Author(s): J. A. Figuerez; J. González; A. Galán

Linked Author(s):

Keywords: ADCP; Transit time ultrasonic flowmeter; Open channel; Velocity distribution; Flow discharge

Abstract: In this work, we present some experimental velocity measures using an acoustic doppler current profiler and a transit time ultrasonic flowmeter and the agreement with an analytical velocity distribution within the cross section. Flow discharge is a very important variable to know in the management and operation of a channel. In this case, the Orellana channel is an irrigation channel of more than 100 kilometres long. Throughout the channel, there are several transit time ultrasonic flowmeters that facilitate and inform the operators of the flows that occur in the channel. This information is very important for the operators since they manipulate floodgates, opening or closing, depending on these measures and the water demand along the channel. For this reason, it is convenient to check that the channel’s flowmeters measure correctly. During the irrigation season, flow measurements are taken with an ADCP in the same sections where ultrasonic flowmeters are located, allowing to compare the measurements of both equipment and verifying that the ultrasonic flowmeters measure correctly. Furthermore, the installed flowmeters using the transit time operating principle only measure the average velocity of a horizontal rope at a certain height from the bottom. The following expression is used: (1) where (see Fig.1) T1 is the travel time of the acoustic pulse between transducer B and transducer A, T2 is the travel time of the acoustic pulse between transducer A and Transducer B, is the angle between the acoustic path and the direction of water flow and L is the path length between transducers. Therefore, the average velocity of the water along acoustic path can be calculated by knowing the path length (L) and path angle ( ) and measuring the time for the acoustic pulse to travel between the transducers in both upstream and downstream directions. From this average velocity value, water level and geometric characteristics of the cross section, the manufacturer infers the value of flow discharge. However, the velocity distribution assumed in the section for the calculation of the flow rate may not coincide with the actual one and, therefore, an error is made. This error can be corrected by comparing the measurements taken by transit time ultrasonic flowmeters with the records taken by an ADCP. The advantage of measuring with an ADCP is that not only the average velocity in a horizontal at a certain height of the bottom is measured, but the velocity distribution is measured in the cross section discretized in cells (see Fig. 2).

DOI: https://doi.org/10.3850/978-981-11-2731-1_315-cd

Year: 2018