WO2003021199A1 - Debitmetre a vortex destine a une canalisation a ecoulement libre - Google Patents

Debitmetre a vortex destine a une canalisation a ecoulement libre Download PDF

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Publication number
WO2003021199A1
WO2003021199A1 PCT/GB2002/003991 GB0203991W WO03021199A1 WO 2003021199 A1 WO2003021199 A1 WO 2003021199A1 GB 0203991 W GB0203991 W GB 0203991W WO 03021199 A1 WO03021199 A1 WO 03021199A1
Authority
WO
WIPO (PCT)
Prior art keywords
fluid
channel
bluff
flow
frequency
Prior art date
Application number
PCT/GB2002/003991
Other languages
English (en)
Inventor
Mike Sanderson
Hoi Yeung
Original Assignee
Severn Trent Water Limited
Yorkshire Water Services Limited
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Severn Trent Water Limited, Yorkshire Water Services Limited filed Critical Severn Trent Water Limited
Priority to GB0406331A priority Critical patent/GB2395790B/en
Publication of WO2003021199A1 publication Critical patent/WO2003021199A1/fr

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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
    • G01F1/002—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow wherein the flow is in an open channel
    • 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
    • G01F1/3209—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 using Karman vortices
    • 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

Definitions

  • This invention relates to improvements in flow measurement, and in particular to apparatus for use in measuring low flow rates.
  • Water is an important resource and in order to treat the many millions of litres of water that are used by consumers every day the water industry have built and operate a large number of water and waste water treatment works. In many rural areas the waste water treatment works may serve only a small population although it is not uncommon for larger works to treat waste water for a whole town or conurbation.
  • the works receive waste water which passes slowly through various filters and eventually discharges as clean treated water. This water is discharged to rivers or other waterways.
  • the Environment Agency has specified that the quantity of water that is discharged from a waste water treatment works over a period of time (the overall flow rate) should be continuously measured.
  • the amount of water that is discharged depends partly on uncontrollable environmental factors such as localised or widespread flooding.
  • the flow rate from a waste water treatment works may be very low.
  • the flow rate may perhaps drop down to 50m 3 /day or perhaps lower in extreme cases of prolonged drought.
  • the flow rate must be continuously measured in sites that have a daily waste water flow of greater than 50m 3 /day which corresponds to an assumed population of 250 people.
  • the flow rate must be measured with a total certainty of the measurement of discharge from treatment works for dry weather flow of 50m 3 /day and above needs to be within ⁇ 8 percent over a given day (although this range may be subject to change) .
  • the invention provides a flow measurement apparatus comprising: a channel along which the overall rate of flow of fluid is to be measured, a bluff element positioned in the channel which presents an obstruction to the flow of fluid in the channel, the bluff element generating vortices in the fluid downstream of the element; a transmitter which transmits radiation onto a portion of the surface of the fluid downstream of the bluff obstruction; a receiver which is adapted to produce an output signal dependent upon a portion of the transmitted radiation which is reflected from the surface of the fluid downstream of the obstruction onto the receiver; and processing means adapted to process the output signal to produce a flow rate signal indicative of the overall rate of flow of fluid along the channel.
  • the apparatus of the invention therefore uses the radiation reflected from the surface of fluid flowing downstream of a bluff obstruction to determine the flow rate from the reflection.
  • the transmitter may transmit ultrasound, or sonic or perhaps electromagnetic radiation signals onto the upper side of the fluid surface (i.e. from above) or onto the underside. It is preferred to direct signals from above as this places the transmitter above the surface and so presents less obstructions to the flow.
  • overall rate of flow we mean the volume of fluid which flows through a cross-section of the channel over a period of time.
  • the fluid to be measured may be a liquid such as water, and in many cases it is envisaged that the fluid will be treated waste water.
  • the invention is envisaged to be especially suitable for monitoring the rate of flow of discharged effluent from a waste water treatment works.
  • the processing means may be adapted to determine from the output signal the frequency at which vortices produced in the fluid downstream of the obstruction are shed from the obstruction.
  • the apparatus may be adapted to detect changes in either or both of the amplitude and the time of arrival/phase of the output signal from the receiver over time, and to produce a flow rate signal which is dependent upon the vortex frequency.
  • the vortices cause localised areas of high flow velocity relative to the overall flow velocity along the channel. This alters the topology, and especially the level, of the surface of the fluid. Changes in level alter the time of flight of signals transmitted onto and reflected from the surface and hence the phase of the output signal. Changes in topology can also affect the direction in which the radiation is reflected from the surface and hence affect the amplitude of the output signal. Of course, changes in level may also have an affect on amplitude and topology on the time of flight of the signal in some cases.
