Vortex-shedding Meter Research Articles

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.

Instantaneous vortex-shedding behaviour in periodically varying flow

Vortex shedding behind a stationary T–shaped cylinder in a circular pipe subjected to periodically varying flow was studied at Reynolds numbers between 6.17 × 103 and 2.46 × 104, whereas the frequency ratio, Fs/Fo, ranged from 0.29 to 14.64. Fs denotes the natural vortex-shedding frequency referred to the mean flow, and Fo denotes the frequency of periodically varying flow. By adopting the Hilbert transform to analyse the velocity signals measured, the instantaneous vortex-shedding frequency was obtained. Based on this quantity, one could categorize the vortex-shedding phenomenon observed into three regimes, namely, quasi-steady vortex shedding for Fs/Fo > 4.37, hysteresis vortex shedding for Fs/Fo= 1.56-4.37 and non-interactive vortex shedding for 0.29 < Fs/Fo < 1.56. In the regime of quasi-steady vortex shedding, the instantaneous vortex-shedding frequency follows the periodically varying flow without phase lag. In the regime of hysteresis vortex shedding, the instantaneous vortex-shedding frequency lags behind the periodically varying flow. Phase lag roughly varies linearly with Fs/Fo. Further, the variations of non-dimensionalized instantaneous vortex-shedding frequencies obtained in the accelerating and decelerating portions of the periodically varying flow are found to depend on Fs/Fo and ΔU/Ū. In the regime of non-interactive vortex shedding, the vortex-shedding frequency tends to vary with the mean velocity of periodically varying flow, excluding the occurrences of primary and secondary lock-on at Fs/Fo= 0.97-1.03 and 0.495-0.514, respectively.

Effects of water in oil and oil in water on single-phase flowmeters

The effect of two-phase flow on the performance of a range of single-phase flowmeters has been investigated experimentally using the National Standard Multiphase Flow facilities at NEL. The flowmeters tested were 2-inch and 4-inch positive displacement meters, venturi meters, helicoidal and flat-bladed turbine meters, 2-inch U-tube, 3-inch and 1.5-inch straight tube Coriolis meters and a 4-inch vortex shedding meter. The flowmeters were tested in oil flow with water and water flow with oil. The second component fractions were varied from 3% up to 15% by volume. The aim of the project was to quantify the effect of second-phase fluid components on the basic uncertainty of a range of single-phase. These tests have provided evidence of the suitability of particular flowmeters for two-component flow applications. Comparisons have been made between generic type and size of flowmeter. The oil-in-water and water-in-oil tests indicated that the uncertainty in the outputs of the flowmeters tested were generally within ±1% relative to the reference flowrates, although some errors as high as 5–10% were also observed. Most of the measurements from the turbine flowmeters and the positive displacement flowmeters were within ±0.4% of the reference flowrates.

Evolution of an improved vortex generator

This paper reviews the process, stretching over several years and with contributions from several workers, by which an improved body shape for use in vortex shedding meters was designed and tested. A priori knowledge of the fluid mechanics involved in vortex shedding, supplemented by information obtained from observation (flow visualization) and measurement (spectral analysis), was used to direct the design process. Particular attention was focused on stabilizing the vortex sheddind so that signal dropout and unnecessary limitations to the operating range could be attacked at their source. After examination of the performance of a number of different cylinder cross-sections, and experiments involving splitters and afterbodies, a detailed study of a generator consisting of a circular cylinder split across its lateral diameter was undertaken. Subsequently, it was found that the performance of this (already good) generator could be improved still further by shaping the rear surface of the cylinder. The split cylinder with concave rear surface resulting from this design process was shown to provide the strongest and most regular vortex shedding of all the shapes tested. Moreover, the performance benefits of this shape can now be explained in terms of the flow structure in the near wake.

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.

An electrostatic vortex shedding meter

The conventional vortex shedding flowmeter performs satisfactorily in the metering of many types of fluid, but the reliability of its sensor can be questionable when exposed to hostile environments. In this paper the standard piezoelectric sensor in a commercially available flowmeter was replaced by electrodes positioned within the flow tube. For air flows the periodic change in magnitude of the electrostatic charge, accumulating on the electrodes, through the action of the streaming current, was seen to occur at a frequency equal to that for the unmodified vortex shedding meter. Its inherent simplicity in construction and robustness given this meter appealing aspects in some applications.

Computation of flow in a vortex-shedding flowmeter

A computational technique for unsteady incompressible viscid flow applicable to any 2-dimensional flow geometry is presented. The method adopts a stream function vorticity approach and uses an Alternate Direction Implicit Technique to march the vorticity in time, and a successive over-relaxation technique to obtain the stream function at each time level. Initial calculations are presented for the vortex shedding from a circular cylinder where the Strouhal number is computed to within 10% of the empirical value over a range of Reynolds numbers up to 1250. The flow within a commercial vortex-shedding meter is also computed and results indicate how the design of the bluff body affects the strength of the shed vortices and they also highlight the best locations for the frequency detector.

An Application of Vortex Shedding Flowmeters

After a study of available flowmetering devices, the Santa Clara Valley Wtr. Dist. installed insertion‐style vortex shedding meters in conjunction with its Penitencia water‐treatment plant and East Pipeline distribution main. The performance of these meters in a practical application in a treated water distribution system is discussed and evaluated in this article.