  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.
