Author(s): Fereshteh Bagherimiyab; Ulrich Lemmin
Linked Author(s): Ulrich Lemmin
Keywords: Fine sediment; Suspension; Accelerating and decelerating flow; ADVP; PTV
Abstract: This experimental investigation describes the effect of suspended sediment concentration and turbulence modulation in unsteady (first accelerating, then decelerating) flow by combining an acoustic Doppler and imaging method (ADVP) with an optical method (PTV) for suspended sediment particle tracking. Quasi-instantaneous profiles of velocity and sediment concentration were taken simultaneously and co-located, resolving turbulence scales. An event structure in suspension is seen by both methods. During the final phase of the accelerating flow range, fine sediment suspension from the bed started in bursts and rapidly created nearly stationary ripples. Thereafter, vortices, shedding from the ripple crests, produced most of the sediment suspension in events. In that state, flow deceleration had less obvious effects on particle motion. PTV velocity vectors varied in speed and orientation, but were organized in large coherent packets, mainly in the near bed layers, supporting the concept that coherent structure events contribute to sediment suspension in unsteady flow.
Year: 2011