Vortex Shedding Flowmeters Research Articles

Lattice gas automaton modelling of a vortex flow meter: Strouhal–Reynolds number dependence

Motivated by recent experimental and computational results concerning a three-dimensional structure of vortices behind a vortex shedding flow meter [M. Reik et al., Forsch. Ingenieurwes. 74, 77 (2010)], we study the Strouhal–Reynolds number dependence in the vortex street in two dimensions behind a trapezoid-shaped object by employing two types of Frisch–Hasslacher–Pomeau (FHP) models. Our geometry is intended to reproduce the operation of a vortex shedding flow meter in a two-dimensional setting, thus preventing the formation of a three-dimensional vortex structure. In particular, we check if the anomalous Reynolds–Strouhal number dependence reported for three dimensions can also be found in our two-dimensional simulation. As we find that the Strouhal number is nearly independent of the Reynolds number in this particular setup, our results provide support for the hypothesis that three-dimensional flow structures are responsible for that dependence, thus hinting at the importance of the pipe diameter to the accurate operation of industrial vortex flow meters.

A vortex-shedding flowmeter based on IPMCs

Ionic polymer–metal composites (IPMCs) are electroactive polymers that can be used both as sensors and actuators. They have been demonstrated for many potential applications, in wet and underwater environments. Applications in fields such as biomimetics, robotics, and aerospace, just to mention a few, have been proposed. In this paper, the sensing nature of IPMCs is used to develop a flowmeter based on the vortex shedding phenomenon. The system is described, and a model is proposed and verified. A setup has been realized, and data have been acquired for many working conditions. The performance of the sensing system has been investigated by using acquired experimental data. Water flux velocities in the range [0.38, 2.83] m s−1 have been investigated. This working range is comparable with ranges claimed for established technologies. Results show the suitability of the proposed system to work as a flowmeter. The proposed transducer is suitable for envisaged post-silicon applications, where the use of IPMCs gives the opportunity to realize a new generating polymeric flowmeter. This has potential applications in fields where properties of IPMCs such as low cost, usability, and disposability are relevant.

A dual phase-locked loop for vortex flow metering

A vortex-shedding flow meter produces an approximately sinusoidal signal whose average frequency is proportional to volumetric flow rate. The frequency of vortex shedding varies over a large range (up to 1:100), depending on the size of the flow meter. The conventional frequency estimator uses a zero-crossing algorithm (ZC), but this approach fails at low flows, where the signal-to-noise ratio is poor. An alternative is to use a phase-locked loop (PLL), but typical single PLL designs cannot cope with a wide frequency range at high noise levels. This paper describes a dual PLL structure that can be used to track the vortex shedding frequency over the flow meter’s full range of operation. This dual PLL provides improved accuracy and tracking ability compared with the conventional zero-crossing algorithm.

Comparison of pressure and ultrasound measurements in vortex flow meters

Commercial vortex shedding flow meters use the relation between the mean flow velocity and the vortex frequency generated by bluff bodies. Usually, the vortices are detected by pressure sensors in the pipe wall or inside the bluff body. Using ultrasound for vortex detection is a powerful, advantageous alternative combination. The ultrasonic beam is modulated by the velocity components of the vortices and varying fluid density. The modulation depends on the structures of the vortices, which are influenced by the bluff body geometry. Measurements and simulations show that conventional triangular bluff bodies with the large size used for pressure measurements are unsuitable for ultrasonic measurements because of the lack of knowledge about secondary vortices. They can be avoided by turning the bluff body facing the tip to the inflow. As ultrasound is very sensitive to the smallest influences, the bluff body size can be reduced considerably. Even the shape can be adapted. The best results are obtained with a 3 mm threaded rod as the bluff body in a pipe of 100 mm diameter. Pressure losses behind such small bluff bodies can be neglected.

Validation of vortex flowmeters

A vortex-shedding flow meter produces an approximately sinewave signal whose average frequency is proportional to volumetric flow rate. The frequency of vortex shedding varies over a large range (up to 1:100), depending on the size of the flow meter. The conventional frequency-estimation method-a zero-crossing algorithm-fails at low flows, where the signal:noise ratio is poor. The paper describes a dual phase-locked loop structure that tracks the frequency over the flowmeter's full range with improved accuracy. The lock indicators associated with each PLL provide the SEVA metrics.

Modelling and tracking a vortex flow-meter signal

The piezoelectric sensor in a vortex-shedding flow meter produces a raw signal whose average frequency indicates volumetric flow rate. Imposed on this signal are amplitude and frequency variations, together with noise caused by plant-specific pressure pulsations. The objective of this paper is to provide and verify a simulation model of the overall signal, so that different frequency-tracking methods can be compared. In particular the performance of a zero-crossing algorithm is evaluated. A prefilter is designed to extend the tracking ability to lower flow rates, where the signal:noise ratio is poor. Experimental tests in real time on a flow rig demonstrate the improvement in turn-down by a factor of two.

