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DY: Fachverband Dynamik und Statistische Physik

DY 19: Franco-German Session on Granular Matter I

DY 19.6: Talk

Tuesday, March 10, 2026, 11:15–11:30, HÜL/S186

Rheology of Granular Sediment Beds from Dense to Creeping Regimes — •Bernhard Vowinckel¹, Pascale Aussillous², and Élisabeth Guazzelli³ — ¹Institute of Urban and Industrial Water Management, Technische Universität Dresden, 01062 Dresden, Germany — ²Aix Marseille Université, CNRS, IUSTI, Marseille, France — ³Université de Paris, CNRS, Matière et Systèmes Complexes (MSC) UMR 7057, Paris, France

We investigate the rheology of sheared sediment beds using grain-resolved direct numerical simulations supported by experimental data. Poiseuille and Couette configurations are examined, extending monodisperse systems to polydisperse beds with diameter ratios up to 10. The simulations provide depth-resolved stress profiles, fluid-particle momentum exchange, particle volume fraction, and granular pressure. For monodisperse beds, shear and normal viscosities and the effective friction coefficient follow established correlations, with a critical particle volume fraction of about 0.3 marking the transition from dense to dilute regimes. In the dilute transport layer, hydrodynamic interactions are screened and the effective viscosity approaches the Einstein relation. For polydisperse mixtures, we generalize µ(J)-rheology by linking its parameters to the maximum packing fraction, achieving good agreement with reference data. Access to very low viscous numbers shows that the friction coefficient in the creeping regime tends to a finite quasi-static value, reducing the critical friction coefficient by a factor of three. These findings refine closure relations for two-phase sediment transport models.

Keywords: Sediment rheology; Grain-resolved simulations; Polydispersity; Sheared granular beds