JP2761122B2 - Vortex flow meter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vortex flowmeter, and more particularly, to a vortex flowmeter for measuring a flow rate in two directions. 2. Description of the Related Art As is well known, a vortex flow meter is a flow meter utilizing the fact that the frequency of occurrence of a vortex is proportional to the flow velocity in a predetermined Reynolds number range. Conventionally, a vortex flowmeter has been required to generate a stable vortex constantly and to have a wide Reynolds number range in which a constant of proportionality (Strouhal (St) number) is constant. It has been done. In the technology for this, the shape of the vortex generator has been an important theme. The generation of the vortex is based on the separation of the fluid from the vortex generator.Therefore, the condition of the vortex generator is excellent in that the separation point is not affected by the Reynolds number and is always constant. Has become. For this reason, the cross-sectional shape of the vortex generator is required to be easy to separate in the flow direction, and a cross-sectional shape that is asymmetric in the flow direction and has a large drag coefficient is selected. For this reason, the conventional vortex flowmeter is a flowmeter that can usually measure only the flow rate flowing in one direction. However, the flows in the flow measurement line to which the vortex flowmeter is applied are not necessarily in the same direction, and there are flows in the opposite direction. In such a case, two vortex flowmeters were interposed for flow measurement in the forward and reverse directions. For this reason, a vortex flowmeter capable of measuring in both forward and reverse directions has been required. The applicant of the present application discloses in Japanese Utility Model Publication No. 55-45296 "Vortex flow meter" that two vortex generators having a triangular cross section and the same size are formed in the main body in the flow direction. A vortex flowmeter with the bottoms facing each other was proposed. In the vortex generator, a flow flowing along a slope of an isosceles triangle having a vertex in a flow direction is caused by a pre-fault that separates near a vertex of a bottom surface and is involved in a slope of an isosceles triangle of a downstream vortex generator. This is based on the generation of vortices.
Usually, in a state where the bottom surfaces are joined, the shape becomes close to a so-called streamline, and vortices are not generated stably. Therefore, in the vortex generator, the bottom surfaces are opposed to each other, and between the opposed bottom surfaces,
By adding the flow of suction and blowing generated by the pressure difference, the separation was forced and stable vortex generation was enabled. However, the stability of vortex generation is a large requirement for constructing a vortex flowmeter, but does not always provide a constant Strouhal number over a wide range of Reynolds numbers. The vortex flowmeter can also be used in a narrow flow range, but is not suitable for use in a wide flow range, because the Strouhal number is not constant at a wide Reynolds number and the accuracy of the flowmeter is reduced. Was. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has an object to provide a vortex generator that generates a stable vortex with a constant and constant Strouhal number in a wide flow rate range in the forward and reverse flow directions. The purpose of the present invention is to provide a vortex flowmeter having the above. According to the present invention, in order to achieve the above object, (1)
In a vortex flowmeter in which a vortex generator is disposed in a flow tube and the flow rate is detected from the number of vortices generated per unit time, the vortex generator is moved in a direction in which the cross section of the vortex generator is perpendicular to the flow direction and flow Each of which is symmetrical to the axis and has a shape with the maximum width on the axis of symmetry, protrudes at a symmetric axis position in the direction perpendicular to the flow at a fixed length in the direction perpendicular to the flow, and extends in the length direction of the vortex generator. (2) In the above (1), the cross-sectional shape of the vortex generator was rhombic, and (3) the ( In 1) or (2), the cross-sectional shape of the vortex generator is circular. Further, (4) in any of the above (1) to (3), the cross-sectional shape of the vortex generator is elliptical. And even
