JPH03108613A - Measuring method of average flow velocity within conduit - Google Patents

Abstract

PURPOSE:To improve the measuring accuracy of an average flow velocity by obtaining an extra coefficient using a specific formula based on a hydraulic mean depth calculated from the depth of water and the diameter of a tube, equivalent roughness of the tube, mounting position of a sensor and the depth of water, and multiplying the obtained extra coefficient with the flow velocity. CONSTITUTION:A sensor 1 is placed at a fixed position (y) from the bottom of a tube 11 by a sensor holder 15. A flow velocity V at the position (y) is detected by a flow velocity sensor of the sensor 1. At the same time, a depth of water H to the surface of water 12 is measured by a level gauge. A cross sectional area A of the flowing water within the tube 11 and a peripheral length L of the tube 11 in contact with the flowing water are calculated from a diameter D of the tube 11 and the depth of water H, and a hydraulic mean depth R is calculated from the cross sectional area A and peripheral length L. Moreover, an extra coefficient alpha is calculated from an equivalent roughness Ks determined by the hydraulic mean depth R, depth of water H, position (y) and kind of the tube 11 with using a formula. The average flow velocity within the tube 11 can be obtained by multiplying the flow velocity V with the coefficient alpha.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for measuring the average flow velocity of a fluid flowing, for example, in a sewer pipe, and particularly to improving measurement accuracy.

[Prior art] For example, highly accurate measurement of waterfalls in sewage pipes, which have large temporal fluctuations, is necessary for overall sewage regulation, process status monitoring and control at treatment plants, etc. .

Conventionally, methods for measuring the flow rate in sewer pipes include using a flume to generate a critical flow and measuring the flow rate by detecting the upstream water depth with a water level meter using ultrasonic waves, etc. Methods such as detecting the flow velocity based on the differential pressure between the two or calculating the flow rate by detecting the flow velocity using an ultrasonic or electromagnetic current meter are used.

However, as shown in the flow velocity distribution diagrams in FIGS. 5(a) and 5(b), even if the pipes 11 have cross-sections with the same diameter, the water depth H from the bottom of the pipe 11 to the water surface 12 will vary. If they are different, the flow velocity distribution 13 will also be different. Therefore, in order to accurately measure the flow rate in the pipe 11, it is necessary to measure the flow velocity at each part of the flowing water cross section in the pipe 11 and calculate the average flow velocity. However, in order to obtain the average flow velocity using this method, it is necessary to repeatedly measure the flow velocity at many measurement positions, which makes the measurement laborious and impractical. Therefore, as shown in U.S. Pat. No. 4.083.246, for example, the tube 1
A method has been adopted in which the average flow velocity VAV is calculated by multiplying the flow velocity V measured at the bottom of 1 by a correction coefficient f(H).

The method for measuring the average flow velocity disclosed in U.S. Pat. No. 4,083,246 is as shown in Fig.
The correction coefficient f (H), which changes at the ratio H/D, is determined in advance, and the water depth H is determined by detecting the pressure at which air bubbles are generated when the air is sent to the air pipe whose tip is inserted into the fluid.
The ratio of the measured water depth H to the pipe diameter, that is, the relative water depth H/
The average flow velocity VAv is calculated by reading out the correction coefficient "(H) from D and multiplying it by the measured flow velocity ■.

[Problems to be Solved by the Invention] However, the flow velocity distribution within the pipe 11 differs not only depending on the pipe diameter and the water GH but also on the type of the pipe 11, that is, the roughness of the inner surface of the pipe. Therefore, in the method of calculating the average flow velocity VAV by correcting the measured flow velocity V using the correction coefficient "(H)" obtained by the ratio H/D of the water depth H to the pipe diameter as described above, There was a disadvantage that an accurate average flow velocity VAv could not be obtained unless the correction coefficient "(H) was determined.

Another disadvantage is that it is not easy to determine the correction coefficient f(H) depending on the type of pipe, and a large-capacity storage means is required to store each of the determined correction coefficients f(H). there were.

The present invention has been made to solve these shortcomings, and it is an object of the present invention to propose a method for measuring the average flow velocity in a pipe conduit, which can easily determine the average flow velocity with high accuracy.

[Means for Solving the Problem] The method for measuring the average flow velocity in a pipe according to the present invention is to install a sensor consisting of a water level meter and a current meter on the bottom surface of the pipe to simultaneously detect the water i f (and the flow velocity) in the pipe. Then, from the water depth H detected by the water level gauge and the pipe diameter, calculate the diameter depth R determined by the cross-sectional area of the flowing water, and calculate the calculated diameter depth R, the equivalent roughness ks determined by the type of pipe, the mounting position rffy of the sensor, and It is characterized in that an additional coefficient α determined by the following formula is calculated from the detected water depth H, and the average flow velocity is calculated by multiplying the calculated additional coefficient α by the flow velocity V detected by the current velocity meter.

