JPS62214320A - Vortex flowmeter - Google Patents

Abstract

PURPOSE:To stabilize instrumental error characteristics within a wide flowmeter measurement range by obtain mutual operation in which an upstream-side vortex generating element and a downstream-side vortex generating element which has a slightly low frequency that is compensate each other as to a Reynolds number characteristics. CONSTITUTION:The vortex generating body composed of vortex generating elements 2a and 2b arranged at right angle to a flow is provided in a flow passage 1 and a flat plate 2c is arranged between the upstream-side vortex generating element 2a and down-stream vortex generating element 2b. The representative length of the elements 2a and 2b is the breadth (d) of the opposite surfaces of the element 2a and 2b. The plate thickness tb of the flat plate 2c is preferably tb=0.1-0.4d and the gap (t) between the elements 2a and 2b is about t=0.1-0.9d. Further, a vortex frequency ratio generated when the elements 2a and 2b are arranged at those positions independently is set to 0.7-0.9 on the basis of the element 2a. Consequently, the instrumental error characteristics are improved.

Description

TECHNICAL FIELD The present invention relates to vortex flowmeters, and more particularly to the structure of vortex generators in vortex flowmeters.

Prior Art The applicant provided a vortex generating element in the fluid flow direction in Japanese Patent Publication No. 55-40804.

A Karman vortex generating element plate having a desired thickness is integrally provided behind this vortex generating element, and at least one or more Karman vortex generating element plates similar to the above are further provided behind this Karman vortex generating element plate. We proposed Karman vortex forming devices that are arranged independently at desired intervals. The above-mentioned vortex generating element has an acute isosceles triangular cross-sectional shape with an apex on the flow axis, and the vortex generated here is transferred to one or more Karman vortex generating element plates disposed at the rear. (hereinafter simply referred to as a flat plate), the vortex is developed to an optimal strength, and the vortex is separated from the final stage flat plate. In this way, the vortex generated by the Karman vortex generating element could be developed into a sufficiently strong vortex, and a stable vortex generator could be obtained.

Problems with the Prior Art In the conventional technology described above, the vortex is amplified by placing a flat plate on the downstream side of the vortex generator, so by selecting an appropriate number of flat plates, separation from the final stage flat plate can be achieved. In this case, a sufficiently developed vortex has been generated by then, so the time required for separation is shortened, and a vortex with an extremely stable frequency is generated.However, in the low Reynolds number region, the instrumental error of the vortex flowmeter is There was a problem in that it had the characteristic of increasing temporarily in a positive manner.

Means for Solving the Problems Regarding the above problems, the present applicant conducted experiments focusing on the frequency ratio of generated vortices in a state where the vortex generating element is disposed in the flow path, and found that the flat plate in the prior art Simply provide the function of vortex amplification, replace the final stage with a flat plate, and set the vortex frequency to 0.7 to 0.9 with respect to the vortex frequency of the upstream generation element.
We have discovered that when vortex generating elements with a vortex frequency ratio of According to the above experiment, when there is no flat plate between the vortex generating elements, the stability of the vortex is poor, but by setting the spacing between the vortex generating elements and the vortex frequency ratio to the above values, the instrumental error characteristics are improved. Ru.

Embodiment FIG. 1(A) is a side sectional view of a vortex flowmeter according to the present invention, (
B) is a plan cross-sectional view, in which there is a vortex generating element 2a+2 in the flow path 1.
b are placed side by side, facing each other perpendicularly to the flow direction A, and a flat plate 2o is arranged parallel to each vortex generating element 2a, 2b between these vortex generating elements 2a, 2b. These vortex generating elements 2a, 2b.

