A vortex flow meter

Abstract: A vortex flow meter having a vortex generator comprises a plurality of vortex generating elements installed in a fluid passage against the fluid's flow and perpendicular thereto. An upstream-side vortex generating element and a down­ stream-side vortex generating element both arranged in par­ allel at a predetermined interval therebetween in the direc­ tion of the fluid's flow. Zero to plural flat plates are arranged in parallel at equal intervals between both vortex generating elements. The representative length portions of the vortex generating elements are located respectively on the surfaces opposed to each other. The frequency ratio of the vortexes generated, when independently arranged, are 0.7 to 0.9 on the standard basis of the upstream-side vortex generating element.

Description: The present invention relates to a vortex flow meter according to the preamble of claim 1. A vortex generator in a vortex flow meter, in which the components of the vortex generator are arranged in parallel at a considerable distance from each other, so as to be opposed to each other vertically in the direction of the flow, is described in the published specifications of Japanese Patent Application No. 46-10233/1971. Furthermore, the present applicant proposed a vortex flow meter as shown in the published specifications of Japanese Utility Model Publication No. 55-45296/1980, in which two vortex generator elements of the same shape and size and a cross section in a triangular shape, are arranged so to be opposed to each other in the distance therebetween is equal to O.1d to 0.9d when the width of the generator is d. By limiting the distance between the vortex generator elements to the above-mentioned claim, it was possible to stabilize the Karman Vortex. The vortex flow meter described in the above-mentioned published specifications of Japanese Utility Model Publication No. 55-45296/1980 achieves the stabilization of the Karman vortex, and the characteristic curve of instrumental error is superior. However, since the instrumental error slowly increases in the range of a low flow rate, in order to enlarge the measurement range of the flow rate at a high accuracy, the range of high flow rate has to be expanded. As a result, there is need for suppressing the increase of pressure loss. Furthermore, by combining of such vortex generators, the magnitude of vortex circulation is changed by the action of the mutual interference of the vortexes, depending on the magnitude of the distance therebetween. The vortex generating frequency at a predetermined condition differs from the frequency of a single vortex generator. In the prior art, the vortex generator is an unsatisfactory one for being installed in a device requiring a flow rate control of quick response, because the vortex generating frequency at a constant flow rate is decreased. The present applicant proposed a Karman vortex generating device in the Karman vortex flow meter described in the published specifications of Japanese Patent Publication No. 55-40804/1980, in which a Karman vortex generator is installed against the flow of a fluid at the most pointed end thereof and a large number of respective independent element plates for generating Karman vortexes are installed behind the vortex generator at desired intervals. The above-mentioned Karman vortex generator has an angular point on the flow axis of the fluid passage and the cross section thereof is in the shape of an equilateral triangle opposed to the flow of fluid and perpendicular thereto. By providing space chambers capable of developing the vortex generated here (i. e. at the Karman vortex generator) to a most suitable intensity by means of a large number of downstream-element plates for generating Karman vortex (called "flat plate (s)" simply hereafter), a sufficiently strong vortex can be developed in proportion to the downstream position. In consequence, a stable vortex generator can be obtained. In the prior art, when a flat plate is installed downstream of the vortex generator the vortex provides an amplifying effect. Concerning the number of flat plates, the number required for obtaining a vortex of such intensity, so that the vortex is peeled off, is sufficient. In the case of the vortex being peeled off from the flat plate in the final stages, an adequate of the number is selected according to the optimum conditions needed. The time required for peeling off the vortex is short because a sufficiently developed vortex has already been produced. Furthermore, the vortex can be produced at a remarkably stable vortex frequency. However, there is a subject matter to be settled with the instrumental error being a plus in the area of the low Reynolds number. The present applicant proposed a vortex flow meter described in the Japanese Patent Application No. 58-60333/1983 (laying-open No. 59-187222/1984), in which a tubular member is disposed behind a vortex generator in a direction of intersecting and at least one pair of pressure guiding holes is formed at a predetermined interval in the direction of the axis of the tubular member. The present applicant noticed that, in the flow meter as mentioned above, the variation of flow is caused by applying a variation to the inside of the tubular member, and the flow of fluid is rectified by guiding a fluid-flow variation into the tubular member having a comparatively small circumference for passing therethrough. In such a manner, a turbulence vortex contained in the flow of the fluid in the fluid passage is not detected as compared with the case when there is no tubular member. Consequently, a noise component of the detection signal of an excellent S/N characteristic is obtained. The detection of the vortex signal already generated is improved in such a manner as mentioned above. And further, with respect to the vortex generator, an acute-angled equilateral triangular element is disposed in direction of the flow and independent flat plates are arranged respectively behind the element, in order, at a desired interval, as shown in the published specifications of Japanese Patent Publication No. 55-40804/1980. In such a manner, an amplifying effect is given to the vortex and thereby a strong and stable vortex can be generated. According to the above-mentioned prior art, a stable vortex