(5) The cross-sectional shape of the vortex generator is hexagonal, and (6) the direction perpendicular to the flow of the vortex generator, not including the width of the conduit and the length of the separation generating piece protruding on both sides. (7) The cross-sectional shape of the tip of the stripped piece has an acute angle symmetrical to the flow direction. Hereinafter, a description will be given based on an embodiment of the present invention. First, conditions for generating vortices with the same Strouhal number for forward and reverse flow will be described. This condition, of course, requires that the geometry of the vortex generator cross section be symmetric with respect to the flow direction and the direction perpendicular to the flow. As these cross-sectional shapes,
Examples include a circle, an ellipse, and a polygon such as a quadrangle and a hexagon. However, in the vortex generator having the cross-sectional shape as it is, when the Reynolds number changes, the separation point moves or re-adheres. As a result, the frequency of vortex emission changes, and not only does the Strouhal number change, but the vortex signal itself tends to become unstable, including low-frequency and high-frequency noise components. In order that the separation point does not move, the Strouhal number is constant over a wide Reynolds number range, and a stable vortex is generated, the vortex generator having the above-mentioned cross-sectional shape must always have the same position. It is necessary to provide a delamination-generating piece as a means for delamination in the above. Fig. 1 (a), (b)
FIG. 1 is a view for explaining an embodiment of a vortex flowmeter according to the present invention, and FIG. 1A is a sectional side view showing a configuration of the vortex flowmeter. In the figure, 1 is a flow tube, 2 is a vortex generator, 3 and 4 are separation generating pieces, 5 is a protection cylinder, and 6 is a vortex flowmeter converter. In FIG. 1A, a vortex generator 2 is fixed to a flow tube 1 having an inner diameter D with both ends. The vortex generator 2
The vortex generated from the vortex is detected by a sensor (not shown), and the detected vortex signal is connected to the vortex signal converter 5 through the inside of the protection cylinder 5 fixed to the flow tube 1. In the vortex signal converter 5, to determine the positive direction of flow Q _F in the opposite direction of flow Q _R to flow displayed each processing the flow rate. In FIG. 1A, the vortex generator 2 is fixed at both ends, but may be fixed at one end. FIG. 1B is a view showing a cross section of the vortex generator. In the drawing, the flow is axially symmetric with respect to a flow direction axis, XX, and a direction axis YY perpendicular to the flow. It has a long diamond shape in the direction. The length in the direction of the axis YY perpendicular to the flow is d
And the relationship between the length d and the inner diameter D of the flow tube is d / D = 0.1.
5 to 0.35. The vertex 2a of the vortex generator 2 in the forward / reverse flow direction is a side perpendicular to the flow direction, and the cross section of the vortex generator 2 is not a rhombus having an acute angle and a correct geometric shape. However, in this case, the concept of the diamond is assumed. Further, the separation generating piece 3 is disposed on the axis YY of the vortex generator 2 with a shape symmetrical to the axis, and is a plate-like body having the same cross section that is long in the axial direction of the vortex generator 2. The cross-sectional shape is such that the end of the protruding portion from the vortex generator 2 has acute angles 3a, 3b equal to the flow direction, and a bottom 3c parallel to the flow.
And has a T-shape with the embedded portion being a fixing piece 3d, and is fixed on the axis YY in the vortex generator 2. FIG. 2 is a flow chart showing the effect of the stripped pieces in the vortex flowmeter of the present invention. The test shown in FIG.
In the case where the vortex generator 2 has the same rhombic cross section, the length δ of the separation generating piece protruding into the flow with respect to the vortex generator 2 is changed, and the streamline in which the vortex generation state is observed is schematically shown. FIG. The length d (d = 2) of the vortex generator in the axis YY direction
2 mm) and flow tube D (D = 116 mm) d / D = 0.1
9, Reynolds number (Re number) = 3.5 × 10 ⁵ constant. Wake of (a) the vortex generator 2, and the flow arrows Q _F direction, a synthetic stream of the recycle stream, flows out as a sinusoidal flow without peeling from the vortex shedder 2. (B) Projection amount of occurrence of peeling: δ = 1 mm (δ / d = 0.04)
5) The peeling is determined by the action of the peeling-generating pieces 3 and 4, but it does not become complete peeling but flows out in a sine wave shape as shown in FIG.
