having the height difference.

  An embodiment of an ultrasonic flow rate measuring method according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a configuration diagram schematically showing an example in which an ultrasonic flow rate measuring apparatus 10 that implements an ultrasonic flow rate measuring method according to the present invention is applied to a hydroelectric power station 11.

  The hydroelectric power plant 11 connects a water tank 12 that is a water storage garden and a water discharge garden 13 by a pipe 14 such as a hydraulic iron pipe. The pipe 14 is laid on an inclined surface of a mountain and includes a portion that is inclined along a height difference.

  In the middle of the pipe 14, a plurality of ultrasonic flow meters 15 (15 a, 15 b) that measure the flow velocity distribution and flow rate of the fluid flowing in the pipe 14, a valve device 16 that controls the opening / closing of the pipe 14, and a water wheel 17 are sequentially provided. It is done.

  The turbine 17 is mechanically connected to the generator 18 and transmits the rotational driving force of the turbine 17 to the generator 18. The generator 18 converts the kinetic energy of the water turbine 17 rotated by a fluid such as river water into electrical energy, and the electric power generated by the generator 18 passes through the circuit breaker 20, the transformer 21, and the switchgear 22. To the power transmission system 23.

  The valve device 16 provided on the upstream side of the water turbine 17 includes a main valve 25 and a bypass valve 26 that bypasses the main valve 25. The pipe 14 that is a hydraulic iron pipe includes an upstream hydraulic iron pipe 27 a that is an inclined pipe from the water tank 12 to the valve device 16, an (intermediate) hydraulic iron pipe 27 b from the valve device 16 to the water wheel 17, and from the water wheel 17 to the water discharge garden 13. And the downstream side hydraulic iron pipe 27c.

  The fluid a such as river water guided from the water tank 12 by the upstream hydraulic iron pipe 27a is guided from the valve device 16 through the hydraulic iron pipe 27b to the water turbine 17 to rotate the water turbine 17. The fluid that has rotated the water turbine 17 is then discharged into the water discharge garden 13 through the downstream hydraulic iron pipe 27c.

  Moreover, in the hydroelectric power station 11, a plurality of, for example, two ultrasonic flow meters 15 are provided at any part of the upstream hydraulic iron pipe 27a. This is because the fluid flowing through the upstream hydraulic iron pipe 27a, which is an inclined pipe, forms a substantially laminar flow, and the flow is not disturbed compared to the fluid flowing through the hydraulic iron pipe 27b between the valve device and the turbine and the downstream hydraulic iron pipe 27c. . A bubble supplying means 30 that also serves as a bubble generating means is installed on the upstream side of the ultrasonic flow meter 15, and the ultrasonic flow measuring device 10 is constituted by the bubble supplying means 30 and the ultrasonic flow meters 15a and 15b.

  The installation position of the ultrasonic flowmeter 15 (15a, 15b) in the upstream side hydraulic iron pipe 27a is determined by the diameter of the pipe 14 of the upstream side hydraulic iron pipe 27a from the relationship between the water tank 12 and the upstream side hydraulic iron pipe 27a, which are bubble supply locations. For example, it is preferable that the distance is 10 times or more of the inner diameter. The pipe 14 having a pipe diameter of 1 mφ to several mφ is appropriately selected and used.

  By installing the bubble supply means 30 on the upstream side of the ultrasonic flowmeter 15 so as to be separated from the pipe diameter by 10 times or more, the bubbles supplied from the bubble supply means 30 are uniformly distributed in the pipe 14 of the upstream hydraulic iron pipe 27a. The ultrasonic flow rate measuring device 10 can be set under conditions suitable for precise fluid flow rate measurement in a dispersed and laminar state.

  As shown in FIGS. 1 and 2, the bubble supply means 30 is provided in the vicinity of the water intake of the water tank 12. The bubble supply means 30 is provided with a fluid pump 32 in a circulation pipe 31 for circulating a fluid b such as river water stored in the water tank 12, and a venturi pipe 33 as a gas-liquid mixing means on the pump discharge side. On the downstream side of 33, the return pipe 31 b of the circulation pipe 31 is opened so as to face the water intake port that is the connection portion between the pipe 14 and the water tank 12. A gas injection pipe 35 from the gas injection means 34 faces the constricted portion of the venturi pipe 33 and opens.

