Lift and drag forces on an inclined plow moving over a granular surface

TL;DR

This study combines experiments and simulations to analyze the forces on an inclined plow over granular media, revealing a universal friction law and detailed stress and velocity field characteristics.

Contribution

It introduces a universal effective friction law for plow forces on granular surfaces, linking force proportionality to a moving wedge of grains and analyzing stress fields.

Findings

Lift and drag are proportional to the wedge weight.

Constants vary with the angle of attack, weakly with velocity.

Shear band exists under the wedge with non-hydrostatic pressure.

Abstract

We studied the drag and lift forces acting on an inclined plate while it is dragged on the surface of a granular media, both in experiment and numerical simulation. In particular, we investigated the influence of the horizontal velocity of the plate and its angle of attack. We show that a steady wedge of grains is moved in front of the plow and that the lift and drag forces are proportional to the weight of this wedge. These constants of proportionality vary with the angle of attack but not (or only weakly) on the velocity. We found a universal effective friction law which accounts for the dependence on all the above-mentioned parameters. The stress and velocity fields are calculated from the numerical simulations and show the existence of a shear band under the wedge and that the pressure is non-hydrostatic. The strongest gradients in stress and shear occur at the base of the plow where the dissipation rate is therefore highest.