Remote Estimation of Turbulence Intensity Variation in Open Channels

Abstract

The open channel flow community has a history of using a set of universal exponential expressions to describe the vertical variation of turbulence intensity in open channel flows. All of these relationships contain an empirical coefficient that varies with the component direction (Du=2.3, Dv=1.27, Dw=1.63). Recent laboratory experiments have demonstrated that for smooth and rough bed open channel flows, these constants are not universal but vary with the Reynolds number, bed composition, and in the presence of streamwise counter-rotating vortices and secondary flows. A robust method for the remote prediction of Du, and hence the vertical variation of the streamwise turbulence intensity is developed here for a wide range of flow conditions. The method uses the free-surface turbulence anisotropy as a proxy for the redistribution of vertical velocity fluctuations into surface-parallel components, enabling a correlation between the free-surface turbulence intensity and Du. Implications for the remote prediction of bed composition, sediment transport, and bed shear stress are discussed.