  The fluid pump 32 pumps up the fluid b such as river water stored in the water tank 12 and guides it to the venturi pipe 33. The venturi pipe 33 actively sucks out the gas c from the gas injection means 34 by the ejector action corresponding to the pump discharge amount from the fluid pump 32. This gas c is mixed with the fluid b to become a fluid d containing bubbles. The gas injection means 34 may be constituted by a gas pump such as an air pump so that the gas is positively supplied to the venturi 33.

  The bubble supply means 30 adjusts and controls the gas mixing amount in the venturi pipe 33 which is a gas-liquid mixing means and the pump discharge amount of the fluid pump 32, and from the return pipe 31b to the vicinity of the joint between the water tank 12 and the upstream hydraulic iron pipe 27a. The size and volume ratio of the bubbles to be discharged are adjusted.

  Specifically, when the amount of gas mixture (gas injection amount) from the gas injection means 34 is increased while the pump discharge amount of the fluid pump 32 is kept constant, the size of the bubbles increases and the volume ratio also increases. On the other hand, if the pumping amount is increased while keeping the gas mixture amount (gas injection amount) constant, the bubbles are small and the volume ratio is also small. Control of the gas mixing amount in the venturi tube 33 is performed by changing the injection pressure in the gas injection means 34.

  The size of the bubbles generated by the bubble supply means 30 is confirmed visually. Specifically, bubbles are experimentally generated in a container containing a scale, and the relationship between the injection pressure of the gas injection means 34 and the pump discharge amount of the fluid pump 32 and the size of the bubbles visually is recorded in advance as a table or the like. It is preferable to perform control at the time of measuring the flow rate of the fluid using this relation table.

  Since the volume ratio of the bubbles at the fluid flow rate measurement site is determined by (bubble volume ratio in fluid d) × (ratio of fluid d in the hydraulic iron pipe), the injection pressure of the gas injection means 34 and the pump discharge amount of the fluid pump 32 Can be adjusted by.

  The volume ratio of bubbles in the hydraulic iron pipe can be obtained by collecting the fluid a of river water and measuring the gas concentration. Specifically, it collects from the measurement hand hole provided in the water tank 12 and measures the gas concentration. As for the volume ratio of the bubbles, the relationship between the injection pressure of the gas injection means 34 and the pump discharge amount of the fluid pump 32 and the size of the bubbles visually is recorded in advance as a table or the like. It is preferable to perform control when measuring the flow rate of the fluid.

  The place where the fluid d containing bubbles is returned to the river water b is preferably in the vicinity of the connection between the water tank 12 and the upstream hydraulic iron pipe 27a where the flow from the water tank 12 to the upstream hydraulic iron pipe 27a is sufficiently developed. This is because if the flow is not developed, the bubbles are stored in the water tank 12 without entering the hydraulic iron pipe 27a. In this way, bubbles having a sufficient size and volume ratio are supplied to the fluid b of the river water, which is suitable for measuring the flow rate of the fluid.

  In this manner, the ultrasonic flowmeter 15 measures the flow velocity distribution and the flow rate of a fluid such as river water flowing in the pipe 14 of the upstream hydraulic iron pipe 27a that is an inclined pipe.

The ultrasonic flowmeter 15 (15a, 15b) is configured as shown in FIG. 3, and an ultrasonic pulse having a required frequency is measured along the measurement line ML (ML ₁ , ML ₂ ) on the fluid a to be measured flowing in the pipe 14. , An ultrasonic transmission unit 37 for receiving the ultrasonic echo reflected from the measurement region of the incident ultrasonic pulse, and a flow velocity distribution measuring unit 38 for measuring the flow velocity distribution of the fluid to be measured, and the fluid 12 to be measured. A computer 39 such as an MPU or CPU serving as a flow rate calculation means for calculating the flow rate of the fluid to be measured by performing calculation processing on the basis of the flow velocity distribution of the fluid and performing radial integration, and outputs from the computer 39 are displayed in time series. Possible display device 40.

