JP2559115B2 - Vortex detection method, vortex detection device, and flow measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention optically detects a vortex generated from a vortex generator in a flow velocity (flow rate) meter utilizing that the Karman vortex generation frequency is proportional to the flow velocity. Vortex detection method and device.

[Prior Art] A vortex flowmeter utilizing the fact that the Karman vortex generation frequency is proportional to the flow velocity has a simple structure, and various proposals have been made for practical use as a flowmeter which can obtain a flow rate signal as a digital value. ing.

With respect to the vortex generator itself, the shape, the related dimension ratio, etc. are selected, and if these are appropriate, a Karman vortex with a Strouhal number that is almost constant over a wide Reynolds number range is generated, and a wide range of flow rate is highly accurate. Can be measured at.

Various proposals have been made regarding the detection of vortices, and roughly classified, a method using the action of the lift force accompanying the generation of the vortex,
There is a method of detecting the vortex itself as a change in the velocity of the vortex.

The former (a vortex detection method that uses the action of lift) detects as a change in stress or strain of the vortex generator that is generated by the force acting on the vortex generator. Direct method of converting to electric signal with a gauge, etc. and pressure change generated on both sides of the vortex generator vibrates a magnetic body by electrostatic capacity, piezoelectric effect or alternating pressure, and this vibration is an electric signal by electromagnetic induction. It can be classified as an indirect method of converting into.

The latter (vortex detection method that detects a vortex as a change in its velocity)
In (1), a vortex is detected as a phase or amplitude modulation signal due to a change in resistance value due to heat dissipation of a heated thermistor, a resistance element such as a resistance wire, or a change in ultrasonic propagation velocity.

[Problems to be Solved by the Invention] In the vortex detection method in the vortex flowmeter described above, the processing of the vortex signal is performed on external turbulent vortices existing other than the Karman vortex, which are noise components mixed with the vortex signal. It is necessary to remove the resulting signal with a bandpass filter or the like, but this is problematic in terms of signal detection.

That is, in the method of detecting the lift force acting on the vortex generator, since the lift force that is synchronized with the generation of the vortex is a function of the square of the flow velocity, a signal in the range of the square of the flow rate to be measured is obtained. Must be detected. As a result, in the signal processing, first, a variable band amplifier for amplifying signals in this range to almost the same level signal is required. However, it is difficult to remove the influence of external noise because the S / N ratio deteriorates with the low level signal by this amplifier. From this point of view, the latter method of detecting the vortex itself is superior.

However, this latter method also has the following problems.

That is, conventionally, in a thermistor which is a thermal method as an example of this method and a detection method using a heat ray as a detection element, an element having a heat detection characteristic of a frequency characteristic corresponding to the vortex generation frequency is required, and this requirement is required. In order to reduce the heat capacity and increase the sensitivity of the resistance element that satisfies the above condition, the wire diameter is reduced and the resistance value is increased. As a result, there are many problems such as disconnection and lack of reliability.

Further, in the method of detecting a vortex by ultrasonic modulation, a sound absorbing material is attached to the inner surface of the flow channel in order to prevent the ultrasonic wave transmission signal from generating a standing wave due to temperature change or the like. This procedure
When the fluid is a gas, the sound absorbing material itself affects the fluid flow, and there is a problem including the need for the sound absorbing material.

Therefore, the present invention is a vortex detection method and device for a current meter that utilizes the fact that the Karman vortex generation frequency is proportional to the flow velocity, and is a vortex detection method that can detect the vortex itself with good response with a simple configuration. And to provide a device.

[Means for Solving the Problems] In order to achieve the above object, the vortex detection method according to the first invention of the present application generates a vortex in a fluid and imparts a thermal change to the passage portion of the vortex. It is characterized in that the generation frequency of the vortex is obtained by irradiating light and detecting an optical change of the irradiating light due to the vortex.

A vortex detection device according to a second invention of the present application is a temperature difference generating means for heating or cooling a vortex generator having an axis in a direction opposed to a fluid flow, and the vortex generator for generating a vortex by the vortex generator. A light irradiation unit that irradiates the wake portion with light and a light detection unit that detects light that has passed through the vortex are provided, and the generation frequency of the vortex is detected according to a change in the output of the light detection unit. Characterize.

As the vortex generator, various modes are possible,
Preferably, a striatum is used. Moreover, this linear body can use only a part of the longitudinal direction as a temperature difference generation part.

[Operation] The present invention is intended to optically detect a vortex in the above-described method for detecting the vortex itself. As the method for optically detecting, the vortex generator is directly heated or cooled, or the vortex generator is used. The fluid is heated or cooled near the upstream side of the separation point to cause a thermal change, and the resulting change in the density of the vortex is used to optically change the irradiation light to the vortex by refraction, etc. Then, the generation frequency of the vortex is detected as the amount of optical change.

