Author(s): S. C. Yeow; H. Wang; H. Chanson

Linked Author(s): Hang Wang, Hubert Chanson

Keywords: Positive surges; Large cylindrical roughness element; Turbulence; Mixing; Physical modelling; Scour

Abstract: In open channels and water supply canals, the brusque operation of control valves and gate may induce large unsteady flow motion called surges. To date the literature focused on the propagation of surges in smooth canals, ignoring the effects of large roughness and debris. Herein a physical study was conducted under controlled flow conditions to study the turbulent mixing in the close vicinity of a large bed roughness element during the upstream propagation of positive surges. Detailed free-surface and instantaneous velocity measurements were conducted with and without the cylindrical element. For some tests, the experiments were repeated 25 times and the results were ensemble-averaged. The data suggested that the positive surge propagation was associated with large instantaneous free-surface fluctuations for all investigated flow conditions. The velocity measurements showed large variations in longitudinal velocity during the surge generation, as well as large fluctuations of all velocity components. The presence of the large bed element modified the velocity fluctuations and unsteady Reynolds stresses in the vicinity of the element. The present results implied the potential for bed scour around the element during surge propagation.

DOI: https://doi.org/10.15142/T3600628160853

Year: 2016