Abstract
The micro-structure and trapped air are believed to be key features in drag reduction utilizing water-repellent surface. Previous numerical simulation has shown that the less the liquid contacts solid surfaces, the larger drag reduction on the textured structure surface becomes, though air layer tends to reduce. In this study, we suggest the compound projections of different length as surface texture. Two combinations of the differently sized projections demonstrated much greater water-repellency on the points of drag reduction (>10% reduced) and of the sustainability of air layer, through the experiment and surface observation.