For example, a vortex generator is arranged to face the flow, a voltage is applied to the vortex generator to heat it, and as a result, a Karman vortex street that flows along the vortex generator and separates and separates as a vortex, A parallel light beam is emitted in a direction orthogonal to this vortex row, that is, in a direction orthogonal to the flow and the vortex generator, and the change in the amount of light of the parallel light beam refracted by the vortex or the light beam converging in the vortex or in the vicinity thereof is detected by a photodiode or the like. It is detected by the photoelectric conversion means of (1) to generate a vortex signal. The frequency of the vortex signal determines the vortex generation frequency.

According to the present invention as described above, it becomes possible to detect the vortex itself with extremely high response, and the reliability is deteriorated due to the thinning of the detection resistance element as in the case of utilizing the resistance change which is the conventional direct detection method of the vortex. Also, there is no increase in thermal resistance due to the adhesion of dust, deterioration of responsiveness, etc., and no need to attach a sound absorbing material such as ultrasonic wave, so it does not affect the flow and the vortex velocity meter or vortex flowmeter can be used. It becomes possible to configure.

EXAMPLES Examples of the present invention will be described in detail below with reference to the drawings. In this embodiment, the fluid is water.

<Structure of Embodiment> FIG. 1 shows a cross-sectional view of an embodiment of the vortex detector according to the present invention, and FIG. 2 shows a vertical cross-sectional view thereof.

1 and 2, the vortex generator 2 is arranged in the diametrical direction inside the flow tube 1 for conducting the fluid to be measured, that is, facing the flow. The vortex generator 2 is a heating element such as a nichrome wire connected to the external power source E via the switch SW, and is electrically heated by the closed circuit of the switch SW during measurement. Therefore, when the flow tube 1 is made of an electrically conductive material, the vortex generator 2 is insulated from the flow tube 1 by the insulating wall 14 and fixedly installed through the insulating wall 14. In this case, it is desirable that the inner surface of the insulating wall 14 be level with the inner wall surface of the flow tube 1.

In the wake of the vortex generator 2, protective cylinders 12 and 13 extending outward are fixed to both wall surfaces of the flow tube 1 on a diameter axis orthogonal to the vortex generator 2. A window 11 is provided on the wall of the flow tube 1 to which the protection tubes 12 and 13 are attached. The window 11 is hermetically sealed with a material having good light transmittance. The laser diode 3 is arranged at the end of the protective cylinder 12. The laser light generated from the laser diode 3 is applied to the rod lens 5 arranged at the position of the focal length inside the protection cylinder 12, and becomes a parallel light or a light beam focused in the vortex or its vicinity by the rod lens 5. Head towards vortex S. A rod lens 6 for receiving the parallel light is provided outside the end opening of the protective cylinder 13, and a photodiode 4 is provided at the focal position of the rod lens 6.

<Operation of Embodiment> The operation of the above-described embodiment of the present invention having the above configuration will be described.

When the fluid to be measured flows in the direction of arrow Q in FIG. 1, Karman vortices are generated in the vortex generator 2 in a cycle that is inversely proportional to the diameter D of the vortex generator 2 and proportional to the flow velocity. This Karman vortex separates and flows out from the vortex generator 2 as a vortex column, but since the power source E is connected to the vortex generator 2 and it is heated, the vortex column is a fluid column whose density is different from that of the surrounding fluid. It is released into and gradually diffuses and mixes. However, the density change is large immediately after the vortex generator 2, and the laser light L undergoes an optical change such as refraction. When there is no flow, the laser beam is applied to the position of point P on the bottom of the protective cylinder 13. However, when a vortex is generated, it is refracted and the angle δ is generated.
Is bent like a dotted line, and light enters the rod lens 6 at a position deviated from the point P. When the photodiode 4 is arranged at the focal position of the rod lens 6, the photodiode 4
The electric signal is detected as a change in the amount of light with time of the density change in the process of the vortex column passing the laser light L.

Fig. 3A shows an example of the vortex detection signal. In the example shown in the figure, the line of the vortex generator has a diameter of 0.16
An example of the vortex signal when a nichrome wire of mm is used is shown.

In this embodiment, the flow velocity distribution can be obtained by moving the optical system along the longitudinal direction of the filament of the vortex generator and detecting the vortex frequency at each position. First
FIG. 3B shows the result of performing the flow velocity with respect to the position on the diameter in the flow tube 1.

FIG. 4 shows the vortex generator 2 in which the vortex generator 2 is not a uniform heating wire, but the heating wire 22 is arranged in the central portion and the both ends thereof are the conductors 21 and 23 having low electric resistance. In this case, only the flow velocity in the portion near the wake of the heat ray 22 is detected. By reducing the length of the heating wire 22, the partial flow velocity is obtained.

It is also possible to obtain the flow velocity distribution at each position in the moving direction by moving such a vortex generator 2 in the axial direction with a thickness that does not affect the flow distribution.
In this case, the optical system is moved corresponding to the axial movement of the vortex generator 2.

The vortex generator 2 may be an arbitrary shape, for example, the vortex generator 24 having a triangular cross section as shown in FIG.
In this case, the heating material is insulated from the vortex generator 24 by the insulating layer 25 made of alumina or the like, in a portion of the vortex generator 24 located in the upstream of the separation point 27 of the vortex generator 24. It is fixed by vapor deposition etc. and heated. The fluid flowing on the heating body thin film 26 is heated, and the vortex columns having a density difference are separated from the vortex generator 24 and flow down as in the case of FIG.

