Vortex Meter Research Articles

Wet gas flow metering by combining a vortex flowmeter with disturbance wave frequency

Based on a conductance-vortex meter dual-modality system, a novel wet gas flow measurement method is proposed, which combines a vortex meter with disturbance wave frequency. A negative relationship between the vortex signal quality and the disturbance wave frequency is found, on which basis a new segmented fast Fourier transform–continuous wavelet transform vortex frequency extraction method is proposed. Uniform exponential equations are derived for meter over-reading, taking into account the liquid-phase Reynolds and gas-phase Weber numbers, the disturbance wave Strouhal number, density ratio, and the liquid-phase Reynolds number. Finally, a Newton–Armijo-based wet gas metering model is developed by combining these two correlation equations. The percentage errors (PEs) of the gas flow in wet gas are within ±1.0% error bands with uncertainty of 0.56%. The full-scale PEs of liquid flow are within ±10% error bands with uncertainty of 4.71%. The disturbance wave frequency is used to correct the meter over-reading. As no liquid film thickness calibration is needed, the proposed method has low requirements on the conductivity of the medium and hence the application scope of media could be expanded.

Wet gas metering using a vortex cross-correlation meter based on fluctuating pressure measurement

A solution for wet gas metering was developed with a vortex meter by using pressure sensors and correlation technology. For the fluctuating pressure measurement, the micro pressure sensors, especially the probe-transducer systems, were designed to acquire reliable vortex signals. For the experiments, an annular mist flow loop with a film metering system was established, and the tests were conducted on various pressure, gas velocity and liquid flowrate conditions. Then, the dimensionless convection velocity, named convection coefficient, and the peak value of the normalized cross-correlation function, named correlation coefficient were calculated. A piecewise function was developed for the convection coefficient with modified Weber number where the segmentation was determined by the correlation coefficient. Finally, the wet gas measurement model was developed and realized by iterative algorithm. Under the present conditions, the ±5% error bands contain 91% of the relative errors for gas flowrate prediction, the mean absolute percentage error is 2.54%, and the uncertainty of gas flowrate prediction is 2.85%. The primary advantage of the proposed method is that the convection coefficient is almost independent of liquid fraction, no extra systems are necessary for watercut measurement, hence providing a cost-effective solution for wet gas metering.

Computational Analysis of Strouhal Number Variation in Vortex Meters

Vortex meters are used to measure the flow rate by measuring the vortex shedding frequency behind a trapezoidal (or triangular)-shaped body. In the current work, analysis of various parameters affecting the performance of vortex flowmeters is carried out, using computational flow simulation. The linear relation between vortex shedding frequency and flow velocity is verified. The variation of Strouhal number with shedder angle, length and width is investigated.

Quadrature Demodulation 을 적용한 초음파 유량계 시스템 개발

There are various methods for measuring flow rate. In measuring the flow rate, types of flow meters include electronic turbine, ultrasonic wave, vortex, and differential pressure meters. Typically, turbine flow meters and ultrasonic flow meters are often used to measure liquid flow rates. Because of a disadvantage whereby the turbine type requires cutting the tubing, this paper presents an ultrasonic flow meter. In this paper, the flow rate is measured using the difference in the time of flight (TOF) for ultrasonic waves. In order to improve TOF accuracy while implementing a simple system at a low cost, TOF was measured using the quadrature demodulation and phase difference of the received ultrasonic signal. Experiment results are compared with two commercial products: a turbine flow meter and an ultrasonic flow meter. The results show that accuracy with the proposed ultrasonic flow meter is similar to the two commercial products.

Development of a pressure based vortex-shedding meter: measuring unsteady mass-flow in variable density gases

An entirely pressure-based vortex-shedding meter has been designed for use in practical time-dependent flows. The meter is capable of measuring mass-flow rate in variable density gases in spite of the fact that fluid temperature is not directly measured. Unlike other vortex meters, a pressure based meter is incredibly robust and may be used in industrial type flows; an environment wholly unsuitable for hot-wires for example. The meter has been tested in a number of static and dynamic flow cases, across a range of mass-flow rates and pressures. The accuracy of the meter is typically better than about 3% in a static flow and resolves the fluctuating mass-flow with an accuracy that is better than or equivalent to a hot-wire method.

