Lift force on an asymmetrical obstacle immersed in a dilute granular flow

TL;DR

This study analyzes the lift force on an elliptical obstacle in a dilute granular flow, combining analytical and simulation approaches to understand how flow parameters influence the force, highlighting the limitations of dilute flow assumptions.

Contribution

It introduces a combined analytical and simulation framework to study lift forces on obstacles in granular flows, revealing the impact of shock wave formation on force predictions.

Findings

The theoretical model captures qualitative lift features but not quantitative data.

Shock wave formation reduces impact velocity and net lift.

Flow parameters like obstacle size and orientation significantly affect lift.

Abstract

This paper investigates the lift force exerted on an elliptical obstacle immersed in a granular flow through analytical calculations and computer simulations. The results are shown as a function of the obstacle size, orientation with respect to the flow direction (tilt angle), the restitution coefficient and ellipse eccentricity. The theoretical argument, based on the force exerted on the obstacle due to inelastic, frictionless collisions of a very dilute flow, captures the qualitative features of the lift, but fails to reproduce the data quantitatively. The reason behind this disagreement is that the dilute flow assumption on which this argument is built breaks down as a granular shock wave forms in front of the obstacle. More specifically, the shock wave change the grains impact velocity at the obstacle, decreasing the overall net lift obtained from a very dilute flow.