[Function] In this invention, the water GH and flow velocity in the pipe are detected by a sensor consisting of a water level meter and a current meter installed at the bottom of the pipe,
From the detected water depth H, the known pipe diameter, the equivalent roughness ks determined by the type of seed, and the sensor installation position y, calculate the additional coefficient α that varies depending on the water depth (and the equivalent roughness ks), and use this additional coefficient as The average flow velocity VAv in the pipe is calculated by multiplying and correcting the detected flow velocity V.

[Embodiment] FIG. 1 is a block diagram showing an average flow velocity measuring device according to an embodiment of the present invention. In the figure, l is a sensor, and sensor I has a truncated pyramid shape at the tip so as not to disturb the flow, as shown in FIG. A water level gauge 3 and a preamplifier 4 are integrally formed, each of which includes a diaphragm 3a that is attached to the rear bottom of the current meter 2 and is deflected by a pressure corresponding to the cross-sectional water level of the flowing water, and a semiconductor strain gauge 3b that detects the deflection of the diaphragm 3a. .

5 is a diameter depth calculation means that calculates the diameter depth R that determines the resistance coefficient of the inner surface of the pipe, that is, the value obtained by dividing the cross-sectional area of flowing water in an open channel by the length of the periphery in contact with water, and 6 is the diameter calculated by the diameter depth calculation means 5. The extra coefficient calculation means calculates the extra coefficient α from the depth R, the water depth H detected by the water level gauge 3, the equivalent roughness ks determined by the roughness of the inner surface of the tube, and the position ff1y of the sensor l attached to the bottom of the tube. 7 multiplies the flow velocity V by the extra coefficient α calculated by the extra coefficient calculation means 6 to calculate the average flow velocity V Al in the pipe.
It is a multiplication means for calculating l, and includes the sensor l, the diameter/depth calculation means 51, the extra coefficient calculation means 61, the multiplication means 7, and the pipe pI! D
The control unit of the average flow velocity measuring device is composed of an input means for inputting the following information.

8 is a flow 1 calculation means, and the Takigawa calculation means 8 calculates the Takigawa Q from the flowing water cross-sectional area A calculated by the diameter depth calculation means 5 and the average flow velocity ■□.
Calculate.

Before explaining the operation of the embodiment configured as described above, the present invention will first be explained in detail.

As shown in FIGS. 5(a) and 5(b), it is assumed that the flow velocity in the pipe 11 by the gravity flow method has a uniform velocity distribution,
The flow velocity distribution 13 changes depending on the position of the water surface 12. Now, the additional coefficient α = VAv, which is the ratio between the flow velocity V measured at the bottom of the tube and the average flow velocity vAv considering the velocity distribution in the tube.
Once /v is determined, the average flow velocity VAv is calculated from the measured flow velocity V and the additional coefficient α.

Here, assuming that the flow velocity distribution 13 is a logarithmic distribution, the velocity distribution of the open channel is expressed by equation (1) according to Kalman's logarithmic law.

However, g: Gravitational acceleration R: Diameter depth I: Pipe bottom gradient I4: Water depth y: Sensor mounting position relative to the pipe bottom kz Kalman constant (=0.4) From formula (1), the average flow velocity vAv is calculated by formula (3). It can be found by

■ = V, □ −-7g R1 (3) From equations (2) and (3), it is generally assumed that a sewage pipe is a completely rough surface, so if the coefficient of fluid friction is f, then V Av/I g RI =I8/f=6.0
+5.75 log(R/ks)” (51, however, k
s is the equivalent roughness. From equation (5), AV = I gRI (6,0+5.75 log(R/k
s) )・・・・(6) From equations (4) and (6), the extra coefficient α can be obtained using equation (7).

・　・　・　・(7) As shown in equation (7), the additional coefficient α is based on the pipe diameter.

It is a function of water G H, sensor mounting position tidy and equivalent roughness ks, and if sensor mounting position y is constant, relative water depth H
It increases as /D increases, but becomes independent of the tube bottom gradient.

Furthermore, although it is difficult to accurately obtain the equivalent roughness ks shown in equation (A), fluctuations in the equivalent roughness ks have little effect on the calculation of the additional coefficient α.

Therefore, as the equivalent roughness ks, an average equivalent roughness ks depending on the type of pipe may be used.

Therefore, by setting the sensor 1 at a fixed position y and measuring the water depth 11 with the pipe diameter and the equivalent roughness ks as known quantities, it is possible to calculate the additional coefficient α corresponding to the water depth H.

The operation of the embodiment of the present invention based on the above principle will be explained below.

First, as shown in the perspective view of FIG. 3, using an annular sensor holder 15 having a turnbuckle 14 at the upper end, a sensor l with its tip facing upstream is installed at a fixed position y from the bottom of the pipe 11. . In addition, in FIG. 3, 16 is a sensor cable.