A new approach to detection of vortices using ultrasound

The measurement principle of vortex flowmeter is based on von Karman vortex shedding phenomenon. Frequency of vortices, behind the bluff body, is proportional to the mean flow velocity. There are different ways of detection of vortices, and different sensors are used (presser sensors, capacitive sensors, thermo-resistance sensors, ultrasonic sensors, etc.). Proposed method to vortex identification, presented in this paper is based on simultaneous detection of pair of vortices with opposite circulation, by means of two pairs of ultrasonic transducers. A beam of ultrasound, from ultrasonic transmitter to ultrasonic receiver is transmitted perpendicularly to the vortex street. The received ultrasonic signal is amplitude and phase modulated. Frequency of demodulated signal is equal to the frequency of vortices. This technique allows a number of advantages comparing to conventional solutions: reduction, or elimination of noises caused by installation vibration and disturbances in the flow, higher sensor sensitivity, which as a result leads to a possibility of a reduction of the bluff body size, i.e. reduction of the pressure drop on the flow meter, increase of the measurement range in the low flow region, the possibility of redundant operation of the flow meter, reduced measurement uncertainty, instrument technology improvements, improved reliability of the instrument, assured improved statement of complete uncertainty contributions, improved metrology of the equipment as such and calibration procedures that contribute to measuring capabilities etc. For experimental testing a prototype vortex flowmeter of a nominal inner diameter (ID) 50mm is developed. A cylindrical bluff body for vortex shedding is used. Ultrasonic transducers based on piezo-crystal PZT-5A, inserted in the wall of the vortex meter casing are utilized. The testing of prototype ultrasonic vortex flowmeter is realized on the calibration station on the water. The results at the testing point to the possibility of measuring flow of liquid fluids at velocities less than 0.5m/s, with an uncertainty better than ±1%.

Flow rate measurement in a pipe flow by vortex shedding

The flow rate measurement of liquid, steam, and gas is one of the most important areas of application for today’s field instrumentation. Vortex meters are used in numerous branches of industry to measure the volumetric flow by exploiting the unsteady vortex flow behind a blunt body. The classical Karman vortex street behind a cylinder shows a decrease in Strouhal number with decreasing Reynolds number. Considering the flow behind a vortex shedding device in a pipe the Strouhal-Reynolds number dependence shows a different behaviour for turbulent flows: a decrease in Reynolds number leads to an increase in Strouhal number. This phenomenon was found in the experimental investigations as well as in the numerical results and has been confirmed theoretically by a stability analysis.

Detection of Vortex Frequency in Gas Flow with Ultrasound

The coincidence of vortices generated by a bluff body in a gaseous flow (Karman vortex street) with an ultrasonic beam crossing these vortices raises a lot of questions concerning physics and signal processing. The ultrasonic signal will be complex modulated. The spectrum of the resulted signal shows the carrier frequency of ultrasound and two narrow sidebands with the information about the modulation. For further signal processing the carrier frequency must be filtered. The carrier frequency can be shifted to zero by digital processing and undersampling the signal by an integer multiple. Then the sideband with its low frequency range can be analysed. The real and imaginary parts of the signal can be determined by sampling the signal shifted by 90 degrees (Hilbert transform). Even the 90 degree shifted angle can be measured by undersampling. The sensitivity of the vortex meter depends on the bluff body size. A simple relation between the bluff body dimension and the sensitivity, the vortex frequency, respectively, is shown.

