JPH06241853A - Vortex flowmeter - Google Patents

Abstract

PURPOSE:To measure a flow velocity and a flow rate with good accuracy and precisely down to a low flow velocity by a method wherein a column-shaped body whose width is at the specific multiple of a column-shaped vortex-generating body installed perpendicularly to a measuring flow passage is arranged in parallel with the vortex-generating body on the upstream side of the vortex-generating body. CONSTITUTION:A column-shaped body 34 which is provided with a width d2 at nearly 0.27 times the width (d) of a column-shaped vortex-generating body 31 installed perpendicularly to a flow 33 and which is situated at a distance L, on the upstream side, at 1.5 to 3.5 times, preferably at 2.5 times, the width (d) from the vortex-generating body 31 is installed in parallel with the vortex-generating body 31 in a measuring flow passage 32. A measuring fluid which has flowed in the measuring flow passage 32 bumps against the column-shaped body 34, and the flow 33 of the measuring fluid is branched into a right flow and a left flow. When the column-shaped body 34 does not exist, a time-average flow line differs between a time- average flow line at a low flow velocity and a time-average flow line at a high flow velocity. However, when the column-shaped body 34 exists, the flow is branched into the right and left flows, and the time-average flow line becomes always identical at a low flow velocity and a high flow velocity. Consequently, the interval between the right street and the left street of Karman's vortex becomes low definite at the low flow velocity and the high flow velocity, and the arrangement of Karman's vortex becomes definite.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vortex flowmeter capable of accurately measuring flow velocity and flow rate even at low flow velocity.

[0002]

2. Description of the Related Art FIG. 7 is a diagram for explaining the configuration of a conventional example that is generally used in the past.
No. 8 (Japanese Patent Application No. 1-033256). 1
Reference numeral 0 is a pipe through which the fluid flows, and 11 is a cylindrical nozzle provided at a right angle to the pipe 10.

Reference numeral 12 is a pipe line 1 with a distance from the nozzle 11.
It is a columnar vortex generator having a trapezoidal cross section that is inserted at a right angle to 0, and one end thereof is supported by a pipe 13 by a screw 13,
The other end is fixed to the nozzle 11 with a flange 14 by screws or welding. Reference numeral 15 denotes a concave portion provided on the flange portion 14 side of the vortex generator 12.

Inside the recess 15, metal first common electrode 16, piezoelectric element 17 and electrode plate 1 are arranged in this order from the bottom.
8, the insulating plate 19, the electrode plate 20, and the piezoelectric element 21 are arranged in a sandwich shape, and these are pressed and fixed by a metal pressing rod 22. Further, from the electrode plate 18, the lead wire 2
3, lead wires 24 from the electrode plate 20 are terminals A,
B has been pulled out.

The piezoelectric elements 17 and 21 are the piezoelectric elements 17 and 2, respectively.
The left side and the right side of FIG. 1 are polarized in opposite directions, and charges of opposite polarities are generated in the upper and lower electrodes with respect to stress in the same direction.

The electric charge generated in the piezoelectric element 17 is applied to the electrode plate 18
The electric charge generated between the terminal A connected to and the conduit 10 connected via the pedestal 16 and generated in the piezoelectric element 21 was connected to the terminal B connected to the electrode plate 20 and the pressing rod 20. It is obtained between the pipe 10 and the pipe 10.

The charges generated on the two electrode plates 18 and 20 are input to charge amplifiers 25 and 26 as shown in FIG. The output of the charge amplifier 25 and the output of the charge amplifier 26 are added to the output via the volume 27 by the adder 28 to obtain a flow rate signal. This flow rate signal is converted into, for example, a current output and transmitted to the load via the two wires (not shown).

Next, the operation of the vortex flowmeter constructed as above will be described with reference to FIGS. 9 and 10. When the fluid flows into the conduit 10, vibrations due to Karman vortices are generated in the vortex generator 12 in the direction indicated by the arrow F. This vibration causes the vortex generator 12 to repeat the stress distribution as shown in FIG.
, The charges + Q and −Q corresponding to the signal stress having the vortex frequency shown in FIG.

