Author(s): Hao Wang; Qiang Zhong
Linked Author(s):
Keywords: Bed load streaky structure; Flume experiments; Turbulent coherent structure; Particle tracing velocimetry; Kalman filters
Abstract: Bed load streaky structure is a typical bed morphological feature, but its formation mechanism remains unclear. The flume experiments were conducted to quantitatively identify the characteristics of turbulent coherent structure, sediment particle movement and bed structure. A workflow combining the particle tracing velocimetry (PTV) method and Kalman Filters algorithm was established to identify the trajectories of sediment particles on the bed surface. Feature matching velocity (FMV) was applied to acquire the flow surface field and structure-from-motion (SFM) was used to reconstruct 3D bed topography. All the flow velocity, sediment movement, and bedforms show streaky feature in the streamwise direction at 0.068<⊙<0.113, and the streaky structures gradually fade away at 0.113<⊙. Their original instantaneous turbulence properties in the spanwise direction disappear, and three fixed time-averaged streaky structures are formed. The streaky structures have larger spatial scales in the middle of the channel than those near the sidewalls. The spanwise distance between adjacent streaky structures remains about twice the whole flow depth. Finally, a formation mechanism based on the interactions of fluid and sediment is proposed. Our results highlight the important role of the interactions among turbulent coherent structure, sediment motion, and bed topography in the formation of streaky structures in a straight open channel.
Year: 2023