Universal friction law at granular solid-gas transition explains scaling of sediment transport load with excess fluid shear stress

Abstract

A key interest in geomorphology is to predict how the shear stress $\tau$ exerted by a turbulent flow of air or liquid onto an erodible sediment bed affects the transport load $M\tilde{g}$ (i.e., the submerged weight of transported nonsuspended sediment per unit area) and its average velocity when exceeding the sediment transport threshold ${\tau }_t$. Most transport rate predictions in the literature are based on the scaling $M\tilde{g}\propto \tau -{\tau }_t$, the physical origin of which, however, has remained controversial. Here we test the universality and study the origin of this scaling law using particle-scale simulations of nonsuspended sediment transport driven by a large range of Newtonian fluids. We find that the scaling coefficient is a universal approximate constant and can be understood as an inverse granular friction coefficient (i.e., the ratio between granular shear stress and normal-bed pressure) evaluated at the base of the transport layer (i.e., the effective elevation of energetic particle-bed rebounds). Usually, the granular flow at this base is gaslike and rapidly turns into the solidlike granular bed underneath: a liquidlike regime does not necessarily exist, which is accentuated by a nonlocal granular flow rheology in both the transport layer and bed. Hence, this transition fundamentally differs from the solid-liquid transition (i.e., yielding) in dense granular flows even though both transitions are described by a friction law. Combining this result with recent insights into the nature of ${\tau }_t$, we conclude that the transport load scaling is a signature of a steady rebound state and unrelated to entrainment of bed sediment.

References in corpus (16)

• SediFoam: A general-purpose, open-source CFD-DEM solver for particle-laden flow with emphasis on sediment transport
• Non-local rheology in dense granular flows -- Revisiting the concept of fluidity
• Direct numerical simulation of pattern formation in subaqueous sediment
• Interface-resolved direct numerical simulation of the erosion of a sediment bed sheared by laminar channel flow
• Rheological properties of dense granular flows
• Flow regime transitions in dense non-Brownian suspensions: rheology, microstructural characterisation and constitutive modelling
• Formation of sediment patterns in channel flow: minimal unstable systems and their temporal evolution
• Direct numerical simulations of aeolian sand ripples
• Dense granular flow rheology in turbulent bedload transport
• A two-species continuum model for aeolian sand transport
• A minimal coupled fluid-discrete element model for bedload transport
• The Cessation Threshold of Nonsuspended Sediment Transport Across Aeolian and Fluvial Environments
• Revisiting slope influence in turbulent bedload transport: consequences for vertical flow structure and transport rate scaling
• Fluid forces or impacts: What governs the entrainment of soil particles in sediment transport mediated by a Newtonian fluid?
• The role of grain dynamics in determining the onset of sediment transport
• The fluctuation energy balance in non-suspended fluid-mediated particle transport

Cited by in corpus (13)

• The physics of sediment transport initiation, cessation, and entrainment across aeolian and fluvial environments
• Unification of Aeolian and Fluvial Sediment Transport Rate from Granular Physics
• Local Rheology Relation with Variable Yield Stress Ratio across Dry, Wet, Dense, and Dilute Granular Flows
• Megaripple mechanics: bimodal transport ingrained in bimodal sands
• Turbidity currents propagating down an inclined slope: particle auto-suspension
• Fluid-particle interaction regimes during the evolution of turbidity currents from a coupled LES/DEM model
• Single-dopant band bending fluctuations in MoSe${}_2$ measured with electrostatic force microscopy
• Large Effects of Particle Size Heterogeneity on Dynamic Saltation Threshold
• Scaling laws for planetary sediment transport from DEM-RANS numerical simulations
• Anomalous Scaling of Aeolian Sand Transport Reveals Coupling to Bed Rheology
• Comment on "Distinct Thresholds for the Initiation and Cessation of Aeolian Saltation From Field Measurements" by Raleigh L. Martin and Jasper F. Kok: Alternative Interpretation of Measured Thresholds as two Distinct Cessation Thresholds
• On the testing of grain shape corrections to bedload transport equations with grain-resolved numerical simulations
• Addressing bedload flux variability due to grain shape effects and experimental channel geometry