Line-velocity distribution in trapezoidal open channel
Line-velocity is an important foundation for flow computation.In order to analyze the line-ve-locity distribution of trapezoidal open channel,a typical standard channel was selected.It enjoyed a top width of 27 m and a bottom width of 6 m,with the slope angle of 21.80°.Besides,a 10-path ultrasonic line-velocity measuring device was employed with symmetrical crossed paths arrangement to measure the line-velocities at typical heights.The tested results showed that the line-velocities measured by the two crossed paths at the same typical height agreed with each other well when the height was smaller than 0.6H,indicating that the flow was stable and consistency of line-velocities varying with the height was good.By comparison,for the area above 0.6H,the line-velocity differences between the two crossed paths got larger and the representativeness was relatively poor due to lateral flows.And in general,the line-velocities increased approximately exponentially gradually with the increasing height.However,the height of the maximum line-velocity depended on the average velocity of the whole cross section.It could take the value of 0.8H for relatively small cross-sectional average velocities while it should be H for large ones.In addition,the cross-sectional average velocities actually corresponded to the line-velocities at 0.35H～0.37H.These results can provide technical supports to the selection of representative line-veloci-ties and plan making for the flow measurement.
metrologyflow measurementtrapezoidal open channelline-velocity distributionmulti-path ultrasonic flow measurement device
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