In FIG. 9, for convenience of explanation, the electrode plate 18 or 21 is divided into two parts on the left and right with respect to the paper surface, and one of the upper and lower electrodes is the pedestal 16 or the pressing rod 2.
It is equivalent to 2.

On the other hand, in the pipeline 10, pipeline vibration that causes noise is also generated. This pipeline vibration is divided into a drag force direction that is the same as the fluid flow direction, a lift force direction that is perpendicular to the fluid flow direction, and a longitudinal component of the vortex generator. this house,
The stress distribution with respect to the vibration in the drag direction is as shown in FIG. 9 (b), and positive and negative charges are canceled out within one electrode, and noise charges are not generated. Further, with respect to the vibration in the longitudinal direction, it is canceled in the electrode as shown in FIG. 9C, and noise charge is not generated as in the drag direction.

However, the vibration in the lift direction has the same stress distribution as the signal stress, and noise charge is generated. Therefore, the following calculation is executed in order to erase this noise charge. The charges of the piezoelectric elements 17 and 21 are Q ₁ and Q ₂ , the signal component is S ₁ ,
If S ₂ and the noise components in the lift direction are N ₁ and N _2, and the polarization is reversed in the piezoelectric elements 17 and 21, Q ₁ and Q ₂ are represented by the following equations. _{Q 1 = S 1 + N 1} -Q 2 = -S 2 -N 2

However, the vector directions of S ₁ and S ₂ , and N ₁ and N ₂ are the same. Here, the relationship between the signal component and the noise component of the piezoelectric elements 17 and 21 is as shown in FIG. 10 (this figure shows the relationship between the noise in the lift direction and the bending moment of the vortex generator with respect to the signal). Therefore, as shown in FIG. 8, when the output of the charge amplifier 25 on the piezoelectric element 17 side is added by the adder 28, it is multiplied by N ₁ / N ₂ together with the volume 27 and added to the output of the charge amplifier 26 on the piezoelectric element 21 side. Then, Q ₁ −Q ₂ (N ₁ / N ₂ ) = S ₁ −S ₂ (N ₁ / N ₂ ), and the pipeline noise is removed.

Thus, the first common electrode 16, the piezoelectric element 17, the electrode plate 18, the insulating plate 19, the electrode plate 20, and the piezoelectric element 21 are pressed and fixed in the recess 15 by the pressing rod 22.
Here, the vortex generator 12, the first common electrode 16, the piezoelectric element 1
7, electrode plate 18, insulating plate 19, electrode plate 20, piezoelectric element 2
1. If the temperature expansion of the pressing rod 22 is made equal, the initial pressing force does not change even if the measured fluid temperature changes, so there is no problem.

[0014]

In short, the vortex flowmeter measures the flow velocity and the flow rate by placing a vortex generator in the measurement flow path and measuring the frequency of the generated Karman vortex. The principle of the vortex flowmeter utilizes the phenomenon that the frequency of the Karman vortex generated by the vortex generator is proportional to the flow velocity.

When the product of the frequency f and the width d of the vortex generator is divided by the flow velocity u, a Strouhal number St, which is a dimensionless quantity, is constant over a wide flow velocity range, so the frequency must be measured. Thus, the flow velocity can be measured relatively easily using the following formula (1). u = (f · d) / St (1)

However, since the Strouhal number St is not constant when the flow velocity becomes small, it becomes impossible to obtain an accurate flow velocity even if the vortex frequency is substituted into the equation (1). That is, the vortex flowmeter of the conventional example shown in FIG. 7 cannot perform accurate measurement. The present invention solves this problem. An object of the present invention is to provide a vortex flowmeter capable of accurately measuring a flow velocity and flow rate even at a low flow velocity.

[0017]

In order to achieve this object, the present invention relates to a vortex flowmeter which detects an alternating force acting on a vortex generator by a Karman vortex to measure a flow velocity flow rate,
A column-shaped vortex generator provided perpendicular to the measurement flow path, and having a width of approximately 0.27 times the width of the vortex generator, and approximately 1.5 times the width of the vortex generator from the vortex generator. To 3.5 times the upstream side of the vortex generator, and a columnar body arranged in parallel with the vortex generator.

