JPH0572219A - Method and apparatus for detecting velocity of fluid - Google Patents

Abstract

PURPOSE:To enable execution of highly precise detection by a method wherein a pressure in an internal space of a surrounding body in the wall surface of which a hole is bored is made to fluctuate at a prescribed frequency, the hole of the wall surface is so disposed as to be in contact with the flow of a fluid and the velocity of the fluid is calculated from a change in the pressure generated. CONSTITUTION:First and second surrounding means 12a and 12b have holes 13 and 14 bored in the wall surfaces thereof respectively, while a third surrounding means 12c has no hole bored in the wall surface. These means 12a to 12c are provided adjacently and the wall surfaces of the means 12a to 12c are formed partially of elastic vibrating bodies 15a and 16a. Moreover, a fluid is made to flow through so that it comes into contact with the holes 13 and 14 provided in the means 12a and 12b and a pressure fluctuation is generated in the means 12b through one hole 14. Fluctuations in the means 12a and 12c accompanying the aforesaid pressure fluctuation are detected by sound pressure detecting means 17 and 18 and the velocity of the fluid is measured therefrom.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid velocity detecting method and apparatus for detecting the velocity (flow velocity) of a fluid flowing through a pipe or the like.

[0002]

2. Description of the Related Art As a conventional fluid velocity detecting method, an air flow sensor will be described as an example. That is, in the air flow sensor, a thin heater wire is arranged in the gas flow so as to be orthogonal to the gas flow direction, a constant current is supplied to the heater wire in a pulsed manner, and the resistance change due to heat radiation of the heater wire is changed. By detecting, the flow velocity of the flowing fluid was detected.

[0003]

However, in such a conventional fluid velocity detecting method, since the heater wire is in direct contact with the fluid, dust, chemical vapor, etc. are mixed into the fluid. If it is attached to the heater wire, or the surface of the heater wire is in direct contact with the chemical vapor in the fluid for a long period of time, the heat dissipation state changes over time, There is a possibility that the thermal relationship between the fluid and the heater wire may change and the error may gradually increase.

Further, since a very thin heater wire is used in order to obtain a large change in the resistance value of the heater wire, when the dust is large and it moves at a high speed, the heater wire is very Since a large external force may cause plastic deformation, it is necessary to provide a filter on the windward side.

Furthermore, since an external force proportional to the velocity of the fluid hits the thin heater wire and the heater wire always acts on the fluid as a flow resistance, when the fluid with high velocity is to be measured, the heater is used. There is a risk that the wire will be stretched and the measurement error will increase, and that if the external force acts so as not to exceed the elastic limit of the heater wire, the heater wire will have a resistance value different from the initial resistance value.

The present invention solves the above-mentioned problems by adapting the principle of acoustic technology, that is, a research field of a completely different student from the above-mentioned technical field, for example, as an acoustic component. To propose a fluid velocity detecting method and its device, which can simplify the measuring method by using a generally well-known speaker and a microphone, which is cheaper, more accurate, and has a simpler device configuration than ever before. With the goal.

[0007]

According to the present invention, the pressure in the internal space of an enclosure (enclosure means) having a hole formed in a wall surface is varied at a predetermined frequency, and the hole in the wall surface is measured. The fluid is arranged so as to come into contact with a flow of a certain fluid, and the velocity of the fluid is calculated based on the pressure change in the internal space of the enclosure generated thereby.

