Transverse velocity profiling under positive surges in channels

Abstract

A positive surge is a sudden rise in water surface elevation in an open channel flow. It is an unsteady rapidlyvaried flow which may propagate over long distances. Herein new transverse velocity profiling experiments were conducted in steady and unsteady rapidly-varied flows. The measurements were performed with a transverse ADV Profiler and an array of two ADV Profilers, installed perpendicular to each other. The results were systematically compared to ADV Vectrino+ data. Ensemble-averaged velocity measurements demonstrated that the transverse Profiler gave satisfactory performances in a highly unsteady positive surge flow. The ensemble-averaged velocity and Reynolds stress characteristics measured by the transverse Profiler, alone or in an array, were similar to results with a traditional ADV and the vertical Profiler alone, although it is acknowledged that the ADV Vectrino II Profiler instrument has intrinsic limitations. The onedimensional integral turbulent time and length scales were comparable in magnitudes in the transverse or vertical directions, with the turbulent length scale ranging from 10-3 m to 10-2 m and turbulent time scales from 10-2 s and 10-1 s, depending upon the flow phase. The turbulent length and time scales tended to increase during and after the surge passage, in comparison to those during the initially steady flows.