JP2002174538A - Vortex flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vortex flowmeter which achieves improvements in linearity characteristic and measuring accuracy. SOLUTION: The vortex flowmeter for measuring the flow rate of a measuring fluid flowing through a pipeline using a Karman's vortex includes a vortex generation body disposed orthogonal to the pipeline and a curvature part which is installed at an angle part on the rear rim of the vortex generation body and has a specified curvature according to the caliber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vortex flowmeter having improved linearity characteristics and improved measurement accuracy.

[0002]

2. Description of the Related Art FIG. 3 is a diagram for explaining the configuration of a conventional example generally used in the prior art.
No. 8 (Japanese Patent Application No. 1-033256). 4 is an electric circuit diagram of FIG. 3, FIGS. 5 and 6 are operation explanatory diagrams of FIG. 3, and FIG. 7 is an enlarged view of a main part of the vortex generator 12 of FIG.

In FIG. 1, a conduit 10 is a conduit through which a measurement fluid FL flows. The nozzle 11 is provided at a right angle to the pipe 10 and has a cylindrical shape. The vortex generator 12 is inserted at a right angle to the pipeline 10 while keeping a gap from the nozzle 11, has a trapezoidal cross section, and has a columnar trapezoidal portion 121. At both ends of the trapezoidal portion 121, column-shaped pedestal portions 122 are provided, respectively.

[0004] One end of the vortex generator 12 is supported on the conduit 10 by a screw 13, and the other end of the vortex generator 12 is connected to a nozzle 11 by a flange portion 14.
Are fixed by screws or welding. The recess 15
The vortex generator 12 is provided on the flange portion 14 side.

In the recess 15, a first common electrode 16, a piezoelectric element 17, an electrode plate 18, an insulating plate 19, an electrode plate 20, and a piezoelectric element 21, which are all made of metal, are sandwiched in this order from the bottom. Arranged, by pressing rod 22 made of all genus,
These are pressed and fixed. Further, a lead wire 23 is provided from the electrode plate 18, a lead wire 24 is provided from the electrode plate 20,
These are drawn out to terminals A and B, respectively.

Each of the piezoelectric elements 17 and 21 is
The left and right sides of the paper 21 are polarized in opposite directions, respectively, and generate opposite-polarity charges on 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 1.
The electric charge generated between the terminal A connected to the electrode plate 8 and the conduit 10 connected via the first common electrode 16 and generated in the piezoelectric element 21 is connected to the terminal B connected to the electrode plate 20, It is obtained between the pressing rod 20 and the connected line 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 via the poly 27 are added by an adder 28 to obtain a flow signal.

The flow signal is converted into, for example, a current output and transmitted to a 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 measurement fluid FL flows through the conduit 10, vibrations are generated in the vortex generator 12 by Karman vortices in the direction indicated by the arrow F. FIG. 5 shows that
The stress distribution shown in FIG. 1A and the reverse stress distribution are repeated.

Each of the piezoelectric elements 17 and 21 has a charge of 10 Q and 1 Q corresponding to a signal stress having a vortex circulation number shown in FIG.
Is repeated. In FIG. 5, for convenience of explanation, the electrode plate 18 or 21 is placed on the left stone with respect to the paper surface.
One of the upper and lower electrodes is equivalent to the first common electrode 16 or the pressing rod 22.

On the other hand, the pipe line 10 also generates a pipe line vibration which causes noise. The pipeline vibration is divided into three components: a drag direction in the same direction as the flow of the fluid, a lift direction perpendicular to the flow of the fluid, and a longitudinal direction of the damage generating body.

Among them, the stress distribution with respect to the vibration in the drag direction is as shown in FIG. 5 (b). Positive and negative charges are canceled in one electrode, and no noise charge is generated. Further, as shown in FIG. 5C, the vibration in the longitudinal direction is canceled in the electrode, and no noise charge is generated as in 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 executed to eliminate the noise charge.

The electric charges of the piezoelectric elements 17 and 21 are represented by Q ₁ , Q ₂ ,
The signal components are S ₁ and S ₂ , and the noise components in the lift direction are N ₁ and N ₂
When the polarization is reversed by the piezoelectric elements 17 and 21, Q ₁ ,
Q ₂ is represented by the following equation.

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 shown in FIG. 6 (this diagram shows the relationship between the noise in the lift direction and the bending moment of the vortex generator with respect to the signal). It has become.

Therefore, as shown in FIG.
When the output of the charge amplifier 25 on the side is added by the adder 28, the output of the piezoelectric element 2 is multiplied by N ₁ / N ₂ together with the poly 27.
When added to the output of the charge amplifier 26 on the 1 side,

Q ₁ -Q ₂ (N ₁ / N ₂ ) = S ₁ -S ₂ (N ₁ /
N ₂ ), and the line noise is removed.

