Effect of the surface pattern on the drag property of the superhydrophobic surface

Abstract

Superhydrophobic surfaces with a slip effect have been proven to be effective to achieve surface drag reduction. In this paper, we fabricated superhydrophobic disks via laser ablation and chemical modification, and their drag-reduction performance is tested by a rheometer. However, the superhydrophobic disk achieves a limited drag-reduction effect (33.5% in maximum) with poor consistency (decay rapidly as rotating speed increases). To enhance the drag-reduction performance of the superhydrophobic surfaces, surfaces with tunable patterns consisting of superhydrophobic and hydrophobic surfaces are proposed. The difference in wettability and slip length between different regions is employed to control the flow direction. The effect of different patterns is investigated both experimentally and numerically, and the results indicate that the pattern distribution performs a great impact on the drag-reduction effect. The pattern consistent with the primary flow can not only enhance the effect (60.3% in maximum) but also the consistency (maintained at a higher rotating speed) of drag-reduction. On the contrary, the pattern perpendicular to the flow direction is harmful to drag reduction and can even increase the drag.