JP3114411B2 - Vortex flow meter - Google Patents

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 and accurately measuring a flow velocity even at a low flow velocity.

[0002]

2. Description of the Related Art FIG. 7 is an explanatory view of the structure of a conventional example generally used in the prior art.
No. 8 (Japanese Patent Application No. 1-033256). 1
Reference numeral 0 denotes a pipe through which a fluid flows, and reference numeral 11 denotes a cylindrical nozzle provided at right angles to the pipe 10.

[0003] Reference numeral 12 denotes a pipe 1 at an interval from the nozzle 11.
It is a column-shaped vortex generator having a trapezoidal cross section inserted at a right angle to 0, one end of which is supported by a pipe 13 by a screw 13,
The other end is fixed to the nozzle 11 by a screw or welding at a flange portion 14. Reference numeral 15 denotes a concave portion provided on the flange portion 14 side of the vortex generator 12.

A first common electrode 16 made of metal, a piezoelectric element 17, and an electrode plate 1 are sequentially placed in the recess 15 from the bottom thereof.
8, an insulating plate 19, an electrode plate 20, and a piezoelectric element 21 are arranged in a sandwich shape, and these are pressed and fixed by a metal pressing rod 22. Further, the lead wire 2 is
3. A lead wire 24 is connected from the electrode plate 20 to the terminal A,
B has been drawn.

The piezoelectric elements 17 and 21 correspond to the piezoelectric elements 17 and 2 respectively.
The left and right sides of the sheet 1 are polarized in opposite directions, and charges of opposite polarities are generated in the upper and lower electrodes with respect to the 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 the piezoelectric element 21 and the conduit 10 connected through the base 16 is connected to the terminal B connected to the electrode plate 20 and the pressing rod 20. Obtained between 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 by the adder 28 via the volume 27 to obtain a flow signal. This flow signal is converted into, for example, a current output and transmitted to the load via two wires (not shown).

Next, the operation of the vortex flowmeter configured as described above will be described with reference to FIGS. When the fluid flows through the pipe 10, vibrations due to the Karman vortex are generated in the vortex generator 12 in the direction indicated by the arrow F. This vibration causes the vortex generator 12 to repeat a stress distribution as shown in FIG.
9A, repetition of charges + Q and -Q corresponding to signal stress having a vortex frequency shown in FIG. 9A occurs.

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
It is equivalent to 2.

[0010] On the other hand, the pipeline 10 also generates pipeline vibrations that cause noise. The pipeline vibration is divided into a drag direction in the same direction as the fluid flow, a lift direction perpendicular to the fluid flow, 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 the positive and negative charges are canceled in one electrode and no noise charge is generated. Further, as shown in FIG. 9C, the vibration in the longitudinal direction is canceled in the electrode, and no noise charge is generated as in the case of the drag direction.

However, the vibration in the lift direction has the same stress distribution as the signal stress, and generates noise charges. Therefore, the following calculation is performed to eliminate this noise charge. The charges of the piezoelectric elements 17 and 21 are Q ₁ and Q ₂ , the signal components are S ₁ ,
S ₂ , the noise components in the lift direction are N ₁ and N _2, and when the polarization is reversed by the piezoelectric elements 17 and 21, Q ₁ and Q ₂ are expressed 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 diagram shows the relationship between the noise and the signal in the lift direction and the bending moment of the vortex generator). 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, the output 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 line noise is removed.

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 to 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, even if the temperature of the measured fluid changes, the initial pressing force does not change, so that there is no problem.

[0014]

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

When the product of the frequency f multiplied by the width d of the vortex generator is divided by the flow velocity u, a non-dimensional quantity called the Strouhal number St is obtained. However, this becomes constant over a wide flow velocity range. Thus, the flow velocity can be measured relatively easily using the following equation (1). u = (f · d) / St (1)

However, when the flow velocity decreases, the Strouhal number St becomes inconsistent, so that an accurate flow velocity cannot be obtained even if the vortex frequency is substituted into the equation (1). That is, accurate measurement cannot be performed with the conventional vortex flowmeter in FIG. The present invention solves this problem. SUMMARY OF THE INVENTION An object of the present invention is to provide a vortex flowmeter capable of accurately and accurately measuring a flow velocity even at a low flow velocity.

[0017]

In order to achieve this object, the present invention provides a vortex flow meter for measuring a flow rate by detecting an alternating force acting on a vortex generator by Karman vortex.
A column-shaped vortex generator provided perpendicularly to the measurement flow path, and having a width of approximately 0.27 times the width of the vortex generator and extending from the vortex generator to approximately 1.5 times the width of the vortex generator And a columnar body arranged in parallel with the vortex generator 3.5 times upstream of the vortex flowmeter.

[0018]

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

The Karman vortices are generated alternately from both sides of the vortex generator. In the arrangement of the vortices in a state where the Karman vortices are generated stably, the interval between the vortices in the flow direction and the interval between the left and right vortex rows of the vortex generator Is constant. Since the Karman vortex moves according to the time-average streamline, when there is a columnar body, the interval between the left and right rows of the Karman vortex is constant at the low flow velocity and the high flow velocity. That is, the interval between the vortices in the flow direction is also constant, and the arrangement of the Karman vortices is always constant.

