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This manuscript presents an experimental study to evaluate the applicability of the ultrasonic pulse-train Doppler method (UPTD) to the disturbed flow in a pipe. The UPTD can expand the detectable velocity range compared with the conventional ultrasonic pulse Doppler method and has an advantage of trouble-free installation into conventional hardware. Comparative experiments were conducted using two different transducer frequencies, 1 MHz and 4 MHz. The UPTD was only applied to the 4-MHz condition to expand the velocity range fourfold, which is equal to the velocity range of a 1-MHz transducer. The probability density distributions of the measured velocities were almost the same between 1 MHz and 4 MHz, even though the measurement position was not only downstream of a long straight pipe but also downstream 10 or 5 pipe diameters from an obstacle plate. To estimate the influence of aliasing on the velocity measurement for a large fluctuating flow, experiments using a 2-MHz transducer were also conducted. These results indicated that it is possible to estimate the standard deviation of the velocities measured under the aliasing condition, and the accuracy of flow rate measurement decreases when the standard deviation of the velocity exceeds the measurable velocity by approximately twice. Additionally, the flow rate by the 1-MHz transducer was about −2% smaller than that by the 4-MHz transducer for both the straight pipe and disturbed conditions. Through the validation of the influence of the measurement volume between 1 MHz and 4 MHz conditions, the flow rate difference was found to be likely due to the influences of not only the measurement volume but also the standing wave formed by the pulses reflected on the opposite pipe wall. • This paper presents the experimental study of the applicability evaluation of the UPTD on the large fluctuating flow. • To generate the large fluctuating flow, the obstacle plate was installed upstream of the measuring position. • The flow rate differences using 1 MHz were approximately −2%, although that using 4 MHz with the UPTD were within ±0.5%. • The flow rate using 1 MHz was likely to be influenced by the reflected pulse from the opposite pipe wall. • The influence of the aliasing on the measured velocity was investigated in the case of the large fluctuating flow. [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]

In transit-time ultrasonic flow meters (TOF), the flow rate is derived from the transit time of an ultrasonic pulse between two ultrasonic transducers. To convert the transit time into flow rate, a profile factor (PF) is required. Because the PF strongly depends on the velocity profile, a precise calibration of the PF is essential to the accuracy of the TOF. Hence, a field calibration, referred to as on-site calibration, is desirable. In this study, a hybrid ultrasonic flow meter that helps calibrate the TOF using ultrasonic Doppler velocimetry (UDV) is proposed for on-site calibration by integrating the velocity profiles over the cross-sectional area of a pipe. Thus, a new system of hybrid ultrasonic flow meter was developed. The maximum flow rate measured using a conventional UDV is significantly lower than that measured using the TOF. Therefore, a system was developed to measure higher velocities and flow rates. The system is novel in that the transit time and velocity profile can be simultaneously measured using a de-aliasing method. To evaluate the influence of the velocity profile on the PF, experiments were conducted under a wide range of flow-rate conditions, which otherwise cannot be implemented using the conventional UDV. To evaluate the influence of the velocity profile in the pipe, an obstacle plate was placed at 8 D upstream the test section. Radially arranged measuring lines were employed. The experimental results show that increasing the number of measuring lines did not improve the accuracy of the TOF. On the other hand, the flow rate could be accurately obtained using the proposed UDV by measuring the velocity profile even under distorted flow conditions. Furthermore, the calibration of the PF based on the flow rate obtained using the proposed UDV was found to be feasible. [ABSTRACT FROM AUTHOR]