  • the processing means may therefore be adapted to determine the height of the surface of the fluid above the base of the channel and/or the topology of a localised area of the fluid surface from the output signal.
  • the processing means may determine the height by calculating the time of flight of an ultrasound signal from transmitter to detector, and monitor changes in amplitude to identify curvature of the surface caused by a vortex.
  • the processing means may determine the frequency of the shedding of vortices by determining the frequency spectrum of the output signal. It may therefore include a time-frequency domain converter.
  • the processing means may be adapted to identify the shortest frequency in the output signal and to assume that the frequency of shedding corresponds to this strongest frequency.
  • the frequency of the variation of the surface may be determined by the processor and the flow velocity subsequently determined according to:
  • two receivers may be provided which respectively monitor radiation reflected from a first region of the surface downstream of the bluff element and a second region which is downstream from the first region, and in which each produces a respective output signal
  • the processing means may be adapted to determine the velocity of vortices moving along the channel by cross- correlating the two output signals.
  • two receivers we may mean two discrete devices, or a single device which is masked to receive radiation from two regions and produces a unique output for each masked area of the receiver.
  • the relative position of the two regions of the surface should be determined to allow an accurate velocity calculation to be made.
  • the bluff element, the first region and the second region may be aligned with the centre of the channel.
  • the overall rate of flow of fluid along the channel may be determined by the processor by providing a combining means which is adapted to combine a value indicative of the frequency of shedding with a value indicative of the level of the fluid in the channel and one or more predetermined values indicative of characteristics of the apparatus. These characteristics may include: the width of the channel, the cross-sectional shape of the channel, the cross-sectional shape of the bluff element, its position relative to the receiver, the dimensions of the bluff element and its position/orientation within the channel.
  • the characteristic value or values may be stored in an area of electronic memory associated with the processing means.
  • the processing means may comprise an electronic circuit which is adapted to receive the output signal from the or each receiver at one or more input terminals.
  • the transmitter and receiver are respectively adapted to transmit and to receive ultrasound radiation. They may be combined into a single transducer with a common housing and may preferably be positioned directly above the channel downstream of the bluff obstruction.
  • the location of the transmitter and receiver could be varied and guiding means could be provided to guide the radiation onto and away from the surface of the fluid.
  • the transmitter and receiver may be arranged to transmit a signal onto a predetermined area of the surface of the fluid downstream of the obstruction and to receive a signal reflected from that area.
  • the transducer may comprise a capacitive type ultrasonic transducer.
  • the transmitter may emit a first controlled cone of radiation perpendicularly downwards onto the surface with the receiver being sensitive to radiation reflected towards it within a second controlled cone.
  • the apparatus therefore is able to monitor an area of the surface corresponding to a spot on the surface.
  • the transmitter may be driven by a pulsed signal or a continuous signal.
  • the processing means may be adapted to combine the pulsed drive signal with the output signal from the receiver to determine the time of flight of the reflected signal.
  • the bluff element may extend upwards from the base of the channel or may extend downwards into the flowing fluid from above. In each case it is preferred that it breaks the surface of the fluid.
  • the bluff body creates vortices in the fluid which are shed in the wake of the body. The vortices move downstream with the flow of the fluid. In an open channel the vortices create high localised velocities which result in a depression in the level of the surface of the fluid.
  • the bluff element comprises an elongate bar which extends perpendicularly up from the base of the channel to a point above the maximum expected level of fluid in the channel.
  • the bluff element may have any one of a variety of shapes. In general, any shape which will shed vortices regularly and strongly may be used.
  • An elongate bar having a triangular cross-section, such as that of an equilateral triangle may be provided, or perhaps a circular cross section.
  • the processing means may be adapted to combine the distance between the detector and the fluid surface with a value indicative of the distance between the bottom of the channel and the detector to determine the depth of the fluid.
  • the processor may apply both approaches in the determination of the rate of flow of the fluid.
  • a minimum depth of the fluid i.e. distance between the bottom of the channel and the fluid surface