flow meter which didn't exist in the past could be realized in combination with a vortex generating means for generating a strong and stable vortex and a detection means for detecting the vortex generated by the vortex generating means having an excellent S/N characteristic. However, in order to perform a wider range of flow rate measurement, it is necessary to get a stronger vortex signal and keep the value of the Strouhal number also constant within a wide range to correspond to the above-mentioned conditions. Furthermore, the vortex flow meter has a plus instrumental error in the low flow rate range, as described in the afore-mentioned published specifications of Japanese Patent Publication No. 55-40804/1980. Therefore, although the vortex generator is stable, it is unsatisfactory for a flow meter requiring a wide range of flow rate measurement. A further vortex generator including more than one vortex generating element is known from DE-A-3242768. The vortex generator which is used in vortex flow meter comprises two vortex generating elements arranged one behind the other in the direction of flow in a predetermined distance. The upstream vortex generating element has a cross section in the form of a triangle while the cross section of the downstream vortex generating element is T-shaped. Very stable vortexes are generated by the combination of these two vortex generating elements. A vortex flow meter according to the preamble of claim 1 is known from GB-A-2160318. This known vortex generator comprises an upstream element having a substantially isosceles triangular cross section and a downstream element having a substantially isosceles trapezoidal cross section. The elements are disposed so that the base of the triangle cross section of the upstream element and the base of the trapezoidal cross section of the downstream element are parallel and adjacent to each other with a predetermined spacing therebetween in the direction of flow. The elements extend perpendicularly to the flow. Further, the projected widths of the upstream element and the downstream element, seen in the direction of the flow, are equal to each other. The angle of the isosceles triangular cross section of the upstream element, the height of the trapezoidal cross section, and the angle formed by the equal sides of the isosceles trapezoidal cross section of the downstream element, the spacing between the elements and the respective widths of the elements, seen in the direction of flow, are chosen so as to achieve a stable vortex generation even at low flow velocities with good linearity. It is the object of the present invention to provide a vortex flow meter according to the preamble of claim 1 which flow meter is improved over the prior art. This object is solved by the features indicated in the characterizing part of claim 1. The present invention provides a vortex flow meter having an improved characteristic of instrumental error in a small flow rate and capable of increasing the frequency of the vortex occurrences. The present invention provides a vortex flow meter having an excellent characteristic of the Reynolds number. The present invention provides a vortex flow meter which performs a wide range of flow rate measurement with high-accuracy. The present invention provides a vortex flow meter capable to improve a characteristic of instrumental error in low Reynolds number range. The present invention provides a vortex flow meter having a wide range of flow rate measurements. The above-mentioned features and other advantages of the present invention will be apparent from the following detailed description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side cross-sectional view showing the construction of a vortex flow meter according to the present invention; Fig. 2 is a plane cross-sectional view showing the same; Figs. 3 and 4 are views for explaining the operation of the flow meter according to the present invention; Fig. 5 is a graph showing the characteristics of the instrumental error. Fig. 6 is a side cross-sectional view of a vortex flow meter according to the present invention; Fig. 7 is a plane cross-sectional view thereof; Figs. 8 and 9 are explanatory views for explaining the positional relationship for getting the vortex frequency of the vortex generator alone. Figs. 10 and 11 are, respectively, a side cross-sectional view and a plane cross-sectional view of the vortex flow meter according to the present invention; Figs. 12 and 13 are plane cross-sectional views of cases for installing, respectively, vortex generating elements alone in a fluid passage. Fig. 14 is a side cross-sectional view of a vortex flow meter according to the present invention; Fig. 15 is a plane cross-sectional view thereof; Fig. 16 is a view showing a tendency of the vortex frequency in the fundamental symmetrical cross section; Fig. 17 shows cross-sectional views showing the other embodiments of the vortex generator. Fig 18 is a plane cross-sectional view of a vortex flow meter according to the present invention; Fig. 19 is a cross-sectional view taken along the line B-B of Fig. 18. Figs. 20 and 21 are structural views of the prior art vortex flow meter. Figs. 22 through 25 are structural views for explaining an embodiment of the vortex flow meter according to the present invention, wherein Fig. 22 is a side cross-sectional view thereof, Fig. 23 a cross-sectional view taken along the line B-B of Fig. 22, Fig. 24 a detailed view of a tubular member, and Fig. 25 a detailed view of raw cloth; and Figs. 26 is a cross-sectional view showing another embodiment of the vortex flow meter according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present applicant noticed the importance of the ratio of the vortex frequency caused by the vortex generator installed perpendicular to the flow in the fluid passage, and consequently carried out several experiments. As a result, it was confirmed that, in the case of selecting the distance t (t = 0. 1d ∼ 0. 9d) between the bottom surfaces of the vortex generators wherein d is the length of the base side of the vortex generator, the instrumental error in a small flow rate area is remarkably improved by the combination of the vortex frequency ratio of 0. 7 to 0. 