CA1186916A - Vortex shedding flow measurement - Google Patents
Vortex shedding flow measurementInfo
- Publication number
- CA1186916A CA1186916A CA000417538A CA417538A CA1186916A CA 1186916 A CA1186916 A CA 1186916A CA 000417538 A CA000417538 A CA 000417538A CA 417538 A CA417538 A CA 417538A CA 1186916 A CA1186916 A CA 1186916A
- Authority
- CA
- Canada
- Prior art keywords
- vortex shedding
- displacement
- bluff body
- bistable
- flow
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/05—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects
- G01F1/20—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by detection of dynamic effects of the flow
- G01F1/32—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by detection of dynamic effects of the flow using swirl flowmeters
- G01F1/325—Means for detecting quantities used as proxy variables for swirl
- G01F1/3259—Means for detecting quantities used as proxy variables for swirl for detecting fluid pressure oscillations
- G01F1/3266—Means for detecting quantities used as proxy variables for swirl for detecting fluid pressure oscillations by sensing mechanical vibrations
Abstract
VORTEX SHEDDING FLOW MEASUREMENT
ABSTRACT OF THE DISCLOSURE
An improved vortex shedding flowmeter sensor and method are disclosed. The vortex shedding sensor is a bistable element. The element is constrained to operate in a transition deflection region between two stable stages. The element tends to alternate states at the frequency of vortex shedding, thereby amplifying the input signal at low levels and extending the low range of flow rate measurement.
ABSTRACT OF THE DISCLOSURE
An improved vortex shedding flowmeter sensor and method are disclosed. The vortex shedding sensor is a bistable element. The element is constrained to operate in a transition deflection region between two stable stages. The element tends to alternate states at the frequency of vortex shedding, thereby amplifying the input signal at low levels and extending the low range of flow rate measurement.
Description
~8~ 6 VORTEX SHEDDING FLOW MEASUREMENT
FIELD AND BACKGROUND OF THE INVENTION
The invention relates, in general, to flow measurement and flow meters, and, more particularly, to a new and useful method ~or ~ortex shedding flow measuremQnt.
Vortex shedding flow measurement deals with the eddies or vortices which shed from an obstruction) known as a bluff body or strut, which is placed in the path of a flow stream. As the flow stream contacts the bluff body, the surface layer separates ~rom opposite sides of the bluff body. Shedding alternatingly occurs at both of the opposite sides. ~he vortex shedding Ere~uency is pro-portional to the flow rate acxoss the bluf body.
In known vortex shedding arran~ements, the differential pres~ure induced by vortex shedding has been sensed by a variety o~ monostable analog elements. Among these elemen~s are diaphr~gms which deflect proportional to the differential pressure, the deflection of the bluff body itself or a secondary body due to the pressure drop, or fluid flow whiah is induced due to this differential.
A disadvantage of these sensing means is that the fre-quency of vortex shedding is proportional to flow rate as well as the amplitude of the differential pressure pulse.
Therefore, at low flow rates the output of an analog sen-sor can be too 1GW to measure.
K\I;V O' " 11: l~lV'~10~1 In accordance with the invention, a bistablemechanical element is utilized to sense vortex shedding.
Moreover, the element, which is preferably a bistable diaphraym or a diaphragm actuating a bistable sensor, is constrained to operate within a transition range so as to react with relatively large displacements for very small input force.
Thus, in accordance with the invention, there is provided, in a vortex shedding flowmeter of the type having a bluff body mounted in a flowstream, the improvement comprising a bistable element connected to the bluff body, means for constraining the element for movement responsive to vortex shedding of flow about the bluff body within a transition region preferably between the stable states of the bistable element, and means for measuring the displace-ment of the element.
The invention also provides an improved method of sensing vortex shedding in flow measurement comprising the steps of constraining a bistable element for displacement in a transition region and measuring the displacement of the element.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. Eor a better understanding of th~ invention, its operating advan-tages and specific objects attained by its uses, reference is made to the accompanying drawings iIl which a preferred embodiment of the invention is illustrated.
BRIEF DESCRIPTION OF THE DRAWING
In the Drawing:
Fig. 1 is a schematic xepresentation of a bluff body arranged within a flow conduit;
Fig. 2 is a deflection diagram ~chematically illustra-ting the states of a diaphragm;
Fig. 3 is a orce-displacement diagram illustrating the loading of the diaphragm of Fig. 2 at stable states A
and B, as well as in the so-called transition region between states A and B.
'~
Fig. 4 is a front end view, partly brcken away, viewed from the downstream end o~ a bluff body according to the invention;
Fig. 5 is a sec-tional view taken along view line V-V of Fig. 4; and Fig. 6 is a bottom view of the bluff body o~ Fig. 4.
