Anisotropic surface friction

Contrary to the literature, we find that altering the surface roughness has a large effect on intruder drag in the quasi-static regime. Moreover we pattern the surface with a sawtooth texture and observe anisotropic drag: when the texture is comparable in size to the bead diameter the frictional force is 1/3rd greater for the flow directed against the sawtooth versus the opposite flow. We present a systematic study showing the dependence of the anisotropy on the texture's orientation.