JPS642204B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Karman vortex flow meter that measures the flow rate or flow velocity of a fluid flowing in a pipe by utilizing Karman vortices generated in the fluid.

A Karman vortex flow meter that uses a ring as a vortex generator generally has a ring-shaped vortex generator 2 arranged concentrically within a pipe 1 and a vortex detector such as a thermistor installed downstream of the ring-shaped vortex generator 2, as shown in Fig. 1. It consists of a container 3 attached. The ring-shaped vortex generator 2 is arranged concentrically at a radius position corresponding to the average flow velocity of the flow in the pipe (indicated by arrow U), thereby making the vortex lines form a closed curve without being affected by the flow velocity distribution. A Karman vortex 4 can be generated, and this Karman vortex can be detected by the detector 3 to measure the flow rate or flow velocity of the fluid. In such a Karman vortex flowmeter, the Karman vortex 3 has instability of the vortex ring itself based on self-induced velocity, so it is inherently unstable on its own compared to a two-dimensional vortex, and therefore the vortex ring collapses. It had the disadvantage of being easy to use. Furthermore, depending on the condition of the pipe line 1, the flow within the circular pipe may cause distortion of the flow velocity distribution or swirling flow on the upstream side of the vortex generator 2, and these may disturb or obstruct the steady vortex generation. There was a drawback. Furthermore, the conventional Karman vortex flowmeter as shown in FIG. 1 has another problem in that it is difficult to install the vortex generator 2 vertically.

The purpose of this invention is to reduce the instability of the vortex ring itself based on self-induced velocity, and to obtain a more stable periodic Karman vortex downstream of the vortex generator.
Furthermore, it is an object of the present invention to provide an improved Karman vortex flowmeter that can be applied to usage conditions such as curved pipes and pipes where the inner diameter changes, where distortion of the flow velocity distribution and effects of swirling flow are a concern.

In other words, the Karman vortex flowmeter of the present invention measures the flow rate or flow velocity of fluid in a pipe by using Karman vortices, and has a central structure in which the head is dome-shaped, the body is columnar, and the tail end is cone-shaped. The body is fixed concentrically within the tube by a vane-like support structure with its head facing upstream of the fluid flow, and within an annular channel formed between the inner wall of the tube and the central structure. A ring-shaped vortex generator is attached concentrically by the vane-shaped support structure, and the Karman vortex generated by the ring-shaped vortex generator is detected to measure the flow rate or flow velocity of the fluid. , actively constricts and rectifies the flow on the upstream side of the ring-shaped vortex generator, stabilizes vortex generation and suppresses the collapse of the generated vortex ring, thereby creating a more stable cycle on the downstream side of the flow. In addition to making it possible to obtain a vortex, it has also become possible to measure flow rate and flow velocity without being affected by distortion of flow velocity distribution or swirling flow in curved pipes or pipes with varying inner diameters. In addition to greatly contributing to expanding the usage conditions of seed flowmeters, it also strengthens and stabilizes the support of the vortex generator.

An embodiment of this invention is shown below in Figures 2 and 3.
This will be explained in detail with figures. In FIGS. 2 and 3, reference numeral 1 indicates a conduit, and this conduit 1 is filled with fluid, and this fluid flows in the direction shown by arrow U. Reference numeral 5 denotes a streamline torpedo-shaped central structure, in which the head 5a is shaped like a hemispherical dome, the center part 5b is shaped like a column, and the tail end 5c is shaped like a cone whose diameter gradually decreases with respect to the flow direction of the fluid. has been done. This central structure 5
is fixedly supported in the pipe line 1 by radial vane-shaped support structures 6a, 6b, and 6c at its central part 5b, and is aligned with the central axis in the pipe line 1 with its head 5a facing upstream of the flow. They are arranged concentrically on a line. In this case, the head 5a and tail end 5c of the central structure 5 are connected to the vane-like support structures 6a, 6.
b, 6c protrude upstream and downstream from the leading edge and trailing edge, respectively.