9 on the standard basis of the upstream side vortex generator, and further, the vortex frequency had been increased. Figs. 1 and 2 are, respectively, a side cross-sectional view of a vortex flow meter according to the present invention and a plane, cross-sectional view of the same. In a fluid passage 1, vortex generators 2a and 2b arranged in parallel against the flow direction A and perpendicular to the flow direction. A vortex signal converted to an electric signal by the vortex detector, not shown in Figs. 1 and 2, is amplified and reshaped (converted to a rectangular wave form) by a preamplifier 3. The vortex generators 2a and 2b contain, respectively, angular points P and Q on the axis of the flow. The cross section of both of the vortex generators is in the shape of an equilateral triangle with vertical angles α and β and base sides d₁ and d₂. The respective bottom surfaces thereof are arranged at a predetermined distance t. Moreover, the vertical angles are determined by the vortex frequency as a condition of the present invention. Fig. 3 and Fig. 4 show, respectively, occurrence states of the vortex rows B and C in the case of installing each of the vortex generators 2a and 2b alone against the flow. Those states are shown for explaining the present invention. According to the results of the experiment, the frequency of the vortex, generated by the vortex generators in a shape of an equilateral triangle with the vertical angles α and β (α=β=40°) and the base sides d₁ and d₂ (d₁=d₂), is equal to 340 Hz in Fig. 3, and equal to 190 Hz in Fig. 4. The ratio of those frequencies is 0. 56 on the standard basis of the vortex generator 2a. The combinational vortex frequency turns out to be 170 Hz. When the vortex generators are arranged at an interval t (t=0.1 d), the characteristic of instrumental error tends to increase in a plus direction, in the low flow rate area as shown by the curve (a) in Fig. 5. On the contrary, supposing that the vertical angles α and β increase and get nearer to a flat plate condition, the vortex frequency also increases. For example, in the case of α=90°, β=100°, and d₁=d₂, the respective frequencies of the vortexes shown in Fig. 3 and Fig. 4 are 310 Hz and 260 Hz. The ratio of those frequencies is 0. 86. The characteristic of instrumental error on the condition of t=0. 2d is considerably improved in the low flow rate area as shown by the curve (a) in Fig. 5. The vortex frequency turns out to be 300 Hz and increases to approximately 1. 8 times compared with the characteristics of the conventional flow meter (shown by the curve (b) in Fig. 5). It has been possible to improve the accuracy of an instrument such as that disclosed in Japanese Patent Publication No. 55-40804/1980, by measuring the vortex frequencies of the individual vortex generators and providing a certain ratio of such vortex frequencies. Furthermore, the frequency of the vortex occurrence increases and the application area is enlarged in the field of the vortex flow meter combined with the control system requiring a quick response. The present applicant observed the vortex generation frequency ratio of the vortex generator which is installed in the fluid passage, and further conducted several experiments. As a result, it was discovered that, by noticing the vortex generation frequency ratio of the vortex generator, located on the upstream position, and the flat plate capable of amplifying the vortex, in particular, the flat plate located in the final stages, in the case where the other vortex generator is installed in the final stages in place of the above-mentioned flat plate and the ratio of vortex generation frequency has a value of predetermined ratio, the Reynolds number : the characteristic of instrumental error was improved. The present invention was created in order to propose a vortex generator having an excellent Reynolds number characteristic on the basis of this discovery. Fig. 6 and Fig. 7 are, respectively, a side cross-sectional view of a vortex flow meter, according to another embodiment, and a plane cross-sectional view of the same. In the fluid passage 1, a pair of vortex generators 2a and 2b are arranged in parallel against the direction of flow A perpendicular thereto. The vortex generators 2a and 2b contain, respectively, angular points P and Q on the axis of the flow. The cross section of both the vortex generators is in the shape of an equilateral triangle, respectively, with vertical angles α and β and base sides d₁ and d₂. Between the respective vortex generators 2a and 2b, a flat plate 2c having a width d₃ and a thickness t b of 0.1d₁ to 0.4d₁ (t b =0.1d₁∼0.4d₁) is installed between the vortex generators 2a and 2b at an equal distance from both of them. The vortex signal is converted to an electric signal by the vortex detector not shown in Figs. 6 and 7, and is amplified and reshaped (i. e. converted to a rectangular wave form) by a preamplifier 3. Moreover, although, in Figs. 6 and 7, only one flat plate 2c is shown for an explanation thereof, it might be possible to use multiple flat plates. The corresponding flat plates act as a vortex amplifying member in the prior art. The circulation of the vortex, at the moment when the vortex is peeled off from the final-stage flat plate, is represented as the sum of the vortex's circulation around the respective flat plates and the sum of the vortex's revolution occurring between the respective flat plates in the prior art. Although the vortex frequency is proportional to the Strouhal number, the latter (i.e. the Strouhal number, ) is an inverse function of the circulation. Consequently, the value of the vortex frequency in the prior art is approximately close to that of the flat plate group which is a combination of the individual flat plates. However, the vortex frequency of the upstream-side vortex generator alone is higher than that of the flat plate group. Therefore, when the amplifying action of the flat plate group is small in the low Reynolds number area, the vortex frequency of the vortex generator alone has priority over the other. When the Reynolds number becomes sufficiently high and the vortex intensity also becomes high, by the action of vortex amplification, the vortex frequency of the flat plate controls the device instead of that of the vortex generator. In such a manner, the instrumental error is transferred to the plus value with higher on-going frequency in the lower Reynolds number area. On the contrary, the characteristic of the instrumental error becomes safe and flat in the higher Reynolds area. However, in the case of installing a vortex generator having a vortex frequency near to that of the upstream-side vortex generator, in parallel therewith, instead of the final stage flat plate, it is considerably affected by the following stage. Therefore, the subject matter as mentioned before is settled, and a vortex meter having a flat Reynolds characteristic can be obtained. According to the results of the experiment, on the standard basis of the vortex frequency of the upstream-side vortex generator 2a, the ratio of the frequency of the vortex generator and that of the lower stage (downstream-side) vortex generator 2c becomes equal to approximately 0. 