Tangential Forces Govern the Viscous-Inertial Transition in Dense Frictional Suspensions

TL;DR

This study uses particle-resolved simulations to investigate how tangential forces influence the transition from viscous to inertial regimes in dense frictional suspensions, revealing a Stokes number of 10 as a key transition point.

Contribution

It demonstrates that the viscous-inertial transition is governed by tangential contact and lubrication forces, independent of packing fraction, and explores the effect of inter-particle friction.

Findings

Transition occurs at Stokes number of 10.

Shear stress transitions slower than particle pressure.

Frictional contact shift from rolling to sliding influences the transition.

Abstract

We present particle-resolved simulations of dense frictional suspensions undergoing the viscous-inertial transition using pressure-imposed rheology. By varying the fluid viscosity, shear rate, and granular pressure, we find that the transition is independent of the packing fraction and occurs at a Stokes number of 10. Our results reveal that the shear stress exhibits a slower transition than the particle pressure, attributed to the combined effect of tangential contact and lubrication forces, as the frictional particles concurrently shift from rolling to sliding contacts. This shift is controlled by the Stokes number but also by the distance from jamming. Additionally, we examine the role of increasing inter-particle friction on the viscous-inertial transition.