In the body portion 5b of the annular flow path formed between the central structure 5 and the inner wall of the conduit 1, that is, in the annular flow path, a ring-shaped vortex generator 7 is provided with vane-like support structures 6a, 6b. , 6c and are disposed concentrically with the conduit 1 and the central structure 5.
These central structures 5 and vane-like support structures 6
a, 6b, 6c and the ring-shaped vortex generator 7 may, for example, be constructed integrally with each other, and the central structure 5
Ultrasonic transducers 8a, 8b, 8c and 9a, 9b, each forming a pair at a suitable location on the downstream side of the ring-shaped vortex generator 7 and the corresponding inner wall of the conduit 1.
9c is attached, and by detecting the number of generated vortices 10, etc., the flow rate or flow velocity of the fluid is measured.

In the Karman vortex flowmeter of the present invention having such a configuration, the head 5a of the central structure 5 in the fluid flow is formed in the shape of a hemispherical dome. In addition, the ring-shaped vortex generating body 7 is smoothly constricted, and a flow with a uniform velocity distribution is guided to the parallel portion of the body portion 5b on the downstream side. When functioning, stable generation of periodic Karman vortices is achieved. Further, since the body portion 5b and the tail end portion 5c of the central structure 5 are formed in a cone shape whose diameter gradually decreases, the Karman vortex 1 generated on the downstream side of the ring-shaped vortex generator 7
The instability of the vortex ring itself based on the self-induced speed of However, this flow can be rectified into a parallel laminar flow, and in this way, the flow is adjusted in the direction of the main flow of the parallel laminar flow, and the flow that has been throttled and accelerated is guided to the ring-shaped vortex generator 7. By swinging, a stable and periodic vortex train is formed.

Although various methods can be applied to detect the vortex 10, it is particularly preferable to use the vane-like support structures 6a, 6.
It is preferable to arrange pairs of ultrasonic transducers 8a, 8b, 8c and 9a, 9b, 9c in each fan-shaped area partitioned by b and 6c, and to average the detection results for each area. In other words, the drifted flow that occurs in the main stream due to the upstream pipe conditions is divided into independent flows and introduced in a distributed manner into each zone, and the frequency of the vortices in each divided flow is adjusted accordingly. A more accurate average flow velocity can be determined by independently detecting the flow rate using an ultrasonic transducer in the area and averaging the results. The transmission path of the ultrasonic waves may be perpendicular to the mainstream as in the illustrated embodiment, or may be diagonal to the mainstream to prevent multiple reflections. In addition to the above-mentioned method of detecting vortices using ultrasonic waves, for example, methods that measure flow velocity fluctuations around the ring-shaped vortex generator 7, pressure or fluid force acting on the ring-shaped vortex generator 7, etc. It is also possible to use a device that measures fluctuations in .

The present invention is as described above, in which the ring-shaped vortex generating body is fixed vertically and a stable Karman vortex is generated downstream thereof, and the generation of this vortex is periodic and there is little collapse of the vortex ring. In addition, the vane-shaped support structure also has a rectifying effect, allowing extremely accurate flow rate and velocity measurements, and can be applied to curved pipes and pipes with varying diameters, contributing to an expansion of usage conditions. It is important to do so.

[Brief explanation of drawings]

Figure 1 is a sectional view of the conventional example from the side of the pipe.
FIG. 2 is a rear view of an embodiment of the present invention as seen from the front of the pipe, and FIG. 3 is a sectional view taken along the line A--A in FIG. 1: Pipeline, 5: Central structure, 5a: Head, 5
b: body, 5c: tail end, 6a, 6b, 6c: vane-shaped support structure, 7: ring-shaped vortex generator, 8
a, 8b, 8c, 9a, 9b, 9c: Ultrasonic transducer, 10: Vortex.

Claims (1)

[Claims] 1. In a Karman vortex flowmeter that measures the flow rate or flow velocity of a fluid using Karman vortices in a pipe, a central structure with a dome-shaped head, a column-shaped body, and a reduced-diameter cone-shaped tail end is connected to the is fixed concentrically within the tube by a vane-shaped support structure toward the upstream side of the fluid flow, and a ring-shaped vortex generator is placed in the annular flow path formed between the inner wall of the tube and the central structure. The Karman vortex flow rate is characterized in that the Karman vortex is mounted concentrically by the vane-shaped support structure and the Karman vortex generated by the ring-shaped vortex generator is detected to measure the flow rate or flow velocity of the fluid. Total.