CLE-TURBULENCE

The research reported herein has been aimed at improving the present level of understanding of the physical processes involved in the transport of individual sediment particles in the near bed region of a turbulent open channel flow. Two different aspects of this phenomenon are examined, namely the mode of transport denoted as saltation, and the process of particle entrainment into suspension. The main approach followed is experimental, using visualizations of flow and particles, as well as particle trachng techniques to study particle motion and its interaction with near wall turbulence. A high-speed video system is used extensively which yields a good temporal resolution of particle motion. The experimental information is used to develop conceptual and quantitative models of the phenomena analyzed. A Lagrangian approach is used to model both saltation and particle entrainment into suspension. Inthe former case, the interaction between saltating particles and the bed is modelled stochastically, and the effect of turbulence on saltation is investigated separately by means of a random walk model. To model particle entrainment into suspension it is assumed that particles interact with near bed coherent flow structures which are characterized using a heuristic model. Results of the study on particle saltation provide new insights as well as unprecedented data on the characteristics of particle trajectories and velocities, particle collisio