Experimental Investigation on Drag Properties of Surface with Composite Wettability

Superhydrophobic surfaces with drag-reduction performance have received extensive attention in many fields. In this paper, we demonstrated a surface with composite wettability composed of hydrophobicity and superhydrophobicity fabricated by laser selective texturing. In order to investigate the influence of the composite wettability distribution on the drag properties, a fully-superhydrophobic and three composite wettability disks with different distributions were constructed to compare with the original disk. The drag properties of these disks were tested via a rheometer. The tested results indicate that although a disk with a fully superhydrophobic surface can reduce the drag effectively, the drag-reduction effect attenuates rapidly and almost disappears as the rotating speed increases. The distribution pattern of composite wettability has a significant impact on drag reduction performance. Both annulus-shaped distribution at low rotating speed and spiral-shaped distribution at high rotating speed perform a remarkable drag reduction effect. In contrast, the fan-shaped distribution shows a poor drag reduction effect and even leads to a rise of drag as the rotating speed increases. Moreover, the influence mechanism of the composite wettability distribution on the drag performance was also analyzed theoretically. It can be supposed that this approach provides a novel way to construct drag-reduction surfaces.