Entrainment of single particles in a turbulent open-channel flow: a numerical study

ABSTRACT

This paper investigates erosion events in a turbulent open channel flow laden with monodisperse spherical particles. The data were generated in a previous study using direct numerical simulations with a phase-resolving immersed boundary method. The particles have a mobility below their nominal threshold of incipient motion and settle onto the rough bed that consists of a hexagonally packed layer of spheres with the same size. Conditioned averaging is employed to extract the characteristic features of an erosion event, defining a suitable criterion for detection and accounting for possible asymmetry of flow structures. The highly resolved dataset provides detailed insight into the key-mechanisms of erosion. The results show that a particle collision, together with a subsequent sweep event on time scales of several bulk units, is responsible for the erosion.

Keywords:

• direct numerical simulations
• erosion processes
• fluid–particle interactions
• immersed boundary method
• open-channel flow
• particle entrainment
• particle-laden flows

Acknowledgements

The authors would like to thank V. Nikora, M. Uhlmann, C. Chan-Braun, and M. Witz for useful discussions throughout the course of this project.

Additional information

Funding

The present work is funded by the German Research Foundation (DFG) [project FR 1593/5–2]. The authors gratefully acknowledge the Gauss Centre for Supercomputing (GCS) for providing computing time on the supercomputer JUQUEEN at the Jülich Supercomputing Centre (JSC) [grant 5122]; and the Centre for Information Services and High Performance Computing (ZIH), Dresden, Germany, for making available disc space to store large databases.