DETAILED DESCRIPTION OF P~EF~RRED EMBODIMENT
... .. .. ~
Referring to the drawing with particular emphasis on Fig.l a bluff body 10 is shown, having a shape tapering from an upstream end to a downs-tream end, disposed in a flow conduit 14. As the fluid flow, the direc-tion of which is represented by arrow 12, passes from the upstream to the downstream end of the bluff body 10, vortices 16 form at and are shed from opposite sides of the b]uff body 10.
A bistable element 18, such as a diaphragm, is mounted to the bluff body 10 and restrained to operate in a transition region with the movemen-t of the element 18 being monitored by a transducer 20. Structurally, such a restraint can be achieved, for example, by attaching ~e bistable diaphragm 18 to the bluff body 10 with a weld of a known type, such as a laser weld, electron beam weld, TIG weld or the like, such that it creates a seal across the body. Structura:L supports 3 are also attached adjacent to the bistable device to restrain the opexation to a transition region which will be explained later. Glass sealed conductors 1, such as the kind that can be purchased from Glasseal Products Inc., Part No. TF120~20FBBE, are installed in the body 10 to bring the electrical signal out of the flow conduit. The electrical signal is cxeated in a displacement transducer 8 which can be a strain gage, as illustrated in Fig. 4, for example as produced by BLII Elec-tronics Corp., Part No. FAES4-44-35SX¦, or a piezoelectrical crystal, a magnetic proximity sensor, a capacikance displace ment sensor, or LVDT type mounted on the bistable device or restraining support so as to sense the motion.
The displacement transducer 8 can be sealed in a cavity 6 filled with an inert fluid ~for example: Dow Corning 200 Fluid) and sealed with a plug 7, such as is produced by Lee Co~, ,. ,~
' Part No. PLGAl250020), between a low spring rate, high volu-metric capacitance diaphragm 5 and the sensing diaphragm 18.
The displacement transducer 8 can also be encapsulated in some non-rigid encapsulant (such as G~E~ silicone rubber ad-hesive sealant RTV126). The transducer can be metallized orcovered with a metal coating similar in composition to the bluff body by plating, cladding or welding. Any of these methods will protect it Erom the process fluid flowing through the conduit.
Finally, this vortex sensing assembly can be assembled in a separate enclosure which can be inserted i~to or connected to the bluff body using welding, fasteners, or the like.
Since the diaphragm 18 is restrained to operate only in the transition region, very small differential pressures can generate the force necessary to cause the large deflections because, as is best seen in Fig. 3, ih the center of the tran-sition region a very small force in either direction causes the device to move toward one of its stable states. In addition, the magnitude of the displacement will not depend strictly on the input force. The large deflections of the bistable sensor 18 can be measured very easily using the displacement trans-ducer such as a strain gauge model FAES4-44-35SX manu~actured by BLH Electronics Corp. The diaphragm type strain gauge chanyes resistance with the strain induced to the diaphragm by its dis-placement.
The displacement is converted into an electricalsignal and can be used as a straight frequency output or can be input to a signal conditioner. Circuitry is known for convert-ing the displacement into an electrical signal. For example, an instruction manual by the Yokogawa Electric Work Inc. illus trates electrical schematic diagrams for current control and signal conditioning in connection with vortex flow measurement.
The inventive arrangement not only reduces -the vari-ation in the magnitude of the sensing pulses with flow rate but also allows the device to be used at much lower flow rate~
than was previously possible.
Fig. 3 graphically illustrates force as the ordinate and displacement as the abscissa of a force displacement dia-gram of a bistable diaphragm sensing element restrained in accordance with the invention. In the so-called tra~sition region, the spring rate (Force-Displacement) decreases with displacement in the transition or "oil can" region of the device. This can be analogized to the pressing of the bottom of an oil can in a first direction and the automatic opposite return thereof. The bistable sensor is constrained to operate in the transition region, either by restricting its displace-ment or by providing an external restoring force to maintain the device in the "oil can" regionn Operating in transition the sensor will react with relatively large displacements for very small input force. In this way a bistable diaphragm, or a diaphragm actuating a bistable sensor, can sense the differen-tial pressures generated by the formation of vortex about a bluff body in a flow stream.
In order to limit the displacement of a bistable device, an external restoring force can be used to insure operation in transition region. This force can be supplied by a spring mechanically connected to the device or the diaphragm 5 being provided with the appropriate spring rate, a~d being hydraulically coupled to the bistable sensiny diaphragm 18.
