Influence of slip on vortex-induced motion of a superhydrophobic cylinder

The partial slip boundary condition produced by a superhydrophobic surface in the Cassie state has been shown capable of reducing skin friction drag as well as influencing the flow around coated bodies including cylinders and spheres. In this paper, we investigated how the changes in vortex shedding and separation previously observed on superhydrophobic cylinders affects the rms lift force and the resulting oscillations induced on an elastically mounted cylinder. Two hydrophobic polytetrafluoroethylene cylinders were studied. The first was smooth and the second was roughened to make it superhydrophobic and to induce slip. The presence of slip was found to decrease rms lift and amplitude of the oscillating cylinder by up to 15% with no measurable impact on drag or the natural frequency of the elastically mounted system. We show that the observed reductions are a direct result of reduced fluid forcing on the superhydrophobic cylinder.