Velocity Profile of Turbulent Clear Water Open-Channel Flows: Implication for Suspended Sediment Grains Transport

Abstract

Understanding sediment transport process requires adequate knowledge of the mechanism of grains motion which is primarily controlled by flow characteristics including the distribution of time-averaged streamwise velocities, Reynold shear stress distributions as well as the turbulence of flow. Knowledge of the velocity profile in both clear and sediment-laden flows provide clues to understanding this sediment transport mechanism. This paper presents the characterisation of turbulent flow velocity profile based on the physical expression of the mixing length theory as originally proposed by Prandtl, O'Brien and Bagnold, for the prediction of flow interaction with suspended sediment grains. The study utilises the most current flow velocity sampling technology to directly sample flow velocity fluctuations in six cases of open channel flume experiments to characterise the turbulent velocity profile and ascertain the turbulence model's relevance and continuous application in solving sediment grain transport problems. With over 30,000 flow velocity data generated, the analysis demonstrates that, in all six clear water turbulent flows cases investigated, time-averaged velocity versus height is defined in the vicinity of the flow bed by the logarithmic law and well approximated by the turbulence model. Also, modelled and measured vertical streamwise velocities show a significant positive relationship with an R-squared value of almost unity.