Laminar drag reduction in a closed channel using bioinspired textured surfaces

Low flow drag is of great importance to a variety of engineering applications, and an effective way to achieve low drag is to use bioinspired microstructured surfaces. This work aims to reduce the skin-friction drag in closed channel flow using textured surfaces inspired by leaves of indocalamus and rice. A channel formed from a polydimethylsiloxane chunk and a silicon wafer was fabricated to study the drag reduction behavior for water or liquid paraffin oil in laminar flow. Bioinspired textures were processed on the silicon wafer surface using the deep silicon plasma etching method. The pressure drop of water or paraffin oil passing through textured channels with different velocities was measured. The maximum pressure drop reductions for the paraffin oil flow with a low velocity (Re ?1) and for the water flow with a high velocity (Re < 1000) were about 5.1 and 27.3%, respectively. The contact angles of the bioinspired textured surface are also presented, and mechanisms to explain the drag reduction are proposed. Hydrophobicity leading to a change from a liquid-solid interface to a liquid-air interface is believed to provide the drag reduction for water flow, while the thin oil film formed on the textured surface due to oleophilicity helps reduce the oil flow drag.