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

[0021]

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

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

[0023]

In the above construction, the measurement fluid flowing through the measurement flow path 32 hits the columnar body 34, and the flow of the measurement fluid is divided into right and left. When there is no columnar body 34, the time-average streamline A at a low flow rate shown in FIG. 2 is different from the time-average streamline B at a high flow rate shown in FIG. However, due to the presence of the columnar body 34, as shown in FIG. 4, the flow is divided into right and left, and the time average streamline C is always the same at the low flow velocity and the high flow velocity.

The Karman vortices are alternately generated from both sides of the vortex generator 31. The arrangement of the stable Karman vortex streets is shown in FIG.
As shown in the figure, the ratio of the interval a between the vortices in the flow direction and the interval b between the left and right vortex rows of the vortex generator 31 is constant. Since the Karman vortex moves according to the time-average streamline C, the columnar body 3
When there is 4, the interval b between the left and right rows of the Karman vortex is constant at the low flow rate and the high flow rate. That is, the interval a of the vortex in the flow direction
Is also constant, and the arrangement of Karman vortices is always constant.

The cycle of the Karman vortex generation is greatly affected by the interval a of the Karman vortex in the wake, and in this case, the Strouhal number also becomes constant from a low flow rate to a high flow rate. FIG. 5 is a graph showing a change in the number of Strouhals when there is a cylindrical columnar body 34 and when there is no cylindrical columnar body 34. In this case, assuming that the width of the vortex generator is d, the diameter d ₂ of the cylinder is 0.
At 27d, the interval L is 2.5d. The rise of the Strouhal number at low flow velocity is considerably suppressed in the presence of a cylinder, and approaches a substantially constant value.

At this time, the diameter d ₂ of the column 33 and the column 34
And since the distance L of the vortex generator 31, will be different in shape of the time-averaged flow lines, the diameter d ₂ of the best cylinder was determined by experiments spacing L. FIG. 6 shows that the flow velocity is from 0.5 m / s to 8 m / s.
The ratio L between the width d and the interval L of the vortex generator is obtained by dividing the change in the number of Strouhals when there is a small cylinder up to m / s by the change in the number of Strouhals when there is no small cylinder. / D.

Further, the diameter d ₂ of the cylinder is from 0.2 d to 0.
5d. The smaller the rate of this change, the smaller the fluctuation of the Strouhal number. According to FIG. 6, the change ratio is less than one-third of the case where 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 seen from FIG.

The pressure drop due to the Karman vortex is caused by
Through the pressure guiding holes 36a, 36b and the pressure guiding tubes 37a, 37b,
It is led to the pressure sensor 35. The output of the pressure sensor 35 is
The signal enters the signal processing circuit 38, is subjected to signal processing, and the Kalman vortex frequency is calculated. The flow velocity is calculated based on the frequency, the Strouhal number and the width of the vortex generator which are obtained in advance by experiments.

As a result, by providing the columnar members 34 having a diameter smaller than that of the vortex generator 31 at an appropriate interval upstream of the vortex generator 31, the number of straw hulls becomes constant up to a low flow velocity. Therefore, it is possible to measure the flow velocity with high accuracy up to a low flow velocity.

(1) The columnar body 34 may not be a cylinder, but may be a triangular prism,
It may be a square pillar, trapezoidal pillar, or elliptical pillar. (2) The vortex generator 31 does not need to be trapezoidal, but may be, for example, a quadrangle, in other words, any shape that can stably generate Karman vortices. (3) The Karman vortex frequency is detected using a pressure sensor. However, the present invention is not limited to this. For example, an ultrasonic system, a hot wire system, or an optical system may be used.

[0031]

As described above, the present invention relates to a vortex flowmeter for detecting an alternating force acting on a vortex generator by a Karman vortex to measure a flow velocity flow rate. Of the vortex generator and the width of the vortex generator of about 0.2
A column having a width of 7 times and being arranged in parallel with the vortex generator upstream from the vortex generator by approximately 1.5 to 3.5 times the width of the vortex generator. The vortex flowmeter was characterized as follows.

As a result, by providing a columnar body having a smaller diameter than the vortex generator at an appropriate interval upstream of the vortex generator, the number of straw hulls becomes constant up to a low flow velocity.
In other words, high-precision flow velocity measurement can be performed up to a low flow velocity.

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

[Brief description of the 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 a low flow velocity.

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

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

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

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

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

8 is a block diagram illustrating a configuration of a conversion unit that converts a charge detected by the detection unit illustrated in FIG. 2 into a voltage.

FIG. 9 is an operation explanatory diagram of FIG. 2;

FIG. 10 is an operation explanatory diagram of FIG. 2;

[Explanation of symbols]

 31 ... vortex generator 32 ... measurement channel 33 ... flow 34 ... column 35 ... pressure sensor 36a ... pressure guide hole 36b ... pressure guide hole 37a ... pressure guide tube 37b ... pressure guide 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)

(57) [Claims] 1. A vortex flowmeter for measuring a flow rate by detecting an alternating force acting on a vortex generator by a Karman vortex, wherein a columnar vortex generator provided vertically to a measurement flow path, Having a width of about 0.27 times the width of the vortex generator and arranged in parallel with the vortex generator on the upstream side of about 1.5 to 3.5 times the width of the vortex generator. A vortex flowmeter comprising a body.