Author(s): Niansheng Cheng
Linked Author(s):
Keywords: Bedload; Shear Stress; Fluctuation; Turbulence; Laminar flow; Viscous effect
Abstract: The objective of this study is to demonstrate analytically how turbulence fluctuation affects bedload transport. Many formulas available in the literature for computing sediment transport rates are expressed only in terms of time-mean variables, such as, time-mean bed shear stress or time-mean flow velocity. Turbulence intensity, e. g., bed shear stress fluctuation, is never included in these formulas. On the other hand, it is noted that any flow parameter for turbulent flows generally comprises of its time-mean component as well as its rms value or fluctuation. Turbulence fluctuation is relatively limited in laboratory open-channel flows, but varies markedly in engineering applications, e. g., for the case of local scour and wave breaking. This study is conducted with stochastic considerations. First, bed particle instability is analyzed in the absence of turbulence. Following that, a bedload function is proposed based on Einstein’s idea, but limited to the condition of laminar flows. Then, this function is extended for computing sediment transport in turbulent flows by considering the skew probability distribution of bed shear stress. Analytical results are finally verified using data that were collected recently from specifically-designed laboratory experiments. The present analysis is largely applicable for the condition of a flat bed comprising of uniform sediment particles subject to unidirectional flows.
Year: 2004