8. This value is considered to be the best one. Thereby, the Reynolds number due to the representative length d of the vortex generator turns out to be 2. 5 x 10³ or more, namely, a flat characteristic of instrumental error can be obtained. Moreover, in the case that the representative widths (lengths) d₁, d₂ and d₃ of the preceding and following vortex generators are made equal to each other (d₁ =d₂ =d₃), the thickness t b of the flat plate is 0.1d₁ to 0.4d₁ (t b =0.1d₁∼0.4d₁), and the values of the respective distances t between the flat plate and both the vortex generators are also equal to each other. With respect to the values as mentioned above, the most superior characteristic in the Reynolds number and stability can be obtained when the other condition is selected within the area of t=0.1d₁∼0.9d₁. Concerning the angular points α and β of the vortex generators 2a and 2b, both of α and β are equal to 90° (α=β=90°). Needless to mention, even though a is not equal to β (α≠β), it will be permitted to satisfy the vortex frequency ratio of the afore-mentioned vortex generators alone. Moreover, the vortex frequency of the vortex generators alone can be obtained as a construction in which the representative widths (lengths) d are located at the downstream-side and at the upstream-side as shown in Figs. 8 and 9. As it is apparent from the foregoing description, according to the present embodiment, it is possible to obtain a vortex generator having the excellent characteristic of instrumental error and the Reynolds number, while keeping the vortex stable. Furthermore, since the vortex frequency is high, the device according to the present invention can be applicable to a wide range of flow rate measurements. And further it can be applicable also to a vortex flow meter for employment in a control system requiring a quick response. Furthermore, the present applicant noticed the vortex generating frequency ratio of the vortex generator while in the state of being installed in a fluid passage, and conducted further several experiments. As a result, it was discovered that the Reynolds number for the characteristic of instrumental error especially that of characteristic in the low Reynolds number area is improved, in the case of applying the preceding-stage flat plate of the prior art to the element performing the function of vortex amplification, and arranging the final-stage flat plate so as to be opposed to the vortex generating element having certain vortex frequency, wherein the ratio of the vortex frequency thereof and that of the upstream-side vortex generating element is 0.7 to 0.9. Furthermore, it was necessary to provide a vortex flow meter having a constant instrumental error characteristic over a wide range of a low rate measurement, in case that the shape of the cross section of the upstream-side vortex generating element is arc-shaped in order to satisfy the above-mentioned condition, and the shape of the downstream-side vortex generating element's cross section is T-shaped. Fig. 10 is a side, cross-sectional view of another embodiment of the vortex flow meter according to the invention, and Fig. 11 is a plane, cross-sectional view thereof. In Figs. 10 and 11, vortex generating elements 2a and 2b are installed in a fluid passage 1 against the fluid's flow in parallel so as to be opposed to each other in the direction of the flow A and perpendicular thereto. The vortex generating element 2a has an arc-shaped cross section, the arc of which faces the fluid's flow. A semi-circular cross section of the diameter d₁ is shown in Fig. 11. A cross section of the vortex generating element 2b is T-shaped, and its bottom portion has a width d₂ and is parallel to the chord of the afore-mentioned vortex generating element 2a. A flat plate element 2c of width d₃ is disposed between the respective vortex generating elements 2a and 2b at an equal interval therefrom. It is preferable to make the widths d₁, d₂ and d₃ of the vortex generating elements 2a and 2b and the flat plate element 2c equal to the width d (d=d₁=d₂=d₃), respectively. The respective distances t between 2a and 2c and between 2c and 2b are 0.1d to 0.9d (t=0.1d∼0.9d). The vortex signal is converted to an electric signal by a vortex detector, (not shown in Figs. 10 and 11), and it is amplified and reshaped (converted to a rectangular wave form) by a preamplifier 3. The vortex signal is processed in such a manner. Although the flat plate element gives a vortex amplifying action, the afore-mentioned prior art vortex generator in combination with a triangular pillar and a flat plate, has the characteristic of instrumental error increasing in the low flow rate area. The vortex frequency is proportional to Strouhal number, but the Strouhal number decreases in proportion to the increase of the vortex intensity. Therefore, the vortex frequency is an inverse function of the vortex intensity. In combining the flat plate with the others, the vortex intensity increases through by the action of the vortex amplification. However, the vortex intensity of the triangular pillar alone is located at the upstream-side. In the case of constructing the vortex generator in combination with those elements, the respective vortex characteristics mutually exert an influence upon each other. And further, since a combination is newly created in connection with the flow velocity, the influence exerted by the triangular pillar located at the upstream-side is large in the low flow rate area of the prior art as mentioned before. It follows that the flow meter has an increasing characteristic of instrumental error in the low flow rate area. As mentioned before, the present applicant proposed to make the ratio of the vortex frequency of the downstream-side vortex generating element and that of the upstream-side vortex generating element 0. 