Coupling between freesurface fluctuations veloci

Authors: Xinqian Leng Hubert Chanson

Publish Date: 2015/11/27

Volume: 16, Issue: 4, Pages: 695-719

PDF Link

Abstract

In open channel canals and rivers a rapid increase in flow depth will induce a positive surge also called bore or compression wave The positive surge is a translating hydraulic jump Herein new experiments were conducted in a largesize rectangular channel to characterise the unsteady turbulent properties including the coupling between freesurface and velocity fluctuations Experiments were repeated 25 times and the data analyses yielded the instantaneous median and instantaneous fluctuations of freesurface elevation velocities and turbulent Reynolds stresses The passage of the surge front was associated with large freesurface fluctuations comparable to those observed in stationary hydraulic jumps coupled with large instantaneous velocity fluctuations The bore propagation was associated with large turbulent Reynolds stresses and instantaneous shear stress fluctuations during the passage of the surge A broad range of shear stress levels was observed underneath the bore front with the probability density of the tangential stresses distributed normally and the normal stresses distributed in a skewed singlemode fashion Maxima in normal and tangential stresses were observed shortly after the passage of a breaking bore roller toe The maximum Reynolds stresses occurred after the occurrence of the maximum freesurface fluctuations and this time lag implied some interaction between the freesurface fluctuations and shear stress fluctuations beneath the surge front and possibly some causal effectThe authors thank Dr Carlo Gualtieri University of Napoli “Federico II” Italy and Professor Shinichi Aoki Osaka University Japan for their valuable comments They also thank Professor Pierre Lubin University of Bordeaux France for his contribution The authors acknowledge the technical assistance of Jason Van Der Gevel and Stewart Matthews The University of Queensland The financial support through the Australian Research Council Grant DP120100481 is acknowledged

Keywords: