Dimpled Surfaces

 A SolidWorks rendition of the dimpled surfaces. Dimpled areas (gray) are super-hydrophobic while the outer (white) area is hydrophilic.

A SolidWorks rendition of the dimpled surfaces. Dimpled areas (gray) are super-hydrophobic while the outer (white) area is hydrophilic.

Uniform, superhydrophobic surfaces have been proven to lower the frictional drag of  water vehicles by trapping a thin air layer between the vehicle’s body and the surrounding liquid. Because the air layer’s viscosity is orders of magnitude lower than that of water, the frictional drag around the vessel is reduced.  However, the induced air layer is not stable: it can be removed by the flow around the vessel. The surface can also lose its hydrophobic qualities in the face of the flow, affecting its ability to maintain an air layer and reduce drag.

To address these concerns, we are investigating the use of non-uniformly coated dimpled surface to increase air stability and maintain drag reduction capabilities. The indented dimples are super-hydrophobic in order to keep water out and air in while the flat, outer area is hydrophilic. The dimples are also equipped with small air injectors. Thus, when the surface is submerged in water, the injected air is trapped in the indented regions. The air bubble in each dimple thus experiences less shear force since its cap is the only part exposed to the outer water flow.