The amplitude increases and the flow becomes unstable near the top. (C) Projection amount of peeling-off piece: δ = 2 mm (δ / d = 0.0)
91) The action of the separation generating pieces 3 and 4 shows an effect and the flow separates, and the shear layer is involved for the first time, but has not yet fully developed. (D) Projection amount of peeling occurrence wall: δ = 3 mm (δ / d = 0.1)
40) The separation point of the flow is defined by the separation generation piece, the shear layer entrainment develops, and the outflow of the vortex becomes regular. (E) Projection amount of peeling-off piece: δ = 4 mm (δ / D = 0.1
88) The vortex is stably generated with the separation point determined by the effect of the separation generation piece. As described above, the vortex has a separation position determined at the positions of the triangle vertices 3a and 3b of the separation generation pieces 3 and 4, and the vortex flows out stably. FIG. 3 is a diagram showing the Reynolds number characteristics of the Strouhal (St) number in the vortex flowmeter of the present invention, in which the horizontal axis represents the Reynolds number and the vertical axis represents the Strouhal (S).
t) Indicates a number. In the flow rate test, the cross-sectional shape of the vortex generator to be tested was made into two types, a square and a rhombus.
Was performed for two types of protrusion amounts δ = 2 mm and 4 mm into the measured fluid portion. Even when the protrusion amount δ = 2 mm, the Re number was 0.5 to 2.0 × 10 ⁻ as a vortex flowmeter. ^In the range of ⁶ , satisfactory Reynolds number characteristics were exhibited, and it was confirmed that the characteristics of the vortex generator were the same in the forward and reverse directions because they were axisymmetric. In the drawings, the results obtained when the cross-sectional shape of the vortex generator 2 is square or rhombic have been described.
The same effect can be obtained by providing the separation generating piece on the shaft. 4 (a), (b) and (c) are diagrams schematically showing the cross-sectional shape of the vortex generator and the stripping pieces.
4A shows a case of a circular shape, FIG. 4B shows a case of an elliptical shape, and FIG. 4C shows a case of a hexagonal shape. In FIG. Also axis XX (flow axis), axis Y-
It has an axially symmetric cross section in Y (an axis perpendicular to the flow), and the separation occurrence pieces 3 and 4 are provided on the axis YY. As is apparent from the above description, according to the present invention, the cross-sectional shape of the vortex generator is made axially symmetric in the flow direction and the direction perpendicular to the flow, so that the flow in the forward and reverse flow directions is achieved. In the same shape in two directions, and since the separation generating piece is disposed so as to protrude in the axial direction perpendicular to the flow, the separation point of the vortex is determined at the end protruding portion of the separation generating piece,
Vortices with a constant Strouhal number are generated over a wide Reynolds number range. As a result, the flow rates in the forward and reverse flows in two directions can be measured with a single vortex flowmeter with equal accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view for explaining an embodiment of a vortex flow meter according to the present invention. FIG. 2 is a streamline diagram showing the effect of a separation-producing piece in the vortex flowmeter of the present invention. FIG. 3 is a diagram showing a Straw hull (S) in the vortex flowmeter of the present invention.
It is a figure which shows the Reynolds number characteristic of t) number. FIG. 4 is a diagram schematically showing a vortex generator cross-sectional shape and a separation generating piece. [Description of References] 1 ... flow tube, 2 ... vortex generator, 3, 4 ... peeling off piece, 5 ... protective cylinder, 6 ... vortex flow meter converter.

Claims (1)

(57) [Claims 1] In a vortex flowmeter having a vortex generator disposed in a flow tube and detecting a flow rate from the number of vortices generated per unit time, the vortex generator is connected to the vortex generator. The cross-section of the vortex generator is symmetrical with respect to the axis in the flow direction and the direction perpendicular to the flow, and has a shape with the maximum width on the axis of symmetry. A vortex flowmeter characterized in that a separation generating piece protruding in the length of the vortex generator and extending in the longitudinal direction of the vortex generator is provided, and the flow rate in the forward and reverse directions is measured. 2. The vortex flowmeter according to claim 1, wherein the cross-sectional shape of the vortex generator is rhombic. 3. The vortex flowmeter according to claim 1, wherein the vortex generator has a circular cross section. 4. The vortex flowmeter according to claim 1, wherein the vortex generator has an elliptical cross section. 5. The vortex flowmeter according to claim 1, wherein the vortex generator has a hexagonal cross section. 6. The ratio of the width of the conduit to the length in the direction perpendicular to the flow of the vortex generator not including the length of the stripping projecting pieces protruding on both sides is 0.15 to 0.35. Item 6. The vortex flowmeter according to any one of Items 1 to 5. 7. The exfoliating piece has a cross-sectional shape having an acute angle symmetrical with respect to the flow direction.
A vortex flowmeter according to any one of the above.