Ultrasonic Transit-time Discharge Determination in Rectangular Open Channel

Ultrasonic Transit-time method is a good choice to measure the open channel discharge. To investigate its performance in the rectangular open channels, a 26m long, 2m wide, 1.2m deep open channel facility was built with an over-fall head tank providing a very stable flowrate of 1.5m 3 /s in maximum and 39 typical cases were tested. The tested results verified that ultrasonic transit-time method can be well used to measure the discharge in rectangular open channels. However, due to unavoidably disturbing the flow patterns and introducing some errors, thus the transducers should be made as small as possible to improve the measuring accuracy. In addition, more paths should be used to produce smaller errors. And at least two paths are suggested to be mounted in the range of h i /H >0.7 to better reflect the influence of the free surface. Comparing sub-discharges in all zones, it can be found that substantial differences between mean-section method and Giordano Law exist below the lowest path. Larger K b , for example 0.9, makes mean section method produce closer measurements to Giordano Law.