Low Velocity Granular Drag in Reduced Gravity

TL;DR

This study investigates how the drag force on objects in granular materials varies with effective gravity, finding a proportional relationship that holds across a wide range of gravitational conditions.

Contribution

It demonstrates that granular drag force scales linearly with effective gravity, confirming the theoretical relation over a 20-fold gravity variation.

Findings

Granular drag force is proportional to effective gravity.

The dimensionless constant η remains unchanged over four orders of magnitude.

The relation Fprobe = η ρgrain geff dprobe hprobe^2 holds across tested conditions.

Abstract

We probe the dependence of the low velocity drag force in granular materials on the effective gravitational acceleration (geff) through studies of spherical granular materials saturated within fluids of varying density. We vary geff by a factor of 20, and we find that the granular drag is proportional to geff, i.e., that the granular drag follows the expected relation Fprobe = {\eta} {\rho}grain geff dprobe hprobe^2 for the drag force, Fprobe on a vertical cylinder with depth of insertion, hprobe, diameter dprobe, moving through grains of density {\rho}grain, and where {\eta} is a dimensionless constant. This dimensionless constant shows no systematic variation over four orders of magnitude in effective grain weight, demonstrating that the relation holds over that entire range to within the precision of our data.