[0018]

In the above structure, the measurement fluid flowing through the measurement flow path collides with the columnar body, and the flow of the measurement fluid is divided into left and right. In the absence of columns, the time-averaged streamlines are different at low and high flow velocities. However, due to the presence of the columnar body, the flow is divided into right and left, and the time-averaged streamline is always the same at low flow velocity and high flow velocity.

Karman vortices are alternately generated from both sides of the vortex generator, but in the arrangement of vortices in a state in which the Karman vortices are stably generated, the spacing between vortices in the flow direction and the spacing between the vortex rows on the left and right of the vortex generator. Is constant. Since Karman vortices move according to the time-averaged streamline, when there is a columnar body, the interval between the left and right columns of Karman vortices is constant at low and high flow velocities. That is, the spacing between vortices in the flow direction is also constant, and the array of Karman vortices is always constant.

Since the period of Karman vortex generation is greatly affected by the interval of the Karman vortices in the wake, in this case, the Strouhal number also becomes a constant value from low flow velocity to high flow velocity. Hereinafter, detailed description will be given based on examples.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of the essential structure of an embodiment of the present invention. Reference numeral 31 is a column-shaped vortex generator provided in the measurement flow channel 32 perpendicularly to the flow 33. In this case, the trapezoid is a regular leg. 34 has a width d ₂ that is approximately 0.27 times the width d of the vortex generator 31, and to a distance L on the upstream side that is approximately 2.5 times the width d of the vortex generator 31 from the vortex generator 31. It is a columnar body arranged in parallel with the vortex generator 31. In this case, form a cylinder.

Reference numeral 35 is a pressure sensor for detecting pressure fluctuations. Reference numerals 36a and 36b are pressure guiding holes provided on the side surface of the vortex generator 31. 37a and 37b are pressure guide holes 36a and
36b is a pressure guiding tube that communicates with the pressure sensor 35. Reference numeral 38 is a signal processing circuit that processes the output of the pressure sensor 35.

[0023]

In the above structure, the measurement fluid flowing through the measurement flow path 32 collides with the columnar body 34, and the flow of the measurement fluid is divided into right and left. In the case where the columnar body 34 is not provided, the time average streamline is different between the low flow velocity time average streamline A shown in FIG. 2 and the high flow velocity time average streamline B shown in FIG. However, due to the presence of the columnar body 34, the flow is divided into right and left as shown in FIG. 4, and the time average streamline C is always the same at low flow velocity and high flow velocity.

Although Karman vortices are alternately generated from both sides of the vortex generator 31, the stable array of Karman vortices is shown in FIG.
As shown in FIG. 5, the ratio of the distance a between the vortices in the flow direction and the distance b between the left and right vortex rows of the vortex generator 31 is constant. Since the Karman vortex moves according to the time-averaged streamline C, the columnar body 3
When there is 4, the interval b between the left and right columns of the Karman vortex becomes constant at low flow velocity and high flow velocity. That is, the spacing a of the vortices in the flow direction
Also becomes constant, and the array of Karman vortices is always constant.

Since the cycle of Karman vortex generation is greatly affected by the interval a of the Karman vortices in the wake, in this case, the Strouhal number also becomes a constant value from low flow velocity to high flow velocity. FIG. 5 shows a graph of changes in the Strouhal number when the cylindrical columnar body 34 is present D and when it is not E. In this case, if the width of the vortex generator is d, the diameter d ₂ of the cylinder is 0.
At 27d, the spacing L is 2.5d. The increase in the Strouhal number at low flow velocity is considerably suppressed when there is a cylinder, and is close to a constant value.

At this time, the diameter d ₂ of the cylinder 33 and the cylinder 34
Since the shape of the time-average streamline differs depending on the distance L between the vortex generator 31 and the vortex generator 31, the optimum diameter d ₂ of the cylinder and the distance L were obtained by experiments. FIG. 6 shows a flow rate of 0.5 m / s to 8
The amount of change in the Strouhal number when there is a small cylinder up to m / s divided by the amount of change in the Strouhal number when there is no small cylinder is the ratio L between the width d of the vortex generator and the distance L. / D.