The ultrasonic transmission means 37 includes an oscillator 43 as an oscillator for generating an electric signal having a required fundamental frequency f ₀ of 0.25 MHz to several MHz, preferably 0.25 MHz to 1 MHz, and the electric signal at a predetermined time interval ( A signal generator 45 including an emitter 44 that outputs a pulse shape every 1 / Frpf) is provided. Pulse electrical signal of the fundamental frequency _{f 0} from the signal generator 45 is input to the ultrasonic transducer 46 (46a, 46b).

  A plurality of, for example, two ultrasonic transducers 46 (46a, 46b) are installed along the outer circumferential direction of the pipe on the common cross section of the upstream hydraulic iron pipe 27a which is an inclined pipe. FIG. 4 is a diagram showing an installation state of the ultrasonic transducers 46 (46a, 46b) constituting the ultrasonic flow measuring device 10. As shown in FIG. 4A is a simplified side view showing the installation state of the ultrasonic transducers 46a and 46b as viewed from the side of the upstream hydraulic iron pipe 27a, and FIG. 4B is the installation state of the ultrasonic transducers 46a and 46b. FIG. 4 (C) shows the installation state of the ultrasonic transducers 46a and 46b positioned on the cross section perpendicular to the axial direction of the upstream side hydraulic iron pipe 27a on the downstream side in the pipe axial direction. It is the figure seen from.

  The upstream hydraulic iron pipe 27a, which is an inclined pipe, is laid so as to be inclined downward by an angle θ with respect to the horizontal direction, and the ultrasonic transducers 46a and 46b are disposed on the outer circumference of the common pipe cross section of the upstream hydraulic iron pipe 27a. Are installed with a central angle η.

The central angles formed by the straight lines connecting the installation points of the ultrasonic transducers 46a and 46b and the center of the hydraulic iron pipe section on the outer circumference of the same pipe cross section of the upstream hydraulic iron pipe 27a and the vertical direction are η ₁ and η _2. Then, as shown in FIG. 4C, the central angle η between the ultrasonic transducers 46a and 46b is represented by (η ₂ −η ₁ ).

One of the ultrasonic transducers 46a, compared cross section of the upstream penstock 27a, at any angle of incidence forming an angle alpha ₁ in the penstock central axis of the fluid downstream, as shown in FIG. 4 (A), also, other ultrasonic transducer 46b, as shown in FIG. 4 (B), at any angle of incidence forming an angle alpha ₂ in the penstock central axis of the fluid downstream, respectively, along the measurement line ML _1, ML ₂ each Installed to transmit ultrasound. 4A, 4B, and 4C, the symbol P indicates the flow direction of the fluid flowing in the upstream hydraulic iron pipe 27a, and the symbol G indicates the direction in which the gravitational acceleration acts.

Ultrasonic transducer 46 (46a, 46b) is by application of a pulse electrical signal is an ultrasonic pulse of a fundamental frequency _{f 0} is allowed outgoing along the measurement line _{ML (ML 1, ML 2)} . Each ultrasonic transducer 46a, 46b is, the cross section of the pipe 14 constituting the upstream penstock 27a is an inclined pipe to be provided to be inclined in the flow direction P of the angle alpha ₁ and alpha ₂ only fluid a, respectively. Ultrasonic transducer 46 (46a, 46b) also serves as an ultrasonic transceiver, the ultrasonic transducer 46 (46a, 46b) measuring line ultrasonic pulses required frequency _{f 0} from _{ML (ML} 1, _ML 2) , The ultrasonic pulse is reflected by a bubble as a reflector uniformly distributed on the measurement line ML (ML ₁ , ML ₂ ), and is reflected by one of the reflected ultrasonic echoes. Are returned to the ultrasonic transducer 46 (46a, 46b) along the measurement line. The ultrasonic transducer 46 serves as both a transmitter and a receiver, but the receiver and the receiver may be configured separately.

The ultrasonic echo signals respectively received by the ultrasonic transducers 46 (46 a and 46 b) are amplified by the amplifier 47, converted into digital signals by the AD converter 48, and sent to the flow velocity distribution calculation circuit 49. The flow velocity distribution calculation circuit 49 corrects the influence of the flow velocity distribution of the fluid along the measurement line ML (ML ₁ , ML ₂ ) on the flow velocity due to the buoyancy effect of the bubbles by performing signal processing on the digital signal of the ultrasonic echo. Is calculated. Reference numeral 50 denotes an acoustic coupling.