  • the channel may be so constructed and arranged to provide a minimum level of fluid in the channel over a range of flow rates. It is preferred that the channel provides a substantially constant depth of fluid over a wide range of flow rates.
  • a back-up weir may be provided downstream of both the bluff obstruction and the region (or regions) of the surface from which radiation is reflected to control the depth of fluid in the channel.
  • a weir may comprise a plate positioned across the channel which may have a v-shaped notch which extends upwards from an apex positioned above the level of the base of the channel.
  • the invention provides a method of measuring the rate of flow of fluid along a channel comprising the steps of: positioning a bluff element in the channel which presents an obstruction to the flow of fluid in the channel, the bluff element generating vortices in the fluid downstream of the element; transmitting radiation onto a portion of the surface of the fluid downstream of the bluff element; generating an output signal dependent upon the transmitted radiation which is reflected from the surface of the fluid downstream of the obstruction which is received; and processing the output signal to produce a flow rate signal indicative of the rate of flow of fluid along the channel.
  • the method may include a step of determining from the output signal the frequency at which vortices produced in the fluid downstream of the bluff element are shed from the bluff element.
  • the frequency of shedding of the vortices may be determined by detecting changes in either or both of the amplitude and the time of arrival/phase of the output signal over time.
  • the method may comprise determining the frequency of the shedding of vortices by determining the frequency spectrum of the output signal.
  • the frequency of the variation of the determined surface level or height or topology over time may be determined according to:
  • the method may comprise measuring radiation reflected from two different regions of the surface of the fluid, a first region of the surface being located downstream of the bluff element and a second region being downstream from the first region, and determining the velocity of vortices moving along the channel by cross-correlating the two measurements.
  • the overall rate of flow of fluid along the channel may be determined by combining a value indicative of the frequency of shedding with a value indicative of the level of the fluid and one or more predetermined values indicative of characteristics of the apparatus.
  • the method may comprise transmitting ultrasound onto the surface and measuring ultrasound reflected from the surface.
  • Figure 1(a) is a side view of a flow measuring apparatus in accordance with the present invention.
  • Figure 1(b) is a view from overhead of the flow measuring apparatus of Figure 1(a) ;
  • Figure 2(a) illustrates the reflection of transmitted signals from a still fluid and (b) from a vortex which disturbs the surface of a flowing fluid in the channel;
  • Figure 3 illustrates a typical frequency spectrum for an output signal obtained from the receiver of the apparatus of Figure 1;
  • Figure 4 is a block diagram illustrating the key elements of the apparatus; and Figure 5 illustrates a second embodiment of a flow measuring apparatus in accordance with the present invention.
  • FIG. 1(a), Figure 1(b) and Figure 4 of the accompanying drawings the flow of fluid out of a treatment works (not shown) is directed into an open topped channel 1 which has a rectangular cross section.
  • the base 2 of the channel 1 is horizontal whilst the side walls 3,4 extend vertically upwards from the base 2.
  • a channel of 200mm width and of 100mm width was employed but in practice other sizes could be used. In general, the size of channel will depend upon the expected flow rate for the fluid from the treatment works.
  • an optional back up weir may be provided close to the end of the channel towards which the fluid flows.
  • a plate could be provided which extends transversely across the width of the channel 1 with a narrow v-shaped notch of arcuate section provided in the plate in a known manner.
  • a bluff body 7, in this example an elongate bar having a triangular cross- section is placed in the flow of fluid in the channel.
  • the cross section is that of an equilateral triangle and it is disposed in the fluid path such that one side of the triangle is orthogonal to the direction of flow and the major axis of the bar is orthogonal to the base of the channel.
  • the length of the bar is chosen to exceed the maximum expected level of fluid in the channel.
  • the level of the surface 8 of the fluid in the channel is visible in Figure 1(b) of the accompanying drawings.
  • the bar 7 introduces vortices into the flow downstream of the bar in the channel.
  • the vortices, which are shed in the wake of the obstruction move downstream along the channel.
  • the frequency at which the vortices are shed from the bluff element is a function of the geometry of the bluff element, the dimensions of the element and the flow velocity according to:
  • the Strouhal number is about 0.14.
  • the Strouhal number is around 0.2 for high Reynolds numbers.
  • a triangular body or other shape with sharp defined edges is preferred as it provides clear vortex shedding points and the Strouhal number is not as dependent upon the Reynolds number as a cylindrical shape.
  • the vortices create areas of high local velocity which in turn causes a slight lowering of the level of the surface of the fluid in the region of a vortex. This causes the topology of the surface to vary downstream of the blocking element.