The diameter d ₂ of the cylinder is from 0.2d to 0.
It is 5d. The smaller the rate of this change, the smaller the variation of the Strouhal number. According to FIG. 6, the rate of change is less than one-third that when there is no cylinder when the diameter d _{2 of} the cylinder is 0.27d and the interval L is 1.5d.
It can be understood that this is the case of 3.5d.

The pressure drop due to the generation of the Karman vortex is
Passing through the pressure guiding holes 36a and 36b and the pressure guiding tubes 37a and 37b,
It is guided to the pressure sensor 35. The output of the pressure sensor 35 is
The signal processing circuit 38 is entered, signal processing is performed, and the Karman vortex frequency is calculated, and the flow velocity is calculated by this frequency, the Strouhal number and the width of the vortex generator which are previously obtained by experiments.

As a result, by installing the columnar bodies 34 having a diameter smaller than that of the vortex generator 31 at appropriate intervals upstream of the vortex generator 31, the Strouhal number becomes constant up to a low flow velocity. Therefore, highly accurate flow velocity measurement can be performed even at low flow velocity.

(1) The columnar body 34 need not be a cylinder, but may be a triangular prism or
It may be a square pillar, a trapezoidal pillar, or an elliptical pillar. (2) The vortex generator 31 does not need to be trapezoidal, and may be, for example, a quadrangle, as long as it has a shape capable of stably generating a Karman vortex. (3) The Karman vortex frequency is detected using a pressure sensor, but the present invention is not limited to this. For example, an ultrasonic method, a heat ray method, or an optical method may be used.

[0031]

As described above, according to the present invention, in the vortex flowmeter for detecting the alternating flow force acting on the vortex generator by the Karman vortex to measure the flow velocity flow rate, the columnar shape provided vertically to the measurement flow path is used. And the width of the vortex generator of about 0.2
A columnar body having a width of 7 times and arranged in parallel with the vortex generator on the upstream side from the vortex generator about 1.5 to 3.5 times the width of the vortex generator. A vortex flowmeter characterized by

As a result, the Strouhal number becomes constant up to a low flow velocity by installing columnar bodies having a smaller diameter than the vortex generator at appropriate intervals upstream of the vortex generator.
That is, highly accurate flow velocity measurement can be performed even at low flow velocity.

Therefore, according to the present invention, it is possible to realize a vortex flowmeter capable of accurately measuring the flow velocity and flow rate even at a low flow velocity.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a main part configuration of an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of FIG. 1, showing a case of low flow velocity.

FIG. 3 is an operation explanatory diagram of FIG. 1, showing a case of low flow velocity.

FIG. 4 is an operation explanatory diagram of FIG. 1, showing a vortex street.

5 is an operation explanatory diagram of FIG. 1. FIG.

FIG. 6 is an operation explanatory diagram of FIG. 1.

FIG. 7 is an explanatory diagram of a configuration of a conventional example that is generally used in the past.

FIG. 8 is a block diagram showing a configuration of a conversion unit that converts charges detected by the detection unit shown in FIG. 2 into a voltage.

9 is an explanatory diagram of the operation of FIG.

10 is an explanatory diagram of the operation of FIG.

[Explanation of symbols]

 31 ... Vortex generator 32 ... Measurement channel 33 ... Flow 34 ... Columnar body 35 ... Pressure sensor 36a ... Pressure guiding hole 36b ... Pressure guiding hole 37a ... Pressure guiding tube 37b ... Pressure guiding tube 38 ... Signal processing circuit A ... Time average streamline B ... time average streamline C ... time average streamline D ... with small cylinder E ... without small cylinder

Claims (1)

[Claims] 1. A vortex flowmeter for detecting an alternating force acting on a vortex generator by a Karman vortex to measure a flow velocity and flow rate, and a columnar vortex generator provided vertically to a measurement flow path, and the vortex generator. A column having a width of approximately 0.27 times the width of the vortex generator and arranged in parallel with the vortex generator at an upstream side of approximately 1.5 to 3.5 times the width of the vortex generator. A vortex flowmeter having a body.