超撥水面への空気供給による摩擦抵抗低減に関する研究 : 第1報,気相膜形成時の流動状態と安定性(<小特集>異相界面における諸現象の物理)

抄録

A frictional drag reduction using a specific coating surface (Super Water-Repellent Surface) has been studied. Experiments were carried out by injecting a small amount of air to a rectangular horizontal duct with super water-repellent wall. Three kinds of flow patterns, i.e., bubble, slug and stable air film flow, were defined based on the observation of flow behaviors. It was shown that the friction factors with super water-repellent wall duct were smaller than those of the smooth acrylic wall when the thin air film was formed. The maximum drag reduction ratio was about 32% at Reynolds number around 24000. At higher Reynolds number, the drag reduction ratio decreased due to air film-bubble flow transition occurring.