Hydrodynamically induced particle drift near corrugated surfaces

We study the hydrodynamic interactions between sedimenting spheres and nearby corrugated surfaces, whose grooves are tilted with respect to the gravitational force. Our experiments show oscillatory particle trajectories with an overall drift along the sinusoidal surface corrugations, which agree quantitatively with our analytical perturbation theory. The theoretical predictions further reveal that the interactions of the flows induced by the particle motion with the surface shapes generate local pressure gradients, which explain the observed oscillatory dynamics. Additionally, we demonstrate that this behavior is generic for various surface shapes, including rectangular, sinusoidal, and triangular grooves. Finally, we theoretically and experimentally quantify the particle drift as a function of the shape and wavelength of the corrugations and the particle size to identify the parameters, which lead to an optimal transport of the particles.