The flat plates 2c cooperate to form a vortex generator. Further, the representative length d of the vortex generating element is the width of the upstream and downstream vortex generating elements 2a and 2b on opposing surfaces. flat plate 2
The optimal value for plate FX tb of c is tl = 0.1d to 0.4d, and the gap t with each vortex generating element is t = 0.1d.
~0.9d is required. The vortex signal is converted into an electric signal by an eddy detector (not shown), and is shaped and amplified by a preamplifier 3 for signal processing. In addition, in the figure, only one flat plate 2C is shown for explanation, but a plurality of flat plates 2C may be used, and they may be removed as necessary. Looking at the characteristics of conventional vortex flowmeters from the perspective of circulation, firstly, the vortex circulation at the moment when the vortex separates from the final plate is the sum of the circulation around each plate and the vortex circulation occurring between the plates. He will appear as peace. The vortex frequency is proportional to the flow velocity if the Strouhal number is constant, but when the Strouhal number is constant and the Strouhal number changes,
Naturally, it is proportional to the Strouhal number. Fluid mechanics shows that the Strouhal number is given as an inverse function of the magnitude of circulation. Therefore, in the conventional technology, the vortex frequency is determined by the above-mentioned circulation that has an amplifying effect on the vortices on the flat plate, so the vortex frequency becomes low in the high Reynolds number region where the amplifying effect is applied, but in the low Reynolds number region, the vortex on the flat plate side The amplification effect becomes smaller and the circulation of the upstream vortex generating element becomes dominant, and since the circulation is small, the vortex frequency increases and shifts to a positive instrumental difference. That is, the overall instrumental error characteristic is flat in the large flow rate region and becomes positive in the small flow rate region.

Although FIG. 1 shows an example in which the upstream vortex generating element 2a has an isosceles triangular shape and the downstream vortex generating element 2b has a rectangular shape, FIG. The change trend of the generated eddy frequency is shown. Here, we have excluded the circular-arc 2-C shape, etc., but these tend to be common to the isosceles triangle and rectangle. Figure 2 shows the trapezoidal shapes of I and TII, the triangular shapes of n and v, and the rectangular shapes of frequency, and (b) is in the middle. Even with the same shape, the vortex frequency differs depending on whether the representative length d is on the upstream or downstream side, and is lower in the former.

The latter generates high vortex frequencies. Therefore, in order to realize the present invention, the basic components shown in FIG. 2 can be combined. As a specific example, FIG. 3 shows the cross-sectional shape of the vortex generator. (a), (b).

(c), (d), (e), and (f) are upstream vortex generating elements 2
The downstream vortex generating element 2b is a combination of a trapezoidal arc, a rectangle, and a triangle, with a being an isosceles triangular shape, and by selecting the dimensions from the trend of the vortex frequency shown in Fig. 2, the flow direction A , or B. It is also possible to configure the structure so that the water flows in from either direction. (g) is a trapezoid and a triangle;
(h) is a combination of a triangle and a T-shape, and in this case, the inflow direction is limited to A.

As described above, according to the vortex flow meter of the present invention, the upstream vortex generating element and the downstream vortex generating element having a slightly lower vortex frequency are complementary to each other in Reynolds number characteristics. By obtaining a strong interaction, it is now possible to measure a wide range of flow rate of 1:50 or more, whereas the conventional flow rate range was 1:2C1 degree.Moreover, the amplification effect of the vortex is added, so a stable vortex can be measured. 6. Can provide flow meter

[Brief explanation of drawings]

FIG. 1(A) is a side sectional view of the vortex flow meter according to the present invention, FIG. 1(B) is a plan sectional view, and FIG. FIG. 3 is a sectional view showing a vortex generator as another embodiment. 1... Channel, 2a, 2b... Vortex generating element, 2c...
・Flat plate. Figure 1 Figure 2 r rl m vv 3rd Cσ diagram

Claims (1)

[Claims] The vortex generator includes a plurality of vortex generators disposed perpendicularly to the flow in the flow path, and the upstream vortex generator and the downstream vortex generator are arranged at a predetermined interval in the flow direction. and zero to a plurality of flat plates are placed side by side at equal intervals between the upstream vortex generating element and the downstream vortex generating element, and the representative length of each vortex generating element is on the opposing surface, and,
When each vortex generating element is individually arranged at the above position, the vortex frequency ratio generated is 0.0 with respect to the upstream vortex generating element.
A vortex flow meter characterized in that the flow rate is 7 to 0.9.