[0008]

The fluid velocity method and apparatus according to the present invention are
The pressure of the gas in the enclosure is changed by changing the pressure of the gas in the enclosure at the Helmholtz resonance frequency determined by the dimensions of the enclosure, the hole, etc., and the pressure in the enclosure means at that time by acting with the fluid to be measured through the hole of the enclosure. The velocity of the fluid is simply measured by detecting the variation.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An outline of the theory of the basic principle of the present invention will be described with reference to FIG. In FIG. 1, reference numeral 1 is a pipe having a wall thickness h, and a gas (fluid) to be measured flows from one end A to the other end B at a flow velocity V _f . 2 is the pipe 1
The small-diameter hole 2r having a diameter 2r formed in the wall surface of the pipe 3 is a sound pressure generating means such as a speaker, which is arranged to face the hole 2 formed in the wall surface of the pipe 1 at a predetermined interval. Driven by frequency. Reference numeral 4 denotes a diffracted wave of a sound wave generated by the sound pressure generating means 3 (which has the same meaning as the sound pressure here) becomes a compressional wave and is diffused and formed in an arc shape after passing through the hole 2.

Next, the principle of obtaining the flow velocity V _f based on the above basic configuration will be described with reference to FIGS. 2 to 4. First, as shown in FIG. 2, a cylinder of air (density ρ) having a diameter 2r and a thickness (wall thickness) h is formed in a portion of the hole 2 formed in the wall surface of the pipe 1 as shown by the diagonal lines. It is considered that the acoustic tube 5 having a diameter 2r and a length h in terms of acoustics is formed thereby. The sound pressure generating means 3 is arranged so as to face the acoustic tube 5 from below (see FIG. 1), and the sound pressure generating means 3 is driven by a sine wave at a predetermined frequency.

Here, when the sound pressure generating means 3 is driven by a sine wave at a predetermined frequency, at the upper open end of the acoustic tube 5,
As shown in FIG. 3, a cylindrical air portion (mass: m) 6 of air (density ρ) having a radius r and a thickness (πr) / 2 is generated by the sound pressure generating means 3 and the air spring (in the acoustic tube 5). It is considered that the air spring 1c in FIG. 6 and the single vibration up and down at a velocity V _v (t) (displacement: X (t)). At this time, the mass m of the cylindrical air portion 6 (hereinafter referred to as additional mass) is expressed by the following equation.

[0012]

[Equation 1]

However, (π · r) / 2 can be theoretically calculated. Also, the kinetic energy of this vibration system is
(1/2) m · v _v ² .

Here, as shown in FIG. 1, the gas flows in the pipe 1 from the direction A to the direction B at the flow velocity V _f , and the gas also flows at the upper end surface of the acoustic tube 5 at the velocity V _f . Assuming that, the cylindrical air portion 6 in the portion of the additional mass m shown by the diagonal lines in FIG. 3 receives an external force by the gas flowing from the A direction, and the velocity V _f is shown by the diagonal lines C and D in FIG. Is flowed downstream (direction B) by an amount proportional to (indicated by L in FIG. 4). As a result, the cylindrical air portion 6 in the portion shown by the solid line in FIG. The energy stored in the portion of the additional mass m of is also carried away by the flow of air in the leeward direction, that is, in the B direction.
In other words, energy dissipation occurs. Therefore, when a displacement amount (displacement amount) L occurs during the time t and the plane sectional area of the portion of the additional mass m is A

[0015]

[Equation 2] Becomes However, K is a constant. The amount of energy D · t dissipated during time t is

[0016]

[Equation 3]

Energy amount D dissipated per unit time
Is

[0018]

[Equation 4]

However, d = (mKV _f ) / (πr ² ). Substituting equation 1 into equation 4

[0020]

[Equation 5]

At this time, the velocity V _f of the fluid is

[0022]

[Equation 6]

[0023] That is, if the damper coefficient d of the acoustic tube 5 is known, the flow velocity V _f can be known.

Next, each specific configuration will be shown, and how to obtain the damper coefficient d and how to obtain the flow velocity V _f will be described with reference to FIGS. 5 and 6. First, it demonstrates based on FIG. In the figure, the same components as those in FIG. 1 or their equivalents are designated by the same reference numerals and the description thereof will be omitted.