7 to 0. 9. However, as shown in Figs. 12 and 13, the ratio of the vortex frequency of the arc-shaped vortex generating element 2a (in Fig. 12) of chord length (width) d₁ installed in the fluid passage 1 against the flow, in the direction of the flow A and perpendicular to that of the T-shaped vortex generating element 2b (in Fig. 13) of the width d₂ was in the afore-mentioned range of 0. 7 to 0. 9. Both of the widths d₁ and d₂ were equal to d (d₁=d₂=d). A flat plate element of the width d₃ (d₃=d) was disposed at the center position between those elements. When the respective distances t between 2a and 2c and between 2c and 2b were made 0.1d to 0. 9d, the flow meter had a flat characteristics of the flow rate and instrumental error over a wide range of flow rate measurement from a small flow rate area to a large flow rate area. All of the above-mentioned matters are confirmed in the present invention. Furthermore, the flow meter of the present invention has a stable characteristic and generates a strong vortex signal. As it is apparent from the foregoing description, according to present invention, it is possible to provide, in practice a vortex flow meter which performs a wide-range of a flow rate measurement with high-accuracy and a stable flow rate measurement of a small instrumental error in a wide Reynolds number area. Moreover, according to the experiment performed above, the stability of the vortex is inferior when the flat plate doesn't exist between the vortex generating elements. However, if the distance between the vortex generating elements and the vortex frequency ratio are respectively set to the value mentioned before, the characteristic of the instrumental error is improved. Fig. 14 is a side cross-sectional view of a vortex flow meter according to another embodiment of the invention, and Fig. 15 is a plane cross-sectional view of the same. In a fluid passage 1, a pair of vortex generators 2a and 2b are arranged in parallel against the flow in the direction of flow A and perpendicular thereto. A flat plate 2c is placed in a central position between the vortex generating elements 2a and 2b and parallel to those elements. A vortex generator is constructed in combination with the vortex generating elements 2a, 2b and the flat plate 2c. The representative length d of the vortex generating element is equal to the width of the opposing surfaces of the upstream-side and downstream-side vortex generating elements 2a, 2b. The most optimum thickness t b of the flat plate 2c is 0.1d to 0.4d (t b =0.1 d∼0.4d). The distance t between the respective vortex generating elements needs to be 0.1d to 0.9d (t=0.1d∼0.9d). The vortex signal is converted to an electric signal by the vortex detector not shown in Figs. 14 and 15, and it is amplified and reshaped and converted to a rectangular-shaped wave form by a preamplifier 3. The vortex signal is processed in such a manner. Moreover, although only one flat plate 2c is shown in Figs. 14 and 15, it's possible to use plural flat plates or to omit the fiat plate as the occasion demands. In consideration of the characteristics of the 'prior art' vortex flow meter, from the view point of its circular action, the action of the vortex, at the moment when the vortex is peeled off from the final stage (the downstream-side), the flat plate is represented by the sum of the vortex action around the respective flat plates and the sum of the vortex action occurring between the respective flat plates. The vortex frequency is proportional to the Strouhal number, even of the velocity of flow is constant when the Strouhal number changes. In accordance with the theory of hydrodynamics, the Strouhal number is in inverse proportion to the magnitude of the circular action. In consequence, the vortex frequency in the prior art is determined by the afore-mentioned circular action having a vortex amplifying function at the flat plate side, and thereby the vortex frequency is lower in the high Reynolds number area of the amplifying function range, the extent of the vortex amplifying function having decreased in the low Reynolds number area, and the action of the upstream-side vortex generating element has priority over the other. And further, since the magnitude of its circular action is small, the vortex frequency becomes higher and the instrumental error tends to the plus side. Namely, the total instrumental error is such that it is flat in the large flow rate area and it increases to a plus value in the small flow rate area. In Figs. 14, 15 an embodimemt is shown in which the upstream-side vortex generating element 2a is in the shape of on equilateral triangle while the down-stream side vortex generating element 2b is rectangular. Fig. 16 shows various forms of representative cross sections of the vortex generating element and frequency variation tendencies of the vortex caused by the flow in the direction A. Although a form, such as a circular arc or a T-shape is omitted in this embodiment, there are similarities to the equilateral triangle and the rectangle. Fig. 16 shows trapezoids in I and III, triangles in II and V, and a rectangle in IV. With respect to the respective forms of the cross section, the vortex generating element of group (a) generates a vortex of the highest frequency, that of group (c) generates a vortex of the lowest frequency, and that of group (b) generates a vortex of medium frequency. Even though the vortex generating elements have the same shape, the vortex frequencies differ from each other depending on whether the representative lengths d of the elements are located at the upstream-side or at the downstream-side. The upstream-side element generates a low vortex frequency, while the downstream-side element generates a high vortex frequency. Fig. 17 shows various forms of the vortex generator cross section for example. In Fig. 17, the respective figures of 17 (a) through 17(d) show various combinations of the upstream-side vortex generating element 2a as an equilateral triangle with the