Lift force acting on an intruder in dense, granular shear flows

TL;DR

This paper introduces a new model for the lift force on intruders in dense granular shear flows, accounting for granular temperature, pressure, and density differences, and validates it with DEM simulations.

Contribution

The paper develops an extended lift force model incorporating granular temperature, pressure, and density effects, validated against DEM simulations for intruder behavior in shear flows.

Findings

Model accurately predicts intruder rising and sinking.

DEM simulations confirm the model's predictions.

Intruder size influences buoyancy and movement direction.

Abstract

We report a new lift force model for intruders in dense, granular shear flows. Our derivation is based on the thermal buoyancy model of Trujillo & Hermann[L. Trujillo and H. J. Herrmann, Physica A 330, 519 (2003).], but takes into account both granular temperature and pressure differences in the derivation of the net buoyancy force acting on the intruder. In a second step the model is extended to take into account also density differences between the intruder and the bed particles. The model predicts very well the rising and sinking of intruders, the lift force acting on intruders as determined by discrete element model (DEM) simulations and the neutral-buoyancy limit of intruders in shear flows. Phenomenologically, we observe a cooling upon the introduction of an intruder into the system. This cooling effect increases with intruder size and explains the sinking of large intruders. On the other hand, the introduction of small to mid-sized intruders, i.e. up to 4 times the bed particle size, leads to a reduction in the granular pressure compared to the hydrostatic pressure, which in turn causes the rising of small to mid-sized intruders.