A study on signal quality of a vortex flowmeter downstream of two elbows out-of-plane

Experiments were made with a vortex meter situated downstream of two elbows out-of-plane, at Reynolds numbers between 7.8×10 4 and 2.1×10 5. Analysis on the signals obtained from a piezo-electric sensor embedded in the vortex shedder shows that the signal quality, concerned with the vortex shedding frequency component, deduced in the vicinity of 15 pipe diameters downstream is superior to that at other locations, and is remarkably better than that found in the region of fully-developed turbulent pipe flow. The vortex shedding frequencies measured in this region, in terms of the Strouhal value, fall within 0.129±0.001, that 0.129 is the reference value reduced in the fully-developed turbulent pipe flow region. Also noted, the uncertainty interval associated with the vortex shedding frequency measured in this region is smaller than that reduced in the region of fully-developed turbulent pipe flow.

Vortex flowmeter with enhanced accuracy and reliability by means of sensor fusion and self-validation

Due to the complementary qualities of the principles of vortex frequency estimation and vortex time of flight estimation they are ideally suited for an effective sensor fusion within flow measurement. A flow meter which combines the results of the two individual systems in an intelligent manner was built and beside theoretical considerations the performance of the fused system is demonstrated by a variety of measurements. In comparison with conventional vortex meters which only use the vortex frequency to estimate the flow rate, the measuring range can be extended by a factor of 8–10 and the accuracy of the system as well as the robustness to disturbances like a second fluid phase or depositions on the bluff body are strongly increased.

Linearity of the vortex meter as a function of fluid viscosity

The vortex phenomenon has found many applications in flow metering. The vortex shedding flowmeter is recommended for use with relatively clean liquids, high pressure gases and vapours, but is not recommended for high viscosity liquids. In this paper we describe experiments concerning the dependence of the linearity on the fluid viscosity.

Development of the T-ring vortex meter

A new type of vortex-shedding meter has been developed, in which the bluff body is in the form of an annular ring with a T-shaped cross-section. Because this is axi-symmetric it disturbs the flow much less than a transverse bluff body. This leads to a meter which is considerably more repeatable, and hence potentially more accurate, than a conventional vortex meter. It also has excellent linearity, and an exceptionally low pressure drop. The paper describes the design and performance as well as the current problems with development of a vortex detector.

Vortex flowmeters — Installation effects

The calibrations of flowmeters are dependent to some extent on the geometry of the pipework and fittings both upstream and downstream, and on the steadiness of the flow. The vortex flowmeter is no exception and all manufacturers recognize this by specifying minimum straight lengths on either side of the meter. There is a surprising lack of experimental data, however, and no international standards or codes of practice exist to enable the meter user to judge whether or not the straight lengths recommended by the manufacturer are adequate. This paper will review data on vortex meter installation effects recently obtained at the University of Surrey and NEL. These include results with a metering package consisting of a vortex flowmeter and a perforated plate flow straightener.

Effects of unsteady phenomena on flow metering

After classification of the various steady and unsteady phenomena that can disturb gas flow, information gathered by Gaz de France's Research Division on the effects of unsteady disturbances, such as those generated by pressure reducers, is reviewed. Experimental results are given for orifice plates, turbine, vortex and ultrasonic meters, showing that the errors induced can be of the same order as, or greater than, those created by steady disturbances. Methods for minimizing these effects and research that still needs to be done are discussed.