  The flow velocity distribution signal of the river water fluid calculated by the flow velocity distribution calculation circuit is sent to a computer 39 which is a flow rate calculation means, where the flow velocity distribution signal is integrated in the radial direction of the upstream side hydraulic iron pipe 27a and the river water a Can be obtained in a time-dependent manner.

By the way, the bubble flow velocity V ₁ (x), V ₂ (x) at the point of the distance x from the central axis of the hydraulic iron pipe measured by the ultrasonic transducers 46a and 46b is expressed by the following equation.

  The point of distance x radially outward from the center of the hydraulic iron pipe measured by the ultrasonic transducers 46a and 46b is displaced in the pipe axis direction because each transducer 46a and 46b is installed inclined to the pipe axis direction. Are not exactly the same. However, it can be considered that the deviation between the flow velocity Va of the fluid and the rising velocity Vb of the bubbles due to the displacement of the positions of the ultrasonic transducers 46a and 46b in the tube axis direction is sufficiently small.

Thus, by solving equations (1) and (2) simultaneously, the true fluid flow velocity Va in the tube axis direction can be obtained by the following equation and used as a data correction value.

The bubble levitation velocity Vb (x) due to buoyancy is a function of the position, but in the measurement region, the levitation velocity Vb is not dependent on the position, and Vb is a constant and all the values obtained in the preliminary measurement are measured. This can be applied to data correction on the line ML (ML ₁ , ML ₂ ).

As described above, the ultrasonic flow rate measuring method of the present invention is a method of measuring the flow velocity distribution and the flow rate of the fluid flowing in the pipe 27a inclined along the height difference using ultrasonic waves. This ultrasonic flow rate measuring method includes a step of supplying bubbles to the fluid flowing through the inclined pipe 27a by the bubble supply means 10 provided on the upstream side of the ultrasonic flow meter 15 (15a, 15b), and the fluid supplied with the bubbles. In order to measure the flow velocity distribution, an ultrasonic transmission step of transmitting ultrasonic waves from the ultrasonic flowmeter 15 (15a, 15b) to the fluid flowing in the inclined pipe 27a along the plurality of measurement lines ML ₁ and ML ₂ And the ultrasonic echoes reflected by the reflector of the bubbles contained in the fluid flowing in the inclined pipe 27a, signal processing is performed, and the flow velocity of the fluid flowing in the inclined pipe 27a on the plurality of measurement lines ML ₁ and ML ₂ This is a measurement method having a flow velocity distribution / flow rate measurement step for measuring a distribution and measuring a flow rate.

By the way, in FIG. 1, if the flow rate of the river water a at time t is m (t), the flow rate m (t) of the fluid can be expressed by Equation (5).
[Equation 3]
m (t) = ρ · ∫v (x · t) · dA (5)
Where ρ is the density of the fluid to be measured
v (x · t): a velocity component in the x direction at the speed t.

From equation (5), the flow rate m (t) at time t flowing through the pipe 14 of the upstream hydraulic iron pipe 27a can be rewritten as polar coordinate equation (6).
[Equation 4]
m (t) = ρ · ∬vx (r, θ · t) · r · dr · dθ (6)
Where vx (r, θ · t) is a velocity component in the tube axis direction at a distance r and an angle θ from the center on the tube cross section at time t.

  As represented by Expression (6), the ultrasonic flowmeter 12 can obtain the spatial distribution of the flow of the fluid a in the river water instantaneously, for example, by the computer 39 at a response speed of about 50 msec to 100 msec.

  The obtained flow rate of the fluid a can be instantaneously displayed on the display device 40 in a time-dependent manner. The display device 40 can display the bubble velocity distribution along the measurement line ML in the upstream side hydraulic iron pipe 27a of the river water a, and the influence of the bubble buoyancy on the velocity from the bubble velocity distribution. It can correct | amend and can also display the flow velocity distribution of a fluid, and the flow velocity distribution of a hydraulic iron pipe cross section.

  When the flow rate is measured by the ultrasonic flow meter 15, the volume ratio (volume density) of bubbles at the flow rate measurement site is preferably in the range of 20 ppm to 2000 ppm, more preferably 200 ppm to 800 ppm. If the volume ratio of the bubbles is less than 20 ppm, it does not function sufficiently as a reflector, and conversely if it is more than 2000 ppm, the possibility of affecting the turbine efficiency increases.