The element will alternate states at the frequency of vortex shedding, thereby amplifying the input signal at low signal levels, extending the range of the device towards lower 10w rates. Also, at variakle input signal levels, the output remains relatively fixed in magnitude.
An element suitable as a diaphragm would predictively be composed of stainless steel or a nickel alloy, have a di-ameter ranging from one-~uarter inch (63.5 mm) to one inch (~54 mm), a thickness of .001 inch (0.254 mm) and a displace-ment of .0001 inch (0.0254 mm).
Using this approach the bluff body dimensions in terms of pipe diameter (D) would be approximately as illust~ated in Figures 4 through 6. The size is only limited by manufacturing -~
~6~
capabilities and would be from pipe di~neters o about 0.5 inch (12.7 mm) or 1 inch (25,5 mm3 to 8.0 inch (203.2 ~n) or 12.0 inch ~304.8 mm) and fluid velocities down to less than 1 Ftlsec.
(.3048 m/s) perhaps down ~o .1 Ftjsec ~.0304 mls) and up to 33 Ft/sec, ~10,0584 m/s).
While a specific embodiment of the in~ention has been shown and described in detail to illustra~e the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing rom c ~r~ c 1~
FIELD AND BACKGROUND OF THE INVENTION
The invention relates, in general, to flow measurement and flow meters, and, more particularly, to a new and useful method ~or ~ortex shedding flow measuremQnt.
Vortex shedding flow measurement deals with the eddies or vortices which shed from an obstruction) known as a bluff body or strut, which is placed in the path of a flow stream. As the flow stream contacts the bluff body, the surface layer separates ~rom opposite sides of the bluff body. Shedding alternatingly occurs at both of the opposite sides. ~he vortex shedding Ere~uency is pro-portional to the flow rate acxoss the bluf body.
In known vortex shedding arran~ements, the differential pres~ure induced by vortex shedding has been sensed by a variety o~ monostable analog elements. Among these elemen~s are diaphr~gms which deflect proportional to the differential pressure, the deflection of the bluff body itself or a secondary body due to the pressure drop, or fluid flow whiah is induced due to this differential.
A disadvantage of these sensing means is that the fre-quency of vortex shedding is proportional to flow rate as well as the amplitude of the differential pressure pulse.
Therefore, at low flow rates the output of an analog sen-sor can be too 1GW to measure.
K\I;V O' " 11: l~lV'~10~1 In accordance with the invention, a bistablemechanical element is utilized to sense vortex shedding.
Moreover, the element, which is preferably a bistable diaphraym or a diaphragm actuating a bistable sensor, is constrained to operate within a transition range so as to react with relatively large displacements for very small input force.
Thus, in accordance with the invention, there is provided, in a vortex shedding flowmeter of the type having a bluff body mounted in a flowstream, the improvement comprising a bistable element connected to the bluff body, means for constraining the element for movement responsive to vortex shedding of flow about the bluff body within a transition region preferably between the stable states of the bistable element, and means for measuring the displace-ment of the element.
The invention also provides an improved method of sensing vortex shedding in flow measurement comprising the steps of constraining a bistable element for displacement in a transition region and measuring the displacement of the element.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. Eor a better understanding of th~ invention, its operating advan-tages and specific objects attained by its uses, reference is made to the accompanying drawings iIl which a preferred embodiment of the invention is illustrated.
BRIEF DESCRIPTION OF THE DRAWING
In the Drawing:
Fig. 1 is a schematic xepresentation of a bluff body arranged within a flow conduit;
Fig. 2 is a deflection diagram ~chematically illustra-ting the states of a diaphragm;
Fig. 3 is a orce-displacement diagram illustrating the loading of the diaphragm of Fig. 2 at stable states A
and B, as well as in the so-called transition region between states A and B.
'~
Fig. 4 is a front end view, partly brcken away, viewed from the downstream end o~ a bluff body according to the invention;
Fig. 5 is a sec-tional view taken along view line V-V of Fig. 4; and Fig. 6 is a bottom view of the bluff body o~ Fig. 4.
DETAILED DESCRIPTION OF P~EF~RRED EMBODIMENT
... .. .. ~
Referring to the drawing with particular emphasis on Fig.l a bluff body 10 is shown, having a shape tapering from an upstream end to a downs-tream end, disposed in a flow conduit 14. As the fluid flow, the direc-tion of which is represented by arrow 12, passes from the upstream to the downstream end of the bluff body 10, vortices 16 form at and are shed from opposite sides of the b]uff body 10.
