Discretization of sequential impulse force of coherent flow structures and its impact on sediment entrainment at threshold conditions

Abstract

In this paper, a new analysis of bursting events and their influences on bed sediment entrainment at threshold condition of motion is presented. A new concept of categorization, namely splitting bursting events into “group” and “single” cycles of bursting events is proposed. Categorization of these two cycles enables adequate estimation of the impulse force and its influence on the initiation of sediment motion. To achieve these outcomes, a Micro-ADV and a high-speed camera were concurrently used to assess the influence of “group” and “single” cycles of bursting events on the entrainment of sediment particles. At threshold condition, the contributions of sweep events as a “group” were found to be consistently more important than “single” sweep events. The ejection group events provided a secondary role after the sweep group events for particle entrainment. Additionally, the contributions of group outward interactions vary significantly with increasing the average shear stress. Finally, the contribution of inward interaction events was found to be insignificant for all experimental conditions.