Author(s): Xinqian Leng, Hubert Chanson
Linked Author(s): Xinqian Leng
Keywords: Open channel flow, turbulence, velocity profiling, unsteady flows
Abstract: The propagation of positive surges in rivers and open channels is a highly unsteady turbulent process, with intensive sediment scouring and mixing. Despite its ecological and engineering significance, systematic physical studies of the unsteady turbulent characteristics of tidal bores remain limited. The present investigation performs ensemble-averaged velocity measurements using an array of two Vectrino II Profilers to investigate the vertical and transverse variability of the instantaneous velocity field during the propagation of breaking bores in open channel flows. Results highlight satisfactory performances of Vectrino II Profilers in highly unsteady turbulent open channel flows. Rapid longitudinal deceleration, transient recirculation and large velocity fluctuations in all directions are observed with the bore passage. The vertical velocity increased then decreased with the sharp free-surface rise. The transverse velocity data highlighted drastic transverse motions of bores and existence of large vortical structures in the flow. Overall, the results suggest that the propagation of tidal bore is a highly unsteady turbulent process, and a three-dimensional phenomenon. The process is associated with large fluctuations in all velocity components, as well as formation of large vortical structures and intense turbulent mixing in the wake of the surge
Year: 2017