FIG. 5 (b) shows a front view when the vortex generator 24 is arranged in the flow tube 1, and the width D of the vortex generator 24 is set to a relative dimension ratio for generating the vortex most stably. To be

In the above embodiment, the separation point of the vortex generator 2 or 24
Although the method of heating the upstream portion of 27 has been described, a method of cooling the vortex generator may be used.

The hollow shaft 28 in FIG. 5 (a) is a refrigerant flow hole through which a fluid that cools the vortex generator 24, such as cold water or liquefied gas, passes.
By cooling the vortex generator 24, a density difference is given to the vortex. The cooling means may be provided by the Peltier effect or the like. The point is that the heating / cooling means gives an optical mark called a density difference to the vortex column that flows out from the vortex generator arranged in the flow of the fluid to be measured. The detection of the above-mentioned optical change for detecting the vortex is not limited to the photodiode, and may be a phototransistor or other photoelectric conversion element.

Further, in the above-mentioned embodiment, the light source is laser light, but white light may be used. Further, the fluid is not limited to water, and other liquids and even gas can be applied.

[Effects] As described above, according to the vortex detection method and device of the present invention, it is possible to detect the vortex itself with extremely high response, and it is possible to use the resistance change which is the conventional direct vortex detection method. In addition, there is no decrease in reliability due to thinning of the detection resistance element, increase in thermal resistance due to adhesion of dust, decrease in response, etc. Also, it is not necessary to attach a sound absorbing material such as ultrasonic wave, which affects the flow It is possible to configure a vortex velocity meter or a vortex flowmeter without giving the above.

Moreover, by selecting either heating or cooling of the vortex generator, the heating means suitable for the fluid can be selected, and the safety is high.

Furthermore, the method of heating by reducing the cross-sectional area of the vortex generator makes it possible to easily measure the flow velocity distribution.
There is no need to use an expensive and difficult-to-adjust device such as a laser Doppler system.

[Brief description of drawings]

FIG. 1 is a transverse sectional view of an embodiment of the vortex detector of the present invention,
FIG. 3 is a longitudinal sectional view of the device of FIG. 1 viewed from the flow direction, FIG. 3A is a graph showing an example of the vortex detection signal measured by the vortex detection method and device of the present invention, and FIG. 3B is the longitudinal direction of the vortex generator. FIG. 4 is a partial cross-sectional view of another embodiment of the present invention, FIG. 5 (a) is a cross-sectional view of a heating element of still another embodiment of the present invention, and FIG. 5 (b) is the fifth
It is sectional drawing which arrange | positioned the heat generating body of FIG. 1 …… Flow tube 2,24 …… Vortex generator 3 …… Laser diode 4 …… Photodiode 5,6 …… Rod lens 12,13 …… Protective cylinder

Claims (6)

(57) [Claims] 1. A vortex is generated in a fluid, the vortex is heated or cooled, and a passage portion of the vortex in the fluid is irradiated with light, and an optical change amount of the light passing through the vortex is measured as time. A method of detecting a vortex, characterized by detecting the vortex generation frequency from the optical change amount according to the progress. 2. A linear vortex generator is used to generate the vortex, the generation frequency of the vortex generated at each position along the longitudinal direction of the vortex generator is determined, and the longitudinal direction of the vortex generator is determined. The vortex detection method according to claim 1, characterized in that the flow velocity distribution is calculated. 3. A temperature difference generating means for heating or cooling the vortex generator so that the vortex generated from the vortex generator having an axis in the direction opposite to the flow of the fluid has a temperature different from that of the fluid. Light irradiating means for irradiating the passage portion of the vortex in the wake portion of the vortex generator with light, and in order to obtain the generation frequency of the vortex, the optical change amount of the light passing through the vortex is changed with time. A vortex detection device having a light detection means for detecting. 4. A temperature difference generating means for heating or cooling the vortex generator so that the vortex generated from the vortex generator having an axis in a direction opposite to the flow of the fluid has a temperature different from that of the fluid. The vortex generator has a light irradiating means for irradiating the passage portion of the vortex in the wake portion with light, and a light detecting means for detecting the light passing through the vortex. A vortex detector which is a body and also serves as the vortex generator. 5. A temperature difference generating means for heating or cooling the vortex generator so that the vortex generated from the vortex generator having an axis in the direction opposite to the flow of the fluid has a temperature different from that of the fluid. The vortex generator has a light irradiating means for irradiating the passage portion of the vortex in the wake of the vortex generator with light, and a light detecting means for detecting the light passing through the vortex. A vortex detector characterized by heating or cooling only a part of the generator in the longitudinal direction. 6. A temperature difference generating means for heating or cooling the vortex generator so that the vortex generated from the vortex generator having an axis in the direction opposite to the flow of the fluid has a temperature different from that of the fluid. A flow measuring device comprising: a light irradiating means for irradiating the passage portion of the vortex in the wake portion of the vortex generator with light; and a light detecting means for detecting the light passing through the vortex.