In the figure, 7 is a hole 2 formed in the wall surface of the pipe 1.
Airtight housing that covers the outside from the outside (enclosure)
A sound pressure generating means 10 such as a thin speaker is attached to the wall surface of the housing 7 so as to form a part of the wall surface. The sound pressure generating means 10 has a volume V _{0 of the} housing 7 and a hole 2 Drive circuit 1 in which the output frequency is set to the Helmholtz resonance frequency determined by the size of the diameter 2r of the
1 drives a sine wave to change the internal pressure in the housing 7 at the Helmholtz resonance frequency.

Although the hole 2 is formed in the wall surface of the pipe 1 in FIG. 5, part of the wall surface of the housing 7 forms a part of the wall surface of the pipe 1, and the hole 2 is formed in the wall surface.
May be provided and the wall surface may be shared, and the shape of the hole 2 may be not only a circle but also a rectangle such as a rectangle or a square, and the size and shape thereof are determined by design specifications at that time. Needless to say. Reference numeral 8 is a condenser microphone (sound pressure detection means), which is mounted in the housing 7 and has a pressure (sound pressure) in the housing
Detect fluctuations. Reference numeral 9 is a coefficient circuit including an amplifier circuit,
The detection output from the microphone 8 is amplified by a predetermined amplification factor to detect and output the air flow velocity V _f in the pipe 1.

Next, the calculation logic of the damper coefficient d of the acoustic tube 5 based on the configuration shown in FIG. 5 will be described with reference to FIG.

First, in FIGS. 5 and 6, P ₀ is the atmospheric pressure, ΔP (t) is the change amount of the pressure (sound pressure) in the housing 7 generated by the driving of the sound pressure generating means 10, and X (t ) Is the vertical displacement of the cylindrical air portion 6 forming the additional mass m generated in the hole 2 of the pipe 1, U (t) is the displacement of the pressure receiving surface of the sound pressure generating means 10, and r is the pipe. Radius of the hole 2 of 1 (also the radius of the cylindrical air portion 6 forming the additional mass m),
V ₀ is the actual space volume in the housing 7, S is the area of the pressure receiving surface of the sound pressure generating means 10, γ is the specific heat ratio of the gas (1.4 in the case of air), V _f is the flow velocity of the gas to be measured, A is additional mass m
5 is a cross-sectional area (opening area of the hole 2) of the columnar air portion 6 forming m, m is the mass of the columnar air portion 6 (additional mass), and d is a damper coefficient generated in the acoustic tube 5. The configuration can be considered equivalent to the physical model of the vibration system shown in FIG.

That is, the portion of the cylindrical air portion 6 in the physical model is the additional mass m of the cylindrical air portion 6 itself,
It is composed of control elements such as an air spring 1c generated in the housing 7 and a damper 1b generated in the acoustic tube 5.
Therefore, in FIG. 6, the following equations 7 and 8 are established.

[0030]

[Equation 7]

[0031]

[Equation 8]

The above equations 7 and 8 are Laplace transformed and arranged. Here, since it is a prerequisite that the flow velocity V _f of the gas in the pipe 1 and the damper coefficient d are in a proportional relationship, when the drive frequency of the sound pressure generating means 10 is set to the Helmholtz resonance frequency as described above. , Its resonance angular frequency ω _r is

[0033]

[Equation 9]

By

[Equation 10]

Can be set. Ie

[0036]

[Equation 11]

Is satisfied. Next, from the above equation 11, ΔP
The transfer function from (s) to U (s) is

[0038]

[Equation 12]

In Equation 12, the drive frequency (or drive angular frequency) of the sound pressure generating means 10 is set to the Helmholtz resonance frequency (Helmholtz resonance angular frequency), and the drive voltage is set to a sine wave having a constant peak value. So U
(iω) = constant value, ΔP (iω) = output voltage value of the microphone 8 can be set. Therefore, by calculating the damper coefficient d from the above equation 12 by arithmetic calculation and substituting the result into the equation 6,

Then, the flow velocity V _f of the fluid to be measured is obtained.

Next, FIG. 8 shows an input / output characteristic diagram obtained by making an experiment with the above structure and conducting an experiment. As shown in this input / output characteristic diagram, the input / output characteristic of the flow velocity detecting device is shown to be linear.