Optimization of acoustic signals in a vortex-shedding flowmeter using numerical simulation

Abstract Most commercial vortex-shedding flowmeters rely on a known relationship between the vortex-shedding frequency and the mass flow, needing a regular and well-defined vortex structure as well as a shedding mechanism. However, in most known current designs, the pressure sensors are included into the bluff body, imposing severe restrictions on the shape of the body. This results in rather irregular pressure signature of the vortex system, leading to problems in the signal processing. In the present work, the flow about the bluff body in a vortex-shedding flowmeter is numerically investigated using a Navier–Stokes solver, capable of handling unsteady, compressible and viscous flows in two-dimensional and three-dimensional geometries. The computations are compared with experimental results obtained by ultrasonic measurements downstream of the bluff body. Several different body shapes are studied, trying to optimize the resulting pressure signature downstream of the body. Recommendations regarding an aerodynamically optimal shape of the bluff body are made.

カルマン渦流量計の渦発生体形状の最適化と不確かさの算出法に関する研究

A vortex shedding flowmeter is widely used for measurements of various fluids in many fields of industry because of its numerous advantages, such as wide rangeability, long term reliability and low maintenance cost. Today, vortex flowmeters of various designs are manufactured by many companies in the world although the flowmeter design is not specified in the present industrial standards. The research project presented in this paper consists of a series of experimental studies and its objective is to develop a new design of a vortex shedding flowmeter, which can be used without any calibration using the actual fluid. This paper describes the first result of the project, i.e. optimization of the flowmeter design and determination of the measurement uncertainty. First, four of the bluff body dimensions were selected and optimized through series of systematic experiments so that the Strouhal number was least dependent on the Reynolds number. Next, the optimized design has been applied to flowmeters with inner diameters from 100mm to 400mm. These flowmeters were calibrated and the Strouhal number was precisely determined. Finally, a new method to calculate the uncertainty of the Strouhal number from the dimensional deviations of the parts of the flowmeter was developed experimentally and analytically. This project has been carried out by National Research Laboratory of Metrology and 10 collaborating companies in Japan. The results shown in this report are obviously very important for future standardization of a vortex flowmeter and for improvement of the accuracy in flow measurement in the world.

渦発生体基部の間隙によるカルマン渦流量計の特性改善

By placing a gap around the bases of the bluff body, a linearity of a vortex shedding flowmeter has been significantly improved. Measurement error caused by an upstream pipe fitting has also been remarkably reduced.

Fiber-optic Fabry-Perot flow sensor

A new design of a vortex-shedding flowmeter with a fiber-optic Fabry–Perot interferometer (FFPI) as the sensing element is described here to measure the liquid flow velocity in a pipe. The flow velocity is determined by measuring the frequency at which the reflected optical power from the FFPI is modulated. Experimentally, a linear dependence of optical modulation frequency on flow velocity is observed over the range from 0.14 to 3.0 m/s, in good agreement with theoretical prediction. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 18: 209–211, 1998.

Vortex shedding flowmeters and ultrasound detection: signal processing and influence of bluff body geometry

The present paper investigates vortex shedding flowmeters coupled with a detection of the vortex frequency by an ultrasound barrier behind the bluff body. After a short explanation of the measurement principle a novel digital algorithm for determining the vortex frequency is presented. Another issue deals with the influence of the bluff body geometry on the measurement process. Comparisons between numerical simulations and experiments were performed in order to analyse the relationship between the shape of the vortex body and the vortices developing behind it.

The Effects of Turbulence and Unsteadiness on Vortex Shedding From Sharp-Edged Bluff Bodies

Motivated by a desire to evaluate vortex shedding flow meters for measuring velocity in unsteady turbulent flow applications, the objective of our work was to study the effects of flow disturbances on vortex shedding from sharp-edged bluff bodies. In particular, the combined effects of turbulence and unsteadiness were examined, as well as their separate effects using controlled wind tunnel tests. After causing an initial and sudden decrease in the Strouhal number, increasing turbulence intensity from 2.5 to 10 percent resulted in only a 2.4 percent increase in the Strouhal number, for turbulence with a length scale of 0.5 bluff body diameters. Turbulence integral length scale had a significant influence on the Strouhal number, with the greatest effect exhibited for length scales near 3 bluff body diameters. Turbulence of this length scale caused a 26 percent decrease in the Strouhal number, as compared to a low-turbulence base case. Fluctuating pressure amplitude and signal-to-noise ratio were also affected by turbulence, and decreased significantly when the integral length Kali was increased from 0.25 to 0.75 bluff body diameters for a turbulence intensity of 10 percent. Unsteadiness caused lock-on for forcing at the Strouhal frequency, twice and four times the Strouhal frequency, while no lock-on was observed for forcing at half the Strouhal frequency. The range of lock-on increased with increasing perturbation amplitude and was asymmetric about the resonant frequency. For the cases investigated, the effects of combined turbulence and unsteadiness were additive, with the turbulence shifting the Strouhal frequency, and the unsteadiness causing lock-on about the shifted Strouhal frequency. The results of this study suggest that vortex shedding flow meters should be calibrated in turbulent flows and turbulence length scale must be controlled at the bluff body. Lock-on can be avoided by sizing the bluff body so that the shedding frequency is always much greater than any disturbance frequency in the flow.