  • the transmitter/receiver forms part of an electrical circuit represented by the block 10 in Figure l(a,b) of the accompanying drawings.
  • the transducer 9 is supported above the surface of the fluid.
  • a drive signal applied to the transducer causes it to emit ultrasonic waves which strike the surface of the fluid flowing along the channel.
  • the transmitter emits ultrasound in a tight cone which has a central axis of rotation that is orthogonal to the base of the channel.
  • Figure 2(a) illustrates the reflection of ultrasound from a surface of a still body of fluid.
  • Figure 2(b) shows the effect of a passing vortex which disturbs the surface and hence alters the amount of ultrasound reflected to the receiver. It is also noticeable that the distance between the surface and the receiver has slightly changed which will alter the time of flight of the ultrasound between leaving the transmitter and being reflected back to the receiver.
  • Both the changes in amplitude of the output signal and the time of flight of the ultrasound are determined from the output signal of the receiver.
  • the electronic circuit shown schematically in Figure 4 of the accompanying drawings incorporates the ultrasound transducer and comprises a pulse generator 20 which produces short duration square wave pulses that are passed to a drive circuit 21 for the transmitter.
  • the transmitter emits a square wave ultrasound signal that is reflected from the surface and detected by the receiver. This in turn produces a pulsed output signal from the receiver that is passed to an amplifier 22.
  • the output of the amplifier is passed to a processing unit 23.
  • the processing unit 23 comprises an input stage 24a, 24b, 24c which receives at one input terminal the output signal of the receiver.
  • the processing unit monitors the amplitude of the deleted signal over time using an amplitude detector 24a. Alternatively, the time of arrival of the detected signal is monitored 24b.
  • the phase of the detected signal is compared with the phase of the transmit signal using a phase comparator 24c.
  • the drive signal for the transducer is time delayed and applied to a terminal of the phase comparator.
  • the processed output from the comparator will comprise a pulse width modulated signal with the width modulated in accordance with the phase difference between the output signal and the time delayed signal.
  • the length of the time delay is selected to equal the time of flight for a signal from the transmitter, reflected from the surface and back to the receiver when the level of the fluid is midway between its highest expected and lowest expected levels. This ensures that zero phase difference is present for the average height.
  • other delays could be used and in some cases it is foreseeable that the time delay could be omitted altogether.
  • the processed signal from the comparator provides information indicative of the level of the surface of the flowing fluid. This will vary by small amounts at relatively high frequency due to the passing of vortices across the surface from which the signal is reflected. It will also vary at a slower rate over time as the overall average level of fluid in the channel varies.
  • the amplitude of the raw output signal from the receiver will also vary over time as the surface changes due to passing vortices and changes in the level of the fluid. These vortices cause the surface of the fluid to become curved which changes the direction in which the ultrasound signal is reflected away from the receiver.
  • the processing means takes the output signal from the receiver together with the processed output signal and combines these values with pre-set values dependent upon the geometry of the apparatus to determine the flow rate of the fluid.
  • the predetermined values include the distance between the transducer and the base of the channel, the width of the channel and the geometry of the bluff blocking element.
  • the raw output signal is also passed to a frequency analyser 25 which determines the frequency spectrum of the signal.
  • a typical spectrum is illustrated in Figure 3 of the accompanying drawings. A dominant frequency is clearly apparent in the signal which corresponds to the frequency at which vortices are shed.
  • the flow rate of the fluid is determined by the processor according to:
  • V typical representative velocity from equation 1.
  • the value of the calibration factor may be determined experimentally and stored in a memory to be accessed by the processor together with the area value. The area is determined from a knowledge of the width of the channel and the level of the surface determined from the time of flight measurement.
  • two pairs of transmitters/receivers 31 , 32 are provided.
  • the first pair 31 transmit ultrasound onto and receive a reflection from a first region of the fluid surface downstream of a bluff obstruction 33.
  • the second pair 32 transmit ultrasound onto and receive a reflection from a second region of the fluid surface downstream of the first region of the surface.
  • Each transmitter is driven with an identical signal which may be pulsed or continuous depending upon the application.
  • Each of the receivers produces an output signal which is modulated by the changes in the surface created as vortices are shed from the blocking element. Both output signals are fed to a correlator 33 which determines the velocity of vortices in the fluid by monitoring the movement of surface disturbances along the channel.