Next, based on the apparatus shown in FIG.
That is, a flow velocity detection method and apparatus of an embodiment that does not use a sound pressure changing means such as a speaker will be described. In FIG. 7, FIG.
The same components as those shown in (1) or their equivalents are denoted by the same reference numerals and the description thereof will be omitted.

That is, in the figure, 12 is a housing (enclosure), which is a first housing (first housing) having the same volume.
An enclosure 12a and a third housing (third enclosure),
Second volume having a volume V _h slightly smaller than the volume of the housing (volume smaller by expansion ΔV due to turbulent flow generated)
The first housing 1 is composed of a housing (second enclosure).
The upper wall of 2a has a first hole 13 formed therein, and communicates with the inside of the pipe 1. The second housing 12b also has a second hole (same as the opening area of the hole 13) 14 in the upper wall thereof. The side walls of the first housing 12a and the second housing 12b adjacent to each other are shared by a partition plate 15, and a part of the partition plate 15 is formed of an elastic diaphragm 15a. The second housing 12
The adjacent side walls of b and the third housing 12c are also
It is shared by the partition plate 16, and a part of the partition plate 16 is also formed of the elastic vibration plate 16a.

Both of the elastic diaphragms 15a and 15b have the same shape and the same characteristics, and the first diaphragm
The holes 13 in the first housing 12a do not generate turbulence due to the gas flowing in the pipe 1, that is, do not generate sound, and turbulence occurs in the second holes 14 described later. An opening is formed so that the turbulent flow (the frequency component of this turbulent flow is set to include a frequency component that causes Helmholtz resonance) easily enters the second housing 12c. A pair of rectifying plate members 13a and 13b are provided in parallel on the windward side and the leeward side of the pipe 1 inward of the pipe 1 and toward the downstream side of the flowing fluid. From the upper side, the first flow direction changing plate 1 is directed toward the inside of the second housing 12b.
4a is extended, and the second flow direction changing plate 14b is extended in parallel from the leeward side toward the windward side in the pipe 1.

Reference numeral 19 denotes a differential amplifier circuit, which is the third housing 1
A detection output from a microphone (having the same characteristics as the first microphone 17) 18 for detecting a sound pressure fluctuation in 2c, and a first microphone provided in the first housing 12a for detecting a sound pressure fluctuation in the first housing. The difference from the detection output output from 17 is calculated, and the difference is multiplied by a predetermined coefficient to output a signal. Reference numeral 20 denotes a first coefficient circuit, which is provided in the third housing 12c, receives a detection output output from the second microphone 18 that detects a sound pressure fluctuation in the third housing, and inputs a predetermined coefficient into the input signal. Multiply and output.

Reference numeral 21 is a first absolute value circuit, which is a first coefficient circuit 2
The absolute value of the output signal from 0 is calculated. A second absolute value circuit 22 receives the output from the differential amplifier circuit 19 and obtains its absolute value. 23 is a first absolute value circuit 21 and a second absolute value circuit
Each output signal from the absolute value circuit 22 is input, and the output signal from the first absolute value circuit 21 is input to the second absolute value circuit 22.
Divide by the output signal from and output the division result. A second coefficient circuit 24 multiplies the output signal from the division circuit 24 by a predetermined coefficient to obtain the target fluid velocity V _f .

