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To obtain the specific values of the flowrate measurement uncertainty using the ultrasonic Doppler velocity profile (UVP) method under disturbed flow conditions, experimental measurements were performed. To generate a disturbed flow, obstacle plates were installed upstream of the test section. To estimate which experimental parameter dominates the uncertainty, parametric examinations are conducted for the obstacle plate configuration, the distance between the obstacle plates and the measurement section, the incident angle of the ultrasonic beam, and the flowrate. The maximum deviation of the measured flowrate from the reference flowrate exceeds 2% when the flowrate is measured 8 D downstream of the obstacle plate. At a distance of 25 D downstream, the deviation is within the fundamental uncertainty level of the flowrate measurement using the UVP method. Because several uncertainty factors in this examination are cross-correlated with each other, the uncertainties of these factors are evaluated independently using analysis of variance (ANOVA). The total uncertainty is 7.98%, 1.97%, and 1.14% at 8 D , 16 D , and 25 D , respectively. [ABSTRACT FROM AUTHOR]

Abstract: This study proposes a new method that determines the number of transducers for accurate flow rate measurements using the ultrasonic velocity profile (UVP) method downstream of double elbows. Because the UVP method can measure velocity profiles over a pipe diameter and integrate them to obtain the flow rate, it is also expected to obtain an accurate flow rate using multiple transducers under asymmetric flow conditions formed downstream of elbows. The new estimation method employs the wavenumber of velocity profile fluctuation along a circle on a pipe cross-section, obtained by fast Fourier transform (FFT). The number of transducers was determined as twice the wavenumber at the foot of maximum Fourier amplitude, on the basis of the sampling theorem. The method was evaluated by a preliminary experiment and numerical simulations using computational fluid dynamics (CFD). The experimental and simulated velocity profiles were located at three times the pipe diameter (3D) and 1D downstream of the second elbow, respectively. Reynolds numbers for the experiment and simulations were set at 4×104 and 5×106, respectively. Using the number of transducers estimated by FFT, the standard deviations of flow rate errors were less than 1% or 2%, verifying the efficacy of the new method. [Copyright &y& Elsevier]

[Display omitted] • False detection depends on the pulse position in the reference window and SNR. • False detection rate increases as the number density of reflectors decreases. • Proposed method is able to improve accuracy in the flow rate measurement. • The boundary value of the edge cutoff time of the proposed method is 1.7 T 0. • The edge cutoff time is better to be set at 1.7 T 0 with the threshold of at least 0.6. This paper discusses the influence of decreasing the number density of reflectors on the false detection rate of ultrasound time-domain correlation (UTDC) measurements. False detections are expected to be inhibited when the number density of reflectors decreases. This is because the sidelobe peaks of the cross-correlation coefficient becomes smaller when each pulse can be recognized separately, rather than when some pulses overlap. However, this separated waveform pattern is expected to occur more frequently as the number density of reflectors decreases. This pattern develops because parts of individual pulses exist in the reference window. In this study, the influence of the positional relationship between the pulse and the reference window in the presence of noise was investigated by simulating the UTDC signal process using an assumed pulse waveform. The simulation results show that there is a high probability of an increase in the false detection rate when the pulse length is under approximately 1.7 times the ultrasound period. The simulation results also showed that damped waveform region has a high potential to cause false detection. The flow rate was measured for three different reflector number densities at a national standard calibration facility for water flow measurements in Japan. The conditions under which false detection occurred and the influence on the flow rate error were evaluated. The measurement results showed good agreement with the simulation results. In addition, this paper also presents an application of a new signal processing method for UTDC measurements for reducing the rate of false detections caused by the pulse pattern. The experimental results show that this effectively reduces the flow rate error. [ABSTRACT FROM AUTHOR]