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  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Measuring Volume Flow (AREA)

Abstract

L'invention concerne un appareil et un procédé de mesure de débit. L'appareil de mesure de débit comprend : un canal (1) le long duquel le débit de fluide total est mesuré ; un élément de résistance à l'écoulement (7) positionné dans le canal (1) et constituant une obstruction au débit de fluide dans le canal (1),générant des vortex dans le fluide en aval ; un émetteur (9) envoyant des rayons sur une partie de la surface (8) du fluide en aval de l'élément de résistance à l'écoulement (7) ; un récepteur (9) adapté pour produire un signal de sortie dépendant d'une partie des rayons émis réfléchis par la surface (8) du fluide en aval de l'élément de résistance à l'écoulement (7) vers le récepteur (9) ; et un moyen de traitement (23) conçu pour le traitement du signal de sortie afin de produire un signal de débit indiquant le débit de fluide total le long du canal (1).
PCT/GB2002/003991 2001-09-01 2002-09-02 Debitmetre a vortex destine a une canalisation a ecoulement libre WO2003021199A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB0406331A GB2395790B (en) 2001-09-01 2002-09-02 Vortex shedding flowmeter for open channel

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB0121256.2A GB0121256D0 (en) 2001-09-01 2001-09-01 Flow measurement
GB0121256.2 2001-09-01

Publications (1)

Publication Number Publication Date
WO2003021199A1 true WO2003021199A1 (fr) 2003-03-13

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WO (1) WO2003021199A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113167609A (zh) * 2018-12-14 2021-07-23 恩德斯+豪斯流量技术股份有限公司 用于测量在管道中流动的流体的流动参数的测量系统
CN114858227A (zh) * 2022-04-27 2022-08-05 北京奥特美克科技股份有限公司 一种明渠流量的测量装置

Families Citing this family (2)

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Publication number Priority date Publication date Assignee Title
DE102016116070A1 (de) 2016-08-29 2018-03-01 Endress + Hauser Flowtec Ag Verfahren zur Erkennung von Fremdkörpern bei einem Vortex-Durchflussmessgerät, ein Vortex-Durchflussmessgerät, eine Anordnung mit einem Vortex-Durchflussmessgerät und eine Abfüllanlage mit einer Anordnung
DE102016116072B4 (de) 2016-08-29 2022-06-02 Endress + Hauser Flowtec Ag Verfahren zur Erkennung von Fremdkörpern bei einem magnetisch-induktiven Durchflussmessgerät, ein magnetisch-induktives Durchflussmessgerät, eine Anordnung mit einem magnetisch-induktiven Durchflussmessgerät und eine Abfüllanlage mit einer Anordnung

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US5170671A (en) * 1991-09-12 1992-12-15 National Science Council Disk-type vortex flowmeter and method for measuring flow rate using disk-type vortex shedder

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US5170671A (en) * 1991-09-12 1992-12-15 National Science Council Disk-type vortex flowmeter and method for measuring flow rate using disk-type vortex shedder

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XIAOFENG LI ET AL: "The sea surface imprint of island lee waves as observed by RADARSAT synthetic aperture radar", GEOSCIENCE AND REMOTE SENSING SYMPOSIUM PROCEEDINGS, 1998. IGARSS '98. 1998 IEEE INTERNATIONAL SEATTLE, WA, USA 6-10 JULY 1998, NEW YORK, NY, USA,IEEE, US, PAGE(S) 763-766, ISBN: 0-7803-4403-0, XP010293070 *
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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113167609A (zh) * 2018-12-14 2021-07-23 恩德斯+豪斯流量技术股份有限公司 用于测量在管道中流动的流体的流动参数的测量系统
CN113167609B (zh) * 2018-12-14 2024-05-24 恩德斯+豪斯流量技术股份有限公司 用于测量在管道中流动的流体的流动参数的测量系统
CN114858227A (zh) * 2022-04-27 2022-08-05 北京奥特美克科技股份有限公司 一种明渠流量的测量装置

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GB2395790B (en) 2005-04-06
GB2395790A (en) 2004-06-02
GB0121256D0 (en) 2001-10-24
GB0406331D0 (en) 2004-04-21

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