Evaluation of Vortex-Shedding Flow Meters for Monitoring Air Flows in HVAC Applications

This paper describes the evaluation of vortex-shedding flow meters under highly disturbed flow conditions that occur in HVAC ducts. Field data were acquired from a typical HVAC duct to quantify the disturbed flow conditions, and to set the bounds for controlled wind tunnel experiments. Wind tunnel experiments were then used to demonstrate that vortex shedding flow meters can be used for measuring air flows in the highly disturbed conditions that occur in HVAC ducts, but that care must be taken in their design and application. The results imply that vortex shedding flow meters should be calibrated in turbulent flows, and that the turbulence length scale at the bluff body must be controlled to ensure accurate meter calibration. Periodic unsteadiness in the mean flow caused the vortex shedding to lock-on to a sub-harmonic of the disturbance frequency for disturbances at various multiples of the shedding frequency. No lock-on was observed for a forcing frequency at half the shedding frequency, indicating that...

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.

Intensity-modulated optical-fibre vortex-shedding flowmeter

Optical-fibre intensity sensing of fluid flow rate is achieved using single-mode fibre tapers to detect the shedding frequency in a vortex-shedding flowmeter. Single-mode fibre tapers are characterized by their transmission versus bending at 1.3 μm and modelled using local normal modes and modal coupling techniques. A prototype vortex-shedding flowmeter is realized with the fibre taper acting as a secondary sensing strut.

Installation effects on vortex shedding flowmeters

Numerous measurements of the effects of pipe fittngs on vortex shedding flowmeters are carried out as a contribution to flow metering standards. A water test line of 150 mm diameter is used in the experiments covering a Reynolds number range of about 2 × 10 5 to 10 6. The effects of six kinds of piping configurations are examined at various upstream straight pipe lengths and all four kinds of liquid vortex shedding flowmeters, which were commercially available in Japan, are tested. The vortex shedding flowmeters are compared with a turbine meter in experiments designed to evaluate reproducibility of measurements. The uncertainty of the measured data is estimated at about 0.1%. It is found that the magnitude of each installation effect strongly depends on the design of the flowmeter. The experimental results are presented in detail and a table is given of the minimum upstream straight pipe lengths needed to suppress the effects to less than 0.5% for each of the tested flowmeters. This can be used as guidance in the installation of vortex shedding flowmeters.

An optical fibre vortex sensor for flowrate measurements

An optical fibre vortex shedding flowmeter is presented, which uses the detected light intensity variations induced by the vortices at the output of a multimode optical fibre in order to determine the vortex shedding frequency. This frequency gives a measure of the flowrate crossing the flowmeter. The device is tested on industrial test rigs in the case of water flow. Applications of such an optical fibre device could be found in industrial processes where the flowrate of explosive media has to be measured or in areas with strong electromagnetic interferences.

Air flow measurement by vortex shedding from multimode and monomode optical fibres

Wind tunnel experiments to investigate flow-induced vibration by vortex shedding from both multimode and monomode optical fibres are described, covering Reynolds numbers from 30 to 240. The fibre vibration frequency was a linear function of air flow speed over the range 2 to 8 m s-1. Multimode fibre vibration was detected by the modulated bend loss at the fibre clamping points. A fibre Mach-Zehnder interferometer enabled the strain, and hence vibration amplitude, of a monomode fibre to be determined under similar flow conditions. It was thus shown that for vortex shedding flowmeters with fibre sensing elements, interferometric techniques offer no significant performance advantage over simpler bend loss modulated devices.

The influence of shedder shape on the performance of the electrostatic vortex flowmeter

The results of an experimental investigation into the influence of the cross-sectional bluff body (shedder) shape on the performance of an electrostatic vortex shedding flowmeter are presented. This flowmeter uses the modulated signal of the electrostatic charge deposited on an electrode as a means of registering vortex shedding frequency. In this study, the dimensionless signal to noise ratio was used to assess the performance of each bluff body and various electrode configurations. The results indicate that the meter incorporating a rectangular electrode positioned on the front face of a T-shaped shedder produces the best signal quality and best meter performance.

A passive signal processing technique for monomode fibre optic vortex shedding flowmeters

A passive signal processing technique is described for the recovery of the frequency of large amplitude oscillatory measurements from interferometric fibre optic sensors. The technique was developed for vortex shedding flowmeters, and was evaluated in this application and compared with other signal processing schemes. The flow-induced vibration frequency of one arm of a fibre Mach-Zehnder interferometer was measured in wind-tunnel experiments, demonstrating a linear frequency flow characteristic over the range 2.5-8 m s-1. Values for the fibre strain amplitude were also obtained.