Numerical investigation on the incipient motion of non-spherical sediment particles in bedload regime of open channel fl
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Numerical investigation on the incipient motion of non-spherical sediment particles in bedload regime of open channel flows Boxi Zhang1 · Dong Xu1
· Bingchang Zhang1 · Chunning Ji1,2
· Antonio Munjiza3 · John Williams4,5
Received: 14 October 2019 / Revised: 13 February 2020 / Accepted: 19 February 2020 © OWZ 2020
Abstract Theoretical analysis and nowadays advanced numerical simulations for bedload particle transport widely share a popular assumption: All sediments are spherical and can be simplified as spheres, which apparently differs from reality. In order to explore the shape effects of sediment particles on their transport and to find out the possible consequence originated from the spherical assumption, a particle resolved computational model is established by combining the large eddy simulation for fluid and the discrete element method for the solid particles using an immersed boundary (IB) technique. Using this model, simulations are conducted for spherical and non-spherical bedload particles in both laminar and turbulent open channel flows. Simulation results show that shape of sediment particles has direct influence on the incipient motion in both laminar and turbulent flows. In laminar flows, the widely adopted spherical particles tend to exhibit over 5 times higher traveling speed compared with the non-spherical particles, and over 4 times longer time lag during incipient motion. In turbulent flows, the disk-shaped non-spherical particle yields up to 60% higher travel speed, 50% larger saltation height and 126% longer saltation length compared with spherical particles. The travel modes of non-spherical sediment particles during incipient motion are also analyzed. Keywords Sediment particle · Computational fluid dynamics · Discrete element method · Immersed boundary method · Incipient motion
1 Introduction Sediment transport is fundamental for the understanding of both river and coastal dynamics. A large number of empirical or semiempirical sediment transport theories have been developed, e.g., critical shield diagram, Meyer–Peter and Muller formula, etc. Based on field observation or experimental results, those theories are often proven effective
B
Dong Xu [email protected]
1
State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin 300072, China
2
Key Laboratory of Earthquake Engineering Simulation and Seismic Resilience of China Earthquake Administration, Tianjin University, Tianjin 300350, China
3
FGAG, University of Split, Split, Croatia
4
School of Engineering and Materials Science, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
5
State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu 610065, China
in solving engineering problems. However, limited by the experimental techniques, our knowledge on the detailed mechanism of fluid–sediment interaction still remains insufficient up to now. With the development of computational fluid dynamics (CFD) [8, 9], high-resolution numerical simulati
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