Research on Flow Diagnosis of Multipath Ultrasonic Flowmeter

摘要

In the application of ultrasonic flowmeter, flow measurement has a low accuracy, since the length of straight pipe near the ultrasonic sensor is insufficient, especially the presence of the upstream disturbance. In this paper, in order to analyze the inherent relationship between the measurement error and the characteristics of flow field, two flow diagnostic criterions are proposed: asymmetry index (AR1, AR2) and cross flow (cf) indicator. Then the threshold range of the indexes is predicted by computational fluid dynamics numerical simulation in three non-ideal installations (single elbow, single elbow & rectifier, single elbow & 5 pipe diameter & rectifier). Finally, this diagnostic criterion is put forward to distinguish the three operating conditions, and verified by flow experiments. When AR1>0.019 or AR2 > 0.037 and cf > 0.005, the asymmetry and cross flow in the flow field cannot be ignored. At this time, flow measurement accuracy is greater than 1%. It is indicated that disturbance affect measurement accuracy. On the contrary, when diagnostic indexes are less than the threshold values, measurement accuracy can be guaranteed within 1%, which shows that disturbance have little impact on flow measurement.