On measurement uncertainty of a vortex flowmeter

The measurement uncertainty of a T-shaped vortex flowmeter was examined with a gas flow calibration facility, for Reynolds numbers, Re_d, in a range of 2.56 × 10⁴-1.56 × 10⁵. The total uncertainty interval of the Strouhal values deduced from a Fourier spectral analysis was ±0.745%, and the linearity of the data was ±1.78%. Meanwhile, a scheme based on pulse counting in reference to the analog signals measured gave the total uncertainty interval of the meter factor as ±0.568%, with the linearity ±1.89%. Further, the flowmeter was tested in a fully developed water pipe flow facility, for Re_d of 5.6 × 10³-5.29 × 10⁴. The vortex shedding frequencies were obtained with the techniques of Fourier transform and autocorrelation, respectively. At low flow rates, the autocorrelation technique gave a smaller uncertainty interval than the Fourier analysis did; at higher flow rates the situation was reversed. The linearity of the St values obtained in the water pipe flow experiment was ±0.391%, noticeably smaller than that obtained in the gas flow facility.