  Furthermore, the size of the bubbles at the flow rate measurement site is preferably in the range of 1/10 to 1/2 of the wavelength of the ultrasonic wave applied to the fluid to be measured (river water fluid a). If the bubble size (diameter) at the flow rate measurement site is smaller than 1/10 of the ultrasonic wavelength, it will not function sufficiently as a reflector, and conversely if it is larger than 1/2 of the ultrasonic wavelength, The velocity difference between the two is not negligible, and the transmittance of the ultrasonic wave in the fluid to be measured is lowered, so that the flow velocity distribution cannot be measured with high accuracy. The ultrasonic wavelength is about 1.5 mm to 6 mm when an ultrasonic pulse of 0.25 MHz to 1 MHz is used.

  It is also possible to change the wavelength of the ultrasonic wave according to the size of the bubble that is a reflector. In the measurement of the flow velocity distribution of the fluid by the ultrasonic flow meter 15, a frequency of 0.2 MHz to several MHz, preferably 0.25 MHz to 1 MHz is suitable, and the wavelength adjustment is within this range, specifically about 1. Limited to 5 mm to 6 mm. When the ultrasonic wave is longer than the upper limit wavelength, the spatial resolution is lowered and is not sufficient. When the ultrasonic wave is shorter than the lower limit wavelength, the attenuation of the ultrasonic wave is increased, and both are not suitable for high-accuracy measurement.

  By the way, the part (bubble supply part) where the water tank 12 to which the bubble is supplied by the bubble supply means 30 and the upstream side hydraulic iron pipe 27a (the bubble supply part) is a part where the flow velocity distribution of the fluid is measured by the ultrasonic flowmeter 15 (15a, 15b). Since it is upstream and higher than the flow rate measurement part), the bubbles in the flow rate measurement part are smaller than at the time of supply, and the volume ratio (volume density) is also small.

The change in the size of the bubble is a fluid pressure difference caused by the difference in height between the bubble supply site and the flow rate measurement site, and can be expressed by Expression (7).

  Changes in the bubble size and volume ratio according to the equation (7) can be estimated from the difference in altitude between the position of the bubble supply means 30 and the installation position of the ultrasonic flowmeter 15. The change in diameter, which is the size of the bubble, is proportional to the cube root of the fluid pressure. For example, the volume ratio is about 1/10 with a fluid drop of 90 m, but the change in diameter is about 1 / 2.2. It can be calculated in advance by the size and volume ratio of the bubbles at the flow rate measurement position.

  By correcting the pump discharge amount and the gas mixture amount in the bubble supply means 30 from the calculated bubble size and volume ratio, a bubble having a size suitable for measurement at the flow rate measurement site is determined to be a size suitable for fluid flow measurement. Now, it can be supplied at an appropriate volume ratio.

  Furthermore, based on the calculated bubble size, the wavelength of the ultrasonic wave irradiated to the fluid a to be measured by the ultrasonic flow meter 15 (15a, 15b) can be corrected.

  By moving the installation position of the ultrasonic flow meter 15 (15a, 15b), the difference in altitude between the flow rate measurement site and the bubble supply site can be changed, and the size and volume ratio of the bubbles can be adjusted.

  Moreover, the ultrasonic flow rate measuring method of the flow rate of the fluid flowing in the pipe 14 of the hydroelectric power station 11 is implemented as follows.

  After laying the pipe 14 along an inclined portion with a height difference, a plurality of, for example, two ultrasonic flow meters 15 (15a, 15b) are installed in the middle of the pipe 14, preferably in the middle of the upstream hydraulic iron pipe 27a. At the same time, the bubble supply means 30 is installed on the upstream side of the ultrasonic flowmeter 15 so as to be separated from the pipe diameter by 10 times or more in the pipe axis direction. The bubble supply means 30 is preferably provided in the water tank 12 at the inlet of the upstream hydraulic iron pipe 27a. The piping 14 is also provided with a valve device 16 and a water wheel 17, and the piping 14 is disposed so as to connect between the water tank 12 and the water discharge garden 13.