downstream-side vortex generating element 2b being a rectangle, a triangle, a triangle and T-shaped respectively. In the arrangements of Figs 17a, 17b, it is possible to construct a vortex generator capable of receiving fluid that is flowing in either direction A or B by selecting the size or dimension from the tendency of the vortex frequency as shown in Fig. 16. Fig. 17 (c) shows a combination of a trapezoid and a triangle and Fig. 17 (d) shows another combination of a triangle and a T-shape. The direction of the fluid's flow is limited to A only. As is apparent from the foregoing description, according to the present invention, it will be possible to provide a vortex flow meter in which a wide range of the flow rate of 1:50 or more can be gotten, as compared with the narrow range of the prior art flow rate measurement of 1:20, as a result of the mutual action of the upstream-side vortex generating element and the downstream-side vortex generating element. Having a little lower vortex frequency, both compensate for each other in the Reynolds number characteristic thereof, and further, since the amplifying action of one vortex is added to the other, a stable vortex flow measurement can be realized. Fig. 18 is a plane cross-sectional view of a vortex flow meter according to another embodiment of the invention, and Fig. 19 is a cross-sectional view taken along the line B - B of Fig. 18. In the vortex flow meter shown in Figs. 18 and 19, an ultrasonicbeam is used as a vortex detecting means. In a fluid flowing passage 1, vortex generating elements 2a and 2b are arranged in parallel against the flow in the direction of the flow A and perpendicular thereto. The vortex generator 2 is constructed in combination with those vortex generating elements 2a and 2b. At the downstream-side of the vortex generating element 2b, a tubular body 4 is fixedly installed so as to intersect the element 2b and pass through the tube wall of the fluid passage 1. A pair of pressure-guiding holes 41 are formed on the tube wall of the tubular body 4. By guiding the pressure variation, caused at the time of a vortex occurrence, into the tubular body 4, the flow variation occurring in the tubular body 4 is received by a receiving element 6 as a signal modified by the velocity vector sum of the ultrasonic waves transmitted from the ultrasonic oscillation element 5 and the afore-mentioned fluid flow variation. According to the result of the experiments, the vortex frequency of the vortex generating element 2a was 310 Hz and that of the vortex generating element 2b was 250 Hz. The ratio of both frequencies is approximately 0.8 on the standard basis of the former (the element 2a). When the representative length of both elements is d, the optimum point exists in the case that the distance between both elements is 0.1d to 0.9d, and thereby an excellent characteristic of the flow rate range of 1: 50 or more is realized. Furthermore, the vortex frequency is increased and a more stable vortex of about 1. 5 times can be obtained compared with that of the prior art. In other experiments the vortex frequency ratio of the upstream-side vortex generating element 2a and the downstream-side vortex generating element 2b became an important factor in the instrumental error of the flow meter. It was found that the above-mentioned characteristic cannot be obtained if the frequency ratio was out of the range of 0.7 to 0.9. Although there are many combinations of the vortex generating elements, an excellent characteristic was obtained by the use of the combination of the two shapes i. e. the equilateral triangle and the T-shape, according to the present invention. Moreover, the vortex is detected by the phase modulation method by use of an ultrasonic detection means and, as a matter of course, it's possible to use pressure, heat, light rays or other means as a means of detection instead of ultrasonic beams. As is apparent from the foregoing description, according to the present invention, the characteristic of instrumental error has been improved by noticing the vortex frequency ratio of the vortex generators alone and by combining them with each other. Furthermore, it follows that the frequency of the vortex occurrences increases and the application area has been enlarged in the field of the vortex flow meter combined with a control system requiring a quick response. The present applicant proposed a vortex flow meter described in the Japanese Patent Application No. 58-60333/1983 (laying-open No. 59-187222/1984, in which a tubular member 4 is disposed behind a vortex generator 2 in a direction of intersecting it as shown in Fig. 20 (Fig. 21 is a cross-sectional view taken along the line B - B of Fig. 20) and at least one pair of pressure guiding holes 41 are formed at a predetermined interval in the direction of the tubular member's 4 axis. The present applicant noticed that, in the flow meter as mentioned above, the fluid variation of flow is caused by applying a variation to the inside of the tubular member 4, and the fluid flow is rectified by guiding a fluid-flow variation into the tubular member 4 having a comparatively small circumference for passing therethrough. In such a manner, a turbulence vortex contained in the flow of the fluid in the fluid passage is not detected as compared with the case when there is no tubular member. Consequently, a noise component of the detection signal decreased and thereby the detection signal of an excellent S/N characteristic is obtained. The detection of the vortex signal already generated was improved in such a manner as mentioned above. And further, with respect to the vortex generator, an acute-angled equilateral triangular element was disposed of in direction A of the fluid flow and independent flat plates were arranged respectively behind the element, in order, at a desired interval, as shown in the published specifications of Japanese Patent Publication No. 55-40804/1980. In such a manner, an amplifying effect is given to the vortex and thereby a strong and stable vortex can be generated. According to the above-mentioned prior art, a stable vortex flow meter which didn't exist in the past could be realized in combination with a vortex generating means for generating a strong and stable vortex and a detection means for detecting the vortex generated by the