Then, the first common electrode 16, the piezoelectric element 1
7, electrode plate 18, insulating plate 19, electrode plate 20, piezoelectric element 2
1 is pressed and fixed to the recess 15 by a pressing rod 22.

Here, the vortex generator 12 and the first common electrode 1
6, piezoelectric element 17, electrode plate 18, insulating plate 19, electrode plate 2
If the temperature expansion of 0, the piezoelectric element 21 and the pressure rod 22 are made equal, even if the temperature of the measured fluid changes, the initial pressing force does not change, so that no problem occurs.

[0022]

FIG. 7 is an enlarged view of a main part of the vortex generator 12 shown in FIG. FIG. 8 is an operation explanatory diagram of FIG. The curvature R of the curved surface portion 121 (provided at the downstream apex of the vortex generator 12 having a trapezoidal cross section) shown in FIG. 7 is approximately R irrespective of the pipe diameter of the flow meter.
It was about 0.2 mm.

(H / d ≒ 0.95, d / D ≒ 0.28) Here, D is the diameter of the inner diameter of the conduit 10. In such an apparatus, it was found that the value of the radius of curvature R of the curved surface portion 121 had a large effect on the linear characteristics.

That is, in the vortex flow meter, the flow separates from the corner of the leading edge of the vortex generator 13, and a Karman vortex is generated (a main vortex F (Primary Vortex) in FIG. 8). In the case of the vortex generator 13 shown in FIG. 7, it has been confirmed that a part of the flow separates not only from the corner of the leading edge but also from the corner of the trailing edge, and a small vortex-like one is formed (the sub-vortex in FIG. 8). G (Secondary Vortex)).

If the corner of the trailing edge, that is, the R of the trailing edge is sharp or extremely large, the sub-vortex G becomes large or irregularly generated, thereby generating the main vortex F originally required. And may be added as noise when measuring the vortex.

In the conventional example shown in FIG.
Radius of curvature R tends to vary, and the Reynolds number Re
-Strohals number St The curve shape varies from one item to another and the reproducibility is low. As a result, the occurrence rate of defective precision products also increases.

The radius R of curvature of the non-optimal curved surface portion 121
When the manufactured vortex generator 12 is used, the Strohars number St greatly changes with a change in the Reynolds number Re, and the linearity accuracy deteriorates. In general,
When the radius of curvature R is small, the Strohars number St tends to increase in the low Reynolds number Re region.

An object of the present invention is to solve the above-mentioned problems, and the present invention is to set the radius of curvature R of the curved surface portion 121 of the vortex generator 12 to an optimum value determined for each diameter. The generation of the secondary vortex is suppressed to a regular and small one, and the main vortex (Primary Vortex) is generated stably regardless of the Reynolds number Re. This allows
It is an object of the present invention to provide a vortex flowmeter with a small change in the Strohars number St even when the Reynolds number Re changes, and to provide a vortex flowmeter with improved linearity characteristics and improved measurement accuracy.

[0029]

According to the present invention, there is provided a vortex flow meter for measuring a flow rate of a measurement fluid flowing through a pipeline by Karman vortex. A vortex generator provided orthogonally to the road, and a curved surface portion provided at a corner of the trailing edge of the vortex generator and having a predetermined curved surface in accordance with the diameter of the vortex generator are characterized in that it is provided.

According to a second aspect of the present invention, in the vortex flowmeter according to the first aspect, the predetermined curved surface is a curved surface in which the change in the Strohars number becomes smaller with respect to the change in the Reynolds number of the measurement fluid. And

According to a third aspect of the present invention, in the vortex flowmeter according to the first or second aspect, there is provided a vortex generator having a trapezoidal cross-sectional shape whose bottom side is arranged so as to correspond to the flow of the fluid to be measured. The ratio of (the radius of curvature of the curved surface portion / the length of the base of the trapezoid) is within a predetermined range.

According to a fourth aspect of the present invention, in the vortex flowmeter according to the third aspect, the predetermined range is approximately 0.05 to 0.05.
It is characterized by being about 0.1.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is an explanatory diagram of a main part configuration of an embodiment of the present invention,
FIG. 2 is an explanatory diagram of the operation of FIG.

In the figure, the curved surface 311 of the vortex generator 31
Is the Strohars number St against the change in Reynolds number Re
(The radius of curvature R /
The ratio of the length d) of the base of the trapezoid is approximately 0.02 to 0.2.

In the above configuration, FIG.
3, when only the radius of curvature R of the curved surface portion 311 is changed, the Reynolds number Re−Strohals number St
This is the result of a curve obtained by an actual flow experiment.

FIG. 2 shows that in this case, the data of the R / d optimum value (= 0.08) has a small change in the Strohars number St. On the other hand, even if R / d is small (=
0.007), it can be seen that even if R / d is large (= 0.20), the change in the number of Stokes number St becomes large (a curve that rises to the left).

