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 rapidly-varied 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 one-dimensional 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.