vortex generating means having an excellent S/N characteristic. However, in order to perform a wider range of flow rate measurement, it was necessary to get a stronger vortex signal and keep the value of the Strouhal number with a wide-range and also constant to correspond to the above-mentioned conditions. Furthermore, the vortex flow meter had a plus instrumental error in the low flow rate area, as described in the afore-mentioned published specifications of Japanese Patent Publication No. 55-40804/1980. Therefore, although the vortex generator was stable, it was unsatisfactory for a flow meter requiring a wide range of flow rate measurement. The present invention was created in consideration of the above-mentioned subject matter. The present applicant noticed that, in the construction of the vortex detection means, in which the prior art pressure guiding holes 41 had been arranged, in the direction of the tubular member 4's axis, the vortex generated by the vortex generator had been peeled off therefrom three-dimensionally as a vortex pillar, and the present applicant formed pressure guiding holes in the direction of the vortex pillar in order to effectively guide the pressure variation. The present applicant further noticed that the vortex generating elements which made up the vortex generator had an independent vortex frequency ratio for the purpose of obtaining a flow meter having an excellent linear characteristic with a wide range of flow rate measurement by improving the characteristic inherent in the vortex generator. As a result, the subject matter of the prior art was settled. Figs. 22 through 25 are structural views for explaining another embodiment of the invention. In Figs. 22 through 25, the same reference numeral is attached to the part of the same construction as that of the prior art shown in Figs. 20 and 21. The vortex generator 2 is constructed with a vortex generating element 2a made of an equilateral triangular cross section placed at the upstream-side, a vortex generating element 2b made of a T-shaped cross section disposed at the downstream-side, and a flat plate element 2c disposed therebetween. Those elements are arranged in order 2a, 2c, and 2b at the upstream-side, and the representative length d thereof is opposed to the other respectively. A tubular member 4, for guiding the pressure variation due to a vortex, is supportedly placed behind a vortex generator 2, installed in such a manner as mentioned above, so as to intersect the vortex generator 2 and pass through the wall of the fluid passage 1. Fig. 24 shows the details of the tubular member 4. A pair of tube members 42 are firmly fixed onto the tubular member 4 so as to cross the same perpendicular thereto and to communicate therewith. And further, the end surface of the tube members 42 is closed, and a plurality of pressure guiding holes 43 are opened on the wall of the straight tube member 42. The pressure variation is guided into the pressure guiding holes 43 and fluid displacement, corresponding thereto, is caused as shown by the arrows C in Fig. 24. In the case of detecting the fluid displacement, a modulated ultrasonic signal, sound absorbing material 44 such as unwoven raw cloth, is stuck on the inner-wall surface of a pair of tube members 42 so as to coat the same for the purpose of preventing a turbulent component of ultrasonic waves, contained in the flowing fluid, from entering into the tube members 42. Fig. 25 is a perspective view of sound absorbing material 44. A notch 45 is formed so as not to close the pressure guiding hole 43. On the other hand, the vortex generator 2 is constructed in such a way that the ratio of the vortex frequency of the vortex generating element 2a and that of the vortex generating element 2b turns out to be 0.7 to 0.9. The flat plate element 2c is placed between those vortex generating elements parallel thereto. With respect to the position relationship of those elements, dimensions t₁, t₂ and t₃, as shown in Fig. 22, are determined respectively, wherein t₁ is a certain distance between elements 2a and 2c, t₂ is a certain thickness of element 2c, and t₃ is a certain distance between elements 2c and 2b. The values of t₁ to t₃ are selected so as to be equal to 0.1d and 0.4d (t₁∼t₃-0.1d∼0.4d). The vortex flow meter, constructed in such a manner as shown in Figs. 22 through 25, is capable of getting a vortex of an excellent linear characteristic through the action of the interference due to the vortex frequency difference between the respective vortex generating elements. To state in more detail, since the vortex generating frequency of the downstream-side vortex generating element 2b is low, the circulation of the vortex is strong and dominates the high-Reynolds number area, and the frequency difference of the vortex generated at the low Reynolds number regulates the vortex frequency in the low-Reynolds number area by the action of the interference, with the vortex, of the vortex generating element 2a occurring in the gaps between vortex generating elements 2a and 2b. The vortex peeled off from the vortex generator as mentioned above flows down as a vortex pillar, parallel to the axis of the vortex generator, and therefore a pressure variation appears with a tendency following the vortex flow. Consequently, the guided pressure difference is increased, and made even. And further, a flat plate element 2c is employed for guiding the vortex generated by the vortex generating element 2a into the area between the gaps t₁ and t₃ and for obtaining an increasing amplification effect. In addition to the construction of the vortex generator shown in Fig. 22, other constructions thereof, e.g. the construction of Fig. 26, can be realized. It is important to add the afore-mentioned conditions to those constructions. As is apparent from the foregoing description, according to the present invention, it will be possible to provide a vortex flow meter in which a stable vortex signal of an excellent linear characteristic proportional to the rate flow of can be generated over a wide range of the vortex generating frequency, and on the other hand, since a stronger pressure variation can be obtained at the time of detecting the vortex, the measurement range of the flow meter, becomes considerably wider in relation to both of the above-mentioned matters.