Next, the logic by which the damper coefficient d and the flow velocity V _f are calculated by using the structure shown in FIG. 7 will be described. That is, ΔP ₁ (t) is the second housing 12b
Due to the turbulent flow guided inside, the internal pressure change amount (sound pressure change amount) ΔP ₂ (t) in the first housing 12a induced via the elastic vibration plate 15 is guided into the third housing 12b. Turbulent flow induced by the turbulent flow through the elastic diaphragm 16a, the internal pressure change amount in the third housing 12c, ΔP is the internal pressure change amount generated by the turbulent flow guided in the second housing 12c, P ₀ Is the atmospheric pressure, X (t) is the vertical displacement of the air column 6 generated in the hole 13 portion of the pipe 1, U (t) is the displacement of the elastic diaphragms 15a, 16a in the vibration direction of the pressure receiving surfaces, r is the radius of the hole 13 of the pipe 1 (also the radius of the air column 6),
V ₀ is the actual space volume of both chambers 7a and 7b, S is the area of the elastic diaphragms 15a and 16a, γ is the specific heat ratio of gas (fluid) (1.4 in the case of air), and V _f is in the pipe 1. Flow velocity of the gas, A is the cross-sectional area of the air column 6 (equal to the opening area of the holes 13 and 14), k _s is the spring constant of the elastic diaphragms 15a and 16a, m is the mass of the air column 6, and d is the sound. Set as a damper coefficient generated in the pipe 5, and formulating a sound pressure fluctuation in the first housing 12a and the third housing 12c

[0048]

[Equation 13]

[0049]

[Equation 14]

However, m = ρ (π / 2) rA d = K (π / 2) rρV _f k = (γP ₀ / V ₀ ) A ²

[0051] Further, the elastic diaphragm 15a, erected an expression for the force acting on each of 16a and U (s) = (△ P / k s) · S. Here, considering the second housing 12b, the second housing 12b swells a little due to turbulent flow entering through the flow direction changing plates 14a and 14b projecting from the peripheral portion of the second hole 14. Assuming that the volume before swelling is V _h and the pressure of the turbulent flow that enters is ΔP _d , the formula for the sound pressure change in the second housing 12b is established.

[0052]

[Equation 15] Further, when formulating the force acting on the added mass m,

[0053]

[Equation 16] If you convert the number 16 by Laplace conversion and arrange

[0054]

[Equation 17] Here, substituting Equation 17 into Equation 15 and rearranging

[0055]

[Equation 18] Here, if the volume V of the second housing 12b is set as in the following Equation 19,

[0056]

The maximum bulge amount V _h of the second housing 12b is

[0057]

[Equation 20] Here, from Equations 13 and 14, ΔP
_{When 2} (t)-△ P ₁ (t) is calculated

[0058]

Since the pressure fluctuation in the first housing 12a fluctuates at the Helmholtz resonance frequency, ms ² + k = 0 at the angular frequency ω _r.

[0059]

Since (Equation 22) (the output of the differential amplifier circuit 19), Δ
Taking the ratio of the absolute value of P ₂ (t) and the absolute value of ΔP ₂ (t) −ΔP ₁ (t)

[0060]

(23) (the output of the division circuit 3). Furthermore, the number 6
Substituting equation 23 into

[0062]

[Equation 24] And the fluid velocity V _f is

[Equation 25] is obtained, and the characteristic according to the experimental result is shown in FIG.
The linearity like is obtained. As shown in Equation 25,
Since the equation does not include the term of the speed of sound C _0, the flow velocity V _f can be obtained regardless of the ambient temperature.

Further, the structure described with reference to FIG.
The case where the temperature in the manufacturing process of the device and the temperature in the place of use are almost the same is targeted, but in the case where the temperature is different or the temperature greatly changes during use, the case shown in FIG. As shown in FIG.
Even when the pressure fluctuations due to the ambient temperature change occur in any of the first to third housings 12a, 12b and 12c, the first to third housings 12a are provided via the fine holes 26a and 26b. The static pressure (meaning a loose pressure change) may be made to be the same by circulating the air of Nos. 12, 12b and 12c. In FIG. 8, a screw hole is provided in the bottom wall of the second housing 12b, and a bolt 25 is screwed into the screw hole so that the volume of the second housing 12b can be adjusted.

