A ray theory approach to investigate the influence of flow velocity profiles on transit times in ultrasonic flow meters for gas and liquid

摘要

USM technology is today recognized as a competitive alternative for fiscal flow metering of gas, and is also considered for fiscal metering of oil and petroleum products. However, there are un-exploited potentials to reduce systematic errors, achieve higher accuracy, and to improve measurement traceability, giving perspectives for further development of the technology. The paper addresses the influences of flow velocity profile effects on transit times (sound refraction) and consequences for the measured flow velocity and sound velocity (VOS) in a USM. Systematic effects of axial and transversal flow velocity profiles at different Reynolds numbers and under various installation conditions are investigated using a ray propagation model with CFD calculated flow profiles as input. It has been found that for a wide range of axial and transversal profiles the measured flow velocity is not influenced significantly by sound refraction effects, except for relatively high flow velocities, assumed that compensation for uniform transversal flow is made (by configuration or software). Similarly, the measured VOS is not affected severely by sound refraction for a wide range of symmetrical and asymmetrical axial profiles, except for relatively high flow velocities. However, refraction effects due to transversal flow are significant also at more moderate velocities, and correction of current USM expressions may be needed for accurate VOS measurement.