  With the pipe 14 installed, bubbles of a required size and volume ratio (volume ratio) are injected from the bubble supply means 30 into the fluid a to be measured. In this bubble injection step, the volume ratio of the bubbles at the fluid flow rate measurement site is in the range of 20 ppm to 2000 ppm, more preferably in the range of 200 ppm to 800 ppm. The size and volume ratio of the bubbles are adjusted and controlled so as to be in the range of 1/10 to 1/2.

Ultrasonic flow meter 15 (15a, 15b) irradiates the ultrasonic transducer 46a in fluid bubbles are injected from 46b and directed along an ultrasonic pulse to the measurement line _ML 1, ML _2, contained in a fluid The ultrasonic echoes reflected from the bubbles as the reflectors are received by the ultrasonic transducers 46a and 46b, the ultrasonic echo signals are signal-processed by the fluid distribution measuring means 38, and the flow velocity distribution of the fluid flowing in the pipe 14 is measured. The flow rate distribution of the fluid can be corrected from the flow velocity distribution, and the flow rate of the true fluid can be calculated instantaneously (flow rate measurement step).

  In the bubble injection process, the size and volume ratio of the bubbles can be adjusted by adjusting and controlling the pump discharge amount of the fluid pump 32 and the gas inflow amount from the gas injection means 34 (gas mixture amount in the gas mixing means). The bubble injection step and the flow rate measurement step are linked, and instead of the pump discharge amount and the gas injection amount, the installation position of the ultrasonic flow meter 15 and the oscillation frequency of the ultrasonic wave are adjusted and controlled, so that the bubbles at the flow rate measurement site And the volume ratio may be adjusted to be in the range of 1/2 to 1/10 of the ultrasonic wavelength.

  FIG. 5 is a diagram for explaining a second embodiment of the ultrasonic flow rate measuring method according to the present invention.

  In describing the ultrasonic flow rate measuring method of the second embodiment, the same components and members as those of the first embodiment are denoted by the same reference numerals, and illustration and description thereof are omitted.

In the ultrasonic flow rate measuring method according to the first embodiment, a plurality of, for example, two ultrasonic transducers 46a and 46b are installed at an arbitrary central angle η, and ultrasonic waves are measured at an arbitrary incident angle α ₁ and α ₂ with a measurement line ML. ₁ , an example in which the fluid a to be measured is irradiated along ML ₂ is shown. However, in the ultrasonic flow measurement method shown in FIG. 5, the installation state (central angle η ₂ ) and incident angle of the ultrasonic transducers 46 a and 46 b Is set as a specific condition.

  Using the ultrasonic flowmeter 15 (15a, 15b) installed under specific conditions, the flow velocity distribution of the fluid flowing through the upstream hydraulic pipe 27a, which is an inclined pipe, is measured, and the rising speed of the bubbles, which are reflectors, is determined from this flow velocity distribution. The flow velocity distribution of the true fluid is obtained by correcting the influence of the flow velocity on the flow velocity (flow velocity distribution), and the flow rate is measured from this flow velocity distribution.

  By installing the ultrasonic flow meters 15a and 15b as shown in FIG. 5 and measuring the ultrasonic flow rate under specific conditions, it is possible to more easily separate the bubble floating motion.

In Figure 5, the center angle zero degrees ultrasonic transducer 46a, as well as installed such that the incident angle zero degrees, the ultrasonic transducer 46b has a central angle of 90 degrees, the installation angle of incidence so that the arbitrary angle alpha ₂ It is a thing.

In this installation state, Formula (1) and Formula (2) are

  In Expression (10), the ascent speed Vb can be independent of the position from the center of the upstream pipe 27a. In this case, separation of the ascending speed Vb of the bubbles by preliminary measurement using only the ultrasonic transducer 46b. Is possible. As a result, the influence on the flow velocity due to the floating movement of the bubbles can be corrected, and the true flow velocity distribution of the fluid a flowing in the upstream hydraulic pipe 27a can be obtained simply and easily, and the fluid flow rate can be accurately and accurately determined. Can be sought.

  In addition, although the example applied to the hydroelectric power plant was shown in the embodiment of the present invention, it may be applied to the pumped-storage power plant. Moreover, although the bubble supply means 30 showed the example comprised by the mechanical bubble generation means which combined the fluid pump 32 and the venturi pipe 33, the means by electric bubble generation | occurrence | production, such as an ultrasonic radiator, and saturated water are shown. The bubble supply means may be configured by the reduced pressure precipitation method used, the method of shearing and refining bubbles by a stirring action of a flow such as a swirling flow, or the method of ejecting air from fine holes.

