JPS62289729A - Karman vortex flow meter - Google Patents

Abstract

PURPOSE:To take a stable measurement even in the transient state of a flow velocity by forming a downstream columnar body so that its section is shaped almost in a slit circular curved surface and also rounding the edge of the isoceles triangular bottom part of the section of an upstream columnar body. CONSTITUTION:A columnar body 7 put in a flow of fluid at right angles consists of the upstream columnar body 5 and downstream columnar body 8. The upstream columnar body 5 is sectioned almost in an isoceles triangular shape and the downstream columnar body 8 is sectioned almost in the slit circular curved surface shape. The, the columnar bodies 5 and 8 are so arranged that their base parts 9 and 10 which have almost equal length (d) are held parallel at a specific interval (a) in the direction of the flow and cross the flow at the right angles. Further, the vertical angle alpha of the columnar body 5 is almost 90 deg. and the edge of the base part is rounded; and the height (h) of the columnar body 8 is 0.3-0.6d and the radius (r) is <=0.75d. This constitution stabilizes Karman vortexes against a transient change in flow velocity.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Technical Field to Which the Invention Pertains] The present invention relates to a Karman vortex that regularly occurs downstream of a columnar body vertically inserted into a fluid flow. From the column frequency λ,
Karman vortex flow meters are related to measuring the flow rate or flow rate of fluids.

[Prior art and its problems] FIG. 6 shows a schematic diagram of a conventional Karman vortex flow meter. In the figure, 1 is a pipe, 2 is a columnar body with one effect of one Karman vortex light generator, and 4 is a -1 vortex detection section.

The vortex detection unit 4 includes upper and lower housings 21.
22 is provided and holds 24 images.

By the way, as shown in FIG. 7, the columnar body 2 consists of an upstream columnar body 5 whose cross section is approximately isosceles triangular, and a downstream columnar body (6) whose cross section is approximately trapezoidal. inserted perpendicular to the flow.

Due to this columnar body 2, the pressure fluctuation of the Karman vortex 23 generated near both side surfaces passes through the openings 3A and 3B to the vortex detection unit 4.
introduced and detected. By the way, the length of the bottom of the upstream and downstream columnar bodies 5 and 6 is dl.

They are arranged perpendicularly to the flow direction of the conduit 1 with d2 being equal and at a constant interval a. For this reason, this columnar body 2 has a small pressure loss of the fluid and can obtain good flow characteristics with mouth linearity over a wide measurement range.

However, the columnar body 2 had the following problems. In other words, in the low flow velocity region of the fluid, the Karman vortex 23 generated from the downstream columnar body 6 formed in the shape of an isosceles trapezoid or the downstream columnar body 6
The visualization results reveal that the spacing of the vortices becomes irregular as they move away from each other, resulting in a rapid change in flow velocity from a low velocity region to a high velocity region, which continues to occur in a transient state. It is thought that the growth of the Karman vortex 23 may be hindered, and there is a possibility that the flow rate measurement may become unstable.

[Objective of the Invention] In view of the above-mentioned points, the present invention effectively solves the problems of the prior art, and enables the generation of Karman vortices to stably follow transient changes in flow velocity such as pulsating flow, and improves its accuracy. It is an object of the present invention to provide a Karman vortex flowmeter that can improve performance, has a simple configuration, and is easy to manufacture.

[Summary of the Invention] In order to achieve the above object, the present invention is characterized in that the downstream columnar body has a curved surface having a substantially split circle shape in cross section.

According to an embodiment of the present invention, in the downstream column state, the height h of the split circular curved surface is 0.3 to 0.0 of the length d of the base.
The radius r is ≦0.7 of the base length d.
5.

According to another embodiment of the invention, the downstream column has an isosceles triangular base with rounded edges.

(Embodiments of the invention) Next, embodiments of the invention will be described in detail based on the drawings.

FIG. 1 shows a schematic diagram of an embodiment of the present invention.

In the figure, parts having the same functions as those in FIG. 7 are given the same reference numerals. The columnar body 7 includes a downstream columnar body 5 and a downstream columnar body 8. The upstream columnar body 5 has a substantially isosceles triangular cross section, and the downstream columnar body 8 has a curved surface that has a substantially split circular cross section. Further, the upstream and downstream f main bodies 5, 8 are inserted perpendicularly, with the bottom portions 9.10 having approximately equal lengths d maintaining a predetermined distance a with respect to the fluid flow direction,
They are arranged parallel to each other and at right angles to the flow direction.

By the way, assuming that the apex angle of the downstream columnar body 5 having an isosceles triangular cross section is α, the height of the downstream columnar body 8 is h, and the radius of the curved surface is r, by determining each dimension as follows. , a stable Karman vortex with little pressure loss23
The experimental results revealed that this occurs. That is, the apex angle α of the upstream columnar body 5 is approximately 90 degrees. Further, the height h of the downstream columnar body 8 is set to 0.3 to 0.6 d, and the radius r is set to r≦0.75 d. Note that the upstream and downstream columnar bodies 5
．． The interval a of 8 is approximately 0.2 to 0.3 d.

Therefore, the separation point when the Karman vortex 23 generated by the columnar body 7 is generated from the downstream columnar body 8 as shown in FIG. The problem of instability of the Karman vortex 23 in the normal state is effectively solved.

Next, FIG. 2 shows a schematic diagram of an embodiment of the present invention. In the figure, the upstream columnar body 12 of the columnar body 11 is the bottom part 13.
There are two rounded radius marks on the edges. This means that when a pulsating flow in which the flow velocity transiently changes (increases) occurs as shown in FIG. 3, in the columnar body 7 shown in FIG. Karman vortex 23 from 8
It was confirmed from the visualization results that along with the generation of 0, a small vortex 23A with a high frequency was generated from the edge of the bottom portion 9 of the upstream columnar body 5. In the upstream columnar body 12 of this embodiment, whether this vortex 23A makes the generation of the Karman vortex 23 unstable, or
The roundness R of the edge of the bottom part 13 weakens the generation of the vortex 23A,
Therefore, as shown in FIG. 4, the Karman vortex 23 is stably generated.

