Influence of sediment and secondary currents on velocity

Abstract

This paper investigates the vertical profile of horizontal velocity in sediment-laden flows. In contrast to previous investigators who assume that the velocity follows the log-law, this study demonstrates that the velocity in sediment-laden flows follows the power law, rather than the log-law. The mechanism of this shift has been attributed to the presence of upwards wall-normal velocity v caused by density stratification. Starting from Reynolds equations, this paper clearly shows that the log-law can be obtained only when v = 0. For flows with v ≠ 0, the momentum flux (uv) causes the deviation of Reynolds shear stress (−u′v¯′) from the standard linear distribution, and subsequently the integration of Reynolds equation yields the power law. The notable experimental datasets in the literature support the theory that the velocity profile in sediment-laden flows follows the power law, rather than the log-law. The validity of the proposed model has been verified using experimental data, and good agreement between the predicted and observed profiles has been achieved.