The block diagram which applied the ultrasonic flowmeter measuring apparatus to which the ultrasonic flow measuring method which concerns on this invention is applied to the hydroelectric power station. The figure which shows an example of the bubble supply means which comprises an ultrasonic flow measuring device. The figure which shows an example of the ultrasonic flowmeter which comprises an ultrasonic flow measuring device. This shows the installation state of the ultrasonic transducer in the ultrasonic flowmeter to the pipe. (A), (B), and (C) are a side view, a plan view, and a downstream view of the pipe. Sectional drawing. 4 shows a second embodiment of the ultrasonic flow rate measuring method according to the present invention, wherein (A), (B) and (C) are side surfaces corresponding to (A), (B) and (C) of FIG. The figure, a top view, and sectional drawing. The figure explaining the floating effect | action of the bubble which acts on the fluid which flows through the inside of inclined piping.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Ultrasonic flow measuring device 11 Hydroelectric power plant 12 Water tank 13 Drainage garden 14 Piping 15, 15a, 15b Ultrasonic flow meter 16 Valve device 17 Water wheel 18 Generator 20 Circuit breaker 21 Transformer 22 Switching equipment 23 Power transmission system 25 Main valve 26 Bypass valve 27a Upstream hydraulic iron pipe 27b (intermediate) hydraulic iron pipe 27c Downstream hydraulic iron pipe 30 Bubble supply means (bubble generating means)
31 Circulating piping 32 Fluid pump 33 Venturi tube (gas-liquid mixing means)
34 Gas injection means 35 Gas injection pipe 37 Ultrasonic transmission means 38 Fluid distribution measurement means 39 Computer 40 Display device 43 Oscillator 44 Emitter 45 Signal generators 46, 46a, 46b Ultrasonic transducer 47 Amplifier 48 AD converter 49 Flow velocity distribution measurement circuit

Claims (4)

In a method for measuring the flow velocity distribution and flow rate of a fluid flowing in a pipe inclined along a height difference using ultrasonic waves,
Supplying bubbles to the fluid flowing in the inclined pipe by bubble supply means provided on the upstream side of the ultrasonic flowmeter;
In order to measure the flow velocity distribution of the fluid supplied with the bubbles, an ultrasonic transmission step of transmitting ultrasonic waves from the ultrasonic flowmeter to the fluid flowing in the inclined pipe along a plurality of measurement lines;
The transmitted ultrasonic waves are applied to the fluid flowing in the inclined pipe, the ultrasonic echoes reflected from the reflectors of the bubbles included in the fluid are received and signal-processed, and the plurality of fluids flowing in the inclined pipe are received. Has a flow velocity distribution / flow rate measurement step for measuring the flow velocity distribution in the measurement line and measuring the flow rate ,
In the flow velocity distribution / flow meter measurement step, the flow velocity distribution in the plurality of measurement lines is used to correct the influence on the flow velocity due to the rising motion of bubbles in the fluid flowing in the inclined pipe, Measurement method. In the flow velocity distribution / flow meter measurement step, regarding the flow velocity distribution in the plurality of measurement lines, by formulating equations relating to the flow velocity at the same distance from the pipe center on each measurement line, the bubbles in the fluid flowing in the inclined pipe are The ultrasonic flow rate measuring method according to claim 1 , wherein an influence on the flow velocity due to the levitation movement is corrected. In the ultrasonic wave transmitting step, a plurality of ultrasonic measurement lines transmitted from a plurality of ultrasonic transducers of the ultrasonic flowmeter are provided, and at least one measurement line is in the pipe axis direction with a zero central angle on the inclined pipe. 2. The ultrasonic flow rate measuring method according to claim 1, wherein the ultrasonic flow rate measuring method is formed by a vertically mounted ultrasonic transducer. 2. The ultrasonic flow rate measuring method according to claim 1, wherein the bubble supply means supplies bubbles to the fluid flowing in the pipe at a position separated by 10 times or more of the pipe inner diameter upstream of the ultrasonic flowmeter. .

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