Next, the flow velocity V at the sensor mounting position fty is measured by the current meter 2 of the sensor l, and at the same time, the water depth H to the water surface 12 is measured by the water level meter 3. On the other hand, the tube 11 to be measured by the input means
The pipe diameter, equivalent roughness ks, and sensor mounting position y are input manually to the control section of the average flow velocity measuring device. Based on the input pipe diameter and the water depth H measured by the water level meter 3, the diameter depth calculation means 5 calculates the cross-sectional area A of the flowing water in the pipe II and the pipe 1 in contact with the flowing water.
The circumferential length of 1 is calculated, and the diameter depth R is calculated from the calculated cross-sectional area of flowing water and the circumferential length. The calculated diameter depth R is sent to the extra coefficient calculation means 6, which calculates the diameter depth 7, the water depth H measured by the water level gauge 3, the equivalent roughness ks inputted by the input means, and the sensor mounting position y. The calculation shown in equation (7) is performed to calculate the extra coefficient a.

Figure 4 shows the relative water depth H/D on the horizontal axis and the extra coefficient α on the vertical axis. The distribution characteristics of the additional coefficient σ obtained from the average flow velocity obtained by measuring the flow velocity at multiple locations including the sensor mounting position y are shown. In the figure, curve a is the theoretical value obtained by equation (7),
The multiple points are measured values obtained through actual measurements. As shown in the figure, the error between the extra coefficient α obtained from equation (7) and the extra coefficient α obtained from the actual measured value is all within the control limit of 3σ, and most of the errors are within lσ. It is. Therefore, the extra coefficient calculating means 6 can calculate an actually suitable extra coefficient α.

This calculated extra coefficient α is sent to the multiplication means 7.

On the other hand, the flow velocity ■ measured by the current meter 2 of the sensor l is also sent to the multiplication means 7, and the multiplication means 7 multiplies the flow velocity V by an additional coefficient a to calculate the average flow velocity VAv in the pipe II.

Then, the calculated average flow velocity ■. is sent to the flow rate calculation means 8 and multiplied by the flowing water cross-sectional area A calculated by the diameter depth calculation means 5, the flow ff1Q in the pipe 11 can be calculated. By measuring the flow velocity V multiple times and calculating the average flow velocity V All from the average value, the average flow velocity vAv can be calculated with high accuracy.

[Effects of the Invention] As explained above, this invention detects the water depth H and flow velocity V in the pipe with a sensor consisting of a water level meter and a current velocity meter installed at the bottom of the five pipes, and detects the detected water? 2H, the known pipe diameter, the equivalent roughness ks determined by the type of pipe, and the sensor installation position y, calculate the additional coefficient α that varies depending on the water depth H and the equivalent roughness ks, and calculate the flow velocity at which this additional coefficient α is detected. Since the average flow velocity VAV in the pipe is calculated by multiplying and correcting V, the average flow velocity vAv can be calculated by considering the relative water depth H/D and the resistance coefficient of the inner surface of the pipe, and the average flow velocity VAv
The measurement accuracy can be greatly improved.

In addition, by measuring the flow velocity V and water EH with the current meter and water level meter installed integrally with the sensor, the average flow velocity V
Since the AV can be obtained, the flow rate in the sewer pipe, which has large temporal fluctuations, can be obtained with high accuracy.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an average flow rate measuring device according to an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the structure of the sensor of the above embodiment, and Fig. 3 is a perspective view showing how the sensor is attached to a pipe. , FIG. 4 is a characteristic diagram of relative water depth H/D and additional coefficient α, and FIG. 5(a). (b) is a flow velocity distribution diagram showing the flow velocity distribution in each pipe, and FIG. 6 is a correction coefficient characteristic diagram showing the correction coefficient f (H) in the conventional example. ■...sensor, 2...current meter, 3...water level meter, 5...diameter depth calculating means, 6...additional coefficient calculating means, 7...multiplying means .

Claims (1)

[Claims] A sensor consisting of a water level meter and a current meter is installed at the bottom of the pipe to detect the water depth H and flow velocity inside the pipe, and the cross-sectional area of the flowing water is calculated from the water depth H and the pipe diameter D detected by the water level gauge. Calculate the determined diameter depth R, calculate the additional coefficient α determined by the following formula from the calculated diameter depth R, the equivalent roughness ks determined by the type of pipe, the mounting position y of the above sensor, and the detected water depth H, and calculate 1/ α=1+(1+2.3
log(y/H))/0.4{6.0+5.75log
(R/ks)} A method for measuring an average flow velocity in a pipe, characterized in that the average flow velocity is calculated by multiplying the calculated additional coefficient α by the flow velocity V detected by the current velocity meter.