A bistable element 18, such as a diaphragm, is mounted to the bluff body 10 and restrained to operate in a transition region with the movemen-t of the element 18 being monitored by a transducer 20. Structurally, such a restraint can be achieved, for example, by attaching ~e bistable diaphragm 18 to the bluff body 10 with a weld of a known type, such as a laser weld, electron beam weld, TIG weld or the like, such that it creates a seal across the body. Structura:L supports 3 are also attached adjacent to the bistable device to restrain the opexation to a transition region which will be explained later. Glass sealed conductors 1, such as the kind that can be purchased from Glasseal Products Inc., Part No. TF120~20FBBE, are installed in the body 10 to bring the electrical signal out of the flow conduit. The electrical signal is cxeated in a displacement transducer 8 which can be a strain gage, as illustrated in Fig. 4, for example as produced by BLII Elec-tronics Corp., Part No. FAES4-44-35SX¦, or a piezoelectrical crystal, a magnetic proximity sensor, a capacikance displace ment sensor, or LVDT type mounted on the bistable device or restraining support so as to sense the motion.
The displacement transducer 8 can be sealed in a cavity 6 filled with an inert fluid ~for example: Dow Corning 200 Fluid) and sealed with a plug 7, such as is produced by Lee Co~, ,. ,~
' Part No. PLGAl250020), between a low spring rate, high volu-metric capacitance diaphragm 5 and the sensing diaphragm 18.
The displacement transducer 8 can also be encapsulated in some non-rigid encapsulant (such as G~E~ silicone rubber ad-hesive sealant RTV126). The transducer can be metallized orcovered with a metal coating similar in composition to the bluff body by plating, cladding or welding. Any of these methods will protect it Erom the process fluid flowing through the conduit.
Finally, this vortex sensing assembly can be assembled in a separate enclosure which can be inserted i~to or connected to the bluff body using welding, fasteners, or the like.
Since the diaphragm 18 is restrained to operate only in the transition region, very small differential pressures can generate the force necessary to cause the large deflections because, as is best seen in Fig. 3, ih the center of the tran-sition region a very small force in either direction causes the device to move toward one of its stable states. In addition, the magnitude of the displacement will not depend strictly on the input force. The large deflections of the bistable sensor 18 can be measured very easily using the displacement trans-ducer such as a strain gauge model FAES4-44-35SX manu~actured by BLH Electronics Corp. The diaphragm type strain gauge chanyes resistance with the strain induced to the diaphragm by its dis-placement.
The displacement is converted into an electricalsignal and can be used as a straight frequency output or can be input to a signal conditioner. Circuitry is known for convert-ing the displacement into an electrical signal. For example, an instruction manual by the Yokogawa Electric Work Inc. illus trates electrical schematic diagrams for current control and signal conditioning in connection with vortex flow measurement.
The inventive arrangement not only reduces -the vari-ation in the magnitude of the sensing pulses with flow rate but also allows the device to be used at much lower flow rate~
than was previously possible.
Fig. 3 graphically illustrates force as the ordinate and displacement as the abscissa of a force displacement dia-gram of a bistable diaphragm sensing element restrained in accordance with the invention. In the so-called tra~sition region, the spring rate (Force-Displacement) decreases with displacement in the transition or "oil can" region of the device. This can be analogized to the pressing of the bottom of an oil can in a first direction and the automatic opposite return thereof. The bistable sensor is constrained to operate in the transition region, either by restricting its displace-ment or by providing an external restoring force to maintain the device in the "oil can" regionn Operating in transition the sensor will react with relatively large displacements for very small input force. In this way a bistable diaphragm, or a diaphragm actuating a bistable sensor, can sense the differen-tial pressures generated by the formation of vortex about a bluff body in a flow stream.
In order to limit the displacement of a bistable device, an external restoring force can be used to insure operation in transition region. This force can be supplied by a spring mechanically connected to the device or the diaphragm 5 being provided with the appropriate spring rate, a~d being hydraulically coupled to the bistable sensiny diaphragm 18.
The element will alternate states at the frequency of vortex shedding, thereby amplifying the input signal at low signal levels, extending the range of the device towards lower 10w rates. Also, at variakle input signal levels, the output remains relatively fixed in magnitude.
An element suitable as a diaphragm would predictively be composed of stainless steel or a nickel alloy, have a di-ameter ranging from one-~uarter inch (63.5 mm) to one inch (~54 mm), a thickness of .001 inch (0.254 mm) and a displace-ment of .0001 inch (0.0254 mm).
