Erosion of cohesive grains by an impinging turbulent jet

TL;DR

This study investigates how inter-particle cohesion affects the erosion of granular beds by turbulent jets, introducing a cohesive Shields number and scaling law to predict erosion thresholds and crater shapes.

Contribution

It provides the first experimental characterization of cohesion effects on jet erosion, introducing a cohesive Shields number and a scaling law for erosion threshold prediction.

Findings

Cohesion raises the erosion threshold compared to non-cohesive grains.

A cohesive Shields number effectively predicts erosion behavior.

Cohesion influences crater shape and grain transport.

Abstract

The erosion and transport of particles by an impinging turbulent jet in air is observed in various situations, such as the cleaning of a surface or during the landing of a spacecraft. The presence of inter-particle cohesive forces modifies the erosion threshold, beyond which grains are transported. The cohesion also influences the resulting formation and shape of the crater. In this paper, we characterize the role of the cohesive forces on the erosion of a flat granular bed by an impinging normal turbulent jet in air. We perform experiments using a cohesion-controlled granular material to finely tune the cohesion between particles while keeping the other properties constant. We investigate the effects of the cohesion on the erosion threshold and show that the results can be rationalized by a cohesive Shields number that accounts for the inter-particles cohesion force. Despite the complex nature of a turbulent jet, we can provide a scaling law to correlate the jet erosion threshold, based on the outlet velocity at the nozzle, to a local cohesive Shields number. The presence of cohesion between the grains also modifies the shape of the resulting crater, the transport of grains, and the local erosion process.