Abstract
The micro-structured water-repellent surface has been reported to reduce friction coefficient. The surface has been microscopically observed in this study to clarify whether it holds air layer that is believed to cause drag reduction on the surface. The observation certified the existence of the air layer and its state is affected by some condition such as flow rate or air-solubility of the fluid. In air-saturated water, the air layer exists for hours during the experiment. The air-saturated water flow enhanced the stability of the air layer, while degassed water quickly penetrate the microscale concave on the surface.
