Numerical approach to estimate the accuracy of ultrasonic flowmeter under disturbed flow condition

摘要

The multi-path ultrasonic flowmeter is a well established method for accurate discharge measurement in large closed conduits. Although multi-path configuration and crossed paths are used to increase measuring accuracy, the error due to flow field distortions can not be ignored. This paper focuses on the numerical approach to estimate the accuracy of ultrasonic flowmeter under the disturbed flow condition. The flow field in the ultrasonic flowmeter can be simulated using FLUENT, and virtual acoustic paths are placed to investigate the flow error, which is the difference between the indicated flow and the real flow. The indicated flow can be integrated from the projected velocities on the acoustic paths, and the real flow can be calculated from the node velocities of the measuring section. To give a clear description, the flow error is divided to two parts: the. axial error arising from the numerical integration of the axial velocities and the transverse error due to transverse flow effects. As an example, based on the simulated flow field in the penstock of the 3-Gorge hydropower station, the flow error is estimated, and the influence of the number of acoustic paths is analyzed, which may provide a suggestion for ultrasonic flowmeter design under the similar flow condition.