Claims: A vortex flowmeter including: a vortex generator comprising a plurality of vortex generating elements disposed within a fluid passage (1), each said element extending is a direction perpendicular to the direction of a fluid flow through said passage (1); said plurality comprising at least two elements (2a,2b) arranged one behind the other, as seen in the direction of the fluid flow, and arranged in parallel at a predetermined distance t there between, said cross-section of the downstream vortex generating element (2b), in a plane parallel to the fluid flow direction, being in the shape of a triangle, a rectangle or a T-shape, characterised in that said two vortex generating elements are provided such that the ratio of the vortex frequency generated by the downstream element (2b), if it were disposed alone within the fluid passage, and the vortex frequency generated by the upstream element (2a), if it were disposed alone within the fluid passage, is between 0.7 and 0.9. A vortex flow meter as defined in claim 1 characterised in that the cross section of the two elements (2a,2b), in a plane parallel to the fluid flow direction, is in the shape of an equilateral triangle and each of the two elements has an angular point on the axis of said fluid passage. A vortex flow meter as defined in Claim 1 characterised in that the cross section of the upstream element (2a), in a plane parallel to the fluid flow direction, is in the shape of an equilateral triangle and the upstream element has an angular point on the axis of the passage, and the cross section of the downstream element (2b), in a plane parallel to the fluid flow direction, is T-shaped. A vortex flow meter as defined in Claim 1 characterised in that the cross section of the upstream element (2a), in a plane parallel to the fluid flow direction, is arch-shaped on its upstream side, and the cross section of the downstream element (2b), in a plane parallel to the fluid flow direction, is T-shaped. A vortex flow meter as defined in at least one of the foregoing claims characterised in that the width d of said opposing surfaces of said two elements are made equal to each other. A vortex flow meter as defined in at least one of the foregoing claims characterised in that the distance t between the two elements (2a,2b) equals 0.1 to 0.9d, wherein d is the width of said opposing surfaces. A vortex flow meter as defined in at least one of the foregoing claims characterised in that at least one flat plate (2c) is disposed between said two elements (2a,2b) in parallel to said opposing surfaces thereof. A vortex flow meter as defined in Claim 7 characterised in that the width of said flat plate (2c) and the width d of said two opposing surfaces are equal to each other. The vortex flow meter as defined in Claims 7 or 8 characterised in that the distances between the flat plate (2c) and the upstream element (2a) and between the flat plate (2c) and the downstream element (2b) are equal to each other. A vortex flow meter as defined in at least one of the Claims 7 through 9 characterised in that the thickness of the flat plate (2c) is 0.1 to 0.9d, wherein d is the width of said opposing surfaces. A vortex flow meter as defined in at least one of the foregoing claims characterised in that said vortex flow meter comprises a tubular body firmly fixed to said fluid passage so as to pass therethrough at the downstream side of said vortex generator in a direction crossing said vortex generating element, as seen in the direction of the fluid flow, and provided with a pair of first-pressure guiding holes formed at a place near the fixing position of said tubular body, and a pair of cavity chambers fixedly formed on the outer wall of said tubular body and having a pair of second-pressure guiding holes communicating with said pair of first-pressure guiding holes formed on the wall surface of said two cavity chambers, and the displacement of fluid flowing in said tubular body is detected by the vortex pressure-variations occurring in said pair of first-pressure guiding holes and in said pair of second-pressure guiding holes.

Inventors: ATSUMI KOJI C O OVAL ENGINEERI, MISUMI MASAO C O OVAL ENGINEER, ATSUMI, KOJI C/O OVAL ENGINEERING CO., LTD., MISUMI, MASAO C/O OVAL ENGINEERING CO., LTD.
Applicants: OVAL ENG CO LTD, OVAL ENGINEERING CO., LTD.
Application year: 1987
Main classification: G01F1
IPC codes: G01F1