Air-propelled, herringbone-textured platelets

Solids can be levitated by actively nourishing an air cushion beneath them, using air blown through a porous substrate. It has recently been demonstrated that introducing asymmetry in the airflow close to a hovercraft can lead to its propulsion by viscous entrainment. In this work, we focus on the major consequence of a simple modification in the set-up: instead of engraving the texture on the substrate as in previous works, we directly carve it into the hovercraft. Provided that air-flux is strong enough, propulsion at any Reynolds number is observed. However, motion happens in the direction opposite to the viscous scenario. To understand experimental observations, an analytical model is proposed to account for the force of propulsion and the pressure needed for levitation, emphasizing asymptotic situations at low and high Reynolds numbers, further confirmed by numerical simulations.