However, the optimum value of the radius of curvature R of the curved surface portion 311 is the shape of the vortex generator 31, the optimum value is the cross-sectional shape of the vortex generator 31, the R of the trapezoidal corner of the cross section, the vortex It depends on various parameters such as the value of the gap between the generator and the body.

Since the vortex flow meter obtains the flow velocity from V = d × f / St (V: flow velocity f: vortex frequency), an error occurs if the Strobels number St changes.

In FIG. 2, the length d of the base of the trapezoidal base is d = 1.
In 4.3, when R / d = 0.08, the change in the Strohars number St is the smallest, and when the radius of curvature R of the curved surface portion 311 is the value, it can be said that the flow rate measurement has the highest accuracy.

As a result of repeating the actual flow experiment as described above, the vortex flowmeter using the vortex generator 31 having the shape and dimensions as described below has a curved surface of the vortex generator 31 which has the best linearity. The value of the radius of curvature R of the portion 311 can be adopted.

The optimum value of the radius of curvature R of the curved surface portion 311 is R / d of 0.05 to irrespective of the size of the flow meter.
It was confirmed experimentally that it was about 0.1.

The optimum value varies depending on various parameters such as the cross-sectional shape of the vortex generator, the R of the trapezoidal corner of the cross section, and the value of the gap between the vortex generator and the body.

[0043]

As a result, by setting the radius of curvature R of the curved surface portion 311 of the vortex generator 12 to an optimum value determined for each aperture, even if the Reynolds number Re changes, the change in the Strohars number St does not change. Since a small vortex flowmeter can be realized, a vortex flowmeter with improved linearity characteristics and improved measurement accuracy can be obtained.

Although the vortex generator 13 has a trapezoidal cross section in the above embodiment,
The present invention is not limited to this. For example, a triangular cross section may be used. In short, the radius of curvature that stabilizes the generation of the primary vortex (Primary Vortex) F by suppressing the generation of the secondary vortex (Secondary Vortex) G to a regular and small one. What is necessary is just to have the curved surface part 131 which has the dimension R.

It should be noted that the foregoing description has been directed to specific preferred embodiments for the purpose of illustration and illustration of the invention. Therefore, the present invention is not limited to the above-described embodiments, and includes many more modifications without departing from the spirit thereof.
This includes deformation.

[0047]

As described above, according to the first aspect of the present invention,
According to the fourth aspect, the following effects are obtained. By setting the radius of curvature of the curved surface of the vortex generator to an optimal value determined for each aperture, it is possible to realize a vortex flowmeter with a small change in the Strohars number even if the Reynolds number changes, thus achieving linearity characteristics. And a vortex flowmeter with improved measurement accuracy is obtained.

Therefore, according to the present invention, a vortex flowmeter with improved linearity characteristics and improved measurement accuracy can be realized.

[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;

FIG. 3 is an explanatory diagram of a configuration of a main part of a conventional example generally used in the related art.

FIG. 4 is an electric circuit diagram of FIG.

FIG. 5 is an operation explanatory diagram of FIG. 3;

FIG. 6 is an operation explanatory diagram of FIG. 3;

FIG. 7 is an enlarged view of a main part of the vortex generator 12 of FIG.

FIG. 8 is an operation explanatory diagram of FIG. 7;

[Explanation of symbols]

 Reference Signs List 10 conduit 11 nozzle 12 vortex generator 121 trapezoidal part 122 pedestal part 123 curved surface part 13 screw 14 flange part 15 concave part 16 first common electrode 17 piezoelectric element 18 electrode plate 19 insulating plate 20 electrode plate 21 piezoelectric element 22 pressing rod 23 lead Line 24 Lead wire 25 Charge amplifier 26 Charge amplifier 27 Porium 28 Adder 31 Vortex generator 311 Curved surface D Diameter of inner diameter of conduit FL Measurement fluid F Main vortex G Secondary vortex R Radius of curvature d Length of base of trapezoid h Trapezoid height

Claims (4)

[Claims] 1. A vortex flowmeter for measuring a flow rate of a measurement fluid flowing through a pipeline by Karman vortex, wherein a vortex generator provided orthogonal to the pipeline and a corner of a rear edge of the vortex generator are provided. A vortex flowmeter provided with a curved surface portion having a predetermined curved surface according to a diameter of the vortex flowmeter. 2. The vortex flowmeter according to claim 1, wherein the predetermined curved surface is a curved surface such that a change in the Strohars number becomes small with respect to a change in the Reynolds number of the measurement fluid. 3. A vortex generator having a trapezoidal cross section whose base is disposed so as to flow the measurement fluid, wherein a ratio of (radius of curvature of the curved surface portion / length of the base of the trapezoid) is within a predetermined range. 3. The vortex flowmeter according to claim 1, wherein 4. The vortex flowmeter according to claim 3, wherein said predetermined range is approximately 0.05 to 0.1.