Advantages of and developments in dual bluff-body vortex flowmeters

The paper begins by reviewing the main performance characteristics of vortex flowmeters - eg, signal stength, signal-to-noise ratio, frequency, repeatability, meter factor and blockage ratio. It then develops a performance equation which calculates the total time required to capture sufficient cycles to achieve a given overall repeatability. From this equation we see that for a typical single bluff-body vortex meter the time required to achieve an overall repeatability of 0.02% is 387min. This underlines the point that single bluff-body meters are in general not very useful for fiscal metering or custody-transfer applications. The paper then reviews the general principles of vortex shedding from two bluff bodies in tandem, explaining that there are two distinct flow regimes, depending on whether the bluff-body separation is less than, or greater than, a critical value. A summary of results is presented for initial tests on 15 combinations of two rectangular bluff bodies in tandem, together with three single bluff bodies for comparison. These initial tests were carried out in a 300 mm diameter wind tunnel at a free-stream velocity of 6.5 mls and a turbulence intensity of 0.5%. Seven combinations with optimum separations were then tested over a free-stream velocity range between 0.6 and 13.0 mls and at three turbulence levels. Detailed results showing the variation in RMS vortex velocity, signal-to-noise ratio, meter factor and percentage frequency standard deviation with free-stream velocity are presented. Certain of these combinations give a far more regular and repeatable vortex signal than single bluff bodies; the time required to achieve an overall repeatability of 0.02% is as low as 33 min. All of the above dual combinations have a small separation, so that vortex shedding takes place behind the downstream bluff body only. Detailed maps of the vortex field around certain dual combinations are presented which show that, in certain cases, the oscillations of boundary layers in the gap are strongly correlated with the oscillations of boundary layers moving around the bluff bodies. Thus the vortex shedding from the downstream bluff body is reinforced by oscillating boundary layers moving through the gap.

Application of Sonic Nozzles in Field Calibration of Natural Gas Flows

This paper presents Chevron Oil Field Research Company’s operating experience using the sonic nozzle as a proving device for measuring natural gas flows in field tests. The nozzle reference flow rate was used for calibrating orifice, turbine, and vortex meters in three tests with a pipeline quality gas and an unprocessed natural gas as the working fluid. For pipeline gas, the field calibration results show good agreement between the sonic nozzle reference and a turbine meter while the accuracy of orifice metering is size dependent. The 4-in. (102-mm) orifice meter flow rates agree well with the nozzle reference, but the 16-in. (406-mm) orifice flow measurements are up to 2 percent lower. Deviations between the test meters and the sonic nozzles are generally larger for the unprocessed gas. These field projects demonstrate that sonic nozzles can be operated successfully as a prover for processed natural gas, while more work is needed to study the critical flow in nozzles for unprocessed natural gas.

Installation Effects on Vortex Flowmeters

Most types of flowmeter are affected by flow disturbances caused by nearby pipe fittings. In the case of the vortex flowmeter, users currently have to rely on manufacturers' recommendations on minimum straight pipe lengths on either side of the meter as there are no relevant standards or codes of practice and little published experimental data. The paper presents some experimental results on the effects of upstream pipe roughness, single 90† bends, and pairs of 90† offset bends on the calibration in air of a vortex meter with a rectangular section bluff body. The results show that this particular vortex meter is sensitive to the roughness of the upstream pipework and required straight pipe lengths of about 55 diameters to avoid significant calibration changes caused by upstream bends. Installation lengths can be reduced by placing a flow straightener upstream of a meter particularly if the straightener-meter package can be calibrated as a unit. This concept has been explored using a Mitsubishi flow straightener with the vortex meter and promising results have been obtained with a package of 10 diameters overall length.

An Investigation of the Trailing Vortex System Generated by a Jet‐Flapped Wing Operating at High Wing Lift Coefficients

Abstract : The purpose of the investigation was to measure the geometry of the trailing vortex generated behind a jet-flapped wing. Such vortices can pose a serious hazard to aircraft that penetrate them. Previous investigations performed on conventional wings indicate that these vortices persist for some time and have maximum tangential velocities which increase linearly with the lift coefficient. As future aircraft may employ high lift devices such as jet-flapped wings, the vortices generated could be even stronger. Two semispan models of a jet-flapped wing were tested in a subsonic wing tunnel. Parameters varied during testing included the jet flap angle, angle of attack, aspect ratio, and jet momentum coefficient. Vortex measurements were obtained using a vortex meter which measured the rotational speed of the fluid within the vortex. Values obtained were numerically integrated to yield the tangential velocity and circulation distributed through the vortex. Experimental results indicate that the maximum tangential velocity increases to a maximum and then decreases with continually increasing jet blowing. At high values of jet blowing, the vortex was found to decay rapidly downstream. (Author)