[0064]

As described above, according to the present invention, the first and second enclosing means having holes formed in the wall surface and the third enclosing means having no holes formed in the wall surface are provided adjacent to each other. A part of the wall surface of the adjacent first to third enclosures is formed of an elastic vibrating body, and a fluid is circulated so as to contact the holes and the holes provided in the first and second enclosure means, A fluid characterized in that a pressure fluctuation is generated in the second surrounding means through the one hole, and the velocity of the fluid is obtained based on the magnitude of the pressure fluctuation in the first surrounding means due to the pressure fluctuation. A velocity detecting method and a first enclosing means and a second enclosing means, each of which is provided with a hole in each wall surface, and each of the holes is positioned so as to be in contact with a fluid flow; In order to propagate the pressure fluctuation, the first to And a flow velocity detecting means for calculating the velocity of the fluid based on pressure fluctuations in the first and third surrounding means. Since it is a fluid velocity detection device that operates, the measurement method is simplified, the flow velocity can be measured accurately, the measurement device becomes inexpensive, and the maintenance management is very effective. Is demonstrated. Also, since it can be created with a small-scale manufacturing facility, it has an extremely large industrial effect that requires less capital investment.

[Brief description of drawings]

FIG. 1 is a configuration explanatory view for explaining the principle of the present invention.

FIG. 2 is an operation explanatory view for explaining FIG.

FIG. 3 is an operation explanatory view for explaining FIG. 1.

FIG. 4 is an operation explanatory view for explaining FIG. 1.

FIG. 5 is a diagram shown for explaining the basic principle of the present invention.
It is a structure explanatory view which materialized the structure explanatory drawing of.

FIG. 6 is a physical model of a vibration system equivalent to the model of the configuration explanatory diagram shown in FIG.

FIG. 7 is a diagram for explaining an example of the present invention.

FIG. 8 is an explanatory diagram illustrating another embodiment of the embodiment shown in FIG.

9 is a graph showing an experimental result (accuracy) according to the example shown in FIG.

[Explanation of symbols]

 1 Pipes 2, 13, 14 Holes 3, 10 Speakers (sound pressure generating means) 7, 12a, 12b, 12c Housings 8, 17, 18 Microphones (sound pressure detecting means) 9, 20, 24 Coefficient circuit 11 Driving circuit 13a, 13b Rectifying plate members 14a, 14b Flow direction changing plate 19 Differential amplifier circuit 21, 22 Absolute value circuit 23 Dividing circuit

[Equation 13]

[Equation 13]

[Equation 14]

[Equation 14]

[Equation 15]

[Equation 15]

[Equation 16]

[Equation 16]

[Equation 17]

[Equation 17]

[Equation 18]

[Equation 18]

[Formula 19]

[Formula 19]

[Equation 20]

[Equation 20]

[Equation 21]

[Equation 21]

[Equation 22]

[Equation 22]

[Equation 23]

[Equation 23]

Claims (2)

[Claims] 1. First and second enclosing means (12a) and (12b), wherein holes (13) and (14) are formed in the wall surface,
And third enclosing means (12c) in which no hole is formed in the wall surface
Are provided adjacent to each other, and the adjacent first to third
Part of the wall surface of the enclosure is made up of elastic vibrating bodies (15a), (16
a), and a fluid is circulated so as to come into contact with the holes (13) and (14) provided in the first and second enclosing means (12a) and (12b), and the one hole ( 14) to generate a pressure fluctuation in the second enclosing means (12b), and to obtain the velocity of the fluid based on the magnitude of the pressure fluctuation in the first enclosing means (12a) accompanying the pressure fluctuation. Characteristic fluid velocity detection method. 2. Holes (13), (14) on each wall
A first enclosing means (12a) and a second enclosing means (12b), each of which is positioned so as to be in contact with a fluid flow, and a third enclosing means (1) which is closed.
2c), and the first to third for transmitting the pressure fluctuation
The velocity of the fluid is calculated based on the vibration transmission means (15a) and (16a) formed on the respective wall surfaces of the enclosing means and the pressure fluctuations in the first and third enclosing means (12a) and (12c). Flow velocity detecting means (17, 18, 1)
9, 20), and a fluid velocity detecting device.