Characteristics of the flow around a superhydrophobic obstacle

The flow around a partially buried circular cylinder on a smooth plane boundary is studied using Particle Image Velocimetry. The cylinder axis is perpendicular to the incoming flow. The burial ratio B/D is equal to 0.5 , where B is the burial depth and D is the diameter of the cylinder. The ratio between the span of the obstacle and its diameter is equal to 11.7 . The flow is considered nominally two-dimensional. The case in which the obstacle is coated with a random-textured superhydrophobic surface is compared with the case of a smooth surface. In the superhydrophobic case the surface was prepared by using a double layer spray coating method (NeverWet solution). An extreme contact angle of about 165° was evaluated. Measurements were carried out in a closed-loop water tunnel for a Reynolds number, based on the cylinder diameter and on the incoming flow velocity Ue , of about 360. The incoming boundary layer is laminar and the boundary layer thickness, in absence of the obstacle, is of the same order of the obstacle height. The present research is related to the understanding of the role of slip conditions in presence of pressure gradients in order to provide useful information for flow control strategy.