Author(s): Alireza Khodabakhshi; Hafizul Rahman Koshan; Bernhard Vowinckel
Linked Author(s): Bernhard Vowinckel
Keywords: Sediment transport; Rheology; Dense suspensions; Numerical simulations
Abstract: Understanding sediment transport in rivers and other shallow flows is key to their sustainable management. Towards this end, in-depth knowledge of the rheology of sheared sediments opens up the possibility for predictive modeling of sediment processes. Such models, however, require constitutive relations to describe the stress exchange between the fluid and the particulate phase. This gives rise to the idea of a macroscopic friction μ=τ/P as the anisotropy of the shear stress τ to the granular pressure P as the overburden of the overlying sediments felt by the grains within the sediment bed. It has been shown by Boyer et al. (2011) that μ and the volume fraction φ scale by the viscous number J=ηfγ̇/P in overdamped systems, where ηf is the dynamic fluid viscosity and γ̇ is the local shear rate. For more violent granular flows, the scaling goes by the inertial number I=Dpγ̇√ρp/P, where ρp and Dp are the particle density and diameter, respectively. The transition, albeit more relevant to subaqueous sediment transport, is less well explored. It has been proposed that the scaling in this regime is a linear combination K=J+αI² (Trulsson et al., 2012, Tapia et al., 2022). Here, the coefficient α marks the inverse of the critical Stokes number St=I²/J at the transition. However, the implications of this regime transition to sediment transport modeling are still unknown. This study therefore presents results of particle-resolved Direct Numerical Simulations (pr-DNS) to investigate the rheology of sediments sheared by laminar flows at the transition from the viscous to the inertial regime.
Year: 2025