Author(s): Clara Streule; Gabor Suss; Mohammadreza Maddahi; Robert M. Boes; Ismail Albayrak

Linked Author(s): Ismail Albayrak, Robert Boes

Keywords: Turbulence; Acoustic Doppler Velocimeter (ADV); Ultrasonic Velocity Profiler (UVP); Flume experiments

Abstract: Open channel flows consist of 3D turbulent flow structures at different scales affecting transport and mixing processes. To advance the understanding of such turbulent flow structures, accurate velocity measurements at high spatial and temporal resolutions are necessary. In this study, we systemically investigated the accuracy of an in-house developed four-transducer Ultrasonic Velocity Profiler (UVP). Velocity measurements using an Acoustic Doppler Velocimetry (ADV) system and the UVP configuration were conducted in an 8.0 m long, 0.7 m deep and 0.5 m wide laboratory flume at the Laboratory of Hydraulics, Hydrology and Glaciology of ETH Zurich. To create a complex accelerating flow for the measurements, an elliptical segment shaped restrictor with a length of 0.50 m and width of 0.25 m was installed in the flume. The four mono-static transducers, arranged with a 90° radial spacing and an angle of 10° to the vertical, measure velocities successively with an emitted frequency of 4 MHz, resulting in a sampling frequency between 3 and 28 Hz. The results show that the four-transducer UVP configuration is a reliable method to measure the profiles of the mean flow velocities, Reynolds stresses and TKE in a complex accelerating open channel flow when benchmarked with ADV results. Despite some discrepancies in the measured velocity profiles, the UVP-derived TKE and Reynold's shear stress values calculated using an empirical formula are in a good agreement with the ADV-based values. This indicates that the formula, developed for ADCP, also works well for the UVP. Overall, under certain conditions, the UVP configuration presents a promising and time-efficient alternative to ADV for laboratory and field applications. However, more research is still needed to further improve measurement accuracy and capabilities of the UVP by testing different UVP geometric configurations, transducers, and bed roughness under various flow conditions. The present study is expected to underpin the follow-up of studies on these issues.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p0676-cd

Year: 2023