Using this approach the bluff body dimensions in terms of pipe diameter (D) would be approximately as illust~ated in Figures 4 through 6. The size is only limited by manufacturing -~
~6~
capabilities and would be from pipe di~neters o about 0.5 inch (12.7 mm) or 1 inch (25,5 mm3 to 8.0 inch (203.2 ~n) or 12.0 inch ~304.8 mm) and fluid velocities down to less than 1 Ftlsec.
(.3048 m/s) perhaps down ~o .1 Ftjsec ~.0304 mls) and up to 33 Ft/sec, ~10,0584 m/s).
While a specific embodiment of the in~ention has been shown and described in detail to illustra~e the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing rom c ~r~ c 1~
Claims (4)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a vortex shedding flowmeter, of the type having a bluff body mounted in a flowstream, an improved sensor compris-ing a bistable element connected to the bluff body, means for constraining said element for displacement within a transition region responsive to vortex shedding of flow about the bluff body, and means for measuring the displacement of said element.
2, The improvement as set forth in claim 1, wherein said constraining means comprises means for restricting displacement of said element.
3. The improvement as set forth in claim 1, wherein said constraining means comprises means for applying an external restoring force to said element to maintain the element within the transition region.
4. An improved method of sensing vortex shedding flow in vortex shedding flow measurement comprising constraining a bistable element for displacement within a transition region responsive to vortex shedding, and measuring the displacement of the element.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/331,057 US4453416A (en) | 1981-12-15 | 1981-12-15 | Vortex shedding flow measurement |
| US06/331,057 | 1981-12-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1186916A true CA1186916A (en) | 1985-05-14 |
Family
ID=23292452
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000417538A Expired CA1186916A (en) | 1981-12-15 | 1982-12-13 | Vortex shedding flow measurement |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US4453416A (en) |
| JP (1) | JPS58160814A (en) |
| CA (1) | CA1186916A (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0110321B1 (en) * | 1982-11-25 | 1988-09-07 | Oval Engineering Co., Ltd. | Vortex flow meter |
| US6003383A (en) * | 1994-03-23 | 1999-12-21 | Schlumberger Industries, S.A. | Vortex fluid meter incorporating a double obstacle |
| US5808209A (en) * | 1994-03-23 | 1998-09-15 | Schlumberger Industries, S.A. | Vortex fluid meter including a profiled pipe |
| US7603914B2 (en) * | 2006-07-21 | 2009-10-20 | Endress + Hauser Flowtec Ag | Measuring system with a flow conditioner arranged at an inlet of a measuring tube |
| TW200825382A (en) * | 2006-12-15 | 2008-06-16 | Univ Nat Taiwan | Eddy current precision flow meter |
| US7882751B2 (en) * | 2007-07-19 | 2011-02-08 | Endress + Hauser Flowtec Ag | Measuring system with a flow conditioner for flow profile stabilization |
| US8966970B2 (en) * | 2012-12-18 | 2015-03-03 | General Electric Company | Flow sensor assembly having a hybrid sensor response |
| US9599493B2 (en) * | 2014-10-31 | 2017-03-21 | Invensys Systems, Inc. | Split flow vortex flowmeter |
| CN104729591B (en) * | 2015-01-16 | 2017-09-29 | 合肥工业大学 | A kind of signal processing method for the strong transient impact vibration of the anti-low frequency of vortex-shedding meter replaced based on data |
| CN112654842A (en) * | 2018-08-30 | 2021-04-13 | 微动公司 | Non-invasive sensor for vortex flowmeter |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3564915A (en) * | 1967-09-27 | 1971-02-23 | Yokogawa Electric Works Ltd | Current meter or flow meter |
| DE2458901C3 (en) * | 1974-04-23 | 1986-07-10 | The Foxboro Co., Foxboro, Mass. | Flow meter |
| US4006083A (en) * | 1975-10-09 | 1977-02-01 | Caterpillar Tractor Co. | Pressure differential switch |
| US4003251A (en) * | 1976-03-19 | 1977-01-18 | Fischer & Porter Co. | Acceleration-proof vortex-type flowmeter |
| JPS54145571A (en) * | 1978-05-06 | 1979-11-13 | Nissan Motor | Karman vortex flow meter |
-
1981
- 1981-12-15 US US06/331,057 patent/US4453416A/en not_active Expired - Fee Related
-
1982
- 1982-12-13 CA CA000417538A patent/CA1186916A/en not_active Expired
- 1982-12-15 JP JP57218536A patent/JPS58160814A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS58160814A (en) | 1983-09-24 |
| US4453416A (en) | 1984-06-12 |
| JPS635687B2 (en) | 1988-02-04 |
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Legal Events
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|---|---|---|---|
| MKEC | Expiry (correction) | ||
| MKEX | Expiry |