Next, FIG. 5 shows a characteristic diagram showing the following state of Karman vortex generation when the fluid generates a pulsating flow. In the figure, V is the flow velocity of the fluid pulsating at pulsation amplitude ΔV1 or Δ2, Δp
a is the pressure based on the Karman vortex generated near the columnar body 7 according to the present invention shown in FIG. 1, and Δpb is the pressure ' due to the Karman vortex generated near the columnar body 2 in the conventional device shown in FIG. 7. I'll go. Thus, Fig. 3 (△) shows the respective pressures ΔPa, △Pb during the fluid pulsation amplitude △V1, while Fig. 3 (B) shows the fluid pulsation amplitude △2 (〉△
Pa to each pressure in the same way as in V1).

Indicates Δpb.

According to FIG. 3(A), when the fluid pulsation amplitude ΔV1 is (
Both the pressure △Pa due to the Karman vortex generated near the one-character body 7 according to the present invention and the pressure △Pb based on the Karman vortex generated near the columnar body 2 in the conventional device follow the applied pulsation amplitude well. It can be seen that good pressure fluctuations are occurring.

However, according to FIG. 3(B), when the pulsation amplitude of the fluid becomes large and reaches ΔV2 (>ΔVl), the pressure Δ due to the Karman vortex generated near the columnar body 7 according to the present invention
Pa follows the pulsation amplitude △V2 well and produces good pressure fluctuations, or the pressure △Pb based on the Karman vortex generated near the columnar body 2 in the conventional device is indicated by a dot-dashed circle. As a result of the actual test, it became clear that the pressure fluctuations were disturbed without following the pulsation amplitude ΔV2. Therefore, according to FIG. 3(B), it can be seen that even if the pulsation amplitude becomes large, in the case of the columnar body 7 according to the present invention, the Karman vortex is stably generated.

[Effects of the Invention] As described above, the present invention provides a structure in which a columnar body is formed into a groove by an upstream columnar body having an approximately isosceles triangular cross section and a downstream columnar body having a curved surface having a cross section approximately in the shape of a split circle. By making the lengths of the bases of the upstream and downstream columnar bodies approximately equal, parallel to each other, with a predetermined interval, and perpendicular to the flow direction, and further rounding the edges of the bottoms of the upstream columnar bodies, The technical problem has been effectively solved, the Karman vortex from the downstream columnar body is accelerated, and the growth of the subsequent Karman vortex is not hindered, so even when the flow velocity changes are very large,
It is possible to follow this and generate a Karman vortex,
In addition, the structure is simple, manufacturing is easy, and measurement efficiency is improved.

By the way, according to Japanese Patent Publication No. 54-37511, a vortex generating body is known which is composed of a trapezoidal cross-sectional upper civil society-like body and a semicircular cross-sectional downstream +↑ main body. However, in the case of such a vortex generator, since the upstream columnar body has a trapezoidal cross section, the direction can be changed at the upper base perpendicular to the flow direction at the trapezoid's upper base etch &[-. The problem is that the flow collides with the original flow, causing turbulence, resulting in a loss or increase in pressure.

On the other hand, compared to such known vortex generators, the present invention (
When generating a single Uru vortex, the upstream columnar body is formed to have an approximately isosceles triangular cross section, and as a result of experiments it has been found that a strong and stable vortex is generated and the pressure loss is the lowest. Furthermore, it has been found that when the apex angle of the triangle is about 90 degrees, good characteristics can be obtained both in steady state and in transient state.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment of the present invention, FIG. 2 is a schematic diagram of another embodiment of the present invention, and FIG. 3 is a diagram of the Karman vortex generation state of the columnar body shown in FIG. Figure 4 is a state diagram of Karman vortex generation in the columnar body shown in Figure 2, Figure 5 is a diagram showing the following state of Karman vortex generation when fluid or pulsating flow is generated, and Figure 6 is a diagram of the conventional Karman vortex generation state. Schematic diagram of vortex flow meter, No. 7
The figure is a schematic diagram of the columnar body shown in FIG. 6. 5, "12: Upstream main body, 7.11-Column body, 8: Downstream column body, 9.10: Base part, A: Spacing, R: Roundness. Patent applicant Fuji Electric Co., Ltd. + p7"'J Figure 1゛) Figure 3]

Claims (1)

[Claims] 1) In order to measure the flow velocity or flow rate from the frequency of the Karman vortex street generated in the vicinity of the columnar body inserted into the flow of fluid, the columnar body is constructed so that the cross-sectional shape is approximately an isosceles triangle. It is composed of an upstream columnar body and a downstream columnar body shaped into a shape, the lengths of the bottom sides of the upstream columnar body and the downstream columnar body are approximately equal, and the base sides are parallel to each other and are spaced at a predetermined interval. The Karman vortex flowmeter is arranged perpendicularly to the flow direction of the fluid, wherein the downstream columnar body has a curved surface having a substantially split circular cross section. 2) In the Karman vortex flowmeter according to claim 1, the height of the curved surface of the downstream columnar body is approximately 0.3 to 0.6 times the length d of the base portion; A Karman vortex flowmeter characterized in that its radius r is ≦0.75 of the length of the base portion. 3) In the Karman vortex flowmeter according to claim 1 or 2, the upstream columnar body having a substantially isosceles triangular cross section has a rounded bottom edge. A Karman vortex flow meter characterized by the following features: